type nuclear reactor. While in the component development phase, this program was discontinued due to a presidential decision to halt work on nuclear systems for space. NASA and the United States Department of Energy (DOE) collaborated in 1976 to direct and fund the development of a 1.3 kW radioisotope-powered closed Brayton cycle system that could be used on military surveillance satellites [12, 13]. Fluid Systems was responsible for the design and development of this CBC system, which was similar to the previous NASA Engine B system, but scaled down (Figs. 6 and 7). One major improvement was the use of self-actuating foil gas bearings, which used the cycle gas as a lubricant, as did the solid geometry bearings of Engine B, but which required no stored, pressurized gas for start-up. This engine was successfully run for 1000 hours in a vacuum chamber in 1978. This system met all of the projected performance goals. However, as no mission for its use was available at the time, no further work was conducted on this system. Present With this background and the continued development of materials, design techniques, and performance predictions due largely to activities in the aircraft gas turbine field, the closed Brayton technology is considered mature for today's space applications. Currently, there are two active closed Brayton cycle space power programs. These programs will provide CBC systems for both the Space Station Freedom Solar Dynamic Power Module and the Dynamic Isotope Power System (DIPS). NASA has selected the CBC system to power the solar dynamic power modules for the Space Station. During the second phase of NASA's space station deployment approach, the 75 kW of photovoltaic power generation deployed in Phase 1 will be supplemented by the addition of 50 kW of solar dynamic power. Solar dynamic power generation, which is four to five times more efficient than photovoltaic power generation, will be used to incrementally raise the Space Station power level from 75 to 325 kW by adding 50 kW solar dynamic power modules in pairs of 25 kW units each. The Rocketdyne Division of Rockwell International is the prime contractor for Space Station Work Package 4, Electric Power System (EPS), under the direction of NASA's Lewis Research Center, Cleveland, Ohio. Under this contract, Rocketdyne
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