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Venus Probe's Grand Finale: a Fiery Fall Into Planet : Science: A final lesson is sought in Magellan's destruction. Four-year trek called profoundly revealing.


Behind three locked security doors in a windowless operations room at the Jet Propulsion Laboratory, James M. Stewart patiently is arranging the destruction of a $900-million spacecraft.

The NASA craft, called Magellan, is orbiting Venus. Since its arrival at the evening star in 1990, the probe has overcome repeated misfortunes and transmitted to Earth a revealing portrait of a seared planet pockmarked by towering volcanoes and etched by sinuous canyons longer than the River Nile. Because of Magellan, scientists have come to know the planet in more detail than they do parts of Earth.

Now the spacecraft has faltered. Its solar power sails, alternately frozen and broiled every day for four years, are coming apart. Power is falling to dangerous lows. Money to carry on the mission has diminished steadily.

Rather than turn off its transmitters and abandon the craft, the mission team decided that there could be one last thing to learn about Venus from a spacecraft's fiery fall from grace.

On Tuesday the craft will be ordered to begin a fatal plunge into the planet's dense, acidic atmosphere. Scientists hope that they can learn more about aerodynamics in the superheated sulfuric mist enveloping the planet, as the thick gases pull at the spacecraft.

Presiding over a planning meeting this week, mission director Stewart listened stolidly as, amplified on a speaker phone, a disembodied voice from Denver argued with a voice from Washington about how best to nurse the damaged spacecraft until then.

There was no joy in the debate. Project manager Douglas G. Griffith interrupted the technical discussion. "We are trying to live long enough to get to our funeral," he said sardonically.

The impending destruction of Magellan is a bittersweet ending to what scientists say is one of the most successful missions in the history of space exploration.

"Magellan was responsible for a very profound revelation of the planet," said Clark Chapman, a senior scientist at the Planetary Science Institute in Tucson, Ariz. "It showed a wealth of surprising features, toppled a bunch of hypotheses and showed us more detailed geological mapping than for any other planet, including our own."

The Magellan mission has returned more information than all other U.S. planetary missions combined. And, because they have been recorded on small computer CD-ROM disks instead of bulky computer tapes, its images have been more widely distributed.

Many high school science teachers have a set for their students. The images are even on the Internet.

Yet surprisingly few scientists will be able to analyze the data in detail because funding for planetary studies has dwindled, scientists said.

Last week, the Venus data analysis program was canceled. Next week, a special panel of NASA officials and their science advisers plan to meet to consider funding cuts of up to 20% in the agency's entire space research and analysis program, to free up money for other projects, agency officials said.

In all, NASA allocates about $90 million a year for the study of all the data gathered from 25 years of planetary missions--barely a quarter of the cost of a single space shuttle flight.

Some space scientists are dismayed that the funding for studying the data Magellan gathered at Venus is vanishing just when they are beginning to understand the fundamental features of the planet.

"A lot of really interesting discoveries about Venus now are only beginning to come home, especially in the question of how Venus works in comparison to Earth," said Victor Baker, a professor of geosciences and planetary science at the University of Arizona who has been involved in NASA's exploration of the solar system since the early 1970s.

Since its inception more than a decade ago, the Magellan mission has taxed the ingenuity of JPL engineers and scientists to the limit.

Magellan began as an act of recovery when the Ronald Reagan Administration canceled a more ambitious Venus mission to save money. JPL mission planners then created Magellan as a replacement from spare parts and leftover antennas. Delays caused by the space shuttle, which launched the probe in 1989, swelled the program's cost.

When the spacecraft arrived at Venus in 1990 after a perilous 15-month flight, it vanished--just as the space agency's $900-million Mars Observer space probe would do during its approach to the red planet last year.

Unlike the Observer, Magellan resurfaced. Fourteen hours after Magellan disappeared from their screens, JPL operations engineers re-established contact. Griffith remembers the loss of Magellan's signal as the single worst moment in a mission filled with emergencies. Four more times, the spacecraft vanished during the mission, only to be recovered by imaginative acts of engineering millions of miles away in Pasadena.

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