Mission Type: Orbiter
Launch Vehicle: Space Shuttle Atlantis (STS-34R)
Launch Site: Cape Canaveral, United States, launch complex 39B
NASA Center: Jet Propulsion Laboratory
Spacecraft Mass:
Orbiter: 2,223 kg
Probe: 339 kg
Spacecraft Instruments:
Orbiter: 1) imaging system; 2) near-infrared mapping spectrometer; 3) ultraviolet spectrometer; 4) photopolarimeter-radiometer; 5) magnetometer; 6) energetic-particles detector; 7) plasma detector; 8) plasma wave; 9) heavy ion counter and 10) radio system
Atmospheric entry probe: 1) atmospheric structure instrument; 2) neutral mass spectrometer; 3) helium abundance detector; 4) net flux radiometer; 5) nephelometer
and 6) lightning/energetic-particles experiment
Spacecraft Dimensions:
Orbiter: 6.15 meters
Probe: 86 cm
Spacecraft Power: Two Radioisotope Thermoelectric Generators
Maximum Power: 570 watts
Antenna Diameter: 4.8-meter
Program Manager: Donald T. Ketterer, NASA Headquarters
Project Manager: William J. O'Neil, Jet Propulsion Laboratory
Principal Scientists: Dr. Torrence V. Johnson, Jet Propulsion Laboratory, and Henry C. Brinton, NASA Headquarters, Dr. Richard E. Young, NASA Ames Research Center
Total Cost: Original projection: $1.3 billion
References:
Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, Monographs in Aerospace History No. 24, by Asif A. Siddiqi

National Space Science Data Center, http://nssdc.gsfc.nasa.gov/

Galileo, one of NASA's most ambitious deep space exploration projects, was the result of plans dating back to the early 1980s to deploy a Jupiter orbiter and probe. In its final configuration, the orbiter was a 4.6-meter-tall spacecraft designed to operate for 22 months in Jovian orbit using 10 instruments/experiments to study the planet's atmosphere, satellites and magnetosphere. Galileo carried a 337 kg probe designed to return data as it entered the Jovian atmosphere to identify materials and conditions that cannot be detected from outside.

Because of limitations of a Space Shuttle/IUS combination, NASA decided to use a complex multiple-gravity-assist scheme that required three flybys (two of Earth and one of Venus) on its way to Jupiter. The STS-34R crew released the spacecraft 6.5 hours after launch; an hour later the two-stage IUS fired to send Galileo on its way.

Galileo flew past Venus at 05:58:48 UT on 10 February 1990 at a range of 16,106 km. It conducted an extensive survey of the planet (including imaging). Having gained 8,030 kilometers per hour in speed, the spacecraft flew past Earth twice, the first time at a range of 960 km at 20:34:34 UT on 8 December 1990, when it clearly detected traces of life in atmospheric trace elements on our home planet. The spacecraft also conducted lunar observations.

A major problem occurred on 11 April 1991 when the high-gain antenna failed to fully deploy, thus eliminating any possibility of data transmission during its flyby of the asteroid Gaspara. Becoming the first humanmade object to fly past an asteroid, Galileo approached the minor planet to a distance of 1,604 km at 22:37 UT on 29 October 1991. The encounter provided much data, including 150 images of the asteroid. Galileo then sped to its second encounter with the Earth-Moon system, with a flyby of Earth at 303.1 km at 15:09:25 UT on 8 December 1992, adding 3.7 kilometers per second to its cumulative speed. Despite extensive attempts to salvage the high-gain antenna, ground controllers eventually had to restructure the mission to use only the low-gain antenna, which would allow about 70 percent of the originally planned scientific return (using software and hardware improvements on Earth).

Galileo flew by a second asteroid, Ida, at 16:51:59 UT on 28 August 1993 at a range of 2,410 km, providing further data on minor planets, including the discovery of Dactyl, the first known a natural satellite of an asteroid. Later, in July 1994, as it was speed toward Jupiter, Galileo provided astronomers' only direct observations of Comet Shoemaker-Levy 9's impact with the Jovian atmosphere.

Galileo's atmospheric entry probe was finally released on 13 July 1995, when the spacecraft was still 85 million kilometers from Jupiter. The probe hit the atmosphere at 22:04 UT on 7 December 1995 and returned valuable data for 58 minutes as it plunged into the Jovian cauldron. Data, originally transmitted to its parent craft and then later transmitted back to Earth, indicated an intense radiation belt 50,000 km above Jupiter's clouds, few organic compounds and winds as high as 640 meters per second.