Space-grade CPUs: How do you send more computing power into space?
Phobos-Grunt, perhaps the most ambitious deep space mission ever attempted by Russia, crashed down into the ocean at the beginning of 2012. The spacecraft was supposed to land on the battered Martian moon Phobos, gather soil samples, and get them back to Earth. Instead, it ended up helplessly drifting in Low Earth Orbit (LEO) for a few weeks because its onboard computer crashed just before it could fire the engines to send the spacecraft on its way to Mars.
In the ensuing report, Russian authorities blamed heavy charged particles in galactic cosmic rays that hit the SRAM chips and led to a latch-up, a chip failure resulting from excessive current passing through. To deal with this latch-up, two processors working in the Phobos-Grunt’s TsVM22 computer initiated a reboot. After rebooting, the probe then went into a safe mode and awaited instructions from ground control. Unfortunately, those instructions never arrived.
Antennas meant for communications were supposed to become fully operational in the cruise stage of Phobos-Grunt, after the spacecraft left the LEO. But nobody planned for a failure preventing the probe from reaching that stage. After the particle strike, the Phobos-Grunt ended up in a peculiar stalemate. Firing on-board engines was supposed to trigger the deployment of antennas. At the same time, engines could only be fired with a command issued from ground control. This command, however, could not get through, because antennas were not deployed. In this way, a computer error killed a mission that was several decades in the making. It happened, in part, because of some oversights from the team at the NPO Lavochkin, a primary developer of the Phobos-Grunt probe. During development, in short, it was easier to count the things that worked in their computer than to count the things that didn’t. Every little mistake they made, though, became a grave reminder that designing space-grade computers is bloody hard. One misstep and billions of dollars go down in flames.
