Mission Type: Orbiter
Launch Vehicle: Space Shuttle Atlantis (STS-34R)
Launch Site: Cape Canaveral, United States, launch complex 39B
NASA Center: Jet Propulsion Laboratory
Orbiter: 2,223 kg
Probe: 339 kg
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
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
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 ten instruments/experiments to study the planet's atmosphere, satellites, and magnetosphere.
Galileo carried a 337-kilogram probe designed to return data as it entered the Jovian atmosphere to identify atmospheric materials and conditions that cannot be detected from outside. Because of limitations of a Space Shuttle/IUS combination, NASA decided to use a complex multiplegravity-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; as it did so, it conducted an extensive survey of the planet (including imaging).
Having gained 8,030 km per hour in speed, the spacecraft flew by 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 the possibility of data transmission during its flyby of the asteroid Gaspra.
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 km 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, thus providing further data on minor planets. The spacecraft found Ida had a natural satellite (Dactyl), the first discovery on a moon orbiting an asteroid.
Later, in July 1994, as it was speeding 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 80 million km from Jupiter. The probe hit the atmosphere at 6.5°north latitude and 4.4° west longitude at 22:04 UT on 7 December 1995 and returned valuable data for 57 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.
The Galileo orbiter, meanwhile, fired its engine at 00:27 UT on 8 December, becoming Jupiter's first humanmade satellite. Its orbital period was 198 days. Soon after, Galileo began its planned eleven tours over twenty-two months, exploring the planet and its moons, beginning with a first encounter with Ganymede on 27 June 1996 and ending with a flyby of Europa on 6 November 1997 (which also included flybys of Callisto).
Having fulfilled the mission's original goals, NASA extended the mission extension, during which the spacecraft conducted numerous flybys of Jupiter's moons, each encounter yielding a wealth of scientific data. These included flybys of Europa nine times (eight between December 1997 and February 1999 and one in January
2000); Callisto four times (between May 1999 and September 1999); and Io three times (in October 1999, November 1999, and February 2000).
Galileo flew only 198 km from the surface and sent back the highest resolution photos at the time of the volcanically active moon.
On 8 March 2000, NASA announced plans to extend Galileo's mission further, renaming the flight the Galileo Millennium Mission. Galileo coordinated investigations of Jupiter and its environs with the Cassini spacecraft (on its way to Saturn) in December 2000. Earlier, under the new Millennium Mission, Galileo flew by Ganymede, the largest moon in the solar system, on 20 May 2000 at a range of 809 km. It completed a second flyby of the same moon on 28 December 2000.
On 15 March 2001, NASA extended the Galileo mission a third time by planning five more flybys of the planet's moons: Callisto (in May 2001), Io (in August and October 2001 and January 2002), and Amalthea (in November 2002). During the 25 May 2001 encounter with Callisto, a heavily cratered moon about the size of Mercury, the spacecraft flew by the surface at a scant 138 km, closer than any previous encounter.
In December 2000, the National Research Council of the National Academy of Sciences approved plans for ending the Galileo mission. After finishing its imaging mission in 2002, Galileo will continue studies of Jupiter's massive magnetic field with seven instruments.
After a final orbit shaped like an elongated loop, the spacecraft was deliberately destroyed to protect one of its own discoveries - a possible ocean beneath the icy crust of the moon Europa. Galileo plunged into Jupiter's crushing atmosphere on Sept. 21, 2003.
In its six-year exploration of the Jovian system, Galileo has discovered far less lightning activity (about 10 percent of that found in an equal area on Earth) than anticipated, helium abundance in Jupiter very nearly the same as in the Sun (24 percent compared to 25 percent), extensive resurfacing of Io's surface due to continuing volcanic activity since the Voyagers flew by in 1979, and evidence for a liquid water ocean under Europa's surface.
Galileo has also discovered organic compounds on Callisto, Ganymede, Europa, and even Io. The spacecraft has also discovered the first internal magnetic field of a moon.
Ganymede's intrinsic magnetic field actually produces a "mini magnetosphere" embedded within Jupiter's huge magnetosphere. The spacecraft returned thousands of images back to Earth.