ROANOKE TIMES 
                      Copyright (c) 1995, Roanoke Times

DATE: Thursday, December 7, 1995             TAG: 9512070065
SECTION: NATL/INTL                PAGE: A-16 EDITION: METRO 
DATELINE: SEATTLE
SOURCE: BILL DIETRICH SEATTLE TIMES 


6-YEAR JOURNEY REACHES JUPITER

GALILEO GALILEI, whose telescope spotted the first four Jupiter moons in 1610 after building a crude telescope, would no doubt be impressed.

The Galileo spacecraft mission to Jupiter has been dogged with bad luck and patched with long-distance scientific ingenuity.

The payoff for persistence is to come today, when Galileo climaxes its six-year, 2.3 billion-mile journey. That's when a probe it released in July enters Jupiter's atmosphere. At the same time, the mother craft begins a two-year elliptical orbit of the gas planet.

While a stuck antenna means Galileo will return only 1,500 photographs to Earth instead of the 50,000 originally intended, planetary scientist Torrance Johnson of NASA's Jet Propulsion Laboratory estimates the $1.46 billion mission will complete at least 50 percent of its original objectives.

Included will be the first exploration inside Jupiter's atmosphere; close-up examination of four of its moons; and detailed examination of its powerful magnetic field, its radiation, and dust.

Because smaller surviving antennas take so long to transmit, initial data from the atmospheric probe may not be available until Dec. 19. Pictures from the main craft may not appear for months.

For scientists who have been working on planning and building Galileo for 20 years, however, a bit more time hardly matters. As University of Idaho electrical engineer David Atkinson, who started working on Galileo's probe in 1981, notes, ``Of all the principal investigators on the probe science team, I'm the youngest.'' He is 40.

First scheduled for launch in 1982, Galileo was not sent on its way until 1989 after problems with the space shuttle and booster rockets. Still lacking a powerful booster, the spacecraft had to be sent on a long, looping six-year-long course instead of flying directly to Jupiter. The roundabout course used the gravity of the inner planets to fling the spacecraft that far.

Astronomers have persisted because the gas planet is a wonderfully weird place to visit. As big as 1,400 Earths, it is only one-quarter as dense because it is made primarily of hydrogen (89 percent) and helium (10 percent), the gases used to lift airships and blimps.

Scientists believe the planet has no surface we can easily visualize, but rather its atmosphere gradually condenses with depth into a hot liquid, a churning sea of hydrogen penetrated by a constant rain of heavier helium. Huge lightning bolts flash in its upper atmosphere. Its Great Red Spot, centuries old, is a hurricane as big as three Earths.

The hydrogen ocean eventually becomes dense enough to act like a stewing metal, providing the electrical conductivity to generate the most powerful magnetic field of the planets. There may also be a hard core the size of several Earths at Jupiter's center.

Jupiter is in essence a star that never became big enough to ignite, but it still radiates more heat from its interior than it receives from the sun, possibly from the energy of its own gravity.

Containing 70 percent of the total mass of all the planets in the solar system, Jupiter is like a miniature solar system itself, surrounded by 16 moons. The planet's atmosphere is also believed to be a time capsule, the best surviving example of the nebula of gas and dust from which the solar system originally formed.

In July 1994, Jupiter was also the site of the biggest comet collision ever recorded, when Comet Shoemaker-Levy slammed into its atmosphere. Galileo took pictures of the resulting atmospheric explosions.

That bit of serendipity was typical of the mixture of good and ill fortune that has accompanied Galileo. It was supposed to be launched by the space shuttle in January 1982.

Shuttle and booster problems pushed that back to 1986, and then the space shuttle Challenger blew up.

Meanwhile, Galileo - trucked from California to Cape Canaveral, Fla., before the Challenger explosion - was trucked back to California while space missions were put on hold and then trucked again to Florida for its 1989 launch from the space shuttle Atlantis. Scientists believe all those road miles jostled Galileo's graphite lubricant. On April 11, 1991, when they tried to deploy the spacecraft's main antenna, it stuck.

The deployment motor was turned on and off more than 13,000 times and the spacecraft was sent tumbling in hopes it would jar loose, but nothing worked. Instead of being able to transmit about a picture a minute at 134,400 bits per second, Galileo is limited to a smaller antenna transmitting at best 1,000 bits per second, even after ingenious software enhancements beamed from Earth to the spacecraft.

Even with the problems, Galileo's six-year transit to Jupiter has had some benefits.

On Oct. 29, 1991, it became the first spacecraft to make a close pass of an asteroid.

Galileo flew by the Moon in 1992, better mapping its North Pole.

In 1994 Galileo was in a position to photograph the comet Shoemaker-Levy.


LENGTH: Medium:   93 lines
ILLUSTRATION: GRAPHIC:  Charts & illustrations (4) by AP (ran on A-9). color. 


































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