The big red things in this picture are 28V, 5A (DC) solid state relays (SSRs). They basically allow you to turn on high current and voltage devices, via a signal from some sort of IC (Integrated Circuit) or chip or computer or whatever.
We were going to use them to turn the rocket valves off and on. Check out the large chunks of aluminum they're bolted to called heat sinks, for disipating the heat they generate when switching. Not really needed in our case, but better safe than sorry.