Scientists Hope to Salvage Photos in Galileo Project : Space: Despite a stuck antenna, new techniques to transmit data may be used during the 1995 Jupiter flyby.

As last-ditch efforts loom to free a stuck antenna on the spacecraft Galileo, researchers at the Jet Propulsion Laboratory in Pasadena are preparing to face a 1995 encounter with Jupiter without the important piece of equipment.

Scientists would lose about 30% of the information they had hoped for and would be forced to wait months, rather than minutes, to receive it. “It will be like having a supercomputer and only a (slow) 300-baud modem to talk to it with,” said Torrence V. Johnson, Galileo project scientist.

Still, that prospect is a bright one compared to earlier predictions of near-total failure for the $1.4-billion Galileo project if the antenna remained incapacitated.

With new techniques, 2,000 to 4,000 photographs--instead of the 50,000 originally planned--can be obtained if the antenna remains inoperative, scientists said at a JPL press conference Thursday. Previously it was feared that all of the photos would be lost.

The craft’s instruments are collecting data well, but the high-gain antenna is needed to send the information in a radio beam concentrated so narrowly that receiving stations on Earth can quickly pick up the signals.

In October, 1989, Galileo was launched from the space shuttle Atlantis. In April, 1991, the motors that drive its gold-plated high-gain antenna were turned on. The $3.7-million contraption was supposed to open like an inverted umbrella, but only 15 of its 18 ribs unfurled. The antenna cannot work in that position.

The backup, a low-gain antenna, disperses the signals more widely, so they are more difficult to detect on Earth. The reserve antenna is 10,000 times weaker than the high-gain antenna.

Scientists have struggled to loosen the main antenna by turning the craft toward and away from the sun, alternately warming and cooling the stuck ribs. Meanwhile, suggestions have poured in from the public: Send a communications satellite to Jupiter. Use lasers to pry the ribs open. Have Uri Geller, of spoon-bending fame, train his thoughts on the hobbled craft.

In reality, scientists have concluded that they probably have only two chances left. Another round of warming and cooling maneuvers is planned late this month and in early July. If that fails to free the stuck ribs, a later maneuver is planned when the craft swings by Earth for the last time to get a gravity boost toward Jupiter and reaches the warmest point left in its journey.

As Galileo leaves the vicinity of Earth, in early 1993, the motors driving the ribs will be at their most efficient. They will be turned on and off more than 1,000 times in an attempt to force the jammed “umbrella” open.

“We are a long way from having given up,” said Galileo Project Manager William J. O’Neil. Still, said Johnson: “As time goes on, there’s less chance that it’s something easy.”

Failure after the Earth flyby, O’Neil said, “does not mean at that point that we give up our efforts, but it will change our focus” toward transmitting data by the weaker antenna as Galileo heads toward a two-year study of Jupiter and its four brightest moons.

And that means changing the way the signals are picked up on this planet. At receiving stations around the globe, JPL has reconfigured antennas and come up with new computer programs that allow researchers to halve the number of data bits needed to piece together a picture.

“There is information lost in this process, but it is negligible,” said Leslie J. Deutsch, JPL’s technology development manager for tracking and data.

Galileo has already sent some data, illustrating both the promise and the problems of using the low-gain antenna.

The newest photograph is the second from the spacecraft’s historic rendezvous with an asteroid, a rocky remnant known as Gaspra. When Galileo was 10,000 miles off Gaspra in October, 1991, its cameras snapped photos and stored them on tape.

With the high-gain antenna, Johnson said, “we could have run the whole tape back in a few hours.”

The first Gaspra photo, revealing a jagged, pockmarked object, was publicly unveiled more than two weeks after the encounter. Over a period of two to three weeks in May and June, as Galileo moved closer to Earth, the low-gain antenna transmitted the second shot, three times more detailed.

With that, scientists could estimate Gaspra’s dimensions, with roughly 11 1/4 miles dividing the furthest points on the surface seen so far. The photograph showed more than 600 craters, the largest measuring about 0.9 of a mile, apparently formed when very small objects slammed into the asteroid. Two sets of grooves on the surface are presumably the vestiges of collisions with larger objects.

There are still lots of questions about Gaspra, however, and if the high-gain antenna isn’t fixed next month, it will be December before scientists know if the answers lie on Galileo’s tape.

“Then, when it passes real close to the Earth again, we can get the rest” via the weaker antenna before the craft heads toward Jupiter, Johnson said. “But at Jupiter, we don’t have that option.”