Kosmos 1867 (Russian: Космос 1867) was a nuclear powered radar ocean reconnaissance satellite (RORSAT) that was launched by the Soviet Union on July 10, 1987.

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 100.8 minutes.

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

It is suspected that the coolant tube had leaked NaK metal, in a manner similar to Kosmos 1818 in 2008.

[citation needed] The coolant tube of Kosmos 1867 may have cracked due to thermal stresses by repeated solar heating, or by an impact.