Robot Explorers: US Unmanned Space Missions

Robot Explorers: US Unmanned Space Missions: page 17

On October 18, 1989 at Cape Canaveral, the Space Shuttle Atlantis climbs into the sky, with the Galileo spacecraft in the payload bay. Galileo's mission: the exploration of Jupiter and its moons.
Atlantis launch.	Jupiter

On its voyage to Jupiter, Galileo passed through the asteroid belt and made a startling discovery of an asteroid with its own tiny moon in orbit around it. This color picture is made from images taken from the Galileo spacecraft about 14 minutes before its closest approach to asteroid 243 Ida on August 28, 1993. The image was taken when the spacecraft was about 6,500 miles away. The tiny moon, Dactyl, is visible to the right of the asteroid. The color is "enhanced" in the sense that the CCD camera is sensitive to near infrared wavelengths of light beyond human vision; a "natural" color picture of this asteroid would appear mostly gray.

Galileo reached Jupiter in December of 1995 and began its two-year study of the Jovian system. There were two parts to the spacecraft, an orbiter and atmospheric probe.

The purpose of the probe was to return data on Jupiter's atmosphere. The probe was traveling 106,000 mph when it sliced into Jupiter's atmosphere. During the first two minutes of plunging into the atmosphere, the probe encountered temperatures twice as hot as the Sun's surface temperature and experienced deceleration forces as high as 230 g's (that's 230 times the acceleration of gravity at the surface of the Earth). As the probe continued to descend through 95 miles of the upper atmosphere it collected data on the local conditions. The data were radioed to the orbiter portion of Galileo overhead, then transmitted back to Earth. Measurements from the probe showed a drier atmosphere than expected, few clouds, and lightning in the distance. Near the end of its 58 minute plunge, the probe measured 450 mph winds. The probe was finally melted and vaporized by the intense heat and pressure of the atmosphere.

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Artist's rendition of probe descent into Jupiter's upper atmosphere.

Meanwhile, the Galileo orbiter continued to carry out its mission of studying Jupiter and its moons. Galileo orbited Jupiter in elongated ovals that took the spacecraft close to the planet and its four largest moons.

Approaching Io, Jupiter's innermost moon, meant surviving Jupiter's intense radiation, so these encounters were saved until last. When radiation upset the spacecraft's computer, engineers worked all night to get them back on line. But Galileo came through again, and even discovered a lava fountain erupting on Io.

The spacecraft came so close to Europa that if there were something there the size of a school bus, Galileo would have detected it. The additional observations of Europa supported the theory that an ocean of water currently exists below the surface. NASA began considering plans for future missions to orbit Europa, and perhaps to send a lander.

Galileo's prime mission ended on December 7, 1997. With more to learn, and the spacecraft in good health, NASA approved a two-year study called "GEM" -- the Galileo Europa Mission. For fourteen more orbits, the spacecraft focused on ice, water, and fire: the icy moon Europa, which might have an ocean; Jupiter's majestic thunderstorms; and the fiery volcanoes of Io.

galileo-comparison.jpg (78680 bytes)


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	Copyright ©2004 Colleen Gino	Images and content courtesy JPL and NASA.