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(NASA)

When Spacecraft Misbehave

Engineers get creative when the error message comes from 50 million miles away.

Hayabusa

(NASA )

From the very beginning, Hayabusa was plagued with problems. The spacecraft, launched by the Japan Aerospace Agency (JAXA) in May 2003, had a bold mission: Rendezvous with the asteroid Itokawa, 200 million miles away, collect a piece of it, and bring it to Earth.

Just a few months into its two-year voyage to Itokawa, a solar flare hit Hayabusa, severely damaging its solar batteries. The reduction in electricity hindered the efficiency of the spacecraft’s ion engines, delaying arrival by three months. Hayabusa’s relatively small target was racing through space at 57,000 mph, and since the spacecraft had to leave Itokawa by November 2005 to be on the proper orbital path to reach Earth, the delay forced engineers to recalculate the probe’s trajectory and shorten its stay.

Shortly before the probe arrived at Itokawa, two of its four reaction wheels failed. Loss of these fuel-conserving attitude adjusters forced the team to make creative use of the chemical thrusters to maintain its orientation. “There were some long days and a few sleepless nights wondering if the spacecraft would survive,” says Don Yeomans, a scientist at the Jet Propulsion Laboratory and member of the Hayabusa team.

By September 2005, Hayabusa was on final approach to Itokawa. The plan was for the spacecraft to release its grasshopper-size mini-lander, MINERVA, to collect data and images from the surface. The main spacecraft would then approach and bump the asteroid to kick up and capture particle samples. But because of the communications delay due to Hayabusa’s distance from ground control, the command to release MINERVA arrived just after the main spacecraft’s automatic altimeter fired its thrusters to keep the craft away from the asteroid. Result: It was too high for MINERVA’s launch. The tiny lander drifted off into space. (contd.)

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