Systems Nuclear Auxiliary Power Program

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The Systems Nuclear Auxiliary Power Program (SNAP) was a program of experimental radioisotope thermoelectric generators (RTGs) and space nuclear reactors flown during the 1960s by NASA. Odd-numbered SNAPs were RTG tests and even-numbered SNAPs were compact reactor system tests. One even-numbered unit, the SNAP-10A, has the distinction of being the only nuclear reactor launched into space by the United States.

Contents

[edit] Odd Numbered SNAPs - The Radioiostope Thermoelectric Generators

SNAP-1 was not deployed, but was designed to use cerium-144 in a Rankine cycle, with mercury as the heat transfer fluid; it operated for 2500 hours successfully.[1]

SNAP-7 was designed for marine applications such as lighthouses and buoys;[2] at least six units were deployed in the mid-1960s, with names SNAP-7A through SNAP-7F. SNAP-7D produced thirty watts of electric power[3] using 225 kilocuries[4] (about four kilograms) of strontium-90 as SrTiO3. These were very large units, weighing between 1870 and 6000 pounds.[5]

In 1961, the first RTG used in a space mission was launched aboard a U.S. Navy Transit 4A and 4B navigation satellites. The electrical power output of this RTG, which was called (SNAP-3), was a mere 2.7 watts. SNAP-9A served aboard the rest of the Transit satellite series.

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

SNAP-19s powered Pioneer 10 and Pioneer 11 missions[6] as well as the Viking 1 and Viking 2 landers.

SNAP-21[7] and SNAP-23 were designed for underwater use[8][9] and used strontium-90 as the radioactive source, encapsulated as either strontium oxide or strontium titanate. They produced about ten watts.

Five SNAP-27 units provided electric power for the Apollo Lunar Surface Experiment Packages (ALSEP) left on the Moon by Apollo 12, 14, 15, 16, and 17. The fuel capsule, containing 3.8 kilograms (8.4 pounds) of plutonium-238 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 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 70 watts.

The fuel cask from the SNAP-27 unit carried by the Apollo 13 mission currently lies in 20,000 feet (6,500 m) of water at the bottom of the Tonga Trench in the Pacific Ocean. This mission failed to land on the moon, and the lunar module 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,[10] 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).[11]

[edit] Even Number SNAPs - The Compact Nuclear Reactors

SNAP Experimental Reactor (SER) was the first reactor to be built by the specifications established for space satellite applications. Criticality was achieved in September 1959 with final shutdown completed in December 1961. 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 but with only one reflector. The project was considered a success. It gave continued confidence in the development of the SNAP Program; it also led to in depth research and component development.

SNAP-2 Developmental Reactor was the second SNAP reactor built. This device used Uranium-zirconium hydride fuel and had a design reactor power of 55 kWt. It was the first model to use a flight control assembly and was tested from April 1961 to December 1962. Studies were performed on the reactor, individual components and the support system. The SNAP2DR used a similar reactor reflector moderator device as the SNAP-10A but with two movable and internal fixed reflectors. The system was designed so that the reactor could be integrated with a Mercury- Rankine cycle to generate 3.5 KW of electricity. There were no major problems in the testing of the SNAP-2DR.

SNAP-8 was a Rankine cycle nuclear reactor which used sodium and potassium to transfer heat to the mercury working fluid. It was capable of generating between 35 to 90 Kilowatts of power.

The SNAP-10A produced 500 W of electrical power during an abbreviated 43-day flight test.

[edit] References

  1. ^ http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660005486_1966005486.pdf
  2. ^ http://www.davistownmuseum.org/cbm/Rad8f.html
  3. ^ http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=4713816
  4. ^ http://www.davistownmuseum.org/cbm/Rad8f.html
  5. ^ http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660005486_1966005486.pdf
  6. ^ SNAP-19: Pioneer F & G, Final Report, Teledyne Isotopes, 1973
  7. ^ http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=4816023
  8. ^ http://ieeexplore.ieee.org/iel6/8271/26019/01161004.pdf?arnumber=1161004
  9. ^ http://www.davistownmuseum.org/cbm/Rad8f.html
  10. ^ Apollo 12 ALSEP Off-load transcript, containing comment about re-entry survivability of fuel cask
  11. ^ Space FAQ 10/13 - Controversial Questions, faq.org

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