NASA's SNAP-10A, launched in 1965, was the only nuclear reactor the United States had previously deployed in space before current lunar plans.
Notes on verification
Confirmed by multiple independent sources including DOE, Wikipedia, World Nuclear Association, and an encyclopedia entry, all consistent on the 1965 launch and its status as the only U.S. space reactor. [cascade flags: wikipedia_dropped_other_sources_exist | tier=silver indep_score=0.867 clusters=3 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://world-nuclear.org/information-library/non-power-nuclear-applications/transport/nuclear-reactors-for-space (corroboration)
- https://www.daviddarling.info/encyclopedia/S/SNAP.html (corroboration)