It was a technical specification that became a geopolitical event. Kosmos 954 was a Soviet radar ocean reconnaissance satellite, or RORSAT. Its mission required more power than solar panels could provide in low Earth orbit. The solution was a BES-5 nuclear reactor, containing approximately 110 pounds of highly enriched uranium-235. On January 24, 1978, after a control failure prevented its boost into a safe disposal orbit, it re-entered the atmosphere over northern Canada.
The satellite did not vaporize completely. It fragmented, scattering thousands of radioactive pieces across 124,000 square kilometers of the Northwest Territories' frozen tundra, along a path dubbed the "Trail of Debris." The U.S. and Canada initiated Operation Morning Light, a joint military and scientific effort conducted in extreme cold and secrecy. Teams in protective gear used helicopters and sleds to locate fragments. They found some, like fuel elements, emitting 5,000 rads per hour—a lethal dose in minutes. Only an estimated 0.1% of the reactor's mass was recovered. The rest remains, its radioactivity decayed, buried in the permafrost.
The incident was not an explosion. It was a dispersal. It demonstrated a precise, quiet danger: the marriage of orbital mechanics and atomic power, where a failure of calculation could seed a continent with invisible poison. The Soviet Union later paid Canada C$3 million for cleanup costs, a fraction of the actual expense. The treaty governing liability for such events was found to be inadequate.