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Review: Mission to Jupiter

Mission to Jupiter: A History of the Galileo Project
by Michael Meltzer
NASA, 2007
hardcover, 318 pp., illus.
NASA SP-2007-4231

At a time when NASA’s planetary exploration program has yet to decide on its future goals and suffers from a lack of reliable funding, it is useful to look back at one of the most successful deep space missions in the agency’s history. The Galileo mission to Jupiter was dreamt up in the earliest days of the US space program. It was put on the back burner when the Voyager Grand Tour probes were given higher priority, but in 1977, over the objections of Congressman Edward Boland of Massachusetts, the US House voted to begin funding the Jupiter Orbiter Program at the same time it funded the Hubble space telescope. What this shows is that even at a time of economic stress, the US can still begin work on more than one high value space science project at once.

The mission was not only plagued by the normal funding problems, but also by the inability of NASA and Congress to make up their minds about the type of booster it would use to escape from low Earth orbit and head out for Jupiter. The shuttle’s cargo bay could accommodate a fairly large Inertial Upper Stage (IUS) but the authorities had a hard time deciding if the IUS should be solid-fueled or not. If so, it would require a long flight through the inner solar system in order to gain enough velocity to reach the target. The alternative was a liquid-fueled system based on the older and more powerful Centaur upper stage.

The Challenger disaster in January 2006 forced the agency to accept the solid-fueled system. The mission planners found that a Venus-Earth-Earth gravity assist trajectory (VEEGA) would work. This would give them a chance to test and calibrate some of the spacecraft’s sensors long before they arrived at the ultimate destination.

Just before the Challenger explosion, JPL had shipped the spacecraft, including its plutonium-fueled radioisotope thermoelectric generators (RTGs) to Florida. These generators would set off a series of legal and political fights that continue to this day. A coalition of left-wing groups including the Christic Institute, the Florida Coalition for Peace and Justice, and even the German Green Party all tried to use legal maneuvers to delay and hopefully cancel the mission. NASA, however, had followed proper environmental procedures and the judges who heard the cases pretty much laughed them out of court.

Finally, after many delays and frustration, on October 17, 1989, the shuttle Atlantis launched the probe on its long voyage to the giant planet. Galileo consisted of three major elements: a spinning section which housed the fields and particles instruments, such as the magnetometer and the energetic particles detector; the non-spinning or despun part, which carried the remote sensing systems, and the atmospheric entry probe, which would be launched into Jupiter itself. As project scientist Torrence V. Johnson put it, “What Galileo became was basically a massive compromise in trying to get all the various scientific disciplines on board.”

In spite of a dry and understated tone, inevitable when writing an official history of this kind, Michael Meltzer manages to convey the real excitement and sense of wonder that all, or almost all, of those involved in the project must have felt.

After its encounter with Venus in February 1990 and its first Earth flyby in December of that year, Galileo flew out into the asteroid belt where it encountered Gaspra in October 1991, sending back some extraordinary images. Its final encounter with Earth was in December 1992. In August 1993 it flew within 2,400 kilometers of the asteroid Ida, discovering a small moon, Dactyl. This was the first of many surprising discoveries that would emerge over the years from the program.

The greatest long-term challenge to the mission was the failure of the High Gain Antenna (HGA) to fully deploy. The mission team was able to find ways of using the Low Gain Antenna to compensate for the loss of the HGA. The first software fix was radioed to Galileo in March 1995. Later software improvements were able to insure that the mission achieved all of its objectives and more. This success in fixing a damaged probe in deep space have given NASA space scientists and engineers a reputation for can-do excellence that has survived even the loss of a pair of Mars missions.

Galileo arrived in orbit around Jupiter in December 1995. The atmospheric probe entered the planet’s atmosphere and for 61 minutes sent back a treasure trove of data that now provides a new basis on which astronomers can build their theories about the formation of solar systems and gas giants. The rest of the spacecraft would spend the next two years carrying out its prime orbital tour, which would repeatedly carry it past three of the major Galilean moons, Ganymede, Callisto, and Europa.

After this, it would carry out flybys of the mysterious Io and of Europa, where there were signs of a possible subsurface ocean. Operations continued until the final demise of the craft in September 2003. Working inside Jupiter’s intense radiation belts with a spacecraft whose technology may have been cutting edge in the early 1980s—at a time of 16-bit microprocessors and dot matrix printers—the team’s ability to extract the “last full measure of devotion” from the distant robot stands as a tribute to the skill and devotion of all involved.

In spite of a dry and understated tone, inevitable when writing an official history of this kind, Michael Meltzer manages to convey the real excitement and sense of wonder that all, or almost all, of those involved in the project must have felt. This book will stand the test of time, not only as a history of the project but also as a record of the accomplishments of an exceptional group. The personnel and leadership may have changed over the years, but the team spirit of the project’s individual members remained alive in spite of all the difficulties.

In the end, despite the problems with the HGA and later with the data recorder, Galileo was a model for what a successful large-scale deep space probe program should be. Today’s Cassini spacecraft orbiting around Saturn owes a lot to its predecessor. As NASA begins work on its next flagship planetary mission, which may in fact be a trip to Jupiter to take up where Galileo left off, space industry leaders should not only keep in mind the technical lessons of this project, but the human and political ones as well. Above all they should remember that nothing worthwhile is ever easy.