ACTIVE SHAPE CONTROL OF A MEMBRANE REFLECTOR FOR A SPACE APPLICATION

Abstract

Flexible reflectors are used for a number of applications in space, including resource monitoring, weather analysis, hazard assessment, reconnaissance, and imaging. With the rapid advances in deployable membrane and mesh antenna technologies, the feasibility of developing large, lightweight reflectors has greatly improved, though high-precision surface control is needed in order to achieve the required surface accuracy. Current space-based imaging platforms are significantly constrained in both size and weight by the launch vehicle. Increased payload size and weight results in increased cost and a decrease in launch responsiveness. Membrane material like Kapton, Mylar etc. have very good strength is to weight ratio. These materials are not only light in weight but also good in strength and thermal stability. These large space structures are also susceptible to large amplitude vibrations and other environmental factors while in orbit, which makes it very challenging to maintain the actual shape required for the reflector and surface errors induced because of this degrades the performance of the inflatable structures. To reduce this degradation, two types of systems active and passive control systems can be used to sense the error and control the shape of the antenna which can be done by using piezoelectric films that are either attached to or are part of the inflatable structures. Piezoelectric actuators have proven to be useful in suppressing disturbances and for shape control of these flexible large space structures and Piezo patches like PVDF, PZT, MFC and Shape Memory Alloys etc. will be used to make these structures membrane adaptive in nature to minimize the wrinkles area and shape error. These structures need to be ultra-light in weight so only a limited number of piezo actuators can be used. Consequently, in order to obtain the most effective shape control system, the location of the piezoelectric elements should be optimized. The placement and optimization of grouping of piezoelectric elements will be done through the optimization technique like Genetic Algorithm etc. Analysis has been carried out on ABAQUS, a commercially available finite element package. The deviation in the shape of membrane is shown by the out of plane displacements of different mode shapes at different thermal and tensile loading boundary conditions. It has been observed that wrinkles/deviations appears close to corners and diagonal regions and rms out of plane displacements increases with increasing temperature loading and decreases with increasing tensile load and thickness of the membrane.