The Development of an Integrated Experiment to Study the Controls/Structures Interaction Problem in Large Optical Systems

Abstract

The next generation of ground and space-based optical systems is characterized by their large size and high performance requirements. They rely heavily on active control to compensate for inadequate mechanical accuracy caused by manufacturing processes, thermal distortions, and gravitational or dynamic loads. Because of the prohibitive weight penalty incurred by fabricating a monolithic reflector with sufficient stiffness, as well as the problem of packaging a large, fragile optical element for transport to orbit, the use of segmented large optical components is the only practical approach for large space systems. This paper describes an experimental apparatus developed at the Lockheed Palo Alto Research Laboratory called the Advanced Structures/Controls Integrated Experiment (ASCIE). The ASCIE is a laboratory test bed designed to support a number of interdisciplinary studies, especially experiments pertaining to the interaction between structural dynamics and control systems in large segmented optical systems. The test article emulates a Cassegrain telescope with a segmented primary mirror. The segments and the secondary mirror are actively controlled to simultaneously provide the correct alignment as well as image stabilization. The segment alignment control system utilizes a self-referenced ensemble of edge sensors, and an independent optical measurement system provides for initial calibration and scoring. A light-weight truss structure supports both the secondary and primary mirror elements. The whole assembly is tuned to replicate the dynamic behavior of a large system. Details of the segment alignment control system, as well as preliminary experimental results are presented.