In the end exploration will remain a cultural creation, and it will assume the character of its sustaining society. How that civilization hybridizes with its technologies will shape the future of geographic discovery and decide the future cadences of cruising and encountering.
A second option points to the rhythms of great ages, and suggests not only that the Third Age, too, will wax and then wane, but that its ebb might take the ages with it. In this conception, if the Voyagers could see beyond the termination shock of the golden age, they would find a future exploration that may look a lot like the past, only different. Exploration will go back to the future, with the Third Age recapitulating the First, and then perhaps reverting to its pre-exploring ancestry.
The possibility for a rekindling of rivalries that will translate into geographic discovery exists. Political contests may boil over into space, for example, if China declares a colony on the Moon as essential to its prestige and the European Union or Japan joins the fray. There is a prospect that the search for life will take on an imaginative, even a theological cast, sufficient that a significant fraction of the culture wants to pursue it among the planets. It may happen that extreme arts, brash new sciences, an as-yet-undeveloped commerce, an astro-politics, and some critical personalities will combine to yield a Third Age echo of the Second Age. In some form or another, a virtuous cycle is possible. But it is not likely. As Damon Runyon advised, the race is not always to the swift nor the battle to the strong, but that’s where you place your money.
The most plausible prognosis is that the future will resemble the past, that the Second Age’s monadnock of activity will mark an axis around which the evolving contours will unfold with rough historical symmetry. The Third Age will resemble the early Second, though in reverse. Expeditions will slide toward a new steady state—for space, perhaps on the order of one or two a year. These will be complicated probes, requiring years of preparation, not unlike the expeditions launched during the Great Voyages and quite unlike the brawling swarm of state-sponsored and individually motivated treks that so inflated the Second Age. They will be targeted to some particular purpose—commercial, scientific, technological, national prowess and prestige. They are unlikely to spill out from colonization: they will rather resemble those expeditions that established trading factories on islands or episodically visited coastlines for barter or sought out new routes. If the process thrives, there will be several competitors, not some collective United Earth Space Agency; and that institutional unrest is what will keep the pot simmering. Steadily, more and more of the solar system will be visited, catalogued, mapped, assessed. Perhaps, here and there, an outpost will appear, staffed for a few years.
The Third Age will then burn itself out, as other ages have before it. Its narrative will end as exploring expeditions traditionally end: it will return to its origins. It will have a beginning, a middle, and a conclusion. It will advance from launch to journey to splashdown. Reversing this trend would require an immense, global commitment that could come only from some dark necessity or irresistible rivalry, say, the discovery amid the asteroids of some mineral absolutely vital to national existence—the equivalent of the Potosí mines of Mexico, perhaps—or from Venutians announcing that they intend to colonize Mars and the moons of Saturn, and daring earthlings to stop them.
As the Third Age winds down, it may perhaps carry the great ages of discovery with it. They were created; they may expire. The conditions that sustained them may cease altogether; they may no longer inspire interest as a tradition worthy of institutional support. One can even imagine a robotic Columbus ceremoniously announcing an end to the enterprise. If the late nineteenth century marks a bilateral middle in this saga, that passing may happen some four hundred years later, the early twenty-third century, where Star Trek now resides in the popular imagination. Exploration, even of space, may then exist only in literature, history, film, and popular imagination, and in a past where no one, boldly or otherwise, wishes any longer to go.
Or there is a third figuration of the future. We might create an alternative to the narrative that has characterized previous eras, as different from its cadence as Third Age terrains are from the isles and lands of previous ages.
A counter version might hold that the traditional narrative structure might not apply. Like the Voyagers, the process will simply go on and on, constantly redefined and redirected. What makes the Third Age distinctive will allow it not so much to endure as to ultimately morph into a successor. It will retain some features—enough to have it be recognizable as exploring—and discard others. That sorting process will permit it to persist. It will survive by becoming different. It will simply continue.
In such speculations the Voyagers still have something to say. Their journey may yet write a different kind of narrative, pushing through the heliosphere of a greater modernism. The Grand Tour did not end with Neptune. The Voyager mission will not end with the solar system. The Voyagers continue to surprise.
DAY 4,083 - 4,084
20. Last Light
Looking back.
Before the Grand Tour ended, Voyager had a chance to peer back for one last time and reflect in its lenses something of what it had accomplished. Since Saturn, Voyager 1 had cruised with its cameras shuttered, while Voyager 2 continued to assemble its brilliant photo portfolio of new worlds. Now Voyager 1 was roused from hibernation to perform a task that would, for many observers, distill the entire enterprise into an enduring, defining image.
The post-encounter phase of every planet had included backlit shots of the planet and its satellites, and often of many such scenes into a single image. The practice had begun when Voyager 1 turned around and photographed Earth and the Moon together on September 18, 1977, two weeks after launch. Now Voyager 1 was asked to turn back on behalf of the entire Grand Tour and photograph the planets as part of a grand ensemble. On February 13 to 14, 1990, it did just that.236
The idea emanated from Carl Sagan, who conceived it after the Saturn encounter. He wanted a space-based version of the celebrated earthrise images from Apollo. These, he thought, had revolutionized humanity’s sense of itself. We could see ourselves as others might see us. Now it was time to expand that horizon, to see how we might look “to an alien spacecraft approaching the Solar System after a long interstellar voyage.”237
But mission officials balked. Some dismissed the gesture as a stunt, far removed from engineering necessity or scientific duty. Most believed it was better to wait until the programmed tasks were done; better not to point those lenses toward a still-vibrant Sun and risk scorching sensitive instruments; better to see the whole once than to juggle commands and slew scan platforms. The hard-science crowd scoffed: this was public entertainment, more postcards, a stunt that might embarrass a real astrophysicist before his peers. But these were the same arguments by the same people who had scorned having cameras at all. They never realized that the power of Voyager lay not in its scientific role but in its cultural context. The American public did not spend $600 million to record the magnetosphere of Neptune and the rotational period of Titania. They sought the wonder of new worlds and a reflection of their own.
After Saturn, Voyager 1 had no further duties for its cameras, and after Neptune, neither did Voyager 2. JPL’s Voyager staff faced a dramatic downsizing. The DSN had more urgent tasks. If the scheme was to be done, it had to be done soon. Like the alignment of planets that made the Grand Tour plausible, an alignment of planets, particularly Earth, made a parting gesture possible. NASA administrator Rear Admiral Richard Truly ordered the photos taken .238
On February 14, Valentine’s Day, 32 degrees above the ecliptic, traveling at over 64,300 kilometers per hour, almost 6 billion kilometers from the Sun, Voyager 1 shot 39 wide-angle views and 21 narrow-angle ones that encompassed 6 of the 9 planets. Mercury and Mars were too close to the Sun to show, and Pluto too minute amid the stellar glare. Neptune and Uranus were so dark that the long exposures caused smearing. Earth, freakishly, caug
ht a bounce of sunlight off the spacecraft that allowed it to appear “in a beam of light.” Over the next three months, as the DSN schedule allowed, Voyager 1 transmitted the 640,000 pixels of each image from its magnetic tapes to Earth, then some 5.5 light-hours away. Each photo required 30 minutes. The Voyager Family Portrait, as it came to be called, thus complemented the record of Earth that the spacecraft carried.239
NASA spokesperson Jurrie van der Woude and Sagan quickly dismissed any special status for Earth, which only occupied 0.12 of a pixel and had to be magnified sixfold to show at all. The point of the exercise, Woude insisted, was to show “how insignificant we are.” Sagan elaborated: the Earth was a mere “pale blue dot.” That phrase became the title for his final book on space exploration, published in 1994. The story of Voyager’s farewell photos provided the opening chapter in what Sagan proclaimed as “a vision of the human future in space.” Such pronouncements, however, were the flip side of those that dismissed the exercise as merely a publicity stunt. Most participants probably echoed Candice Hansen’s judgment that this was “the picture of the century.” It fell to Ed Stone to craft the right alloy of poetry and science. He turned to the practice of astronomers, who call the initial imaging by a telescope “first light.” This, the final use of the spacecraft’s lenses, Stone labeled Voyager’s “last light.”240
It was a scene, the self-portrait, often found in exploration history.
In the past, when the portrait couldn’t be photographed or painted on site, it might be done later in a studio with the explorer outfitted in full expedition regalia. It was not the place that mattered so much as the explorer positioned within it. It was a ritual act: the quest achieved, the hero returned. By the end of the Second Age, such staged events were expected. Think of the triumphant photo of Robert Peary at the North Pole, or the haggard image of exhaustion evident in the self-portrait taken by Robert Scott’s sledging party at the South Pole, each in its way a concluding record of the Second Age.
In the Third Age it was not possible, either geographically or philosophically, to position a camera or an artist to record the explorer in his milieu. There was no way to include Voyager within the frame of its accomplishment. Often Voyager would appear to the side in composites, but this was a studio confection. Voyager 1’s “family portrait” was in truth a self-portrait, a record of the places it had visited and of the people who had sent it. Much as its golden record was not a message to extraterrestrials but to Earth, so its gallery mosaic was less a vision of how the solar system might appear to visiting aliens than an invitation to earthlings to see themselves as others might, or perhaps more accurately as they would like themselves to appear to others. The self-reflexive event testifies that in Voyager the sojourner and the journey had become one. The encountered Other has become the exploring self. In that gesture the Grand Tour found a way to bracket its journey.
The Grand Tour, yes. But the Voyagers’ journey was not yet over.
part 3
BEYOND THE UTMOST BOND: JOURNEY TO THE STARS
And this grey spirit yearning in desire
To follow knowledge like a sinking star,
Beyond the utmost bond of human thought.
—Alfred Tennyson, “Ulysses”
Beyond Bow Shock
21. Voyager Interstellar Mission
On January 1, 1990, the Voyagers commenced the Voyager Interstellar Mission (VIM), a cruise without a hard encounter at its end, only the soft frontier where the solar wind buffets against and finally yields to the interstellar media.
The instruments so vital to interrogate planetary hard geography were turned off. The infrared interferometer and spectrometer and radiometer. The imaging cameras. The photoelectric photometer. While the rest could still perform usefully, they did so at greater costs, which Voyager could less and less afford. The amount of hydrazine, needed by thrusters to perform rolls for magnetometer recalibrations and to keep antennas pointed to Earth, was finite, and consumed at a rate of six to eight grams per week. The ultraviolet spectrometer remained on in order to sample hydrogen in the outer regions of the heliosphere, but then it and the scan platform were powered down to save energy. Supplemental heaters were turned off. Throughout, the power yield from the radioisotope thermoelectric generators steadily decayed; by 2001 overall production had dropped from 470 to 315 watts; by 2008, to 285. And if they were to reach bow shock, the Voyagers had a long way to go.1
The mission’s budget was draining even more dramatically. From May 1972, when planning began for MJS 77, up to the encounter with Uranus in 1986, with an inflationary storm in between, the Voyager mission had cost $600 million. In the favored analogy, this amounted to the price of a candy bar each year for every American citizen. Hard as it was to scrounge money for a new mission, so much harder was it to find funds to maintain an old one. The political regime that authorized a program would be long gone when the program succeeded, though it might be remembered at encounter. No one would honor those who sustained a cruise. It became harder and harder to argue for VIM when termination shock would occur years away and no new worlds might flash the event across TV screens.
As the second Bush administration projected a crewed mission to Mars (or sought to pay off cronies in aerospace, as cynics argued), money became even tighter, and the persistence of old missions such as Voyager seemed like leaches that sucked the lifeblood out of new ones. In 2005 the Voyagers still had a staff of ten (down from three hundred in 1989) and an annual budget of $2 million when NASA sought to shut down the operation along with five others. But once again Voyager survived a political threat to kill it. It would end only when its internal power finally drained away. For now, it continued to send back reports from new settings. It was doing what no other spacecraft could. Its narrative simply defied closure from Earth.2
The border between the solar system and the stars is broad, sloppy, and untraced. The bubble of gases, or heliosphere, that contains the solar winds has a complex structure. Its outer perimeter, the heliosheath, has two edges, one facing the solar wind and the other, the interstellar winds. At its inner border, or termination shock, the supersonic solar wind slows to subsonic speeds. This was believed to occur around eighty to ninety astronomical units (AUs) from the Sun. To reach it from Neptune would take Voyager 2 as long as it had taken the spacecraft to reach Neptune from Earth, or roughly twelve years. Within the heliosheath the pressures of solar and interstellar winds roughly balance. Its thickness varies because the entire solar system moves, which compresses the heliosheath in the direction of that movement and extends it on the downwind side, much as comets have compact heads and long tails. The outer border, or bow shock, thus ranges in thickness from 10 AUs on the windward side to 100 AUs on the lee. That geography defines the three phases of the Voyagers’ Interstellar Mission. When they finally pass through the outer bow shock, they will be sailing amid the winds of stars.3
Voyager 1 was fastest and farthest, and at 85 AU, in August 2002, it recorded fluctuations that were reported as possible evidence of termination shock. This could not be confirmed, however; the billowing border is unstable, full of pulses and pauses from gusty solar breezes and their turmoil with interstellar winds, and the magnetic disturbances that shape them; and the plasma science instrument on Voyager 1 no longer functioned, which forced researchers to infer shock from indirect sources. But on December 16, 2004, at some 95 AU, it unblinkingly passed through termination shock and entered the heliosheath. Voyager 2 crossed that bar at 84 AU on August 30, 2007, and then reexperienced passage at least five times over the course of several days as the shock boundary twisted and bubbled.
Since the Voyagers entered the heliosheath at different places some sixteen billion kilometers apart, their encounters helped map the geography of that frontier. As predicted, the heliosphere was “squashed” on top and bottom. But the amount of variance was more than expected, and so were the temperature differences on both sides of the border; the heliosheath was far cooler than expe
cted. Voyager, as its then program scientist Eric Christian noted, “has once again surprised us.”4
But surprise had been a Voyager specialty since launch. On January 5, 2005, the mission surpassed 10,000 days of operation. In August and September 2007, the Voyagers reached thirty years. Measured in robot lifetimes, they were Methuselahs. They were leaving the solar system with computing power inadequate to run a cell phone, and electrical power insufficient to animate a clock radio. Yet they had much yet to survey: the dynamics of the solar wind, sunspot effects on the interplanetary medium, low-energy cosmic rays, reversals in the Sun’s magnetic field, interstellar particles, radio emissions from various sources within and beyond the heliosphere, and of course the interstellar medium, if all went well. Of particular interest are their UVS instruments in that they observe spectra no other spacecraft can.5
Their trek continues.
They have enough energy that, if conserved, they might still be able to transmit after passage through bow shock at the outer heliosheath. By 2015 Voyager 1 will have to shut down its data tape recorder, and Voyager 2 its gyros. A year later, Voyager 1 will cease its gyros, and after another year, Voyager 2, its data tape recorder. Steadily, in a creeping paralysis, the Voyagers will trade dead instruments for only the most basic functions—ultimately, the measurements of interstellar wind and the communication of that information to Earth. By 2016 for Voyager 2 and 2018 for Voyager 1, those few instruments still online will need to share power. By 2020, barring a sudden collapse, the robotic equivalent of a stroke or heart attack, their RTGs will no longer be able to support even a solitary instrument. The spacecraft will wither, like an organism wasting with scurvy. They might still be able to send signals, useful for tracking, but even that capacity will eventually fail. Sometime in the mid-2020s they will cease to function and become inert time capsules in a realm beyond time.6
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