Galileo launches to Jupiter

On the afternoon of 18 October 1989, Space Shuttle Atlantis climbed away from Kennedy Space Center with a Jupiter spacecraft folded in its payload bay. Galileo had waited years for this ride. Conceived in the 1970s and repeatedly delayed, it lost its powerful Centaur upper stage to post-Challenger safety rules, leaving a booster too weak to fly direct. So navigators plotted a six-year detour, one swing past Venus and two past Earth, stealing speed from each planet. Hours after launch the astronauts released Galileo, and its solid-fuel stage fired it out of Earth orbit for good.

The cruise became a saga in itself. In April 1991 the umbrella-like high-gain antenna jammed partly open, threatening the entire mission, until engineers reinvented it in flight, using data compression and upgraded ground stations to recover most of the planned science through a small low-gain antenna. Along the way Galileo made the first close flyby of an asteroid, Gaspra, in October 1991, discovered the first known asteroid moon, Dactyl, orbiting Ida in 1993, and in July 1994 held the only direct view of comet Shoemaker-Levy 9's fragments slamming into Jupiter.

On 7 December 1995 it all converged. The 339-kilogram probe Galileo had released months earlier hit Jupiter's atmosphere at roughly 47.6 kilometres per second, the fastest atmospheric entry ever flown, survived deceleration approaching 230 times Earth's gravity, and transmitted for about 58 minutes as it sank into the clouds. That same day the orbiter braked into orbit, becoming the first spacecraft ever to orbit an outer planet. Across 34 orbits it built the case for a saltwater ocean beneath Europa's ice, found hints of hidden water inside Ganymede and Callisto, and discovered that Ganymede generates its own magnetic field.

Galileo flew almost eight years at Jupiter, far past its design life, its instruments slowly battered by radiation. By 2003 the fuel was nearly gone, and NASA faced a question Galileo's own discoveries had created: an abandoned spacecraft might one day crash into Europa and contaminate a possibly habitable ocean. So on 21 September 2003 controllers deliberately flew Galileo into Jupiter at about 48 kilometres per second, destroying the spacecraft to protect the worlds it had revealed.