Similarly to

   - The first [transistors](https://space.stackexchange.com/questions/21959/the-first-transistors-in-space-germanium-or-silicon-what-about-in-orbit) in space: Germanium or Silicon? What about in orbit?
   - First [LED](https://space.stackexchange.com/questions/46645/first-led-left-on-another-planet%e2%81%ba-by-humans) left on another planet⁺ by humans? w/list of space electronic "firsts" questions
   - First [TTL](https://space.stackexchange.com/questions/54100/first-ttl-chip-in-space-and-in-orbit-was-it-a-7400-series-or-something-that-pre) chip in space and in orbit? Was it a 7400 series or something that predates?

which mission used the first multiprocessor in space? 

The Saturn V rocket control computer used three processors executing the same program to increase reliability by redundancy.

This question is about the first distributed computing in space, several independent digital processors executing different programs within a single space probe. General purpose processors with a memory for data and program.