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When NASA astronauts return to the Moon and begin establishing a lunar outpost, they will need power sources on the lunar surface. Engineers at NASA's Glenn Research Center (GRC) in Cleveland have been exploring the possibility of nuclear fission to provide the necessary power and have taken the initial steps toward a non-nuclear system-level technology demonstration of this type of power system.

A potential fission surface power system on the Moon would generate a steady 40 kilowatts of electric power, enough for about 8 houses on Earth. Fission surface power systems depend on splitting uranium atoms in a reactor to generate heat that is converted into electric power. They offer many potential advantages over other power sources, including the ability to produce large amounts of power in harsh environments, like the surfaces of the moon and Mars, without depending on sunlight. The primary components of fission surface power systems are a heat source, power conversion, heat rejection, and power conditioning and distribution.

"Our goal is to build a technology demonstration unit with all the major components of a fission surface power system and conduct non-nuclear, integrated system testing in a ground-based space simulation facility," said Lee Mason, principal investigator at GRC for the test. "Our long-term goal is to demonstrate technical readiness early in the next decade, when NASA is expected to decide on the type of power system to be used on the lunar surface."

An artist's concept of a fission surface power system on the surface of the Moon. The nuclear reactor has been buried below the lunar surface to make use of lunar soil as additional radiation shielding. The engines that convert heat energy to electricity are in the tower above the reactor, and radiators extend out from the tower to radiate into space any leftover heat energy that has not been converted to electricity. The power system would transmit a steady 40 kW of electric power, enough for about 8 houses on Earth, to the lunar outpost. (Photo courtesy of NASA)

GRC recently contracted for the design and analysis of two different types of advanced power conversion units as an early step in the development of a full system technology demonstration. These power conversion units are necessary to process the heat produced by the nuclear reactor and efficiently convert it to electrical power.

The first design concept by Sunpower, Inc., of Athens, Ohio, uses free-piston Stirling conversion in the form of two opposed piston engines coupled to alternators that produce 6 kilowatts each, or a total of 12 kilowatts of power. The second contract with Barber Nichols, Inc., of Arvada, Colorado, is for development of a closed Brayton cycle engine that uses a high-speed turbine and compressor coupled to a rotary alternator that also generates 12 kilowatts of power.

"Development and testing of the power conversion unit will be a key factor in demonstrating the readiness of fission surface power technology and provide NASA with viable and cost-effective options for nuclear power on the Moon and Mars," said Don Palac, manager of GRC's Fission Surface Power Project.

After a one-year design and analysis phase, a single contractor will be selected to build and test a prototype power conversion unit. When complete, this unit will be integrated by GRC with the other Technology Demonstration Unit's major components. GRC will develop the heat rejection system and provide the space simulation facility. GRC will also work in conjunction with the Department of Energy and NASA's Marshall Space Flight Center in Huntsville, Alabama, which will develop and provide a non-nuclear reactor simulator with liquid metal coolant as the heat source unit for this technology demonstration.

A nuclear reactor used in space is much different than Earth-based systems. There are no large concrete cooling towers, and the reactor is about the size of an office trash can. The energy produced from a space reactor is also much smaller, but is more than adequate for the projected power needs of a lunar outpost. The main technical challenge is developing a compact and reliable power system that can be used on the Moon and possibly later on Mars.

Testing of the non-nuclear system is expected to take place at GRC in 2012 or 2013. These tests will verify system performance projections, develop safe and reliable control methods, gain valuable operating experience, and reduce technology and programmatic risks. This system-level technology demonstration is the central focus of the Fission Surface Power Systems Project, conducted under NASA's Exploration Technology Development Program.