NASA's SNAP-10A, launched in 1965, was the only nuclear reactor the United States had previously deployed in space.
Notes on verification
Confirmed by NASA, DOE, and Wikipedia. Minor nuance: SNAP-10A was a joint AEC/Air Force/NASA program launched by the Air Force, not solely a NASA mission, though NASA's own materials describe it this way. [cascade flags: wikipedia_dropped_other_sources_exist | tier=bronze indep_score=0.539 clusters=2 claim_tier=notable]
Sources
- Inside NASA's audacious plan to build a nuclear-powered ... (seed:science_and_space)
- https://www.energy.gov/etec/articles/lasting-legacy-snap-program-laid-critical-groundwork-space-nuclear-power-systems (corroboration)
- https://www.nasa.gov/space-technology-mission-directorate/tdm/space-nuclear-propulsion/ (corroboration)