Satellites in general. Once you've built out a ground infrastructure for a spacecraft, it makes zero sense to ever make dramatic changes to it. The risk is too

Satellites in general. Once you've built out a ground infrastructure for a spacecraft, it makes zero sense to ever make dramatic changes to it. The risk is too high. In 2015 I worked on a piece of software that was related to command and control of the Cassini spacecraft that ran on Sun Solaris machines. That infrastructure would have been first brought up prior to launch in 1997. Granted, I have to assume that these were not the original physical computers and that there are still ways even today to source new solaris machines for exactly this type of scenario, but still.