For me what has always been amazingly fascinating about all of these missions (even more so for the Voyager missions) is to be able to work with so much latency! In today's world, where we are used to working with millisecond latencies across thousands of kilometers, just to be able to do something with latency of minutes to tens of hours, boggles my mind! Amazing accomplishment of humankind!
From the little I understand, these chips behave a quite a bit different than the types of stuff we work with. For one, you have to assume that your programs will be corrupted via cosmic rays causing bit-flips. Chips are slower and more rigorous as a result.
This being HN, there may be a person on here that can speak more to program design with space rated hardware. I'd love to learn a bit more!