Kosmos 1818 was a nuclear powered Soviet surveillance satellite in the RORSAT program, which monitored NATO vessels using radar.

It was put into an orbit about 800 km (500 mi) above the Earth's surface at an inclination of 65° and a period of 100.6 minutes.

This was cooled by liquid sodium-potassium, NaK, metal, it used a high-temperature moderator containing hydrogen and highly enriched uranium fuel.

[4] About July 4, 2008, either Kosmos 1818 was hit by an object or a coolant tube cracked due to thermal stresses by repeated solar heating.

Russian Space Forces chief of staff General Alexander Yakushin indicated that the debris was high above the orbit of the International Space Station and did not pose any threat of radioactive contamination to the Earth.