TIMBERWIND (1987–1992)

The Timberwind space nuclear thermal propulsion program was initiated by the Strategic Defense Initiative Organization in November 1987. Timberwind was a highly classified program to develop technology for a very high acceleration nuclear-powered rocket to launch missile interceptors into space. The project was transferred to the Air Force in 1991 and terminated in 1992, at which point some of the material was declassified. The Project Timberwind concept was based on a particle-bed reactor using tiny uranium carbide pellets as fuel to heat hydrogen propellant. The exhaust would have been highly radioactive. Preliminary designs had been selected but no prototype components had been tested before the program was canceled. No system was ever launched.

TOPAZ-2 (1980s–1990s)

Launching dozens of nuclear reactors into space during the 1970s and 1980s, the Soviet Union had a far more active space nuclear power program than did the United States. Although full details remain inaccessible, the Soviet Union is known to have had several separate space nuclear reactor programs under development in the late 1980s. One of these projects, mistakenly labeled “Topaz-2” in the United States but actually known as “Enisey,” was purchased by the U.S. Ballistic Missile Defense Organization in the early 1990s. (Two Soviet nuclear reactors known as Topaz were flown in orbit in the later 1980s but were an entirely different design.) Six Topaz-2 reactors and supporting equipment were flown from Russia to the United States, where several of the reactors were extensively ground tested by a joint team of U.S., British, French, and Russian engineers. The reactors’ unique design allowed them to be tested without nuclear fuel. Topaz utilized a thermionic design for directly converting heat energy into electricity without using a circulating heat transfer fluid or turbine. Although the test program was considered highly successful and the United States retained several flight-capable reactors, no plans were pursued to actually use the equipment in any flight programs.


Aftergood, Steven, “Background on Space Nuclear Power,” Science & Global Security 1(1–2): 93–108, 1989.

Department of Defense Inspector General Audit Report, The Timber Wind Special Access Program, Report Number 93-033, December 16, 1992. See <http://www.fas.org/sgp/othergov/dod/tw.pdf> last accessed February 2, 2006.

Dewar, James A., To the End of the Solar System: The Story of the Nuclear Rocket, University Press of Kentucky, Lexington, Ky., 2003.

Dyson, George, Project Orion: The True Story of the Atomic Spaceship, Owl Books, 2003.

General Accounting Office, Space Nuclear Propulsion: History, Cost, and Status of Programs, T-NSIAD-93-2. See <>.

General Accounting Office, The SP-100 Nuclear Reactor Program: Should It Be Continued?, T-NSIAD-92-15. See <>.

General Accounting Office, TOPAZ II Space Nuclear Power Program: Management, Funding, and Contracting Problems, OSI-98-3R. See <>.

Mondt, Jack F., “SP-100 Space Reactor Power System for Lunar, Mars and Robotic Exploration,” IAF 92-0563, 43rd Congress of the International Astronautical Federation, August 28–September 5, 1992.

National Research Council, Assessment of the Topaz International Program, Aeronautics and Space Engineering Board, June 27, 1996.

National Research Council, Thermionics Quo Vadis? An Assessment of the DTRA’s Advanced Thermionics Research and Development Program, National Academy Press, Washington, D.C., 2001.

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