The Systems Nuclear Auxiliary POWER (SNAP) program was a program of experimental

radioisotope thermoelectric generator A radioisotope thermoelectric generator (RTG, RITEG), sometimes referred to as a radioisotope power system (RPS), is a type of nuclear battery that uses an array of thermocouples to convert the heat released by the decay of a suitable radioacti ...

s (RTGs) and space nuclear reactors flown during the 1960s by

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedi ...

Odd-numbered SNAPs: radioisotope thermoelectric generators

Radioisotope thermoelectric generators use the heat of

radioactive decay Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...

to produce electricity.

SNAP-1

SNAP-1 was a test platform that was never deployed, using cerium-144 in a

Rankine cycle The Rankine cycle is an idealized thermodynamic cycle describing the process by which certain heat engines, such as steam turbines or reciprocating steam engines, allow mechanical work to be extracted from a fluid as it moves between a heat sou ...

with mercury as the heat transfer fluid. Operated successfully for 2500 hours.

SNAP-3

SNAP-3 was the first RTG used in a space mission (1961). Launched aboard U.S. Navy Transit 4A and 4B navigation satellites. The electrical output of this RTG was 2.5 watts.

SNAP-7

SNAP-7A D and F was designed for marine applications such as lighthouses and buoys; at least six units were deployed in the mid-1960s, with names SNAP-7A through SNAP-7F. SNAP-7D produced thirty watts of electricity using (about four kilograms) of

strontium-90 Strontium-90 () is a radioactive isotope of strontium produced by nuclear fission, with a half-life of 28.8 years. It undergoes β− decay into yttrium-90, with a decay energy of 0.546 MeV. Strontium-90 has applications in medicine and ...

as SrTiO₃. These were very large units, weighing between .

SNAP-9

After SNAP-3 on Transit 4A/B, SNAP-9A units served aboard many of the Transit satellite series. In April 1964 a SNAP-9A failed to achieve orbit and disintegrated, dispersing roughly of

plutonium-238 Plutonium-238 (238Pu or Pu-238) is a fissile, radionuclide, radioactive isotope of plutonium that has a half-life of 87.7 years. Plutonium-238 is a very powerful alpha emitter; as alpha particles are easily blocked, this makes the plutonium-238 ...

over all continents. Most plutonium fell in the southern hemisphere. Estimated 6300

GBq The becquerel (; symbol: Bq) is the unit of radioactivity in the International System of Units (SI). One becquerel is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. For applications relatin ...

or 2100 person-Sv of radiation was released.

SNAP-11

SNAP-11 was an experimental RTG intended to power the Surveyor probes during the lunar night. The

curium-242 Curium (96Cm) is an artificial element with an atomic number of 96. Because it is an artificial element, a standard atomic weight cannot be given, and it has no stable isotopes. The first isotope synthesized was 242Cm in 1944, which has 146 neutr ...

RTGs would have produced 25 watts of electricity using 900 watts of thermal energy for 130 days. The hot junction temperature was , the cold junction temperature was . They had a liquid NaK thermal control system and a movable shutter to dump excess heat.SNAP-11 Surveyor Program, Third Quarterly Report
/ref>SNAP-11 Surveyor Program, Thirteenth Quarterly Report
/ref> They were not used on the Surveyor missions.

In general, the SNAP 11 fuel block is a cylindrical multi-material unit which occupies the internal volume of the generator. TZM (molybdenum alloy) fuel capsule, fueled with
curium-242 Curium (96Cm) is an artificial element with an atomic number of 96. Because it is an artificial element, a standard atomic weight cannot be given, and it has no stable isotopes. The first isotope synthesized was 242Cm in 1944, which has 146 neutr ...
(Cm₂O₃ in an iridium matrix) is located in the center of the fuel block. Capsule is surrounded by a platinum sphere, approximately inches in diameter, which provides shielding and acts as an energy absorber for impact considerations. This assembly is enclosed in graphite and beryllium sub-assemblies to provide the proper thermal distribution and ablative protection.

SNAP-19

SNAP-19(B) was developed for the Nimbus-B satellite by the Nuclear Division of the Martin-Marietta Company (now Teledyne Energy Systems). Fueled with plutonium-238, two parallel lead telluride thermocouple generators produced an initial maximum of approximately 30 watts of electricity. Nimbus 3 used a SNAP-19B with the recovered fuel from the Nimbus-B1 attempt. SNAP-19's powered the

Pioneer 10 ''Pioneer 10'' (originally designated Pioneer F) is an American space probe, launched in 1972 and weighing , that completed the first mission to the planet Jupiter. Thereafter, ''Pioneer 10'' became the first of five artificial objects to ac ...

and

Pioneer 11 ''Pioneer 11'' (also known as ''Pioneer G'') is a robotic space probe launched by NASA on April 5, 1973, to study the asteroid belt, the environment around Jupiter and Saturn, solar winds, and cosmic rays. It was the first probe to encounte ...

missions. They used n-type 2N-PbTe and p-type TAGS-85 thermoelectric elements. Modified SNAP-19B's were used for the Viking 1 and Viking 2 landers. A SNAP-19C was used to power a telemetry array at

Nanda Devi Nanda Devi is the second-highest mountain in India, after Kangchenjunga, and the highest located entirely within the country (Kangchenjunga is on the border of India and Nepal). It is the 23rd-highest peak in the world. Nanda Devi was consi ...

Uttarakhand Uttarakhand ( , or ; , ), also known as Uttaranchal ( ; List of renamed places in India, the official name until 2007), is a States and union territories of India, state in the North India, northern part of India. It is often referred to as t ...

for a CIA operation to track Chinese missile launches.

SNAP-21 & 23

SNAP-21 and SNAP-23 were designed for underwater use and used

as the radioactive source, encapsulated as either strontium oxide or strontium titanate. They produced about ten watts of electricity.

SNAP-27

Five SNAP-27 units provided electric power for the

Apollo Lunar Surface Experiments Package The Apollo Lunar Surface Experiments Package (ALSEP) comprised a set of scientific instruments placed by the astronauts at the landing site of each of the five Apollo missions to land on the Moon following Apollo 11 (Apollos 12, 14, 15, 16, ...

s (ALSEP) left on the Moon by

Apollo Apollo, grc, Ἀπόλλωνος, Apóllōnos, label=genitive , ; , grc-dor, Ἀπέλλων, Apéllōn, ; grc, Ἀπείλων, Apeílōn, label=Arcadocypriot Greek, ; grc-aeo, Ἄπλουν, Áploun, la, Apollō, la, Apollinis, label= ...

12, 14, 15, 16, and 17. The SNAP-27 power supply weighed about 20 kilograms, was 46 cm long and 40.6 cm in diameter. It consisted of a central fuel capsule surrounded by concentric rings of thermocouples. Outside of the thermocouples was a set of fins to provide for heat rejection from the cold side of the thermocouple. Each of the SNAP devices produced approximately 75 W of electrical power at 30 VDC. The energy source for each device was a rod of plutonium-238 providing a thermal power of approximately 1250 W. This fuel capsule, containing of

in oxide form (44,500 Ci or 1.65 PBq), was carried to the Moon in a separate fuel cask attached to the side of the

Lunar Module The Apollo Lunar Module (LM ), originally designated the Lunar Excursion Module (LEM), was the lunar lander spacecraft that was flown between lunar orbit and the Moon's surface during the United States' Apollo program. It was the first crewed ...

. The fuel cask provided thermal insulation and added structural support to the fuel capsule. On the Moon, the Lunar Module pilot removed the fuel capsule from the cask and inserted it in the RTG. These stations transmitted information about moonquakes and meteor impacts, lunar magnetic and gravitational fields, the Moon's internal temperature, and the Moon's atmosphere for several years after the missions. After ten years, a SNAP-27 still produced more than 90% of its initial output of 75 watts. The fuel cask from the SNAP-27 unit carried by the

Apollo 13 Apollo 13 (April 1117, 1970) was the seventh crewed mission in the Apollo space program and the third meant to land on the Moon. The craft was launched from Kennedy Space Center on April 11, 1970, but the lunar landing was aborted af ...

mission currently lies in of water at the bottom of the Tonga Trench in the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contine ...

. This mission failed to land on the moon, and the

lunar module The Apollo Lunar Module (LM ), originally designated the Lunar Excursion Module (LEM), was the lunar lander spacecraft that was flown between lunar orbit and the Moon's surface during the United States' Apollo program. It was the first crewed ...

carrying its generator burnt up during re-entry into the Earth's atmosphere, with the trajectory arranged so that the cask would land in the trench. The cask survived re-entry, as it was designed to do, and no release of plutonium has been detected. The corrosion resistant materials of the capsule are expected to contain it for 10 half-lives (870 years).

Even-numbered SNAPs: compact nuclear reactors

A series of compact nuclear reactors intended for space use, the even numbered SNAPs were developed for the U.S. government by the Atomics International division of

North American Aviation North American Aviation (NAA) was a major American aerospace manufacturer that designed and built several notable aircraft and spacecraft. Its products included: the T-6 Texan trainer, the P-51 Mustang fighter, the B-25 Mitchell bomber, the ...

SNAP Experimental Reactor (SER)

The SNAP Experimental Reactor (SER) was the first reactor to be built by the specifications established for space satellite applications. The SER used uranium zirconium hydride as the fuel and eutectic sodium-potassium alloy ( NaK) as the coolant and operated at approximately 50 kW thermal. The system did not have a power conversion but used a secondary heat air blast system to dissipate the heat to the atmosphere. The SER used a similar reactor reflector moderator device as the

SNAP-10A SNAP-10A (Systems for Nuclear Auxiliary Power, aka Snapshot for Space Nuclear Auxiliary Power Shot, also known as OPS 4682) was a US experimental nuclear powered satellite launched into space in 1965 as part of the SNAPSHOT program.lithium hydride. The reactor was at the small end and the crew capsule/payload was in the shadow of the large end. Studies were performed on the reactor, individual components and the support system. Atomics International, a division of North American Aviation did the development and testing work. The SNAP-2 Shield Development unit was responsible for developing the radiation shield. Creating the shield meant melting lithium hydride and casting it into the form required. The form was a big truncated cone. Molten lithium hydride had to be poured into the casting mold a little at a time otherwise it would crack as it cooled and solidified. Cracks in the shield material would be fatal to any space crew or payload depending on it because it would allow radiation to stream through to the crew/payload compartment. As the material cooled, it would form kind of a hollowed vortex in the middle. The development engineers had to create ways to fill the vortex while maintaining the shield's integrity. And, in doing all this they had to keep in mind that they were working with a material that could be explosively unstable in a moist oxygen rich environment. Analysis also revealed that under thermal and radiation gradients, the lithium hydride could disassociate and hydrogen ions could migrate through the shield. This would produce variations of shielding efficacy and could subject the payloads to intense radiation. Efforts were made to mitigate these effects. The SNAP 2DR used a similar reactor reflector moderator device as the

SNAP-10A SNAP-10A (Systems for Nuclear Auxiliary Power, aka Snapshot for Space Nuclear Auxiliary Power Shot, also known as OPS 4682) was a US experimental nuclear powered satellite launched into space in 1965 as part of the SNAPSHOT program.National Aeronautics and Space Administration The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding ...

. Two SNAP-8 reactors were produced: The SNAP 8 Experimental Reactor and the SNAP 8 Developmental Reactor. Both SNAP 8 reactors used the same highly enriched uranium zirconium hydride fuel as the SNAP 2 and SNAP 10A reactors. The SNAP 8 design included primary and secondary NaK loops to transfer heat to the mercury rankine power conversion system. The electrical generating system for the SNAP 8 reactors was supplied by Aerojet General. The SNAP 8 Experimental Reactor was a 600 kW_t reactor that was tested from 1963 to 1965. The SNAP 8 Developmental Reactor had a reactor core measuring , contained a total of of fuel, had a power rating of 1 MW_t. The reactor was tested in 1969 at the Santa Susana Field Laboratory.

SNAP-10A

The SNAP-10A was a space-qualified nuclear reactor power system launched into space in 1965 under the SNAPSHOT program.SNAPSHOT
NASA Glenn Research Center, March 20, 2007. Retrieved 3 April 2019.
Gunther's Space Page. Retrieved 3 April 2019. It was built as a research project for the Air Force, to demonstrate the capability to generate higher power than RTGs. The reactor employed two moveable beryllium reflectors for control, and generated 35 kW_t at beginning of life. The system generated electricity by circulating NaK around lead tellurium thermocouples. To mitigate launch hazards, the reactor was not started until it reached a safe orbit. SNAP-10A was launched into Earth orbit in April 1965, and used to power an Agena-D research satellite, built by Lockheed/Martin. The system produced 500W of electrical power during an abbreviated 43-day flight test. The reactor was prematurely shut down by a faulty command receiver. It is predicted to remain in orbit for 4,000 years.

Citations

General sources

NUCLEAR POWER IN SPACE ''U.S. Department of Energy, Office of Nuclear Energy, Science & Technology''

External links

SNAP-8 Electrical Generating System Development Program, Final Report

SNAP-19, Phase 3. Quarterly Progress Report, 1 January – 31 March 1966

SNAP 19, Phase 3. Quarterly Progress Report, 1 Apr. – 30 Jun. 1966

Analysis of the need for Agena command destruct and/or generator eject systems on the Nimbus B/SNAP-19 mission

SNAP-19/Nimbus B integration experience

SNAP-27, Volume 1. Quarterly Report, 1 Jul. – 30 Sep. 1966

SNAP-27, Volume 2. Quarterly Report, 1 Jan. – 31 Mar. 1966

"Space Nuclear Power: Opening the Final Frontier"
by G. L. Bennett (2006)

{{Nuclear Technology Atomics International Electrical generators NASA programs North American Aviation Nuclear power in space Nuclear technology United States Atomic Energy Commission