December 7, 1995
Web posted at: 12:40 p.m. EST
From Science Correspondent Miles O'Brien
PASADENA, California (CNN) -- It's pins and needles time at NASA's Jet Propulsion Laboratory. More than six years after it was launched toward Jupiter -- and nearly two decades after it was first proposed -- the star-crossed Galileo spacecraft is on final approach.
But after a journey of more than 2 billion miles, many things could still go wrong. A 746-pound probe that separated from the mother ship in July must pierce the Jovian atmosphere at a precise angle about 5 p.m. EST Thursday, (1.4M QuickTime movie) but scientists said they would have to wait about an hour for confirmation that it was on the mark. "It's a very anxious time," said Galileo probe manager Marcie Smith. (85K AIFF sound or 85K WAV sound)
The probe's heat shield must protect a mini-chemistry lab from temperatures twice as hot as the sun. And its parachute must deploy in time. Otherwise, the Galileo probe could ricochet into space or burn up too fast as it plows into the atmosphere. It eventually will burn up anyway, but if all goes well, there will be a 75-minute window for the probe to relay atmospheric information to the Galileo mother ship.
Once the probe's kamikaze dive is complete, controllers will fire rockets hoping to place Galileo into orbit around Jupiter. Scientists hope it will be the start of a two year tour of the planet and three of its largest moons -- a huge system that has barely changed since the solar system was born, said NASA scientist David Morrison. (94K AIFF sound or 94K WAV sound)
Launched into space aboard the shuttle Atlantis in October 1989, Galileo already had been delayed by the Challenger disaster. Then it was forced to abandon a direct flight to Jupiter when a powerful booster rocket design was discarded. Instead, Galileo was propelled by a slingshot maneuver around Venus.
Problems continued when the spacecraft's high-capacity main antenna failed to open properly, forcing scientists to find alternative methods to beam data home by using a slow-speed antenna. That reduced Galileo's capacity for capturing and sending home pictures; scientists had hoped for thousands of images.
But some of the bad luck led to accidental good fortune for Galileo and its team of scientists. Despite the jammed transmission antenna, the spacecraft offered the closest views ever of asteroids, stunning pictures of Earth and the only direct glimpse of the Shoemaker Levy 9 comet collision on Jupiter in July 1994.
"Anyone who has worked on this mission a long time feels a lot of pride in being able to develop ways to get the job done in spite of the difficulties," said Galileo Project scientist Torrence Johnson. But the most difficult moments may still ahead. (111K AIFF sound or 111K WAV sound)
All images from NASA
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AP contributed to this report.