Although there’s a lot of good software being written at Johnson, the computers on the shuttle are so obsolete that the manufacturers don’t make them anymore. The memories in them are the old kind, made with little ferrite cores that have wires going through them. In the meantime we’ve developed much better hardware: the memory chips of today are much, much smaller; they have much greater capacity; and they’re much more reliable. They have internal error-correcting codes that automatically keep the memory good. With today’s computers we can design separate program modules so that changing the payload doesn’t require so much program rewriting. Because of the huge investment in the flight simulators and all the other hardware, to start all over again and replace the millions of lines of code that they’ve already built up would be very costly.