New Opportunities for Satellite Integrated Power and Attitude Control Systems

Francois Ayer, Richard Coca, and William Kelleher

Abstract:	The use of energy storage wheels having the dual function of kinetic accumulator (replacing conventional batteries) and attitude control has been recognized for some time as attractive for low earth orbit satellite applications. Recent technology advances in high energy density composite rotors, high speed motor/generator, ball bearings and magnetic bearings, and power electronics have created new opportunities for the practical and cost effective realization of the concept. Indeed the attitude control/energy storage (ACES) system offers potential substantial improvement in life, energy efficiency and power surge, and weight over batteries resulting in significant savings in overall satellite weight and complexity. for In order to be competitive the system must invoke the most advanced technologies in several critical areas and resort to innovative and ingenious design solutions. Wheel angular speeds must be increased dramatically over those of traditional reaction wheels thus enforcing the use of high strength composites for the rotor, stressing the design of both motor/generator and bearing assemblies, and exacerbating rotordynamics and thermal management. This paper presents results of the feasibility study of a high specific energy flywheel to meet the energy and momentum exchange needs of a LandSat class, low earth orbit satellite. Based on a six-wheel system configuration for redundancy each flywheel offers a 354 Wh energy storage capability with a maximum angular speed of 60,000 rpm. While every subsystem was optimized as a contributor to overall system weight minimization, the paper focuses on two critical components, the high speed composite rotor and the suspension system. A thin composite disk of constant thickness incorporating a mixture of circumferential and radial plies is selected as the best contender to achieve the maximum possible energy storage of a composite wheel. Two options are considered for suspending the flywheel: ball bearings and magnetic bearings. The Draper retainerless ball bearing assembly using an oozing flow lubricator provides a simple, lightweight and low power bearing system. The Draper homopolar magnetic bearing utilizing pole tip shaping and permanent magnet bias gives a long lifetime system with built-in redundancy while providing active position control and vibration damping. The mechanical system is integrated with a stiffness and damping distribution carefully selected to avoid potential rotordynamics instabilities. Finally the control system is architectured to manage the speeds of six wheels operating simultaneously as energy- and momentum- exchange devices.
Published in:	Proceedings of the 52nd Annual Meeting of The Institute of Navigation (1996) June 19 - 21, 1996 Royal Sonesta Hotel Cambridge, MA
Pages:	831 - 841
Cite this article:	Ayer, Francois, Coca, Richard, Kelleher, William, "New Opportunities for Satellite Integrated Power and Attitude Control Systems," Proceedings of the 52nd Annual Meeting of The Institute of Navigation (1996), Cambridge, MA, June 1996, pp. 831-841.
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