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The two major factors that affect auxiliary power system design decisions are: the working fluid to be used, and vehicle mission requirements. It has been found that optimum turbine designs will be similar for the two working fluids (hydrazine or hydrogen-oxygen) considered for the shuttle orbiter system due to the constraints imposed by geometrical and mechanical design limitations. As a consequence, variations in power level and/or working fluid selection can be efficiently accommodated by relatively minor modifications to turbine nozzle design. Analytical techniques for optimization of turbine aerodynamic design parameters have been developed. These techniques can be extended to include transient-state simulation and design optimization of the other system components, including the turbine controller, in a manner similar to that used for development of control systems for multi-spool fan-jet engines.

The preliminary design of electromechanical (EM) servosystems is a complex engineering problem due to the numerous parameters, constraints, and performance requirements which must be satisfied. When this is coupled with optimization, the task becomes even more difficult. This paper discusses (1) the variables that must be considered in the design phase of an EM servosystem, (2) the main constraints that must be addressed during preliminary design, and (3) a reasonable strategy for designing and optimizing an EM servosystem. Also, a computer program developed by AiResearch for the preliminary design of EM servosystems (EMSYS) and methods used by EMSYS to address the above are briefly described.