Posted: Sat, Jan 27, 2001, 12:45 PM ET (1745 GMT)
A short circuit has disabled one of the reaction control wheels on NASA's Mars Global Surveyor (MGS) spacecraft, but officials say the problem should not adversely affect the mission. One of the three wheels used to control the orientation of the spacecraft failed without warning on January 18, according to a mission status report issued Thursday. The spacecraft immediately switched to a backup wheel, allowing operations to continue as normal while ground controllers worked to resolve the problem. Engineers now believe that the wheel failed when a short circuit zapped a fuse into an open position, permanently disabling the wheel. The loss of the wheel is not considered to be a major problem as even if a second wheel malfunctions the spacecraft can maintain its orientation with attitude-control thrusters. MGS's primary mission -- 687 days, or one Martian year, in its prime mapping orbit -- will come to an end next week, but the spacecraft will continue to conduct observations for 14 months as part of an extended mission. Project officials also hope to use the spacecraft as a communications relay for the two rovers scheduled to land on Mars in early 2004.

Related Links:

•  MGS status report for January 25, 2001