Thursday, February 2, 2012

Short Sharp Science - Stirling' power for ultra-efficient space probes

David Shiga, reporter

A new way to use plutonium for power could help NASA explore the solar system, and should be flight tested as soon as possible, a new report says.
Many NASA space probes have been powered by plutonium – especially those, like the Cassini mission to Saturn, that travel too far from the sun to use solar power.
These power sources, called radioisotope thermoelectric generators (RTGs), are not to be confused with nuclear reactors, which artificially speed up nuclear reactions to generate power. Instead they use heat from the passive decay of plutonium-238, whose nuclei are unstable and split spontaneously.
But the US supply of plutonium-238 is left over from the Cold War – and it is running out.
Enter the Advanced Stirling Radioisotope Generator (ASRG). It can squeeze more than four times as much power out of the same mass of plutonium as an RTG. That makes it one of the top technologies that NASA should be developing, says a new report from the National Research Council.
The design is based on a 200-year-old engine in which temperature differences between chambers of gas drive a piston. ASRGs use the heat of decaying plutonium to drive a piston, generating electricity. By contrast, RTGs heat one end of a thermocouple, a device in which a temperature difference between its two ends creates an electric current.
If NASA goes ahead with ASRGs, which have so far only been tested on Earth, they could be used in a proposed mission to send an uncrewed plane to Saturn's moon Titan, among other ideas.
The report, which NASA had requested in order to help prioritise its technology goals, also highlights the importance of developing orbiting fuel depots, among other technologies.

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