Spirit began a four-sol stand-down on sol 94, which ended at
8:37 p.m. on April 8, 2004. During this time, the rover will receive a flight software update that should make its remaining martian days even safer and more productive. The upload will run through sol 97 with a rover re-boot on sol 98, Monday, April 12. Opportunity will be receiving the same update package in upcoming sols.Spirit is currently parked in front of the rock called "Route 66," and will remain there for the duration of the flight software update, with the Mössbauer spectrometer integrating on the rock, and the alpha particle X-ray spectrometer pointed up to the sky.
The flight software update package includes three key changes. First is an update to the autonomous navigation software that will allow Spirit to travel longer distances autonomously over the extremely rocky Gusev Crater terrain. The current autonomous navigation software sometimes gets stuck when it detects a hazard that it can't navigate around. The new version will allow Spirit to turn in place to find the best possible path.
The second part of the flight software update will allow Spirit to recover more easily from an anomaly like the one that occurred on sol 18. Although operational processes and software have already been updated to prevent something like this from ever happening again, engineers have included additional safety nets in the software that would allow the rover to autonomously react to a similar anomaly and recover to a more stable state.
The third portion of the update is specific to Opportunity and is intended to mitigate against energy loss associated with the stuck heater on Opportunity's instrument deployment device. The fix allows rover planners to put the rover in a deep sleep mode, where the batteries are totally removed from being able to power the stuck switch. Therefore, with no power reaching the stuck heater switch, the Opportunity rover battery will not be drained. Rover controllers will not initiate the deep sleep capability on Spirit unless it becomes necessary.