This is an artist's concept of the Mars Reconnaissance Orbiter during its critical Mars Orbit Insertion process. NASA's Mars Reconnaissance Orbiter is headed into a perilous phase after a seven-month journey from Earth, aiming to start looping around the Red Planet on March 10, 2006, space agency officials said on Friday. (NASA/JPL/Reuters)

NASA's Mars Reconnaissance Orbiter is in safe mode after its computer unexpectedly rebooted, likely as a result of the spacecraft being hit by a cosmic ray or solar particle.

The agency said this is the sixth time the orbiter has gone into safe mode since it began its primary science mission in November 2006. The spacecraft's computer enters safe mode automatically in response to any condition its programming does not comprehend.

NASA said the rebooting Wednesday night resembled an event on Feb. 23, which engineers concluded was triggered by a cosmic ray or solar particle hitting the orbiter's electronics, causing an erroneous voltage reading.

"The flight team is cautiously bringing the orbiter back to normal operations," Jim Erickson, project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif., said in a statement. "We should be resuming our exploration of Mars by next week."

Erickson said the spacecraft is continuing to beam home high-rate engineering data and is otherwise in good condition.

The $720-million US orbiter successfully completed its initial two-year mission in the fall of 2008. Its Mars survey has been extended through at least 2010.