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SNAP-10A was first and so far only known launch of a U.S. nuclear reactor into space (although many radioisotope thermoelectric generators have also been launched). The Systems Nuclear Auxiliary Power Program (SNAP) reactor was developed under the SNAPSHOT program overseen by the U.S. Atomic Energy Commission. Launched by an ATLAS Agena D rocket on April 3, 1965, SNAP-10A maintained a low earth orbit for 43 days, while its nuclear electrical source, made up of thermoelectric elements, produced over 500 watts of electrical power. An onboard voltage regulator within the spacecraft -- unrelated to the SNAP reactor itself -- failed, causing the reactor core to be shut down. The reactor was left in a earth orbit having an expected duration of 4000 years.

SNAP 10A Space Nuclear Power Plant

Construction and Operation

The SNAP-10A has three major components: a compact nuclear reactor, the reactor reflector and control system, a heat transfer and power conversion system.

The reactor measured 22.4 cm wide by 39.62 cm long and held 37 fuel rods containing uranium-zirconium-hydride fuel. The SNAP-10A reactor was designed for a power output of 30 kW and unshielded weighed . The reactor can be identified at the top of the SNAP-10A unit.

Reflectors were arranged around the outside of the reactor to provide the means to control the reactor. The reflectors were composed of a layer of beryllium which would reflect neutrons thus allowing the reactor to begin and maintain the fission process. The reflectors were held in place by a retaining band anchored by an explosive bolt. When the reflector was ejected from the unit, the reactor could not sustain the nuclear fission reaction and the reactor permanently shut down.

The eutectic sodium-potassium (NaK) alloy was used as a coolant in the SNAP-10A. The NaK was circulated through the core and thermoelectric converters by a liquid metal direct current conduction-type pump. The thermoelectric converters (identified as the long white 'apron') were doped silicon germanium materials thermally coupled but electrically isolated from the NaK heat transfer medium. The temperature difference between the NaK on one side of the thermoelectric converter and the cold of space on the other created an electric potential and usable electricity.


The SNAP reactor program necessitated a safety program and led to the inception of the Aerospace Nuclear Safety Program. The program was established to evaluate the nuclear hazards associated with the construction, launch, operation and disposal of SNAP systems and to develop designs to assure their radiological safety.

Atomics International had primary responsibility for safety while Sandia National Laboratorymarker was responsible for the Aerospace Safety Independent Review and conducted many of the safety tests. Before launch was permitted, proof had to be obtained that under all circumstances the launch of the reactor would not pose a serious threat.

A variety of tests were successfully completed and video of the destructive tests is available for viewing (see below).


Atomics Internationalmarker, then a division of North American Aviation was the prime contractor for the SNAP-10A development. Most of the systems development and reactor testing was conducted at the Santa Susana Field Laboratory, Ventura County, California using a number of specialized facilities.

The company also developed and tested other compact nuclear reactors including the SNAP Experimental Reactor (SER), SNAP-2, SNAP-8 Developmental Reactor (SNAP8-DR) and SNAP-8 Experimental Reactor (SNAP-8ER) units at the Santa Susana Field Laboratory. Atomics International also built and operated the Sodium Reactor Experimentmarker, the first U.S. nuclear power plant to supply electricity to a public power system.

The testing and development involving radioactive materials caused environmental contamination at the former Atomics International Santa Susana Field Laboratory (SSFL) facilities. The US Department of Energy is responsible for the identification and cleanup of the radioactive contamination. (The SSFL was also used for the unrelated testing and development of rocket engines by Rocketdyne primarily for NASAmarker.) The DOE website supporting the site cleanup (see below) details the historical development of nuclear energy at SSFL including additional SNAP testing and development information.



See also

  • RORSAT, the Soviet Union nuclear reactor powered satellites.

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