Advanced Stirling Radioisotope Generators (ASRGs)
are a new type of RPS that is being developed by NASA and the Department of Energy. Like an RTG
, the ASRG converts heat energy to electricity, but it has moving parts. Inside the device, a moving piston is driven by the heat of the nuclear fuel source. The piston moves a magnet back and forth through a coil of wire more than 100 times per second to generate electrical current in the wire. To prevent physical wear, the piston is suspended in a helium gas bearing, meaning it does not actually touch the inside of the mechanism.
An ASRG features a power output of more than 130 Watts electric (or We) using two general purpose heat source (GPHS) modules - slightly more power than the more conventional MMRTG, which uses eight GPHS modules. With an operational efficiency goal of over 25 percent, the ASRG would be about four times more efficient than the more traditional MMRTG.
Like the MMRTG, the ASRG is designed to be modular, meaning that more than one unit could be used in different combinations depending on a mission's scientific and operational needs.
NASA is currently studying the first potential in-space use of the ASRG. No flight opportunity has yet been selected.
In addition to space applications, the technology being developed for the ASRG could be utilized for other long-life, low- or no-maintenance applications requiring conversion of heat to mechanical or electrical power, such as electricity generation here on Earth.
Fact sheet: ASRG - Advanced Stirling Radioisotope Generator (PDF, 627 KB)