Monday, April 27, 2009

Roll Over Rover

NASA's Mars Exploration Rover Spirit is back in working order, sort of. The robotic rover crawled last week for the first time in two weeks after its recent struggle with amnesia and rebooting. It plodded 5.6 feet toward its goal of about 500 feet away.

Three times in the past two weeks, Spirit has failed to record data from a day's activity period into 128 megabytes of flash memory, (why so small, I carry a 1 gig in my pocket). That is where information is preserved even when power is off, such as when the rover naps to conserve power.

Spirit has also suffered from failing to wake up for three consecutive communication sessions (I have the same problem). Engineers have not found any links among the three types of events.

Spirit was given commands from NASA engineers who are still investigating the cause behind its recent glitches. The rover has moved its high-gain dish antenna and its camera mast, diagnostic activities used to check for any mechanical problems. Both components may be related to the reboots, the amnesia events, or the failure to wake up for three consecutive communication sessions weeks ago.

Spirit's daily routine was changed in order to assist the diagnostic work if the rover experiences another failure to record data into flash memory.

To conserve energy, Spirit has typically included a nap between its main activities for the day and the day's main downlink transmission of data to Earth. Data stored only in the rover's random-access memory (RAM), instead of in flash memory, is lost during the nap, so when Spirit has flash amnesia on that schedule, Spirit gives up no data from the activity interval. The new schedule puts the nap before the activity period (you couldn’t do that to kids). Even if there is a flash amnesia event, data from the activity would likely be available from RAM during the downlink.

On the other side of Mars, Opportunity completed a drive of more than 1000 feet in the last week in its long distance trek toward a crater more than 20 times larger than the biggest it has visited so far.

Spirit, and its twin Opportunity, finished their three-month prime mission on Mars five years ago and have kept operating through multiple mission extensions. They have already operated more than 20 times longer than their original primary task on Mars.

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