Opportunity began a four-sol stand-down on sol 75, which ended at 8:58 a.m. PST on April 9, 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 78 with a rover re-boot on sol 79, Tuesday, April 13.
Opportunity is currently parked near the trench it dug on its73rd martain sol. It will remain there for the duration of the flight software update. To keep the battery charge high, engineers are not planning to integrate the rover spectrometers on a target in the trailings of the trench during the flight software update.
The flight software update package includes three key changes. First is an update to the autonomous navigation software that will allow both rovers to travel longer distances autonomously. The current autonomous navigation software sometimes gets stuck when it detects a hazard that it can't navigate around. The new version will allow the rovers to turn in place to find the best possible path.
The second part of the flight software update will allow the rovers to recover more easily from an anomaly like the one that occurred on Spirit's 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 rovers 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.