Volume 9, Number 6 • November/December 2001 • Small Business/SBIR

SBIR-Produced Converter Provides Thrust

Another step toward longer, speedier deep-space missions was taken when an SBIR-produced Stirling converter provided the electricity to a Hall effect electric thruster in recently completed tests at the NASA Glenn Research Center, Cleveland, Ohio. 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.

A Stirling converter (top) provided the electricity to a Hall effect electric thruster (bottom) in tests at Glenn Research Center. Together, the technologies signal the arrival of lower mass, higher efficiency propulsion for NASA’s deep-space missions. Photo provided by Glenn Research Center.

“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 converter was built by Stirling Technology Co., of Kennewick, Washington, under an SBIR agreement with Glenn. The Hall effect electric thruster was chosen to match the Stirling converter’s output from Glenn’s inventory of such thrusters. Glenn researchers designed the power processor unit that took the electrical output from the converter and distributed it to all the loads of the thruster.

A Stirling converter 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 produces thrust on ejection from the thruster.

Fitted with a nuclear heat source, Stirling converters 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, costing 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,” Mason concluded. Q

For more information, contact Lee Mason at NASA Glenn Research Center, 216/977-7106, Lee.S.Mason@grc.nasa.gov. Please mention you read about it in Innovation.

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