Mars Express has been a fixture in orbit around the Red Planet for almost eight years, but problems with the spacecraft’s computer memory has put the orbiter into safe mode and science observations have been halted for the time being. The spacecraft has gone into safe mode three times since mid-August, twice being recovered successfully. It has also had additional problems with its memory during this time. ESA says a technical work-around is being investigated that will enable the resumption of a number of observations, which will hopefully evolve into a long-term solution.
Safe mode is operational mode designed to safeguard both the spacecraft itself and its instrument payload in the event of faults or errors.
The portion of Mars Express’s computer the Solid-State Mass Memory (SSMM) system, which stores data before sending it on to Earth was not able to either write new data or read the previous data already in memory. The SSMM is a critical subsystem, central to all spacecraft and instrument operations.
This is not the first time the spacecraft has gone into safe mode. Three years ago a similar event took place, but now this multiple occurrence of problems has the Mars Express team looking for inventive solutions. The memory system has been switched to the “B” side or redundant computer, but the same fault took place, putting the spacecraft back in safe mode.
Another issue with the spacecraft going into safe mode is that is uses a lot of reserve fuel – as much as is required for six months of normal operations — so the frequent instances of this mode has engineers looking for a long-term solution. Most of the fuel consumption when entering safe mode is the ‘Sun acquisition’ process for letting the spacecraft know where it is in space, which requires a significant amount of spacecraft maneuvering.
ESA says they are making good progress with finding an alternative approach to commanding Mars Express, and will test it soon, and work continues on the finding a full solution to the memory problems.