Nasa Engineers Resolved Spacecraft Computer Issue

Engineers have found the root cause of a computer reset that occurred two months ago on NASA’s Mars Science Laboratory and have determined how to correct it. The fix involves changing how certain unused data-holding locations, called registers, are configured in the memory management of the type of computer chip used on the spacecraft. Billions of runs on a test computer with the modified register configuration yielded no repeat of the reset behavior. The mission team made this software change on the spacecraft’s computer last week and confirmed this week that the update is successful. The reset occurred November 29, 2011, three days after launch, during use of the craft’s star scanner. The cause has been identified as a previously unknown design idiosyncrasy in the memory management unit of the Mars Science Laboratory computer processor. In rare sets of circumstances unique to how this mission uses the processor, cache access errors could occur, resulting in instructions not being executed properly. The Mars-bound spacecraft performed a brief alignment activity using its star scanner and sun sensor on January 26. During the alignment observations, the star scanner detected Mars.The spacecraft began normal use of its star tracker and true celestial navigation this week after its software update. As of 9 a.m. PST (noon EST, or 1700 Universal Time) on Friday, February 10, the spacecraft will have traveled 127 million miles (205 million kilometers) of its 352-million-mile (567-million-kilometer) flight to Mars. It will be moving at about 17,800 miles per hour (28,600 kilometers per hour) relative to Earth and at about 63,700 mph (102,500 kilometers per hour) relative to the sun.
source:www.nasa.gov