Tests should put Mars orbiter back in play

NASA mission controllers for the Mars Odyssey orbiter have tested a spare reaction wheel as part of the effort to get the spacecraft back to full operation. One of the orbiter's three reaction wheels stuck for a few minutes last week causing Odyssey to put itself into safe mode, a precautionary status with reduced activity, June 8, NASA's Jet Propulsion Laboratory in Pasadena, Calif., reported. Odyssey engineers, determining that the wheel as no longer reliable, said the spare reaction wheel passed preliminary tests Wednesday, spinning at up to 5,000 rotations per minute forward and backward. The spacecraft's three reaction wheels work together to adjust and maintain its orientation, as increasing the rotation rate of a reaction wheel in the spacecraft causes the spacecraft itself to rotate in the opposite direction. Three wheels at right angles to each other to provide control in all directions but the orbiter carries a fourth reaction wheel skewed at angles to all three others so that it can be used as a substitute for any one of them. "We are taking steps to assess the replacement of the troublesome wheel with the spare that Odyssey has been carrying for exactly this purpose," Mars Odyssey JPL Project Manager Gaylon McSmith said. "If the assessment results are positive, this will put us on a path toward resuming full use of Odyssey." Odyssey has worked at Mars for more than 10 years, longer than any other Mars mission in history, NASA said.