Stirling Radioisotope Generator - AbsoluteAstronomy.com

The Stirling radioisotope generator (SRG) is based on a Stirling engine

Stirling engine

A Stirling engine is a heat engine operating by cyclic compression and expansion of air or other gas, the working fluid, at different temperature levels such that there is a net conversion of heat energy to mechanical work....

Radioisotope heater unit

Radioisotope heater units are small devices that provide heat through radioactive decay. They are similar to tiny radioisotope thermoelectric generators , and normally provide about one watt of heat each, derived from the decay of a few grams of plutonium 238, although other radioactive isotopes...

. The hot end of the Stirling converter reaches high temperature and heated helium

Helium

Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

drives the piston, heat being rejected at the cold end of the engine. A generator or alternator converts the motion into electricity. This Stirling converter produces about four times as much electric power

Electric power

Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...

from the plutonium

Plutonium

Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...

fuel than a 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...

(RTG). The Stirling generators have been extensively tested but have not yet been deployed on actual missions.

Stirling engine development began at NASA Glenn Research Center

Glenn Research Center

NASA John H. Glenn Research Center at Lewis Field is a NASA center, located within the cities of Brook Park, Cleveland and Fairview Park, Ohio between Cleveland Hopkins International Airport and the Cleveland Metroparks's Rocky River Reservation, and has other subsidiary facilities in Ohio...

in the early 1970s (then NASA Lewis.) The Space Demonstrator Engine (or SPDE) was the earliest 12.5 kWe per cylinder engine that was designed, built and tested. A later engine of this size, the Component Test Power Converter (or CTPC), used a "Starfish" heat-pipe heater head, instead of the pumped-loop used by the SPDE. In the 1992-93 time period, this work was stopped due to the termination of the related SP-100

SP-100

SP-100 was a U.S. research program for nuclear fission reactors in space. It was started in 1983 by NASA, the US Department of Energy and other agencies. It developed a reactor with heat pipes transporting the heat to thermionic converters...

nuclear power system work and NASA's new emphasis on "better, faster, cheaper" systems and missions.

A current effort, the Advanced Stirling Radioisotope Generator

Advanced Stirling Radioisotope Generator

The Advanced Stirling Radioisotope Generator is a radioisotope power system using Stirling power conversion technology currently being developed under joint sponsorship by the United States Department of Energy and NASA for potential future space missions...

(ASRG), is based on a 55-watt electric converter. The thermal power source for this system is the General Purpose Heat Source

General Purpose Heat Source

The General Purpose Heat Source is a radioactive heat source designed for Radioisotope Thermoelectric Generators or Stirling radioisotope generators . It is meant for space applications and is packaged as a stackable module.-Characteristics:...

(GPHS). Each GPHS contains four iridium-clad

Iridium

Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second-densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C...

Pu-238 fuel pellets, stands 5 cm tall, 10 cm square and weighs 1.44 kg. The hot end of the Stirling converter reaches 650°C and heated helium drives a free piston reciprocating in a linear alternator, heat being rejected at the cold end of the engine. The AC is then converted to 55 watts DC. Thus each ASRG unit will utilise two Stirling converter units with about 500 watts of thermal power supplied by two GPHS units and will deliver 100-120 watts of electric power. The ASRG is currently undergoing qualification testing at NASA Glenn, and is baselined as a power supply for a future NASA Discovery

Discovery Program

NASA's Discovery Program is a series of lower-cost, highly-focused American scientific space missions that are exploring the Solar System. It was founded in 1992 to implement then-NASA Administrator Daniel S. Goldin's vision of "faster, better, cheaper" planetary missions...

mission to be selected in 2011.

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