The Spacecraft That Could
Vindication can be a long time coming -- as the beleaguered and belittled engineers sweating out the flight of the spacecraft Galileo know all too well. Like its astronomer namesake, the craft has endured a veritable Inquisition. Its first Torquemada appeared with the 1986 Challenger explosion. The spindly 2.5-ton craft was supposed to be released from a later shuttle and rocket directly to Jupiter on a liquid-fueled Centaur, but astronauts re-belied at carrying what amounted to the world's biggest Roman candle in their cargo bay. NASA had to sub a wimpy, solid-fuel rocket, requiring Galileo to take the scenic route: it swung past Earth twice and Venus once (diagram) to gain speed from those planets' gravity. Then the real torture began. In 1991 Galileo's main data-transmitting antenna refused to unfurl, behaving like a recalcitrant, 16-foot umbrella; three of the 18 ribs are apparently stuck together and the antenna remains a useless tangle of metal mesh. Then, this October, a data recorder failed to stop rewinding; now part of it can't be used. Galileo, which project director Neal Ausman of NASA's Jet Propulsion Laboratory calls "the most demanding planetary mission ever launched," was shaping up to be the little spacecraft that couldn't.
But vindication for the $1.6 billion mission finally came last week, and when it came, it came gloriously. After a 2.3 billion-mile trip, the battle-scarred Galileo and a little acorn-shaped Probe that had been severed from the mother ship on July 12 got within 150,000 miles of Jupiter's cloudtops. Ten minutes after this closest approach, the 2.8-foot-high Probe plunged like an aluminum meteor into Jupiter's atmosphere for an unprecedented kamikaze mission: for the first time, an emissary from Earth had entered the atmosphere of a planet beyond Mars. The Probe streaked through the swirling, daffodil-and-lemon-colored cloudtops at 106,000 miles an hour, fast enough to fly from Washington, D.C., to San Francisco in 100 seconds. The speed generated so much friction and hence heat -- 28,000 degrees Fahrenheit -- that the descent was like flying through a nuclear fireball. After 113 seconds the craft, designed by NASA's Ames Research Center, deployed two parachutes, shedding its heat shield. That exposed an inner module to the hellish environment around it and allowed the six on-board instruments to take the measure of Jupiter's atmosphere: how hot it is, how dense, how sunny and how lightning-slashed. Perhaps most important, the Probe measured what Jupiter's atmosphere is made of. It is thought to be the same stuff from which the solar system formed, and so should offer clues to its beginnings.
Like an injury-plagued athlete who pulls it together for the Olympics, the Probe performed flawlessly. Or so the mission team hopes. In fact, the reality of last week's events was of the virtual sort. Data received by Galileo from the Probe will be downloaded to Earth this week, so until then scientists don't know how long the Probe survived, much less what it discovered. But in all likelihood it lasted a mere 75 minutes before friction and pressure crushed and vaporized it. Invisible to the scientists at the JPL in Pasadena, a hard rain of aluminum, titanium and carbon with a pinch of gold, silicon and germanium then fell to the gaseous "surface" of Jupiter. "They become part of the atmosphere of Jupiter itself," said JPL chief of mission planning Jan Ludwinski.
Galileo had to execute its own white-knuckle maneuver. During the Probe's suicide dive, Galileo fired its rockets for 49 minutes, slowing enough to be captured by the gravity of Jupiter for a planned 11 looping orbits of the planet. By all indications Galileo had put itself "not only in orbit but in a good orbit," said project manager William O'Neil of the JPL. "We're ecstatic." The first spacecraft to circle a giant planet for an extended time, Galileo will probe Jupiter's weather, photograph four of its 16 moons, investigate what makes its winds alternate direction and try to figure out what creates its colors. By November 1997 the mission will go dark and silent, as Galileo's nuclear fuel becomes depleted and radiation fries its electronics.
Computer upgrade: All this is possible only because NASA's space jocks performed the equivalent of a long-distance brain transplant. After losing the main antenna, Galileo had to rely on a backup that normally transmits no more than 16 bits per second, compared with the main antenna's 134,000. At that rate, scientists would have been receiving Galileo's data for years -- not an inviting prospect given the lousy job security at NASA these days. So, starting in March, the ground team re-programmed Galileo's computers to compress the data they sent and eliminate the boring stuff (like black pictures of empty space). Such a maneuver had never been attempted before, says the JPL's Walt Hoffman, who likens it to "upgrading your word processor while you're using it." For 26 days the computer team radioed up digital code that rewrote on-board software. It was a feat akin to sending instructions over your modem in San Jose to reprogram a computer in Tokyo--except that this computer was speeding through space at 18,000 mph. The fix upped the data rate to 160 bits per second. That should allow Galileo to accomplish about 70 percent of its goals, though it will send no more than 4,000 photos instead of the 50,000 once planned. And not until July '96.
In the 20 years since Congress funded Galileo, four team members have died and 80 have retired. Young hotshots are now white-haired eminences, their numbers augmented by women and minorities, their specialties as much cyber as space. As Galileo pulled it out last week, the team at the JPL erupted in cheers, applause and raised fists. At least one wiped a tear from his eye. As Galileo Galilei told his inquisitors more than 300 years ago, it still moves.
Originally slated for launch in 1982, Galileo didn't get underway until 1989, and then had to take a long, winding road to Jupiter to gain speed from Earth's and Venus's gravity. The craft passed and studied the asteroids Ida and Gaspra, and released a "Probe" last July.
Aug. 28, 1993 Ida flyby
Feb. 10, 1990 Venus flyby
July 12, 1995 Probe separates from Galileo, beginning solo
flight to Jupiter
Dec. 7, 1995 Galileo enters orbit around Jupiter; Prove
makes suicide dive into Jovian atmosphere
Oct. 18, 1989 Launch from space shuttle
Oct. 29, 1991 Gaspra flyby
Probe deploys parachutes that rip off heat shield, exposing instruments in descent module
Probe plunges an estimated 400 miles, taking data on Jupiter's atmosphere
Galileo begins first of 11 looping orbits of Jupiter, which will last until November 1997, to study the planet and four of its moons