Mission to Jupiter: 25 Years Since the Launch of Galileo (Part 1)

When the Galileo spacecraft drifted out of Shuttle Atlantis’ payload bay on the evening of 18 October 1989—25 years ago, next week—on the first leg of its voyage to Jupiter, the sight was a moving one for Shannon Lucid. As STS-34’s lead mission specialist, she was primarily responsible for the deployment of one of the most important payloads ever launched by NASA. For almost a dozen years, Lucid had lived and worked with the reality that her job was an overwhelmingly technical one, drawing from its roots in engineering and pure science … but on this day, as Galileo and its Inertial Upper Stage (IUS) booster floated silently into the inky void, she beheld a new reality: the romance of adventure. Emblazoned across the base of the spacecraft which would one day circle Jupiter and deposit an instrumented probe into its atmosphere were two names: “Galileo” in script and “NASA” in worm-like block capitals. To Lucid, those two words symbolized exactly what the mission stood for: The script represented the romance of adventure and exploration, whilst the worm was indicative of the outstanding engineering and scientific talent which had brought this awesome project from the drawing board to fruition. Yet Galileo’s journey to the launch pad had been a long and tortured one, and its voyage to Jupiter would be longer and harder still.

The mission traced its genesis back to the mid-1970s. Named in honor of the great Italian scientist, Galileo Galilei, whose endeavors in the early 17th century included the discovery of Jupiter’s four large moons—Ganymede, Callisto, Europa, and Io—but which also assured him a retirement under house arrest, courtesy of the Roman Inquisition.

Originally known as “Jupiter Orbiter and Probe” (JOP), the name “Galileo” seemed an obvious one and the project received Congressional approval on 1 October 1977, with a planned launch four years later. However, delays to the first flight of the shuttle and the limited capability of Boeing’s IUS to boost Galileo on its way to Jupiter raised concerns. In 1979, Washington Post journalist Thomas O’Toole highlighted that problems with certifying the shuttle’s main engines to operate at the 109 percent performance threshold needed to lift Galileo posed additional obstacles.

By now, the launch had slipped until 1982 at the earliest. O’Toole noted that if the 109-percent-capable main engines were not ready for this date, Galileo could slip even further. Timing was critical, since a 1982 launch depended upon a Mars gravity assist and if it was delayed much further, the potential existed to halve the scientific mission at Jupiter, from 11 to just five orbits of the giant planet. At length, in late 1980, under pressure from Rep. Edward Boland, a Democrat from Mass., NASA was obliged to abandon the IUS plan and initiate planning for a launch on General Dynamics’ liquid-propeled Centaur-G Prime, which Administrator Robert Frosch had earlier opposed.

The situation for Galileo’s future dimmed substantially for much of 1981, with Congressional mutterings of closing down the California Institute of Technology’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif., which managed many of NASA’s planetary projects. A massive letter-writing campaign to George Keyworth, head of the White House’s Office of Science and Technology Policy, was spearheaded by Galileo investigator and famed physicist James van Allen. In a speech to the National Academy of Sciences, van Allen identified Galileo as one of the most exciting missions of exploration ever undertaken and that its cancellation would prove devastating.

Thankfully, in December 1981 the Office of Management and Budget relented, reinstated Galileo and it was rescheduled for 1983. There was a caveat, however: Galileo would not use the powerful Centaur-G Prime. In January 1982, NASA rescoped the mission and returned to the less powerful IUS fitted with a third, “injection stage” to provide increased propulsion. As a consequence, Galileo’s launch was rescheduled for August 1985, but the absence of the powerful Centaur meant that it would take five years, instead of two, and the spacecraft would be injected into a two-year-long elliptical solar orbit, would require a gravity assisted boost from Earth in June 1987, and would finally reach Jupiter in January 1990.

By the summer of 1982, some members of Congress—led by New Mexico Sen. Harrison “Jack” Schmitt, a former Moonwalker and chairman of the Senate Space Subcommittee of the Science, Commerce and Transportation Committee—were pushing vigorously for a return to the Centaur and a reduced journey time. Despite worries about additional expense in changing boosters again, coupled with concerns about further delays to the mission, in July President Reagan approved the move and NASA was forced to replan. The Centaur would be used to boost Galileo, but launch would be unavoidably postponed until May 1986, with a two-year flight time to the giant planet.

At this stage, the mission truly entered the phase of equipment testing. In the early summer of 1983, the parachute for the instrumented probe, which would descend into Jupiter’s atmosphere, successfully passed full-scale tests, and by September of that year the main spacecraft and probe were integrated. A model of the Centaur passed its own tests in September 1984, and the actual flight model was rolled out of General Dynamics’ plant in San Diego, Calif., in August of the following year. By this time, NASA Administrator Jim Beggs had endorsed other possible tasks for Galileo, most notably a flyby of the asteroid Amphitrite, which it was hoped might unlock secrets of the primordial solar nebula from which the Sun and planets formed. An Amphitrite flyby would delay the Jupiter arrival from August to December 1988, however, and it was decided to make a final decision after launch. In December 1985, only weeks before the loss of Challenger, Galileo was transported, cross-country by truck, guarded by police, state troopers, and other guards, and arrived safely at the Kennedy Space Center (KSC) for launch the following May.

When Challenger exploded in the skies above Florida on 28 January 1986, Galileo was undergoing final checkout and preparation for attachment to its Centaur-G Prime booster. In the weeks after the accident, NASA Acting Administrator William Graham spoke of the possibility of a return to flight in the spring of 1987, which kept alive the option to launch Galileo in the next Jovian “window” in June of that year. Eventually, the modifications to the shuttle’s Solid Rocket Boosters (SRBs) and the orbiters themselves inevitably pushed the return to flight further to the right.

On 19 June 1986, newly-reappointed NASA Administrator Jim Fletcher formally canceled Centaur-G Prime and new options had to be found. One of these was an “enlargement” of the IUS, possibly coupled with an additional booster, such as a Special Payload Assist Module (PAM-S). However, as already noted, the IUS was insufficient to send Galileo directly to Jupiter and alternate trajectories, involving planetary gravity assists, were explored. Even before NASA settled on October-November 1989 as the most appropriate “window” for Jupiter, Galileo’s planners were already working toward this date, creating a complex flight profile, known as the Venus-Earth-Earth Gravity Assist (VEEGA), in which the spacecraft would perform a flyby of Venus in February 1990, return to Earth in December, and be placed into a two-year elliptical solar orbit. Returning a second time to Earth in December 1992, it would pick up sufficient energy to reach Jupiter in December 1995.

The VEEGA technique was highly conservative of Galileo’s on-board propellant, with predictions indicating that up to 176 pounds (80 kg) would remain, even after the arrival at Jupiter and completion of its primary mission. The trajectory also permitted possible rendezvous with up to three asteroids—Ausonia, Gaspra, and Ida—and eventually the latter two were selected. However, since the spacecraft would fly much closer to the Sun than had been planned, additional thermal shielding was added in the three-year down time after Challenger. It is interesting that Galileo also “leapfrogged” Ulysses in the launch pecking order. “NASA based its decision on optimising data return from the two missions,” wrote Michael Meltzer in Mission to Jupiter. “Launching Ulysses first would have resulted in too long a wait before Galileo reached Jupiter and began transmitting prime data from the Jovian system.”

As launch neared, with an opening of the Jupiter window at 1:29 p.m. EST on 12 October 1989, there were still last-minute concerns about Galileo … although these were not focused upon its mission, but upon its power system. Since the spacecraft would be traveling so far from the Sun, the use of solar cells for electrical provision was impractical. Therefore, General Electric supplied a pair of Radioisotope Thermoelectric Generators (RTGs), fueled by fracture-resistant pellets of plutonium-238, whose decay produced heat which was in turn converted into electricity. To keep them at a safe distance from the sensitive scientific instruments, the RTGs were mounted on a boom, which extended them 16 feet (5 meters) away from the main body of the spacecraft.

Both power plants produced 570 watts of electricity at launch, which steadily decreased by around half a watt per month and reached around 493 watts by the time Galileo reached Jupiter. Shuttle Atlantis also required modification to incorporate an RTG coolant line and purging system in her payload bay. In the late 1980s, of course, “nuclear” was a dirty word—a word which conjured images of military superpowers, the faceless Department of Defense and Department of Energy, and greedy power corporations. Peace marches were undertaken and representatives of several anti-nuclear groups gathered at the gates of KSC to express their disgust and fear that a Challenger-like explosion could spread radioactive plutonium across much of the United States’ eastern seaboard.

The allegation that NASA was playing “ecological roulette” with the lives of Floridians was not groundless. Memories of the “messy” crash of the Soviet Union’s nuclear-fueled Cosmos 954 satellite in Canada, a decade earlier, were fresh in many minds, and even the noted physicist Carl Sagan remarked that “there is nothing absurd about either side of this argument.” Final approval to proceed with the Galileo launch came from President George H.W. Bush himself in September 1989. Three days before the scheduled launch, on 9 October, outraged protestors staged a mock “death scene” at the Cape and even threatened to sit on Pad 39B itself to prevent Atlantis from launching into orbit.

STS-34 astronaut Franklin Chang-Díaz was astonished by the controversy surrounding a mission which was not a military one, but a scientific odyssey. “It was striking to drive through the gates … and see all these demonstrators, trying to stop the launch,” he told a Smithsonian interviewer, years later. “The topic of nuclear power is going to come up over and over again as we move into space. It’s a key issue we are going to have to resolve, because the survival of people in space, far away from Earth, will totally depend on the use of nuclear power.”

The launch window for Jupiter would close on 21 November 1989, after which the next opportunity would not arise until 1991, so there existed a very real risk that the mission might be canceled. Security was increased at KSC, as guards armed with M-16 assault rifles and 9 mm semi-automatic pistols patrolled the perimeter of the launch site. A faulty main engine controller put paid to the 12 October attempt and launch was rescheduled for the 17th, then the 18th when rain showers drifted within 18 miles (30 km) of the Shuttle Landing Facility (SLF). During these few days, final efforts to stop the launch were rejected by the Circuit Court of Appeals in Washington, D.C. In her summary, Chief Justice Patricia Wald declared that she could find no evidence that NASA had improperly compiled its environmental assessment reports for Galileo, and on 16 October a number of activists were arrested at the Cape for trespassing.

With this final clearance, the last hurdle was removed before Galileo’s long-awaited mission to the King of the Planets.

The second part of this article will appear tomorrow.

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