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Jupiter orbiter to launch in 1989.

Jupiter orbiter to launch in 1989

When the unmanned mission to Jupiter was scheduled to begin in 1982, NASA officials planned to deploy the Galileo orbiter and probe from the space shuttle. The direct voyage was expected to take about 18 months.

Five delays later--due mainly to rocket propulsion problems and the setback in the shuttle program--Galileo is now set for a 1989 launch date during the revamped shuttle program's ninth mission. The setbacks, however, have changed how Galileo will reach the fifth planet from the sun, lengthening the journey to six years.

To avoid possible damage to the shuttle, NASA officials have decided not to launch Galileo with a high-energy, liquid-fueled Centaur rocket. Instead, they will use a smaller launch vehicle and a route that will take advantage of the gravitational fields of Venus and earth.

After Galileo is launched from an apparatus set adrift from the shuttle Discovery during October 1989, it will fly around Venus and then twice around earth before being hurled toward Jupiter, each time changing its trajectory slightly and gaining momentum. The craft will provide the first direct sampling of Jupiter's atmosphere and the first extended observations of the planet and its moons.

Because of Galileo's longer and more complex route, NASA scientists say they will be able to obtain more science from the mission, such as inner-planet observations and the first asteroid flybys. And they are confident the new course will work perfectly.

"There will be no miscues in this billiard game we're playing,' said Galileo project manager John Casani last week at a NASA news conference in Washington, D.C., announcing the mission, which was named after the Italian scientist who discovered Jupiter's four large moons in 1610.

During February 1990, the 5,870-pound Galileo will fly within 9,300 miles of Venus and will search for evidence of lightning storms that were suggested during the Pioneer 12 flight. It also will measure the planet's atmospheric composition and distribution.

During the first return to earth 10 months later, Galileo will fly by at an altitude of about 620 miles. Then, during October 1991, it will pass within 620 miles of the asteroid Gaspra, located in the asteroid belt between Mars and Jupiter. Galileo will take pictures of the 10-mile-wide asteroid to correct its flight path, and will also observe Gaspra's composition.

After a 200-mile-altitude flyby of earth during December 1992, Galileo will pass the asteroid Ida, which also is located in the asteroid belt and which is twice as wide as Gaspra. Here the craft will make observations similar to those made during the Gaspra flyby, thus allowing scientists to directly observe asteroids for the first time.

In addition, during both earth flybys, Galileo will examine the moon's dark side, enabling scientists for the first time to map this section of the lunar surface using infrared.

In July 1995, almost five months before Galileo reaches Jupiter, its probe will be released. Shortly after entering the planet's atmosphere, the 737-pound probe will deploy a parachute, and for 75 minutes the probe will relay information to Galileo, which will have just entered Jupiter's orbit.

For the next 22 months, Galileo will make 10 orbits of Jupiter, each time coming within about 125 miles of Jupiter's four largest moons, which range in size between earth's moon and Mercury. During this part of the voyage, Galileo will take pictures of the moons that will have 20 to 100 times better resolution than those taken by Voyager 2 in 1979. After Galileo's instruments begin to wear out and stop functioning, the orbiter will continue in permanent orbit of Jupiter.

Photo: The Galileo program, which will cost more than $1.3 billion, is a joint effort between the U.S. and West German governments. The West Germans designed the spacecraft's propulsion system and several of the 16 instruments that the orbiter and probe will carry on its unorthodox route.
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Author:Eisenberg, Steve
Publication:Science News
Date:Dec 12, 1987
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