Kosmos 954 nuclear-powered reentry over Canada (January 1978)

On 24 January 1978, the Soviet Kosmos 954 — a radar ocean-reconnaissance satellite (RORSAT) powered by an onboard nuclear reactor — made an uncontrolled re-entry over the Northwest Territories of Canada, scattering radioactive debris across a remote stretch of the subarctic.

Operation Morning Light Because the satellite carried a reactor with enriched uranium, the re-entry prompted a months-long Canadian and US recovery effort known as Operation Morning Light, which located and removed radioactive fragments spread along the satellite's ground track near Great Slave Lake. The Soviet Union later paid Canada partial compensation for the cleanup.

A landmark for space law and safety Kosmos 954 remains one of the most serious examples of a hazardous re-entry and a foundational case for international liability for space objects. It sharpened global concern about nuclear power sources in low Earth orbit and the consequences of objects that cannot be commanded to a safe disposal.