Breakdown on Galileo May Limit Images of Jupiter

On the brink of its arrival at Jupiter after a six-year odyssey through the solar system, the Galileo spacecraft has developed another communications problem that may seriously impair its ability to phone home images of the giant planet.

Ground engineers are struggling to figure out why a tape recorder on board ignored a command to stop rewinding.

Meanwhile, scientists who have waited almost a dozen years to get data and pictures from the deep space voyager are crossing their fingers. Earlier, Galileo lost its primary high-gain antenna when it failed to deploy properly after launch. That reduced its ability to send back data by 30%.

If the tape recorder cannot be fixed, said Project Manager William J. O’Neil of NASA’s Jet Propulsion Laboratory, the satellite will be able to beam back only about 35% of the scientific information researchers had hoped to retrieve.

Due to arrive at its Jupiter orbit Dec. 7, the 2 1/2-ton craft has suffered through violent dust storms, a spastic camera shutter that wouldn’t stop fluttering, and a near-death experience in Congress after the Challenger space shuttle explosion led to a delay of its launch.

If the recorder breakdown is permanent, O’Neil said, “we’d have to invent a new way to get images back.” In a worst-case scenario, the spacecraft might not be able to send back any high-resolution images, although it could still send other kinds of data.

In 1991, Galileo’s $3.7-million, 16-foot-wide, gold-plated antenna, designed to open like an umbrella, became permanently stuck in a useless claw-like position.

The tape recorder was to serve as a backstop, storing data sucked up in rapid bursts during close encounters with interesting space objects. The data, stored as digital bits, would then be slowly relayed to Earth through the smaller antenna. On Earth, JPL can reconstruct the bits into images.

Without the recorder, O’Neil said, scientists will have to store the data in the main computer’s memory, “which is nowhere near as large” as that of the recorder.

Reached at a gathering of planetary scientists in Hawaii, Galileo imaging team member Clark Chapman said that people at the meeting were aware of what was going on, but he didn’t detect any panic.

“I can think of 20 times during this mission when I’ve felt the way I [did when I heard this latest news],” he said. “And most of them meant nothing.”

The loss of the tape recorder is not quite as disastrous as the initial loss of the antenna. “If we had to trade the antenna for [the] tape recorder, we’d rather have the antenna,” said Clark. “But if both of them are gone, that would be very bad.”

Images gobble up the most data space, so the ability to send back pictures would be most seriously impaired.

“The good news,” said Clark, “is we still have time.” In a scene right out of Apollo 13, engineers are valiantly fiddling with a full-scale mock-up of the tape recorder, trying to figure out how to jury-rig a fix.

The $1.4-billion Galileo, Clark points out, was built before the National Aeronautics and Space Administration’s current push to make spacecraft “smaller, faster, cheaper,” and has many backup systems. That means, he says, “they are very resilient.”

Clark remembers when the spacecraft lost its ability to control its position in space as it flew by the asteroid Ida. “If you had called and told me that, I would have thought that sounded dreadful. But they used a different procedure and it worked like a charm.”

Based on JPL’s past ability to recoup, he said, “I’m optimistic.”

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A Star-Crossed Mission?

Here are key events in Galileo’s mission to Jupiter:

1970s and early 1980s: Originally scheduled to launch in 1982 for a 1985 arrival at Jupiter, the project is delayed by a string of technical problems.

January, 1986: The explosion of the space shuttle Challenger imperils the spacecraft’s launch.

Oct. 18, 1989: After major mission redesign, craft is launched on a loopy, six-year trajectory that uses the gravity of Earth and Venus to slingshot toward Jupiter.

April, 1991: Main communications antenna fails to unfurl. (It remains only partly open.) Smaller secondary antenna is adapted to collect and store information, but fewer and lower-quality photos (2,000 instead of the planned 50,000) are expected.

July, 1994: In the right place at the right time to record what JPL calls “the cosmic collision of the decade”--as Comet Shoemaker Levy-9 hits Jupiter.

July, 1995: Releases probe that will parachute into Jupiter’s atmosphere and relay weather information for 75 minutes before being crushed in the giant planet’s atmosphere.

October, 1995: Set to begin a two-year orbit of the planet and its moons, spacecraft develops a major communications problem that may seriously impair its ability to transmit data to Earth.

Source: Times files