Voyager - Exploration, Space, And The Third Great Age Of Discovery

by Stephen J. Pyne

  Yet the scientists who initially distrusted the cameras, particularly TV, were right in their suspicions. The romantic horizon that captivated so many nineteenth-century painters had acquired a high-tech reincarnation. Perhaps the most famous distortion was the oft-reproduced image from the Magellan mission to Venus, in which the radar-measured surface of Venus was exaggerated twenty-fold to turn lumpy lava into mountains and basins. But Voyager had its enhancements, too. Some of the mission’s most celebrated images were, as literary journalists might say, composites. The Voyager 1 shot of Earth and Moon began as three images with different color filters, which were then synthesized into a single composition at JPL’s imaging processing lab, where the lunar scene was brightened threefold in order to yield a more pleasing and informative contrast. The images that brought spontaneous gasps from the press were almost all manipulated in some way to enhance one or another feature; and some of those images simply charmed because they were gorgeous. The outer planets were worlds of beauty as well as data.

  Once again, the sublime competed with the scientific. The software engineers at the Image Processing Laboratory were the artists of the Grand Tour.136

  Yet the Third Age, once again, broke simple continuities. It reversed the thematic arc of the Second by which art had fastened itself to exploration. The classic grand tour of the eighteenth century had been a journey to centers of art and antiquity, but by trekking across the Alps and visiting Etnas in eruption, visitors had to confront nature as well as Old Masters, and travelers appealed to the new sciences to decipher nature’s hieroglyphs and illuminate its meaning beyond what classical texts could do. Art and science together pulled the cart of travel.

  Yet just as space science had changed, so had art, and so had the intrinsic character of those encountered landscapes that both science and art sought to wrestle into meaningful form, which meant the Voyagers saw differently from exploring naturalist-artists of the Second Age. This was a modernist nature: abstract, conceptual, minimal, alien to the human presence. It was a world only a robot could visit and only a robot’s instruments could record. The human observer was, even at the speed of light, an hour and a half distant, with the studio banks of electronics further distancing him between the real and the reconstructed. Much as those on the grand tour sought to recreate the new into the venue of the ancient, so the imagers labored to place the Voyagers into the inherited traditions of discovery in which the wonder of first contact was an expected outcome.

  But the shock of the new also spoke to a different realm of art, a comparable shift for the arts to that which the sciences were making as they refocused from hard to soft geographies. Willingly or not, the Voyagers’ was a modernist art. The issue went beyond obvious visual parallels that made false-colored rings into something like a Barnett Newman painting, or the blotchy surfaces of Titan and Saturn into the abstract expressionism of Mark Rothko. It had to do with the position of the artist-explorer in the scene, and it went well beyond what computer enhancement could do.

  The classic views of exploring art included observers in their foreground. The painting looked over the shoulder of the explorer. It saw not only the view of the explorer but also the explorer doing the viewing. Often, too, it attempted to imagine the explorer as seen by the explored, looking over the shoulder of Fijians or Fuegians or the putatively awed gaze of Aborigines, or it found in the wondering faces of encountered indigenes a reflection of the encountered explorer. The artist could view the expedition from the outside, or at times even place himself within the scene as viewed by an outside observer.

  But no one could view Voyager. The twins were too far apart for one to image the other. There was no other platform by which to see Voyager sweep past Jupiter, Saturn, Iapetus, Titan, the rings, and the rest. This was a fundamental condition of the Third Age: there would be no Other to receive, bestow awe, or even witness. There was no one on Ganymede or Rhea, no village on the F Ring, or fishing vessel on the cloud seas of Jupiter, from whose perspective it might be possible to imagine Voyager’s arrival. Its only audiences were the imaging team, the press corps, and the T V-viewing public. Yet continuity with the understood heritage of exploration seemingly required a perspective that the Third Age could not offer. Voyager might hurtle blithely through the void of interplanetary space; it could not so easily leap that looming void of solipsism, the threat posed by the missing perspective outside the spacecraft.

  So when the time came to create computer movies of the flybys, the producers inserted Voyager into the frame. The animation follows the plucky spacecraft as it pitches and yaws and rotates its scan platform past exotic new worlds, just as we knew it would. Much as the camera, though initially vilified by space scientists, came to define discovery for the public, so old perspectives intruded into what might have been a purely modernist moment. That the Voyagers made the compromise allowed them to bond better with a public that regarded modernist art as something best kept in a museum. An image of the spacecraft went into the scene, rather as its curiously awkward trek went into the grand narrative of Western exploration.

  There Voyager sailed, while we looked over its shoulder, and while five hundred years of exploration history looked over ours.

  PARTING

  The Voyagers bid farewell not only to Saturn but to each other.

  So far they had been linked, with Voyager 1 breaking trail for Voyager 2, and Voyager 2 sending data on solar winds to Voyager 1, and the twins programmed to complement each other as they soared past the satellite islands and planetary continents of new worlds. Now they split. Voyager 1 left the plane of the ecliptic entirely in a rising ascent to the borders of the heliosphere. Voyager 2 careened around Saturn for a rendezvous with Uranus. They would never again share routes or pass in tandem. Almost a quarter century later they would meet termination shock separately.

  They were both scarred and limping. Shortly after encounter, Voyager 1’s plasma science instrument had ceased transmitting. This had happened also after Jupiter, and engineers had successfully rekindled the system by temperature cycling. This time it failed to spark. Its photopolarimeter remained broken. The scan platform stubbornly resisted slewing, although this mattered little, since its cameras were turned off on December 19. For the next decade it would transmit only data about the soft geography of the solar system .137

  Voyager 2 also had a defective scan platform. After restoring control, engineers eventually determined that the frenzied pace of the near-encounter—the rapid rotations of the platform, almost minute by minute—had overworked the system, driven out its lubricant, and caused the mechanism to seize up. Through temperature cycling and a pause sufficient to allow some lubrication to seep back, engineers regained enough control to permit the platform to image Phoebe. Then, save for experiments to diagnose the problem, further maneuvering ceased. With enforced rest and fast-slewing prohibited, the system performed as desired. This, too, mattered little for the present, since Voyager 2’s cameras were also shut down. Until it reached Uranus, it would emulate its twin and measure and map only the soft geography of interplanetary space.138

  On September 30, 1981, the primary Voyager mission officially ended, succeeded on October 1, 1981, by the Voyager Uranus/Interstellar Mission (VUIM). The spacecraft were well beyond their warranty, though not beyond their encoded ambitions. The goal for Voyager 1 was now to monitor the interplanetary medium preparatory to leaving the solar system and entering the interstellar realm. The goal for Voyager 2 was a flyby of Uranus, another miniature planetary system, while preserving the option to continue to Neptune. 139

  The projected mission was long and lonely, almost 4.5 years and 724 million kilometers away. Uranus was farther from Saturn than Saturn was from Earth. The gravity assists Voyager 2 had received from Jupiter and Saturn helped it pare that immense distance to a perhaps manageable stretch. But there was no way to disguise the fact that the journey was far and the risks high. The cruise phase was longer than the cycle for presidential elections.
Five course corrections would be needed to steer the spacecraft through the Uranus system, a place about which only the crudest facts were known. With the euphoria of encounter over and the space shuttle hemorrhaging money, NASA demanded major budget cuts, including 60 percent of staff, which left the Voyagers to sail through solar winds and gravitational tides on something like autopilot. If a crisis developed, JPL would activate a Spacecraft Anomaly Team (SCAT), packed with Voyager veterans, to grapple with the issue. Without money, staff, and knowledge, it was daunting to plan for an encounter at a place so remote that even the simplest exchange of messages would require 328 minutes, or 5.5 hours.140

  DAY 1,031-2,492

  15. Cruise

  Voyager 2’s cruise to Uranus was longer than its trek from Earth to Saturn. That prolonged stint offered a chance for the spacecraft to rehabilitate, for programmers to study a poorly known planet in preparation for encounter, and for both Voyager and JPL to improve their ability to communicate. In the end, Voyager was only as good as the commands it could be given and the means available to give them. As time and distance increased, both messages and means became more arduous, which left cleverness to compensate for aging, and upgraded communication for remoteness. 141

  When they launched, the Voyagers’ capacity for reprogramming and their power packs were revolutionary. Today, when computers sit on every desk and microchips make cell phones into miniature PCs, those software uploads seem as quaint as their transmitting power, about a billionth the wattage of a digital watch. When Voyager left Saturn, the first personal computers were just entering the market; for an IBM PC, the choice for RAM was either 64k or 128k, and program software ran on the same diskette as its output files. Voyager 2’s computer command subsystem held a scant 2,500 words of memory for sequencing. For each instruction, one word specified the event, and the other, the time. Yet Voyagers’ constraints were even more formidable: it would not be possible to swap out a new hard drive or install a new modem. But while Voyager’s hardware could not be updated, the earthbound antennas for sending and receiving could.

  The success of Voyager 2 at Uranus depended on the capabilities of the Deep Space Network. But, then, the DSN became what it was largely because it had to do what Voyager required.

  DEEP SPACE NETWORK

  The Deep Space Network performed three tasks. It assisted navigation and guidance by tracking spacecraft. It sent and received messages. And its signals could serve as an instrument of radio astronomy, particularly during occultations. But the network had to do all this on a twenty-four-hour basis; it had to receive from every spacecraft in orbit, a number that swelled yearly; and it had to connect even as spacecraft, notably Voyager, ranged farther and farther afield. In this, as in other matters, Pioneers 10 and 11 had pushed technology and procedures, forcing the DSN, further hobbled by Pioneer’s antiquarian hardware and its algorithms, to its limits.142

  These were only the known challenges. There were unknowns, too, such as the intensity of planetary radiation, which at Jupiter had caused wobbles in Voyager 2’s receiver. And there were known but uncontrollable variables, related to weather both on the Sun and Earth. The solar wind caused turbulence, and passing behind the Sun overwhelmed receivers with noise. Rain in Spain caused a blackout of Jupiter data. As it had for explorers trekking for a year to distant lands to measure the transit of Venus, a wisp of cloud could wipe out the observation period.

  Uranus strained both Voyager and the DSN. Even as it downloaded data from Voyager 2, the DSN had to track Voyager 1, along with Pioneer Venus and the ever-receding Pioneers 10 and 11. It had to maintain contact with the Russian Vega and European Space Agency’s Giotto Halley probes. It communicated with the Japanese spacecraft MST-5 and Planet A. It transmitted and received with the Giacobini-Zinner comet probe ICE. It still followed Helios and the earlier Pioneers (6, 7, and 9). The complexity of multisatellite tracking was daunting. But none of these issues equaled the challenge posed by Voyager’s Uranus encounter.143

  The spacecraft could not perform as it had at Saturn. It was losing power at a rate of seven watts annually. It was using fuel in the RPG, and as it aged it became less efficient with what it had. It could no longer power the IRIS flash-off heater while also transmitting on both the X band and the S band; yet all those operations were required for particular experiments. The solution was to shut down those components not absolutely needed, to turn off the IRIS heater when both transmitters were working, and to prohibit the simultaneous use of X-band and S-band transmitters in their high-power mode. By meticulous sequencing, IRIS could take its critical readings, the Uranus ring occultation measurements could proceed under high-power X band and low S band, and the planetary occultation at high S band and low X band. Another fix was to upload new software that could compress the data stream, allowing more kilobits to be sent for the same expenditure of power.144

  Still, the signal was weakening at an exponential rate. For every doubling of distance, the strength of the signal fell by a fourth. Saturn was twice as far from Earth as Jupiter, and Uranus twice again as far as Saturn. The maximum rate of data transmission at Saturn had been 44.8 kilobits per second. At Uranus, it would be 21.6 kbps and 14.4 kbps. At Uranus, Voyager’s radio signal would be “several billion times weaker than the power of a watch battery.” The only way to compensate was to upgrade the DSN facilities. By a quirk of celestial geometry, the Canberra Deep Space Communication Complex in Australia could track the near-encounter for twelve hours. That was where the DSN and JPL Telecommunication Division would concentrate their efforts. The long cruise phase allowed time to consider options.145

  A straightforward solution was to upgrade the receiving dishes; but this was unlikely since it was very expensive. NASA was investing everything in the space shuttle, and there were no other planetary missions on the books until Galileo in 1986, for which the existing arrangement sufficed. DSN would have to amplify what it had.

  In 1982 it commissioned a global survey of large antenna facilities, what became known as the Interagency Array Study, which issued a report in April 1983. The study recommended as the best option to expand a technique developed for Saturn by which the several receivers at a station could be electronically linked and, in effect, establish a collective range far greater than the instruments could manage individually. Uranus, however, exceeded even these capabilities; the Canberra complex would have to link with another large dish, and the obvious candidate was the Parkes Radio Telescope, which also had a 64-meter antenna. By effectively connecting all the receivers together, the DSN had the equivalent of a 100-meter antenna, an escalation in capacity of 20-25 percent. The Voyager imaging team had wanted 330 images every 24 hours. The DSN could now guarantee 320 under ideal conditions.146

  The other way to sharpen reception was to target the DSN array more accurately, which would reduce background noise (not a trivial concern given the lower wattage and the vast distances involved). To prevent degradation, DSN had to point its sixty-four-meter antennas to less than 6/1000th of a degree. One approach, called “blind pointing,” was to estimate the location of the spacecraft and direct the antenna to the forecast spot, a technique applied during occultation and signal acquisitions. Instead of visible stars such as Canopus to assist navigation, the radio telescopes relied on radio stars for fixed points. The other strategy was to scan the estimated region in a conical sweep and acquire a signal from the spacecraft, which could then be used to track its location precisely. 147

  For Voyager 2 the two techniques were complementary, and both were necessary. To complicate the procedure, however, suitable radio stars in the region were unavailable, and the spacecraft’s balky receiver demanded extra tending to locate its shape-shifting downlink signal. New software, practice drills at blind pointing, the installation of a Mark IVA system, and weekly meetings between DSN and JPL brought the apparatus to working requirements. At Uranus the DSN could support up to 29.9 kilobits per second, improve navigation, and bolster the radio science expe
riments.148

  Or it could in principle. In practice, upgrading facilities, crafting interagency agreements to bind individual antennas into arrays, and writing code had consumed time and money that would otherwise have gone into training. This was the mission cost of those sharp staff cuts after Saturn; continuities, once broken, were not easily regained. When, two weeks prior to the Uranus observation phase, the flight team conducted a dress rehearsal of near-encounter, it became clear that DSN was not sufficiently fluent; it needed more training and more people. But unearthing such outcomes was the reason behind the operational tests. DSN responded by adding technical staff and using the observation phase to conduct drills, as JPL used the information received from that period to refine targeting and the final sequencing for near-encounter, and of course to correct last-minute glitches .149

  One such glitch emerged only shortly before closest approach, as images became marred by light and dark streaks. The first thought was that the error came from computer processing on Earth. But a scurried survey isolated the difficulty instead in a faulty memory spot in the onboard image processor. Within three days new software had been written to use an alternate location, and only six days before closest approach, the package was uploaded. The streaks vanished.150