Galileo Energetic Particles Detector

Mission Timetable

Launch. The Galileo orbiter and probe were launched October 18, 1989, aboard the space shuttle Atlantis (STS-34) and an inertial upper stage (IUS) rocket on a Venus-Earth-Earth gravity assist trajectory (VEEGA) to provide sufficient energy to reach Jupiter.

Venus Flyby. On February 10, 1990, Galileo came within about 16000 kilometers (9500 miles) of Venus, using the planet's gravitational force to increase the energy of the vehicle on its trajectory.

First Earth Flyby. This flyby (December 8, 1990), at an altitude of about 1000 kilometers (620 miles), confirmed the existence of a huge ancient impact basin in the southern part of the Moon's far side. Galileo imaged the Moon's north pole at several wavelengths and found evidence that the Moon has been more volcanically active than researchers previously thought.

Asteroid Gaspra Flyby (October 29, 1991). Nine months into its two year Earth-to-Earth orbit, Galileo entered the asteroid belt, passing about 1600 kilometers (1000 miles) from Gaspra. Pictures and other data collected reveal Gaspra to be a cratered, complex, and irregular body about 19 by 12 by 11 kilometers (12 by 8 by 7 miles), with a thin covering of dirt-like regolith and a possible magnetic field.

Second Earth Flyby. December 1992.

Asteroid Ida Flyby. Galileo's second asteroid encounter on August 28, 1993, found Ida to be a larger, more distant body than Gaspra. Ida is about 55 kilometers (34 miles) long and very irregular in shape. It rotates every 4.6 hours around its offset axis, and, apparently, may have a magnetic field. Galileo also discovered the first moon of an asteroid. Ida's satellite, named Dactyl, was estimated to be about 100 kilometers (63 miles) from the center of the asteroid.

Comet Shoemaker-Levy Impact Observation (July 1994). Though comet Shoemaker-Levy had not been discovered at the time of Galileo's launch, an observation program was planned for Galileo's remote sensing instruments. Thus, Galileo was the only observation platform capable of making measurements in line of sight to the comet's impact area on Jupiter's far side from the Earth. Galileo's observations were recorded in a tape recorder and computer memory and then played back and transmitted to Earth. Because of slower transmission necessary due to failure of the high-gain antenna soon after launch (see Frequently Asked Questions), the playback continued until January 1995.

Jupiter Probe Release. On July 13, 1995, the Galileo spacecraft, spinning up to 10 rpm, aimed its probe toward Jupiter at a distance of about 82 million kilometers (51 million miles) from Jupiter's atmosphere. Cables connecting the probe and main spacecraft were severed, and the probe was released for its solo flight to Jupiter. The main spacecraft received transmissions from the probe and stored the information in an on-board tape recorder and computer memory for transmission to Earth. The spacecraft continued towards an orbital tour of Jupiter.

Jupiter Encounter.

• Orbital Tour of Galilean Satellites (December 7, 1995 - December 7, 1997). The spacecraft's orbital tour consisted of 11 different elliptical orbits around Jupiter, during which information was gathered from the planet and its satellites. Three satellites--Ganymede, Callisto, and Europa--provided gravity assists, in turn, on all but one of the orbits. Jupiter's moon Io was observed on every orbit, and the orbiter was expected to return a nearly continuous, real-time survey of the Jovian magnetosphere.
• Galileo Europa Mission. The Galileo Europa Mission (GEM) was a follow-up to Galileo's exploration of the Jupiter system and a precursor to future missions to Europa and Io. GEM conducted a detailed 14-month study of Europa comprised of 8 close encounters. Additional orbits also focused on Io and on Jupiter's thunderstorms.
• Galileo Millennium Mission. Galileo completed its closest-ever flyby of Io, at an altitude of 124 miles, as well as a successful close flyby of Ganymede. When the Cassini spacecraft passed Jupiter in December 2000, observations by Galileo and Cassini were coordinated to examine Jupiter's magnetosphere and other parts of the Jovian system.

Galileo End of Mission. NASA repeatedly extended Galileo's original two-year mission in orbit; but as the spacecraft ran out of the propellant needed to keep the antenna pointed toward Earth, the Galileo team, knowing they would eventually lose control of and contact with the spacecraft, chose a planned impact with Jupiter. This was to insure that Galileo would avoid hitting Europa, which may have a melted saltwater ocean under its icy crust, making that moon of great interest for future study of the possibility of life. The plunge into Jupiter's atmosphere occurred on September 21, 2003.

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