Further investigation of the body torques on a square solar sail due to the displacement of the sail attachment points

This paper presents further investigation of the idea of performing orientation change and attitude control of solar sail spacecraft by moving one or more of the attachment points of the sail material. In its normal mode of operation, a rigid-type solar sail flies with its sail membrane flat and taut. Moving one of the attachment points of the sail will cause the sail material to sag under the action of solar radiation. Such a sag can lead to system asymmetry resulting in a body moment on the system; and such a moment can be exploited for orientation control. The focus of this study is on the determination of the shape that the sail membrane assumes when one of its attachment points is displaced a known amount. Comparisons are made between the exact shape of the sail membrane as determined in this study, and a simpler but approximated shape suggested in previous studies. Errors in the force and body moment predictions that would result from the use of a simpler model of the deformed sail are also assessed. Finally, the effect of the solar radiation incidence angle on the magnitude of the moment applied to the solar sail body is also investigated.