5-4. The Future of Closed Brayton Cycle Space Power Systems WILLIAM B. HARPER JR., ANTHONY PIETSCH & WILLIAM G. BAGGENSTOSS Introduction Closed Brayton cycle (CBC) power conversion systems have several key characteristics which make them well suited for use in space and extraterrestrial environments. These systems provide a high cycle efficiency using any high-temperature heat source and operate on a single-phase, inert gas working fluid which is not affected by the environment. In addition, the ability to operate using different molecular weight gases and variable system pressure levels can allow a given design to operate efficiently over a wide power range. The systems designed and developed by the Fluid Systems Division of the Allied-Signal Aerospace Company (and its predecessor The Garrett Corporation) have additional features that further enhance their suitability for use in the space environment. The compressor and turbine are connected to the rotor of a brushless alternator, forming a one-piece assembly that is supported on self-actuating, non-contact, hydrodynamic foil bearings which use the working fluid as the lubricant. Thus, the basic system has only one moving part, resulting in high reliability, and can be tested on earth with the centerline aligned vertically to simulate operation in a zero g environment. In addition to technical features which are well matched to the space environment, closed Brayton cycle systems also represent a mature technology, benefitting from both a long history of closed cycle system development and an extensive technology base provided by the open cycle gas turbine industry. The purpose of this paper is to examine the background and current status of CBC power conversion systems for space applications, and then look at the future of these systems from both an application and technological standpoint. Past Perhaps it is worthwhile to start by asking, ‘What is the Brayton cycle?'. The Brayton cycle is recognized as a power-producing thermodynamic cycle that functions by the mechanical compression of a gas, further heating of the gas at constant pressure, expansion of the gas to produce mechanical energy, and rejection of the waste heat at William B. Harper Jr., Manager Space Power Engineering, Anthony Pietsch, Consultant, William G. Baggenstoss, Development Specialist, Allied-Signal Aerospace Company, Fluid Systems Division, Tempe, AZ, USA. Paper number IAF-ICOSP89-5-4.
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