NASA's SNAP-10A satellite operated for 43 days before stopping.
Notes on verification
Confirmed by DOE, Wikipedia, Gunter's Space Page, and academic/journalistic sources; consistent 43-day figure across government and independent references. [cascade flags: wikipedia_dropped_other_sources_exist | tier=silver indep_score=0.925 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://space.skyrocket.de/doc_sdat/snapshot.htm (corroboration)