I was just providing an illustrative example, the exact implementation details are irrelevant. Android phones have been used as the central processors for a number of CubeSAT missions so without any circuit design you can get a sub $500 CPU kit which is much faster and cheaper than a $100k RAD CPU (and available at any electronics store unlike single board CPU modules).

Telecom satellites already require tons of specialised integrated circuits because general purpose CPUs are too complex and power hungry for the amount of bandwidth the satellites process. This SpaceX constellation will certainly have custom designed electronics, even if they don't use any rad hardened ICs.

> Why not just bare Linux, possibly with the PREEMPT_RT patchset

That'd be a really bad idea. Linux is too complex to trust, and lacks WCET making it unsuitable for hard realtime.

There's open source options, but Linux isn't among them. I'd look at seL4 for this purpose.

SpaceX already runs Linux on their rockets; apparently near-real-time is good enough for that purpose.

Yes, I was saying why would you use Android instead of just bare Linux (as in Yocto). I doubt you will be writing an ADCS application in Java using a GUI.

Also, I think the Falcon 9 uses VxWorks for at least some of its realtime control: http://blogs.windriver.com/vxworks/2010/12/vxworks-helping-c...

http://lwn.net/Articles/540368/ doesn't mention VxWorks.

Looks like Dragon runs VxWorks, see under Flight Software.

http://www.spacex.com/sites/spacex/files/pdf/DragonLabFactSh...

Can anyone who works at SpaceX chime in?

That article also says

> One of the areas they focus on is scheduler performance. They do not have hard realtime requirements, but do care about wakeup latencies, he said.

It sounds like their hard real time controls are on non-Linux OSs.