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ESA wrestles with software errors on Mars Express probe

Posted: November 1, 2011

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European officials have temporarily halted scientific observations aboard the Mars Express spacecraft after a spate of software hiccups, but managers are hopeful the mission can resume research after eight years at Mars.

Artist's concept of the Mars Express spacecraft in orbit at Mars. Credit: ESA
The Mars Express probe's 12-gigabit solid-state mass memory unit, which stores scientific and engineering data before transmission to Earth, has triggered a series of "safe modes" since mid-August, ultimately leading mission managers to suspend the science mission Oct. 16.

Launched in June 2003, Mars Express entered orbit around the Red Planet six months later and has studied the planet with a high-resolution color camera, a ground-piercing radar, and a suite of other instruments.

Mars Express has discovered underground water ice deposits, evidence of past liquid water and detected methane in the Martian atmosphere. The spacecraft also flew by the moon Phobos and collected the sharpest imagery ever of the planet's largest natural satellite.

Mars Express, which circles Mars in an oval-shaped elliptical orbit, initially entered safe mode due to a "complex combination of events relating to reading from and writing to memory modules" in the craft's solid-state mass memory system, according to the European Space Agency. It was the mission's first safe mode in three years.

After controllers executed a standard recovery sequence and resumed normal operations, Mars Express was again placed in safe mode, and engineers switched to a redundant B-side memory unit controller to avoid future anomalies.

But two more safe modes in September and October, plus another error that did not interrupt science operations, compelled managers to suspend the mission to find a solution to the recurring problem.

The errors in the B-side unit occurred during communication between two subsystems of the solid-state memory unit.

Officials wish to avoid continued safe mode events because the spacecraft consumes propellant to change its orientation to point toward the sun, a crucial activity designed to ensure its batteries remain charged. ESA says each safe mode uses the same amount of fuel Mars Express would normally burn in six months of operations.

Mars Express has enough fuel for at least 10 more years, but managers worry more safe modes would reduce the mission's life. Mars Express is now in an extended mission through the end of 2014 after a two-year primary campaign that ended in 2005.

Controllers at the European Space Operations Center in Darmstadt, Germany, are preparing a workaround to "allow at least partial resumption of science observations," according to a posting on ESA's website.

Fred Jansen, the Mars Express mission manager, said the spacecraft has recovered from its last safe mode event and successully completed initial testing of the workaround, which involves a new way of storing commands aboard the probe before they are executed.

Instead of using a special file in the solid-state mass memory unit, the commands would be housed in a hardware-based timeline store outside the memory system, bypassing the issue believed to be the cause of the safe modes.

Jansen said the Mars Express radar sounding instrument, named MARSIS, conducted test observations Monday with no problems.