> This does make one wonder about an architecture that has 4 or more identical processors hooked up to the same inputs and two watchdogs watching them (and each other). If any processor starts disagreeing with the rest it is instantly reset. If any processor starts to draw too much or too little current it is reset. If either watchdog stops responding to the other it is reset.
This is a common set of techniques in critical systems. The smallsat built by students that I mentored didn't have voting, but it had processors with moderately sophisticated watchdogs performing mutual-power-monitoring and simple hardware failsafes. Aerospace control systems often run in lockstep and have voting, etc.
> Keeping the working data synchronized would be the real trick. One could imagine all of these CPUs are hooked to a single bank of redundant and ECC stabilized memory, and all access goes through the watchdog processes which will only let through the ones that are in agreement.
Typically you make the memory redundant too, and just ensure that input and outputs are common and all code is deterministic. e.g. There's Tandem / HP NonStop which use these techniques.
> The end result could be a system that is lighter and faster than the traditional RAD hardened system simply because it's built on a smaller process.
Handling upsets by voting makes a lot of sense. But radiation can cause permanent damage of small geometry circuits. And even with fast mechanisms to crowbar power in the event of a latchup, you're not really sure that you'll save the day.
It's a great way to handle things on the cheap for cutting edge payloads and research projects, though.