Visit to a Large, Hot Planet: Galileo Heads for Jupiter
By JOHN NOBLE WILFORD
Published: October 17, 1989
CAPE CANAVERAL, Fla., Oct. 16— Scientists hope the Galileo spacecraft's planned explorations of Jupiter, probing deep into the planet's hot, dense hydrogen atmosphere, will yield important clues to primordial conditions in the solar system and also insights about the ''big bang'' that may have created the universe.
With expectations like these, the $1.4 billion Galileo mission scheduled to begin Tuesday afternoon is the most ambitious interplanetary undertaking yet in the history of space flight. The 2.5-ton spacecraft, described by some exuberant scientists as the ''Rolls-Royce'' of planetary vehicles, will be the first to orbit Jupiter and conduct a sustained investigation of the four major Jovian moons, which Voyager photography disclosed as diverse and puzzling worlds unto themselves. Galileo will also be the first mission to probe the atmosphere of one of the giant outer planets. 'The Grandest Mission'
''It's the grandest mission we've attempted,'' said William J. O'Neil, science and mission design manager for Galileo at the Jet Propulsion Laboratory in Pasadena, Calif. ''Jupiter is most important to us in trying to understand how the solar system evolved.''
Galileo's six-year journey to Jupiter will begin in the cargo bay of the space shuttle Atlantis, now scheduled for liftoff at 12:57 P.M. Once in orbit, the crew of five astronauts are to release the spacecraft. Then an attached rocket should fire the spacecraft on a roundabout trajectory to Jupiter by way of Venus and two passes by Earth. At each of these encounters Galileo will pick up momentum from the force of the planets' gravity.
The launching, originally set for last Thursday, was delayed five days while technicians replaced a faulty electronic control unit in one of the shuttle's three main engines.
Officials of the National Aeronautics and Space Administration said the newly installed controller had been tested and was ''functioning flawlessly.'' Weather is predicted to be favorable.
Potential legal obstacles were swept awa today when a three-judge panel of the United States Court of Appeals for the District of Columbia ruled against anti-nuclear organizations attempting to obtain a temporary restraining order to halt the launching. The groups complained that Galileo's plutonium electric-generator posed a public hazard in case of an accident during liftoff. NASA insists that its studies show the risks of radioactivity escaping in a launching disaster are virtually nil.
About 40 demonstrators marched this morning on the gate to the Kennedy Space Center headquarters. Gary L. Wistrand, deputy director of the security office, said seven were arrested when they tried to enter the restricted area and charged with illegal trespass. He said additional security patrols would be on duty until the launching to prevent intruders from getting near the shuttle. Launching Chances 'Excellent'
At a news conference today, Richard H. Truly, the NASA administrator, said the chances for launching Tuesday were ''excellent.'' Noting the many scheduling problems that have beset Galileo, and he said, ''It's been a long haul for this marvelous science mission.'' This delay was nothing, Mr. O'Neil said, ''when you consider how long we've waited already.'' Authorized in 1978, the project was almost canceled in 1981, the first year of the Reagan Administration, for budget reasons. A planned launching in 1982 was deferred because the shuttle was not ready. Galileo was set for a shuttle launching in April 1986,but after the Challenger blew up that January everything was delayed indefinitely.
So by the time Galileo does reach Jupiter, in December 1995, it will be 10 years behind the original arrival plan.
On the way, Galileo will be transmitting pictures of and data about Venus, Earth's Moon and an asteroid, but scientists will have to wait patiently until the summer of 1995 for the main events to begin. That is when the lower segment of the spacecraft, a 745-pound capsule encased in an oval heat shield, will separate and spin away on a trajectory aimed at a spot just above Jupiter's equator.
Jupiter, the largest planet, contains more mass than all the other planets combined. Its Great Red Spot, a raging storm system in the southern hemisphere, is itself twice the size of Earth. The gravity of such a massive object is a powerful force, more than 350 times Earth's gravity, and this will draw the instrument-laden capsule in at increasingly accelerating speeds.
On Dec. 7, 1995, the spacecraft will slam into the high white ammonia clouds of Jupiter's atmosphere at 115,000 miles an hour. Friction between the plunging craft and the thickening Jovian atmosphere will create a fiery shock wave reaching temperatures of 28,000 degrees Fahrenheit. But the friction's braking action will slow the craft to 100 miles an hour in only a few minutes.
By this time, the capsule will deploy a parachute and drift slowly through the brilliantly colored clouds and violent winds into the hot, dense atmosphere below. It is expected to survive for at least 75 minutes and reach a depth in the Jovian atmosphere of about 400 miles before being crushed into silence by the tremendous heat and pressure, according to predictions by designers at the Ames Research Center in Mountain View, Calif. The craft was built by Hughes Aircraft Company. Range of Instruments