For Release: July 16, 2001
Media Relations Office
Another step toward longer, speedier deep space missions was taken when a Stirling convertor provided the electricity to a Hall effect electric thruster in recently completed tests at the NASA Glenn Research Center, Cleveland, OH. Together, the two technologies, which had never before been operated as an integrated system, signal the arrival of lower mass, higher efficiency propulsion for NASA's deep space missions.
"Both of these technologies are now at a development level that allows them to be considered by NASA mission planners. Since Glenn has long been involved in developing these concepts into space technologies, the idea of putting them together was a natural for us," said Glenn project engineer Lee Mason. "We broke new ground with this test in that we established the feasibility of this system."
The 350-watt Stirling convertor was built by Stirling Technology Co., Kennewick, WA, under a Small Business Innovative Research agreement with Glenn. The Hall effect electric thruster was chosen to match the Stirling convertor's output from Glenn's inventory of such thrusters. Glenn researchers designed the power processor unit that took the electrical output from the convertor and distributed it to all the loads of the thruster.
A Stirling convertor changes heat energy into electricity through the action of an expanding fluid that drives a piston through an alternator's magnetic field. An electric thruster uses electricity to ionize (or strip an electron from) its propellant, which on ejection from the thruster produces thrust.
Fitted with a nuclear heat source, Stirling convertors become strong candidates for providing electrical power for robotic missions to the outer solar system where solar panels would be ineffective. Their potential for high power output also makes them attractive in any type of mission with power-hungry systems like electric thrusters.
Electric thrusters produce much less thrust but are up to 10 times more fuel efficient than chemical rockets. Because of this the spacecraft they propel can be smaller and lighter and cost much less to launch. Despite their miniscule thrust, electric thrusters can make longer trips in shorter times, as they can operate continually and fly directly to their destinations without the circuitous gravity-assist maneuvers that chemical rockets often require.
The next development goal, according to Mason, is to increase the efficiency of the power transfer. A direct drive system, eliminating the power processor unit, would increase efficiency and reduce mass -- making the technology even more attractive, he said.
Among its many research and development activities, Glenn, one of the Nation's leading federal research laboratories for 60 years, conducts basic research in propulsion and power for NASA's robotic science and human exploration missions.
For more information about Stirling convertors, electric propulsion, and NASA's Small Business Innovative Research Program, see, respectively,
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Print quality images are available at: http://www.grc.nasa.gov/WWW/PAO/pressrel/2001/01-056addm.html
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