Strain actuated solar-arrays for precision pointing of spacecraft

Abstract

Next generation telescopes for space exploration are being planned with unprecedented levels of pointing and wavefront stability as science enabling capabilities - i.e., sub-milli-arcsecond class pointing, and pico-meter class RMS wave-front error). Current methodologies for attaining these levels of stability are approaching the limit of what is possible with the use of isolation, intensive and risky structural dynamic tailoring, exquisite broad-band Attitude Control System (ACS) sensors and actuators, and ultra-precise fast steering mirrors commanded to compensate for pointing errors through feedback of camera measurements. This paper explores the benefits of using Strain Actuated Solar Arrays (SASA) - currently under Research at the Jet Propulsion Laboratory and the University of Illinois Urbana Champagne - in new ACS architectures for applications requiring very tight precision pointing of a SC and on-board instrumentation. A strain actuated solar array has the following characteristics: (1) Strain actuation and sensing is distributed throughout the SA panels to obtain control authority and observability over the strain state of the SA–enabling SA jitter control. (2) Large motion (up to 10 degrees or relative motion) strain based mechanisms are used in between SA panels and in between the SC and the solar array–enables SC slewing and limited momentum management. (3) The mechanical (i.e., stiffness and configuration) and inertia/mass properties of the SA have been designed to optimize its ability to control its vibrations and the vibration and attitude of the host SC. This paper discusses ACS architectures that use the above SASA system while avoiding the use of the Reaction Wheel Actuator (RWA) during key science observation periods. The RWA being the dominant source of pointing jitter and wave front jitter in a telescope based observatory; hence, not flying RWAs amounts to not flying the main source of jitter! At least two architectures based on the SASA system are studied - one is an earth orbiter, the other is assumed to be in an L2 orbit. Simulation results for one of these cases are discussed along with what developments are needed going forward to enable the use of this technology.

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