The software update should make the rest of the mission undertaken by Spirit and Opportunity safer and more productive, NASA said.

NASA sent the $820 million pair of rovers to Mars to prospect for evidence that the now-frozen planet once had water. Both have found such evidence. The space agency recently extended the mission through September.

The new software, beamed across 188 million miles of space, should permit Spirit to travel longer distances across the rocky terrain by allowing it to independently negotiate obstacles that previously stumped its navigation software. Opportunity's landing site on the far side of the planet is relatively obstacle-free.

A second part of the software package should allow the rovers to recover from computer memory problems like the one that struck Spirit less than three weeks into its mission.

The third portion should allow Opportunity to enter into "deep sleep'' mode at night. That will cut off electricity to a stuck heater that had been coming on unnecessarily.

NASA feared that the power drain could curtail Opportunity's mission. NASA has no plans to use "deep sleep'' on Spirit unless it becomes necessary.

• Mars Rovers: Complete Coverage