Mission controllers are making excellent progress in returning Mars Express to routine service. Some science activities have already resumed after being temporarily suspended last month following a series of faults related to the onboard data storage system.
Having arrived around Mars in December 2003 for an initial two-year mission, the spacecraft is now in its eighth year of science operations. It has returned some of the most stunning images and valuable science data ever obtained from the Red Planet.
In mid-October 2011, anomalies in the operation of its Solid-State Mass Memory (SSMM) system caused science observations to be temporarily halted.
The problem had surfaced several weeks earlier, when, on several occasions, the spacecraft autonomously entered safe mode. This is an operational mode designed to safeguard both the spacecraft and its instrument payload in the event of internal faults or errors.
Data storage problems
The cause was a complex combination of events relating to reading from and writing to memory modules in the SSMM system.
This is used to store data acquired by the instruments and housekeeping data from the spacecraft's subsystems, prior to transmission to Earth. It is also used to store commands that have been received from ground stations while awaiting execution.
This problem was unanticipated by the spacecraft designers, so everyone on the mission control team is learning as we go.
The mission control team at ESOC, ESA's Space Operations Centre, Darmstadt, have been working closely with technical experts from the spacecraft's manufacturer as well as other experts at ESA to troubleshoot and isolate the problem. However, it has not been possible to date to understand nor resolve the problem with the SSMM directly.
Therefore the team are now designing a series of new procedures that will enable commands to be stored without critical dependency on the problem-plagued SSMM.
"The entire team have worked intensively to implement a provisional fix. Limited science observations were able to resume on 31 October," said Michel Denis, Mars Express Spacecraft Operations Manager.
"This problem was unanticipated by the spacecraft designers, so everyone on the mission control team is learning as we go."
The newly designed approach implies that commands will now be sent up in much smaller batches, and that additional protections will be implemented to avoid safe mode or an unpredictable spacecraft status should one of the command batches fail to execute.
Solving this problem is like writing a really terrific mystery novel.
"This has been our first permanent anomaly in eight years of orbit," said James Godfrey, Mars Express Spacecraft Operations Engineer. "Solving it is like writing a really terrific mystery novel."
By mid-November, the spacecraft had returned to gathering science observations for longer periods during each orbit, one instrument at a time. The team expect that combined science operations with all instruments will resume in early 2012.
"We're still studying the issue to formulate a long-term solution, and we're aiming to return to as high a level of normal science operations as possible – quite close to 100%, actually," said Denis.
"The team are doing an excellent job at designing ingenious and safe solutions; I'm very impressed with their skills and dedication to our otherwise very fit spacecraft."
LINKS http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=49549 MEX web pages OPS ESOC