One of the main things I remember about these old CCSs is the low level hardware redundancy:
> The Viking CCS had two of everything: power supplies, processors, buffers, inputs, and outputs. Each element of the CCS was cross strapped which allowed for “single fault tolerance” redundancy so that if one part of one CCS failed, it could make use of the remaining operational one in the other. [1]
Modern systems like that of curiosity rover also use hardware redundancy, (triple redundancy even), but I believe this happens at a much higher level, i.e whole computer.
In a smallish embedded system there are not too many (software) difficulties in keeping the software running virtually forever.
Getting the hardware to keep running without any fault for 42 years, on the other hand...