THE VOYAGER MISSION
Genesis of Voyager
Voyager had its origin in the Outer Planets Grand Tour, a plan to send
spacecraft to all the planets of the outer solar system. In 1969, the
same year in which the Pioneer Project received Congressional approval,
NASA began to design the Grand Tour. At the same time, the Space Science
Board of the National Academy of Sciences completed a study called “The
Outer Solar System,” chaired by James Van Allen of the University of
Iowa, which recommended that the United States undertake an exploration
program:
1. To conduct exploratory investigations of the appearance, size,
mass, magnetic properties, and dynamics of each of the outer planets
and their major satellites;
2. To determine the chemical and isotopic composition of the
atmospheres of the outer planets;
3. To determine whether biologically important organic substances
exist in these atmospheres and to characterize the lower atmospheric
environments in terms of biologically significant parameters;
4. To describe the motions of the atmospheres of the major planets and
to characterize their temperature-density-composition structure;
5. To make a detailed study for each of the outer planets of the
external magnetic field and respective particle population, associated
radio emissions, and magnetospheric particle-wave interactions;
6. To determine the mode of interaction of the solar wind with the
outer planets, including the interaction of the satellites with the
planets’ magnetospheres;
7. To investigate the properties of the solar wind and the
interplanetary magnetic field at great distances from the Sun at both
low and high solar latitudes, and to search for the outer boundary of
the solar wind flow;
8. To attempt to obtain the composition, energy spectra, and fluxes of
cosmic rays in interstellar space, free of the modulating effects of
the solar wind.
The report also noted that “exceptionally favorable astronomical
opportunities occur in the late 1970s for multiplanet missions,” and
that “professional resources for full utilization of the
outer-solar-system mission opportunities in the 1970s and 1980s are
amply available within the scientific community, and there is a
widespread eagerness to participate in such missions.”
An additional Academy study, chaired by Francis S. Johnson of the
University of Texas at Dallas and published in 1971, was even more
specific: “An extensive study of the outer solar system is recognized by
us to be one of the major objectives of space science in this decade.
This endeavor is made particularly exciting by the rare opportunity to
explore several planets and satellites in one mission using long-lived
spacecraft and existing propulsion systems. We recommend that
[Mariner-class] spacecraft be developed and used in Grand Tour missions
for the exploration of the outer planets in a series of four launches in
the late 1970s.”
Thus the stage was set to initiate the Outer Planets Grand Tours. NASA’s
timetable called for dual launches to Jupiter, Saturn, and Pluto in 1976
and 1977, and dual launches to Jupiter, Uranus, and Neptune in 1979, at
a total cost over the decade of the 1970s of about $750 million.
A necessary step was to obtain from the scientific community the best
possible set of instruments to fly on the spacecraft. Following its
initial internal studies, NASA turned for its detailed scientific
planning to an open competition in which any scientist or scientific
organization was invited to propose an investigation. In October 1970
NASA issued an “Invitation for Participation in the Mission Development
for Grand Tour Missions to the Outer Solar System,” and a year later it
had selected about a dozen teams of scientists to formulate specific
objectives for these missions. At the same time, an advanced spacecraft
engineering design was carried out by the Caltech Jet Propulsion
Laboratory (JPL), and studies were also supported by industrial
contractors. In fiscal year 1972, plans called for an appropriation by
Congress of $30 million to fund these developments, leading toward a
first launch in 1976.
Even as the scientific and technical problems of the Grand Tour were
being solved, however, political and budgetary difficulties intervened.
The Grand Tour was an ambitious and expensive concept, designed in the
enthusiasm of the Apollo years. In the altered national climate that
followed the first manned lunar landings, the United States began to
pull back from major commitments in space. The later Apollo landings
were canceled, and in fiscal year 1972 only $10 million of the $30
million needed to complete Grand Tour designs was appropriated. It
suddenly became necessary to restructure the exploration of the outer
planets to conform to more modest space budgets.
[Illustration: The original plan for the Outer Planets Grand Tour
envisaged dual launches to Jupiter, Saturn, and Pluto in the
mid-1970s, and dual launches to Jupiter, Uranus, and Neptune in
1979. However, political and budgetary constraints altered the plan,
and the Voyager mission to Jupiter and Saturn, with an optional
encounter with Uranus, was formulated to replace it. Here the
original Grand Tour trajectories from Earth to the outer planets are
shown. [P-10612AC]]
Redesign of the Mission
The new mission concept that replaced the Grand Tour dropped the
objectives of exploring the outer three planets—Uranus, Neptune, and
Pluto. In this way the lifetime of the mission was greatly shortened,
placing less stringent demands on the reliability of the millions of
components that go into a spacecraft. Limiting the mission to Jupiter
and Saturn also relieved problems associated with spacecraft power, and
with communicating effectively over distances of more than 2 billion
kilometers. The total cost of the new mission was estimated at $250
million, only a third of that previously planned for the Grand Tour.
Because it was based on the proven Mariner spacecraft design, the new
mission was initially named Mariner Jupiter Saturn, or MJS; in 1977 the
name was changed to Voyager. In January 1972 the President’s proposed
fiscal year 1973 budget included $10 million specifically designated for
Voyager; after authorization and appropriation by Congress, the official
beginning of Voyager was set for July 1, 1972.
With approval of the new mission apparently assured in the Congress,
NASA issued an “Announcement of Flight Opportunity” to select the
scientific instruments to be carried on Voyager. Seventy-seven proposals
were received; 31 from groups of scientists with designs for
instruments, and 46 from individuals desiring to participate in
NASA-formed teams. Of these 77 proposals, 24 were from NASA
laboratories, 48 were from scientists in various U.S. universities and
industry, and 5 were from foreign sources. After extensive review, 28
proposals were accepted: 9 for instruments and 19 for individual
participation. The newly selected Principal Investigators and Team
Leaders met for the first time at JPL just before Christmas, 1972. To
coordinate all the science activity of the Voyager mission, NASA and JPL
selected Edward Stone of Caltech, a distinguished expert on
magnetospheric physics, to serve as Project Scientist.
The team assembled in 1972 by JPL and its industrial contractors
included more than a thousand highly trained engineers, scientists, and
technical managers who assumed responsibility for the awesome task of
building the most sophisticated unmanned spacecraft ever designed and
launching it across the farthest reaches of the solar system. At the
head of the organization was the Project Manager, Harris (Bud)
Schurmeier. Later, Schurmeier was succeeded by John Casani, Robert
Parks, and Ray Heacock. This team had only four years to turn the paper
concepts into hardware, ready to deliver to Kennedy Space Center for
launch in the summer of 1977.
[Illustration: Project Scientist Edward C. Stone]
[Illustration: Project Manager Harris (Bud) Schurmeier]
The Objectives of Voyager
Voyager is one of the most ambitious planetary space missions ever
undertaken. Voyager 1, which encountered Jupiter on March 5, 1979, was
to investigate Jupiter, its large satellites Io, Ganymede, and Callisto,
and tiny Amalthea; Saturn, its rings, and several of its
satellites—including Titan, the largest satellite in the solar system.
Voyager 2, which arrived at Jupiter on July 9, 1979, was to examine
Jupiter, Europa, Ganymede, Callisto, and Saturn and several of its
satellites, after which it was to be hurled on toward an encounter with
the Uranian system in 1986. Both spacecraft were also designed to study
the interplanetary medium and its interactions with the solar wind.
Scientific objectives as well as the orbital positions of the planets
and satellites influenced the choice of spacecraft trajectories, which
were designed to provide close flybys of all four of Jupiter’s Galilean
satellites and six of Saturn’s satellites—featuring a very close
approach to Titan—and occultations of the Sun and Earth by Jupiter,
Saturn, Titan, and the rings of Saturn. However, all these objectives
could not be accomplished by a single spacecraft. No single path through
the Jupiter system, for instance, can provide close flybys of all four
Galilean satellites. Specifically, a trajectory for Voyager 1 that
included a close encounter with Io precluded a close encounter with
Europa and did not allow the spacecraft the option of being targeted
from Saturn to Uranus without having to travel through the rings of
Saturn. On the other hand, a trajectory that would send Voyager 2 on to
Uranus precluded not only a close encounter with Io, but also a close
encounter with Titan and with Saturn’s rings. The alignment of the
planets and their satellites was such that encounter with Jupiter on or
before April 4, 1979 was necessary for optimum investigation of Io, but
encounter with Jupiter after June 15, 1979 was mandatory for a
trajectory that would maintain the option to go on to Uranus. The latter
trajectory also allowed Voyager 2 to maintain a healthier distance from
Jupiter, avoiding the full dose of radiation that would be experienced
by Voyager 1.
Although the two Voyager trajectories do have certain fundamental
differences, they also have a great deal in common: Both spacecraft were
designed to study the interplanetary medium, and both would investigate
Jupiter and Saturn and have close flybys with several of their major
satellites. Also, if it were decided not to send Voyager 2 on to Uranus,
this spacecraft could be retargeted to a Saturn trajectory similar to
that of Voyager 1, providing a close flyby of Titan and a closer look at
the rings. The flight paths of Voyager 1 and Voyager 2 complement each
other—allowing the planets and some of the satellites to be viewed from
a number of angles and over a longer period of time than would be
possible with only one spaceprobe—yet the trajectories were also
designed to be more or less capable of duplicating each other’s
scientific investigations. This redundancy helps to ensure, so far as is
possible, the success of the mission.
The redundancy built into the mission is evident, not only in the design
of the trajectories, but in the spacecraft themselves. Voyagers 1 and 2
are identical spacecraft. In addition, many crucial elements are
duplicated on each: For example, the computer command subsystem (CCS),
the flight data subsystem (FDS), and the attitude and articulation
control subsystem (AACS)—which function as onboard control systems—each
have multiple reprogrammable digital computers. In addition, the CCS,
which decodes commands from ground control and can instruct other
subsystems from its own memory, contains duplicates for all its
functional units. The AACS, which controls the spacecraft’s
stabilization and orientation, has duplicate star trackers and Sun
sensors. The communications system contains two radio receivers and four
transmitters, two each to transmit both S-band (frequency of about 2295
megahertz) and X-band (frequency of about 8418 megahertz).
[Illustration: Project Manager John Casani]
The Spacecraft
The Voyager spacecraft are more sophisticated, more automatic, and more
independent than were the Pioneers. This independence is important
because the giant planets are so far away that the correction of a
malfunction by engineers on Earth would take hours to perform. Even at
“nearby” Jupiter, radio signals take about forty minutes to travel in
one direction between the spacecraft and Earth. Saturn is about twice as
far away as Jupiter, and Uranus is twice as far as Saturn, slowing
communication even more.
[Illustration: About the same size and weight of a subcompact car,
the Voyager spacecraft carry instruments for eleven science
investigations of the outer planets and their satellites. Power to
operate the spacecraft is provided by three radioisotope
thermoelectric generators mounted on one boom; other booms hold the
science scan platform and the dual magnetometers.]
High-gain directional antenna
Magnetometer
Extendable boom
Planetary radio astronomy and plasma wave antenna
Radioisotope thermoelectric generators
Plasma detector
Cosmic ray detector
Wide angle TV
Narrow angle TV
TV electronics
Ultraviolet spectrometer
Photopolarimeter
Infrared interferometer spectrometer and radiometer
Low energy charged particles
Thrusters
Electronic compartments
Science instrument calibration panel and shunt radiator
Propulsion fuel tank
Planetary radio astronomy and plasma wave antenna
Perched atop the Centaur stage of the launch rocket, each Voyager
spacecraft has a mass of 2 tons (2066 kilograms), divided about equally
between the spacecraft proper and the propulsion module used for final
acceleration to Jupiter. The Voyager itself, with a mass of 815
kilograms and typical dimensions of about 3 meters, is almost the size
and weight of a subcompact car—but enormously more complex. A better
analogy might be made with a large electronic computer—but no
terrestrial computer was ever asked to supply its own power source and
to operate unattended in the vacuum of space for up to a decade.
Each Voyager spacecraft carries instruments for eleven science
investigations covering visual, infrared, and ultraviolet regions of the
spectrum, and other remote sensing studies of the planets and
satellites; studies of radio emissions, magnetic fields, cosmic rays,
and lower energy particles; plasma (ionized gases) waves and particles;
and studies using the spacecraft radios. Each Voyager has a science boom
that holds high and low resolution TV, photopolarimeter, plasma and
cosmic ray detectors, infrared spectrometer and radiometer, ultraviolet
spectrometer, and low energy charged particle detector; in addition,
each spacecraft has a planetary radio astronomy and plasma wave antenna
and a long boom carrying a low- and a high-field magnetometer.
Communication with Earth is carried out via a high-gain antenna 3.7
meters in diameter, with a smaller low-gain antenna as backup. The large
white dish of the high-gain antenna dominates the appearance of the
spacecraft, setting it off from its predecessors, which were able to use
much smaller antennas to communicate over the more modest distances that
separate the planets of the inner solar system. Although the transmitter
power is only 23 watts—about the power of a refrigerator light bulb—this
system is designed to transmit data over a billion kilometers at the
enormous rate of 115 200 bits per second. Data can also be stored for
later transmission to Earth; an onboard digital tape recorder has a
capacity of about 500 million (5 × 10⁸) bits, sufficient to store nearly
100 Voyager images.
[Illustration: Project Manager Ray Heacock]
[Illustration: During the early assembly stage, technicians at
Caltech’s Jet Propulsion Laboratory equip Voyager’s extendable boom
with low- and high-field magnetometers that measure the intensity
and direction of the outer planets’ magnetic fields. [373-7179BC]]
Radioisotope thermoelectric generator (RTGs), rather than solar cells,
provide electricity for the Voyager spacecraft. The RTG use radioactive
plutonium oxide for this purpose. As the plutonium oxide decays, it
gives off heat which is converted to electricity, supplying a total of
about 450 watts to the spacecraft at launch. This power slowly declines
as the plutonium is used up, with less than 400 watts expected at Saturn
flyby five years after launch. Hydrazine fuel is used to make mid-course
corrections in trajectory and to control the spacecraft’s orientation.
Since the Voyagers must fly through the inner magnetosphere of Jupiter,
it was imperative that the hardware systems be able to withstand the
radiation from Jovian charged particles. The electronic microcircuits
that form the heart and brain of the spacecraft and its scientific
instruments are especially susceptible to radiation damage. Three
techniques were used to “harden” components against radiation:
1. Special design using radiation-resistant materials;
2. Extensive testing to select those electronic components which come
out of the manufacturing process with highest reliability; and
3. Spot shielding of especially sensitive areas with
radiation-absorbing materials.
VOYAGER’S GREETINGS TO THE UNIVERSE
The Voyager spacecraft will be the third and fourth human artifacts to
escape entirely from the solar system. Pioneers 10 and 11, which
preceded Voyager in outstripping the gravitational attraction of the
Sun, both carried small metal plaques identifying their time and place
of origin for the benefit of any other spacefarers that might find them
in the distant future. With this example before them, NASA placed a more
ambitious message aboard Voyager 1 and 2—a kind of time capsule,
intended to communicate a story of our world to extraterrestrials.
The Voyager message is carried by a phonograph record—a 12-inch
gold-plated copper disk containing sounds and images selected to portray
the diversity of life and culture on Earth. The contents of the record
were selected for NASA by a committee chaired by Carl Sagan of Cornell
University. Dr. Sagan and his associates assembled 115 images and a
variety of natural sounds, such as those made by surf, wind and thunder,
birds, whales, and other animals. To this they added musical selections
from different cultures and eras, and spoken greetings from Earthpeople
in sixty languages, and printed messages from President Carter and U.N.
Secretary General Waldheim.
Each record is encased in a protective aluminum jacket, together with a
cartridge and needle. Instructions, in symbolic language, explain the
origin of the spacecraft and indicate how the record is to be played.
The 115 images are encoded in analog form. The remainder of the record
is in audio, designed to be played at 16⅔ revolutions per second. It
contains the spoken greetings, beginning with Akkadian, which was spoken
in Sumer about six thousand years ago, and ending with Wu, a modern
Chinese dialect. Following the section on the sounds of Earth, there is
an eclectic 90-minute selection of music, including both Eastern and
Western classics and a variety of ethnic music.
Once the Voyager spacecraft leave the solar system (by 1990, both will
be beyond the orbit of Pluto), they will find themselves in empty space.
It will be forty thousand years before they come within a light year of
a star, called AC + 79 3888, and millions of years before either might
make a close approach to any other planetary system. As Carl Sagan has
noted, “The spacecraft will be encountered and the record played only if
there are advanced spacefaring civilizations in interstellar space. But
the launching of this bottle into the cosmic ocean says something very
hopeful about life on this planet.”
LANGUAGES ON VOYAGER RECORD
Sumerian
Akkadian
Hittite
Hebrew
Aramaic
English
Portuguese
Cantonese
Russian
Thai
Arabic
Roumanian
French
Burmese
Spanish
Indonesian
Kechua
Dutch
German
Bengali
Urdu
Hindi
Vietnamese
Sinhalese
Greek
Latin
Japanese
Punjabi
Turkish
Welsh
Italian
Nguni
Sotho
Wu
Korean
Armenian
Polish
Netali
Mandarin
Gujorati
Ila (Zambia)
Nyanja
Swedish
Ukrainian
Persian
Serbian
Luganada
Amoy (Min dialect)
Marathi
Kannada
Telugu
Oriya
Hungarian
Czech
Rajasthani
SOUNDS OF EARTH ON VOYAGER RECORD
Whales
Planets (music)
Volcanoes
Mud pots
Rain
Surf
Crickets, frogs
Birds
Hyena
Elephant
Chimpanzee
Wild dog
Footsteps and heartbeats
Laughter
Fire
Tools
Dogs, domestic
Herding sheep
Blacksmith shop
Sawing
Riveter
Morse code
Ships
Horse and cart
Horse and carriage
Train whistle
Tractor
Truck
Auto gears
Jet
Lift-off Saturn 5 rocket
Kiss
Baby
Life signs—EEG, EKG
Pulsart
VOYAGER RECORD PHOTOGRAPH INDEX
Calibration circle
Solar location map
Mathematical definitions
Physical unit definitions
Solar system parameters
The Sun
Solar spectrum
Mercury
Mars
Jupiter
Earth
Egypt, Red Sea, Sinai Peninsula and the Nile
Chemical definitions
DNA structure
DNA structure magnified
Cells and cell division
Anatomy (eight)
Human sex organs
Diagram of conception
Conception
Fertilized ovum
Fetus diagram
Fetus
Diagram of male and female
Birth
Nursing mother
Father and daughter (Malaysia)
Group of children
Diagram of family ages
Family portrait
Diagram of continental drift
Structure of Earth
Heron Island (Great Barrier Reef of Australia)
Seashore
Snake River and Grand Tetons
Sand dunes
Monument Valley
Forest scene with mushrooms
Leaf
Fallen leaves
Sequoia
Snowflake
Tree with daffodils
Flying insect with flowers
Diagram of vertebrate evolution
Seashell (Xancidae)
Dolphins
School of fish
Tree toad
Crocodile
Eagle
Waterhold
Jane Goodall and chimps
Sketch of Bushmen
Bushmen hunters
Man from Guatemala
Dancer from Bali
Andean girls
Thailand craftsman
Elephant
Old man with beard and glasses (Turkey)
Old man with dog and flowers
Mountain climber
Cathy Rigby
Sprinters
Schoolroom
Children with globe
Cotton harvest
Grape picker
Supermarket
Underwater scene with diver and fish
Fishing boat with nets
Cooking fish
Chinese dinner party
Demonstration of licking, eating and drinking
Great Wall of China
House construction (African)
Construction scene (Amish country)
House (Africa)
House (New England)
Modern house (Cloudcroft, New Mexico)
House interior with artist and fire
Taj Mahal
English city (Oxford)
Boston
UN Building, day
UN Building, night
Sydney Opera House
Artisan with drill
Factory interior
Museum
X-ray of hand
Woman with microscope
Street scene, Asia (Pakistan)
Rush hour traffic, India
Modern highway (Ithaca)
Golden Gate Bridge
Train
Airplane in flight
Airport (Toronto)
Antarctic expedition
Radio telescope (Westerbork, Netherlands)
Radio telescope (Arecibo)
Page of book (Newton, _System of the World_)
Astronaut in space
Titan Centaur launch
Sunset with birds
String quartet (Quartetto Italiano)
Violin with music score (Cavatina)
MUSIC ON VOYAGER RECORD
Bach Brandenberg Concerto Number Two, First Movement
“Kinds of Flowers” Javanese Court Gamelan
Senegalese Percussion
Pygmy girls initiation song
Australian Horn and Totem song
“El Cascabel” Lorenzo Barcelata
“Johnny B. Goode” Chuck Berry
New Guinea Men’s House
“Depicting the Cranes in Their Nest”
Bach Partita Number Three for Violin; Gavotte et Rondeaus
Mozart Magic Flute, Queen of the Night (Aria Number 14)
Chakrulo
Peruvian Pan Pipes
Melancholy Blues
Azerbaijan Two Flutes
Stravinsky, Rite of Spring, Conclusion
Bach Prelude and Fugue Number One in C Major from the Well Tempered
Clavier, Book Two
Beethoven’s Fifth Symphony, First Movement
Bulgarian Shepherdess Song “Izlel Delyo Hajdutin”
Navajo Indian Night Chant
The Fairie Round from Pavans, Galliards, Almains
Melanesian Pan Pipes
Peruvian Woman’s Wedding Song
“Flowing Streams”—Chinese Ch’in music
“Jaat Kahan Ho”—Indian Raga
“Dark Was the Night”
Beethoven String Quartet Number 13 “Cavatina”
[Illustration: Each Voyager carries a message in the form of a
12-inch gold-plated phonograph record. The record, together with a
cartridge and needle, is fastened to the side of the spacecraft in a
gold-anodized aluminum case that also illustrates how the record is
to be played. [P-19728]]
THE BRAINS OF THE VOYAGER SPACECRAFT[1]
The Voyager spacecraft had greater independence from Earth-based
controllers and greater versatility in carrying out complex sequences of
scientific measurements than any of their predecessors. These
capabilities resulted from three interconnected onboard computer
systems: the AACS (attitude and articulation control subsystem); the FDS
(flight data subsystem); and the CCS (computer command system).
Operating from “loads” of instructions transmitted earlier from Earth,
these computers could issue commands to the spacecraft and the science
instruments and react automatically to problems or changes in operating
conditions.
The complex sequence of scientific observations and the associated
engineering functions were executed by the spacecraft under the control
of an updatable program stored in the CCS by ground command. At
appropriate times, the CCS issued commands to the AACS for movement of
the scan platform or spacecraft maneuvers; to the FDS for changes in
instrument configuration or telemetry rate; or to numerous other
subsystems within the spacecraft for specific actions. The two identical
(redundant) 4096-word memories within the CCS contained both fixed
routines (about 2800 words) and a variable section (about 1290 words)
for changing science sequencing functions. A single 1290-word science
sequence load could easily generate 300 000 discrete commands, thus
providing significantly more sequencing capability than would be
possible through ground commands. A 1290-word sequencing load in the CCS
controlled both the science and engineering functions of the spacecraft
for a period lasting for ¾ day at closest approach and for up to 100
days during cruise.
Each 1290-word program (or load) was built from specific science
measurement units called links. Some links were used repeatedly in a
looping cyclic (like a computer DO loop) to perform the same observation
numerous times; other links that involved special measurement geometry
or critical timing occurred only once. About 175 science links were
defined for the Voyager 1 Jupiter encounter. It took almost two years to
convert the desired science objectives and measurements first into
links, then into a minute-by-minute timeline for the 98-day encounter
period, and finally into the specific computer instructions that could
be loaded into the CCS memory for that portion of the encounter time
represented by a particular load. The total Voyager 1 Jupiter encounter
period used eighteen sequence memory loads, supplemented by about 1000
ground commands to modify the sequences because of changing conditions
or calibration requirements.
For the Voyager 2 encounter, concern about the ailing spacecraft
receiver limited the number of loads that could be transmitted,
particularly while the spacecraft was deep within the Jovian
magnetosphere, where radiation effects caused the receiver frequency to
drift unpredictably. However, a careful redesign of the planned
sequences permitted the accomplishment of very nearly the original set
of observations even with these constraints.
All three approaches were required on the Voyager craft, especially
after Pioneer 10 and 11 demonstrated that the radiation at Jupiter was
even more intense than had been assumed in early design studies.
The steady streams of engineering and scientific data received on Earth
are transmitted from the receiving stations of the Deep Space Network
(DSN) to JPL, where the Voyager control functions are centered. There,
dozens of technicians check and recheck every subsystem to search for
the slightest hint of malfunction. In case of problems, there are thick
notebooks of instructions and racks of precoded computer tapes ready to
be used to correct any apparent malfunction.
Normally Voyager runs itself. Detailed instructions are programmed into
its onboard computers and command systems for dealing with such
potential emergencies as a stuck valve in the fuel system, loss of
orientation in the star trackers, erratic gyroscope functions, failure
of radio communications, or a thousand and one other nightmares. The
instructions for operating the scientific instruments are also stored on
board, with new blocks of commands sent up once every few days to
replace those for tasks already completed. Whether in the calm of cruise
mode or the intense excitement of a planetary encounter, the Voyager
craft is alone in space, continuously sensing and reacting to its
environment, tied by only a tenuous thread of radio communication to the
anxious watchers back on Earth.
[Illustration: Project Manager Robert Parks]
NASA PLANETARY MISSIONS
Spacecraft Launch Destination Encounter Type of
Date Date Encounter
Mariner 2 8/26/62 Venus 12/14/62 flyby
Mariner 4 11/28/64 Mars 7/14/65 flyby
Mariner 5 6/14/67 Venus 10/19/67 flyby
Mariner 6 2/25/69 Mars 7/31/69 flyby
Mariner 7 3/27/69 Mars 8/05/69 flyby
Mariner 9 5/30/71 Mars 11/13/71 orbiter
Pioneer 10 3/03/72 Jupiter 12/04/73 flyby
Pioneer 11 4/06/73 Jupiter 12/03/74 flyby
Saturn 9/01/79 flyby
Mariner 10 11/03/73 Venus 2/05/74 flyby
Mercury 3/29/74 flyby
Viking 1 8/20/75 Mars 6/19/76 orbiter
7/20/76 lander
Viking 2 9/09/75 Mars 7/07/76 orbiter
9/03/76 lander
Voyager 1 8/20/77 Jupiter 3/05/79 flyby
Voyager 2 9/05/77 Jupiter 7/09/79 flyby
Pioneer Venus 5/20/78 Venus 12/04/78 orbiter
8/8/78 Venus 12/09/78 probe
[Illustration: The Voyager scan platform contains sophisticated
instruments that gather data for Voyager’s remote sensing
investigations. Five of the remote-sensing instruments—two TV
cameras, the infrared spectrometer, the ultraviolet spectrometer,
and the photopolarimeter—are mounted together on the scan platform,
which can be pointed to almost any direction in space, allowing
exact targeting of the observations. [373-7146BC]]