Spaceflight Now: Breaking News

Technical snag hits Mars Global Surveyor space probe
BY SPACEFLIGHT NOW
Posted: January 27, 2001

  MGS
An artist's concept of Mars Global Surveyor. Photo: NASA/JPL
 
One of the orientation-controlling reaction wheels has failed aboard NASA's Mars Global Surveyor spacecraft in orbit around the Red Planet, the space agency says.

The craft, which concludes its primary mission at Mars next week, switched to a backup reaction wheel after the main one turned itself off. NASA says Global Surveyor continues its mapping without interruption.

Engineering data from the spacecraft indicate that an electrical short led to the automatic shutdown of the X-axis reaction wheel on January 18. Spacecraft orientation is stabilized by the rotation of three such wheels (X,Y and Z) during normal operations.

Subsequent attempts to restart the X-axis reaction wheel on January 24 lead mission engineers to believe that a short circuit caused the reaction wheel subsystem's 7 amp fuse to become permanently open, which permanently disabled the reaction wheel.

Should another wheel fail, the spacecraft would use its attitude control thrusters to maintain proper orientation much like the previous Mariner and Viking Orbiters. But that would limit the craft's useful life to the remaining propellant supply onboard.

On January 31, Mars Global Surveyor will cap its mapping mission phase having accomplished all of the planned science objectives during a full Mars year (687 days).

Over the next 14 months, continued operation of the science instruments will provide observations of potential future landing sites, make inter-annual seasonal comparisons and obtain measurements of targets selected by guest observers. Following this period, operations personnel at JPL in Pasadena, Calif., and Lockheed Martin Astronautics in Denver, Colo., expect to coax the aging spacecraft to perform telemetry relay during the landing of the Mars Exploration Rovers in January of 2004.

Global Surveyor was launched aboard a Delta 2 rocket from Cape Canaveral in 1996.