Time and Temperature Dependence of Surface Accuracy on CFRP Sandwich Mirror

Abstract

Mirrors of satellite are one of the heaviest parts in the satellite. The maximum weight of the satellite is determined by the launch capacity of the rocket. Of course, the weight of the main mirror is limited but larger mirror enable higher resolution observation. A specific stiffness of the mirror material is hence a key factor. Since carbon fiber reinforced polymeric composite material (CFRP) is superior to not only the specific stiffness also in-plane thermal stability, it may be suitable to use as mirror. Before applying CFRP to the mirror, several problems should be solved; one of them is long-term reliability of mirror surface accuracy. It is reported that there exist a "print-through" problem for CFRP mirror surface. To address this problem, a lot of works regarding surface coating treatment have been done for the mean time. However, the long-term assurance of the surface roughness has not been discussed nevertheless the mechanical property of CFRP is inherently time-dependent. There is a possibility that the time-dependent deformation of the material deteriorates the mirror surface accuracy. The deformation induced by physical ageing, dewater and internal stress relaxation of the matrix may change the surface accuracy. The deformation induced by temperature change is another problem. In this paper, time and temperature dependence of the surface accuracy is studied for CFRP sandwich mirror. The effect of different surface treatment on the surface accuracy is also investigated.