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

by Stephen J. Pyne

  As long as money sloshed through the system and a clearly defined space race was on, the fissures within NASA were small and easily spanned. But the conflicts were present at the creation: military control versus civilian purposes, the need to ensure engineering success versus the desire to expand the frontiers of science, the preference for many small vehicles versus a few opulent ones, the desire—as the Rocket and Satellite Research Panel proposed in November 1958—to conduct “scientific exploration” and, at the same time, to carry out “the eventual habitation of outer space.” One group envisioned a specific political reply to the Soviet challenge; another, an agenda for scientific discovery through prosthetic vehicles that could carry soundings from Earth’s upper atmosphere to those of the other planets; still others, an implied mandate to colonize the solar system for which robotic spacecraft had meaning only as reconnaissance parties for subsequent human settlers; and most, perhaps all, hoped that such ambitions complemented rather than competed. The quarrels over means and ends, they wanted to believe, were merely squabbles over timing.11

  NASA’s charter did not prescribe particular programs, only an institution and a process. Conflicting interests would meet where a democracy best handled them, in open politics. Significantly, NASA’s first administrator, T. Keith Glennan, was at once an academic (Case Institute of Technology), a military researcher (Navy’s New London Underwater Sound Laboratory), and a member of a government agency (Atomic Energy Commission). NASA simply consolidated existing programs, which basically meant continuing NACA research and extending projects begun under the International Geophysical Year, discipline by discipline. At its organization meeting in June 1958, the National Academy of Sciences’ Space Science Board concluded that “the immediate program would integrate results” of the IGY Committee’s study, “which is now or has recently been completed.” In brief, the emerging space establishment rounded up the usual suspects and prepared to give them money and rockets to go “beyond the atmosphere.”

  From the outset planetary exploration was deemed an essential part of a space program. The inspiration and prototype came from the International Geophysical Year (1957-58). As with so much of the Third Age, IGY was catalyst, announcement, and model. It first melded science, exploration, new technologies, and geographies of discovery into a style that was recognizably different from earlier epochs of exploration, and so helped kindle a Third Age, much as the eighteenth century’s endeavors to survey the transits of Venus had galvanized a Second Age. This was evident not only in its themes but in how it had morphed beyond them. IGY had begun more modestly, as a Third International Polar Year that intended to focus on Antarctica. But the opportunities seemed too fabulous not to scale up into a full-body scan of planet Earth, including its upper atmosphere; and it was within this context that Sputnik and Explorer launched. It seemed unavoidable, then, that IGY’s successor institutions such as NASA would likewise leap beyond their founding conceptions, in this case to push beyond Earth to the solar system overall. The real questions were not whether to go but when, where, and how.

  The Moon was an obvious first target, and as soon as the early Sputniks had racked up their orbital triumphs, the Soviets sent Lunik I past the Moon and Lunik II to its surface (both while the IGY was still in progress); and Lunik II sent gasps around the world when it broadcast a photo of the Moon’s dark side. So even before NASA was founded, America planned to launch counter-probes to the Moon under the auspices of the Defense Department’s Advanced Research Projects Agency—three Pioneer spacecraft by the air force and two through a collaboration between the army and the Jet Propulsion Laboratory.

  JPL, in particular, was already imagining a future of planetary exploration far beyond the Moon. It had long ties with the army, not only with the “Propulsion” of its moniker, but more significantly for interplanetary travel, with guidance systems, telemetry, and communications—an early recognition that hardware was only as good as its accompanying software. A mere seventeen days after Sputnik I, the Lab urged that America “regain its stature in the eyes of the world by producing a significant technological advance over the Soviet Union.” Director William Pickering recommended going to the Moon “instead of just going into orbit.” But the institution aspired to much more. In January 1959 NASA accepted JPL’s concept for a deep-space communication network, and in March it approved Project VEGA, an upper-stage rocket and spacecraft, thus partially substantiating JPL’s bid to become the prime center for extra-lunar space flights. Ideas swelled like a supernova.12

  Still, when congressional hearings in March reviewed “The Next Ten Years in Space, 1959-1969,” the focus was on near-Earth sites that were achievable with expected engineering (and likely military) payoffs: orbital settings, the Moon, the neighboring Earth-like planets. Exploration for its own sake had little standing. What was done not only had to be doable. It also had to satisfy a political purpose.

  Meanwhile, the Soviets had essentially claimed the Moon. A true triumph to counter the endless string of Soviet firsts required a still untouched target. That pointed to Venus and Mars. In February 1961 the Soviet Union made two attempts at Venus. Sputnik IV failed on launch, and Venera I missed its rendezvous with the planet. The opportunity for an American coup remained open. In November JPL engineer Allan Hazard submitted “A Plan for Manned Lunar and Planetary Exploration” that would place astronauts permanently on the Moon by the early 1970s, on Mars by mid-decade, and on Mercury, Venus, and “the outer Planets and their satellites” at some unspecified time thereafter. Though officially disavowed, the scheme showed where Lab thinking was headed. Then NASA pulled the plug in December 1959 by reversing itself and canceling Project VEGA.13

  The Moon was far closer and more essential. Whatever might go to the planets would be field-tested on the Moon. NASA’s founding interplanetary mission, in fact, began as a Moon shot before being diverted into orbit between Earth and Venus. While a first for America, Pioneer 5, jointly assembled by the air force, the Space Technology Laboratories, and Goddard Space Flight Center, had the appearance of a consolation prize after the Soviet spectaculars on both sides of the Moon. There seemed little more possible. The United States lacked a rocket capable of launching interplanetary spacecraft, and there was little incentive to push to the planets when the Moon still proved elusive. Nonetheless, Pioneer 5 sparked a need for an administrative structure—what became NASA’s Office of Lunar and Planetary Programs, which included an Office of Space Science and Applications .14

  An office, however, needs missions, and missions need both a vehicle and a purpose. What emerged was Ranger, a program for lunar exploration based on a prototype for a true interplanetary spacecraft, one that was not simply an instrumented hunk of metal but an automated system. A JPL team sketched the basics in February 1960 with a study, “Spacecraft Design Criteria and Considerations; General Concepts, Spacecraft S-1.” This established the foundational framework for JPL vehicles: a hexagonal frame, modular electronics and subsystem compartments, and a “bus-and-passenger” design that could accommodate a variety of payloads in what became a “hallmark of lunar and planetary missions.” Ranger was its prototype, the progenitor for what became Mariner and through Mariner, Voyager.15

  Yet Ranger’s record was ghastly—six failures, finally followed by three redemptive successes. Its successor, the soft-landing Surveyor, hit the Moon five times out of seven. With the announcement by President Kennedy that the United States would seek to put a man on the Moon and return him safely by the end of the decade, the gravitational pull of Earth became less than the political attraction of the Moon.

  Still, the planets beckoned. With a new upper-stage rocket, the Centaur, under development, the idea was floated to use some of its developmental test flights to send a spacecraft to Venus or Mars. The launch would occur anyway; the planetary probe would free-ride. Although the needs of Centaur determined the launch window, here was an opportunity to go beyond the Moon, and with NASA’s acquiescence, JPL projected
a new class of spacecraft, Mariner. The hope was that Mariner A would go to Venus, and Mariner B to Mars, probably in 1962, when planners projected a happy coincidence of developmental timetables and favorable trajectories. Planetary exploration was officially on the books.

  Then Centaur encountered troubles, and scrambling for an alternative, JPL proposed in August 1961 that instead of a Titan/Centaur rocket, the launch could rely on an Atlas/Agena, and instead of a new spacecraft, they could construct one out of Ranger, what became Mariner R. So, despite having gone no farther than orbits around Earth, NASA approved two launches to Venus for July-August 1962. With barely a year to prepare, “not knowing that the proposed mission was almost impossible,” as Oran Nicks recalled, “we laid out a plan, reprogrammed funding and hardware, and went ahead and did it.” Mariner 1 failed on launch; Mariner 2 made the first planetary flyby, coming within 34,400 kilometers of Venus on December 14, 1962. A month before closest approach, NASA approved two Mariner-class spacecraft to go to Mars in 1964.16

  Going to other planets carried the rivalries advertised in Explorer 1 farther out. Escaping Earth did not, for one, mean escaping the cold war, whose rivals soon sought allies among the planets. Mars and Venus were the prizes, and while both superpowers sent probes to each, the United States held a particular fascination with Mars, while the USSR came to regard Venus as its sphere of influence. But neither did leaving Earth dissolve the rivalries within the American space community. In particular, scientists, colonizers, and explorers could squabble over where and when to go.

  Early on, a consensus emerged for Mars. After the success of Mariner 4’s flyby in 1964, proposals for further unmanned probes flashed like meteor showers. The American Astronomical Society sponsored a symposium in 1965 on “Unmanned Exploration of the Solar System.” The NAS Space Science Board declared that Martian exploration, in particular, including a search for life, should be a “National Goal in Space,” a planetary counterpart to the Apollo enterprise. At the same time JPL constituted a Mars Study Committee. Headed by Bruce Murray, the committee stimulated a furious discussion that led to proposals for a dazzling full-bore program of exploration that would include flybys, orbiters, and landers. The last would involve a new state-of-the-art spacecraft called Voyager.17

  But going to Mars in a colossal way was less politically compelling than getting out of Vietnam, and being tied neither to military necessity nor to Great Society programs, the ballooning costs made the project both visible and vulnerable. In August 1967 Congress canceled funding. By various juggling, and by reverting to a plain vanilla Mariner spacecraft, NASA salvaged enough money to keep the planetary program flying. There were two Venus flights scheduled for 1967 and two Mars flights for 1971. The grandiose Voyager program, once killed, was subsequently resurrected as Viking, a mission to Mars timed for (and justified by) the American bicentennial.18

  Much as the planetary program had to insinuate itself, almost by accident, into the dominant Moon agenda, so a scheme to visit the outer planets had to finesse its way past Mars.

  THE GRAND TOUR CONCEIVED

  All the parts came together. Motive: a surrogate cold war played out in space. Means: the rapidly revolving technologies of rockets, spacecraft, communications, and guidance systems. These were trickier, because in the mid-1960s the capabilities for travel beyond the inner planets did not exist. Opportunity: a Grand Tour to the outer planets so compelling it could move the fantastic into the realm of the hypothetical. Although projects were only as good as the capability to encode them into metal and missions, a fabulous idea could—just might—impose a reality of its own.19

  The practical range of space travel remained limited to the combustion that engineers could ram through thrusters, and Mariner 2 was already pushing those limits. While bigger rockets, with bigger payloads, were on the drawing boards, travel beyond the Earth-like inner planets demanded a far greater propellant. Even the most powerful rocket, the Saturn V, would require thirty years to send a probe to Neptune solely on its own impulse. Such propulsion alone could never make the trek quickly enough. The payload spacecraft would expire from natural causes before it reached the farthest planets, and politics would never commit to projects that imposed immediate costs for such remote payback. For scientists, too, the horizons were dim; and for public politics, they were as invisible to the naked eye as Uranus.

  When a solution was found, it came from software rather than hardware. It appeared in the form of a suggestion that it was possible to outflank the superpower sparring around the inner planets and go directly to the outer ones, and that the propulsion to do so was latent within the very purpose of the mission. Robert Frost once explained that a poem, like a block of ice, should “ride on its own melt.” Far planetary exploration needed a mission that could likewise ride on the melt of its design.

  The two vital insights emerged not from machine shops or government offices but from densely mathematical studies of hypothetical trajectories. One involved finding a way to get spacecraft to the outer planets, and the other, a time and reason to do so.

  The first took shape in 1961, from work by a mathematics graduate student, Michael Minovitch, hired for the summer by JPL’s mission-design program to explore trajectories to carry spacecraft from Earth to Venus and back again. Over the next couple of years Minovitch went further and came to realize that a spacecraft behaved like a small planetary body, subject to the same gravitational accelerations and decelerations as asteroids and comets. By approaching a larger body in the same direction as its orbital motion, a spacecraft would accelerate, and thereby achieve additional momentum—a “slingshot” effect. Relative to the planet, it would lose what it gained as it sped away, but relative to the Sun, it would have gained overall, and where the planet producing acceleration was massive, the spacecraft would acquire far more propulsion than it ever could from prospective launch vehicles on Earth, which were soon to approach their upper limits. Moreover, the gravity-assist maneuver could be used more than once in a single mission .20

  Minovitch organized his thoughts in a 1963 technical report to JPL’s trajectory group. His insight did not instantly galvanize his colleagues, however, and they continued to experiment with mixes of propulsion systems, trajectories, and potential projects. Whatever its mathematical elegance, the concept had little engineering relevance until it got coded into a machine and a mission. The defining event came the next year, when Gary Flandro, a postdoc at JPL, distilled the “gravitational perturbation technique” to its essential equations and applied the results to a select suite of trajectories for the outer planets. The “great challenge,” Flandro appreciated, was “to try to make exploration of the outer planets practical.”21

  His research took him to Walter Hohmann, and then to Gaetano Arturo Crocco, an Italian who in 1956 had published a scheme for repeated close flybys of Earth, Mars, and Venus in what he termed a “grand tour.” Mostly Flandro fixed on Krafft Ehricke’s Space Flight, which expressed in general language what might be interpreted as gravity assistance. Then Joe Cutting, the group’s supervisor, recommended Minovitch’s work, particularly that which targeted Jupiter. Here, Flandro thought, was “the key to the outer solar system.” To his mind, however, the work done so far had been “elementary” and abstract. What was needed were calculations for “realistic mission profiles so that estimates of actual flight times, payloads, and planetary approach distances and speeds could be made.” Especially critical was an identification of “launch windows.”22

  What emerged by the spring of 1965 was a stunning recognition that a once-in-176-years alignment of planets meant that a single spacecraft could fling itself from one to another within a period comparable to the life of a probe. The required conjunction would occur in the early 1980s, which meant that a spacecraft launched in the late 1970s could reach Jupiter, the critical accelerant, just in time to ride a gravitational wave train to Saturn, Uranus, and Neptune. It was, Flandro recalled, “a rare moment of great exhilaration.” But
as always the inspiration was only as good as its expression. He found that the “trajectory computer programs” crafted by Minovitch were “not truly adequate,” and he replaced them with a “hand method using tabulations and graphs.” Since Minovitch worked at night, he and Flandro did not meet. It mattered little, since it was not Minovitch’s general solution that made Voyager possible, or his computational methods, but the providential alignment of the outer planets that tipped the scale of possibilities. Flandro circulated his results internally in 1965, even as the American Astronomical Society sponsored a symposium on “Unmanned Exploration of the Solar System.” The next year, he published the scheme for the space community in Acta Astronautica, identifying ideal launch dates and sketching prospective trajectories.23

  Initially, there was ample skepticism, even at JPL. At issue were engineering concerns: guidance, communications, and particularly the durability of spacecraft, for even an accelerated journey to Uranus would take ten years, while existing mechanical and electronic devices could barely survive a nine-month trip to Mars. But the idea itself soon accelerated, flung from one study to another much as the hypothetical spacecraft it imagined might careen from planet to planet. In December 1966 Homer Joe Stewart, director of JPL’s Advanced Studies Office, instantly saw the significance of the idea and published a prospectus in Astronautics and Aeronautics, and it was he who proposed to transfer Crocco’s term “grand tour” from the inner planets to the outer. Meanwhile, Bruce Murray, who had previously headed the Mars Study Committee, was busy outlining the particulars—what seemed to most partisans to be veritable axioms—for the mission, or rather a suite of missions. The scientific harvest was stupendous, the engineering challenge magnificent, the potential cultural impact “great and enduring,” and its value as cold war propaganda immeasurable. Here was a space spectacular that America was especially equipped to win. The Grand Tour was a noble complement to Apollo.24