20 Mar

The iPods rock the Space Shuttle, and single-bit soft errors

I found this article about an iPod that was spotted on the Space Shuttle…

I wonder if the iPod is experiencing single-bit soft errors. In space, unless the electronic equipment such as computers (or iPods!) is “radiation hardened”, using techniques such as single bit correction Error Correcting Codes (ECC), single-bit soft errors can and will occur by radiation from space. Computers are highly susceptible to bit-flips when the spacecraft carrying them is flying over the magnetic poles, and obviously if there is a solar flare.

I remember many years ago I spent long hours (of pure pressure during a Shuttle mission) trying to explain a fail-to-sync (FTS) that occurred in orbit; a FTS is when one of the computers in a redundant-set diverge, taking a different execution path from the other ones; a very bad thing in redundant systems, especially during launch or landing, but not as bad in orbit, unless during rendezvous. Based on downlink data, I attributed the FTS to a single bit-flip. Was my assessment 100% correct? We will never know. But it was the best educated guess I could come up with (after lots of data analysis)… Note that FTS are very rare, and the Shuttle software is extremely stable and next to error free.

This I found interesting:

Getting an iPod into space isn’t easy. The lithium batteries have to be replaced with specially certified alkaline batteries. Once docked, crew members can’t bring them on board the Space Station, however, since they haven’t been certified as safe in that environment.

Related to this see On Self-Modifying Code and the Space Shuttle OS.