Space

The Red Planet is experiencing a partial radio blackout this week, as both of NASA's Mars orbiters have been felled by technical glitches. Until one of the probes can be brought back online later this week, the outages will delay operation of the twin Mars rovers, which use the orbiters to efficiently relay data back to Earth.

The main blow to rover operations comes from NASA's Mars Odyssey, which reached the Red Planet in 2001 and has been the prime communications relay for the rovers Spirit and Opportunity since they landed in 2004.

Odyssey has been down since 28 November, when its computers registered a memory error and sent the spacecraft into "safe mode", which minimises spacecraft operations.

Odyssey's most natural communications backup, NASA's Mars Reconnaissance Orbiter (MRO), has been kept on standby since August, when the spacecraft spontaneously rebooted for the fourth time this year.

Fast connection

The solar-powered Mars rovers can communicate with antennas on Earth directly, but the orbiters can relay information from the rovers to Earth at more than 10 times that speed, using a fraction of the energy.

The outages could delay attempts to free the Spirit rover from a sand pit that has been its home for more than six months (see Mars rover battles for its life). The rover team has been given until at least February to extricate Spirit.

"The rovers are safe. However, future activities are likely delayed, roughly on a day-for-day basis until Odyssey returns to relay operations," says John Callas, the rover programme manager at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.

Unknown trigger

The causes of Odyssey's and MRO's technical problems are not yet clear.

Odyssey has experienced similar memory glitches in the past, and such events are not considered a big problem for the spacecraft, as they occur infrequently and there is a known recovery procedure, says Jeffrey Plaut, Mars Odyssey project scientist at JPL.

"[The glitch] causes a kind of a freeze-up. It's similar to something that might happen to your laptop," Plaut says. "In order to clear it, you reboot the computer."

Odyssey is now steering itself again so that it can keep its instruments pointed at Mars. But it will be at least several days before regular science operations and communications with the Mars rovers will begin. "We expect to be completely back on our feet by the end of the week," Plaut told New Scientist.

Total amnesia

Restoring MRO may take bit longer, as engineers work to update the spacecraft's memory to prevent a potentially catastrophic error.

MRO has been kept in suspended animation since 26 August, when the spacecraft rebooted itself. An investigation into that reboot as well as the three others MRO performed in 2009 revealed a potential problem: if the spacecraft's two sides rebooted within a minute of one another, MRO would lose all memory of being in orbit around Mars.

"It would believe it was at the stage of the mission when it was awaiting launch," says NASA spokesperson Guy Webster of JPL. To prevent irreversible amnesia, engineers have planned to begin uploading a set of revised data files to the spacecraft on Tuesday.

The files will rewrite MRO's default memory, so that it will know that it is in orbit if it experiences back-to-back reboots. The process is set to take a week, and it will take longer before the spacecraft is fully restored, Webster says.

A third spacecraft, the European Space Agency's Mars Express has occasionally acted as a communications relay for the Mars rovers. Unlike MRO and Odyssey, which take near-circular paths around the planet's poles, Mars Express has a highly elongated orbit. This typically reduces the rate by which it can relay data by a factor of four, Callas says.

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