Galileo's Arrival Day---
A Celestial Celebration

Galileo's Arrival Day at Jupiter was marked by white knuckles as well as joyful relief. "Stressful," was how Galileo Engineering Office Manager Ralph Reichert described the spacecraft's long-awaited encounter. The high stakes, long hours, and Galileo's history of frustrations and successes were reflected on the tense faces of many Galileo team members and in the surrounding festivities. "I've been working on this project for 17 years," said Reichert. "Everything I've done has been waiting for this day, this critical event."

Some had worked and waited even longer in a labor of love that had involved an estimated 10,000 people in various capacities over the years. Galileo Project Scientist Torrence Johnson, who began working on the mission concept in 1974, noted that Galileo had finally arrived at Jupiter a decade later than originally planned. Johnson recalled how the Challenger accident in 1986 grounded Galileo just as it was waiting to be launched, forcing spaceflight strategists back to the drawing board. Johnson praised the "innovative billiard shots" of trajectory planners who developed Galileo's new and longer route, allowing the spacecraft to be successfully deployed by the revamped Shuttle 3 years later, headed not to Jupiter but in the opposite direction to slingshot around Venus for the first of several gravity assists.

And there were other problems that forced more workarounds. When the high-gain antenna wouldn't open properly, the Galileo team switched tactics, using Galileo's smaller antenna along with a tape recorder. Then---what else---the tape recorder stuck. "It's like watching one of those old movies, the Perils of Pauline," Johnson noted. "We've had practically everything happen to this poor spacecraft along the way."

And now Galileo's December 7, 1995, Arrival Day was here at last---a day when, if all went well, the Jovian planet would be impacted by an artificial meteor and receive a new and permanent moon called Galileo.

The odd mix of celebration and stress was understandable as employees and family, press and dignitaries, watched and waited everywhere at the Jet Propulsion Laboratory. Meeting rooms were crowded with people staring quietly at video screens. In key project offices, team members huddled over computer terminals. For many, this day was primarily a countdown to the 2 years of the discovery yet to come if all went as planned.

It was a long day. Arrival Day began officially at 6 am (PST) with the flyby of Europa and ended more than 25 hours later with the return of Galileo's signal after its occultation by Jupiter. In between were Galileo's two most critical milestones---the Probe mission, including its relay, and the insertion of the spacecraft into Jupiter orbit.

The world was watching and waiting too. Television news vans clustered at the entrance to JPL and members of the press squeezed into a makeshift press room, where mockups of earlier spacecraft were pushed aside to accommodate them. NASA Administrator Dan Goldin and astronomer Carl Sagan kept vigil along with other dignitaries, including Galileo Mission Shuttle Commander Don Williams and a scientist representing the Italian university of 17th century astronomer Galileo Galilei. Nearly 1000 guests and family swelled the JPL halls.

The first concern was the Probe, which 5 months ago had separated from the mothership to make its own suicide plunge into Jupiter. At 2:56 pm, the Probe was scheduled to slam into Jupiter's atmosphere at a speed great enough to generate heat twice that of the sun, slow to parachute speed in 2 minutes, then drop its shield and sniff out its psychedelic surroundings for 75 minutes or so before being silenced by the hostile Jovian environment. There was little margin for error (see illustration).

Learning the fate of the Probe took about one minute longer than anticipated. The evidence of telemetry lock announced by Mission Control brought jubilation to the audience. Torrence Johnson explained the excitement: "The orbiter asked the receiver on board the spacecraft 'hey, have you heard from the Probe yet?' And it said back, 'yep.'" Mission Planning Chief Jan Ludwinski, who gave the announcement to the Von Kármán Auditorium audience that a signal had been received, couldn't resist joking, "of course, we presume it's [the signal the orbiter received] from the Probe." Several days passed before it was known that the Probe had sent over 57 minutes of data before perishing, but in the meantime crossed fingers turned into hugs of elation, and NASA Administrator Dan Goldin handed out high fives like a Superbowl champ.

It was one down, one to go as the team and Galileo fans waited to hear if Galile o's main engine, a German-built 400-N thruster, had fired and kicked Galileo int o Jupiter orbit. Without the engine burn, Galileo would skitter past the giant planet, doomed to wander aimlessly in deep space. At 6:08 pm, there was more de light as news spread that the engine, dormant nearly 6 years in space (until the Orbiter Deflection Maneuver (ODM) firings last July), had again fired without a hitch at 5:20 pm and stopped as planned 49 minutes later---a perfect maneuver. The "distinct pleasure" of sharing the good news went to Galileo Project Manage r Bill O'Neil, who reported, via remote camera from the control room, "Not only are we in orbit, but we are in a very good orbit." O'Neil added that the Galile o team was "absolutely ecstatic---our two momentous events of the day are accomp lished." The 2-year, 11-orbit tour of Jupiter began. Goldin's rallying cry was "Is this a great day or what?" At Caltech, the Planetary Society hosted its own Galileo party well into the night.

Galileo---NASA's Voyager follow-on mission---was performing like clockwork. It was the lead story on most major national news broadcasts and enjoyed extensive coverage throughout Europe. Traffic on Galileo's Internet home page rose to leve ls never before seen at JPL, recording a staggering 4.7 million visits during en counter month.

On the day following the encounter, Ralph Reichert showed a rarer relaxed side. He described Arrival Day as flawless. "I'd like to just bask in the glory for awhile," he admitted, "but we have lots of work still to do."