Brayton cycle was chosen as the power conversion technology for the DIPS because it offered the best combination of system weight, radiator area, and efficiency. In addition, it has more potential to take advantage of the higher temperatures that will become possible as technology advances. The DIPS heat source is based on the well qualified general purpose heat source (GPHS) used for the NASA Galileo and Ulysses missions. The heat source assembly which uses the GPHS, provides a turbine inlet temperature of 1O33K (1400F). This heat source is used in conjunction with a direct coupled, heat-pipe radiator, which provides a 283K (50F) compressor inlet temperature, resulting in a thermal cycle efficiency of 32.0% and a net overall conversion efficiency (based on electrical power delivered to the user) of 27.8%. The design point cycle data are given in Fig. 11. The DIPS program is currently in the component design phase. The program is scheduled to lead to a system test, using a laboratory heat source, in early 1992. Future The major advancement taking place today in the field of gas turbines is in the area of improved materials. Higher strength and higher temperature materials are providing the means to produce lighter and more efficient aircraft and automotive propulsion systems. Prime examples are ceramics and composite materials that have operating capabilities at temperatures up 2500K (404IF). An example of the application of these higher temperature materials to turbomachinery is the Automotive Gas Turbine (AGT) program conducted from 1979 until 1987 under DOE sponsorship and administered by NASA's Lewis Research Center. As one of the two contractors on this program, Allied-Signal Aerospace, Garrett Auxiliary Power Division successfully built and tested the AGT101 engine (Fig. 12). This engine incorporated an all ceramic hot section and accumulated over 250 hours of testing, including 85 hours at 1477K (2200F). A follow-on program, the five-year Advanced Turbine Technology Applications Project (ATTAP), is currently being conducted with DOE sponsorship under the direction of NASA Lewis. The ATTAP
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