Numerical investigations on thermal deformation of large deployable reflector in space during earth eclipse (2nd report, investigations to suppress thermal deformation by internal force control)

Abstract

Space structures encounter various severe environments in space. One of these environments is severe thermal condition where the difference of temperature during day-time and night-time is about 200 degrees Celsius. During this eclipse time, the midpoint of the large deployable reflector (LDR) mounted on the Engineering Test Satellite -VIII (ETS-VIII) was confirmed to deform by approximately 5 mm, which led to a 65 km transition of the footprint of communication beam on the surface of the earth. This phenomenon was assumed to be caused by thermal deformation of the LDR. It was not a critical issue for the ETS-VIII because the communication beam from the LDR tended to spread in the wide range. However, highly accurate pinpoint communication beams are expected to be required in the future, and this transition of the beams may affect the performance of such satellites. Therefore, in this study, a means to suppress the thermal deformation is proposed and demonstrated by focusing on the internal force generated at the springs used to deploy the antenna. According to the numerical results obtained from finite element analyses, the thermal deformations at all apices that support the reflectors were suppressed at a high correction rate by adjusting the coefficients of thermal expansion in the structural members and by controlling spring forces differently in four areas depending on the distances from the constraint point. These results indicate that the transition of the communication beam on the surface of the earth can be decreased to a range of 5 to 10 km.