>"The book" says that once you have an operational configuration you freeze it. I guess we've been reading different books then. The Shuttle you're referring t

>"The book" says that once you have an operational configuration you freeze it. I guess we've been reading different books then. The Shuttle you're referring to had been constantly modified and tuned (noise suppression to prevent STS-1-like body flap damage, autopilot, the anti-geyser line, LWT, SLWT etc etc etc). The other manned vehicle, Soyuz, is on its 8th major iteration already, and got many minor modifications in between. They looked for old CPUs instead of upgrading because it wasn't worth it. Shuttle program got cancelled in 2004, and it was known well in advance that it will stop flying. The difference is, they don't make headlines nearly as much. (Shuttle did early on, but it was too long ago)