‘Gremlin’s’ Pranks Prep JPL for Worst

Before the Pathfinder spacecraft landed triumphantly on Mars, David Gruel’s mission was to screw it up.

As the project’s full-time “gremlin,” the 27-year-old engineer was assigned to come in the middle of the night to the giant sandbox that was the testing ground for models of the Mars lander and rover. Then he was supposed to make things go wrong.

Gruel was the master of his universe. Traipsing through the 30-by-50-foot sandbox, he built mounds and blocked the Sojourner rover’s path with fake Martian boulders, setting up fixes for his co-workers to try to get out of the next day.

One night, like a teenager toilet-papering a house, he draped Pathfinder’s deflated air bags over its solar panels, blocking the deployment of the rover’s entrance ramp.

That stunt brought him vilification from his flustered co-workers but also taught the crew how to fix the problem, which actually happened Friday and was being repaired Saturday.

“It made all the difference,” Gruel said of the air bag test. “We already had the scenarios for something like that occurring.”

The pranks were part of JPL’s strategy to prepare for the unexpected glitches that always crop up in planetary adventures.

“When you’re bringing something to the surface of Mars, it’s not something that’s going to go perfectly every time you try,” said Gordon E. Wood, chief engineer for mission communications on the Pathfinder project. “Any spacecraft is going to experience irregularities.”

One time, Gruel’s midnight mischief went too far, however, when he corralled Sojourner in a ring of rocks “like a cage,” said Wood. “He was a little too vicious, perhaps maliciously so at times,” but, added Wood, “we’re not mad at him anymore.”

Gruel began his duties as an official troublemaker shortly after Pathfinder’s December 1996 launch, when the crew shifted its focus to preparing for the Mars landing. An engineer at JPL since his graduation from college three years ago, Gruel had up to then worked on other aspects of the spacecraft’s development.

The spectacular successes of the U.S. space program over the decades have sometimes been pulled from the brink of failure; so much so that engineers at the Jet Propulsion Laboratory joke that JPL stands for “Just Plain Lucky.”

But in serious moments, JPL’s scientists will tell you that their luck is the result of careful planning and preparation, including worst-case scenario exercises, and designing equipment to function even after crucial components fail.

“Luck follows around people who do their homework,” said James C. Marr, a veteran JPL engineer.

One difficulty of space missions, Marr said, is that “you’re trying to design something 10 times as complicated as a car, and you don’t have an existing design. We design them from scratch.” And unlike a car, a broken Mars lander can’t be taken to the shop.

Because of that, JPL engineers design spacecraft with backup equipment and alternate operational plans in case of irreparable damage. If, for instance, Saturday’s modem problem blocking communication between Pathfinder and the Sojourner rover had not been fixed, the rover would have automatically begun to roam without directions from the lander.

Sometimes, however, solutions can be long in coming. Marr spent three years leading a team of 150 JPL staffers to repair malfunctioning communications on the Galileo space probe.

Those working on Pathfinder think that the project’s small scale may have helped it to proceed with fewer snags than larger projects. Only 50 people are operating the mission, compared to the 1,000 or so staffers who ran the larger Viking missions in the 1970s, Wood said.

Despite the project’s modest scope, the Pathfinder staff is ready for revolutionary discoveries, thanks to gremlin Gruel.

One night, he took a small potted philodendron from the hallway and placed it in a corner of the sandbox. The ground crew dispatched Sojourner to check it out.

And now, if it finds life on Mars, it will know just what to do.