Probe to Jupiter Booked for 1989; Cloud Lifts at JPL

The space agency has decided to launch its Galileo probe to Jupiter in the fall of 1989, easing apprehension at the Jet Propulsion Laboratory over a mission that has nearly died several times since the space shuttle Challenger exploded in a fireball over Florida in January, 1986.

The decision by the National Aeronautics and Space Administration to commit itself to the launch, despite fierce competition for space aboard the shuttle, was precious news to scientists at the laboratory, located in the hills near Pasadena, who had refused to back down in the face of almost impossible odds.

Because of limitations on spacecraft that can be launched from the shuttle in the post-Challenger era, project scientists plan to fly Galileo past Venus once and the Earth twice, using the gravity of both planets to slingshot the probe out to Jupiter.

For the first time in more than a year, scientists associated with the often-periled project can now see success on a distant horizon.

“This mission has been threatened more times than Pauline on the railroad tracks,” said Torrence Johnson, Galileo project scientist, who was informed this week that the mission will finally fly in October or November, 1989.

But Galileo will not be able to fly directly from the shuttle to Jupiter, as originally planned. Instead, it will have to follow a tortuous bit of trajectory that came about because Galileo will have to use far smaller rockets than originally planned, the Space Age equivalent of trying to power a Rolls-Royce with an outboard motor.

1995 Arrival

And it won’t get there in 1988, its original schedule, but when it does finally arrive in late 1995, Galileo will begin orbiting Jupiter for a two-year tour that will include close flybys of its moons, including Io, the most volcanic body in the solar system and a source of fascination for scientists and laymen alike.

The probe will pass within about 100 miles of Europa, another of Jupiter’s moons, and “that’s really skimming the treetops,” Johnson said.

That payday will come after six years of whipping through the solar system, including two passes by the Earth, one at only about 150 miles out. That is close enough to cause some concern over the possibility of colliding with space debris and other objects orbiting the Earth, although project officials insist they can guide the two-ton probe out of harm’s way.

“There are a lot of white-knuckle times during this mission,” Johnson said.

The hardest time of all came in January of last year, when JPL officials were enjoying one of their greater triumphs, the Voyager encounter with Uranus. On the last day of that historic flyby, the Challenger exploded, killing all seven crew members and placing the U.S. space program on hold.

Galileo had been scheduled for launching from the shuttle in May of that year, four months after the disaster, but the Challenger episode turned out to be only one of many serious threats to the Jupiter mission.

A Harder Look

A stunned NASA began taking a harder look at all of its operations, and when top officials looked at Galileo, they didn’t like what they saw.

Once released from the shuttle’s cargo bay, Galileo was to be powered by liquid-fueled Centaur rockets powerful enough to send it all the way to Jupiter on a direct course. But there had always been some uneasiness about carrying liquid rockets in the shuttle’s cargo bay and, in the era of post-Challenger sensitivities, NASA lost little time in ruling out the Centaur for launches from the shuttle.

That left Galileo with a major scientific mission, but no way to get there.

After a trip back to the drawing boards, JPL proposed launching Galileo from the shuttle by using powerful solid-fueled rockets like those used to send some heavy satellites into high Earth orbit. That proposal looked for awhile like it would fly, but in what one JPL official described as a “thunderbolt,” NASA turned it down.

The reason: The larger rockets would have made the payload too heavy. The shuttle would have been light enough to take off, but it would have been too heavy to land if an emergency forced it to return without deploying the satellite.

Bleak Days at JPL

That was a problem virtually no one at JPL had anticipated, and some officials at the lab are still stunned by the development.

Those days were among the bleakest in years at JPL. Rumors even surfaced that the Soviets had offered to launch Galileo, but the offer was rejected because it would be like “tearing the stars off the American flag,” John Casani, Galileo project manager, told a staff meeting. Casani insisted later, however, that the offer was not serious, and he did not mean for anyone to believe it.

Yet several people who attended the meeting said they did believe it, although there is no evidence that Casani was doing anything other than trying to cheer up the troops with a little patriotic hype. The fact that some believed the story, however, tells something about the sense of desperation at JPL at that time.

No Way There

A project that many scientists had worked on for years was in great jeopardy because it was left “without a way to get to Jupiter,” as Johnson put it.

“What bailed us out was some creative work by Roger Diehl, one of our design people,” Johnson said. “He started fooling around with other trajectories, trying to find any way to get to Jupiter.”

Diehl calculated that with a much smaller solid rocket booster, it would be easy to ship Galileo off toward Venus by simply slowing its speed so that it would, in effect, drop into the lower orbit of Venus, which is closer to the sun than the Earth’s orbit. By tapping something called “gravity assist,” an orbiting technique that has been used extensively during the last 20 years, Galileo could use the gravity of Venus to boost its speed as it whipped around the planet and headed back toward Earth.

The Earth’s gravity, in turn, could be used to boost the speed of the spacecraft still farther. Two loops around the Earth, and Galileo could be sent on toward Jupiter with enough speed to get it there in late 1995.

There is still some concern about the close approach to Earth, because Galileo’s electrical system is powered by radioisotopes, and if the spacecraft were captured by the Earth’s atmosphere and plunged to the ground it could spread radioactive material over a wide area.

Special Precautions

“We are taking special precautions to ensure that will not happen,” said William O’Neil, Galileo’s mission design manager. By aiming at a point well outside the Earth’s atmosphere, there is “not one chance in a million that we would have an atmospheric entry,” he said.

The close approach to Earth is “duck soup compared to what we’ve already accomplished at Mars and Venus” with other space probes, O’Neil said. “Any of them were more difficult than this thing we’re going to do with Earth.”

The “white knuckles,” however, don’t end there.

Galileo will be aimed directly at Jupiter so that a probe can be parachuted into the planet’s atmosphere, sending back data on its chemical composition, temperature and density.

At the last moment, Galileo will have to fire its rockets again to just barely miss the planet. After that, it will use the gravity of Jupiter’s four giant moons as the primary force controlling its course. Johnson described that maneuver as “a 12-cushion billiard shot.”

‘Spectacular Look’

Two predecessors of Galileo, Voyagers 1 and 2, sent back spectacular photographs of the Jovian system, but Johnson expects much better data from Galileo, partly because it will pass so close to the planet and its moons.

It will pass within about 600 miles of Io, “20 times closer than Voyager,” Johnson said. “That will be one spectacular look at Io.”

Io is about the size of our own moon, but it pulses with volcanic activity, pumping more than a ton of ash into space every second. Long mystified by why such a small body should be so active, scientists are concluding that the violent tug and pull of Jupiter and the other moons subjects Io to tidal forces, heating its core.

The volcanoes are so active that “we can actually measure the heat energy with telescopes on Earth,” Johnson said.

During its projected two-year travels through the Jovian system, Galileo will send back thousands of photographs and enough scientific data to fill a few warehouses.

As he sought to describe the significance of all that, Johnson called on a term he used often during a lengthy interview this week at JPL.

“It’s going to be spectacular,” he said.