NASA's Mars Odyssey orbiter put itself into a precautionary standby status early Friday, June 8, Universal Time (Thursday evening, Pacific Time), when the spacecraft detected unexpected characteristics in movement of one of its reaction wheels. The spacecraft uses three of these wheels as the primary method for adjusting and maintaining its orientation. It carries a spare reaction wheel.

Odyssey's flight team is in communication with the spacecraft while planning actions in response to Odyssey entering the standby status, which is called safe mode.

"The spacecraft is safe, and information we've received from it indicates the problem is limited to a single reaction wheel," said Odyssey Mission Manager Chris Potts of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "The path forward is evaluating the health of the reaction wheel and our options for proceeding."

Because the trigger for the incident was limited to a reaction wheel, the spacecraft did not need to completely reboot its computer, as it had in some earlier safing incidents during its record-setting decade of service at Mars. The flight team will be developing a recovery timeline in coming days.

NASA launched the Mars Odyssey spacecraft on April 7, 2001. Odyssey arrived at Mars Oct. 24, 2001. After arrival, the spacecraft spent several months using a technique called aerobraking, which involved dipping into the Martian atmosphere to adjust its orbit. In February 2002, science operations began. Odyssey has worked at Mars longer than any other mission in history. Besides conducting its own scientific observations, it serves as a communication relay for robots on the surface of Mars. NASA plans to use Odyssey and the newer Mars Reconnaissance Orbiter as communication relays for the Mars Science Laboratory mission during the landing and Mars-surface operations of that mission's Curiosity rover.

Odyssey is managed by NASA's Jet Propulsion Laboratory, Pasadena, for NASA's Science Mission Directorate in Washington. Lockheed Martin Space Systems in Denver built the spacecraft. JPL and Lockheed Martin collaborate on operating the spacecraft. For more about the Mars Odyssey mission, visit: http://mars.jpl.nasa.gov/odyssey .