Posted on 03/21/2003 8:23:42 AM PST by boris
Efforts by Stanford University and NASAs Jet Propulsion Laboratory to buy an unusual, bismuth-fueled electric propulsion system from Russia have hit a snag at NASA headquarters, where managers have concerns about the legality of the proposed deal, NASA officials said.
American scientists hope to test the thruster inside a vacuum tank at the Jet Propulsion Laboratory in Pasadena, Calif., and then design their own version. The scientists want to learn whether a thruster fueled by bismuth, a metallic element that is fairly plentiful, has the durability to propel an unmanned probe on long voyages to the outer planets.
The bismuth thruster was designed and built at Russia's Central Scientific Research Institute of Machine Building, known as TsNIIMash. Some NASA officials consider the technology a possible contender to propel the nuclear-electric-powered Jupiter Icy Moons Orbiter proposed for launch in 2011.
American scientists do not question Russia's claims regarding the thruster's fuel-efficiency, but are less certain whether it can operate over a multiyear deep-space mission. "While the performance is there, the Russians have not addressed issues related to life and robustness on-orbit as thoroughly as we would like," said plasma physicist Mark Cappelli of Stanford University, Palo Alto, Calif.
This past September, officials in charge of NASAs Nuclear Systems Initiative, now called Project Prometheus, accepted a proposal by Cappelli and the Jet Propulsion Lab to acquire the thruster. For the deal to proceed, NASA managers would have to consult with the U.S. State Department, which has a role in licensing both the import and export of militarily sensitive technologies. In addition, State's nonproliferation office works with other U.S. agencies to ensure that they do not unwittingly undermine the goal of curbing Russian technology exports to Iran.
"There are obviously policy sensitivities in any potential dealing between the U.S. government and Russian space entities," a State Department official said. NASA officials have not decided whether to bring the proposal to the State Department. The deal "is being held up over policy concerns regarding compliance with the Iran Non-Proliferation Act," said Al Newhouse, NASA's director for Project Prometheus.
The Iran Non-Proliferation Act passed the U.S. House and Senate with no dissenting votes in 2000. It bars NASA from buying international space station hardware from Russia unless the U.S. president can certify that the supplier is not also supplying sensitive technologies to Iran. The law provides exceptions in cases where space station crew safety is at stake.
Newhouse said the thruster proposal is geared toward space science.
Nevertheless, NASA officials are being cautious because the deal would involve a U.S. payment to a Russian institute, he said.
The delay does not reflect any judgment by NASA on the technical merits of the thruster, Newhouse said. "It's an interesting technology. The Russians have done good things and this might be one of them," he said.
The bismuth engine belongs to a class of electric thrusters called Hall Effect thrusters. Unlike the ion propulsion engine tested on NASA's Deep Space 1 spacecraft, Hall thrusters do not have metal grids covering their nozzles.
Deep Space 1 used grids to generate an electric field that sucked xenon ions from a chamber and into space to generate thrust. Hall thrusters use iron magnets to generate magnetic fields that impede electrons and accelerate ions.
"What's really intriguing in a Hall thruster is you have two fluids intermingled, electrons and ions, both of which respond to this [magnetic] field differently," Cappelli said.
The Russian Hall thruster is unique because of its fuel. Hall Effect thrusters typically use inert gases, such as xenon, as their sources of ions. The Russian engine heats a solid block of bismuth metal in an electric oven to slowly convert it into a gas, which is then ionized, Cappelli said.
Bismuth is used for making alloys that melt at low temperatures and in certain medicines. Bismuth can be stored as a solid and therefore takes up less volume.
But the biggest advantage is that bismuth costs a thousand times less than xenon, which could be important for spacecraft that require clusters of thrusters, Cappelli said.
"There isn't a lot of xenon on Earth, but there's a lot of bismuth," Cappelli explained.
Part of the concern over the Russian thruster's durability stems from its gridless design. Without a grid, the ion beam is less focused, which means some of the ions stake the sides of the chamber and the soft-iron magnets, causing erosion, Cappelli said. Cappelli and his team hope to document the rate at which that happens compared to the erosion suffered by gridded-ion thrusters.
There are some really cool bismuth alloys such as Cerrobend that will melt at temperatures less than boiling water.
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