RORSAT
RORSAT is the common name of Radar-equipped Ocean Reconnaissance Satellites, launched in low earth orbit between 1967 and 1988, by the Soviet Union. RORSATs are a sub-class of Cosmos satellites.
The satellites achieved a military purpose; the identification and capability to target (primarily US) naval targets.
More recently, RORSATs have been identified as a prime cause of space debris orbiting some 590 miles (950 km) above earth. Design flaws in the satellites have led many to discharge their sodium-potassium (NaK) eutectic alloy coolant into orbit - in the form of from 110,000 to 115,000 (possibly frozen) drops measuring in size from 50 to 70 mm diameter and below. Since the metal coolant was irradiated with neutrons from the nuclear reactor, unless it has evaporated, it now contains radioactive 39Ar with a half life of 269 years.
The fault arises after the satellites have ejected their nuclear reactor cores into a so-called "disposal orbit" - a higher orbit. An incidental concern is that the disposal orbit will persist only for several hundred years, after which the very highly radioactive cores will return, presumably to be burned up and dispersed in the Earth's atmosphere.
In 1978, a RORSAT, designated Kosmos-954, with a reactor core 30 kg of enriched uranium re-entered the earth's atmosphere and left a trail of radioactive pollution over an estimated 124,000 km² of Canada.
