Bug of the Month

Man Finds Bugs on Mars

Jason Krause

Wherever a computer goes, bugs are sure to follow. When the Mars Pathfinder developed a glitch, NASA had to somehow upload new code without losing valuable time needed for exploration. The most confounding bug on the Pathfinder mission appeared July 10. Steven Stolper, software engineer for the Mars Pathfinder, calls it "one in a million, insidious, and hard to replicate." The snafu arose because the OS, Wind River's VxWorks, developed a mutual-exclusion problem: A low-priority function (in this case, recording weather) interfered with the system's multi-tasking schedule. The system couldn't finish all the tasks it neede d to, missed a real-time deadline, and then shut itself down. "It's a kind of interplanetary Control-Alt-Delete," says Stolper. "When things go wrong , the system goes into a power-safe mode and waits for ground control to help out." Without a fix being implemented, this problem would replay itself over and over.

To identify the bug, engineers recreated the malfunction on Earth, identified the offending subroutine, and uploaded the binary difference between the new code and the buggy code on the Pathfinder.

Send yours to jkrause@mgh.com

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No More to Go A'Rovin

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Pathfinder bugs inhibited the Rover.