SP 100

SP-100 (Space reactor Prototype) was a U.S. research program for nuclear fission reactors usable as small fission power systems for spacecraft. It was started in 1983 by NASA, the US Department of Energy and other agencies.

A reactor was developed with heat pipes transporting the heat to thermionic converters. It was cooled with lithium. The project never advanced to flight hardware and was terminated in 1994.