SE is like an EE or CE or other E, but for software- an SE is not like an architect. On any large building project, you have a lead engineer, the person that says what the architects have planned is possible.

These have embedded systems in them, not a general-purpose operating system such as Windows 95 or any other OTS OS. Each satellite has a custom built and configured embedded system. While it may have a foundation of an older system, it is unique. This is why individuals need to educate themselves by supplementing their reading with a few books from experts in their field. People that built these things! As one individual pointed out, Win9x came out well after many of the GPS satellites were launched. Scarry enough as this may be - ATMs used to run OTS Windows 9x. They have since all wised up.... and again, use a customized system.