SAVING MASS IN OPTIMALLY SIZING A SMALL SATELLITE ENERGY STORAGE AND ATTITUDE CONTROL SYSTEM

摘要

A recent effort to optimally size miniature, single-gimbal variable-speed control moment gyroscopes for combined energy storage and attitude control on small satellites hatched an efficient, structured approach which enables alternative technology comparisons. The method, documented in a separate article, casts the design as a constrained nonlinear programming problem where a performance index constructed from subsystem design margins is optimized for a given set of agility and energy storage requirements. In that article, the available energy capacity is computed as the maximum available isotropic structural capacity of the rotor using the rotor's shape factor (derived from rotor material strength and density) and maximum structural and minimum wheel speeds. However, a more realistic implementation of a satellite flywheel energy storage system is limited in its maximum operating wheel speed. In turn, the usable available capacity, a function of the maximum and minimum operating wheel speeds, is a more accurate quantity to use in the optimal sizing algorithm. In the present paper, this concept is applied to the variable speed control moment gyroscope-based energy storage and attitude control system and is illustrated through parametric numerical examples of optimizing for subsystem mass keeping performance constant in relation to a baseline, conventional secondary battery plus momentum wheel design. The resulting energy capacity comparisons are conducted through the handy restriction of the optimization problem to a near closed-form solution thereby making the comparisons compact yet useful.