Systems for Nuclear Auxiliary Power

The Systems Nuclear Auxiliary Power (SNAP) program was a program of experimental radioisotope thermoelectric generators (RTGs) and space nuclear reactors flown during the 1960s by NASA.

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.

SNAP-3 : 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 2.5 watts.

SNAP-7 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 electric power using 225 kilocuries (8.3 PBq) (about four kilograms) of strontium-90 as SrTiO₃. These were very large units, weighing between 1,870 and 6,000 pounds (850 and 2,720 kg).

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 1 kilogram (2.2 lb) of plutonium-238 over all continents. Most plutonium fell in the southern hemisphere. Estimated 6300GBq or 2100 man-Sv of radiation was released and led to NASA's development of solar photovoltaic energy technology.

SNAP-11, an experimental [[1]] intended to power the Surveyor probes during the lunar night. They were to be powered by curium-242 (900 watts thermal) and produce 25 watts of electricity for 130 days. Designed with 925 °F (496 °C; 769 K) hot junction and 350 °F (177 °C; 450 K) cold junction. They had a liquid NaK thermal control system and a movable shutter to dump excess heat. They were not used on the Surveyor missions.

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