The IEEE Spectrum published an interesting article postulating that Russia’s recently-failed Mars probe may have suffered from bad memory chips. According to the Spectrum article the Russian government’s Official Accident Investigation Results faulted SRAMs:
The report blames the loss of the probe on memory chips that became fatally damaged by cosmic rays.
Both the main computer and the backup computer seem to have failed at the same time, causing the fail-safe system to force the satellite to fall out of its parking orbit.
The Spectrum article quotes a Jet Propulsion Labs expert who said that the SRAMs used in the computers are: “…some of the most sensitive parts to single-event latch-up they had ever seen.”
Memory chips are naturally sensitive to radiation. Today’s memory technologies are all based on charge storage, and these charges can be leaked off when an alpha particle passes through a memory cell.
Future technologies – those that promise to displace existing technologies – don’t use charge storage. MRAMs, PCM, RRAM, and FRAM are all based on alternative storage approaches. In a few cases these technologies have been used in satellites due to their insensitivity to radiation. As these technologies enter high-volume production the Memory Guy would expect to see them find far wider use in space-bound applications.
For more information on one of these technologies – PCM – see the white paper Phase Change Memory Becomes a Realitywhich can be downloaded for free from the Objective Analysis home page.
Also, several US space probes and the US Mars lander in the mid-1990s used IBM 16M DRAMs for memory, a unique design called “Luna Classic’ or ‘Luna-C”, which had built-in ECC on the DRAM chip. This made the system containing them more space (cosmic ray) tolerant, as well as enabling much higher densities of memory than SRAM in smaller confinements. This technology was described by IBM’sHoward Kalter at ISSSCC in about 1989, and was originally for IBM Mainframes. Its production was later resurrected for Loral, which designed a part of the Mars Lander