Sailing in Space

Bo Fu, Cornell University


Solar sail is a type of spacecraft propelled by harvesting momentum from solar radiation. Compared with spacecraft propelled by traditional chemical rockets or the more advanced electric propulsion engines, the unique feature of solar sails is that they do not use fuel for propulsion. This allows for the possibility of return-type (round-trip) missions to other heavenly bodies, which would be difficult or near impossible with conventional propulsion methods. This also makes solar sails highly promising candidates for service as interplanetary cargo ships in future space missions. Solar sail research is quite broad and multi-disciplinary. In this talk, an overview of solar sail technology including the history, the fundamentals of photon-sail interaction, and the state of the art of solar sailing is presented. One specific area solar sail research – attitude dynamics and control – is discussed in detail. Attitude control of large sails poses a challenge because most methods developed for solar sail attitude control require the controller mass to scale with the sail’s surface area. This is addressed by a newly proposed tip displacement method (TDM), where by moving the wing tips, the geometry of sail film is exploited to generate the necessary control forces and torques. The TDM method is described as it applies to a square solar sail that consists of four triangular wings. The mathematical relationship between the displacement of the wing tip and the control torque generated is fully developed under quasi-static condition and assuming the wing takes on the shape of a right cylindrical shell. Results from further investigation by relaxing previous modeling assumptions are presented. Future research directions in aerospace engineering spanning field of autonomy, sensing, controls, and modeling are discussed.