Signals from a Department of Defense satellite launched recently from Vandenberg Air Force Base, California, by an Air Force Thor Able Star booster are being transmitted successfully with electricity from a nuclear power source. The nuclear device, SNAP-9A, is the third lightweight radioisotope-fueled thermoelectric generator to be used in a satellite.
SNAP-9A is designed to provide 25 watts of direct electrical current. It is the first all-nuclear power system used on a satellite. Two similar, but smaller, generators, representing the world's first and second use of atomic power in space, were orbited in DOD satellites in 1961. Those satellites derived part of their electric power from solar cells.
The SNAP-9A device, weighing 27 pounds, was developed for the Atomic Energy Commission by the Nuclear Division of the Martin Company, Baltimore, builder of the two smaller generators. There are no moving parts in the device. Spontaneous decay of the Plutoniuln-238 fuel generates heat inside its tightly-sealed container. This heat is converted directly into electrical energy by an assembly of thermocouples.*
The generator is about 20 inches in diameter, including fins, and 10 inches high, and is mounted on one end of the satellite. The generator's surface is covered with a coating to help reflect the sun's'rays and to radiate the excess heat generated inside the power system. It has a design life-time of five years.
The isotopic generator requires no battery storage system and shows promise of operating for an extended period of time in orbit. Its use in the satellite is significant since all of the power to the satellite is provided by SNAP-9A; none is being supplied by the more conventional solar cell-battery system used on other satellites. The successes of the first two operational tests of the smaller radioisotope-fueled units and the test of SNAP-gA are expected to open the door to numerous space applications in which nuclear energy would be the sole source of power.
The orbiting generators were developed in the AEC's systems for nuclear auxiliary power (SNAP) program. The program includes the * The electrical current is produced when two dissimilar metals are joined in a closed circuit (thermoeouples) and the two junctions are kept at different temperatures. The Plutonium-238 was produced at the AEC Savannah River Plant.