The initial reaction to his study was mixed. The mathematics was formidable, and the physics, in some respects counterintuitive, since it required a shift in reference frames from Earth to the Sun. Viewed from Earth, what a planet gave by gravity to an incoming spacecraft it then took away as the spacecraft departed; but viewed from the Sun, there was a gain or loss depending on the directions in which the spacecraft came and went. With a monster planet such as Jupiter, the momentum added could be significant for the spacecraft, though infinitesimal relative to the mass of Jupiter. For Voyager 2 the impulse acquired was 35,700 kilometers per hour. For Jupiter the impulse shed was a foot of orbital velocity per trillion years.95
The other, more serious problem was personal. As fascination deepened into obsession, Minovitch became more secretive, speaking only to friends and his late-night IBM 7090 computers, avoiding the give-and-take of shared ideas at the lab, more and more resembling a hermetic inventor worried with equal passion that his idea might be ignored and that it might be stolen. JPL had hired him to do work to fit into existing projects, and his supervisor, with whom he did not get along, believed that his independent inquiry, subject only to his own curiosity, interfered with his project assignments, which Minovitch admitted “it did.” Moreover, what Minovitch believed revolutionary the trajectory group considered evolutionary, one of many ideas about how to get spacecraft to farther planets. Other researchers (not all with JPL) were experimenting with trajectories along similar lines. The group did not immediately reconstruct its planning around what they came to call “gravity assist.”96
The technical objections were quickly overcome, and the concept of “Free-Fall Trajectories” took its place amid the assorted inquiries of the group. In 1963, after two more summers of labor, Minovitch was encouraged to write up a summary technical report. A new, more supportive supervisor, Joe Cutting, urged him to publish his results in the AIAA Journal. “I hope you will be able to devote enough time to finish it up,” Cutting wrote, “so it can be submitted soon before anybody else comes up with something similar.” You can’t patent or copyright an idea, only its expression. Still, Minovitch didn’t publish.97
Meanwhile, Cutting decided to push the idea and see if it could apply to a real mission, not to computer-generated curves such as conic sections. He and Francis Sturms plotted a flight to Mercury—an entire profile, with real numbers and actual dates—that relied on a gravity assist from Venus. What it required, and what Minovitch had not reckoned with, was precision navigation and launch dates; others supplied them. Mariner 10 demonstrated the concept’s practicality by whipping around Earth, Venus, and Mercury in 1973. Pioneer 11 then confirmed the concept at Jupiter. Well before then, however, gravity assist had become fundamental to the design of the Grand Tour. Gravity assist was both real and essential. Those who conceived it and coded it into a mission moved on to other projects and, in Minovitch’s case, other institutions.98
Yet, even as the concept passed test after test, Minovitch brooded over what he regarded as a lack of suitable recognition compounded with imagined slights by JPL. He saw his research as a work of individual genius, unprecedented and unique. It was not enough that the trajectory group had included him on its roster, that his technical reports had entered bibliographies of subsequent studies, or that NASA had awarded him an Exceptional Service Award in 1972. He believed he had done something monumental, and indispensable, and in his estimation planetary exploration such as the Grand Tour could not have happened without him.
So when Victor Clarke, his first supervisor, applied for a joint monetary award for the trajectory group’s success with gravity assist, Minovitch sensed conspiracy, an attempt by undeserving others to claim what he autonomously had done. And when a historian, Norriss Hetherington, began research for a scholarly paper on the origins of the concept by interviewing members of the group, Minovitch threatened JPL with lawsuits, ended Hetherington’s study, and began a campaign to have the concept, and hence the entire planetary program since Mariner 10, follow from his lone and unfairly ignored “invention.” He found collaborators in his quest; JPL invited him to return for the Neptune encounter; and he has written up his versions in several papers for the International Astronautical Federation and constructed an elaborate Web site to promote his case in the belief that, as he put it in the third person, “there may be a small group at JPL that may attempt to claim the credit for his invention after he dies.”99
Who discovered gravity assist as a means of propulsion for planetary exploration? How the issue might be answered depends on how the question is asked. Minovitch defined his achievement in terms of a classic theme in celestial mechanics, the restricted three-body problem, and his achievement he regarded as most significant for its mathematical techniques, especially his vector equations, which when combined with the number-crunching power of computers yielded the “first numerical solution.” But gravity assist was, for him, also something more. It was an “invention,” like John Harrison’s chronometer or James Watt’s governor, that made possible a “new philosophy of space propulsion.”100
Others saw it all differently. The personality that made Minovitch’s solitary labors possible also isolated them. Upon investigation there were many antecedents for the idea of gravity perturbations; and it was almost inevitable that the idea would gain currency, if not by mathematical analysis, then by empirical observation as spacecraft ventured to nearby planets and navigational groups recorded unanticipated changes in velocity. Minovitch’s claim to absolute priority stems from his sense that no one else, certainly no one at JPL, was prepared to tackle a general solution to the restricted three-body problem; and because he saw it as a mathematical topic for which only numerical estimates were possible, he had to amass all possible trajectories, with the curve of his calculations asymptotically approaching something like a proof.
But what Minovitch saw as an intellectual puzzle, the JPL trajectory group, all engineers, saw as meaningful only within the context of a mission, and its solution would not come from endless hypothetical trajectories but from scenarios in which a spacecraft had real dates, real weight, and real escape velocities, and mission control had the capacity actually to navigate around planets with the accuracy that could ensure success. In their estimation, instead of elevating the concept, his complex mathematics and endless iterations had tended to depress its pragmatic value, and other trajectory group members, who regarded those solutions as “not truly adequate,” devised simpler methods, including old-fashioned manual techniques with “tabulations and graphs.” JPL was not an academy of science but a laboratory for reconciling science, engineering, and politics. Gravity assist was for them not an invention but a fact awaiting discovery and then, more important, demanding confirmation, development, and expression in a traveling spacecraft.101
What should have shone with the brilliance of its participants has threatened to sink into mires of petty egotism. The episode reminds us that history, too, has its three-body problems. They arise with particular vehemence when someone claims priority and someone else disputes it and when third parties only perturb their interplay, and such dynamics work with special vehemence when one body is smaller than the others. In such contests there is no formal solution, only working approximations. The transfer of gravity assist from mathematical concept to working mission was one such approximation. But, then, so was Voyager.
FIRST DISCOVERY
Disputes over priority—credit for first discovery—are a constant of science, no less than for exploration, and when the two combine, the issue can be both futile and fathomless. There is no scene more common in both enterprises than a quarrel over priority, and perhaps none more unseemly or dismaying.
Both science and exploration thrive on competition. A collectively identified problem approached with shared understanding and techniques—the co-discovery of places, species, ideas, and techniques is so common as to be the norm. Without competition, the drive to discover weakens; but with it comes
the spectacle of rivals converging, and then arguing endlessly over who really got there first. Both Isaac Newton and Gottfried Leibniz invented calculus, independently and more or less simultaneously. Alfred Wallace wrote a dilatory Charles Darwin, then still tinkering as he had for a decade with his ideas, and presented a fully realized articulation of evolution by natural selection. There are precious few scientific discoveries that have not come amid multiple contestants or that would not have been announced, with a slightly different accent, by another.102
So, too, has it been with geographic exploration. The norm is for rivals to converge, and then for explorers and their partisans to argue endlessly and with scholastic tenacity over who deserves priority. Did Portuguese (or Biscayan) cod fishermen rather than Columbus first discover the New World? And even among his small flotilla, did Columbus deserve credit for the initial sighting? On the evening of October 11, 1492, shortly before moonrise, both he and a seaman on the Santa Maria thought they spied a distant light, “like a little wax candle rising and falling,” and others thought they did, too, or might have, before it vanished. At 2:00 p.m. on October 12, Rodrigo de Triana, aloft on the Pinta, cried out, “Tierra! Tierra!” Captain Pinzón confirmed the sighting, and signaled to the flagship, where Columbus agreed. Who, then, discovered the Americas? Those who saw a flickering light? The sailor who happened to be manning the Pinta’s lookout? The captain general of the fleet? Those who sponsored the expedition? Besides, all of these quarrelsome concerns only pertain to those who came from afar, not to those for whom the New World was an ancient homeland.103
Who discovered the Great Salt Lake? Fur trappers were all around the region in the mid-1820s. Etienne Provost almost certainly saw a part of it from the Wasatch Mountains in 1824. Some months afterward, to settle a bet, Jim Bridger followed the Bear River to where it entered the lake, tasted the waters, and reported as his discovery that he had found an “arm of the Pacific Ocean.” Or did David Jackson, who reportedly explored the western shores in 1828-29? Or a party of fur trappers who spent twenty-four days in a bullboat on the lake, never finding the mythical outlet to the sea, the river Buenaventura? Or did discovery lie with the first published map of the enclosed sea by Capt. Howard Stansbury of the Army Corps of Topographical Engineers, after traipsing around the lake in 1849-50?104
Who truly reached the North Pole first? Did Robert Peary really stand at the Pole, or should his ambiguous assertion at the time, “I suppose we cannot say we are not at the pole,” be taken as an admittance of failure? Did Frederick Cook beat out Peary at the last secretive moment, or commit another obvious fraud as with his earlier claim to have climbed Mount McKinley? These are sparse facts, bitter resentments, and strong personalities. Certainly Robert Peary’s character inspired more critics than it did supporters. Moreover, there are institutional claims and jealousies, demands for recognition among this patron or that, this nation rather than another, and questions about whether the person or the sponsor merits special honor.
If not Peary, then who? Richard Byrd? Did he really pilot a Ford Trimotor to the pole, or turn back short? One can sympathize with those who prefer to leave the honor of first discovery to the USS Nautilus and Skate, nuclear-powered submarines that surfaced through the polar pack during IGY. If so, then who can claim priority? The captains? The ships and crews? The U.S. Navy? To those engaged, nothing seems more vital than clearly establishing the pedigree of priorities, and to those less committed, nothing seems so pointless.
Voyager’s quarrels, such as they were, lay in the realm of scientific rather than geographical discovery. Voyager was a corporate enterprise, an exercise in big science. The mission had in place explicit guidelines by which to determine if a new moon or ring was found, and methods by which to corroborate claims. Who, for example, discovered the volcanoes on Io? The first specialist to realize that an anomaly existed? Or the second, who was already moving toward independent discovery? Or the person who appreciated the anomaly for what it was? That no such quarrel bubbled up in public speaks to Voyager’s sense of itself as a collective project.
Where it most differs from predecessors has to do with the peculiar character of Third Age terrains. No one lived on Adrastea, Cressida, or Proteus, so there was no tradition to guide visiting explorers, nor old accounts to translate into a new vernacular. There were no competing discoverers with rival claims or standards of substantiation. The procedures were in place, and followed. Some disputes were inevitable: they are intrinsic to discovery of any kind, and especially to the practice of modern science with which exploration had bonded.
Except for gravity assistance. It was easy, particularly in retrospect, to identify intellectual predecessors for the concept; Michael Minovitch crystallized one of them in elegant form. But the concept could enter into Voyager only by being engineered. It had to be tested against potential trajectories, had to fuse with guidance and communication systems, had to reconcile spacecraft with rockets, had to merge politics with ambition and idea. The recognition of gravity assistance did not make Voyager: by itself it went nowhere. It no more created spacecraft than the enunciation of the second law of thermodynamics created steam engines. The idea had to become a working machine. It had to be embedded in a mission. To those personally removed from it, the quarrel might seem like arguing over who invented the lateen sail that made the caravel possible, or who first identified the prospects for the gran volta.
Gravity assist was one of dozens of ideas—inventions, if you will—that made Voyager possible. Who invented Voyager? Who invented the Grand Tour? Without the discovery of gravity-assist propulsion, it could not have happened. But neither could it have happened without the Deep Space Network, high-speed digital computers to project trajectories, onboard computers to monitor and reset programs, and elaborate instruments and imaging; or without those complex groups, so often tedious to ambitious souls, that did the collective task of adapting, fitting, and testing to ensure that spacecraft could actually perform over long missions; or without support from NASA and OMB; or without the cold war to pry open tax dollars to compete with the Soviet Union among the planets.
Among their payloads each Voyager carried six small aluminum plates on which were engraved the signatures of all the persons who could claim to have contributed to their trek. The roster ran to nearly 5,400 names. What, or who, was Voyager, and who invented it? Many people, and no one.
ACROSS THE VOID
Having made their gran volta, the Voyagers commenced a long, lonely trek to Saturn. Even with a roughly 40,000-kilometer-per-hour boost in velocity, Voyager 1 needed another twenty months, and Voyager 2 another thirty, before they reached their near-encounters with what members of the space community were coming to call the Lord of the Rings. Meanwhile, the shuttle had throttled the U.S. planetary program into silence. Pioneer Venus, designed to do at Venus what Pioneers 10 and 11 had done at Jupiter and Saturn, launched in May 1978. Then nothing. The shuttle took it all. The Grand Tour was the only tour.
The Voyagers flew alone.
DAY 752-1,031
14. Encounter: Saturn
To the Ancients it was known as the Great Conjunction, that moment, roughly every twenty years, when the varying speeds of Jupiter and Saturn cause them to appear to unite momentarily in the night sky.
As Voyager 1 closed on Saturn, a Great Conjunction was under way, with those two giant planets joined by Venus and the star Regulus to create a brilliant predawn constellation. Such alignments had happened forever, interpreted as portents of fortune and fate. But this time the cluster included a new celestial body and it joined humanity to the planets not through astrological magic but by aeronautical engineering in that predawn of solar system exploration. A Great Conjunction now marked Voyager’s encounter with Saturn.105
VOYAGER 1
Well before that moment, as early as January 1980, Voyager 1 began recording radio bursts emanating from Saturn on a roughly ten-hour cycle. These coincided with the rudely known rotation period for
the planet; the refined transmissions allowed for a sharper determination of the precise numbers. But the anticipated spectacle was the spin not of the gaseous planet but of its rings, which had mesmerized viewers from Galileo onward. Where Jupiter stunned and dazzled with its Technicolor weather, Saturn did so with its gorgeous rings.
The observation phase commenced in October 1980. As Voyager 1 barreled toward the planet at 1.3 million kilometers per day, something like weather appeared, with lighter and darker blotches on the generally opaque surface of Saturn, and the rings revealed definitions and structures previously unviewed, a drama heightened by time-lapse movies akin to those made for Jupiter’s Red Spot. Voyager photographed two inner satellites, first identified in 1966 but with properties otherwise unknown. By October 24 the spacecraft had halved its distance to Saturn, enhanced imaging beyond its narrow-angle camera, and brought its other instruments to bear, particularly its ultraviolet and infrared spectrometers. Voyager 1 officially entered its far-encounter phase.106
The rings betrayed not only more and more detail—grooved like a phonograph record—but also inexplicable dark “spokes” that spun among the rings. The phenomenon quickly became an object of special imaging. Analysis on October 25 and 26 led to the discovery of two satellites along the F Ring. Day by day, the resolution sharpened. Saturn displayed yellowish bands and turbulence among its cloud cover; its rings multiplied into hundreds, then thousands; its now-fourteen satellites acquired substance, rendering Saturn, like Jupiter, into a miniature solar system. Among the rings the Cassini Division revealed internal divisions. Computer enhancement and false-color imaging broke down the blurry haze of surface cloud to display a score of weather belts in the southern hemisphere alone. Titan acquired some definition and loomed as what it was: the second largest moon in the solar system. Daily, Voyager imaged the rings in a grand mosaic; every six hours it directed its full battery of instruments toward Titan, while otherwise it searched for unknown satellites and swept the scene with its spectrometers. 107
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