Communications of the ACM
My $500M Mars Rover Mistake: A Failure Story
A large pulse of electricity had gone somewhere other than intended, and telemetry had stopped coming from the spacecraft.
A February evening in 2003 started out routine at NASA's Jet Propulsion Laboratory in Pasadena, CA. I gowned up in cleanroom garb and passed into the High Bay 1 airlock in Building 179 where nearly all of NASA's historic interplanetary spacecraft have been built. After years of work, there were only two weeks remaining before the Spirit Mars Rover would be transported to Cape Canaveral in Florida for launch ahead of its sibling, Opportunity.
The rovers, between them, had 62 brushed-type motors. That night, while my colleagues focused on testing the rover itself, I was tasked with verifying the integrity of the motors in the Rock Abrasion Tool (RAT) attached to the end of Spirit's robotic arm.
Disassembling and inspecting motor components after each round of environmental testing is not practical. However, we can check their internal condition by examining their electrical performance.
Inside the cleanroom, we ran our pre-test confirmation routine. With everything in order, the reference motor was removed and we jumpered-in Spirit's RAT-Revolve motor. The testing steps were confirmed one last time, and we had a green light for pulsing the waiting motor with energy.
The pulse was sent to the motor. As always, the result was immediate, but this time, alarmingly unfamiliar. The strip chart did not look like anything we had seen before. It did not even look like a broken motor. It was decidedly — something else. My mind raced for explanations and in what seemed like an instant, arrived at the most likely explanation. All that power we just released did not go into the RAT-Revolve motor. Due to a mistake I had made with the break-out-box, it went the other direction on the connector interface, sending a surge of electricity straight into the spacecraft, instead of the motor.
From Chris Lewicki
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