Now nuclear power is being considered for lunar and Mars missions because, unlike alternatives such as solar power, it can provide constant energy, a necessity for human life-support systems, recharging rovers, and mining for resources. Solar power systems would also require the use of energy storage devices like batteries or fuel cells, adding unwanted mass to the system. Solar power is further limited because the moon is dark for up to 14 days at a time and has deep craters that can obscure the sun. Mars is farther away from the sun than either the Earth or the moon, so less solar power can be harvested there.
The new nuclear power system is part of a NASA project started in 2006, called Fission Surface Power, that is examining small reactors designed for use on other planets. While nuclear power remains controversial, the researchers say that the reactor would be designed to be completely safe and would be buried a safe distance from the astronauts to shield them from any radiation it would generate.
The recent tests examined technologies that would see a nuclear reactor coupled with a Stirling engine capable of producing 40 kilowatts of energy--enough to power a future lunar or Mars outpost.
To generate electricity, the researchers used a liquid metal to transfer the heat from the reactor to the Stirling engine, which uses gas pressure to convert heat into the energy needed to generate electricity. For the tests, the researchers used a non-nuclear heat source. The liquid metal was a sodium potassium mixture that has been used in the past to transfer heat from a reactor to a generator, says Palac, but this is the first time this mixture has been used with a Stirling engine.
"They are very efficient and robust, and we believe [it] can last for eight years unattended," says Lee Mason, the principal investigator of the project at Glenn. The system performed better than expected, Palac says, generating 2.3 kilowatts of power at a steady pace.
The researchers also developed a lightweight radiator panel to cool the system and dissipate the heat from the reactor. The prototype panel is approximately six feet by nine feet--one-twentieth the size required for a full-scale system. Heat from a water-cooling system is circulated to the radiator where it dissipates.
The researchers tested the radiator panel in a vacuum chamber at Glenn that replicates the lack of atmosphere and the extreme temperatures on the moon--from over 100 degrees Celsius during the day to below 100 degrees Celsius at night. The panel dissipated six kilowatts of energy, more than expected--a "very successfully test," says Palac. On the moon, the panel must also survive the dusty environment cause by the regolith.
Lastly, the researchers tested the performance of the Stirling alternator in a radiation environment at Sandia National Laboratories in Albuquerque, NM. The objective was to test the performance of the motor, ensuring that the materials would not degrade. The alternator was subjected to 20 times the amount of radiation it would expect to see in its lifetime and survived without any significant problems.
Mason says that the tests are very important in showing the feasibility of the system and that the next step is for the researchers to conduct a full system demonstration, by combining a non-nuclear reactor simulator with the Stirling engine and radiator panel. He says that these tests should be completed in 2014.