Computational Modeling of Altitude Control Systems for Solar Sails

The ultimate realization of solar sail systems depends on understanding and modeling the complex interactions among attitude, vibration and deployment dynamics. Recent simulations of attitude control systems that model the deployed solar sail as a rigid body provide a starting point. However, the extreme flexibility of these unique systems portend the need to include the flexible body dynamics in models guiding the development of future solar sail attitude control concepts. Further, during deployment a solar sail system will evolve from a compact rigid structure to a huge extremely flexible one. Ultimately attitude control simulations must consider the changing configuration of the solar sail system. To introduce control moments into deployed solar sails, two current concepts include articulated control vanes at the tips of sail support booms and a gimballed short boom at the hub of the sail [xl - x3]. Both of these concepts are in the general class of attitude control that employs centerof- mass/center-of-pressure difference via structural shape changes. A question of immediate importance is whether these concepts, operating on the extremely flexible sail system rather than a rigid one, produce response that could be considered as perturbation of a rigid-body response. In other words, is one of these concepts a better choice for flexible solar sails? Is the resulting response effectively that of a rigid-body or are vibrational responses more likely to be introduced? If the response can be considered a perturbation of the rigid-body response, it can be efficiently computed. Additionally, are other similar shape-changing concepts better suited for flexible solar sails or more amenable to efficient computation of the combined flexible-body and attitude dynamic response? To model the complex interaction between solar sail deployment and attitude control, similar questions arise. If deployment rates are much slower than characteristic vibrational and attitude response rates, motions may be computed based on a quasi-static configuration. However, in I~ ter stages of ~eployment, as the size and flel'ibility of the deploying system become larger, the vlbr~tlOna~, a ~ ltude cont.rol and deployment aynamics become interrelated and separate consIderation IS?,ot feasIble ..~ question of long-range importance is what modeling approaches ensure computatIOnal tractabIlity of dynamic response as the sail shape changes during deployment? The goal of this task is to.answer these questions. Therefore, the goal of this task is to establish key com~utatlOn~lIy feasIble methods leading to dynamic and attitude control models accurately representmg flexIble solar sail systems.