Glitch Stalls Rover’s Travels on Mars

For the second time since the start of the Mars Pathfinder mission, a whole evening of science was lost because of an eerily familiar communications snafu: When controllers on Earth tried to phone instructions to the spacecraft, it wasn’t listening.

“The phone was off the receiver,” said deputy project manager Brian Muirhead. And by the time Pathfinder tried to call back three hours later, no one was home.

By late Friday, Pathfinder was still being plagued by communications problems. NASA announced just before 11 p.m. that it had reestablished communication with the Pathfinder through its low-gain antenna. But scientists were still scrambling to determine the source of the problems.

The lost communication from Earth contained instructions for the rover Sojourner to back off the rock Yogi, where it got hung up two days ago after overshooting its target, and make another attempt to chemically analyze the bear-shaped boulder.

It was a classic case of “missed connections,” said Muirhead, who allowed that what Pathfinder really needs is an answering machine. In fact, engineers intended to install a version of that ubiquitous device Friday afternoon.

“Instead of calling blind and assuming someone will pick up, [the answering machine will] have the spacecraft say hello,” he said.

The earlier radio signals from Pathfinder and the Jet Propulsion Laboratory passed each other like blips in the night due to an 11-minute miscalculation in the intricate choreography of Pathfinder’s motions relative to the Earth’s, which change continuously.

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Pathfinder has to communicate with JPL through NASA’s Deep Space Network in Madrid. But it shares a party line with other NASA missions, including the Galileo spacecraft at Jupiter, and Ulysses, which is circling the sun.

If the spacecraft misses its communications window, it can mess up a whole day’s worth of science. JPL phones the next day’s instructions to Pathfinder in late afternoon, just in time for the spacecraft to be up and ready to work at the Martian dawn.

All in all, it’s an “intricate dance,” mission manager Richard Cook said.

The previous case of mangled communications on Mars occurred during the first day of the mission, when Sojourner’s modem wouldn’t work.

This time, researchers joked that Pathfinder didn’t listen to their instructions because it needed to rest on the seventh day of its mission, but the human partners in the mission were happy to have downtime, too.

“I think [the scientists and engineers] all appreciated it,” said Cook, “even though it wasn’t intended. Everyone got some sleep.”

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Sojourner spent the night with a wheel rolled up against Yogi. Once communications are reestablished, the solar-powered Sojourner will be ordered to crawl toward a white rock, Scoobie Doo, at its cruising speed of half an inch per second.

Because both the Pathfinder and its rover appear to be healthy, researchers say they aren’t worried about the lost time. Although the rover was designed to last seven days, and the Pathfinder mother ship 30 days, engineers say the pair could continue to send back data from Mars for months to come.