Future Ground Systems High Temperature Stirling Space Engine Presently a space Stirling engine based on the SPDE but with an increased operating temperature of 1050 K is being constructed with the eventual aim of constructing an engine operating at 1300 K. Space Station Ground Demonstrator In order to reduce the risk to the Space Station Freedom solar dynamic program and to reduce costs of testing, NASA is funding a 2 kW Solar Dynamic Demonstrator. This will test a complete, space configured, solar dynamic system with intergral thermal energy in a vacuum chamber. Previous demonstrations have concentrated on testing individual components. This will test the whole system and provide an extensive database of system and component tests. The demonstrator is a scaled down version of that planned for the Space Station producing 2 kW and is based on the closed Brayton cycle. Assuming 20 kW of energy from the sun, the power engine input, after collection and heat losses, is about 8.0 kW which produces 2 kW in the net power output. Dynamic Isotope Power System, DIPS The DIPS technology program was aimed at developing the CBC for converting heat engine from an isotope heat source to electrical energy in the range 1-10 kW.range. The engine developed in this program is being used in the 2 kW ground demonstration. Future Space Applications Space Station Freedom (SSF) For the SSF, it is proposed to use a power system based on a Solar Dynamic System, to supplement the power during the second phase of the program, as shown in Figure 7.10. The receiver will be 1.8 m in diameter with a 3 m height and a weight of 1800 kg. In ground the test receiver had a 50 cm in diameter with a 70 cm height and only 100 kg. The radiator has 2 panels with 456 m2 and the heat transfer performance has already been verified on Earth. The Solar collector concentrator shown in Figure 7.11, is composed of 19 hex panels with 456 facets total. The area of this concentrator is about 193.3 m2 with an efficiency of 81%. Space Flyer Unit (JETRO,1991) Another Solar Dynamic Power generation system was designed and planned by the Japanese Institute of Space and Astronautical Science (ISAS), for a 1994 experiment on the unmanned Space Flyer Unit (SFU). In this mission the power generated will be about 2 kW which will be used to power MPD arcjets to change the SFU orbit. A non-lubricated Stirling engine and a linear induction generator are used for converted thermal energy to mechanical and then to electrical energy. The Thermal storage system receives thermal energy from the collector, stores it and then supplies the Stirling Engine with the necessary energy during eclipses. The energy collected by the solar collector is changed to thermal energy on the inner surface of the receiver and transferred to the hydrogen gas working fluid of the Stirling engine. Then, in the recuperator, this energy is used for expansion work in the Stirling cycle. The linear induction generator consists of permanent magnets on the moving power pistons and winding coils. The AC current is then induced in stationary coils. The efficiency of this Stirling engine generator is 31%. The efficiency of the linear induction generator is around 87%. Therefore the overall system efficiency is about 25%.
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