NASA Elevates Nuclear Power for Robotic Exploration
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.
But that nuclear technology has now matured to a level that makes medium- and low-cost nuclear missions possible.
This has come about with closed-loop Stirling systems four times as powerful as the radioisotope thermoelectric generators (RTGs) used on past missions. Alan Stern, who heads NASA science programs, is anxious to exploit this maturing technology for robotic exploration, and he wants to move fast.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 System’s 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.
Two of the major goals of the IAA assessment are a human mission to a near-Earth asteroid and a human mission to one of the Martian moons, either Phobos or Deimos.
The study also suggests placing new astronomical telescopes at Lagrangian points that have manned system travel distances similar to asteroid missions. An alternative concept involves placing them on the lunar far side.But the new nuclear initiative has equal application for possible future systems use on the Moon and Mars.
The new nuclear planetary program element is dubbed the Discovery and Scout Mission Capabilities Expansion.
It is soliciting "mission concept proposals for small planetary missions that require a nuclear power source, such as the Advanced Stirling Radioisotope Generator (ASRG) currently under development by NASA," says a Sept. 20 NASA memo on the program. "The Discovery and Scout Mission Capabilities Expansion program is intended to foster exploration in the planetary science community of missions enabled by nuclear power," the NASA document says. The program also aims at "encouraging the formation of mission design teams, beginning the discussion of necessary engineering trades, and discovering the breadth of missions possible with the addition of the ASRG nuclear technology."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, Glenn’s 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.