Aviation Week & Space Technology, 10/01/2007, page 37

Craig Covault, Cape Canaveral

In a major advancement for robotic exploration, NASA is moving quickly to make space nuclear power, and eventually nuclear propulsion, an inherent design element in near-term, medium-cost planetary missions.

The objective will be to open previously isolated areas of the Solar System for robotic exploration as early as 2013.

U.S. nuclear-powered space missions have been few and far between, hampered by cost, politics and the pace of technology development at the Energy Dept., NASA and the contractors.

Initial proposals for Discovery and Mars Scout missions to use Stirling closed-loop nuclear power systems are due to NASA headquarters by Nov. 30.

"We are seeking new ideas for exploration that we previously thought was out of the realm of possibility and probability," says Jim Adams, deputy director of the NASA Planetary Science Div.

The new NASA nuclear power initiative is likely also to benefit military space operations and spur technology innovation by space contractors, NASA managers here say.

The nuclear power initiative comes as the Jet Propulsion Laboratory Dawn mission, equipped with revolutionary solar electricion propulsion, is beginning its eight-year, 3-billion-mile journey to the asteroid belt where it will orbit the infant planets Vesta and Ceres (AW&ST July 2, p. 56).

A key objective of the nuclear initiative is to undertake much more aggressive exploration of bodies like those for which Dawn is headed. In the outer Solar System, these include the moons of Jupiter, Saturn, Uranus and Neptune and Kuiper Belt objects that are remnants of the Solar Systems formation (see photo).

The emphasis on planetary moons and small bodies like asteroids is as strong in the science community as enthusiasm for a return to the Moon.

In addition, a new study sponsored by the International Academy of Astronautics (IAA)just released publicly proposes a focus on such small bodies and asteroids as a potential alternative to a return to expensive manned lunar operations. The IAA sees this as a way to develop technologies for future manned Mars exploration without development of a lunar base.

But the new nuclear initiative has equal application for possible future systems use on the Moon and Mars.

The Stirling closed-loop nuclear system is being developed by Lockheed Martin Astronautics at Valley Forge, Penn., under contract to the Energy Dept. in Germantown, Md. In support of this project, the NASA Glenn Research Center established a near-term technology effort to provide some of the critical data to ensure a successful transition to flight for what will be the first dynamic power system to be used in space. The generator will be able to operate in the vacuum of deep space or in an atmosphere such as on the surface of Mars.

High system efficiency is obtained through the use of free-piston Stirling power-conversion technology. The thermal energy will be derived from the decay of the plutonium heat source. Previously, Glenns supporting technology efforts focused only on the most critical technical issues. Now, however, they have been expanded to cover a more comprehensive range of technical issues.