  On August 20, 1977, exactly two years after the launch of the Viking spacecraft to Mars, the first of the Voyagers—actually Voyager 2—was boosted into space at 10:29 a.m. EDT, less than five minutes after the launch window opened on the first day of the thirty-day launch period. Sixteen days later, at 8:56 a.m. EDT on Labor Day, September 5, 1977, Voyager 1 was hurled into space on a shorter, faster trajectory than its twin, zipping past the orbit of the Moon only ten hours after launch. Ultimately, Voyager 1 earned its title by overtaking Voyager 2 as both spacecraft journeyed through the asteroid belt, to arrive at Jupiter four months ahead of Voyager 2. The Voyagers lifted off from Launch Complex 41, Air Force Eastern Test Range, Kennedy Space Center, Cape Canaveral, Florida, atop the giant Titan III-E/Centaur rocket. It was the last time such a launch vehicle was scheduled to be used, as, according to plan, the Space Shuttle would take over in the 1980s. Thus the launching of the two Voyagers signified both an end and a beginning: a once-in-a-lifetime opportunity to explore, in only 8½ years’ time, perhaps fifteen major bodies of the outer solar system. But long before even the first Voyager was to make its closest approach to Jupiter—in fact, even before Voyager 2 was off the launch pad—there were problems to overcome. In early August 1977, about three weeks before launch, failures in the attitude and articulation control subsystem (AACS) and the flight data subsystem (FDS), two of the spacecraft’s three main computer subsystems, prevented the VGR77-2 spacecraft, originally scheduled for launch on August 20, from becoming Voyager 2. Instead, the “spare” spacecraft VGR77-3 was substituted, becoming Voyager 2 upon launch August 20, and VGR77-2, after proper repairs, became Voyager 1. Minor problems continued right up to launch. The low energy charged particle instrument failed and had to be replaced, and as late as T minus five minutes there was a halt in the countdown to check on a stuck valve. Unlike a jinxed dress rehearsal, which is said to “assure” an opening-night success, Voyager 2’s prelaunch problems were a portent of difficulties to come. The Voyager 2 launch was witnessed by thousands as the spacecraft ascended gracefully into the blue Florida sky, accompanied by the deep-throated rumblings of its rocket, echoing for miles across the beaches and scrub forests of Cape Canaveral. The Titan-Centaur performance was nearly flawless, and Voyager 2 quickly achieved an accurate trajectory toward Jupiter. However, even while the engines were still firing, the spacecraft began to experience a baffling series of problems that would absorb the attention of hundreds of persons from Pasadena to Washington, D.C., for the next several weeks until they were brought under control. During the first minutes of flight, there seemed to be two difficulties with the AACS. The Titan-Centaur rocket used to launch Voyager stood as tall as a 15-story building and weighed nearly 700 tons. Here the rocket waits for launch at Kennedy Space Center, with the Voyager spacecraft enclosed in the white protective shroud at the top. [P-19471A] Within an hour after launch, Voyager 2’s science scan platform boom was to have been fully extended and locked. Instructions to deploy were given, and the boom moved outward; however, there was no signal to indicate that the boom was actually locked in place. Efforts to command the boom to move into the locked position were thwarted by the spacecraft. The first maneuver designed to try to lock the boom was aborted by the computer command subsystem (CCS) when the AACS erroneously indicated that it was in trouble. Three days later another maneuver was scheduled to reprogram the faulty computer in the AACS, to align the Sun sensors, and to try to lock the science boom. To provide a direct check of the boom position, the scan platform was turned so that the TV cameras could see the spacecraft. Careful measurement of these pictures verified that the boom was within ½ degree of full deployment, but still there was no indication that it was locked into place. Ultimately, it was decided that the sensor to signal actuation of the lock was at fault, and that the boom itself was almost certainly fully extended and operational. Because of the postlaunch problems of Voyager 2, the launch of Voyager 1 was delayed twice—from September 1 to September 3 and then to September 5—in order to inspect Voyager 1’s science boom and to try to prevent a repetition of Voyager 2’s problems. An extra spring was attached to the science boom to assure its full extension. Finally, as if to make up for the troubles of the first launch, Voyager 1’s launch was both “flawless and accurate.” All launch and postlaunch events went smoothly. The launch window opened at 8:56 a.m. EDT, and Voyager took off promptly at 8:56:01. The booms and antennas deployed and locked in the first hours after launch; all instruments scheduled to be on were on and THE TITAN/CENTAUR LAUNCH VEHICLE The two Voyager spacecraft were carried into space and accelerated toward Jupiter by the Titan III-E Centaur rocket, the largest launch vehicle in the NASA arsenal after the retirement of the Saturn rockets in 1975. The Titan and Centaur vehicles were originally developed separately and have been used with other rocket stages for many NASA launches. They were first combined for the two Viking launches to Mars in 1975, and this powerful four-stage launch vehicle was used again in 1977 for Voyager. The Titan/Centaur stands nearly 50 meters tall, about the height of a fifteen-story building. Fully fueled, it weighs nearly 700 tons. At takeoff, the thrust of the two solid-propellant Stage-0 motors is about 10.7 million newtons. These motors, which burn for 122 seconds, use powdered aluminum as fuel and ammonium perchlorate as oxidizer. Together, they have a mass of 500 tons. The first stage of the liquid propellant core of the Titan rocket ignites about 112 seconds after takeoff. The propellant is hydrazine as fuel and nitrogen tetroxide as oxidizer. The first stage is 3 meters in diameter and 20 meters tall. Fueled, it has a mass of 130 tons. The motor provides a thrust of 2.5 million newtons for a duration of 146 seconds. About 4.3 minutes after takeoff the Titan Stage II liquid propellant motor begins to fire, and the first stage is separated and falls back into the Atlantic. The second stage is 3 meters in diameter and more than 7 meters long, with a fueled mass of 35 tons. The single liquid fuel motor burns for 210 seconds with a thrust of half a million newtons. During the second stage burn, the shroud covering the Voyager spacecraft is jettisoned. The Centaur and Titan vehicles separate 8 minutes into the flight, and the Centaur main engine begins its burn. The Centaur is nearly 20 meters tall and 3 meters in diameter, with a mass of 17 tons. The motors have a thrust of almost 200000 newtons, operating on the most powerful chemical fuels known: liquid oxygen and liquid hydrogen. The Centaur burns for only 1 minute and 36 seconds as it attains Earth parking orbit; the engine then shuts down as the vehicle begins a half-hour coasting period that carries it nearly half way around the Earth. During this time, careful tracking of the spacecraft supplies the data needed for Earth-based computers to calculate the proper time to leave parking orbit and start the long trip toward Jupiter. About 50 minutes after liftoff, from a position high above the Indian Ocean, the second burn of the Centaur main engine begins. Six minutes of additional thrust provides enough energy to break out of Earth’s orbit. The Voyager then separates from the Centaur for a final boost toward Jupiter. The solid rocket motor in the spacecraft propulsion module (acting as final stage of this five-stage launch sequence) fires for 45 seconds at a thrust of 68000 newtons. Just an hour after liftoff, the Voyager spacecraft is on its way, coasting on an orbit toward Jupiter at a speed of more than 10 kilometers per second. The Voyager spacecraft is dominated by the large 3.7-meter-diameter antenna used for communication with Earth. Here the spacecraft undergoes final tests before launch. The science instrument scan platform is folded against the spacecraft on the right; the three cylinders on the left are the RTG power sources. [260-108BC] Voyager 2 was the first of the spacecraft to be launched, on August 20, 1977, propelled into space in a Titan/Centaur rocket. [P-19450AC] The First Year Is the RoughestDuring the autumn of 1977 Voyager 2, and to a lesser extent Voyager 1, continued to plague controllers with erratic actions. Thrusters fired at inappropriate times, data modes shifted, instrument filter and analyzer wheels became stuck, and the various computer control systems occasionally overrode ground commands. Apparently, the spacecraft hardware was working properly, but the computers on board displayed certain traits that seemed almost humanly perverse—and perhaps a little psychotic. In general, these reactions were the result of programming too much sensitivity into the spacecraft systems, resulting in panic over-reaction by the onboard computers to minor fluctuations in the environment. Ultimately, part of the programming had to be rewritten on Earth and then transmitted to the Voyagers, to calm them down so that they would ignore minor perturbations, yet still be ready to perform automatic sequences required to protect the spacecraft from major threats. Meanwhile, however, more serious problems were developing. On February 23, 1978, during a series of movements or slews, Voyager 1’s scan platform slowed and stopped before completing the maneuver. This failure caused a great deal of concern, since the scan platform houses the optical instruments that are crucial to the observation of the Jovian system—the ultraviolet spectrometer, the IRIS, the photopolarimeter, and the two TV cameras. At JPL, tests were run on a proof-test model—an exact copy of the Voyager spacecraft—to try to find out why Voyager 1’s scan platform had become stuck. On March 17, Voyager 1’s scan platform was tested—JPL engineers instructed the platform to move slowly for a short distance, and Voyager responded as ordered. Further tests were conducted on March 23. This time the scan platform was ordered to execute a sequence of four slews, moving away from the part of the sky where the original failure had occurred and ending with the position that it would be most useful to leave the platform in—just in case the platform should become stuck again. On April Voyager 1 was launched on September 5, 1977. The launch was delayed 5 days to make last-minute adjustments to avoid the postlaunch difficulties experienced by Voyager 2. [P-19480AC] An even more serious crisis soon endangered the Voyager 2 spacecraft. In late November 1977, the S-band radio receiver began losing amplifier power in its high-gain mode, so the solid-state amplifier was switched to its low-power position. No further problems were noted until April 5, 1978, when Voyager 2’s primary radio receiver suddenly failed, and shocked engineers discovered that the backup receiver was also faulty. The trouble was detected after Voyager’s computer command subsystem directed the spacecraft to switch from the primary radio receiver to the backup receiver. This command was issued as part of a special protection sequence: If the primary radio receiver receives no commands from Earth for seven days, the backup receiver is switched on instead; if the secondary receiver in turn receives no instructions over a twelve-hour period, the system reverts to the main receiver. When, on April 5, Voyager 2’s radio reception was switched from the primary to the secondary receiver, flight engineers found that they were unable to communicate with the spacecraft—the secondary receiver’s tracking loop capacitor was malfunctioning. That meant that the secondary receiver could not follow a changing signal frequency sent out from Earth. The frequencies of signals transmitted from Earth are affected by the Doppler effect—just as the siren on a fire engine seems first to rise in pitch as the truck approaches, then falls as the truck speeds away, so the frequency of signals transmitted from Earth fluctuates with the Earth’s rotation as the Deep Space Network’s radio antennas move toward or away from the spacecraft. The engineers had to wait until the primary radio receiver was switched back on before they could communicate with the spacecraft. Once the primary receiver was on, Voyager 2 began receiving instructions from Earth, but approximately thirty minutes later, there was an apparent power surge in the receiver. The fuses blew. Each Voyager spacecraft follows a billion-kilometer path to Jupiter. Except for minor thruster firings to achieve small trajectory corrections, each Voyager coasts from Earth to Jupiter, guided by the gravitational pull of the Sun. At Jupiter, the powerful tug of the giant planet deflects the spacecraft and speeds them up, imparting an extra kick to send them on their way toward Saturn.
Because the switching of the radio receivers was still controlled by the special protection sequence discussed earlier, flight engineers would have to wait for seven days—until April 13—before they could attempt communication with the spacecraft again. During that week special procedures were established and rehearsed so that commands could be sent to Voyager in the short time that the backup receiver would be on. On Thursday, April 13, 1978, the seven days were up and the spacecraft should have shifted from the dead main receiver to the sick backup system. There was just a twelve-hour “window” in which to restore communication. At about 3:30 a.m. PST the Madrid tracking station of the Deep Space Network sent its first order to the spacecraft, approximately 474 million kilometers away. Almost an hour later, word arrived from Voyager that the command had been accepted. (One-way light time for a signal to travel the distance from Earth to Voyager at that time was almost 27 minutes.) Elated flight controllers went ahead and transmitted nine hours of commands to the spacecraft. Voyager 2 was successfully commanded again on April 18 and April 26. The April 26 commands included a course change maneuver that was executed properly on May 3. On June 23, Voyager 2 was programmed for a backup automatic mission at Saturn in the event that the secondary radio receiver should also fail. These backup mission instructions would operate all the science experiments, but only a minimum amount of data would be returned, since the scan platform would only be programmed to move through three positions rather than thousands as it would in normal operation. Instructions for a backup minimum automatic encounter at Jupiter were transmitted to Voyager 2 in two segments, the second of these on October 12, 1978. With the backup instructions recorded on board the spacecraft, Voyager personnel felt their fears partially allayed. If Voyager 2’s secondary radio receiver failed, the spacecraft would still obtain some science data at Jupiter and Saturn. But that would mean that there would be no mission beyond Saturn; our first opportunity to explore Uranus, its satellites, its newly discovered ring system, and possibly even to get a look at Neptune, would not come in this century. Another major concern affecting both Voyager spacecraft was the proper management of hydrazine fuel reserves. Hydrazine is used by the thrusters on the Voyagers for stabilization of the spacecraft and for trajectory correction maneuvers (TCM). Each Voyager was loaded with 105 kilograms of hydrazine budgeted for use on the long flight to Jupiter, Saturn, and beyond. Because of the excellent performance of the launch rockets, both Voyagers required less hydrazine than anticipated for their final boost into proper trajectory toward Jupiter, and at first it looked as though both spacecraft would have plenty of propellant to spare. Charles E. Kolhase, Manager of Mission Analysis and Engineering for the Voyager Project, later explained the situation: “Voyager 1 should have been launched September 1. Had it been launched on September 1—and I’m glad it wasn’t—the maneuver to correct the trajectory for a Titan flyby would have required a change in velocity of 100-110 meters per second—an enormous maneuver—and we would have had a propellant margin for going on to Saturn of perhaps 4.5 kilograms. But, by launching on the fifth of September we increased our margin to 23 kilograms. Fortunately, for every launch date that went by, that velocity change maneuver was shrinking at a rate of 10 meters per second per day. Now, a 1 meter per second change uses about a pound of hydrazine [about 0.5 kilogram]. So when we launched on the fifth of September, now we suddenly had 40 pounds of hydrazine excess over what we would have had if we had launched on the first of September. As a result, Voyager 1 is in great THE DEEP SPACE NETWORK A vital component of the Voyager Mission is the communications system linking the spacecraft with controllers and scientists on Earth. The ability to communicate with spacecraft over the vast distances to the outer planets, and particularly to return the enormous amounts of data collected by sophisticated cameras and spectrometers, depends in large part on the transmitters and receivers of the Deep Space Network (DSN), operated for NASA by JPL. The original network of these receiving stations was established in 1958 to provide round-the-world tracking of the first U.S. satellite, Explorer 1. By the late 1970s, the DSN had evolved into a system of large antennas, low-noise receivers, and high-power transmitters at sites strategically located on three continents. From these sites the data are forwarded (often using terrestrial communications satellites) to the mission operations center at JPL. The three DSN stations are located in the Mohave desert at Goldstone, California; near Madrid, Spain; and near Canberra, Australia. Each location is equipped with two 26-meter steerable antennas and a single giant steerable dish 64 meters in diameter, with approximately the collecting area of a football field. In addition, each is equipped with transmitting, receiving, and data handling equipment. The transmitters in Spain and Australia have 100-kilowatt power, while the 64-meter antenna at Goldstone has a 400-kilowatt transmitter. Most commands to Voyager are sent from Goldstone, but all three stations require the highest quality receivers to permit continuous recording of the data streams pouring in from the spacecraft. Since the mid-1960s, the DSN’s standard frequency has been S-band (2295 megahertz). Voyager introduces a new, higher frequency telemetry link at X-band (8418 megahertz). The X-band signal can carry more information than S-band with similar power transmitters, but it requires more exact antenna performance. In addition, the X-band signal is absorbed by terrestrial clouds and, especially, rain. Fortunately, all three DSN stations are in dry climates, but during encounters the weather forecasts on Earth become items of crucial concern if precious data are not to be lost by storm interference. As a result of the development of larger antennas and improved electronics, the DSN command capabilities and telemetry data rates have increased dramatically over the years. For example, in 1965 Mariner 4 transmitted from Mars at a rate of only 8? bits of information per second. In 1969, Mariners 6 and 7 transmitted picture data from Mars at 16200 bits per second. Mariner 10, in 1973, achieved 117200 bits per second from Mercury. Voyager operates at a similar rate from Jupiter, about six times farther away. Many of these improvements in data transmission result from changes in the DSN rather than in the spacecraft transmitters. Problems with hydrazine management developed, however. Voyager 1’s first trajectory correction maneuver achieved only 80 percent of the required speed change. Exhaust plumes from the thrusters apparently struck part of the spacecraft, causing a 20 percent loss in velocity. That being the case, Voyager might require more fuel than had been expected to complete the mission. The extra fuel requirements did not threaten Voyager 1 itself, since it held ample fuel to reach Saturn; the concern was for Voyager 2, where the effective loss of fuel might be enough to jeopardize the Uranus mission. Project members. Project members. Because of the plume impingement problem on Voyager 1, Voyager 2’s first trajectory correction maneuver was adjusted to allow for the possibility of a 20 percent loss in thrust. The Voyager 2 maneuver was successful, but controllers felt that additional action was required to conserve fuel. One way to save was by reducing requirements on control of the spacecraft orientation. Less control fuel would be needed if the already miniscule pressure exerted on the spacecraft by the solar wind could be reduced. Flight engineers at JPL calculated that the pressure would be reduced if the spacecraft were tipped upside down; however, to accomplish this, the spacecraft would have to be steered by a new set of guide stars. By reprogramming the attitude control system it was found possible to substitute the northern star, Deneb, in the constellation of Cygnus, for the original reference star, Canopus, in the southern constellation of Carina. With this change, as well as readjustment of Voyager 2’s trajectory near Jupiter, inflight consumption of hydrazine was reduced significantly. In late August 1978 both Voyagers were reprogrammed to ensure better science results at Jupiter encounter; for example, the reprogramming would prevent imaging (TV) photographs from blurring when the tape recorder was operating. By early November, flight crews had begun training exercises to rehearse for the Voyager 1 flyby of Jupiter on March 5, 1979. A near encounter test was performed on December 12-14, 1978: a complete runthrough of Voyager 1’s 39-hour near encounter period, which would take place March 3-5, 1979. Participants included the flight team, the Deep Space Network tracking stations, the scientists, and the spacecraft itself. Results: Voyager and the Voyager team were all ready for the encounter. Meanwhile, the spacecraft were busy returning scientific data to Earth. Technically, the Voyagers were in the cruise phase of the mission—a period that, for Voyager 2, would last until April 24, 1979, and for Voyager 1, until January 4, 1979, when each spacecraft would enter its respective observatory phase. Cruise Phase ScienceIn the first few days after launch, the spacecrafts’ instruments were turned on and calibrated; various tests for each instrument would continue to be performed throughout the cruise phase. This period presented a great opportunity for the Voyagers to study the interplanetary magnetic fields, solar flares, and the solar wind. In addition, ultraviolet and infrared radiation studies of the sky were performed. In mid-September 1977 the television cameras on Voyager 1 recorded a number of photographs of the Earth and Moon. A photograph taken September 18 captured both crescent Moon and crescent Earth. It was the first time the two celestial bodies had ever been photographed together. In November both Voyagers crossed the orbit of Mars, entering the asteroid belt a month later. On December 15, at a distance of about 170 million kilometers from Earth, Voyager 1 finally speeded past its slower twin. The journey through the asteroid belt was long but uneventful: Voyager 1 emerged safely in September 1978, and Voyager 2 in October. Unlike Pioneers 10 and 11, the Voyagers carried no instruments to look at debris in the asteroid belt. By April both spacecraft were already halfway to Jupiter and, about two months later, Voyager 1, still approximately 265 million kilometers from Jupiter, began returning photographs of the planet that showed considerable detail, although less than could be obtained with telescopes on Earth. Both the imaging (TV) and the planetary radio astronomy instruments began observing Jupiter, and, by October 2, 1978, officials announced that “the polarization characteristics of Jupiter’s radio emissions have been defined. In the high frequencies, there is consistent right-hand circular polarization, while in the low frequencies, there is a consistent left-hand circular polarization. This was an unexpected result.” In addition to scientific studies of the interplanetary medium and a first look at Jupiter, the plasma wave instrument, which studies waves of charged particles over a range of frequencies that includes audio frequencies, was able to record the sound of the spacecraft thrusters firing, as hydrazine fuel is decomposed and ejected into space. The sound was described as being “somewhat like a 5-gallon can being hit with a leather-wrapped mallet.” On December 10, 1978, 83 million kilometers from Jupiter, Voyager 1 took photographs that surpassed the best photographs ever taken from ground-based telescopes, and scientists were anxiously awaiting the start of continuous coverage of the rapidly changing cloud forms. These pictures, together with data from several ground-based observatories, were carefully scrutinized by a team of scientists at JPL to select the final targets in the atmosphere of Jupiter to be studied at high resolution during the flyby. The observatory phase of Voyager 1’s journey to Jupiter was about to begin. As Voyager 1 approached Jupiter, the resolution of the images steadily improved. In October 1978, at a distance of about 125 million kilometers, the image was less clear than would be obtained with an Earth-based telescope. [P-20790] By December 10, the spacecraft had moved to a distance of 85 million kilometers, and the resolution was about 2000 kilometers, comparable to the best telescopic images. [P-20829C] On January 9, 1979 (c), at a distance of 54 million kilometers, the image surpassed all ground-based views and approached the resolution of the Pioneer 10 and 11 photos. [P-20926C] In this, taken January 24 at a distance of 40 million kilometers, the resolution exceeded 1000 kilometers. [P-20945C] The Observatory PhaseThe observatory phase, originally scheduled to start on December 15, 1978, eighty days before encounter, was postponed until January 4, 1979, to provide the flight team a holiday-season break. For the next two months, Voyager would carry out a long-term scientific study—a “time history”—of Jupiter, its satellites, and its magnetosphere. On January 6, Voyager 1 began photographing Jupiter every two hours—each time taking a series of four photographs through different color filters as part of a long-duration study of large-scale atmospheric processes, so scientists could study the changing cloud patterns on Jupiter. Even the first of these pictures showed that the atmosphere was dynamic “with more convective structure than had previously been thought.” Particularly striking were the changes in the planet, especially near the Great Red Spot, that had taken place since the Pioneer flybys in 1973 and 1974. Jupiter was wearing a new face for Voyager. In mid-January, photos of Jupiter were already being praised for “showing exceptional details of the planet’s multicolored bands of clouds.” Still 47 million kilometers from the giant, Voyager 1 had by now taken more than 500 photographs of Jupiter. Movements of cloud patterns were becoming more obvious; feathery structures seemed painted across some of the bands that encircle the planet; swirling features were huddled near the Great Red Spot. The satellites were also beginning to look more like worlds, with a few bright spots visible on Ganymede and dark red poles and a bright equatorial region clearly seen on Io when it passed once each orbit across the turbulent face of Jupiter. From January 30 to February 3, Voyager sent back one photograph of Jupiter every 96 seconds over a 100-hour period. Using a total of three different color filters, the spacecraft thus produced one color picture every 4¾ minutes, in order to make a “movie” covering ten Jovian “days.” To receive these pictures, sent back over the high-rate X-band transmitter, the Deep Space Network’s 64-meter antennas provided round-the-clock coverage. Voyager 1 was ready for its far encounter phase. The Galilean satellites of Jupiter first began to show as tiny worlds, not mere points of light, as the Voyager 1 observatory phase began. In this view taken January 17, 1979, at a range of 47 million kilometers, the differing sizes and surface reflectivities (albedos) of Ganymede (right center) and Europa (top right) are clearly visible. The view of Jupiter is unusual in that the Great Red Spot is not easily visible, but can just be seen at the right edge of the planet. Most pictures selected for publication include the photogenic Red Spot. [P-20938C] Far Encounter PhaseBy early February Jupiter loomed too large in the narrow-angle camera to be photographed in one piece; 2 × 2 three-color (violet, orange, green) sets of pictures were taken for the next two weeks; by February 21, Jupiter had grown too large even for that, and 3 × 3 sets were scheduled to begin. When these sets of pictures are pasted together to form a single picture, the result is called a mosaic. By February 1, 1979, Voyager 1 was only 30 million kilometers from Jupiter, and the resolution of the imaging system corresponded to about 600 kilometers at the cloud tops of the giant planet. At this time, a great deal of unexpected complexity became apparent around the Red Spot, and movie sequences clearly showed the cloud motions, including the apparent six-day rotation of the Red Spot. [P-20993C] One of the most spectacular planetary photographs ever taken was obtained on February 13 as Voyager 1 continued its approach to Jupiter. By this time, at a range of 20 million kilometers, Jupiter loomed too large to fit within a single narrow-angle imaging frame. Passing in front of the planet are the inner two Galilean satellites. Io, on the left, already shows brightly colored patterns on its surface, while Europa, on the right, is a bland ice-covered world. The scale of all of these objects is huge by terrestrial standards; Io and Europa are each the size of our Moon, and the Red Spot is larger than the Earth. [P-21082C] While the imaging experiments were in the limelight, the other scientific instruments had also begun to concentrate on the Jovian system. The ultraviolet spectrometer had been scanning the region eight times a day; the infrared spectrometer (IRIS) spent 1½ hours a day analyzing infrared emissions from various longitudes in Jupiter’s atmosphere; the planetary radio astronomy and plasma wave instruments looked for radio bursts from Jupiter and for plasma disturbances in the region; the photopolarimeter had begun searching for the edge of Io’s sodium torus; and a watch was begun for the bow shock—the outer boundary of the Jovian magnetosphere. On February 10, Voyager 1 crossed the orbit of Sinope, Jupiter’s outermost satellite. Yet the spacecraft even then had a long way to go—still 23 million kilometers from Jupiter, but closing in on the planet at nearly a million kilometers a day. A week later, targeted photographs of Callisto began to provide coverage of the satellite all around its orbit; similar photos of Ganymede began on February 25. Meanwhile excitement was building. As early as February 8 and 9, delight with the mission and anticipation of the results of the encounter in March were already evident. Garry E. Hunt, from the Laboratory for Planetary Atmospheres, University College, The Voyager Project was operated from the Jet Propulsion Laboratory managed for NASA by the California Institute of Technology. Located in the hills above Pasadena, California, JPL is the main center for U.S. exploration of the solar system. [JB17249BC] The Voyager TV cameras do not take color pictures directly as do commercial cameras. Instead, a color image is reconstructed on the ground from three separate monochromatic images, obtained through color filters and transmitted separately to Earth. There are a number of possible filter combinations, but the most nearly “true” color is obtained with originals photographed in blue (480 nanometers), green (565 nanometers), and orange (590 nanometers) light. Before these can be combined, the individual frames must be registered, correcting for any change in spacecraft position or pointing between exposures. Often, only part of a scene is contained in all three original pictures. Shown here is a reconstruction of a plume on Jupiter, photographed on March 1, 1979. The colors used to print the three separate frames can be seen clearly in the nonoverlapping areas. For other pictures in this book, the nonoverlapping partial frames are omitted. [P-21192] The pictures from Voyager are “clearly spectacular,” said Lonne Lane, Assistant Project Scientist for Jupiter. “We’re getting even better results than we had anticipated. We have seen new phenomena in both optical and radio emissions. We have definitely seen things that are different—in at least in one case, unanticipated—and are begging for answers we haven’t got.” There was already, still almost a month from encounter, a strong feeling of accomplishment among the scientists and engineers; they had done a difficult task and it has been successful. By the last week of February 1979, the attention of thousands of individuals was focused on the activities at JPL. Scientists had arrived from universities and laboratories around the country and from abroad, many bringing graduate students or faculty colleagues to assist them. Engineers and technicians from JPL contractors joined NASA officials as the Pasadena motels filled up. Special badges were issued and reserved parking areas set aside for the Voyager influx. Twenty-four hours a day, lights burned in the flight control rooms, the science offices, the computer areas, and the photo processing labs. In order to protect those with critical tasks to perform from the friendly distraction of the new arrivals, special computer-controlled locks were placed on doors, and security officers began to patrol the halls. By the end of the month the press had begun to arrive. Amid accelerating excitement, the Voyager 1 encounter was about to begin. The smaller-scale clouds on Jupiter tend to be more irregular than the large ovals and plumes. At the lower right, one of the three large white ovals clearly shows internal structure, with the swirling cloud pattern indicating counterclockwise, or anticyclonic, flow. A smaller anticyclonic white feature near the center is surrounded by a dark, cloud-free band where one can see to greater depths in the atmosphere. This photo was taken March 1 from a distance of 4 million kilometers. [P-21183C] |
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