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.
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.
Project Manager Ray Heacock
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”
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.
Project Manager Robert Parks
| NASA PLANETARY MISSIONS | ||||
|---|---|---|---|---|
| Spacecraft | Launch Date | Destination | Encounter Date | Type of 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 | |
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]