Nuclear Power in Space: The TOPAZ Reactor

Jack Craddock III
March 15, 2016

Submitted as coursework for PH241, Stanford University, Winter 2016


Fig. 1: The TOPAZ II reactor. (Source: Wikimedia Commons)

The TOPAZ II reactor was a nuclear device developed by the U.S.S.R. in order to power satellites in low-Earth orbits. [1] It is pictured to the right. The United States purchased several TOPAZ II reactors with hopes of launching them with satellites, but the reactors were never used to power U.S. spaceflight. [2] The reactor was a relative of a previously designed Russian nuclear reactor, the TOPAZ I. This article will provide a brief overview of the TOPAZ reactors and how they were used in both Russia and the United States.

TOPAZ I in Russia

In the early 1960's, the U.S.S.R. began developing reactor technology that would be deployable as a power source for satellites. Two different labs were charged with developing thermionic nuclear systems. These types of systems use heat produced by nuclear reactors to create electricity. [3] One focused on creating a reactor with a multicell thermionic fuel element; the project was named TOPAZ, which is an acronym in Russian for Thermionic Experiment with Conversion in Active Zone. The second lab focused on using single-cell thermionic fuel element technology; this project was named "ENISY," but there will be more on that project later. [1] At this point, the Soviet Union had a much more active nuclear space program than did the United States, and the TOPAZ was a part of this program. [2] After extensive ground tests, the TOPAZ was flight tested twice. In 1987 and then 1988, Russia launched the TOPAZ reactor as the power source for satellites. [4]

TOPAZ II in the United States

In the late 1980's, the United States and Russia began discussions about the sale of space reactors to America. In the scope of these conversations, the reactor known as "ENISY" was mistakenly understood to be a part of the same development program at TOPAZ. To the Americans, "ENSIY" was henceforth referred to as TOPAZ II, and TOPAZ would be called TOPAZ I. [4] When the Soviet Union offered TOPZA II reactors for sale, the United States initially saw the reactors as a potential piece of the Strategic Defense Initiative, a missile defense system colloquially referred to as "Star Wars." Eventually, the United States moved its TOPAZ focus from SDI to the potential for power lunar bases. [5] Although the TOPAZ II was never flown on a mission, the testing program was considered a success. [1]

Concerns About Reactors in Space

The prospect of launching nuclear reactors into space faced some opposition. The specter of the 1986 Challenger disaster was still a relatively recent memory, and the idea that a rocket could explode with a nuclear reactor on board left the public uneasy. [6] Not only were there concerns about nuclear catastrophe, but there is strong opposition to launching nuclear reactors into space from some within the scientific community itself. Astronomers contend that placing too many nuclear satellites in low orbit around the Earth would lead to "radiation pollution" that would render their gamma ray telescopes useless. [7] To date, there have been no catastrophic disasters involving nuclear reactors in space.

© Jack Craddock III. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] G. F. Polanksy and M. G. Houts, "A Preliminary Investigation of the TOPAZ II Reactor as a Lunar Power Supply.," Sandia National Laboratory, SAND95-2974C, November 1995.

[2] Priorities in Space Science Enabled by Nuclear Power and Propulsion, (National Academies Press, 2006).

[3] M. Jiang, "An Overview of Radioisotope Thermoelectric Generators," Physics 241, Stanford University, Winter 2013.

[4] S. S. Voss, "TOPAZ II Design Evolution," AIP Conf. Proc. 301, 791 (1994).

[5] J. P. Hardt and R. F. Kaufman, The Former Soviet Union in Transition (Routledge, 1994), p. 645.

[6] C. Schaerf and G. Longo, Space and Nuclear Weaponry in the 1990s (Palgrave Macmillan, 1992.)

[7] J. A. Simpson, Ed., Preservation of Near-Earth Space Environment for Future Generations. (Cambridge University Press, 1994).