Galileo’s 14-year odyssey of discovery ends

The Galileo spacecraft’s 14-year solar system odyssey — eight of those years in orbit around Jupiter — came to a fiery end, Sunday, Sept. 21, as the gallant craft was intentionally guided into the Jovian atmosphere, where it disintegrated. Galileo worked to the very end, its last signal reaching the Deep Space Network tracking station in Goldstone, Calif., at 12:43 p.m. PDT. Hundreds of former Galileo project members and their families gathered at the Jet Propulsion Laboratory in Pasadena to bid it goodbye.

Galileo, the first spacecraft to orbit one of the outer planets, will go down as one of the most successful planetary exploration missions in history.

"We learned mind-boggling things," said Galileo project manager Claudia Alexander. "This mission was worth its weight in gold."

JPL announced last week that "the hardy spacecraft had endured more than four times the cumulative dose of harmful radiation it was designed to withstand," a final tribute to the radiation-hardened computer chips Sandia designed and built and JPL installed in Galileo. Sandia delivered the chips in 1985. Galileo was eventually launched Oct. 18, 1989. (See "Galileo’s epic odyssey around Jupiter. . . and the Sandia connection," Lab News, Feb. 9, 2001; also at http://www.sandia.gov/LabNews/LN02-09-01/galileo/galileo.pdf.)

The prime mission ended six years ago, but Galileo worked so well that NASA extended the mission three times.

JPL also noted last week, "The mission was possible because it [Galileo] drew its power from two long-lasting radioisotope thermoelectric generators provided by the Department of Energy."

Galileo flew by Venus once and Earth twice on its convoluted, gravity-assisted path to Jupiter. From launch to impact, it traveled 2.878 billion miles (orbiting Jupiter 35 times in eight years) and returned 30 gigabytes of data and 14,000 pictures.

Galileo’s list of discoveries is astounding. Even on its way to Jupiter, in 1993, it discovered and photographed the first moon around an asteroid (Ida and its moon Dactyl). Once in the Jovian system it proceeded to investigate the geologic diversity of Jupiter’s four largest moons. It documented the extraordinary volcanism on Io. It found evidence that Europa may have a salty ocean beneath its fractured, ice-encrusted surface. It showed that Ganymede and Callisto might have a liquid-saltwater layer. It found that Ganymede has a magnetic field, the only moon known to have one. It recorded gigantic thunderstorms and lightning strikes on Jupiter a thousand times more powerful than on Earth and took observations and measurements of Jupiter’s atmosphere and magnetic fields that changed our understanding of the solar system’s largest planet.

Ironically it was that discovery of a probable sub-ice ocean on Europa that led to NASA’s difficult decision, as Galileo’s steering propellant ran low, to cause it to plunge into Jupiter and be destroyed there rather than risk a later accidental crash into Europa where it might bring earthly contamination to a moon that now seems at least to have the possibility of harboring some form of life.

"It was truly exciting to be part of the Sandia team that enabled the Galileo mission to be such a major success," Paul Dressendorfer (1141) told the Lab News last week. Paul and Ron Jones (1741) directed the technology development effort for the rad-hard chips and were responsible for circuit fabrication and manufacture. "At the time Sandia was the only organization capable of designing, fabricating, and qualifying the critical parts needed for the spacecraft, and to see it greatly exceed expectations and generate such a wonderful set of data over the years has been very rewarding."