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SNAP-10A was the first and so far only known launch of a U.S. nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...

 into space (although the US has launched many radioisotope thermoelectric generator
Radioisotope thermoelectric generator
A radioisotope thermoelectric generator is an electrical generator that obtains its power from radioactive decay. In such a device, the heat released by the decay of a suitable radioactive material is converted into electricity by the Seebeck effect using an array of thermocouples.RTGs can be...

s, and the Soviets launched reactors in the RORSAT
Radar Ocean Reconnaissance SATellite or RORSAT is the western name given to the Soviet Upravlyaemyj Sputnik Aktivnyj satellites. These satellites were launched between 1967 and 1988 to monitor NATO and merchant vessels using active radar...

 satellites). The Systems Nuclear Auxiliary Power Program
Systems Nuclear Auxiliary Power Program
The Systems Nuclear Auxiliary Power program was a program of experimental radioisotope thermoelectric generators and space nuclear reactors flown during the 1960s by NASA.-Odd-numbered SNAPs: radioisotope thermoelectric generators:...

 (SNAP) reactor was developed under the SNAPSHOT program overseen by the U.S. Atomic Energy Commission.

Spacecraft history

SNAP-10A was launched from Vandenberg AFB by an ATLAS Agena D rocket on April 3, 1965 into a polar low Earth orbit
Low Earth orbit
A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...

 altitude approx 1,300 km. Its nuclear electrical source, made up of thermoelectric elements, was intended to produce over 500 watts of electrical power for one year. After 43 days, an onboard voltage regulator
Voltage regulator
A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage level. A voltage regulator may be a simple "feed-forward" design or may include negative feedback control loops. It may use an electromechanical mechanism, or electronic components...

 within the spacecraft—unrelated to the SNAP reactor itself—failed, causing the reactor core to be shut down. The reactor was left in a 700 nautical miles (1,296.4 km) earth orbit for an expected duration of 4,000 years.

An anomalous event in November 1979 caused the vehicle to begin shedding an eventual 50 pieces. A collision has not been ruled out and radioactive debris may have been released.

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 (8.8 in) wide by 39.62 cm (15.6 in) long and held 37 fuel rods containing uranium-zirconium-hydride fuel. The SNAP-10A reactor was designed for a thermal power output of 30 kW and unshielded weighed 650 lb (294.8 kg). 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
Pyrotechnic fastener
A pyrotechnic fastener is a fastener, usually a nut or bolt, that incorporates a pyrotechnic charge that can be initiated remotely. One or more explosive charges embedded within the bolt are typically activated by an electric current, and the charge breaks the bolt into two or more pieces...

. 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
NaK, or sodium-potassium alloy, an alloy, of potassium , and sodium , is usually liquid at room temperature. Various commercial grades are available. NaK is highly reactive with water and may catch fire when exposed to air, so must be handled with special precautions...

) 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 Laboratories
Sandia National Laboratories
The Sandia National Laboratories, managed and operated by the Sandia Corporation , are two major United States Department of Energy research and development national laboratories....

 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.


Atomics International
Atomics International
Atomics International was a division of the North American Aviation company which engaged principally in the early development of nuclear technology and nuclear reactors for both commercial and government applications...

, then a division of North American Aviation
North American Aviation
North American Aviation was a major US aerospace manufacturer, responsible for a number of historic aircraft, including the T-6 Texan trainer, the P-51 Mustang fighter, the B-25 Mitchell bomber, the F-86 Sabre jet fighter, the X-15 rocket plane, and the XB-70, as well as Apollo Command and Service...

 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
Santa Susana Field Laboratory
The Santa Susana Field Laboratory is a complex of industrial research and development facilities located on a 2,668 acre portion of the Southern California Simi Hills in Simi Valley, California, used mainly for the testing and development of Liquid-propellant rocket engines for the United States...

, 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 Experiment
Sodium Reactor Experiment
The Sodium Reactor Experiment was a pioneering nuclear power plant built by Atomics International at the Santa Susana Field Laboratory, nearby Simi Valley, California. The reactor operated from 1957 to 1964...

, 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 United States Department of Energy
United States Department of Energy
The United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...

 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
Pratt & Whitney Rocketdyne
Pratt & Whitney Rocketdyne is a United States company that designs and produces rocket engines that use liquid propellants. Pratt & Whitney Rocketdyne, headquartered in Canoga Park, California, is a division of Pratt & Whitney, itself a wholly owned subsidiary of United Technologies Corporation...

 primarily for NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

.) The DOE website supporting the site cleanup details the historical development of nuclear energy at SSFL including additional SNAP testing and development information.

Destructive Testing

The Idaho National Laboratory
Idaho National Laboratory
Idaho National Laboratory is an complex located in the high desert of eastern Idaho, between the town of Arco to the west and the cities of Idaho Falls and Blackfoot to the east. It lies within Butte, Bingham, Bonneville and Jefferson counties...

 conducted three destructive tests of SNAP nuclear reactors at Test Area North prior to the launch of SNAP-10A.The SNAPTRAN-3 destructive experiment, on April 1, 1964, simulated a rocket crash into the ocean, purposely creating a fireball and sending radioactive debris across the Idaho
Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....


See also

    Radar Ocean Reconnaissance SATellite or RORSAT is the western name given to the Soviet Upravlyaemyj Sputnik Aktivnyj satellites. These satellites were launched between 1967 and 1988 to monitor NATO and merchant vessels using active radar...

    , the Soviet Union nuclear reactor powered satellites.
  • Safe Affordable Fission Engine
    Safe Affordable Fission Engine
    Safe Affordable Fission Engine are NASA's small experimental nuclear fission reactors for electricity production in space. Most known is the SAFE-400 reactor producing 400 kW thermal power, giving 100 kW of electric energy using a Brayton cycle gas turbine. The fuel is uranium nitride in...

External links

  • International Designator
    International Designator
    The International Designator, also known as COSPAR designation, and in the United States as NSSDC ID, is an international naming convention for satellites...

    : 1965-027A