Advances of Surface Control Methodologies for Flexible Space Reflectors

Abstract

With the advances in deployable membrane technologies, the possibility of developing large, lightweight reflectors has greatly improved. However, to achieve the required accuracy, precision surface control is needed. The goal of this research was to investigate the feasibility of applying distributed polyvinylidene fluoride actuators and domain control on a flexible reflector and address some of the technical challenges. An analytical model of the integrated reflector-actuator system was developed. A Kapton reflector with polyvinylidene fluoride actuators was experimentally tested and compared with the model. A new least-squares control law is designed to ensure optimal solutions are derived in a rigorous manner when constraints are applied. The model is exercised using individually controlled polyvinylidene fluoride actuators on a large-scale reflector under thermal load. Although the results are promising with the large number of actuators applied, the major challenge is that it is unrealistic to have the same number of power supplies as actuators in actual applications. To resolve this issue, a new optimization methodology was developed, designated as the en masse elimination algorithm, which finds the global optimal solution that groups the actuators to match the limited number of power supplies and achieve minimum surface error. Nomenclature a = planform diameter, m d xy = piezoelectric constants, m∕V E x = electric field in x direction, V∕m E Y = modulus of elasticity, Pa h p = thickness of patch, m h ref = thickness of reflector, m P = inflation pressure, Pa R = radius of curvature, m r, θ, φ = cylindrical coordinates Tr; θ = temperature profile, K T p = membrane tension, N T 0 = bulk temperature shift, K U = strain energy, J u, v, w = coordinate values, m u 0 , v 0 , w 0 = midsurface displacements, m α CTE = coefficient of thermal expansion, K −1 β Y = rotational angles for Love simplification, rad ΔT = linear temperature gradient, K ε = strain ρ = density, kg∕m 3 σ = stress, Pa υ = Poisson's ratio

Shape control of slack space reflectors using modulated solar pressure

“…Piezoceramic macro-fibre composites (MFCs) have been used for excitation and control of out-of-plane modes of solar sail membranes [18]. Employing electroactive polymer (EAP) films such as PVDF (polyvinylidene fluoride) for surface control of space membrane reflectors is currently investigated by [19]. Dielectric elastomers, a type of EAP employing electrostatic forces between two electrodes to squeeze a polymer film, have been tested on the back of flexible mirrors in [20].…”

Thermal–structural analysis of large deployable space antenna under extreme heat loads

“…New structural conceptual designs, such as double-ring truss and folded xed truss and which may present higher sti ness, were mechanically designed and analyzed [10][11][12][13][14]. Further, prestress optimizations and form-nding methods were put forward to enhance the surface accuracy and structural reliability of the antennas [15][16][17][18][19]. Electronic compensation strategies that may enhance the antenna's structural stability are identi ed [20].…”

Sensitivity Study on Optimizing Thickness Distribution for a Membrane Reflector

“…Kitano and Ishida [13] have obtained the discrete distribution of optimum thickness for circular membrane reflector. In order to decrease the W-profile error, DeSmidt et al and Hill et al [14,15] have developed active control of the reflector using optimized gore/seam cable-actuated shape control. Coleman et al [16] have studied the effects of the elastic tendon boundary support and reflector dimensions on surface accuracy of the inflatable antenna by an ideal parabolic form and two different flat panel design patterns.…”