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

by Stephen J. Pyne

  The African Association resembled dozens of lobbying groups, all intent on directing the power of the state, with its capacity to mobilize truly impressive resources, toward their own particular exploring enthusiasms. Each would claim that, without such commitments, the nation would sink into slovenly insignificance. Each sought to keep its ambitions before the public. In Banks’s day it was enough to interest the elite and select officials of the empire. But increasingly, in democracies, it was the public that either drove expeditions or allowed them to expire. That required a public medium, which in the heyday of European imperialism meant popular books, lecture tours, and especially newspapers. The press could make or break an exploring venture. It could browbeat an administration into sending an expedition, or ridicule one into remission, or even sponsor expeditions of its own, as the New York Herald did when it underwrote Stanley’s search for Livingstone. A race to the pole made good copy. Adventures into unknown lands sold papers.

  By the time Voyager launched, however, the American public was plugged into television. The entire space program had grown up with T V: it was, in some respects, staged for T V. The press corps that came to JPL for the Voyager encounters watched the drama unfurl on TV monitors; the most gripping reports from Voyager science came from the imaging team that delivered graphic visuals suitable for rebroadcast. The “Mind of Man” that mattered was the TV-viewing public. Even as Voyager closed on Saturn, PBS was airing Carl Sagan’s block-buster series Cosmos, of which episode six, “Traveler’s Tales,” highlighted Voyager. It was masterly timing, as art and life intertwined into a Great Conjunction of exploration and culture.

  VOYAGER 2

  Seven months after its twin, Voyager 2 began its approach to Saturn.

  It had the same instruments and was visiting the same planetary world, so much would be similar. Yet it would see Saturn differently because it flew on a different trajectory, had a superior camera (50 percent more sensitive), saw Saturn when its rings were turned higher into sunlight and its weather was more boisterous, and could target specific features that its robotic sibling had noted only in passing. But Voyager 2 had always been the troubled twin. It entered Saturn plagued with faulty receivers, and it left with a crippled scan platform. Most of all, constraining its goals was the need for a trajectory that could propel the spacecraft on a 4.5-year cruise to Uranus.

  The narrative of their Saturnian encounters thus differed in their fundamentals. Fraternal twins they might be, but the two Voyagers had different historical DNA, and they had different destinies.

  Voyager 2’s ten-week observation period commenced on June 5, 1981. This time scientists hoped for sharper atmospheric images from Saturn, more detailed photos of the satellites, and greater refinement of the ring structure, including shots of elusive shepherding satellites along with an explanation for the baffling dark spokes on the B Ring. The cameras rolled; the images of white-ringed Saturn loomed large on screens; still photos were strung together into animated movies.121

  Voyager 2’s mechanical ills continued, however. One of the memory chips in its flight data system computer failed, which forced mission control to devise a new encounter sequence—“better” than the original, they insisted. On August 19 the spacecraft executed a final course correction, a day before the fourth anniversary of its launch. Soft geography caused problems because the solar wind was high and gusty and no trailing spacecraft could issue forecasts as Voyager 2 had for Voyager 1; even more than usual, bow shock was a frothy frontier, complicated by the planet’s interaction with Titan and the magnetospheric tail of Jupiter, now in rude alignment. Yet anticipation was high, less in the hope that Voyager 2 might discover whole new phenomena than that it might help clarify the raw mysteries unveiled by Voyager 1. Much as the imaging team resorted to more false-color and computer-enhanced photos to massage out details, so the mission design sought to refine the encounter sequence to illuminate some of Saturn’s more baffling revelations. 122

  Near-encounter began with a close flyby of Iapetus, the outermost of Saturn’s ice moons, on August 22. Thereafter, Voyager intensified its reconnaissance of Saturn’s hard and soft geographies. Although bow shock proved evasive, the spacecraft undertook a complex sequence of rolls to plot out the contours of the magnetosphere and trained its UVS and IRIS instruments on everything in sight. But the hard geography had its fugitive phenomena as well: the satellites that theory demanded be embedded in the rings could not be found. Nor could instant analysis locate any explanation for the dark spokes. What the images did reveal was an ever-multiplying number of rings, now in the thousands. Compensating for the missing moonlets, however, were brilliant images of real moons, now including Hyperion. Slight perturbations in the spacecraft caused by their gravitational pulls allowed for estimations of mass. (Iapetus, it was calculated, was nearly pure ice.) As Voyager 2 crossed bow shock for the last time, those satellites would command much of near-encounter efforts on August 25.

  Guidance was nearly perfect: the spacecraft was within fifty kilometers and three seconds of schedule. The images flashed by—the rings, the moon Tethys, newly discovered satellites with orbits shared with Tethys and Dione. But the mission was science, not merely reconnaissance, and for an astonishing 2.5 hours the photopolarimeter claimed exclusive attention while it measured the occultation of the star Delta Scorpii through the rings. When it ended, with a profile of 82,000 kilometers of rings on chart paper half a mile long, the spacecraft’s cameras scanned the moon Enceladus in riveting detail. Then it passed behind Saturn and plunged through the rings, and completed periapsis, not to reemerge until midnight some ninety-five minutes later. Its record of occultation through Saturn’s atmosphere, its inner passage through the ring plane, and its final scans of Enceladus would not be broadcast until it reconnected with the DSN. There was only minor anxiety about the physical hazards posed by the rings, since Voyager was following the rough trail blazed by Pioneer 11. And on schedule the DNS station in Australia reacquired the telemetry signal from the spacecraft, now boldly hurtling toward Uranus.

  The signal, yes. But the Voyager 2 that emerged was not the Voyager 2 that had entered.

  Something had happened. A few instruments transmitted odd data, and erratically; near the ring plane some control thrusters had made unauthorized firings; the scan platform now pointed not at a receding Saturn but into black space. While fresh news to mission control, this was old news to Voyager 2. Everything had happened ninety minutes earlier. The near-imaging of Enceladus and Tethys; the planned stereo views of the F Ring; a photopolarimeter-recorded occultation of the rings; the backside view of Saturn—all were gone, irretrievably lost in space. The change in temperature caused by passing into Saturn’s immense shadow had also upset the balky receiver, and mission control struggled to identify an acceptable frequency and to reengage. Each new command required multiple transmissions, which even at the speed of light would take more than ninety minutes to reach the crippled spacecraft. Gloom replaced euphoria, until the mood at mission control resembled the abrupt borders of black and white that Voyager had imaged on Iapetus.123

  The primary goal was to spare the spacecraft further harm. Mission control sought to shut down whatever was not essential and to preserve, if possible, the option to go to Uranus. New commands placed the instruments on standby, since they recorded nothing valuable and might complicate attempts to reclaim control and diagnose the disorder. They shut down the preprogrammed command sequence for the encounter, since that sequence was anyway a shambles. And they moved the scan platform away from where it had frozen, a position that might ruin some instruments by making them directly face the Sun. It then remained to wait for the download from the Voyager’s tape recorder, which had held its transmissions while the spacecraft passed behind Saturn.

  That broadcast arrived on Earth at 9:00 a.m. on August 26. Here was Voyager doing what it was supposed to—sighting a magnificent scan of the F Ring, and a crescent profile of an F-Ring shepherd satellite. Then the recor
d entered its problem phase, as the narrow-angle camera sent, instead of crisp images of Enceladus, black screens. The wide-angle camera could still capture the edge view of the rings as the spacecraft crossed through, but anything that had demanded precision targeting was gone. There were no rings, there was no Tethys. Misaligned, the camera got only a marvelous if unanticipated image of the Keeler Gap in the rings. The wide-angle lens got a snippet of a moon. Worse, the scan platform’s ability to move along an azimuth was clearly deteriorating. Finally, the platform froze altogether. The cause of its malfunction remained unknown, and frenetic inquiries were stymied by the faulty receiver. The startling clarity and vigor of the early images made the subsequent losses all the more poignant.124

  The flow of science based on the information successfully sent continued, as it would for months during which analysis would replace brute reconnaissance. There was more data from plasma waves, particularly a burst of energy a millionfold higher than normal as Voyager passed through the ring plane. And there were those brave, cold new worlds, as continued study scrutinized the major satellites of Saturn and continued to find new minor ones. But what had always characterized near-encounters—the brute flood of new data, the sheer awe of first contact and shared discovery—was gone. Voyager continued to transmit empty scenes, each frame “displayed on the monitors at JPL, complete with the commanded exposure time, filter, and so forth,” and they “kept coming, one after another, all day.” Unless Voyager righted itself, it might go to Uranus as a blind chunk of metal rather than a robotic explorer.125

  So engineers continued their inquiry, at once feverish and measured, to diagnose the problem and prescribe remedies. They isolated the trouble to a stuck azimuth platform, the geared mechanism that allowed the scanning instruments to rotate in a plane and point in different directions. One by one, engineers brought back online the other instruments, successfully. The soft geography Voyager could still track; it was the hard geography of visible worlds that was threatened. Then engineers began to massage the azimuth mechanism in ten-degree increments, and they discovered that they could still control the elevation mechanism. With that, and by using the spacecraft as a platform overall, it would be possible to do some basic reconnaissance at Uranus. Step by step, mission control inched Voyager 2 back to where it might at least focus on Saturn rather than continue taking its disheartening images of empty space.

  As the engineering investigation continued into August 27, E. K. Davis, project manager, and Ed Stone, chief project scientist, jointly declared that the principal objective was “to recover the scan platform capability for Uranus.” The mission had nearly five years to tinker and perhaps solve the problem before a Uranus encounter, and they were not willing to do anything “to increase risk by premature activity now.” When asked how much had been lost, Stone preferred to emphasize how much had been gained. The mission, he announced, had been “200 percent” successful—by so much had Voyager 2 exceeded its mandated charge. The full raft of data would take years to assimilate; and even as the spacecraft struggled to return from its passage through the dark side, project science leaders trooped forward to place the latest discoveries before the world. The odd surface of Enceladus. Titan’s hydrogen torus, and apparently missing ionosphere. Plasma discontinuities created by Tethys and Dione. The ever-enigmatic rings.126

  By August 28, diagnostics had progressed sufficiently to identify the problem and suggest, as Dick Laeser, deputy project manager, put it, that “the platform improves with use.” The glitch was in part an outcome of what had earlier doomed the polarimeters: overuse. The science teams had earlier demanded more of Voyager than its engineering could guarantee. Its scan platform had tried to zip too quickly among too many targets, slewing faster than its lubricant could respond, and the apparatus had gagged. The spacecraft needed a mandatory rest, followed by a cautious program of rehabilitation. The worrisome days after the crash met that need. Within hours after identifying the source of the breakdown, on August 28, mission control hoped to get Saturn back into Voyager’s field of vision. They did.

  Encounter officially ended on August 30 with a bittersweet celebration. Once again Voyager 2 had come back from a near-death experience. If much had been lost, far more had been gained. But the real losses were in the future: it was as though Voyager were passing through a gap in the ring plane of American planetary exploration. It was a gap in history, and this one had no shepherding satellites. Voyager was the American planetary program, and would be the only mission to other worlds until the Galileo spacecraft went to Jupiter in 1989. Bradford Smith anticipated a “data gap,” Ed Stone an institutional gap, and others, career gaps. However hobbled, Voyager 2 was the future for planetary exploration.127

  By now the spacecraft had recovered enough mobility that it could exercise its right to the traditional parting shot. On September 4, Voyager 2 photographed Saturn’s most distant and darkest moon, Phoebe. Probably a captured asteroid now in retrograde orbit, the moon seemed to emphasize the retrograde character of the American planetary program as it looked back. Yet there was hope, too, in that new world, and there was faith, as Voyager pointed to the dark promise of Uranus.

  NAMES OF DISCOVERY

  Even wonders require names, and marvels, labels. The cascade of data and images revealed worlds swarming with physiographic novelty ready for both.

  Between them the Voyager twins discovered thirty-five new moons and first mapped twenty known ones; they traced the gaseous contours of Titan and the four outer planets; and they recorded hard geography surface features by the hundreds. Suddenly there were craters to name; valleys and rifts to label; volcanoes, dark splotches, and half rings to categorize; to say nothing of features for which no landscape terminology existed. They were not hollows, washes, mesas, shorelines, hills, or dales, since they expressed a different tectonism and a land sculpture purged of flowing water. They were, rather, ancient Earths, before seas and life; alternative Earths, obedient to stresses and abrasions unknown terrestrially; and simply alien worlds. Spontaneous, slangy expressions sputtered out in order for scientists to talk about just-revealed terrains, as they struggled to place odd features into familiar categories. But these would not be the names recorded on the maps and the gazetteers that would codify them formally.

  Fortunately two decades of planetary exploration could build on a nomenclature and a mechanism developed for traditional planetary astronomy, which in turn reflected both centuries of geographic discovery and the rationalizing instincts of two centuries of Enlightenment exploration. As ever, there were similarities as well as differences.

  All this had happened from the beginning. New places needed names, or else one could not speak of them, but also because naming was a means of possessing. The commissions dispatched under the auspices of the Spanish monarchy were thus enjoined: having arrived “by good providence, first of all you must give a name to the country as a whole, and to the cities, towns, and places.” The chronicler of Juan Ponce de León’s 1513 expedition recorded that “it was the custom of those who discovered new lands to give their own names to the rivers, capes, and other places; or else the name of the saint on whose day they made the discovery; or else, other names, as they wished.” When Ponce de León arrived off the coast of a new land, it was Easter—“Easter of Flowers,” as it was known in Spanish—and the land seemed well blossomed, so for both reasons he named it “Florida.”128

  Common sources for inspiration were legends—hence, Brazil and the Antilles, named for mythical islands in the Atlantic; California, for an island in a romance, ruled by Queen Calafía; or the Amazon River, since women there were rumored to fight like those of ancient legend. Other sources were analogues to places back home—hence, a Nuevo León, a New York, a Neuw Amsterdam—or to rivers and hills reminiscent of those from where they had come. Often some feature of the site sparked a name, as some characteristic or deed inspired a nickname. Turtles led to the Tortugas; famine, to the Starving River; snow, to the White Mounta
ins or Sierra Nevada. Classical allusions led to recommissioned Troys, Syracuses, and Romes. Biblical terms often subjected local terms to a full-immersion baptism into Jordan Rivers and Mounts Pisgah. Mormon pioneers drafted liberally from the Book of Mormon, bestowing Deseret, Bountiful, and Kolob. Some founders, wishing to emphasize the novelty of their ambition (if not settlement), invented neologisms, perhaps from Latin or Greek, as William Penn did with Philadelphia. And not least there was the practical flattery of naming features after patrons: Virginia, for the virgin queen Elizabeth I, and Jamestown for her successor; Mount Hood, for the Lord of the Admiralty; the Jefferson River, for the sponsoring president; and Washington nearly everywhere. The explorers themselves showed varying shades of immodesty. (Cook, for example, discreetly left the inlet beside Anchorage unnamed so a junior officer might insert Cook’s name.)