Mars Reconnaissance Orbiter crashes, reboots for fifth time

On September 15, the Mars Reconnaissance Orbiter (MRO) went into “safe mode” for the fifth time in two years. “Safe mode” is NASA-speak for entry into standby mode following an on-board computer crash and reboot. NASA’s MRO team successfully restarted the MRO’s computer three days later, which is significantly better than the previous such incident in August 2009. Back then, the MRO needed months to wake up. So why is this a memory story? Because the MRO is perhaps the most complex, certainly one of the most distant Flash-based data-acquisition systems yet built. Depending on their orbital positions around the sun, the Earth and Mars can be between 36 and 250 million miles apart. To date according to NASA, the MRO has generated three times more science data than all other deep-space (beyond the orbit of the Earth’s moon) combined. The MRO successfully completed its primary science mission in November 2008, but it continues to observe Mars and to look for possible future landing sites.

The MRO electronics package is based on a 133MHz BAE Systems RAD750 processor, which is itself based on an IBM version of the PowerPC microprocessor. Reportedly, there are about 150 such processors currently serving in space missions so it’s a proven processor for space. The MRO’s CompactPCI single-board computer combines the RAD750 processor with 36Mbytes of rad-hard BAE SRAM, 4Mbytes of EPROM, and a 64Kbyte boot ROM. All on-board memories employ ECC. Further, the MRO has a 20Gbyte Flash memory module, built from more than 700 256Mbit NAND Flash chips. For comparison, one image from the MRO’s HiRISE (High Resolution Imaging Science Experiment) telescopic imager (nominal picture size = 800 Mpixels) requires about 3.5 Gbytes for storage and there are several other instruments on the MRO also collecting data, so 20Gbytes isn’t all that much storage.

It’s not yet clear from NASA’s reports what caused the glitch, but this space-based event dovetails with the extremely interesting talk given by Karl F Strauss of NASA’s Jet Propulsion Lab at last month’s Flash Memory Summit. As Strauss discussed, NAND Flash devices are most susceptible to ion strikes but they have been growing less and less susceptible to such strikes as device features shrink. For a Flash cell, radiation susceptibility is merely a matter of mass--the smaller the amount of oxide insulation in the Flash memory cell, the less the ability of an ion or photon to become trapped at a defect site and induce leakage. Because radiation tolerance is inversely proportional to memory-cell volume, Flash memory’s radiation tolerance has been steeply increasing over the last few years. Consequently, Flash memory is now even more viable as a candidate for data storage on spacecraft than it was when it was designed into the MRO.