J-87 nuclear-turbojet-engine. And I had difficulty wrapping my head around how it worked! If a typical jet engine compresses air and then shoots gas into that air and lights it off then blows it out the back, spinning the turbine blades to keep the thing running, well, you might say, “Yeah, no kidding, that’s how my wife describes it. What’s this got different?” Well, I’ll tell you.
Instead of shooting gas into that compressed air and lighting it off, we just cool the reactor with it but firing that air into the core. It’s cooled that way, yes, but the air exiting crazy hot spun the thing up more than sufficient to create thrust. Sizeable thrust. It even had afterburners if they put a little bit of jet fuel to the exhaust.
Now, the downside was the radioactive waste coming out the tailpipe with all that hot air. The upside? How about boundless range all around the planet? Mitigating that radioactive waste issue was an indirect cycle style engine, where the air didn’t go into the core, but to a heat exchanger, like your air-air intercooler from your WRX-STI. Unfortunately, they didn’t get that one working right, but GE did get their direct cycle engine working regularly.
It was canceled within the first month of Kennedy’s presidency when it became evident Russia didn’t have hardly any operational bombers at the time.