The battered but undefeatable space explorer

Even in its final moments, Galileo went down fighting.

On Sunday morning, as the aging spacecraft swept headlong into the crystalline clouds of the Jovian night on its final, kamikaze mission - taking far more radiation than was ever intended and only seconds away from disintegrating into a fireball of priceless parts - it was still broadcasting a signal to Earth. It was still taking measurements, still collecting data.

To those who worked on the 14-year mission, and who gathered here on a bright late-summer day at NASA's Jet Propulsion Laboratory to mark its conclusion, it was the only appropriate ending.

To each, Galileo was something different and precious: The discoverer of lava lakes more than 120 miles wide on one of Jupiter's moons, or of what could be a vast ocean of water on another - perhaps the most promising spot in the solar system for extraterrestrial life. To all, though, Galileo was a survivor.

Originally scheduled to launch in 1986, the program was nearly killed by the delays following the Challenger disaster. That forced scientists to devise a new way to get Galileo to its destination. But before it arrived at Jupiter, the antenna designed to send scientific data back to Earth broke.

When team members jerry-rigged a way to circumvent the antenna by using an onboard recorder, the tape jammed.

They are tales of triage worthy of the Mir space station, performed by the keystrokes and number-crunching of engineers a half-billion miles removed from the circuit boards they needed to fix. As such, the story of Galileo is not one solely of science. Especially after the Columbia disaster, when NASA's culture has been so deeply criticized, Galileo also harks back to the ingenuity and possibility that characterized early American spaceflight.

"Galileo serves to redeem our faith in NASA," says John Wood of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

Scientists quote a list of Galileo's firsts: the first spacecraft to orbit one of the solar system's outer planets, the first to dispatch a probe into the atmosphere of one of the gas giants, the first to image an asteroid.

But in Sunday's spectacular mission end, project manager Claudia Alexander could see evidence of perhaps its greatest achievement. After all, the decision to ditch Galileo into Jupiter's atmosphere - burning it up in a funeral conflagration worthy of Viking legend - was not the original plan. It only became part of the plan after Galileo discovered ice covering the moon Europa. With evidence to suggest that there might be liquid water beneath - and perhaps primitive life - project members decided that if it were left to wheel around Jupiter rudderless and without fuel, it could crash into Europa, contaminating the environment.

"The results [of Galileo's science] were so compelling that we had to destroy the spacecraft," says Dr. Alexander. "That's a wonderful epitaph."

Beyond Europa, Galileo has relayed other vital information. For example, Ganymede, the largest moon in the system, is also the only moon with a magnetic field, suggesting that its interior - like Earth's - is curiously still active. Moreover, Ganymede and neighbor Callisto seem to have liquid oceans, though they appear to be buried deeper than Europa's.

Yet it is tortured Io that sends volcanologist Rosaly Lopes into raptures. The most volcanic object in the solar system, Jupiter's innermost major moon is wrenched so violently by the gravitational forces of Jupiter and Europa that the moon disgorges is molten core through volcanoes which can send plumes 300 miles into the atmosphere.

Sitting in an office with a promotional poster of the film "Volcano" on her wall, Lopes explains that the daily radiation on Io is 4,000 times the lethal dose, and it is almost as if she is disappointed that this makes a weekend trip impossible.

What she has learned from Galileo sends her scurrying to all corners of the room in excitement. A chart shows that lava on Io is hotter than lava on Earth, confounding theories that lavas cool as planets evolve. Diagrams on her computer show some of the more than 100 volcanoes Galileo discovered. A photo in a magazine retrieved from a bookshelf shows an eruption captured by Galileo's instruments.

On Page 7 of last March's "Planetary Report," the November 1999 image seems no more remarkable than any of the surrounding pictures. But it occupies a unique spot in the broader story of Galileo. It is proof, laid out pixel by pixel, of the Galileo program's ability to press the limits of possibility.

Kathryn Schimmels remembers getting the call just as she had dipped her spoon into the Thanksgiving Day mashed potatoes: Galileo had shut down.

Galileo's science coordinator knew the consequences all too well. In six hours, Galileo would pass by Io on a mission designed specifically to study the moon. In short, Dr. Schimmels and her team had just hours to fix the problem or face the prospect of losing all data from the flyby - or worse, losing Galileo entirely.

While these shut downs - intended to protect the spacecraft when it sensed a potentially fatal error - were not unusual, designers had expected the recovery time to be as long as a month.

In essence, they had to reboot the spacecraft and manually retype every command sequence - without a single error - telling every scientific instrument what to do at what moment in the flyby. And they had to send it 52 minutes ahead of time, given that each command takes 52 minutes to reach Jupiter from Earth.

Current project manager Alexander remembers confirming her equipment's sequence strings over the phone from her relatives' home in the Bay Area while chasing a nephew who had stolen dinner rolls from the kitchen table.

To Bruce McLaughlin, this is Galileo's greatest legacy. As an engineer, he acknowledges that his interests tend toward the technical. But his enthusiasm for the work he and his colleagues did on Galileo, and the broad smile that breaks out on his bearded face is more third-grade recess than grad-school physics. "At a distance of a half-billion miles, we were able to take this ancient set of computers, and we were able to do pretty remarkable things with them," says McLaughlin.

Galileo's technology was designed before the first IBM personal computer hit the market two decades ago. By the time the probe neared Jupiter its technology had to be completely reshaped.

The high-gain antenna was intended to be the only way to relay scientific data to Earth, at a rate of one image a minute. When it didn't unfurl, McLaughlin and others reprogrammed an onboard tape recorder - designed for a completely different purpose - to store scientific data until it could be sent out on the low-gain antenna, which could only manage the equivalent of one picture a month. Shortly after, the tape stuck, and engineers had to teach it to not rewind all the way to the damaged beginning of the tape.

"[Galileo] probably had one of the largest quantity of mission-altering issues we've had to deal with," says McLaughlin.

Yet as Galileo hurtled toward its demise Sunday, it not only kept talking to mission control here in this wooded notch of the San Gabriel Mountains, but it also stubbornly kept sending data until the very end.

Only an hour before it vaporized, engineer Paul Fieseler hopes, Galileo peered at a tiny moon called Amalthea. If all went well, the data might explain flashes of light seen earlier in the mission - perhaps evidence that Amalthea is breaking up or that it's orbit coincides with an inner ring around the planet.

In a time when NASA is increasingly targeting more modest goals at a more modest price, the resilience of the $1.5 billion spacecraft shows that there is still a place in the space program for flagship missions, he says.

And while the recent criticism of NASA has stung workers even here, the mood on this last day of Galileo was buoyant. Members of the program counted down the last 10 seconds of the mission then broke into applause.

"I just don't feel the character of the NASA is different than it was in the early days," says Alexander. "Anyone who participated with Galileo knew the innovation that we used on our mission."