1978 - Cosmos 954 was a Soviet Radar Ocean Reconnaissance Satellite (RORSAT) with an onboard nuclear reactor. The satellite was launched on 18 September 1977 and was designed to track nuclear submarines. The satellite's reactor core failed to separate and boost into a nuclear-safe orbit, and instead remained on board in an orbit that decayed until the satellite re-entered Earth's atmosphere. The USSR (Union of Soviet Socialist Republics) informed the US in a secret meeting at 11:53 GMT on 24 January 1978 that the satellite would impact earth.