You know, I was really just trying to shoot down uNext. He was claiming that NASA did not write its own OS. I provided a link stating otherwise. I did not mean to imply that NASA doesn't use Windows at all, but I really don't know what OS's are in use there, so I won't comment either way.
But oh yeah, << gasp >>. So glad I braced myself before reading your comment. You've taught me so much.
NASA is a large organization. Pick an OS. ... OK, I like "Irix". I'll bet you $100 NASA uses Irix. There are still some VMS installations and of course Solaris, VxWorks and MS Windows and Mac OS. To say the NASA uses something means nothing because they use everything.
As for flight hardware OSes. Only recently have they actually been using an OS in the flight hardware. More typically was it just a "run time environment" and more like an set of interrupt handlers. They would have a set of timers that generate interrupts and then have bits of code hung off each interrupt. If you all that "writting an OS" and it's been re-written many times.