Deployment Repeatability of Pointing Performance for Highly Precise Extensible Optical Bench Considering Uncertainties on Backlash and Friction

Abstract

The authors have investigated the effects of uncertainties on the pointing performance of an extensible optical bench (EOB), used for a large, highly precise, space X-ray telescope. The uncertainties considered are in member length, position due to backlash, and friction at connecting nodes. This study mainly investigates the effect of friction on the pointing performance. First, the pointing performance analysis is briefly investigated. The extended EOB is modeled as a truss structure, and the distortion due to the member length imperfection is evaluated by a nonlinear, finite element analysis (FEA). Subsequently, the backlash at connecting nodes is modeled by introducing a virtual cable element with a natural length equal to the size of backlash. In addition, the deformation due to a friction force acting at the connecting node is calculated as a perturbation from the equilibrium condition without performing a contact analysis. This friction model is further extended to identify effects of friction uncertainty with reduced computational costs. Through numerical examples, the effects of friction uncertainty on the deployment repeatability for the EOB, and effects of the number of stages of EOB on the pointing performance are investigated.