path: root/54585-0.txt

*** START OF THE PROJECT GUTENBERG EBOOK 54585 ***

    [Illustration: Mariner spacecraft]




                                MARINER
                           _MISSION TO VENUS_


Prepared for the National Aeronautics and Space Administration BY THE
STAFF, Jet Propulsion Laboratory, California Institute of Technology
COMPILED BY HAROLD J. WHEELOCK    FOREWORD BY W. H. PICKERING, Director,
Jet Propulsion Laboratory, California Institute of Technology

                                          McGRAW-HILL BOOK COMPANY, INC.
                                New York, San Francisco, Toronto, London


MARINER MISSION TO VENUS

Copyright © 1963 by the Jet Propulsion Laboratory, California Institute
of Technology. All Rights Reserved. Printed in the United States of
America.

Library of Congress Catalog Card Number 63-17489.

This book describes one phase of the U. S. civilian space program—the
journey of the Mariner spacecraft to the vicinity of Venus and beyond.
It reports upon the measurements taken during the “flyby” on December
14, 1962, when Mariner reached a point 21,598 miles from the planet, and
36,000,000 miles from Earth (communication with the spacecraft was
continued up to a distance of approximately 54,000,000 miles from
Earth). The Mariner mission was a project of the National Aeronautics
and Space Administration, carried out under Contract No. NAS 7-100 by
the Jet Propulsion Laboratory, California Institute of Technology.


FOREWORD

For many centuries scientific information about the planets and the vast
void that separates them has been collected by astronomers observing
from the surface of the Earth. Now, with the flight of Mariner II, we
suddenly have in our hands some 90 million bits of experimental data
measured in the region between Earth and the planet Venus. Thus, man for
the first time has succeeded in sending his instruments far into the
depths of space, and indeed, in placing them near another planet. A
whole new area of experimental astronomy has been opened up.

This book is a brief record of the Mariner Project to date and is
designed to explain in general terms the preliminary conclusions.
Actually, it will be months or years before all of the data from Mariner
II have been completely analyzed. The most important data were the
measurements made in the vicinity of the planet Venus, but it should
also be noted that many weeks of interplanetary environmental
measurements have given us new insight into some of the basic physical
phenomena of the solar system. The trajectory data have provided new,
more accurate measurements of the solar system. The engineering
measurements of the performance of the spacecraft will be of inestimable
value in the design of future spacecraft. Thus, the Mariner II
spacecraft to Venus not only looks at Venus but gives space scientists
and engineers information helpful in a wide variety of space ventures.

A project such as Mariner II is first a vast engineering task. Many
thousands of man-hours are required to design the complex automatic
equipment which must operate perfectly in the harsh environment of
space. Every detail of the system must be studied and analyzed. The
operations required to carry out the mission must be understood and
performed with precision. A successful mission requires every member of
the entire project team to do his task perfectly. Whether it be the
error of a designer, mechanic, mathematician, technician, operator, or
test engineer—a single mistake, or a faulty piece of workmanship, may
cause the failure of the mission. Space projects abound with examples of
the old saying, “For want of a nail, the shoe was lost ...,” and so on,
until the kingdom is lost. Only when every member of the project team is
conscious of his responsibility will space projects consistently
succeed.

The Mariner II Project started with the Lunar and Planetary Projects
Office of the Office of Space Sciences at NASA in Washington. Jet
Propulsion Laboratory, California Institute of Technology, personnel
provided the main body of the team effort. They were heavily supported
by industrial contractors building many of the subassemblies of the
spacecraft, by scientists planning and designing the scientific
experiments, and by the Air Force which supplied the launching rockets.
Several thousand men and women had some direct part in the Mariner
Project. It would be impossible to list all of those who made some
special contribution, but each and every member of the project performed
his job accurately, on time, and to the highest standards.

Mariner II is only a prelude to NASA’s program of unmanned missions to
the planets. Missions to Mars as well as Venus will be carried out.
Spacecraft will not only fly by the planets as did Mariner II, but
capsules will be landed, and spacecraft will be put into orbit about the
planets. The next mission in the Mariner series will be a flyby of the
planet Mars in 1965.

By the end of the decade, where will we be exploring, what will new
Mariners have found? Will there be life on Mars, or on any other planet
of the solar system? What causes the red spot on Jupiter? What is at the
heart of a comet? These and many other questions await answers obtained
by our future spacecraft. Mariner II is just a beginning.

  W. H. Pickering
  _Director_
  Jet Propulsion Laboratory_
  California Institute of Technology_
  April, 1963_


CONTENTS


  _FOREWORD_
  _ACKNOWLEDGMENTS_


                             CHAPTER 1 VENUS
  _The Double Star of the Ancient World_
  _The Consensus prior to Mariner II_
  _The Cytherean Riddle: Living World or Incinerated Planet_


                      CHAPTER 2 PREPARING FOR SPACE
  _A Problem in Celestial Dynamics_
  _The Organization_
  _NASA: For Science_
  _JPL: JATO to Mariner_
  _General Dynamics: The Atlas_
  _Lockheed: Agena B_


                         CHAPTER 3 THE SPACECRAFT
  _The Spaceframe_
  _The Power System_
  _CC&S: The Brain and the Stopwatch_
  _Telecommunications: Relaying the Data_
  _Attitude Control: Balancing in Space_
  _Propulsion System_
  _Temperature Control_
  _The Scientific Instruments_


                       CHAPTER 4 THE LAUNCH VEHICLE
  _The Atlas Booster: Power of Six 707’s_
  _The Agena B: Start and Restart_


                       CHAPTER 5 FLIGHT INTO SPACE
  _Mariner I: An Abortive Launch_
  _Mariner II: A Roll before Parking_
  _The Parking Orbit_
  _Orientation and Midcourse Maneuver_
  _The Long Cruise_
  _Encounter and Beyond_
  _The Record of Mariner_


                      CHAPTER 6 THE TRACKING NETWORK
  _Deep Space Instrumentation Facility_
  _The Goldstone Complex_
  _The Woomera Station_
  _The Johannesburg Station_
  _Mobile Tracking Station_


                     CHAPTER 7 THIRTEEN MILLION WORDS
  _Communication Control_
  _The Operations Center_
  _Central Computing Facility_


                   CHAPTER 8 THE SCIENTIFIC EXPERIMENTS
  _Data Conditioning System_
  _Cosmic Dust Detector_
  _Solar Plasma Experiment_
  _High-energy Radiation Experiment_
  _The Magnetometer_
  _Microwave Radiometer_
  _Infrared Radiometer_
  _Mariner’s Scientific Objectives_


                     CHAPTER 9 THE LEGACY OF MARINER
  _Space without Dust?_
  _The Ubiquitous Solar Wind_
  _High-energy Particles: Fatal Dosage?_
  _A Magnetic Field?_
  _The Surface: How Hot?_
  _Cloud Temperatures: The Infrared Readings_
  _The Radar Profile: Measurements from Earth_


                     CHAPTER 10 THE NEW LOOK OF VENUS
  _APPENDIX_
  _INDEX_


ACKNOWLEDGMENTS

Researching the material, gathering and comparing data, preparation of
review drafts and attending to the hundreds of details required to
produce a document on the results of such a program as the Mariner
mission to Venus is a tremendous task. Special acknowledgment is made to
Mr. Harold J. Wheelock who, on an extremely short time scale, carried
the major portion of this work to completion.

Although the prime sources for the information were the Planetary
Program office and the Technical Divisions of the Jet Propulsion
Laboratory, other organizations were extremely helpful in providing
necessary data, notably the George C. Marshall Space Flight Center, the
Lockheed Missiles and Space Company, the Astronautics Division of the
General Dynamics Corporation, and, of course, the many elements of the
National Aeronautics and Space Administration.

JPL technical information staff members who assisted Mr. Wheelock in
production of the manuscript and its illustrations were Mr. James H.
Wilson, Mr. Arthur D. Beeman and Mr. Albert E. Tyler. JPL is also
grateful to Mr. Chester H. Johnson for his help and suggestions in
preparing the final manuscript.




                               CHAPTER 1
                                 VENUS


Halfway between Los Angeles and Las Vegas, the California country climbs
southward out of the sunken basin of Death Valley onto the
3500-foot-high floor of the Mojave desert.

On this immense plateau in an area near Goldstone Dry Lake, about 45
miles north of the town of Barstow, a group of 85-foot antennas forms
the nucleus of the United States’ world-wide, deep-space tracking
network.

Here, on the morning of December 14, 1962, several men were gathered in
the control building beneath one of the antennas, listening intently to
the static coming from a loudspeaker. They were surrounded by the exotic
equipment of the space age. Through the window loomed the gleaming metal
framework of an antenna.

Suddenly a voice boomed from the loudspeaker: “The numbers are changing.
We’re getting data!”

The men broke into a cheer, followed by an expectant silence.

Again the voice came from the speaker: “The spacecraft’s crossing the
terminator ... it’s still scanning.”

At that moment, some 36 million miles from the Earth, the National
Aeronautics and Space Administration’s Mariner[1] spacecraft was passing
within 21,600 miles of the planet Venus and was radioing back
information to the Goldstone Station—the first scientific data ever
received by man from the near-vicinity of another planet.

At the same time, in Washington, D.C., a press conference was in
progress. Mr. James E. Webb, Administrator of the National Aeronautics
and Space Administration, and Dr. William H. Pickering, Director of the
Jet Propulsion Laboratory, stood before a bank of microphones. In a few
moments, Dr. Pickering said, the audience would hear the sound of
Mariner II as it transmitted its findings back to the Earth.

Then, a musical warble, the voice of Mariner II, resounded in the hall
and in millions of radios and television sets around the nation.
Alluding to the Greek belief that harmonious sounds accompanied the
movement of the planets, Dr. Pickering remarked that this, in truth, was
the music of the spheres.

Mariner II had been launched from Cape Canaveral, Florida, on August 27,
1962. Its arrival at Venus was the culmination of a 109-day journey
through the strange environment of interplanetary space. The project had
gone from the drawing board to the launching pad in less than 11 months.
Mariner had taxed the resources and the manpower of the Jet Propulsion
Laboratory, California Institute of Technology; the Atlantic Missile
Range centering at Cape Canaveral; theoretical and experimental
laboratories at several universities and NASA centers; numerous elements
of the aerospace industry; and, of course, NASA management itself.

To the considerable body of engineers scattered around the world from
Pasadena to Goldstone to South Africa to Australia, the warble of
Mariner was something more than “the music of the spheres.” Intercept
with Venus was the climax of 109 days of hope and anxiety.

To the world at large, this warbling tone was a signal that the United
States had moved ahead—reached out to the planets. Mariner was exploring
the future, seeking answers to some of the unsolved questions about the
solar system.


THE DOUBLE STAR OF THE ANCIENT WORLD

Venus, the glittering beacon of our solar system, has intrigued man for
at least 4,000 years. The Babylonians first mentioned the brilliant
planet on clay tablets as early as 2,000 years before Christ. The
Egyptians, the Greeks, and the Chinese had thought of Venus as two stars
because it was visible first in the morning and then in the evening sky.
The Greeks had called the morning star Phosphorus and the evening star
Hesperos. By 500 B.C. Pythagoras, the Greek philosopher, had realized
that the two were identical.

Galileo discovered the phases of Venus in 1610. Because of the planet’s
high reflectivity, Copernicus falsely concluded that Venus was either
self-luminous or else transparent to the rays of the Sun.

Venus was tracked across the face of the Sun in 1761, from which event
the presence of an atmosphere about the planet was deduced because of
the fuzzy edges of the image visible in the telescope. Throughout the
eighteenth and nineteenth centuries, Venus continued to excite growing
scientific curiosity in Europe and America.

    [Illustration: _Venus’ orbit is almost circular. At inferior
    conjunction, the planet is between the Earth and the Sun,
    approximately 26,000,000 miles away; at superior conjunction, Venus
    is on the other side of the Sun. The elongations are the farthest
    points to the east and the west of the Earth._]

Even the development of giant telescopes and the refinement of
spectroscopic and radar astronomy techniques in recent times had yielded
few indisputable facts about Venus. Until radar studies, made from
Goldstone, California, in 1962, neither the rate nor the angle of axial
spin could be determined with any degree of accuracy. The ever-shifting
atmosphere continued to shield the Venusian surface from visual
observation on Earth, and the nature of its atmosphere became an
especially controversial mystery.


THE CONSENSUS PRIOR TO MARINER II

Venus is a virtual twin of the Earth; it approaches our planet closer
than any celestial body except the Moon, a few vagrant comets, and other
such galactic wanderers. Long fabled in song and legend as the most
beautiful object in the sky, Venus has an albedo, or reflectivity
factor, of 59% (the Moon has one of 7%). In its brightest or crescent
phase, Venus glows like a torch, even casting a distinct shadow—the only
body other than the Sun and the Moon yielding such light.

Venus’ diameter is approximately 7,700 miles, compared with Earth’s
7,900. Also as compared with 1.0 for the Earth, Venus’ mean density is
0.91, the mass 0.81, and the volume 0.92.

The Cytherean orbit (the adjective comes from Cytherea, one of the
ancient Greek names for Aphrodite—or in Roman times, Venus—the goddess
of love) is almost a perfect circle, with an eccentricity (or
out-of-roundness) of only 0.0068, lowest of all the planets. Venus rides
this orbital path at a mean distance from the Sun of 67.2 million miles
(Earth is 93 million miles), and at a mean orbital speed of 78,300 miles
per hour, as compared with Earth’s 66,600 miles per hour.

It also has a shorter sidereal period (revolution around the Sun or
year): 224 Earth days, 16 hours, 48 minutes. Estimates of the Venus
rotational period, or the length of the Venus day, have ranged from
approximately 23 Earth hours to just over 224 Earth days. The latter
rotation rate would be almost equivalent to the Venusian year and, in
such case, the planet would always have the same face to the Sun.

Venus approaches within 26 million miles of the Earth at inferior
conjunction, and is as far away as 160 million miles at superior
conjunction, when it is on the opposite side of the Sun.

The escape velocity (that velocity required to free an object from the
gravitational pull of a planet) on Venus is 6.3 miles per second,
compared with Earth’s escape velocity of 7 miles per second. The gravity
of the Earth is sufficient to trap an oxygen-bearing atmosphere near the
terrestrial surface. Because the escape velocity of Venus is about the
same as that of Earth, men have long believed (or hoped) that the
Cytherean world might hold a similar atmosphere and thus be favorable to
the existence of living organisms as we know them on the Earth. From
this speculation, numerous theories have evolved.


THE CYTHEREAN RIDDLE: LIVING WORLD OR INCINERATED PLANET

Before Mariner II, Venus probably caused more controversy than any other
planet in our solar system except Mars. Observers have visualized Venus
as anything from a steaming abode of Mesozoic-like creatures such as
were found on the Earth millions of years ago, to a dead, noxious, and
sunless world constantly ravaged by winds of incredible force.

Conjectures about the Venusian atmosphere have been inescapably tied to
theories about the Venusian topography. Because the clouds forming the
Venusian atmosphere, as viewed from the Earth through the strongest
telescopes, are almost featureless, this relationship between atmosphere
and topography has posed many problems.

Impermanent light spots and certain dusky areas were believed by some
observers to be associated with Venusian oceans. One scientist believed
he identified a mountain peak which he calculated as rising more than 27
miles above the general level of the planet.

Another feature of the Venusian topography is the lack of (detectable)
polar flattening. The Earth does have such a flattening at the poles and
it was reasoned that, because Venus did not, its rate of rotation must
be much slower than that of the Earth, perhaps as little as only once
during a Venusian year, thus keeping one face perpetually toward the
Sun.

Another school of thought speculated that Venus was covered entirely by
vast oceans; other observers concluded that these great bodies of water
have long since evaporated and that the winds, through the Cytherean
ages, have scooped up the remaining chloride salts and blasted them into
the Venusian skies, thus forming the clouds.

Related to the topographic speculations were equally tenuous theories
about its atmosphere. It was reasoned that if the oceans of Venus still
exist, then the Venusian clouds may be composed of water droplets; if
Venus were covered by water, it was suggested that it might be inhabited
by Venusian equivalents of Earth’s Cambrian period of 500 million years
ago, and the same steamy atmosphere could be a possibility.

Other theories respecting the nature of the Venusian atmosphere,
depending on how their authors viewed the Venusian terrain, included
clouds of hydrocarbons (perhaps droplets of oil), or vapors of
formaldehyde and water. Finally, the seemingly high temperature of the
planet’s surface, as measured by Earth-bound instruments, was credited
by some to the false indications that could be given by a Cytherean
ionosphere heavily charged with free electrons.

    [Illustration: _As seen from Earth, Venus is brightest at its
    crescent phases as shown in these six photographs made by the
    100-inch telescope at Mt. Wilson, California._]

However, the consensus of pre-Mariner scientific thinking seemed
generally to indicate no detectable free oxygen in the atmosphere; this
fact inveighed against the probability of surface vegetation, because
Earth-bound vegetation, at least, uses carbon dioxide and gives off
oxygen into the atmosphere. On the other hand, a preponderance of carbon
dioxide in the Venusian atmosphere was measured which would create a
greenhouse effect. The heat of the Sun would be trapped near the surface
of the planet, raising the temperature to as high as 615 degrees F. If
the topography were in truth relatively flat and the rate of rotation
slow, the heating effect might produce winds of 400 miles per hour or
more, and sand and dust storms beyond Earthly experience. And so the
controversy continued.

But at 1:53.13.9 a.m., EST, on August 27, 1962, the theories of the past
few centuries were being challenged. At that moment, the night along the
east Florida coast was shattered by the roar of rocket engines and the
flash of incandescent exhaust streams. The United States was launching
Mariner II, the first spacecraft that would successfully penetrate
interplanetary space and probe some of the age-old mysteries of our
neighbor planet.




                               CHAPTER 2
                          PREPARING FOR SPACE


In the summer of 1961, the United States was pushing hard to strengthen
its position in the exploration of space and the near planets. The
National Aeronautics and Space Administration was planning two projects,
both to be launched by an Atlas booster and a Centaur high-energy second
stage capable of much better performance than that available from
earlier vehicles.

The Mariner program had two goals: Mariner A was ticketed for Venus and
Mariner B was scheduled to go to Mars. Caltech’s Jet Propulsion
Laboratory had management responsibility under NASA for both projects.
These spacecraft were both to be in the 1,000- to 1,250-pound class.
Launch opportunities for the two planets were to be best during the
1962-1964 period and the new second-stage booster known as Centaur was
expected to be ready for these operations.

But trouble was developing for NASA’s planners. By August, 1961, it had
become apparent that the Centaur would not be flying in time to take
advantage of the 1962 third-quarter firing period, when Venus would
approach inferior conjunction with the Earth. JPL studied the problem
and advised NASA that a proposed lightweight, hybrid spacecraft
combining certain design features of Ranger III (a lunar spacecraft) and
Mariner A could be launched to Venus in 1962 aboard a lower-powered
Atlas-Agena B launch vehicle.

    [Illustration: _The Mariner II spacecraft was launched by an Atlas
    first-stage booster vehicle and an Agena B second stage with restart
    capability._]

  ATLAS-AGENA ADAPTER
  AGENA B
  MARINER SPACECRAFT
  SHROUD

The proposed spacecraft would be called Mariner R and was to weigh about
460 pounds and carry 25 pounds of scientific instruments (later
increased to 40 pounds). The restart capability of Agena was to be used
in a 98-statute-mile parking orbit. (The orbit was later raised to 115
statute miles and the spacecraft weight was reduced to about 447
pounds.)

Two spacecraft would be launched one after the other from the same pad
within a maximum launch period extending over 56 days from July to
September, 1962. The minimum launch separation between the two
spacecraft would be 21 days.

As a result of the JPL recommendations, NASA cancelled Mariner A in
September, 1961, and assigned JPL to manage a Mariner R Project to fly
two spacecraft (Mariner I and II) to the vicinity of Venus in 1962.
Scientific measurements were to be made in interplanetary space and in
the immediate environs of the planet, which would also be surveyed in an
attempt to determine the characteristics of its atmosphere and surface.
Scientific and engineering data would also be transmitted from the
spacecraft to the Earth while it was in transit and during the encounter
with Venus.

Scientists and engineers were now faced with an arduous task. Within an
11-month period, on a schedule that could tolerate no delays, two
spacecraft had to be designed, developed, assembled, tested, and
launched. In order to meet the schedule, tested flight assemblies and
instruments would have to be in the Pasadena assembly facility by
mid-January, 1962, just four months after the start of the project.
Probably no other major space project of similar scope had ever been
planned on such a demanding schedule.

    [Illustration: _Mariner II travelled across 180 million miles of
    space within our solar system as it spanned the gap between Earth
    and Venus (shown here as the third and second planets, respectively,
    from the Sun)._]

With the shipment of equipment to Atlantic Missile Range (AMR) scheduled
for 9½ months after inception of the project, management and design
teams went all-out on a true “crash” effort. Quick decisions had to be
made, a workable design had to be agreed upon very early, and, once
established, the major schedule objectives could not be changed. Certain
design modifications and manufacturing changes in the Atlas-Agena launch
vehicle were also necessary.

Wherever possible, Ranger design technology had to be used in the new
spacecraft and adapted to the requirements of a planetary probe. Other
necessary tasks included trajectory calculation; arrangements for
launch, space flight, and tracking operations; and coordination of AMR
Range support.

Following NASA’s September, 1961 decision to go ahead with the Mariner R
Project, JPL’s Director, Dr. William H. Pickering, called on his
seasoned team of scientists and engineers. Under Robert J. Parks,
Planetary Program Director, Jack N. James was appointed as Project
Manager for Mariner R, assisted by W. A. Collier. Dan Schneiderman was
appointed Spacecraft System Manager, and Dr. Eberhardt Rechtin headed
the space tracking program, with supervision of the Deep Space
Instrumentation Facility (DSIF) operations under Dr. Nicholas Renzetti.
The Mariner space flight operations were directed by Marshall S.
Johnson.


A PROBLEM IN CELESTIAL DYNAMICS

In order to send Mariner close enough to Venus for its instruments to
gather significant data, scientists had to solve aiming and guidance
problems of unprecedented magnitude and complexity.

The 447-pound spacecraft had to be catapulted from a launching platform
moving around the Sun at 66,600 miles per hour, and aimed so precisely
that it would intercept a planet moving 78,300 miles per hour (or 11,700
miles per hour faster than the Earth) at a point in space and time some
180.2 million miles away and 109 days later, with only one chance to
correct the trajectory by a planned midcourse maneuver.

And the interception had to be so accurate that the spacecraft would
pass Venus within 8,000 to 40,000 miles. The chances of impacting the
planet could not exceed 1 in 1,000 because Mariner was not sterilized
and might contaminate Venus. Also, much more data could be gathered on a
near-miss flight path than on impact. Furthermore, at encounter (in the
target area) the spacecraft had to be so positioned that it could
communicate with Earth, see the Sun with its solar panels, and scan
Venus at the proper angles.

Along the way, Mariner had to be able to orient itself so that its solar
panels were facing or “locked onto” the Sun in order to generate its own
power; acquire and maintain antenna orientation to the Earth; correct
its attitude constantly to hold Earth and Sun lock; receive, store, and
execute commands to alter its course for a closer approach to Venus; and
communicate its findings to Earth with only 3 watts of radiated power
and over distances never before spanned.

    [Illustration: _Mariner II was launched in a direction opposite to
    the orbital travel of the Earth. The Sun’s gravity then pulled it in
    toward the planet Venus._]

Early in the program it had been decided that two spacecraft would be
launched toward Venus. Only 56 days were available for both launchings
and the planet would not be close enough again for 19 months—the period
between inferior conjunctions or the planet’s closest approach to the
Earth. On any one of these days, a maximum of 2 hours could be used for
getting the vehicles off the launch pad. In addition, the Mariners would
have to leave the Earth in a direction opposite to that of the Earth’s
direction of orbital revolution around the Sun. This flight path was
necessary so the spacecraft could then fall in toward the Sun and
intercept Venus, catching and passing the Earth along the way, about 65
days and 11.5 million miles out.

This feat of celestial navigation had to be performed while passing
through the hostile environment of interplanetary space, where the probe
might be subjected to solar winds (charged particles) travelling at
velocities up to 500 miles per second; intense bombardment from cosmic
radiation, charged protons, and alpha particles moving perhaps 1.5
million miles per hour; radiated heat that might raise the spacecraft
temperatures to unknown values; and the unknown dangers from cosmic
dust, meteorites, and other miscellaneous space debris.

In flight, each spacecraft would have to perform more than 90,000
measurements per day, reporting back to the Earth on 52 engineering
readings, the changes in interplanetary magnetic fields, the density and
distribution of charged particles and cosmic dust, and the intensity and
velocity of low-energy protons streaming out from the Sun.

At its closest approach to Venus, the spacecraft instruments would be
required to scan the planet during a brief 35-minute encounter, to
gather data that would enable Earth scientists to determine the
temperature and structure of the atmosphere and the surface, and to
process and transmit that data back to the Earth.


THE ORGANIZATION

Flying Mariner to Venus was a team effort made possible through the
combined resources of several United States governmental organizations
and their contractors, science, and industry. The success of the Mariner
Project resulted primarily from the over-all direction and management of
the National Aeronautics and Space Administration and the Jet Propulsion
Laboratory, and the production and launch capabilities of the vehicle
builders and the Air Force. Several organizations bore the major
responsibility: NASA Headquarters, JPL, NASA’s Marshall Space Flight
Center and Launch Operations Center, Astronautics Division of General
Dynamics, and Lockheed Missiles and Space Company.


NASA: FOR SCIENCE

The National Aeronautics and Space Administration was an outgrowth of
the participation of the United States in the International Geophysical
Year program and of the nation’s space effort, revitalized following
Russia’s successful orbiting of Sputnik I in 1957.

    [Illustration: _Final NACA meeting, August 21, 1958._]

    [Illustration: _Model of X-1 research plane._]

    [Illustration: _Headquarters of National Aeronautics and Space
    Administration, Washington, D.C._]

    [Illustration: _JPL developed first JATO units in 1941._]

    [Illustration: _Other Laboratory Projects were the Corporal missile
    (left) and Explorer I (right), the first U.S. satellite._]

Under the terms of the law which created NASA, it is a Federal Agency
dedicated to carrying out “activities in space ... devoted to peaceful
purposes for the benefit of all mankind.” NASA is charged to preserve
the role of our nation as a leader in the aeronautical and space
sciences and technology and to utilize effectively the science and
engineering resources of the United States in accomplishing these goals.
Activities associated with military operations in space and the
development of weapons systems are specifically assigned to the Defense
Department.

In November, 1957, before the creation of NASA, President Eisenhower had
established a Scientific Advisory Committee to determine the national
objectives and requirements in space and to establish the basic
framework within which science, industry, and the academic community
could best support these objectives.

The Committee submitted a report to the President in March, 1958,
recommending creation of a civilian agency to conduct the national space
programs. The recommendation, endorsed by the President, was submitted
to the Congress on April 2, 1958. The National Aeronautics and Space Act
of 1958 was passed and became law in July, 1958.

NASA was officially established on October 1, 1958, and Dr. T. Keith
Glennan, President of Case Institute of Technology, was appointed as the
first Administrator. The facilities and personnel of the National
Advisory Committee for Aeronautics (NACA) were transferred to form the
nucleus of the new NASA agency.

NACA had performed important and significant research in aeronautics,
wind tunnel technology, and aerodynamics since 1915, including a series
of experimental rocket research aircraft that culminated in the X-15. It
was natural that it be expanded to include space operations.

Among the NACA Centers transferred to NASA were the Langley Research
Center at Hampton, Virginia; Lewis Research Center, Cleveland, Ohio;
Ames Research Center, Moffett Field, California; Flight Research Center,
Edwards, California; and the rocket launch facility at Wallops Island,
Virginia.

Those personnel of the Naval Research Laboratory who had been working on
Project Vanguard were also transferred to NASA, as was the project.
These personnel are now part of the new Goddard Space Flight Center at
Greenbelt, Maryland.

The October, 1958, transfers also included a number of the space
projects of the Advanced Research Projects Agency of the Defense
Department. In a December, 1958, Executive Order, the President assigned
the former Army facilities of the Jet Propulsion Laboratory at Pasadena,
California, to NASA. At the same time, the group working under Dr.
Wernher von Braun at the Army Ballistic Missile Agency (commanded by
Major General John B. Medaris) was made responsive to NASA requirements.

On July 1, 1960, the George C. Marshall Space Flight Center (MSFC) was
organized at Huntsville under von Braun’s direction. The former
Development Operations Division of ABMA formed the nucleus of the new
Center. The MSFC mission was to procure and to supervise the adaptation
of launch vehicles for NASA space missions, including Atlas, Thor, and
Agena. Marshall is directly responsible for the design and development
of advanced, high-thrust booster vehicles such as the Saturn C-1 and C-5
and the Nova.

An agency to conduct NASA affairs at Cape Canaveral was formed within
MSFC on July 1, 1960. Known then as the Launch Operations Directorate
(LOD), it was directed by Dr. Kurt H. Debus. LOD became independent of
Marshall in March, 1962, when it was redesignated the Launch Operations
Center (LOC), reporting directly to the Office of Manned Space Flight.
This separation resulted largely because the activities at AMR were
becoming more operational in character and less oriented toward research
and development.

LOC handles such functions for NASA as the scheduling of launch dates
and liaison with the Atlantic Missile Range for support activities. The
Center will have the responsibility in the field for assembly, checkout,
and launch of the Saturn and Nova boosters.

Following the election of President Kennedy in 1961, James E. Webb
replaced Dr. Glennan as Administrator of NASA. Shortly after, a new
national goal was announced—placing a man on the Moon and returning him
safely to the Earth in this decade. Meanwhile, JPL had been assigned
responsibility for unmanned exploration of the Moon, the planets, and
interplanetary space, and thus was charged with supporting the NASA
manned flight program through these activities.

In less than five years, NASA grew to include eight flight and research
centers and about 21,000 technical and management personnel. Within
NASA, Dr. Abe Silverstein’s Office of Space Flight Programs was
responsible for the Mariner R Project which was directly assigned to Ed
Cortright, Director of Lunar & Planetary Programs, and Fred
Kochendorfer, who is NASA’s Program Chief for Mariner. A subsequent
reorganization placed responsibility under Dr. Homer Newell’s Office of
Space Sciences, and Oran Nicks became Director of Lunar & Planetary
Programs.


JPL: JATO TO MARINER

The Jet Propulsion Laboratory, staffed and operated for NASA by
California Institute of Technology, had long been active in research and
development in the fields of missiles, rockets, and the space-associated
sciences. The first government-sponsored rocket research group in the
United States, JPL had originated on the Caltech campus in 1939, an
outgrowth of the Guggenheim Aeronautical Laboratories, then headed by
celebrated aerodynamicist Dr. Theodore von Karman.

Von Karman and his associates moved their operation to a remote spot at
the foot of the San Gabriel mountains and, working from this base, in
1941 the pioneering group developed the first successful jet-assisted
aircraft takeoff (JATO) units for the Army Air Force. The Laboratory
began a long association with the Army Ordnance Corps in 1944, when the
Private A test rocket was developed. In retrospect, it is now recognized
that the Private A was the first U. S. surface-to-surface,
solid-propellant rocket. Its range was 10 miles!

JPL’s WAC Corporal rocket set a U. S. high-altitude record of 43.5 miles
in 1945. Mounted on a German V-2 as the Bumper-WAC, it achieved an
altitude record of 250 miles in 1947. More important, this event was the
first successful in-flight separation of a two-stage rocket—the
feasibility of space exploration had been proved.

After the end of World War II, JPL research set the stage for
high-energy solid-propellant rockets. For the first time the solid
propellants, which contained both fuel and oxidizers, were cast in
thin-walled cases. Techniques were then developed for bonding the
propellants to the case, and burning radially outward from the central
axis was achieved. Attention was then turned to increasing the energy of
the propellants.

By 1947, the Corporal E, a new liquid-propellant research rocket, was
being fired. JPL was asked to convert it into a tactical weapon in 1949.
The Corporal E then became the first liquid-propellant
surface-to-surface guided missile developed by the United States or the
Western bloc of nations.

Because of the need for higher mobility and increased firing rate, JPL
later designed and developed the solid-propellant Sergeant—the nation’s
first “second-generation” weapon system. This inertially guided missile
was immune to electronic countermeasures by an enemy.

Meanwhile, JPL scientists had pioneered in the development of electronic
telemetering techniques, which permit an accurate monitoring of system
performance while missiles are in flight. By 1944, Dr. William H.
Pickering, a New Zealand born and Caltech-trained physicist who had
worked with Dr. Robert Millikan in cosmic ray research, had been placed
in charge of the telemetering effort at JPL. Pickering became Director
of the Laboratory in 1954.

Following the launching of Sputnik I, the Army-JPL team which had worked
on the Jupiter C missile to test nose cones, was assigned the
responsibility for putting the first United States satellite into orbit
as soon as possible. In just 83 days, a modified Jupiter C launch
vehicle was prepared, an instrumented payload was assembled, a network
of space communications stations was established, and Explorer I was
orbited on January 31, 1958. Explorer was an instrumented assembly
developed by JPL and the State University of Iowa. It discovered the
inner Van Allen radiation belt.

Subsequently, JPL worked with the Army on other projects to explore
space and to orbit satellites. Among these were Pioneer III, which
located the outer Van Allen Belt, and Pioneer IV, the first U. S. space
probe to reach Earth-escape velocity and to perform a lunar fly-by
mission.


GENERAL DYNAMICS: THE ATLAS

The launch vehicle for Mariner was an Atlas D booster with an Agena B
second stage. Historically, Atlas can be traced to October, 1954, when
the former Convair Corporation (later acquired by General Dynamics) was
invited to submit proposals for research and development of four missile
systems, including a 5,000-mile intercontinental weapon.

In January, 1946, Convair assigned K. J. Bossart to begin a study of two
proposed types of 5,000-mile missiles: one jet powered at subsonic
speeds, with wings for aerodynamic control; the other a supersonic,
ballistic (wingless and bullet-like), rocket-powered missile capable of
operating outside the Earth’s atmosphere.

    [Illustration: _Photo courtesy of General Dynamics/Astro_
    _Atlas missiles in assembly facility at General
    Dynamics/Astronautics plant._]

This was the beginning of Project MX-774, lineal ancestor of Atlas.
After captive testing at San Diego in 1947, three of the experimental
missiles were test-launched at White Sands Proving Ground in New Mexico.
The first flight failed at 6,200 feet after a premature engine burnout.

In 1947, the Air Force shelved the MX-774 project. However, this brief
program had proved the feasibility of three concepts later used in
Atlas: swiveling engines for directional control; lightweight,
pressurized airframe structures; and separable nose cones.

The Korean War stimulated the ICBM concept and, in 1951, a new MX-1593
contract was awarded to Convair to study ballistic and glide rockets. By
September, 1951, Convair was proposing a ballistic missile that would
incorporate some of the features of the MX-774 design. A plan for an
accelerated program was presented to the Air Force in 1953. After a year
of study, a full go-ahead for the project, now called Atlas, was given
in January, 1955.

The unit handling the Atlas program was set up as Convair Astronautics,
with J. R. Dempsey as president, on March 1, 1957.

The first Atlas test flight, in June of 1957, ended in destruction of
the missile when it went out of control. Following another abortive
attempt, the first fully successful flight of an Atlas missile was made
from Cape Canaveral on December 17, 1957.

The Atlas program was in full swing by 1958, when 14 test missions were
flown. The entire missile was orbited in December, 1958, as Project
Score. It carried the voice of President Eisenhower as a Christmas
message to the world. The Atlas missile system was accepted for field
operations by the Air Force in 1958.

Also in 1958, an Atlas achieved a new distance record, flying more than
9,000 miles down the Atlantic Missile Range, where it landed in the
Indian Ocean, off the South African coast.

Atlas has been modified for use by NASA as a space vehicle booster.
Known as the Atlas D, it has launched lunar probes, communications and
scientific Earth satellites, and manned space vehicles.


LOCKHEED: AGENA B

The Lockheed Agena B second-stage vehicle was mounted on top of the
Atlas booster in the launch of the Mariner spacecraft. The U. S. Air
Force had first asked Lockheed Missiles and Space Division, headed by L.
E. Root, to work on an advanced orbital vehicle for both military and
scientific applications in 1956. On October 29 of that year, Lockheed
was appointed prime weapon system contractor on the new Agena Project,
under the Air Force Ballistic Missile Division. In order to speed the
program, the Thor missile was used as the booster stage for the early
Agena flights. The Atlas was also utilized in later operations.

In August, 1957, the Air Force recommended that the program be
accelerated as much as possible. After Russia orbited Sputnik I in
October of 1957, a further speed-up was ordered.

The first of the Agena-Discoverer series was launched into orbit on
February 28, 1959, with the Thor missile as the booster. The first
restart in orbit occurred on February 18, 1961, when the new Agena B
configuration was used to put Discoverer XXI into orbit. All of the NASA
missions using Agena, beginning with Ranger I in August, 1961, have been
flown with the B model.

Agena holds several orbiting records for U. S. vehicles. The first water
recovery followed the 17 orbits of Discoverer XIII on August 11, 1960.
The first air recovery of a capsule from orbit occurred with Discoverer
XIV on August 18, 1960. In all, a total of 11 capsules were recovered
from orbit, 7 in the air, 4 from the sea.




                               CHAPTER 3
                             THE SPACECRAFT


In the 11 brief months which JPL had to produce the Mariner spacecraft
system, there was no possibility of designing an entirely new
spacecraft. JPL’s solution to the problem was derived largely from the
Laboratory’s earlier space exploration vehicles, such as the Vega, the
Ranger lunar series, and the cancelled Mariner A.

Wherever possible, components and subsystems designed for these projects
were either utilized or redesigned. Where equipment was purchased from
industrial contractors, existing hardware was adapted, if practicable.
Only a minimum of testing could be performed on newly designed equipment
and lengthy evaluation of “breadboard” mock-ups was out of the question.

Ready for launch, the spacecraft measured 5 feet in diameter and 9 feet
11 inches in height. With the solar panels and the directional antenna
unfolded in the cruise position, Mariner was 16 feet 6 inches wide and
11 feet 11 inches high.


THE SPACEFRAME

The design engineers were forced to work within the framework of the
earlier spacecraft technology because of the time restrictions, but
Mariner I and II could weigh only about half as much as the Ranger
spacecraft and just over one-third as much as the planned Mariner A.

    [Illustration: _Mariner spacecraft with solar panels, microwave
    radiometer, and directional antenna extended in flight position.
    Principal components are shown._]

  ROLL AXIS
  OMNIANTENNA
  MAGNETOMETER SENSOR
  PARTICLE FLUX DETECTORS (GEIGER TUBES)
  RADIOMETER REFERENCE HORNS
  MICROWAVE RADIOMETER
  INFRARED RADIOMETER
  ION-CHAMBER
  COSMIC DUST DETECTOR
  EARTH SENSOR
  SOLAR PANEL
  COMMAND ANTENNA
  SOLAR SAIL
  ATTITUDE CONTROL GAS BOTTLES
  SOLAR PLASMA DETECTOR
  DIRECTIONAL ANTENNA

The basic structural unit of Mariner was a hexagonal frame made of
magnesium and aluminum, to which was attached an aluminum
superstructure, a liquid-propelled rocket engine for midcourse
trajectory correction, six rectangular chassis mounted one on each face
of the hexagonal structure, a high-gain directional antenna, the Sun
sensors, and gas jets for control of the spacecraft’s attitude.

The tubular, truss-type superstructure extended upward from the base
hexagon. It provided support for the solar panels while latched under
the shroud during the launch phase, and for the radiometers, the
magnetometer, and the nondirectional antenna, which was mounted at the
top of the structure. The superstructure was designed to be as light as
possible, yet be capable of withstanding the predicted load stresses.

The six magnesium chassis mounted to the base hexagon housed the
following equipment: the electronics circuits for the six scientific
experiments, the communications system electronics; the data encoder
(for processing data before telemetering it to the Earth) and the
command electronics; the attitude control, digital computer, and timing
sequencer circuits; a power control and battery charger assembly; and
the battery assembly.

The allotment of weights for Mariner II forced rigid limitation in the
structural design of the spacecraft. As launched, the weights of the
major spacecraft subsystems were as follows:

          Structure                             77 pounds
          Solar panels                          48 pounds
          Electronics                          146 pounds
          Propulsion                            32 pounds
          Battery                               33 pounds
          Scientific experiments                41 pounds
          Miscellaneous equipment               70 pounds
          Gross weight                         447 pounds


THE POWER SYSTEM

Mariner II was self-sufficient in power. It converted energy from
sunlight into electrical current through the use of solar panels
composed of photoelectric cells which charged a battery installed in one
of the six chassis on the hexagonal base. The control, switching, and
regulating circuits were housed in another of the chassis cases.

    [Illustration: _This hexagonal frame, constructed of magnesium and
    aluminum, is the basic supporting structure around which the Mariner
    spacecraft is assembled._]

    [Illustration: _Plan view from top showing six magnesium chassis
    hinged in open position._]

  VIEW LOOKING AFT ASSEMBLIES HINGED IN OPEN POSITION
    SCIENTIFIC EQUIPMENT ASSEMBLY I
    COMMUNICATIONS ASSEMBLY II
    DATA ENCODER AND COMMAND ASSEMBLY III
    ATTITUDE CONTROL AND CC AND S ASSEMBLY IV
    POWER ASSEMBLY V
    BATTERY ASSEMBLY VI

The battery operated the spacecraft systems during the period from
launch until the solar panels were faced onto the Sun. In addition, the
battery supplied power during trajectory maneuvers when the panels were
temporarily out of sight of the Sun. It shared the demand for power when
the panels were overloaded. The battery furnished power directly for
switching various equipment in flight and for certain other heavy loads
of brief duration, such as the detonation of explosive devices for
releasing the solar panels.

    [Illustration: _Mariner spacecraft with solar panels in open
    position. Note extension to left panel to balance solar pressures in
    flight._]

The Mariner battery used sealed silver-zinc cells and had a capacity of
1000 watt-hours. It weighed 33 pounds and was recharged in flight by the
solar panels.

The solar panels, as originally designed, were 60 inches long by 30
inches wide and contained approximately 9800 solar cells in a total area
of 27 square feet. Each solar cell produced only about 230
one-thousandths of a volt. The entire array was designed to convert the
Sun’s energy to electrical power in the range between 148 and 222 watts.
When a later design change required the extension of one panel in order
to add more solar cells, it was necessary to add a blank extension to
the other panel in order to balance the solar pressure on the
spacecraft.

In order to protect the solar cells from the infrared and ultraviolet
radiation of the Sun, which would produce heat but no electrical energy,
each cell was shielded from these rays by a glass filter which was
nevertheless transparent to the light which the cells converted into
power.

The power subsystem electronics circuits were housed in another of the
hexagon chassis cases. This equipment was designed to receive and switch
power either from the solar panels, the battery, or a combination of the
two, to a booster-regulator.


CC&S: THE BRAIN AND THE STOPWATCH

Once the Atlas booster lifted Mariner off the launch pad, the digital
Central Computer and Sequencer (CC&S) performed certain computations and
provided the basic timing control for those spacecraft subsystems which
required a sequenced programming control.

The CC&S was designed to initiate the operations of the spacecraft in
three distinct sequences or “modes”: (1) the launch mode, from launch
through the cruise configuration; (2) the midcourse propulsion mode,
when Mariner readjusted its sights on Venus; and (3) the encounter mode,
involving commands for data collection in the immediate vicinity of the
planet.

The CC&S timed Mariner’s actions as it travelled more than 180 million
miles in pursuit of Venus. A highly accurate electronic clock
(crystal-controlled oscillator) scheduled the operations of the
spacecraft subsystems. The oscillator frequency of 307.2 kilocycles was
reduced to the 2,400- and 400-cycle-per-second output required for the
power subsystem.

The control oscillator also timed the issuance of commands by the CC&S
in each of the three operating modes of the spacecraft.

A 1-pulse-per-minute signal was provided for such launch sequence events
as the extension of the solar panels 44 minutes after launch, turning on
power for the attitude control subsystem one hour after launch, and for
certain velocity correction commands during the midcourse maneuver.

    [Illustration: _The spacecraft used two antennas for communication.
    The omni-antenna (top) was utilized when the directional antenna
    (bottom) could not be pointed at the Earth._]

    [Illustration: _This command antenna (on solar panel) was used to
    receive maneuver commands._]

A 1-pulse-per-second signal was generated as a reference during the roll
and pitch maneuvers in the midcourse trajectory correction phase. One
pulse was generated every 3.3 hours in order to initiate the command to
orient the directional antenna on the Earth at 167 hours after launch.

Finally, one pulse every 16.7 hours was used to readjust the
Earth-oriented direction of the antenna throughout the flight.


TELECOMMUNICATIONS: RELAYING THE DATA

The telecommunications subsystem enabled Mariner to receive and to
decode commands from the Earth, to encode and to transmit information
concerning space and Mariner’s own functioning, and to provide a means
for precise measurement of the spacecraft’s velocity and position
relative to the Earth. The spacecraft accomplished all these functions
using only 3 watts of transmitted power up to a maximum range of 53.9
million miles.

A data encoder unit, with CC&S sequencing, timed the three phases of
Mariner’s journey: (1) In the launch mode, only engineering data on
spacecraft performance were transmitted; (2) during the cruise mode,
information concerning space and Mariner’s own functioning was
transmitted; and (3) while the spacecraft was in the vicinity of Venus,
only scientific information concerning the planet was to be transmitted.
(The CC&S failed to start the third mode automatically and it was
initiated by radio command from the Earth.) After the encounter with
Venus, Mariner was programmed to switch back to the cruise mode for
handling both engineering and science data (this sequence was also
commanded by Earth radio).

Mariner II used a technique for modulating (superimposing intelligent
information) its radio carrier with telemetry data known as phase-shift
keying. In this system, the coded signals from the telemetry
measurements displace another signal of the same frequency but of a
different phase. These displacements in phase are received on the Earth
and then translated back into the codes which indicate the voltage,
temperature, intensity, or other values measured by the spacecraft
telemetry sensors or scientific instruments.

A continually repeating code, almost noise-like both in sound and
appearance on an oscilloscope, was used for synchronizing the ground
receiver decoder with the spacecraft. This decoder then deciphered the
data carried on the information channel.

This technique was called a two-channel, binary-coded, pseudo-noise
communication system and it was used to modulate a radio signal for
transmission, just as in any other radio system.

Radio command signals transmitted to Mariner were decoded in a command
subassembly, processed, and routed to the proper using devices. A
transponder was used to receive the commands, send back confirmation of
receipt to the Earth, and distribute them to the spacecraft subsystems.

Mariner II used four antennas in its communication system. A cone-like
nondirectional (omni) antenna was mounted at the top of the spacecraft
superstructure, and was used from injection into the Venus flight
trajectory through the midcourse maneuver (the directional antenna could
not be used until it had been oriented on the Earth).

A dish-type, high-gain, directional antenna was used at Earth
orientation and after the trajectory correction maneuver was completed.
It could receive radio signals at greater distances than the
nondirectional antenna. The directional antenna was nested beneath the
hexagonal frame of the spacecraft while it was in the nose-cone shroud.
Following the unfolding of the solar panels, it was swung into operating
position, although it was not used until after the spacecraft locked
onto the Sun.

The directional antenna was equipped with flexible coaxial cables and a
rotary joint. It could move in two directions; one motion was supplied
by rolling the spacecraft around its long axis.

In addition, two command antennas, one on either side of one of the
solar panels, received radio commands from the Earth for the midcourse
maneuver and other functions.


ATTITUDE CONTROL: BALANCING IN SPACE

Mariner II had to maintain a delicate balance in its flight position
during the trip to Venus (like a tight-wire walker balancing with a
pole) in order to keep its solar panels locked onto the Sun and the
directional antenna pointed at the Earth. Otherwise, both power and
communications would have been lost.

A system of gas jets and valves was used periodically to adjust the
attitude or position of the spacecraft. Expulsion of nitrogen gas
supplied the force for these adjustments during the cruise mode. While
the spacecraft was subjected to the heavier disturbances caused by the
rocket engine during the midcourse maneuver, the gas jets could not
provide enough power to control the attitude of the spacecraft and it
was necessary to use deflecting vanes as rudders in the rocket engine
exhaust stream for stabilizing purposes.

The attitude control system was activated by CC&S command 60 minutes
after launching. It operated first to align the long axis of the
spacecraft with the Sun; thus its solar panels would face the Sun.
Either the Sun sensors or the three gyroscopes mounted in the pitch
(rocking back and forth), yaw (side to side), and roll axes, could
activate the gas jet valves during the maneuver, which normally required
about 30 minutes to complete.

The spacecraft was allowed a pointing error of 1 degree in order to
conserve gas. The system kept the spacecraft swinging through this 1
degree of arc approximately once each 60 minutes. As it neared the limit
on either side, the jets fired for approximately ¹/₅₀ of a second to
start the swing slowly in the other direction. Thus, Mariner rocked
leisurely back and forth throughout its 4-month trip.

Sensitive photomultiplier tubes or electric eyes in the Earth sensor,
mounted on the directional antenna, activated the gas jets to roll the
spacecraft about the already fixed long axis in order to face the
antenna toward the Earth. When the Earth was “acquired,” the antenna
would then necessarily be oriented in the proper direction. If telemetry
revealed that Mariner had accidentally fixed on the Moon, over-ride
radio commands from the Earth could restart the orientation sequence.


PROPULSION SYSTEM

The Mariner propulsion system for midcourse trajectory correction
employed a rocket engine that weighed 37 pounds with fuel and a nitrogen
pressure system, and developed 50 pounds of thrust for a maximum of 57
seconds. The system was suspended within the central portion of the
basic hexagonal structure of the spacecraft.

This retro-rocket engine used a type of liquid propellant known as
anhydrous hydrazine and it was so delicately controlled that it could
burn for as little as ²/₁₀ of a second and increase the velocity of the
spacecraft from as little as ⁷/₁₀ of a foot per second to as much as 200
feet per second.

The hydrazine fuel was stored in a rubber bladder inside a
doorknob-shaped container. At the ignition command, nitrogen gas under
3,000-pound-per-square-inch pressure was forced into the propellant tank
through explosively activated valves. The nitrogen then squeezed the
rubber bladder, forcing the hydrazine into the combustion chamber.

    [Illustration: _The midcourse propulsion system provides trajectory
    correction for close approach to Venus._]

  FUEL TANK
  NITROGEN TANK
  JET VANE ACTUATOR (ONE OF FOUR)
  THRUST CHAMBER

Hydrazine, a monopropellant, requires a starting ignition for proper
combustion. In the Mariner system, nitrogen tetroxide starting or
“kindling” fluid was injected into the propellant tank by a pressurized
cartridge. Aluminum oxide pellets in the tank acted as catalysts to
control the speed of combustion of the hydrazine. The burning of the
hydrazine was stopped when the flow of nitrogen gas was halted, also by
explosively activated valves.


TEMPERATURE CONTROL

Mariner’s 129 days in space presented some unique problems in
temperature control. Engineers were faced with the necessity of
achieving some form of thermal balance so that Mariner would become
neither too hot nor too cold in the hostile environment of space.

The spacecraft’s temperature control system was made as thermally
self-sufficient as possible. Paint patterns, aluminum sheet, thin gold
plating, and polished aluminum surfaces reflected and absorbed the
proper amount of heat necessary to keep the spacecraft and its
subsystems at the proper operating temperatures.

Thermal shields were used to protect the basic hexagon components. The
upper shield, constructed of aluminized plastic on a fiberglass panel,
protected the top of the basic structure and was designed for maximum
immunity to ultraviolet radiation. The lower shield was installed below
the hexagon; it was made of aluminum plastic faced with aluminum foil
where it was exposed to the blast of the midcourse rocket engine
exhaust.

    [Illustration: _Methods used to control the temperature of the
    Mariner spacecraft in flight._]

  CHROMATE CONVERSION COATING
  UPPER THERMAL SHIELD
  POLISHED ALUMINUM
  LOUVERS
  GOLD PLATE
  BLACK PAINT
  LOWER THERMAL SHIELD
  WHITE PAINT

The six electronics cases on the hexagon structure were variously
treated, depending upon the power of the components contained in each.
Those of high power were coated with a good radiating surface of white
paint; assemblies of low power were provided with polished aluminum
shields to minimize the heat loss.

The case housing the attitude control and CC&S electronics circuits was
particularly sensitive because the critical units might fail above 130
degrees F. A special assembly was mounted on the face of this case; it
consisted of eight movable, polished aluminum louvers, each actuated by
a coiled, temperature-sensitive, bimetallic element. When the
temperature rose, the elements acted as springs and opened the louvers.
A drop in temperature would close them.

Structures and bracket assemblies external to the basic hexagon were
gold plated if made of magnesium, or polished if aluminum. Thus
protected, these items became poor thermal radiators as well as poor
solar absorbers, making them relatively immune to solar radiation.
External cabling was wrapped in aluminized plastic to produce a similar
effect.

The solar panels were painted on the shaded side for maximum radiation
control properties. Other items were designed so that the internal
surfaces were as efficient radiators as possible, thus conserving the
spacecraft’s heat balance.


THE SCIENTIFIC INSTRUMENTS

Four instruments were operated throughout the cruise and encounter modes
of Mariner: a magnetometer, a solar plasma detector, a cosmic dust
detector, and a combined charged-particle detector and radiation
counter. Two radiometers were used only in the immediate vicinity of
Venus.

These instruments are described in detail in Chapter 8.




                               CHAPTER 4
                           THE LAUNCH VEHICLE


The motive power of Mariner itself was limited to a trajectory
correction rocket engine and an ability, by means of gas jets, to keep
its two critical faces pointing at the Sun and the Earth. Therefore, the
spacecraft had to be boosted out of the Earth’s gravitational field and
injected into a flight path accurate enough to allow the trajectory
correction system to alter the course to deliver the spacecraft close
enough to Venus to be within operating range of the scientific
instruments.

The combined Atlas-Agena B booster system which was selected to do the
job had a total thrust of about 376,000 pounds. With this power,
Atlas-Agena could put 5,000 pounds of payload into a 345-mile orbit,
propel 750 pounds on a lunar trajectory, or launch approximately 400
pounds on a planetary mission. This last capability would be taxed to
the limit by the 447 pounds of the Mariner spacecraft.


THE ATLAS BOOSTER: POWER OF SIX 707’S

The 360,000 pounds of thrust developed by the Atlas D missile is
equivalent to the thrust generated by the engines of six Boeing 707 jet
airplanes. All of this awesome power requires a gargantuan amount of
fuel: in less than 20 seconds, Atlas consumes more than a
propeller-driven, four-engine airplane burns in flying coast-to-coast
nonstop.

    [Illustration: _Photo courtesy of General Dynamics/Astronautics_
    _This military version of the Atlas missile is modified for NASA
    space flights._]

The Atlas missile, as developed by Convair for the Air Force, has a
range of 6,300 miles and reaches a top speed of 16,000 miles per hour.
The missile has been somewhat modified for use by NASA as a space
booster vehicle. Its mission was to lift the second-stage Agena B and
the Mariner spacecraft into the proper position and altitude at the
right speed so that the Agena could go into Earth orbit, preliminary to
the takeoff for interplanetary space.

The Atlas D has two main sections: a body or sustainer section, and a
jettisonable aft, or booster engine section. The vehicle measures about
100 feet in length (with military nose cone) and has a diameter of 10
feet at the base. The weight is approximately 275,000 pounds.

No aerodynamic control surfaces such as fins or rudders are used. The
Atlas is stabilized and controlled by “gimbaling” or swiveling the
engine thrust chambers by means of a hydraulic system. The direction of
thrust can thus be altered to control the movements of the missile.

The aft section mounts two 154,500-pound-thrust booster engines and the
entire section is jettisoned or separated from the sustainer section
after the booster engines burn out. The 60,000-pound-thrust sustainer
engine is attached at the center line of the sustainer section. Two
1,000-pound-thrust vernier (fine steering) engines are installed on
opposite sides of the tank section in the yaw or side-turn plane.

All three groups of engines operate during the booster phase. Only the
sustainer and the vernier engines burn after staging (when the booster
engine section is separated from the sustainer section of the missile).

All of the engines use liquid oxygen and a liquid hydrocarbon fuel
(RP-1) which is much like kerosene. Dual turbopumps and valves control
the flow of these propellants. The booster engine propellants are
delivered under pressure to the propellant or combustion chamber, where
they are ignited by electroexplosive devices. Each booster thrust
chamber can be swiveled a maximum of 5 degrees in pitch (up and down)
and yaw (from side to side) about the missile centerline.

The sustainer engine is deflected 3 degrees in pitch and yaw. The
outboard vernier engines gimbal to permit pitch and roll movement
through 140 degrees of arc, and yaw movement through 20 degrees toward
the missile body and 30 degrees outward.

All three groups of engines are started and develop their full rated
thrust while the missile is held on the launch pad. After takeoff, the
booster engines burn out and are jettisoned. The sustainer engine
continues to burn until its thrust is terminated. The swiveled vernier
engines provide the final correction in velocity and missile attitude
before they are also shut down.

The propellant tank is the basic structure of the forward or sustainer
section of the Atlas. It is made of thin stainless steel and is
approximately 50 feet long. Internal pressure of helium gas is used to
support the tank structure, thus eliminating the need for internal
bracing structures, saving considerable weight, and increasing over-all
performance of the missile. The helium gas used for this purpose is
expanded to the proper pressure by heat from the engines.

Equipment pods on the outside of the sustainer section house the
electrical and electronic units and other components of the missile
systems.

The Atlas uses a flight programmer, an autopilot, and the gimbaled
engine thrust chamber actuators for flight control. The attitude of the
vehicle is controlled by the autopilot, which is set for this automatic
function before the flight. Guidance commands are furnished by a ground
radio guidance system and computer.

The airborne radio inertial guidance system employs two radio beacons
which respond to the ground radar. A decoder on board the missile
processes the guidance commands.


THE AGENA B: START AND RESTART

Launching Mariner to Venus required a second-stage vehicle capable of
driving the spacecraft out of Earth orbit and into a proper flight path
to the planet.

    [Illustration: _Photo courtesy of Lockheed Missiles and Space
    Company_
    _The Agena B second stage is hoisted to the top of the gantry at
    AMR._]

The Agena B used for this purpose weighs 1,700 pounds, is 60 inches in
diameter, and has an over-all length of 25 feet, varying somewhat with
the payload. The Agena B fuel tanks are made of 0.080-inch aluminum
alloy.

The liquid-burning engine develops more than 16,000 pounds of thrust.
The propellants are a form of hydrazine and red fuming nitric acid.

The Agena can be steered to a desired trajectory by swiveling the
gimbal-mounted engine on command of the guidance system. The attitude of
the vehicle is controlled either by gimbaling the engine or by ejecting
gas from pneumatic thrusters.

The Agena has the ability to restart its engine after it has already
fired once to reach an Earth orbital speed. This feature makes possible
a significant increase in payload and a change of orbital altitude. A
velocity meter ends the first and second burns when predetermined
velocities have been reached.

After engine cutoff, the major reorientation of the vehicle is achieved
through gas jets controlled from an electronic programming device. This
system can turn the Agena completely around in orbit, or pitch it down
for reentry into the atmosphere. The attitude is controlled by an
infrared, heat-sensitive horizon scanner and gyroscopes.

The principal modification to the Agena vehicle for the Mariner II
mission was an alteration to the spacecraft-Agena adapter in order to
reduce weight.




                               CHAPTER 5
                           FLIGHT INTO SPACE


With the Mariner R Project officially activated in the fall of 1961 and
the launch vehicles selected, engineers proceeded at full speed to meet
the difficult launch schedule.

A preliminary design was adopted in late September, when the scientific
experiments to be carried on board were also selected. By October 2, a
schedule had been established that would deliver two spacecraft to the
assembly building in Pasadena by January 15 and 29, 1962, respectively,
with the spares to follow in two weeks.

During the week of November 6, tests were underway to determine problems
involved in mating a mock-up of the spacecraft with the Agena shroud and
adapter assembly. A thermal control model of the spacecraft had already
gone into the small space simulator at JPL for preliminary temperature
tests.

MR-1, the first Mariner scheduled for flight, was in assembly
immediately after January 8, 1962, and the process was complete by the
end of the month, when electrical and magnetic field tests had been
started. At the same time, assembly of MR-2 was underway. Work on MR-1
was a week ahead of schedule by the end of the month.

A full-scale temperature control model of the spacecraft went into the
large space simulator on February 26. In mid-March, system tests began
on both spacecraft and it was decided that the flight hardware would be
tested only in the small simulator, with the temperature control model
continuing in the large chamber.

    [Illustration: _Technician wears hood and protective goggles while
    working on Mariner spacecraft in Space simulator chamber at Jet
    Propulsion Laboratory, Pasadena._]

On March 26, MR-1 was subjected to full-scale mating tests with the
shroud (cover) and the adapter for mounting the spacecraft on top of the
Agena. MR-2 was undergoing vibration tests during the week of April 16.
By April 30, MR-1 had completed vibration tests and had been mapped for
magnetic fields so that, once compensated for, they would not interfere
with the magnetometer experiment in space.

A dummy run of MR-1 was conducted on May 7 and the spacecraft, space
flight center, and computing equipment were put through a simulated
operations test run during the same week.

By May 14, clean-up and final inspection by microscope had begun on
MR-1, MR-2, and MR-3 (the latter spacecraft had been assembled from the
spares). Soon after, the first two van loads of equipment were shipped
to Cape Canaveral. The final system test of MR-1 was completed on May 21
and the test of MR-2 followed during the same week.

During the week of May 28, all three spacecraft and their associated
ground support equipment were packed, loaded, and shipped to the
Atlantic Missile Range (AMR). At the same time, the Atlas designated to
launch MR-1 went aboard a C-133 freight aircraft at San Diego. On the
same day, an Air Force order grounded all C-133’s for inspection and the
plane did not depart until June 9.

By June 11, 1962, the firing dates had been established and both
spacecraft were ready for launching. The Atlas booster had already been
erected on the launch pad. The dummy run and a joint flight acceptance
test were completed on MR-1 during the week of July 2. Final flight
preparations and system test of MR-1 and the system test of MR-2 were
concluded a week later.

Thus, in 324 days, a new spacecraft project had been activated; the
design, assembly, and testing had been completed; and the infinite
number of decisions pertaining to launch, AMR Range Operations,
deep-space tracking, and data processing activities had been made and
implemented.

Venus was approaching the Earth at the end of its 19-month excursion
around the Sun. The launch vehicles and Mariners I and II stood ready to
go from Canaveral’s Launch Complex 12. The events leading to the first
close-up look at Venus and intervening space were about to reach their
first crisis: a fiery explosion over the Atlantic Ocean.


MARINER I: AN ABORTIVE LAUNCH

After 570 hours of testing, Mariner I was poised on top of the
Atlas-Agena launch vehicle during the night of July 20, 1962. The time
was right, the Range and the tracking net were standing by, the launch
vehicles were ready to cast off the spacecraft for Venus.

    [Illustration: _Atlas for launching Mariner II arrives at Cape
    Canaveral in C-133 aircraft._]

The countdown was begun at 11:33 p.m., EST, July 20, after several
delays because of trouble in the Range Safety Command system. At the
time, the launch count stood at T minus 176 minutes—if all went well,
176 minutes until the booster engines were ignited.

Another hold again delayed the count until 12:37 a.m., July 21, when
counting was resumed at T minus 165 minutes. The count then proceeded
without incident to T minus 79 minutes at 2:20 a.m., when uncertainty
over the cause of a blown fuse in the Range Safety circuits caused the
operations to be “scrubbed” or cancelled for the night. The next launch
attempt was scheduled for July 21-22.

The second launch countdown for Mariner I began shortly before midnight,
July 21. Spacecraft power had been turned on at 11:08 p.m., with the
launch count at T minus 200 minutes. At T minus 135 minutes, the weather
looked good. A 41-minute hold was required at minus 130 minutes (12:17
a.m., July 22) in order to change a noisy component in the ground
tracking system.

When counting was resumed at T minus 130 minutes, the clock read 12:48
a.m. A previously scheduled hold was called at T minus 60 minutes,
lasting from 1:58 to 2:38 a.m. The good weather still held.

At T minus 80 seconds, power fluctuations in the radio guidance system
forced a 34-minute hold. Time was resumed at 4:16 a.m., when the
countdown was set back to T minus 5 minutes.

At exactly 4:21.23 a.m., EST, the Atlas thundered to life and lifted off
the pad, bearing its Venus-bound load. The boost phase looked good until
the Range Safety officer began to notice an unscheduled yaw-left
(northeast) maneuver. By 4:25 a.m., it was evident that, if allowed to
continue, the vehicle might crash in the North Atlantic shipping lanes
or in some inhabited area. Steering commands were being supplied but
faulty application of the guidance equations was taking the vehicle far
off course.

Finally, at 4:26.16 a.m., after 293 seconds of flight and with just 6
seconds left before separation of the Atlas and Agena—after which the
launch vehicle could not be destroyed—a Range Safety officer hit the
“destruct” button.

A flash of light illuminated the sky and the choppy Atlantic waters were
awash with the glowing death of a space probe. Even as it fluttered down
to the sea, however, the radio transponder of the shattered Mariner I
continued to transmit for 1 minute and 4 seconds after the destroy
command had been sent.

Mariner I did not succumb easily.


MARINER II: A ROLL BEFORE PARKING

Ever since Mariner II had arrived at the Cape on June 4, test teams of
all organizations had labored day and night to prepare the spacecraft
for launch. The end of their efforts culminated after some 690 hours of
test time, both in California and in Florida.

Thirty-five days after Mariner I met its explosive end, the first
countdown on Mariner II was underway. At 6:43 p.m., EST, August 25,
1962, time was picked up. The countdown did not proceed far, however.
The Atlas crew asked for a hold at T minus 205 minutes (8:39 p.m.)
because of stray voltages in the command destruct system caused by a
defective Agena battery. After considerable delay, the launch effort was
scrubbed at 10:06 p.m.

    [Illustration: _Two assembly operations and system checkouts are
    performed separated by a trip to the pad to verify compatibility
    with the launch vehicle_]

    [Illustration: _A complete electronic checkout station in the hangar
    supports the spacecraft to ensure operability_]

    [Illustration: _Mariner takes form as the solar panels are attached
    and the final hangar checkout operations are performed before the
    launch._]

    [Illustration: _Wrapped in a dust cover, the spacecraft is
    transferred from Hangar AE at AMR to the explosive safe area for
    further tests._]

    [Illustration: _Inside the bunker-like explosive safe area, the
    powerful midcourse maneuver rocket engine is installed in the center
    of the spacecraft._]

    [Illustration: _Final assembly and inspection complete, Mariner is
    “canned” in the nose shroud that will protect it through the Earth’s
    atmosphere and into space._]

    [Illustration: _At the pad, the shrouded spacecraft is lifted past
    the Atlas ..._]

    [Illustration: _... and the Agena._]

    [Illustration: _Twelfth floor: Mariner reaches its mating level._]

    [Illustration: _The spacecraft is eased over to the top of the Agena
    ..._]

    [Illustration: _... and carefully mated to it._]

The second launch attempt started at 6:37 p.m., August 26, with the
Atlas-Agena B and Mariner II ready on the pad. At 9:52 p.m., T minus 100
minutes, a 40-minute hold was called to replace the Atlas main battery.
By 10:37, with 95 minutes to launch, all spacecraft systems were ready
to go.

A routine hold at T minus 60 minutes was extended beyond 30 minutes in
order to verify the spacecraft battery life expectation. At 11:48 p.m.,
with the count standing at T minus 55 minutes, the spacecraft, the
vehicles, the Range, and the DSIF were all given the green light.

When good launching weather was reported at 12:18 a.m., August 27, just
25 minutes from liftoff, a cautious optimism began to mount in the
blockhouse and among the tired crews.

But the tension began to build again. The second prescheduled hold at T
minus 5 minutes was extended beyond a half-hour when the radio guidance
system had difficulty with ground station power. Counting was “picked
up” and the clock continued to move down to 60 seconds before liftoff.

Suddenly, the radio guidance system was in trouble again. Fluctuations
showed in its rate beacon signals, and another hold was called. Still
another hold for the same reason followed at T minus 50 seconds. This
time, at 1:30 a.m., the count was set back to T minus 5 minutes.

One further crisis developed during this hold—only 3 minutes of
pre-launch life remained in Atlas’ main battery. A quick decision was
made to hold the switchover to missile power until T minus 60 seconds to
help conserve the life of the battery.

At 1:48 a.m., the count was resumed again at T minus 5 minutes. The long
seconds began to drag. Finally, the Convair test director pressed the
fire button.

Out on the launch pad, the Atlas engines ignited with a white puff and
began to strain against the retaining bolts as 360,000 pounds of thrust
began to build up. In a holocaust of noise and flame, the Atlas was
released and lifted off the launch pad on a bearing of 106.8 degrees at
exactly 1 hour, 53 minutes, 13.927 seconds in the morning of August 27,
1962.

Mariner II was on its way to listen to the music of the spheres.

As the launch vehicle roared up into the night sky, the JPL Launch
Checkout Station (DSIF O) tracked the spacecraft until Mariner
disappeared over the horizon. A quick, preliminary evaluation of
spacecraft data showed normal readings and Atlas seemed to be flying a
true course. The AMR in-flight data transmission and computational
operations were being performed as expected. With liftoff out of the
way, the launch began to look good.

After the radio signal from the ground guidance system cut off the
engines and the booster section was jettisoned, the remaining Atlas
forward section, plus the Agena and the spacecraft began to roll.
However, it stabilized itself in a normal attitude. Although the Atlas
had not gone out of the Range Safety restrictions, it was within just 3
degrees of exceeding the Agena horizon sensor limits, which would have
forced another aborted mission.

After the booster separation, the Atlas sustainer and vernier engines
continued to burn until they were shut off by radio guidance command.
Shortly thereafter, spring-loaded bolts ejected the nose-cone shroud
which had protected the spacecraft against frictional heating in the
atmosphere. Simultaneously, the gyroscopes in the Agena were started
and, at about 1:58 a.m., the Agena and the spacecraft separated from the
now-spent Atlas, which was retarded by small retro-rockets and drifted
back into the atmosphere, where it was destroyed by friction on reentry.


THE PARKING ORBIT

As the Agena separated from the Atlas booster vehicle, it was programmed
to pitch down almost 15 degrees, putting it roughly parallel with the
local horizon. Then, following a brief coasting period, the Agena engine
ignited at 1:58.53 a.m. and fired until 2:01.12 a.m. Cut-off occurred at
a predetermined value of velocity. Both the Agena and the spacecraft had
now reached a speed of approximately 18,000 miles per hour and had gone
into an Earth orbit at an altitude of 116.19 statute miles.

The second stage and the spacecraft were now in a “parking orbit,” which
would allow the vehicle to coast out to a point more favorable than Cape
Canaveral for blasting off Mariner for Venus.

During the launch, Cape radar had tracked the radar beacon on the Agena,
losing it on the horizon at 2:00.53 a.m. Radar stations at Grand Bahama
Island, San Salvador, Ascension, the Twin Falls Victory ship, and
Pretoria (in South Africa) continued to track down range. Meanwhile,
Antigua had “locked on” and tracked the spacecraft’s radio transponder
and telemetry from 1:58 to 2:08 a.m. when it went over the Antigua
horizon.

    [Illustration: _Mariner II is accelerated to Earth-escape velocity
    and out of orbit near St. Helena. Rotation of earth causes flight
    path to appear to double back to west over Africa._]

    [Illustration: _The sequence of events in the launch phase of the
    Mariner flight to Venus._]

      EVENT
  1. LIFTOFF
  2. ATLAS BOOSTER ENGINE CUTOFF
  3. ATLAS SUSTAINER ENGINE CUTOFF
  4. ATLAS VERNIER ENGINE CUTOFF
  5. SPACECRAFT SHROUD EJECTION
  6. ATLAS-AGENA B SEPARATION
  7. AGENA B FIRST IGNITION
  8. AGENA B FIRST CUTOFF
  9. AGENA B SECOND IGNITION
  10. AGENA B SECOND CUTOFF
  11. SPACECRAFT SEPARATION
  12. INITIATE AGENA YAW MANEUVER
  13. COMPLETE AGENA YAW MANEUVER
  14. EXPEL UNUSED AGENA PROPELLANT

The second coasting period lasted 16.3 minutes, a time determined by the
ground guidance computer and transmitted to the Agena during the vernier
burning period of Atlas. Then, Agena restarted its engine and fired for
a second time. At the end of this firing period, both the Agena and
Mariner, still attached, had been injected into a transfer trajectory to
Venus at a velocity exceeding that required to escape from the Earth’s
gravity.

The actual injection into space occurred at 26 minutes 3.08 seconds
after liftoff from the Cape (2:19.19 a.m., EST) at a point above 14.873
degrees south latitude and 2.007 degrees west longitude. Thus, Mariner
made the break for Venus about 360 miles northeast of St. Helena, 2,500
miles east of the Brazilian coast, and about 900 miles west of Angola on
the west African shore.

During injection, the vehicle was being tracked by Ascension, telemetry
ship Twin Falls Victory, and Pretoria. Telemetry ship Whiskey secured
the spacecraft signal just after injection and tracked until 2:26 a.m.
Pretoria began its telemetry track at 2:21 and continued to track for
almost two hours, until 4:19 a.m.

Injection velocity was 7.07 miles per second or 25,420 miles per hour,
just beyond Earth-escape speed. The distance at the time of injection
from Canaveral’s Launch Complex 12 was 4,081.3 miles.

The Agena and Mariner flew the escape path together for another two
minutes after injection before they were separated at 2:21 a.m. Agena
then performed a 140-degree yaw or retro-turn maneuver by expelling
unused propellants. The purpose was to prevent the unsterilized Agena
from possibly hitting the planet, and from following Mariner too closely
and perhaps disturbing its instruments.

Now, Mariner II was flying alone and clear. Ahead lay a journey of 109
days and more than 180 million miles.


ORIENTATION AND MIDCOURSE MANEUVER

As Mariner II headed into space, the Deep Space Instrumentation Facility
(DSIF) network began to track the spacecraft. At 2:23.59 a.m., DSIF 5 at
Johannesburg, aided by the Mobile Tracking Station, installed in vans in
the vicinity, was “looking” at the spacecraft, just four minutes after
injection.

Johannesburg was able to track Mariner until 4:04 p.m. because, as the
trajectory took Mariner almost radially away from the Earth, our planet
began in effect to turn away from under the spacecraft. On an Earth map,
because of its course and the rotation of the Earth, Mariner II appeared
to describe a great arc over the Indian Ocean far to the west of
Australia, then to turn north and west and to proceed straight west over
south-central Africa, across the Atlantic, and over the Amazon Basin of
northern South America. Johannesburg finally lost track at a point over
the middle of South America.

While swinging over the Indian Ocean on its first pass, the spacecraft
was acquired by Woomera’s DSIF 4 at 2:42.30 a.m., and tracked until 8:08
a.m., when Mariner was passing just to the north of Madagascar on a
westerly course. Goldstone did not acquire the spacecraft until it was
approaching the east coast of South America at 3:12 p.m., August 27.

With Mariner slowly tumbling in free space, it was now necessary to
initiate a series of events to place the spacecraft in the proper flight
position. At 2:27 a.m., 44 minutes after launch, the Mariner Central
Computer and Sequencer (CC&S) on board the spacecraft issued a command
for explosively activated pin pullers to release the solar panels and
the radiometer dish from their launch-secured positions. At 2:53, 60
minutes after liftoff, the attitude control system was turned on and the
Sun orientation sequence began with the extension of the directional
antenna to a preset angle of 72 degrees.

    [Illustration: _Mariner II was launched while Venus was far behind
    the Earth. During the 109-day flight, Venus overtook and passed the
    Earth. It rendezvoused with the spacecraft at a point about
    36,000,000 miles from the Earth._]

    [Illustration: _During the midcourse maneuver, the trajectory of
    Mariner II was corrected so that the spacecraft would approach
    within 21,598 miles of Venus._]

  ROLL MANEUVER ANTENNA UP
  PITCH MANEUVER
  MOTOR BURN
  SUN REAQUISITION ANTENNA REPOSITION
  EARTH REAQUISITION

The Sun sensors then activated the gas jets and moved the spacecraft
about until the roll or long axis was pointed at the Sun. This maneuver
required only 2½ minutes after the CC&S issued the command. The solar
panel power output of 195 watts was somewhat higher than anticipated, as
were the spacecraft temperatures, which decreased and stabilized six
hours after the spacecraft oriented itself on the Sun.

On August 29, a command from Johannesburg turned on the cruise
scientific experiments, including all the instruments except the two
radiometers. The rate of data transmission was then observed to decrease
as planned and the data conditioning system was functioning normally.

For seven days, no attempt was made to orient the spacecraft with
respect to the Earth because the Earth sensors were too sensitive to
operate properly at such a close range. On September 3, the CC&S
initiated the Earth acquisition sequence. The gyroscopes were turned on,
the cruise scientific instruments were temporarily switched off, and a
search for the Earth began about the roll axis of the spacecraft.

During this maneuver, the long axis of the spacecraft was held steady in
a position pointing at the Sun and the gas jets rolled the spacecraft
around this axis until the sensors, mounted in the directional antenna,
could “see” the Earth. Apparently, the Earth sensor was already viewing
the Earth because the transmitter output immediately switched from the
omni- to the directional antenna, indicating that no search was
necessary.

However, the initial brightness reading from the Earth sensor was 38, an
intensity that might be expected if the spacecraft were locked onto the
Moon instead of the Earth. As a result, the midcourse maneuver was
delayed until verification of Earth lock was obtained.

Mariner’s injection into the Venus trajectory yielded a predicted miss
of 233,000 miles in front of the planet, well within the normal miss
pattern expected as a result of the launch. Because the spacecraft was
designed to cross the orbit of Venus behind the planet and pass between
it and the Sun, it was necessary to correct the trajectory to an
approximate 8,000- to 40,000-mile “fly-by” so the scientific instruments
could operate within their design ranges.

After comparison of the actual flight path with that required for a
proper near-miss, the necessary roll, pitch, and motor-burn commands
were generated by the JPL computers. When, on September 4, it had been
established that the spacecraft was indeed oriented on the Earth and not
the Moon, a set of three commands was transmitted to the spacecraft from
Goldstone, to be stored in the electronic “memory unit” until the start
command was sent.

At 1:30 p.m., PST, the first commands were transmitted: a 9.33-degree
roll turn, a 139.83-degree pitch turn, and a motor-burn command to
produce a 69.5-mile-per-hour velocity change.

At 2:39 p.m., a fourth command was sent to switch from the directional
antenna to the omni-antenna. Finally, a command went out instructing the
spacecraft to proceed with the now “memorized” maneuver program.

Mariner then turned off the Earth and Sun sensors, moved the directional
antenna out of the path of the rocket exhaust stream, and executed a
9.33-degree roll turn in 51 seconds.

Next, the pitch turn was completed in 13¼ minutes, turning the
spacecraft almost completely around so the motor nozzle would point in
the correct direction when fired.

The spacecraft was stabilized and the roll and pitch turns controlled by
gyroscopes, which signalled the attitude control system the rate of
correction for comparison with the already computed values.

With the solar panels no longer directly oriented on the Sun, the
battery began to share the power demand and finally carried the entire
load until the spacecraft had again been oriented on the Sun.

At the proper time, the motor—controlled by the CC&S—ignited and burned
for 27.8 seconds, while the spacecraft’s acceleration was compared with
the predetermined values by the accelerometer. During this period, when
the gas jets could not operate properly, the spacecraft was stabilized
by movable vanes or rudders in the exhaust of the midcourse motor.

The velocity added by the midcourse motor resulted in a decrease of the
relative speed of the spacecraft with respect to the Earth by 59 miles
per hour (from 6,748 to 6,689 miles per hour), while the speed relative
to the Sun increased by 45 miles per hour (from 60,117 to 60,162 miles
per hour).

This apparently paradoxical condition occurred because, in order to
intercept Venus, Mariner had been launched in a direction opposite to
the Earth’s course around the Sun. The midcourse maneuver turned the
spacecraft around and slowed its travel away from the Earth while
allowing it to increase its speed around the Sun in the direction of the
Earth’s orbit. Gradually, then, the spacecraft would begin to fall in
toward the Sun while moving in the same direction as the Earth, catching
and passing the Earth on the 65th day and intersecting Venus’ orbit on
the 109th day.

At the time of the midcourse maneuver, the spacecraft was travelling
slightly inside the Earth’s orbit by 70,000 miles, and was behind the
Earth by 1,492,500 miles.


THE LONG CRUISE

After its completion of the midcourse maneuver, Mariner reoriented
itself on the Sun in 7 minutes and on the Earth in about 30 minutes.
During the midcourse maneuver, the omnidirectional antenna was used;
now, with the maneuver completed, the directional antenna was switched
back in for the duration of the mission.

Ever since the spacecraft had left the parking orbit near the Earth and
been injected into the Venus trajectory, the Space Flight Operations
Center back in Pasadena had been the nerve center of the mission.
Telemetered data had been coming in from the DSIF stations on a 24-hour
schedule. During the cruise phase, from September 5 to December 7, a
total of 16 orbit computations were made to perfect the planet encounter
prediction. On December 7, the first noticeable Venus-caused effects on
Mariner’s trajectory were observed, causing a definite deviation of the
spacecraft’s flight path.

On September 8, at 12:50 p.m., EST, the spacecraft lost its attitude
control, which caused the power serving the scientific instruments to
switch off and the gyroscopes to switch on automatically for
approximately three minutes, after which normal operation was resumed.
The cause was not apparent but the chances of a strike by some small
space object seemed good.

As a result of this event, a significant difference in the apparent
brightness reading of the Earth sensor was noted. This sensor had been
causing concern for some time because its readings had decreased to
almost zero. Further decrease, if actually caused by the instrument and
not by the telemetry sensing elements, could result in loss of Earth
lock and the failure of radio contact.

After the incident of September 8, the Earth sensor brightness reading
increased from 6 to 63, a normal indication for that day. Thereafter,
this measurement decreased in an expected manner as the spacecraft
increased its distance from the Earth.

Mariner II was now embarked on the long cruise. On September 12, the
distance from the Earth was 2,678,960 miles and the spacecraft speed
relative to the Earth was 6,497 miles per hour. Mariner was accelerating
its speed as the Sun’s gravity began to exert a stronger pull than the
Earth’s. On October 3, Mariner was nearly 6 million miles out and moving
at 6,823 miles per hour relative to the Earth. A total of 55,600,000
miles had been covered to that point.

Considerable anxiety had developed at JPL when Mariner’s Earth sensor
reading had fallen off so markedly. This situation was relieved by the
unexplained return to normal on September 8, although the day-to-day
change in the brightness number was watched closely. The apparent
ability of the spacecraft to recover its former performance after the
loss of attitude control on September 8 and again on September 29 was an
encouraging sign.

Another disturbing event occurred on October 31, when the output from
one solar panel deteriorated abruptly. The entire power load was thrown
on the other panel, which was then dangerously near its maximum rated
output. To alleviate this situation, the cruise scientific instruments
were turned off. A week later, the malfunctioning panel returned to
normal operation and the science instruments were again turned on.
Although the trouble had cleared temporarily, it developed again on
November 15 and never again corrected itself. The diagnosis was a
partial short circuit between one string of solar cells and the panel
frame, but by now the spacecraft was close enough to the Sun so that one
panel supplied enough power.

By October 24, the spacecraft was 10,030,000 miles from the Earth and
was moving at 10,547 miles per hour relative to the Earth. The distance
from Venus was now 21,266,000 miles.

October 30 was the 65th day of the mission and at 5 a.m., PST, Mariner
overtook and passed the Earth at a distance of 11,500,000 miles. Since
the spacecraft’s direction of travel had, in effect, been reversed by
the midcourse maneuver, it had been gaining on the Earth in the
direction of its orbit, although constantly falling away from the Earth
in the direction of the Sun.

The point of equal distance between the Earth and Venus was passed on
November 6, when Mariner was 13,900,000 miles from both planets and
travelling at 13,843 miles per hour relative to the Earth. As November
wore on, hope for a successful mission began to mount. Using tracking
data rather than assumptions of standard midcourse performance, the
Venus miss distance had now been revised to about 21,000 miles and
encounter was predicted for December 14. But the DSIF tracking crews,
the space flight and computer operators, and the management staff could
not yet relax. The elation following the successful trajectory
correction maneuver on September 4 had given way alternately to
discouragement and guarded optimism.

Four telemetry measurements were lost on December 9 and never returned
to normal. They measured the angle of the antenna hinge, the fuel tank
pressure, and the nitrogen pressure in the midcourse and attitude
control systems. A blown fuse, designed to protect the data encoder from
short circuits in the sensors, was suspected. However, these channels
could not affect spacecraft operation and Mariner continued to perform
normally.

The rising temperatures recorded on the spacecraft were more serious.
Only the solar panels were displaying expected temperature readings;
some of the others were as much as 75 degrees above the values predicted
for Venus encounter. The heat increase became more rapid after November
20. By December 12, six of the temperature sensors had reached their
upper limits. It was feared that the failure point of the equipment
might be exceeded.

The CC&S performed without incident until just before encounter, when,
for the first time, it failed to yield certain pulses. JPL engineers
were worried about the starting of the encounter sequence, due the next
day, although they knew that Earth-based radio could send these
commands, if necessary.

On December 12, with the climax of the mission near, the spacecraft was
34,218,000 miles from the Earth, with a speed away from the Earth of
35,790 miles per hour, a Sun-relative speed of 83,900 miles per hour.

Only 635,525 miles from Venus at this point, Mariner II was closing fast
on the cloud-shrouded planet. But it was a hot spacecraft that was
carrying its load of inquisitive instruments to the historic encounter.


ENCOUNTER AND BEYOND

On its 109th day of travel, Mariner had approached Venus in a precarious
condition. Seven of the over-heated temperature sensors had reached
their upper telemetry limits. The Earth-sensor brightness reading stood
at 3 (0 was the nominal threshold) and was dropping. Some 149 watts of
power were being consumed out of the 165 watts still available from the
crippled solar panels.

At JPL’s Space Flight Operations Center, there was reason to believe
that the ailing CC&S might not command the spacecraft into its encounter
sequence at the proper time. Twelve hours before encounter, these fears
were verified.

Quickly, the emergency Earth-originated command was prepared for
transmission. At 5:35 a.m., PST, a radio signal went out from
Goldstone’s Echo Station. Thirty-six million miles away, Mariner II
responded to the tiny pulse of energy from the Earth and began its
encounter sequence.

After Mariner had “acknowledged” receipt of the command from the Earth,
the spacecraft switched into the encounter sequence as engineering data
were turned off and the radiometers began their scanning motion, taking
up-and-down readings across the face of the planet. As throughout the
long cruise, the four experiments monitoring the magnetic fields, cosmic
dust, charged particles, and solar plasma experiments continued to
operate.

    [Illustration: _Mariner II approached Venus from the dark side,
    crossed between the planet and the Sun while making three radiometer
    scans of the disk._]

As Mariner approached Venus on its night side, it was travelling about
88,400 miles per hour with respect to the Sun. At the point of closest
approach, at 11:59.28 a.m., PST, the distance from the planet was 21,598
miles.

During encounter with Venus, three scans were made: one on the dark
side, one across the terminator dividing dark and sunlit sides, and one
on the sunlit side. Although the scan went slightly beyond the edge of
the planet, the operation proceeded smoothly and good data were received
on the Earth.

With encounter completed, the cruise condition was reestablished by
radio command from the Earth and the spacecraft returned to transmitting
engineering data, together with the continuing readings of the four
cruise scientific experiments.

After approaching closer to a planet and making more meaningful
scientific measurements than any man-made space probe, Mariner II
continued on into an orbit around the Sun.

December 27, 13 days after Venus encounter, marked the perihelion, or
point of Mariner’s closest approach to the Sun: 65,505,935 miles. The
Sun-related speed was 89,442 miles per hour. As Mariner began to pull
away from the Sun in the following months, its Sun-referenced speed
would decrease.

Data were still being received during these final days and the Earth and
Sun lock were still being maintained. Although the antenna hinge angle
was no longer being automatically readjusted by the spacecraft, commands
were sent from the Earth in an attempt to keep the antenna pointed at
the Earth, even if the Earth sensor were no longer operating properly.

At 2 a.m., EST, January 3, 1963, 20 days after passing Venus, Mariner
finished transmitting 30 minutes of telemetry data to Johannesburg and
the station shut down its operation. When Woomera’s DSIF 4 later made a
normal search for the spacecraft signal, it could not be found.
Goldstone also searched in vain for the spacecraft transmissions, but
apparently Mariner’s voice had at last died, although the spacecraft
would go into an eternal orbit around the Sun.

It was estimated that Mariner’s aphelion (farthest point out) in its
orbit around the Sun would occur on June 18, 1963, at a distance of
113,813,087 miles. Maximum distance from the Earth would be 98,063,599
miles on March 30, 1963; closest approach to the Earth: 25,765,717 miles
on September 27, 1963.


THE RECORD OF MARINER

The performance record of Mariner II exceeded that of any spacecraft
previously launched from Earth:


—It performed the first and most distant trajectory-correcting maneuver
  in deep space, firing a rocket motor at the greatest distance from the
  Earth: 1,492,000 miles (September 4, 1962).

—The spacecraft transmitted continuously for four months, sending back
  to the Earth some 90 million bits of information while using only 3
  watts of transmitted power.

—Useful telemetry measurements were made at another record distance from
  the Earth: 53.9 million miles (January 3, 1963).

—Mariner II was the first spacecraft to operate in the immediate
  vicinity of another planet and return useful scientific information to
  the Earth: approximately 21,598 miles from Venus (December 14, 1962).

—Measurements were made closest to the Sun: 65.3 million miles away
  (December 27, 1962).

—Mariner’s communication system operated for the longest continuous
  period in interplanetary space: 129 days (August 27, 1962, to January
  3, 1963).

—Mariner achieved the longest continuous operation of a spacecraft
  attitude-stabilization system in space, and at a greater distance from
  the Earth than any previous spacecraft: 129 days (August 27, 1962, to
  January 3, 1963), at 53.9 million miles from the Earth.




                               CHAPTER 6
                          THE TRACKING NETWORK


Thirty-six million miles separated the Earth from Venus at encounter.
Communicating with Mariner II and tracking it out to this distance, and
beyond, represented a tremendous extension of man’s ability to probe
interplanetary space.

The problem involved:

  1. The establishment of the spacecraft’s velocity and position
          relative to the Earth, Venus, and the Sun with high precision.
  2. The transmission of commands to activate spacecraft maneuvers.
  3. The reception of readable spacecraft engineering and scientific
          data from the far-ranging Mariner.

The tracking network had to contend with many radio noise sources: the
noise from the solar system and from extragalactic origins; noise
originating from the Earth and its atmosphere; and the inherent
interference originating in the receiving equipment. These problems were
solved by using advanced high-gain antennas and ultra-stable, extremely
sensitive receiving equipment.


DEEP SPACE INSTRUMENTATION FACILITY

The National Aeronautics and Space Administration has constructed a
network of deep-space tracking stations for lunar and planetary
exploration missions. In order to provide continuous, 24-hour coverage,
three stations were built, approximately 120 degrees of longitude apart,
around the world: at Goldstone in the California desert, near
Johannesburg in South Africa, and at Woomera in the south-central
Australian desert.

    [Illustration: _The three tracking stations of the Deep Space
    Instrumentation Facility are located around the world so as to
    provide continuous flight coverage._]

These stations are the basic elements of the Deep Space Instrumentation
Facility (DSIF). In addition, a mobile tracking station installed in
vans is used near the point of injection of a spacecraft into an
Earth-escape trajectory to assist the permanent stations in finding the
spacecraft and to acquire tracking data. The control point for the DSIF
net is located at JPL in Pasadena, California (see Table 1).

The Jet Propulsion Laboratory has the responsibility for the technical
direction of the entire DSIF net and operates the Goldstone facilities
with assistance from the Bendix Corporation as a subcontractor. The
overseas stations are staffed and operated by agencies of the Republic
of South Africa and the Commonwealth of Australia.

The DSIF net tracks the position and velocity of U.S. deep-space probes,
issues commands to direct the spacecraft in flight, receives engineering
and scientific data from the probes, and automatically relays the data
to JPL in Pasadena, where it is processed by computers and interpreted.
(In the tracking operation, a signal is transmitted to the spacecraft,
where it is received and processed in a transponder, which then sends
the signal back to the Earth. The change in frequency, known as the
doppler effect, involved in this operation enables engineers to
determine the velocity at which the spacecraft is moving.)


        _Table 1. Deep Space Instrumentation Facility Stations_

  _Station_         _Location_        _Equipment_       _Functions_

  DSIF 1 (Mobile    Near point of     10-ft antenna     Fast tracking
  Tracking          injection of      25-w, 890-mc      for acquisition
  Station)          spacecraft into   transmitter       of spacecraft
                    Earth-escape
                    trajectory
  Goldstone:        California
     Pioneer Site                     85-ft             Reception of
  (DSIF 2)                            polar-mount       telemetry
                                      antenna;          Tracking
                                      Cassegrain        spacecraft
                                      feed; maser and
                                      parametric
                                      amplifier
     Echo Site                        85-ft             Transmission of
  (DSIF 3)                            polar-mount       commands
                                      antenna;          Tracking
                                      parametric        spacecraft
                                      amplifier         Stand-by
                                      10-kw, 890-mc     reception
                                      transmitter
     Venus Site                       85-ft             Advanced radar
                                      radar-type        astronomy
                                      antenna           Communications
                                                        research
  DSIF 4            Woomera,          85-ft             Reception of
                    Australia         polar-mount       telemetry
                                      antenna;          Tracking
                                      parametric        spacecraft
                                      amplifier
  DSIF 5            Johannesburg,     85-ft             Reception of
                    South Africa      polar-mount       telemetry
                                      antenna;          Tracking
                                      parametric        spacecraft
                                      amplifier         Transmission of
                                      10-kw, 890-mc     commands
                                      transmitter

The stations are equipped with receiving and tracking instruments so
sensitive that engineers estimate that they can detect radio-frequency
energy equivalent to that radiated by a 1-watt light bulb at a distance
of approximately 75 to 80 million miles. Such energy received at the
antenna would measure about 0.00000000000000000002 watt (2 × 10⁻²⁰).

The amount of power received at the antenna during Mariner’s encounter
with Venus has been calculated at about 0.000000000000000001 of a watt
(1 × 10⁻¹⁸). If a 100 percent efficient storage battery were charged
with this amount of energy for some 30 billion years, the battery would
then have stored enough energy to light an ordinary 1-watt flashlight
bulb for about 1 second only.

Furthermore, Goldstone engineers estimate that, if Mariner II had
continued to function in all its systems and to point its directional
antenna at the Earth, useful telemetry data could have been obtained by
the DSIF stations out to about 150 to 200 million miles, and tracking
data could have been secured from as far as 300 to 400 million miles.

Construction of the DSIF net was begun in 1958. The Goldstone station
was ready for the Pioneer III mission in December of that year. In
March, 1959, Pioneer IV was successfully tracked beyond the Moon. Later
in 1959, Pioneer V was tracked out to over 3 million miles.

Goldstone participated in the 1960 Project Echo communication satellite
experiments and the entire net was used in the Ranger lunar missions of
1961-1962. The Goldstone station performed Venus radar experiments in
1961 and 1962 to determine the astronomical unit more precisely and to
study the rotation rate and surface characteristics of the planet.

Following the launch of Mariner II on August 27, 1962, the full DSIF net
provided 24-hour-per-day tracking coverage throughout the mission except
for a few days during the cruise phase. The net remained on the
full-coverage schedule through the period of Venus encounter on December
14.


THE GOLDSTONE COMPLEX

The tracking antennas clustered in a 7-mile radius near Goldstone Dry
Lake, California, are the central complex of the DSIF net. Three
tracking sites are included in the Goldstone Station: Pioneer Site (DSIF
2), Echo Site (DSIF 3), and Venus Site. The Venus Site is used for
advanced radar astronomy, communication research experiments, and radio
development; it took no direct part in the Mariner spacecraft tracking
operations, but was used for the Venus radar experiments.

Pioneer Site has an 85-foot-diameter parabolic reflector antenna and the
necessary radio tracking, receiving, and data recording equipment. The
antenna can be pointed to within better than 0.02 of a degree. The
antenna has one (hour-angle) axis parallel to the polar axis of the
Earth, and the other (declination) axis perpendicular to the polar axis
and parallel to the equatorial plane of the Earth. This “polar-mount”
feature permits tracking on only one axis without moving the other.

The antenna weighs about 240 tons but can be rotated easily at a maximum
rate of 1 degree per second. The minimum tracking rate or antenna swing
(0.250686486 degree per minute) is equal to the rotation rate of the
Earth. Two drive motors working simultaneously but at different speeds
provide an antibacklash safety factor. The antenna can operate safely in
high winds.

The Pioneer antenna has a type of feed system (Cassegrain) that is
essentially similar to that used in many large reflector telescopes. A
convex cone is mounted at the center of the main dish. A received signal
is gathered by the main dish and the cone, reflected to a subreflector
on a quadripod, where the energy is concentrated in a narrow beam and
reflected back to the feed collector point on the main dish. The
Cassegrain feed system lowers the noise picked up by the antenna by
reducing interference from the back of the antenna, and permits more
convenient location of components.

The receiving system at Pioneer Site is also equipped with a low-noise,
extremely sensitive installation combining a parametric amplifier and a
maser. The parametric amplifier is a device that is “pumped” or excited
by microwave energy in such a way that, when an incoming signal is at
its maximum, the effect is such that the “pumped-in” energy augments the
original strength of the incoming signal. At the same time, the
parametric amplifier reduces the receiving system’s own electronic noise
to such a point that the spacecraft can be tracked twice as far as
before.

The maser uses a synthetic ruby mixed with chromium and is maintained at
the temperature of liquid helium—about 4.7 degrees K or -450 degrees F
(just above absolute zero)—and when “pumped” with a microwave field, the
molecular energy levels of the maser material are redistributed so as to
again improve the signal amplification while lowering the system noise.
The maser doubles the tracking capability of the system with a
parametric amplifier, and quadruples the capability of the receiver
alone.

The antenna output at Pioneer is a wide-band telemetering channel. In
addition, the antenna can be aimed automatically, using its own “error
signals.” At both the Pioneer and Echo sites at Goldstone, however, the
antenna is pointed by a punched tape prepared by a special-purpose
computer at JPL and transmitted to Goldstone by teletype.

Pioneer Site has a highly sensitive receiver designed to receive a
continuous wave signal in a narrow frequency band in the 960-megacycle
range. The site has equipment for recording tracking data for use by
computers in determining accurate spacecraft position and velocity.

The instrumentation equipment also includes electronic signal processing
devices, magnetic-tape recorders, oscillographs, and other supplementary
receiving equipment. The telemetered data can be decommutated (recovered
from a signal shared by several measurements on a time basis), encoded,
and transmitted by teletype in real time (as received from the
spacecraft) to JPL.

Echo Site is the primary installation in the Goldstone complex and has
antenna and instrumentation facilities identical to those at Pioneer,
except that there is no maser amplifier and a simpler feed system is
used instead of the Cassegrain. However, Echo was used as a transmitting
facility and only as a stand-by receiving station during the Mariner
mission.

Echo has a 10-kilowatt, 890-megacycle transmitter which was utilized for
sending commands to the Mariner spacecraft. In addition, the site has an
“atomic clock” frequency standard, based on the atomic vibrations of
rhubidium, which permits high-precision measurements of the radial
velocity of the spacecraft. A unit in the Echo system provides for
“readback” and “confirmation” by the spacecraft of commands transmitted
to it. In a sense, the spacecraft acknowledges receipt of the commands
before executing them.

Walter E. Larkin manages the Goldstone Station for JPL.


THE WOOMERA STATION

The Woomera, Australia, Station (DSIF 4), managed by William Mettyear
for the Australian Department of Supply, has essentially the same
antenna and tracking capabilities as Goldstone Echo Site, but it has no
provisions for commanding the spacecraft. A small transmitter is used
for tracking purposes only. The station is staffed and operated by the
Australian Department of Supply.

    [Illustration: _The Mobile Tracking Station (DSIF 1) follows the
    fast-moving spacecraft during its first low-altitude pass over South
    Africa._]

    [Illustration: _Station 5 of the DSIF is located near Johannesburg
    in South Africa._]

    [Illustration: _DSIF 4, at Woomera, dominates the landscape in
    Australia’s “outback.”_]

Woomera, like Johannesburg, is capable of receiving tracking (position
and velocity) data and telemetered information for real-time
transmission by radio teletype to JPL.


THE JOHANNESBURG STATION

DSIF 5 is located just outside Johannesburg in the Republic of South
Africa. This station is staffed by the National Institute of
Telecommunications Research (NITR) of the South African Council for
Scientific and Industrial Research and managed by Douglas Hogg.

The antenna and receiving equipment are identical to the Goldstone Echo
Site installation except for minor details. The station has both
transmitting and receiving capability and can send commands to the
spacecraft. Recorded tracking and telemetered data are transmitted in
real time to JPL by radio teletype.


MOBILE TRACKING STATION

The Mobile Tracking Station (DSIF 1) is a movable installation designed
for emplacement near the point of injection of a space probe to assist
the permanent stations in early acquisition of the spacecraft. This
station is necessary because at this point the spacecraft is relatively
low in altitude and consequently appears to move very fast across the
sky. The Mobile Tracking Station has a fast-tracking antenna for use
under these conditions. DSIF 1 was located near the South African
station for Mariner II. It has a 10-foot parabolic antenna capable of
tracking at a 10-degree-per-second rate. A 25-watt, 890-megacycle
transmitter is used for obtaining tracking information. A diplexer
permits simultaneous transmission and reception on the same antenna
without interference.

The equipment is installed in mobile vans so that the station can be
operated in remote areas. The antenna is enclosed in a plastic dome and
is mounted on a modified radar pedestal. The radome is inflatable with
air and protects the antenna from wind and weather conditions.

These stations of the DSIF tracked Mariner II in flight and sent
commands to the spacecraft for the execution of maneuvers. The telemetry
data received from the spacecraft during the 129 days of its mission
were recorded and transmitted to JPL, where the information was
processed and reduced by the computers of the space flight operations
complex.




                               CHAPTER 7
                         THIRTEEN MILLION WORDS


The task of receiving, relaying, processing, and interpreting the data
coming in simultaneously on a twenty-four-hour basis for several months
from the several scientific and many engineering sources of the Mariner
spacecraft was of truly monumental proportions.

This activity involved five DSIF tracking stations scattered around the
world, a communication network, two computing stations and auxiliary
facilities, and some 400 personnel over a four-month period.

Although the Mariner scientific information could be stored and
subsequently processed at a later (non-real) time, it was necessary to
make tracking and position data available almost as soon as it was
received (in real time) so that the midcourse maneuver might be computed
and transmitted to the spacecraft, and to further perfect the predicted
trajectory and arrival time at Venus.

The engineering performance of the many spacecraft subsystems was also
of vital concern. Inaccurate operation in any of several areas could
endanger the success of the entire mission. The performance of the
attitude control system, the Earth and Sun sensors, the power system,
and communications were all of critical importance. Corrective action
was possible in certain subsystems where trouble could be predicted from
the data or where limited breakdown had occurred.

To integrate all the varied activities necessary to accomplish the
mission objectives, an organization was formed within JPL to coordinate
the DSIF, the communication network, the work of engineering and
scientific advisory panels, and the computer facilities required to
evaluate the data.

This organization was known as the Space Flight Operations Complex. For
operational purposes only, it included the Space Flight Operations
Center, a Communication Center, and a Central Computing Facility (CCF).
The DSIF was responsive to the requirements of the organization, but was
not an integral part of it.

A space flight operations director was responsible for integrating these
many functions into a world-wide Mariner space-flight organization. It
was an exhausting 109-day task, one that would severely tax all the
resources of JPL in terms of know-how, qualified personnel, time, and
equipment before Mariner completed its encounter with Venus.


COMMUNICATION CONTROL

The Communication Center at JPL in Pasadena was one of the most active
areas during the many days and nights of the Mariner II mission. All of
the teletype and radio lines from the Cape, South Africa, Australia, and
Goldstone terminated in this Center. A high-speed data line bypassed the
Communication Center, linking Goldstone directly with the Central
Computing Facility for quick, real-time computer processing of vital
flight information.

From the Communication Center, the teletype data and voice circuits were
connected to the several areas within JPL where the mission-control
activities were centered, and where the data output was being studied.

The Communication Center was equipped with teletype paper-page printers
and paper-tape hole reperforators, which received and transmitted
data-word and number groups. The teletype lines terminating at the
Center included circuits from Goldstone, South Africa, Australia, and
Cape Canaveral.

There were three lines to Goldstone for full-time, one-way data
transmission. Duplex (simultaneous two-way) transmission was available
to Woomera and South Africa on a full-time basis. In each case, a
secondary circuit was provided to the overseas sites for use during
critical periods and in case the primary radio-teletype circuits had
transmission difficulties. These secondary circuits used different radio
transmission paths in order to reduce the chance of complete loss of
contact for any extended period of time.

    [Illustration: _Radio signals from Mariner are received on 85-ft.
    antenna._]

    [Illustration: _The highly sensitive receiver (shown under test) is
    located in the control room of the station._]

    [Illustration: _In Goldstone control room, DSIF personnel await
    confirmation that spacecraft has begun to scan the planet Venus._]

    [Illustration: _From DSIF stations, the data are teletyped in coded
    format to Pasadena._]

Z ZSQSGSGKGKXRGOQOS DNQ XZARZXAVAQQVA XXDRDZ
QSGIGKGKXRGOQOX DXQ XZAIZXAVQQKDZ XXDRDDDRZ
DXQ XZAIZAZVAQQZDZXXDLKKDRA Z DSQSGIGGGQXRDN
G XXDRZSDRA Z DSQSGIGGGQXRGLZOX DXQ XZAIZAZV
QSGIGGGQXRGLZOX DXQ XZAIZGAVAQQSXZXXDRDZDRA
DXQ XQAIZGAVQQKVA XXDRDZDRANGDSSQSGIGGGQXRDI
Z XXDRDDDRZLQ ZSQSGIGGGGXRGVZOA DNQ XZARZGAV
QSGIGGGGXRGVQOA DNQ XZARZGAVQKZZAZXXDRZDDRA
DNQ XZARZAZVAKDDGZXXDRDADIZLA DSQSGIGGGGXRGZ
SZXXDRDDDRXOS DSQSQIGGGGXRDDZOA DNQ XZARZXAV
QSGSGGGGXRDSQOG DXQ XZARZXAVAKDZDZXXDRDLDRA
DXQ XZARZXAZZKZZDZXXDLKADRA Z DSQSGIGGGGXRGX
GZXXDRZXDRZ Z DSQSAQGGGGXRDAZOG DXQ XZAIZAZV
DRDXDRA Z DSQSGIGGGGXRDGSOG DXQ XZAIZAZVQKZS
OGGGXRDGAOG DXQ XZAIZAZVQKZVA XXDRDZDRANGDSS
XZAIZXAZZKZZD XXDRDLZDZHA DSQSGIGGGGXRDQAOQ
DLKADRKHQ ZSQSGIGGGGXRDKZOQ DXQ XZAVZAAVQKZZ
GGGGXRS ZOQ DXQ XZAIZAZVQKZDG XXDRDSDIZ A ZS
XZAIZAZVQQKSX XXDRDDDRZNS ZSQSGIGGGGXRSOAOQ
DRDZDRANGDSSQSAQGGGGXRSOAOK DNQ XZAVZAAVQQKZ
GGGGXRSNZOK DNQ XZAIZAZZSQQZSZXXDLKADRA Z DS
XZAIZGAVQQKZG XXDRZXDRZ Z DSQSAQGGGGXRSLAOK
DRDSDRZ Z DSQSAQGGGGXRSLAOK DNQ XZAIZAZZZQKS
GGGGXRSLAOK DNQ XZAIZAZZZQKVA XXDRDZDRANGDSS
XRSIZHZ DXQ XZAIZAZZZQKQQZXXDRDNDRZNQ DSQSGS
ZXAZSQQZXZXXDLKQDRSQS ZSQSGIGGGQXRSVAHZ DXQ

    [Illustration: _Messages are received and routed at the JPL
    Communications Center._]

    [Illustration: _Data are routed to the digital computer at JPL._]

    [Illustration: _Printout data are made available to experimenters._]

    [Illustration: _Spacecraft status is posted in Operations Center._]

The Mobile Tracking Station in South Africa used the Johannesburg
communication facilities.

Two one-way circuits for testing and control purposes were open to Cape
Canaveral from a month before until after the spacecraft was launched.
Lines from the Communication Center to the Space Flight Operations
Center at JPL terminated in page printers and reperforators in several
locations.

Voice circuits connected all of the stations with Operations Center
through the Communication Center. Long-distance radio telephone calls
were placed to South Africa to establish contact before the launch
sequence was started. Woomera used the Project Mercury voice circuits to
the United States during launch and for three days after.


THE OPERATIONS CENTER

The actual nerve center of the Mariner operation was the Space Flight
Operations Center (SFOC) at Pasadena. Here, technical and scientific
advisory panels reported to the Project Manager and the Mariner Test
Director on the performance of the spacecraft in flight, analyzed
trajectories, calculated the commands for the midcourse trajectory
correction, and studied the scientific aspects of the mission.

These panels were a Spacecraft Data Analysis Team, a Scientific Data
Group, an Orbit Determination Group, a Tracking Data Analysis Group, and
a Midcourse Command Group.

The Spacecraft Data Analysis Team analyzed the engineering data
transmitted from the spacecraft to evaluate the performance of the
subsystems in flight. The Team was composed of one or more of the
engineers responsible for each of the spacecraft subsystems, and a
chairman.

The Science Data Group was composed of the project scientist and certain
other scientists associated with the experiments on board the
spacecraft. This Group evaluated the data from the scientific
experiments while Mariner was in flight and advised the Test Director on
the scientific status of the mission.

The Science Data Group was on continuous duty until 48 hours after
launch, and at other times during the mission. During encounter with
Venus, the Group was also in contact with the scientific experimenters
from other participating organizations who were working with JPL.

    [Illustration: _Closed circuit television monitors are used for
    instant surveillance of the internal activities of the Operations
    Center._]

A Tracking Data Analysis Group analyzed the tracking data to be used in
orbit determination. They also assessed the performance of the DSIF
facilities and equipment used to obtain the data.

The Orbit Determination Group used the tracking data to produce
estimates of the actual spacecraft trajectory, and to compute the
spacecraft path with respect to the Earth, Venus, and the Sun. These
calculations were made once each day before the midcourse maneuver, once
a week during the cruise phase, and daily during and immediately after
the planet encounter.

The Operations Center was equipped with lighted boards on which the
progress of the mission was displayed. This information included
trajectory data, spacecraft performance, temperature and pressure
readings, and other data telemetered from the spacecraft subsystems.

Closed-circuit television was used for coordinating the activities of
the SFOC. Operating personnel could use television monitors in four
consoles which were linked to six fixed cameras viewing teletype page
printers. The entire Operations Room could be kept under surveillance by
the Project Manager, the Test Director, or the DSIF Operations Manager,
using cameras controlled in “pan,” “tilt,” and “zoom.”


CENTRAL COMPUTING FACILITY

During the Mariner II mission, the JPL Central Computing Facility (CCF)
processed approximately 13.1 million data words, or over 90 million
binary bits of computer data. (Binary bit = a discrete unit of
information intelligible to a digital computer. One data word = 7 binary
bits.)

In the four-month operation, about 100,000 tracking and telemetering
data cards were received and processed, yielding over 1.2 million
computer pages of tabulated, processed, and analyzed data for evaluation
by the engineers and scientists. Approximately 1,000 miles of magnetic
tape were used in the 1,056 rolls recorded by the DSIF.

The Central Computing Facility processed and reduced tracking and
telemetry data from the spacecraft, as recorded and relayed by the
stations of the DSIF. The tracking information was the basis for orbital
calculations and command decisions. After delivery of telemetry data on
magnetic tapes by the DSIF, the CCF stored the data for later reduction
and analysis. Where telemetry data were being processed in real or
near-real time, certain critical engineering and scientific functions
were programmed to print-out an “alarm” reading when selected
measurements in the data were outside specified limits.

The CCF consists of three stations at JPL: Station C, the primary
computing facility; Station D, the secondary installation; and the
Telemetry Processing Station (TPS).

Station C was the principal installation for processing both tracking
and telemetry data received from the DSIF tracking stations, both in
real and non-real time. The Station was equipped with a high-speed,
general-purpose digital computer with a 32,168-word memory and two
input-output channels, each able to handle 6 tape units. The associated
card-handling equipment was also available.

Tape translators or converters were provided for converting teletype
data and other digital information into magnetic tape format for
computer input. The teletype-to-tape unit operated at a rate of 300
characters per second.

A smaller computer acted as a satellite of the larger unit, performing
bookkeeping and such related functions as card punching, card reading,
and listing.

A high-speed unit microfilmed magnetic-tape printout was received from
the large computer. It provided “quick-look” copy within 30 minutes of
processing the raw data. Various paper-tape-to-card and
card-to-paper-tape converters were used to eliminate human error in
converting teletype data tape to computer cards.

Station C also utilized another computer as a real-time monitor and to
prepare a magnetic tape file of all telemetered measurements for input
to the large computer.

Station D was the secondary or backup computational facility, primarily
intended for use in case of equipment failure in Station C. During
certain critical phases of the Mariner mission—launch, orbit
determination, midcourse maneuver—this facility paralleled the
operations in Station C.

Station D is equipped with three computers and various card-to-tape
converters and teletype equipment.

The Telemetry Processing Station received and processed all demodulated
data (that recovered from the radio carrier) on magnetic tapes recorded
at the DSIF stations. The TPS output was digital magnetic tapes suitable
for computer entry.

The TPS equipment included FM discriminators, a code translator, a
device for converting data from analog to digital form, and
magnetic-tape recorders. Basically, the equipment accepted the digital
outputs from the tape units, the analog-to-digital converter, and the
code translator and put them in digital tape format for the computer
input.

As the launch operation started on August 27, the powered-flight portion
of the space trajectories program was run at launch minus 5 minutes (L
minus 5) and was repeated several times because of holds at AMR. The
orbit determination program was run at lift-off to calculate the first
orbit predictions used for aiding the DSIF in finding the spacecraft in
flight.

During the 12 hours following launch, both C and D Stations performed
parallel computations on tracking data. Station D discontinued space
flight operations at L plus 12 hours and resumed at the beginning of the
midcourse maneuver phase.

Tracking data processing and midcourse maneuver studies were conducted
daily until the midcourse maneuver was performed at L plus eight days.
For the following 97 days, tracking data were processed once each week
for orbit determination. Starting three days before the encounter,
tracking data were processed daily until the beginning of the encounter
phase.

Tracking data processing was conducted in near-real time throughout
encounter day, and daily for two days thereafter. For these three days,
tracking data were handled in Station D in order to permit exclusive use
of Station C for telemetry data processing and analysis. After this
three-day period, including the encounter, Station C processed the
tracking data every sixth day until the mission terminated on L plus 129
days.

Telemetry data were processed in a different manner. Following the
launch, DSIF Station 5 at South Africa received the telemetry signal
first, demodulated it, and put it in the proper format for teletype
transmission to JPL. The other DSIF stations followed in sequence as the
spacecraft was heard in other parts of the world. For two days after
launch, the computers processed telemetry data as required by the
Spacecraft Data Analysis Team.

During those periods when the large computer was processing tracking
data, a secondary unit supplied quick-look data in near-real time. When
Goldstone was listening to the spacecraft, quick-look data were
processed in real time, using the high-speed data line direct to the
Central Computing Facility.

For the 106 days that Mariner was actually in Mode II (cruise), the
telemetry data were processed twenty-four hours a day, seven days a
week. Data were presented to the engineering and science analysis teams
in quick-look format every three hours, except for short maintenance
interruptions, one computer failure, and a major modification requiring
three days, when a back-up data process mode of operation was used. The
large computer performed full processing and analysis of engineering and
science data seven days a week from launch until the Venus encounter.

On encounter day, the secondary Station C computer processed telemetry
data from the high-speed Goldstone line. Data on magnetic tapes produced
by the computer were processed and analyzed by the large unit in
near-real time every 30 minutes. The computer processing and delivery
time during this operation varied from 4½ to 7 minutes.




                               CHAPTER 8
                       THE SCIENTIFIC EXPERIMENTS


After a year of concentrated effort, in which the resources of NASA, the
Jet Propulsion Laboratory, and American science and industry had been
marshalled, Mariner II had probed secrets of the solar system some
billions of years old.

Scientists and engineers had studied the miles of data processed in
California from the tapes recorded at the five DSIF tracking stations
around the world. Two and a half months of careful analysis and
evaluation yielded a revised estimate of Venus and of the phenomena of
space. As a result, the dynamics of the solar system were revealed in
better perspective and the shrouded planet stood partially unmasked.
When the Mariner data were correlated with the data gathered by JPL
radar experiments at Goldstone in 1961 and 1962, the relationships
between the Earth, Venus, and the Sun became far clearer than ever
before.

Two experiments were carried on the spacecraft for a close-up
investigation of Venus’ atmosphere and temperature characteristics—a
microwave radiometer and an infrared radiometer. They were designed to
operate during the approximate 35-minute encounter period and at a
distance varying from about 10,200 miles to 49,200 miles from the center
of the planet.[2]

    [Illustration: _Cosmic dust detector._]

    [Illustration: _Solar plasma spectrometer._]

  COLLECTOR CUP
  PROGRAMMER
  ELECTROMETER
  DEFLECTION PLATES

    [Illustration: _Magnetometer._]

    [Illustration: _High-energy particle detector._]

  COLLECTOR
  SHIELD CAN
  QUARTZ FIBER

    [Illustration: _Microwave and infrared radiometers._]

  REFERENCE HORNS
  MICROWAVE RADIOMETER
  INFRARED RADIOMETER


                     _Table 2. Mariner Experiments_

  _Experiment_            _Description_           _Experimenters_

  Microwave radiometer    Determine the           Dr. A. H. Barrett,
                          temperature of the      Massachusetts
                          planet surface and      Institute of
                          details concerning      Technology; D. E.
                          its atmosphere          Jones, JPL; Dr. J.
                                                  Copeland, Army
                                                  Ordnance Missile
                                                  Command and
                                                  Ewen-Knight Corp.;
                                                  Dr. A. E. Lilley,
                                                  Harvard College
                                                  Observatory
  Infrared radiometer     Determine the           Dr. L. D. Kaplan, JPL
                          structure of the        and University of
                          cloud layer and         Nevada; Dr. G.
                          temperature             Neugebauer, JPL; Dr.
                          distributions at        C. Sagan, University
                          cloud altitudes         of California,
                                                  Berkeley, and Harvard
                                                  College Observatory
  Magnetometer            Measure planetary and   P. J. Coleman, NASA;
                          interplanetary          Dr. L. Davis,
                          magnetic fields         Caltech; Dr. E. J.
                                                  Smith, JPL; Dr. C. P.
                                                  Sonett, NASA
  Ion chamber and         Measure high-energy     Dr. H. R. Anderson,
  matched                 cosmic radiation        JPL; Dr. H. V. Neher,
  Geiger-Mueller tubes                            Caltech
  Anton special-purpose   Measure lower           Dr. J. Van Allen and
  tube                    radiation (especially   L. Frank, State
                          near Venus)             University of Iowa
  Cosmic dust detector    Measure the flux of     W. M. Alexander,
                          cosmic dust             Goddard Space Flight
                                                  Center, NASA
  Solar plasma            Measure the intensity   M. Neugebauer and Dr.
  spectrometer            of low-energy           C. W. Snyder, JPL
                          positively charged
                          particles from the Sun

Four experiments for investigation of interplanetary space and the
regions near Venus employed: a magnetometer; high-energy charged
particle detectors, including an ionization chamber and Geiger-Mueller
radiation counters; a cosmic dust detector; and a solar plasma detector.

These six scientific experiments represented the cooperative efforts of
scientists at nine institutions: The Army Ordnance Missile Command, the
Ewen-Knight Corp., the California Institute of Technology, the Goddard
Space Flight Center of NASA, Harvard College Observatory, the Jet
Propulsion Laboratory, the Massachusetts Institute of Technology, the
State Universities of Iowa and Nevada, and the University of California
at Berkeley. Table 2 lists the experiments, the experimenters, and their
affiliations.

At the Jet Propulsion Laboratory, the integration of the scientific
experiments and the generation of a number of them were carried out
under the direction of Dr. Manfred Eimer. R. C. Wyckoff was the project
scientist and J. S. Martin was responsible for the engineering of the
scientific experiments.


DATA CONDITIONING SYSTEM

Mariner’s scientific experiments were controlled and their outputs
processed by a data conditioning system which gathered the information
from the instruments and prepared it for transmission to the Earth by
telemetry. In this function, the data system acted as a buffer between
the science systems and the spacecraft data encoder.

The pulse output of certain of the science instruments was counted and
the voltage amplitude representations of other instruments were
converted from analog form to a binary digital equivalent of the
information signals. The data conditioning system also included circuits
to permit time-sharing of the telemetry channels with the spacecraft
engineering data, generation of periodic calibration signals for the
radiometer and magnetometer, and control of the direction and speed of
the radiometer scanning cycle.

During Mariner’s cruise mode, the data conditioning system was used for
processing both engineering and science data. If the spacecraft lost
lock on the Sun or the Earth during the cruise mode, no scientific data
would be telemetered during the reorientation period. Engineering data
were sampled and transmitted for about 17 seconds during every 37-second
interval. The planetary encounter mode involved only science and no
engineering data transmission. In this mode, the science data were
sampled during 20-second intervals.


COSMIC DUST DETECTOR

The cosmic dust detector on Mariner II was designed to measure the flux
density, direction, and momentum of interplanetary dust particles
between the Earth and Venus. These measurements were concerned with the
particles’ direction and distance from the Sun, the momentum with
respect to the spacecraft, the nature of any concentrations of the dust
in streams, variations in cosmic dust flux with distance from the Earth
and Venus, and the possible effects on manned flight.

Mariner’s cosmic dust instrument could detect a particle as small as
something like a billionth of a gram, or about five-trillionths of a
pound. This type of sensor had been used on rockets even before Explorer
I. It had yielded good results on Pioneer I in the region between the
Earth and the Moon. The instrument was a 55-square-inch acoustical
detector plate, or sounding board, made of magnesium. A crystal
microphone was attached to the center of the plate. The instrument could
detect both low- and high-momentum particles and also provide a rough
idea of their direction of travel.

The dust particle counters were read once each 37 seconds during the
cruise mode. This rate was increased to once each 20 seconds during the
encounter with Venus.

The instrument was attached to the top of the basic hexagonal structure;
it weighed 1.85 pounds, and consumed only 0.8 watt of power.


SOLAR PLASMA EXPERIMENT

In order to investigate the phenomena associated with the movement of
plasma (charged particles of low energy and density streaming out from
the Sun to form the so-called “solar wind”) in interplanetary space,
Mariner carried a solar plasma spectrometer that measured the flux and
energy spectrum of positively charged plasma components with energies in
the range 240 to 8400 volts. The extremely sensitive plasma detector
unit was open to space, consumed 1 watt of power, and consisted of four
basic elements: curved electrostatic deflection plates and collector
cup, electrometer, a sweep amplifier, and a programmer.

The curved deflector plates formed a tunnel that projected from the
chassis on the spacecraft hexagon in which the instrument was housed.
Pointed toward the Sun, the gold-plated magnesium deflector plates
gathered particles from space. Since the walls of the tunnel each
carried different electrical charges, only particles with just the
correct energy and speed could pass through and be detected by the
collector cup without striking the charged walls. A sensitive
electrometer circuit then measured the current generated by the flow of
the charged particles reaching the cup.

The deflection plates were supplied by amplifier-generated voltages
which were varied in 10 steps, each lasting about 18 seconds, allowing
the instrument to measure protons with energies in the 240 to 8,400
electron volt range. The programmer switched in the proper voltage and
resistances.


HIGH-ENERGY RADIATION EXPERIMENT

Mariner carried an experiment to measure high-energy radiation in space
and near Venus. The charged particles measured by Mariner were primarily
cosmic rays (protons or the nuclei of hydrogen atoms), alpha particles
(nuclei of helium atoms), the nuclei of other heavier atoms, and
electrons. The study of these particles in space and those which might
be trapped near Venus was undertaken in the hope of a better
understanding of the dynamics of the solar system and the potential
hazards to manned flight.

The high-energy radiation experiment consisted of an ionization chamber
and detectors measuring particle flux (velocity times density), all
mounted in a box measuring 6 × 6 × 2 inches and weighing just under 3
pounds. The box was attached halfway up the spacecraft superstructure in
order to isolate the instruments as much as possible from secondary
emission particles produced when the spacecraft was struck by cosmic
rays, and to prevent the spacecraft from blocking high-energy radiation
from space.

The ionization chamber had a stainless steel shell 5 inches in diameter,
with walls only 1/100-inch thick. The chamber was filled with argon gas
into which was projected a quartz fibre next to a quartz rod.

A charged particle entering the chamber would leave a wake of ions in
the argon gas. Negative ions accumulated on the rod, reducing the
potential between the rod and the spherical shell, eventually causing
the quartz fibre to touch the rod. This action discharged the rod,
producing an electrical pulse which was amplified and transmitted to the
Earth. The rod was then recharged and the fibre returned to its original
position.

In order to penetrate the walls of the chamber, protons required an
energy of 10 million electron volts (Mev), electrons needed 0.5 Mev, and
alpha particles 40 Mev.

The particle flux detector incorporated three Geiger-Mueller tubes, two
of which formed a companion experiment to the ionization chamber; each
generated a current pulse whenever a charged particle was detected. One
tube was shielded by an 8/1,000-inch-thick stainless steel sleeve, the
other by a 24/1,000-inch-thick electron-stopping beryllium shield. Thus,
the proportion of particles could be determined.

The third Geiger-Mueller tube was an end-window Anton-type sensor with a
mica window that admitted protons with energies greater than 0.5 Mev and
electrons, 40,000 electron volts. A magnesium shield around the rest of
the tube enabled the instrument to determine the direction of particles
penetrating only the window.

The three Geiger-Mueller tubes protruded from the box on the
superstructure of the spacecraft. The end-window tube was inclined 20
degrees from the others and 70 degrees from the spacecraft-Sun line
since it had to be shielded from direct solar exposure.


THE MAGNETOMETER

Mariner carried a magnetometer to measure the magnetic field in
interplanetary space and in the vicinity of Venus. Lower sensitivity
limit of the instrument was about 5 gamma. A gamma is a unit of magnetic
measurement and is equal to 10⁻⁵ or 1/100,000 oersted, or 1/30,000 of
the Earth’s magnetic field at the equator. The nails in one of your
shoes would probably produce a field of about 1 gamma at a distance of
approximately 4 feet.

Housed in a 6- × 3-inch metal cylinder, the instrument consisted of
three magnetic core sensors, each aligned on a different axis to read
the three magnetic field components and having primary and secondary
windings. The presence of a magnetic field altered the current in the
secondary winding in proportion to the strength of the field
encountered.

The magnetometer was attached near the top of the superstructure, just
below the omni-antenna, in order to remove it as far as possible from
any spacecraft components having magnetic fields of their own.

An auxiliary coil was wound around each of the instrument’s magnetic
sensor cores to compensate for permanent magnetic fields existing in the
spacecraft itself. These spacecraft fields were measured at the
magnetometer before launch and, in flight, the auxiliary coils carried
currents of sufficient strength to cancel out the spacecraft’s magnetic
fields.

The magnetometer reported almost continuously on its journey and for 20
days after encounter. During the encounter, observations were made each
20 seconds on each of the three components of the magnetic field.


MICROWAVE RADIOMETER

A microwave radiometer on board Mariner II was designed to scan Venus
during encounter at two wavelengths: 13.5 and 19 millimeters. The
radiometer was intended to help settle some of the controversies about
the origin of the apparently high surface temperature emanating from
Venus, and the value of the surface temperature.

The equipment included a 19-inch-diameter parabolic antenna mounted
above the basic hexagonal structure on a swivel driven in a 120-degree
scanning motion by a motor. The radiometer electronics circuits were
housed behind the antenna dish. The antenna was equipped with a
diplexer, which allowed it to receive both wavelengths at once without
interference, and to compare the signals emanating from the two
reference horns with those from the planet. The reference horns were
pointed away from the main antenna beam so they would look into deep
space as Mariner passed Venus. This feature allowed the antenna to
“bring in” a reference temperature of approximately absolute zero during
encounter.

The microwave radiometer was to be turned on 10 hours before the
encounter began. An electric motor was then to start a scanning or
“nodding” motion of 120 degrees at the rate of 1 degree per second. Upon
radiometer contact with the planet, this scanning rate would be reduced
to 1/10 degree per second as long as the planetary disk was scanned. A
special command system in the data conditioning system would reverse or
normalize the direction of scan as the radiometer reached the edge or
limb of the planet.

The signals from the antenna and the reference horns were to be
processed and the data handled in a receiver, located behind the
antenna, which measured the difference between the signals from Venus
and the reference signals from space. The information was then to be
telemetered to the Earth.

The microwave radiometer was automatically calibrated twenty-three times
during the mission by a sequence originating in the data conditioning
system, so that the correct functioning of the instrument could be
determined before the encounter with Venus.


INFRARED RADIOMETER

The infrared radiometer was a companion experiment to the microwave
instrument and was rigidly mounted to the microwave antenna so that both
radiometers would look at the same area of Venus with the same scanning
rate. The instrument detected radiation in the 8 to 9 and 10 to 10.8
micron regions of the infrared spectrum.

The infrared radiometer had two optical sensors. As the energy entered
the system, it was “chopped” by a rotating disk, alternately passing or
comparing emissions from Venus and from empty space. The beam was then
split by a filter into the two wavelength regions. The output was then
detected, processed, and transmitted to the Earth.

The infrared radiometer measured 6 inches by 2 inches, weighed 2.7
pounds, and consumed 2 watts of power. The instrument was equipped with
a calibration plate which was mounted on a superstructure truss adjacent
to the radiometer.


MARINER’S SCIENTIFIC OBJECTIVES

Equipped with these instruments and with the mechanism for getting the
measurements back to Earth, Mariner II was prepared to look for the
answers to some of the questions inherent in its over-all mission
objectives:

  1. The investigation of interplanetary space between the Earth and
          Venus, measuring such phenomena as the cosmic dust, the
          mysterious plasma or solar winds, high-energy cosmic rays from
          space outside our solar system, charged particles from the
          Sun, and the magnetic fields of space.
  2. The experiments to be performed near Venus (at about 21,150 miles
          out from the surface) in an effort to understand its magnetic
          fields, radiation belts, the temperature and composition of
          its clouds, and the temperature and conditions on the surface
          of the planet.




                               CHAPTER 9
                         THE LEGACY OF MARINER


If intelligent life had existed on Venus on the afternoon of the Earth’s
December 14, 1962, and if it could have seen through the clouds, it
might have observed Mariner II approach from the night side, drift down
closer, cross over to the daylight face, and move away toward the Sun to
the right. The time was the equivalent of 12:34 p.m. along the Pacific
Coast of the United States, where the spacecraft was being tracked.

Mariner II had reached the climax of its 180-million-mile, 109-day trip
through space. The 35-minute encounter with Venus would tell Earth
scientists more about our sister planet than they had been able to learn
during all the preceding centuries.


SPACE WITHOUT DUST?

Before Mariner, scientists theorized about the existence of clouds of
cosmic dust around the Sun. A knowledge of the composition, origin, and
the dynamics of these minute particles is necessary for study of the
origins and evolution of the solar system.

Tiny particles of cosmic dust (some with masses as low as 1.3 × 10⁻¹⁰
gram or about one-trillionth of a pound) were thought to be present in
the solar system and have been recorded by satellites in the near-Earth
regions.

These microcosmic particles could be either the residue left over after
our solar system was formed some 5 billion years ago, possibly by
condensation of huge masses of gas and dust clouds; or, the debris
deposited within our system by the far-flung and decaying tails of
passing comets; or, the dust trapped from galactic space by the magnetic
fields of the Sun and the planets.

Analysis of the more than 1,700 hours of cosmic dust detector data
recovered from the flight of Mariner II seems to indicate that in the
region between the Earth and Venus the concentration of tiny cosmic dust
particles is some ten-thousand times less than that observed near the
Earth.

During the 129 days (including the post-encounter period) of Mariner’s
mission, the data showed only one dust particle impact which occurred in
deep space and not near Venus. Equivalent experiments near Earth (on
board Earth satellites) have yielded over 3,700 such impacts within
periods of approximately 500 hours. The cause of this heavy near-Earth
concentration, the exact types of particles, and their source are still
unknown.

The cosmic dust experiment performed well during the Mariner mission.
Although some calibration difficulty was observed about two weeks before
the Venus encounter, possibly caused by overheating of the sensor
crystal, there was no apparent effect in the electronic circuits.


THE UBIQUITOUS SOLAR WIND

For some time prior to Mariner, scientists postulated the existence of a
so-called plasma flow or “solar wind” streaming out from the Sun, to
explain the motion of comet tails (which always point away from the Sun,
perhaps repelled by the plasma), geomagnetic storms, aurorae, and other
such disturbances. (Plasma is defined as a gas in which the atoms are
dissociated into atomic nuclei and electrons, but which, as a whole, is
electrically neutral.)

The solar wind was thought to drastically alter the configuration of the
Sun’s external magnetic field. Plasma moving at extreme velocities is
able to carry with it the lines of magnetic force originating in the
Sun’s corona and to distort any fields it encounters as it moves out
from the Sun.

It was believed that these moving plasma currents are also capable of
altering the size of a planet’s field of magnetic flux. When this
happens, the field on the sunlit face of the planet is compressed and
the dark side has an elongated expansion of the field. For example, the
outer boundary of the Earth’s magnetic field is pushed in by the solar
wind to about 40,000 miles from the Earth on the sunward side. On the
dark side, the field extends out much farther.

The solar wind was also known to have an apparent effect on the movement
of cosmic rays. As the Sun spots increase in the regular 11-year cycle,
the number of cosmic rays reaching the Earth from outside our solar
system will decrease.

Mariner II found that streams of plasma are constantly flowing out from
the Sun. This fluctuating, extremely tenuous solar wind seems to
dominate interplanetary space in our region of the solar system. The
wind moves at velocities varying from about 200 to 500 miles per second
(about 720,000 to 1,800,000 miles per hour), and measures up to perhaps
a million degrees Fahrenheit (within the subatomic structure).

With the solar plasma spectrometer working at ten different energy
levels, Mariner required 3.7 minutes to run through a complete energy
spectrum. During the 123 days, when readings were made, a total of
40,000 such spectra were recorded. Plasma was monitored on 104 of those
123 days, and on every one of the spectra, the plasma was always
present.

Mariner showed that the energies of the particles in the solar winds are
very low, on the order of a few hundred or few thousand electron volts,
as compared with the billions and trillions of electron volts measured
in cosmic radiation.

The extreme tenuousity or low density of the solar wind is difficult to
comprehend: about 10 to 20 protons (hydrogen nuclei) and electrons per
cubic inch. But despite the low energy and density, solar wind particles
in our region of the solar system are billions of times more numerous
than cosmic rays and, therefore, the total energy content of the winds
is much greater than that of the cosmic rays.

Mariner found that when the surface of the Sun was relatively inactive,
the velocity of the wind was a little less than 250 miles per second and
the temperature a few hundred thousand degrees. The plasma was always
present, but the density and the velocity varied. Flare activity on the
Sun seemed to eject clouds of plasma, greatly increasing the velocity
and density of the winds. Where the particles were protons, their
energies ranged from 750 to 2,500 electron volts.

The experiment also showed that the velocity of the plasma apparently
undergoes frequent fluctuations of this type. On approximately twenty
occasions, the velocity increased within a day or two by 20 to 100%.
These disturbances seemed to correlate well with magnetic storms
observed on the Earth. In several cases, the sudden increase in the
solar plasma flux preceded various geomagnetic effects observed on the
Earth by only a short time.

The Mariner solar plasma experiment was the first extensive measurement
of the intensity and velocity spectrum of solar plasma taken far enough
from the Earth’s field so that the Earth would have no effect on the
results.


HIGH-ENERGY PARTICLES: FATAL DOSAGE?

Speculation has long existed as to the amount of high-energy radiation
(from cosmic rays and particles from the Sun with energies in the
millions of electron volts) present within our solar system and as to
whether exposure would be fatal to a human space traveler.

This high-energy type of ionizing radiation is thought to consist of the
nuclei of such atoms as hydrogen and helium, and of electrons, all
moving very rapidly. The individual particles are energetic enough to
penetrate considerable amounts of matter. The concentration of these
particles is apparently much lower than that of low-energy plasma.

The experiments were designed to detect three types of high-energy
radiation particles: the cosmic rays coming from outside the solar
system, solar flare particles, and radiation trapped around Venus (as
that which is found in the Earth’s Van Allen Belt).

These high-energy radiation particles (also thought to affect aurorae
and radio blackouts on the Earth) measure from about one hundred
thousand electron volts up to billions of volts. The distribution of
this energy is thought to be uniform outside the solar system and is
assumed to move in all directions in a pattern remaining essentially
constant over thousands of years.

Inside the solar system, the amount of such radiation reaching the Earth
is apparently controlled by the magnetic fields found in interplanetary
space and near the Earth.

The number of cosmic rays changes by a large amount over the course of
an 11-year Sun-spot cycle, and below a certain energy level (5,000 Mev)
few cosmic rays are present in the solar system. They are probably
deflected by plasma currents or magnetic fields.

Mariner’s charged particles experiment indicated that cosmic radiation
(bombardment by cosmic rays), both from galactic space and those
particles originating in the Sun, would not have been fatal to an
astronaut, at least during the four-month period of Mariner’s mission.

The accumulated radiation inside the counters was only 3 roentgens, and
during the one solar storm recorded on October 23 and 24, the dosage
measured only about ¼ roentgen. In other words, the dosage amounts to
about one-thousandth of the usually accepted “half-lethal” dosage, or
that level at which half of the persons exposed would die. An astronaut
might accept many times the dosage detected by Mariner II without
serious effects.

The experiment also showed little variation in density of charged
particles during the trip, even with a 30% decrease in distance from the
Sun, and no apparent increase due to magnetically trapped particles or
radiation belts near Venus as compared with interplanetary space.
However, these measurements were made during a period when the Sun was
slowly decreasing in activity at the end of an 11-year cycle. The Sun
spots will be at a minimum in 1964-1965, when galactic cosmic rays will
sharply increase. Further experiments are needed to sample the charged
particles in space under all conditions.

The lack of change measured by the ionization chamber during the mission
was significant; the cosmic-ray flux of approximately 3 particles per
square centimeter per second throughout the flight was an unusually
constant value. A clear increase in high-energy particles (10 Mev to
about 800 Mev) emitted by the Sun was noted only once: a flare-up
between 7:42 and 8:45 a.m., PST, October 23. The ionization chamber
reading began to increase before the flare disappeared. From a
background reading of 670 ion pairs per cubic centimeter per second per
standard atmosphere, it went to a peak value of 18,000, varied a bit,
and remained above 10,000 for 6 hours before gradually decreasing over a
period of several days. Meanwhile, the flux of the particles detected by
the Geiger counter rose from the background count of 3 to a peak of 16
per square centimeter per second. Ionization thus increased much more
than the number of particles, indicating to the scientists that the
high-energy particles coming from the Sun might have had much lower
average energies than the galactic cosmic rays.

    [Illustration: _Data obtained by microwave radiometer are
    illustrated at left; results of infrared radiometer experiment are
    shown at right. Note how moving spacecraft sees more of atmosphere
    along limb or edge of planet, less in center._]

In contrast, the low-energy experiment detected the October 23 event,
and eight or ten others not seen by the high-energy detectors. These
must have been low-penetrating particles excluded by the thicker walls
of the high-energy instrument. These particles were perhaps protons
between 0.5 and 10 Mev or electrons between 0.04 and 0.5 Mev.

At 20,000 miles from the Earth, the rate at which high-energy particles
have been observed has been recorded at several thousand per second.
With Mariner at approximately the same distance from Venus, the average
was only one particle per second, as it had been during most of the
month of November in space. Such a rate would indicate a low planetary
magnetic field, or one that did not extend out as far as Mariner’s
21,598-mile closest approach to the surface.

Mariner II measured and transmitted data in unprecedented quantity and
quality during the long trip. In summary, Mariner showed that, during
the measuring period, particles were numerous in the energy ranges from
a few hundred to 1,000 electron volts. Protons in the range 0.5 to 10
Mev were not numerous, but at times the flux (density) was several times
that of cosmic rays.

Almost no protons were shown in the 10 to 800 Mev range, except during
solar flares when the particles in this range were numerous. Above 800
Mev (primarily those cosmic rays entering interplanetary space from
outside the solar system) the number decreased rapidly as the energy
increased, the average total being about 3 per centimeter per second.

During one 30-day period in November and December, the low-energy
counter saw only two small increases in radiation intensity. At this
time, the mean velocity of the solar wind was considerably lower than
during September and October. This might suggest that high-velocity
plasma and low-energy cosmic rays might both originate from the same
solar source.


A MAGNETIC FIELD?

Prior to the Mariner II mission, no conclusive evidence had ever been
presented concerning a Venusian magnetic field and nothing was known
about possible fluid motions in a molten core or other hypotheses
concerning the interior of the planet.

Scientists assumed that Venus had a field somewhat similar to the
Earth’s, although possibly reduced in magnitude because of the
apparently slow rate of rotation and the pressure of solar plasma. Many
questions had also been raised concerning the nature of the atmosphere,
charged particles in the vicinity of the planet, magnetic storms, and
aurorae. Good magnetometer data from Mariner II would help solve some of
these problems.

Mariner’s magnetometer experiment also sought verification of the
existence and nature of a steady magnetic field in interplanetary space.
This would be important in understanding the charged particle balance of
the inner solar system. Other objectives of the experiment were to
establish both the direction and the magnitude of long-period
fluctuations in the interplanetary magnetic field and to study solar
disturbances and such problems in magnetohydrodynamics (the study of the
motion of charged particles and their surrounding magnetic fields) as
the existence and effect of magnetized and charged plasmas in space.

The strength of a planet’s field is thought to be closely related to its
rate of rotation—the slower the rotation, the weaker the field. As a
consequence, if Venus’ field is simple in structure like the Earth’s,
the surface field should be 5 to 10% that of the Earth. If the structure
of the field is complex, the surface field in places might exceed the
Earth’s without increasing the field along Mariner’s trajectory to
observable values.

Most of the phenomena associated with the Earth’s magnetic field are
likely to be significantly modified or completely absent in and around
Venus. Auroral displays and the trapping of charged particles in
radiation belts such as our Van Allen would be missing. The field of the
Earth keeps low- and moderate-energy cosmic rays away from the top of
the atmosphere, except in the polar regions. The cosmic ray flux at the
top of Venus’ atmosphere is likely to correspond everywhere to the high
level found at the Earth’s poles.

    [Illustration: _As it encountered Venus, Mariner II made three scans
    of the planet._]

  SUN
  DIRECTION OF SCAN
  DATA READINGS (18 TOTAL)

In contrast to Venus, Jupiter, which is ten times larger in mass and
volume and rotates twice as fast as the Earth, has a field considerably
stronger than the Earth’s. The Moon has a field on the sunlit side
(according to Russian measurements) which, because of the Moon’s slow
rotation rate, is less than ⅓ of 1% of the Earth’s at the Equator. Thus,
a planet’s rotation, if at a less rapid rate than the Earth’s, seems to
produce smaller magnetic fields. This theory is consistent with the idea
of a planetary magnetic field resulting from the dynamo action inside
the molten core of a rotating planet.

The Sun, on the whole, has a fairly regular dipole field. Superimposed
on this are some very large fields associated with disturbed regions
such as spots or flares, which produce fields of very great intensities.

These solar fields are drawn out into space by plasma flow. Although
relatively small in magnitude, these fields are an important influence
on the propagation of particles. And the areas in question are very
large—something on the order of an astronomical unit.

Mariner II seemed to show that, in space, a generally quiet
magnetic-field condition was found to exist, measuring something less
than 10 gamma and fluctuating over periods of 1 second to 1 minute.

As Mariner made its closest approach to Venus, the magnetometer saw no
significant change, a condition also noted by the radiation and solar
plasma detectors. The magnetic field data looked essentially as they had
in interplanetary space, without either fluctuations or smooth changes.

The encounter produced no slow changes, nor was there a continuous
fluctuation as in the interplanetary regions. There was no indication of
trapped particles or near-Venus modification in the flow of solar
plasma.

On the Earth’s sunny side, a definite magnetic field exists out to
40,000 miles, and on the side away from the Sun considerably farther. If
Venus’ field had been similar to the Earth’s, a reading of 100 to 200
gamma, a large cosmic-ray count, and an absence of solar plasma should
have been shown, but none of these phenomena were noted by Mariner.

These results do not prove that Venus definitely has no magnetic field,
but only that it was not measurable at Mariner’s 21,598-mile point of
closest approach. The slow rotation rate and the pressure of the solar
winds probably combine to limit the field to a value one tenth of the
Earth’s. Since Mariner passed Venus on the sunlit side, readings are
required on the dark side in order to confirm the condition of the
magnetic field on that side of the planet, which normally should be
considerably extended.


THE SURFACE: HOW HOT?

Before Mariner, scientists had offered two main theories about the
surface of Venus: It had either an electrically charged ionosphere
causing false high-temperature readings on Earth instruments despite a
cool surface, or a hot surface with clouds becoming increasingly colder
with altitude.

The cool-surface theory supposed an ionosphere with a layer of electrons
having a density thousands of times that of the Earth’s upper
atmosphere. Microwave radiations from this electrical layer would cause
misleading readings on Earth instruments. As a space probe scanned
across such an atmosphere, it would see the least amount of charged
ionosphere when looking straight down, and the most concentrated amount
while scanning the limb or edge. In the latter case, it would be at an
angle and would show essentially a thickening effect of the atmosphere
because of the curvature of the planet.

As the probe approached the edge, the phenomenon known as “limb
brightening” would occur, since the instruments would see more of the
electron-charged ionosphere and little if any of the cooler surface. The
temperature readings would, therefore, be correspondingly higher at the
limbs.

The other theory, held by most scientists, visualized a hot surface on
Venus, with no heavy concentration of electrons in the atmosphere, but
with cooler clouds at higher altitudes. Thus, the spacecraft would look
at a very hot planet from space, covered by colder, thick clouds.
Straight down, the microwave radiometer would see the hot surface
through the clouds. When approaching the limb, the radiations would
encounter a thicker concentration of atmosphere and might not see any of
the hot surface. This condition, “limb darkening,” would be
characterized by temperatures decreasing as the edges of the planet were
approached.

An instrument capability or resolution much higher than that available
from the Earth was required to resolve the limb-brightening or
limb-darkening controversy. Mariner’s radiometer would be able to
provide something like one hundred times better resolution than the
Earth-based measurements.

At 11:59 a.m., PST, on December 14, 1962, Mariner’s radiometers began to
scan the planet Venus in a nodding motion at a rate of 0.1 degree per
second and reaching an angular sweep of nominally 120 degrees. The
radiometers had been switched on 6½ hours before the encounter with
Venus and they continued to operate for another hour afterward.

The microwave radiometer looked at Venus at a wavelength of 13.5
millimeters and 19 millimeters. The 13.5-millimeter region was the
location of a microwave water absorption band within the electromagnetic
spectrum, but it was not anticipated that it would detect any water
vapor on Venus. These measurements would allow determination of
atmospheric radiation, averaging the hot temperatures near the surface,
the warmer clouds at lower levels, and the lower temperatures found in
the high atmosphere. If the atmosphere were a strong absorber of
microwave energy at 13.5 millimeters, only the temperature of the upper
layers would be reported.

Unaffected by water vapor, 19-millimeter radiations could be detected
from deeper down into the cloud cover, perhaps from near or at the
planet’s surface. Large temperature differences between the 19- and 13.5
millimeter readings would indicate the relative amount of water vapor
present in the atmosphere. The 19-millimeter radiations would also test
the limb-brightening theory.

During its scanning operation, Mariner telemetered back to Earth about
18 digital data points, represented as voltage fluctuations in relation
to time. The first scan was on the dark side, going up on the planet:
the distance from the surface was 16,479 miles at midscan, and the
brightness temperature was 369 degrees F. The second scan nearly
paralleled the terminator (junction of light and dark sides) but crossed
it going down; it was made from 14,957 miles at midscan and showed a
temperature of 566 degrees F. The final scan, 13,776 miles at midpoint,
showed 261 degrees F as it swept across the sunlit side of Venus in an
upward direction.

The brightness temperature recorded by Mariner’s radiometer is not the
true temperature of the surface. It is derived from the amount of light
or radio energy reflected or emitted by an object. If the object is not
a perfect light emitter, as most are not, then the light and radio
energy will be some fraction of that returned from a 100% efficient
body, and the object is really hotter than the brightness measurement
shows. Thus, the brightness temperature is a minimum reading and in this
case, was lower than the actual surface temperature.

Mariner’s microwave radiometer showed no significant difference between
the light and dark sides of Venus and, importantly, higher temperatures
along the terminator or night-and-day line of the planet. These results
would indicate no ionosphere supercharged with electrons, but a definite
limb-darkening effect, since the edges were cooler than the center of
the planet.

Therefore, considering the absorption characteristics of the atmosphere
and the emissivity factor derived from earlier JPL radar experiments, a
fairly uniform 800 degrees F was estimated as a preliminary temperature
figure for the entire surface.

Venus is, indeed, a very hot planet.


CLOUD TEMPERATURES: THE INFRARED READINGS

Mariner II took a close look at Venus’ clouds with its infrared
radiometer during its 35-minute encounter with the planet. This
instrument was firmly attached to the microwave radiometer so the two
devices would scan the same areas of Venus at the same rate and the data
would be closely correlated. This arrangement was necessary to produce
in effect a stereoscopic view of the planet from two different regions
of the spectrum.

Because astronomers have long conjectured about the irregular dark spots
discernible on the surface of Venus’ atmosphere, data to resolve these
questions would be of great scientific interest. If the spots were
indeed breaks in the clouds, they would stand out with much better
definition in the infrared spectrum. If the radiation came from the
cloud tops, there would be no breaks and the temperatures at both
frequencies measured by the infrared radiometer would follow essentially
the same pattern.

The Venusian atmosphere is transparent to the 8-micron region of the
spectrum except for clouds. In the 10-micron range, the lower atmosphere
would be hidden by carbon dioxide. If cloud breaks existed, the 8-micron
emissions would come from a much lower point, since the lower atmosphere
is fairly transparent at this wavelength. If increasing temperatures
were shown in this region, it might mean that some radiation was coming
up from the surface.

As a result of the Mariner II mission, scientists have hypothecated that
the cold cloud cover could be about 15 miles thick, with the lower base
beginning about 45 miles above the surface, and the top occurring at 60
miles. In this case, the bottom of the cloud layer could be
approximately 200 degrees F; at the top, the readings vary from about
minus 30 degrees F in the center of the planet to temperatures of
perhaps minus 60 degrees to minus 70 degrees F along the edges. This
temperature gradient would verify the limb-darkening effect seen by the
microwave radiometer.

At the center of Venus, the radiometer saw a thicker, brighter, hotter
part of the cloud layer; at the limbs, it could not see so deeply and
the colder upper layers were visible. Furthermore, the temperatures
along the cloud tops were approximately equally distributed, indicating
that both 8- and 10-micron “channels” penetrated to the same depth and
that both were looking at thick, dense clouds quite opaque to infrared
radiation.

Both channels detected a curious feature along the lower portion of the
terminator, or the center line between the night and day sides of the
planet. In that region, a spot was shown that was apparently about 20
degrees F colder than the rest of the cloud layer. Such an anomaly could
result from higher or more opaque clouds, or from such an irregularity
as a hidden surface feature. A mountain could force the clouds upward,
thus cooling them further, but it would have to be extremely high.

The data allow scientists to deduce that not enough carbon dioxide was
present above the clouds for appreciable absorption in the 10-micron
region. This effect would seem to indicate that the clouds are thick and
that there is little radiation coming up from the surface. And, if
present, water vapor content might be 1/1,000 of that in the Earth’s
atmosphere.

Since the cloud base is apparently at a very high temperature, neither
carbon dioxide nor water is likely to be present in quantity. Rather,
the base of the clouds must contain some component that will condense in
small quantities and not be spectroscopically detected.

As a result of the two radiometer experiments, the region below the
clouds and the surface itself take on better definition. Certainly,
heat-trapping of infrared radiation, or a “greenhouse” effect, must be
expected to support the 800 degree F surface temperature estimated from
the microwave radiometer data. Thus, a considerable amount of
energy-blanketing carbon dioxide must be present below the cloud base.
It is thought that some of the near-infrared sunlight might filter
through the clouds in small amounts, so that the sky would not be
entirely black, at least to human eyes, on the sunlit side of Venus.
There also may be some very small content of oxygen below the clouds,
and perhaps considerable amounts of nitrogen.

The atmospheric pressure on the surface might be very high, about 20
times the Earth’s atmosphere or more (equivalent to about 600 inches of
mercury, compared with our 30 inches). The surface, despite the high
temperature, is not likely to be molten because of the roughness index
seen in the earlier radar experiments, and other indicators. However,
the possibility of small molten metal lakes cannot be totally ignored.

The dense, high-pressure atmosphere and the heat-capturing greenhouse
effect could combine over long periods of time to carry the extremely
high temperature around to the dark side of Venus, despite the slow rate
of rotation, possibly accounting for the relatively uniform surface
temperatures apparently found by Mariner II.


THE RADAR PROFILE: MEASUREMENTS FROM EARTH

In 1961, the Jet Propulsion Laboratory conducted a series of experiments
from its Goldstone, California, DSIF Station, successfully bouncing
radar signals off the planet Venus and receiving the return signal after
it had travelled 70 million miles in 6½ minutes.

In order to complement the Mariner mission to Venus, the radar
experiments were repeated from October to December, 1962 (during the
Mariner mission), using improved equipment and refined techniques. As in
1961, the experiments were directed by W. K. Victor and R. Stevens.

The 1961 experiments used two 85-foot antennas, one transmitting 13
kilowatts of power at 2,388 megacycles, the other receiving the return
signal after the round trip to and from Venus. The most important result
was the refinement of the astronomical unit—the mean distance from the
Earth to the Sun—to a value of 92,956,200 ±300 miles.

Around 1910, the astronomical unit, plotted by classical optical
methods, was uncertain to 250,000 miles. Before the introduction of
radar astronomy techniques such as those used at Goldstone, scientists
believed that the astronomical unit was known to within 60,000 miles,
but even this factor of uncertainty would be intolerable for planetary
exploration.

In radar astronomy, the transit time of a radio signal moving at the
speed of light (186,000 miles per second) is measured as it travels to a
planet and back. In conjunction with the angular measurement techniques
used by earlier investigators, this method permits a more precise
calculation of the astronomical unit.

Optical and radar measurements of the astronomical unit differ by 50,000
miles. Further refinement of both techniques should lessen the
discrepancy between the two values.

The 1961 tests also established that Venus rotates at a very slow rate,
possibly keeping the same face toward the Sun at all times. The
reflection coefficient of the planet was estimated at 12%, a bright
value similar to that of the Earth and contrasted with the Moon’s 2%.
The average dielectric constant (conductivity factor) of the surface
material seemed to be close to that of sand or dust, and the surface was
reported to be rough at a wavelength of 6 inches.

The surface roughness was confirmed in 1962. Since it is known that a
rough surface will scatter a signal, the radar tests were observed for
such indications. Venus had a scattering effect on the radar waves
similar to the Moon’s, probably establishing the roughness of the
Venusian surface as more or less similar to the lunar terrain.

Some of the most interesting work was done in reference to the rotation
rate of Venus. A radar signal will spread in frequency on return from a
target planet that is rotating and rough enough to reflect from a
considerable area of its surface. The spread of 5 to 10 cycles per
second noted on the Venus echo would suggest a very slow rotation rate,
perhaps keeping the same face toward the Sun, or possibly even in a
retrograde direction, opposite to the Earth’s.

In the Goldstone 1962 experiments, Venus was in effect divided into
observation zones and the doppler effect or change in the returned
signal from these zones was studied. The rate of rotation was derived
from three months of sampling with this radar mapping technique. Also,
the clear, sharp tone characteristic of the transmitted radar signal was
altered on return from Venus into a fuzzy, indistinct sound. This effect
seemed to confirm the slow retrograde rotation (as compared with the
Earth) indicated by the radar mapping and frequency change method.

In addition to these methods of deducing the slow rotation rate, two
other phenomena seemed to verify it: a slowly fluctuating signal
strength, and the apparent progression of a bright radar spot across
from the center of Venus toward the outside edge.

As a result, JPL scientists revised their 1961 estimate of an equal
Venusian day and year consisting of 225 Earth days. The new value for
Venus’ rotation rate around its axis is 230 Earth days plus or minus 40
to 50 days, and in a retrograde direction (opposite to synchronous or
Sun-facing), assuming that Venus rotates on an axis perpendicular to the
plane of its orbit.

Thus, on Venus the Sun would appear to rise in the west and cross to the
east about once each Venusian year. If the period were exactly 225 days
retrograde, the stars would remain stationary in the sky and Venus would
always face a given star rather than the Sun.

A space traveller hovering several million miles directly above the Sun
would thus see Venus as almost stopped in its rotation and possibly
turning very slowly clockwise. All the other planets of our system
including the Earth, rotate counterclockwise, except Uranus, whose axis
is almost parallel to the plane of its orbit, making it seem to roll
around the Sun on its side. The rotation direction of distant Pluto is
unknown.

The Goldstone experiments also studied what is known as the Faraday
rotation of the plane of polarization of a radio wave. The results
indicated that the ionization and magnetic field around Venus are very
low. These data tend to confirm those gathered by Mariner’s experiments
close to the planet.

The mass of Venus was another value that had never been precisely
established. The mass of planetary bodies is determined by their
gravitational effect on other bodies, such as satellites. Since Venus
has no known natural satellite or moon, Mariner, approaching closely
enough to “feel” its gravity, would provide the first opportunity for
close measurement.

The distortion caused by Venus on Mariner’s trajectory as the spacecraft
passed the planet enabled scientists to calculate the mass with an error
probability of 0.015%. The value arrived at is 0.81485 of the mass of
the Earth, which is known to be approximately 13.173 septillion
(13,173,000,000,000,000,000,000,000) pounds. Thus, the mass of Venus is
approximately 10.729 septillion (10,729,408,500,000,000,000,000,000)
pounds.

In addition to these measurements, the extremely precise tracking system
used on Mariner proved the feasibility of long-range tracking in space,
particularly in radial velocity, which was measured to within 1/10 of an
inch per second at a distance of about 54 million miles.

As the mission progressed, the trajectory was corrected with respect to
Venus to within 10 miles at encounter. An interesting result was the
very precise location of the Goldstone and overseas tracking stations of
the DSIF. Before Mariner II, these locations were known to within 100
yards. After all the data have been analyzed, these locations will be
redefined or “relocated” to within an error of only 20 yards.

Mariner not only made the first successful journey to Venus—it also
helped pinpoint spots in the Californian and Australian deserts and the
South African veldt with an accuracy never before achieved.




                               CHAPTER 10
                         THE NEW LOOK OF VENUS


The historic mission of Mariner II to the near-vicinity of Venus and
beyond has enabled scientists to revise many of their concepts of
interplanetary space and the planet Venus.

The composite picture, taken from the six experiments aboard the
spacecraft and the data from the DSIF radar experiments of 1961 and 1962
revealed the following:


—Interplanetary space between the Earth and Venus, at least as it was
  during the four months of Mariner’s mission, had a cosmic dust density
  some ten-thousand times lower than the region immediately surrounding
  the Earth.

—During this period, the extremely tenuous, widely fluctuating solar
  winds streamed continually out from the Sun, at velocities ranging
  from 200 to 500 miles per second.

—An astronaut travelling through these regions in the last quarter of
  1962 would not have been seriously affected by the cosmic and
  high-energy radiation from space and the Sun. He could easily have
  survived many times the amount of radiation detected by Mariner’s
  instruments.

—111

—The astronomical unit, as determined by radar, the yardstick of our
  solar system, stands at 92,956,200, plus or minus 300 miles.

—The mass of Venus in relation to the Earth’s is 0.81485, with an error
  probability of 0.015%.

—The rotation rate of Venus is quite slow and is now estimated as equal
  to 230 Earth days, plus or minus 40 to 50 days. The rotation might be
  retrograde, clockwise with respect to a Sun-facing reference, with the
  Sun rising in the west and setting in the east approximately one
  Venusian year later. The planet seems to remain nearly star-fixed
  rather than permanently oriented with one face to the Sun.

—Venus has no magnetic field discernible at the 21,598-mile approach of
  Mariner II and at that altitude there were no regions of trapped
  high-energy particles or radiation belts, as there are near the Earth.

—The clouds of Venus are about 15 miles thick, extending from a base 45
  miles above the surface to a top altitude of about 60 miles.

—At the resolution of the Mariner II infrared radiometer, there were no
  apparent breaks in the cloud cover. Cloud-top temperature readings are
  about minus 30 degrees F near the center (along the terminator), and
  ranging down to minus 60 degrees to minus 70 degrees F at the limbs,
  showing an apparent limb-darkening effect, which would indicate a hot
  surface and the absence of a supercharged ionosphere.

—A spot 20 degrees F colder than the surrounding area exists along the
  terminator in the southern hemisphere: a high mountain could exist in
  this region, but such an hypothesis is purely conjectural. A bright
  radar reflection is also found on the Equator in the same general
  region. Causes of these phenomena are not established.

—At their base, the clouds are about 200 degrees F and probably are
  comprised of condensed hydrocarbons held in oily suspension. Below the
  clouds, the atmosphere must be heavily charged with carbon dioxide,
  may contain slight traces of oxygen, and probably has a strong
  concentration of nitrogen.

—112

—As determined by the microwave radiometer, Venus’ surface temperature
  averages approximately 800 degrees F on both light and dark sides of
  the planet. Some roughness is indicated and the surface reflectivity
  is equivalent to that of dust and sand. No water could be present at
  the surface but there is some possibility of small lakes of molten
  metal of one type or another.

—Some reddish sunlight, in the filterable infrared spectrum, may find
  its way through the 15-mile-thick cloud cover, but the surface is
  probably very bleak.

—The heavy, dense atmosphere creates a surface pressure of some twenty
  times that found on the Earth, or equal to about 600 inches of
  mercury.


The mission was completed and the spacecraft had gone into an endless
orbit around the Sun. But before Mariner II lost its sing-song voice, it
produced 13 million data words of computer space lyrics to accompany the
music of the spheres.




                                APPENDIX
                             SUBCONTRACTORS


Thirty-four subcontractors to JPL provided instruments and other
hardware for Mariners I and II.

The subcontractors were:

  Aeroflex Corporation                 Jet vane actuators
    Long Island City, New York
  American Electronics, Inc.           Transformer-rectifiers for flight
    Fullerton, California                telecommunications
  Ampex Corporation                    Tape recorders for ground telemetry
    Instrumentation Division             and data handling equipment
    Redwood City, California
  Applied Development Corporation      Decommutators and teletype encoders
    Monterey Park, California            for ground telemetry equipment
  Astrodata, Inc.                      Time code translators, time code
    Anaheim, California                  generators, and spacecraft signal
                                         simulators for ground telemetry
                                         equipment
  Barnes Engineering Company           Infrared radiometers
    Stamford, Connecticut                Planet simulator
  Bell Aerospace Corporation           Accelerometers and associated
    Bell Aerosystems Division            electronic modules
    Cleveland, Ohio
  Computer Control Company, Inc.       Data conditioning systems
    Framingham, Massachusetts
  Conax Corporation                    Midcourse propulsion explosive
    Buffalo, New York                    valves
                                         Squibs
  Consolidated Electrodynamics Corp.   Oscillographs for data reduction
    Pasadena, California
  Consolidated Systems Corporation     Scientific instruments
    Monrovia, California                 Operational support equipment
  Dynamics Instrumentation Company     Isolation amplifiers for telemetry
    Monterey Park, California            Operational support equipment
  Electric Storage Battery Company     Spacecraft batteries
    Missile Battery Division
    Raleigh, North Carolina
  Electro-Optical Systems, Inc.        Spacecraft power conversion
    Pasadena, California                 equipment
  Fargo Rubber Corporation             Midcourse propulsion fuel tank
    Los Angeles, California              bladders
  Glentronics, Inc.                    Power supplies for data
    Glendora, California                 conditioning system
  Groen Associates                     Actuators for solar panels
    Sun Valley, California
  Houston Fearless Corporation         Pin pullers
    Torrance, California
  Kearfott Division                    Gyroscopes
    General Precision, Inc.
    Los Angeles, California
  Marshall Laboratories                Magnetometers and associated
    Torrance, California                 operational support equipment
  Matrix Research and Development      Power supplies for particle flux
    Corporation                          detectors
    Nashua, New Hampshire
  Menasco Manufacturing Company        Midcourse propulsion fuel tanks and
    Burbank, California                  nitrogen tanks
  Midwestern Instruments               Oscillographs for data reduction
    Tulsa, Oklahoma
  Mincom Division                      Tape recorders for ground telemetry
    Minnesota Mining & Manufacturing     and data handling equipment
    Los Angeles, California
  Motorola, Inc.                       Spacecraft command subsystems,
    Military Electronics Division        transponders, and associated
    Scottsdale, Arizona                  operational support equipment
  Nortronics                           Attitude control gyro electronic,
    Division of Northrop Corporation     autopilot electronic, and antenna
    Palos Verdes Estates, California     servo electronic modules,
                                         long-range Earth sensors and Sun
                                         sensors
  Ransom Research                      Verification and ground command
    Division of Wyle Laboratories        modulation equipment
    San Pedro, California
  Rantec Corporation                   Transponder circulators and monitors
    Calabasas, California
  Ryan Aeronautical Company            Solar panel structures
    Aerospace Division
    San Diego, California
  Spectrolab                           Solar cells and their installation
    Division of Textron Electronics,     and electrical connection on
    Inc.                                 solar panels
    North Hollywood, California
  State University of Iowa             Calibrated Geiger counters
    Iowa City, Iowa
  Sterer Engineering & Manufacturing   Valves and regulators for midcourse
    Company                              propulsion and attitude control
    North Hollywood, California          systems
  Texas Instruments, Inc.              Spacecraft data encoders and
    Apparatus Division                   associated operational support
    Dallas, Texas                        equipment, ground telemetry
                                         demodulators
  Trans-Sonic, Inc.                    Transducers
    Burlington, Massachusetts

In addition to these subcontractors, over 1,000 other industrial firms
contributed to the Mariner Project.




                               FOOTNOTES


[1]Throughout this book “Mariner” refers to the successful Mariner II
    Venus mission. Mariner I was launched earlier but was destroyed when
    the launch vehicle flew off course.

[2]For scientific reasons, distances from Venus are calculated from the
    center of the planet. Hereafter in this chapter, these distances
    will be reckoned from the surface.




                                 INDEX


                                   A
  ABMA, 17
  Agena B, 21, 22, 40
  Antennas, 66
      Goldstone, description, 70, 71, 73
      onboard, description, 30, 31
          directional control, 30
      Pioneer tracking site, 70, 71
  ARPA, 17
  Astronomical unit, 111
      refinement, 107
  Atlantic Missile Range, 2, 10, 43, 83
  Atlas-Agena B, 63, 52
  Atlas D, 19, 21, 36-39, 89
  Attitude control
      Atlas D, 38
      Earth acquisition, 58
      loss of control and reorientation, 56, 60
  Attitude control system, 31, 32


                                    B
  Battery, 25, 27
  Bumper-WAC, 18


                                    C
  C-133 aircraft, 43
  Centaur, 8
  Central Computer and Sequencer, 28
      commands, 56, 58
      failure at encounter, 62
      midcourse maneuver control, 59
  Central Computing Facility, 81, 82
  Charged particles, 13, 90
  Charged particle detector, 35, 88
  Computers, data processing, 84
  Corporal E, 18
  Cosmic dust, 13
      density, 110
      distribution and mass, 94, 95
      measurement, 89
  Cosmic dust detector, 35, 68, 87, 89
  Cosmic radiation, 13, 96
  Cosmic ray flux, 98


                                    D
  Data conditioning system, 88
  Data processing, 30, 74, 85
      CCF, equipment and operation, 82, 83
      launch and tracking operations, 83
      telemetry data, 84
      transmission time, 88
  Detectors
      charged particle, 35
      cosmic dust, 35
      solar plasma, 35
  DSIF, 73, 74, 75, 82, 83, 84
      functions, 68
      Goldstone, 1, 64, 67-79, 68, 69, 70, 71, 73, 75, 84, 107, 108,
          109
      Johannesburg, 64, 67, 68, 73
      Mobile, 68, 73, 80
      tracking during midcourse maneuver, 56
      orientation, 56
      Woomera, 67, 68, 71, 73, 75


                                    E
  Earth sensor
      final orientation commands, 64
      September 8, crises and recovery, 60
  Echo Project, 69
  Echo site functions, 71
  Electronics equipment weight, 25
  Explorer I, 19
  Experiments, 35
      Anton special purpose tube, 87
      atmospheric investigation, 85
      charged particle detector, 88, 96-100
          density variation data, 98
          radiation hazard findings, 98
      cosmic dust detector data, 87-89, 94, 95
      high energy radiation, 90
      infrared radiometer, 87, 93
      ion chamber and Geiger-Mueller tubes, 87
      magnetometers, 87, 88
      microwave radiometer, 87, 91-93
      objectives, 13, 93
      processing of data, 85
      radiometers, 85, 105, 106
      responsible organizations, 88
      results, 110-112
      solar plasma detector, 87-90
      temperature investigation, 85
      transmission of data, 88
      weight, 25


                                    G
  Geiger counter, 98
  Geiger-Mueller tubes, 87, 91
  George C. Marshall Space Flight Center, 13, 17
  Goldstone Tracking Station, 64, 67, 69, 75, 84, 107
      Echo site, 68, 69, 71, 73
      Pioneer site, 56, 68, 70
      Venus site, 69, 70, 108, 109
  Guidance, 13


                                    H
  High-energy radiation experiments, 90, 91


                                    I
  Infrared radiometer experiment
      cloud observations, 103, 105, 106
      description, 93
      dimensions, 93
      operating characteristics, 85, 93
  Interplanetary magnetic field, 13, 99
  Interplanetary space
      cosmic dust density, 110
          distribution, 95
      hazards to spacecraft, 13
  Ion chamber, 98


                                    J
  Johannesburg tracking station, 67, 68
      equipment, 68, 73
      functions, 68, 73
  JPL, 2, 8, 13, 75, 76, 80, 82, 84
      accomplishments, 18, 19
      background, 18
      DSIF control point, 67, 68
      pre-Mariner spacecraft, 23
  Jupiter, contrast to Venus, 101
  Jupiter C, 19


                                    L
  Launch Operations Center, 12, 17
  Launching, 56
      Atlas performance, 52, 53
      Atlas-Agena B, 52
      battery, 52
      gyroscopes, 53
      radio guidance system, 52
      time limitations, 12


                                    M
  Magnetometer experiment, 35, 88
      data, 101, 102
      description, 91
      function, 91
      objectives, 100
      onboard location, 91
  Mariner I, 43-45
  Mariner R, 41
  Masers, 70
  Materials, thermal shielding, 33
  Microwave radiometer experiment
      description, 91
      function, 91
      measurements, 103, 105
      operating characteristics, 85, 92-93
  Midcourse maneuver, 32, 58-59, 60, 65
  Mission achievements, records, 65
  Mobile tracking station, 68, 80
      location, equipment and function, 73
  MX-774 Project, 21


                                    N
  NACA, precursor of NASA, 16
  NASA, 8, 16, 17


                                    P
  Parking orbit, 55
  Pioneer III, 19
  Pioneer IV, 19
  Pioneer project, 69
  Pioneer tracking site, 70, 71
  Power system, 25
  Private A, 18
  Propellants
      Atlas D, 38
      attitude control system, 32
      spacecraft, controlled burning, 32
          rocket thrust system, 32
  Propulsion system, Mariner
      spacecraft, hydrazine propellant, 33
          propellant storage, 32, 38
      weight, 25


                                    R
  Radiation, 98-100
  Ranger III, 8
  Receivers, 66
  Records, Mariner
      attitude control system, 65
      measurements near Sun, 65
      operation near Venus
      telemetry measurements, distance, 65
      trajectory correction maneuver, 65
      transmission, continuous performance, 65


                                    S
  Sensors
      Earth, for attitude control, 32
      Sun, for attitude control, 32
  Sergeant missile, 19
  Shielding, 33, 34
  Solar cells, 27, 28
  Solar flares, 98, 99
  Solar panels
      description, 25
      design, 27
      output deterioration, 61
      release, 11
      support, 25
      weight, 27
  Solar plasma detector, 35, 88, 96, 97
      description, 87, 89, 90
      function, 87, 89, 90
      recordings, 96, 97
  Solar plasma flux
      correlation with geomagnetic effects, 97
  Solar wind
      effects on cosmic-ray movements, 96
          magnetic fields, 95, 96
      low density and energy, 96
      measurement, 89
      particle concentration near Earth, 96
      particle energies, 96
      temperature, 96
      theories, 95
      velocities, 13, 95, 96, 97, 110
  Space Flight Operations Center, 60
      organization and operation, 75, 80, 81
  Space simulator, temperature control, 41
  Spacecraft, 31
      attitude control system, 31
      Central Computer and Sequencer, 28
      components and subsystems, 27
      configuration, 23
      electronic equipment, 25
      frame materials, 23, 25
      launching, 12
      power system, 25
      preliminary design, 41
      propulsion system, 32
      shroud and adapter, 43
      system tests, 41
      telecommunications subsystem, 30
      temperature, 33
      test models, 41
      testing, 23
      trajectory, 11
      weight, 25
  Sun sensor, 32


                                    T
  Telemetry
      continuous transmission, 65
      data processing, 84
      description, 30
      loss of monitoring data, 62
      phase-shift modulation, 30
      transmission cutoff, 64
  Telemetry processing station, 82, 83
  Telemetry system
      data processing, 30
      onboard, description, 30
  Temperature control
      coatings, 34
      heating problems, 62
      housing structures, 35
      materials, 33
      problems, 33
      solar panels, 35
      solar radiation shielding, 35
      thermal shielding, 33
  Tracking
      Antigua, 53
      Ascension, 53, 55
      DSIF, 52, 66, 67, 68, 69
      Earth noise, 66
      Grand Bahama Island, 53
      Johannesburg, 56
      Pretoria, 53, 55
      problems, 66
      radio noise, 66
      San Salvador, 53
      solar noise, 66
      Twin Falls Victory, 53, 55
      Whiskey, 55
      Woomera, 56
  Trajectory, 11, 63, 64, 83


                                    V
  V-2 rocket, 18
  Van Allen radiation belt, 19, 97
  Venus
      atmosphere, 3, 5, 104, 105, 112
      atmospheric temperature, 85
      atmospheric winds, 5
      CO₂ content above clouds, 106
      cloud cover, 105, 106
      cloud observations, 104, 105
      clouds, data, 111
      compared with Earth, 5
      description, 4
      dielectric constant, surface material, 107
      encounter, 93, 94
      historical data, 2
      inferior and superior conjunctions, 4
      magnetic field, 98, 100, 111
          comparison with geomagnetic, 100, 101
          data, 100, 101, 102
          strength, 100, 101, 102
      mass, 109, 111
      orbit, 4
      radar experiments, 1961, 106, 107
      radar experiments during mission, 107
      reflection coefficient, 107
      revolution, 4
      rotation, 4, 101, 108, 111
      surface, 106
      brightness temperature, 103, 104
      characteristics, theories, 102, 103
      “greenhouse” effect, 106
      measurements, 103, 104
      pressure, 112
      reflectivity, 111
      roughness, 107, 108
      temperature, 106, 111
      temperature, 85, 111
      topography, 5
      water vapor in atmosphere, 106
  Venus encounter, 63


                                    W
  WAC Corporal, 18
  Woomera Tracking Station, 67, 68, 75
      equipment, 68, 71, 73




                          Transcriber’s Notes


—Retained publication information from the printed edition: this eBook
  is public-domain in the country of publication.

—In the text versions only, text in italics is delimited by
  _underscores_.

—Silently corrected a few typos.

—In the index, entry “propellant storage”, replaced one nonsensical page
  number (200) with a plausible conjecture (38).







End of the Project Gutenberg EBook of Mariner Mission to Venus, by 
Jet Propulsion Laboratory

*** END OF THE PROJECT GUTENBERG EBOOK 54585 ***