Article Posted on : - Jul 01, 2010

NASA's Dawn spacecraft, illustrated in this artist's concept, is propelled by ion engines: NASA/JPL photo

PASADENA, CALIFORNIA (BNS): Engineers are studying the reaction wheels on NASA's Dawn spacecraft after automatic sensors detected excess friction building up in one of them.

Reaction wheels spin to help a spacecraft maintain attitude control, and Dawn, which is exploring the asteroid belt, uses three wheels in normal operations.

The three other reaction wheels are functioning normally. Mission managers said plans for Dawn to visit the asteroid Vesta in 2011 and 2012 and dwarf planet Ceres in 2015, will not be not affected.

"We're looking at the data carefully in order to understand what the long-term prospects are for this reaction wheel," said Marc Rayman, Dawn's chief engineer.

"In the meantime, we're continuing our planned activities with the spacecraft," he said.

Flight controllers had uploaded software to Dawn's primary flight computer on June 15. As a planned part of that activity, all four reaction wheels had been powered on.

Two days later, while the spacecraft was not performing any science or engineering activities, the one reaction wheel built up excess friction. The spacecraft's fault protection system acted as designed and turned the wheel off, NASA said.