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21 July 2003 |
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http://www.space.com/spacenews/spacenews_businessmonday_030721.html |
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With its selection of Boeing’s Rocketdyne Power and Propulsion unit to develop a modernized nuclear-electric generator as an option for NASA space probes, the U.S. government has set the stage for a competition between that concept and a radically different approach being pursued by Lockheed Martin, an agency official said. “Each [concept] has its own virtues and it’ll be a shootout,” said Al Newhouse, who heads NASA’s Project Prometheus space-nuclear power effort. Boeing’s Multi-Mission Radioisotope Thermoelectric Generator (RTG) will be a more powerful variant of the generators built by its teammate, Teledyne Energy Systems Inc. of Hunt Valley, Md., for NASA’s Viking 1 and 2 landers. While the Multi-Mission RTG will not be as powerful as the RTGs aboard NASA’s Cassini Saturn probe, it will be more flexible, adaptable to both orbiter and lander missions, a Boeing official said. RTGs work by using the heat from radioactive plutonium 238 to create temperature differences across pairs of small metal rods, which in turn generates an electrical current. The Viking craft that landed on Mars in 1976 were each equipped with two RTGs to power their scientific instruments. The Department of Energy awarded the Multi-Mission RTG contract to Boeing in June using NASA funds. The contract could be worth $118 million over 10 years if the Department of Energy, which under U.S. law manages all U.S. nuclear programs, exercises all of its options. Under a separate contract of similar value, Lockheed Martin is developing a new type of space nuclear power system called a Stirling radioisotope generator. The Stirling generator would use the heat from plutonium 238 to vibrate pistons between pieces of metal to generate electricity, NASA and Energy Department officials explained. Plans call for choosing one of these nuclear technologies as the leading option to power a host of deep space probes envisioned by NASA managers. The first such mission likely will be NASA’s Mars Science Laboratory rover mission in 2009. However, a yet-to-be-selected mission under NASA’s New Frontiers initiative also would be a candidate, Newhouse said. The first of the New Frontiers missions is slated for launch around the end of the decade, Newhouse said. The Stirling and Multi-Mission RTG projects will proceed on roughly parallel schedules, said Earl Wahlquist who oversees the contracts as head of the Energy Department’s office of Space and Defense Power Systems. The technical tradeoffs between the Multi-Mission RTG and the Stirling approach have been studied, but the competition will clarify how those trade-offs balance out, Wahlquist and Newhouse said. “The major trade is that Stirling is a higher efficiency device where you require less plutonium 238,” Wahlquist said. Studies show that the Multi-Mission RTG could convert about 7 percent of its heat to electricity whereas the Stirling device has a conversion ratio of roughly 25 percent, Wahlquist said. That is significant because the United States currently does not produce plutonium 238. The Energy Department plans to purchase the plutonium from Russia, and it is Newhouse’s responsibility to use that plutonium as efficiently as possible. “The less plutonium we need, the more [generators] we can build,” he said. A potential drawback to the Stirling device is that it relies on moving pistons that could be prone to breaking down in space, Wahlquist and Newhouse said. By pitting the two concepts against each other, Newhouse hopes to produce two viable options while giving the contractors an incentive to meet NASA’s aggressive schedule for future science missions, he said. An engineering model of the Multi-Mission RTG must be completed by late 2005, in time for the scheduled preliminary design review for the Mars Science Laboratory, Wahlquist said. “We’ve been running with one RTG in our inventory, which is going to Pluto,” he said, referring to NASA’s New Horizons mission, which is slated to launch in early 2006. Boeing’s Multi-Mission RTG will generate 110 watts of power, said Rich Rovang, the program manager at Boeing’s Rocketdyne unit of Canoga Park, Calif. By contrast, each of two RTGs on the Viking landers generated 35-watts, according to a Department of Energy fact sheet.
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