[wfbarks]

For the first time, period. Doesn’t look like we had one 60 years ago...

[ceejayoz]

We did: https://en.wikipedia.org/wiki/NERVA

Tested successfully (on the ground) in the 60s.

Real pity about its cancellation, too. It was considered for the "Grand Tour" that the Voyager probes wound up doing; they could've sent nearly 30x the spacecraft mass with NERVA rockets.

[autokad]

I don't have time to verify the video at the moment, but I believe this is them testing said engine 60 years ago: https://www.youtube.com/watch?v=GmxPRCyR-Co