Influence of Shape Change Caused by Warp of Thin-film Device on Solar Radiation Pressure Torque in Solar Sail

Abstract

Solar sail technique was demonstrated in the IKAROS mission. However, the membrane of IKAROS has deformed to a shape that was not flat. The whole membrane changes greatly like an umbrella shape or a saddle shape depending on the warping direction of the thin-film devices on the membrane, such as thin-film solar cells, reflectivity control devices and dust counters. Objection of this study is to clarify mechanism of influence on solar radiation pressure (SRP) torque due to warp of thin-film device and its solution method. Therefore, the shape of the overall membrane is clarified by using a simple finite element model and the SRP torque with respect to the shape is calculated, and the mechanism of the overall shape change in warpage and its influence is clarified. As a result, the influence on SRP is related to membrane stiffness and warped direction and it is found that the suitable conditions to minimize SRP torque are as follows: a) the sail is warped in the radial direction, b) the base film of the sail has low stiffness, c) the outermost part of the sail has high stiffness, and d) the length of bridges between petals is short.