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Galileo Probe Release Status


Douglas Isbell
Headquarters, Washington, DC                      July 11, 1995
(Phone:  202/358-1753)

Franklin O'Donnell
Jet Propulsion Laboratory, Pasadena, CA
(Phone: 818/354-5011)

Diane Farrar
Ames Research Center, Mountain View, CA
(Phone: 415/604-3934)

RELEASE:  95-108


A rugged, conical-shaped probe will separate from NASA's Galileo spacecraft later this week and head for Jupiter's cloud tops, the first time in history a human-made object will enter the atmosphere of an outer planet in our solar system.

The probe and its payload of scientific instruments will be deployed from the main Galileo spacecraft at 1:30 a.m. EDT July 13 and fly solo the remaining 51 million miles to Jupiter over the next five months. Confirmation of the release will be received 37 minutes later, the time necessary for the radio signal to travel back to Earth at the speed of light.

The 747-pound probe will slam into the giant gas planet's atmosphere on Dec. 7, 1995, then begin a parachute descent toward the planet, where it will make the first-ever measurements within Jupiter's atmosphere.

Designed to survive the highest impact speed ever achieved by a human-made object (106,000 mph), Galileo's atmospheric probe should provide extraordinary new details about Jupiter's chemical makeup and atmospheric dynamics.

At separation, Galileo will be 412 million miles from Earth and on a flight path headed toward the probe's aimpoint in Jupiter's atmosphere. Before the separation, controllers will line up Galileo's spin axis so that it is pointed along the path the probe will take as it enters Jupiter's atmosphere, and spin up the combined spacecraft and probe to 10.5 rpm. The spin stabilizes the probe's attitude, or orientation in space, as it flies toward Jupiter.

In the sequence of events leading to probe release, ground controllers and Galileo's onboard systems are sending a series of commands to prepare the probe for its mission. These include programming the probe's coast timer, an onboard clock that will "wake up" the probe's systems and scientific instruments six hours before it enters Jupiter's atmosphere.

After completing checks of command, data, power and other subsystems, a built-in cable cutter has severed the umbilical between the atmospheric probe and Galileo. Before deployment, small explosive charges on nuts that secure the probe to Galileo will detonate to free the probe. Three small springs will gently push the probe away from the main spacecraft, sending it on the last leg of its voyage to Jupiter.

Two weeks later, on July 27, Galileo is scheduled to fire its main engine to deflect its own course toward an orbit high above Jupiter's cloud tops. The probe and main spacecraft will communicate again on Dec. 7 as the descending probe transmits its data to the Galileo spacecraft, where it will be recorded for later broadcast back to Earth. The probe will send data to the Galileo orbiter for up to 75 minutes.

The ultimate fate of the probe may be determined by its battery lifetime, or it may succumb to either the high temperatures or the immense pressure of Jupiter's atmosphere. Galileo, meanwhile, will begin two years of close-up studies of Jupiter, its moons, rings and powerful magnetic environment as it orbits the planet.

Galileo was launched in October 1989 aboard the Space Shuttle Atlantis, and has flown by Venus, Earth (twice), and two asteroids during its trip to the outer solar system.

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