A paper discusses a concept for controlling the attitude and thrust vector of a three-axis stabilized Solar Sail spacecraft using only four single degree of freedom articulated spar-tip vanes. The vanes, at the corners of the sail, would be turned to commanded angles about the diagonals of the square sail. Commands would be generated by an adaptive controller that would track a given trajectory while rejecting effects of such disturbance torques as those attributable to offsets between the center of pressure on the sail and the center of mass. The controller would include a standard proportional + derivative part, a feed forward part, and a dynamic component that would act like a generalized integrator. The controller would globally track reference signals, and in the presence of such control actuator constraints as saturation and delay, the controller would utilize strategies to cancel or reduce their effects. The control scheme would be embodied in a robust, nonlinear algorithm that would allocate torques among the vanes, always finding a stable solution arbitrarily close to the global optimum solution of the control effort allocation problem. The solution would include an acceptably small angle, slow limit-cycle oscillation of the vanes, while providing overall thrust vector pointing stability and performance.

This work was done by Edward Mettler, Ahmet Acikmese, and Scott Ploen of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Mechanics category.

The software used in this innovation is available for commercial licensing. Please contact Karina Edmonds of the California Institute of Technology at (626) 395-2322. Refer to NPO-42156.

Topics:
Computer software and hardware Mathematical models Mechanical Components Mechanics Pressure Research and development Sensors and actuators Simulation and modeling Spacecraft Vehicles
This Brief includes a Technical Support Package (TSP).
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Controlling Attitude of a Solar-Sail Spacecraft Using Vanes

(reference NPO-42156) is currently available for download from the TSP library.

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NASA Tech Briefs Magazine

This article first appeared in the July, 2006 issue of NASA Tech Briefs Magazine (Vol. 30 No. 7).

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Overview

The document titled "Controlling Attitude of a Solar-Sail Spacecraft Using Vanes" is a technical support package from NASA that discusses advancements in the control of solar sail spacecraft. Solar sails utilize sunlight for propulsion, and their attitude control is crucial for effective navigation and mission success.

The paper outlines the dynamics of solar sails equipped with control vanes, which are essential for adjusting the orientation of the sail in response to solar radiation pressure. The authors present a mathematical model that describes the attitude dynamics of a solar sail, focusing on a configuration with four tip-mounted vanes. The equations of motion are derived, highlighting the interactions between the sail's angular velocity, control torques, and disturbances.

A key contribution of the document is the development of an adaptive attitude control strategy. This strategy employs a proportional-derivative (PD) controller combined with a feed-forward component and a dynamic element that functions as a generalized integrator. The controller is designed to track reference trajectories while effectively rejecting disturbances, such as those arising from offsets between the center of mass and the center of pressure.

The research emphasizes the importance of stability and performance in the control system, particularly under conditions of actuator saturation and delays. The authors introduce a control allocation algorithm that distributes the control torque among the four vanes, ensuring robust performance even in challenging operational scenarios.

Simulation results presented in the document demonstrate the effectiveness of the proposed control strategy, showing good stability characteristics and the ability to maintain desired orientations. The authors note that the control system intentionally allows for bounded limit-cycling around the roll axis, a behavior that can be adjusted by varying the vane areas and the commanding intervals.

In conclusion, the document provides a comprehensive overview of the challenges and solutions associated with the attitude control of solar sail spacecraft. It highlights the innovative control algorithms developed to enhance the performance and reliability of solar sails, paving the way for future missions that leverage solar propulsion technology. The findings contribute to the broader field of astrodynamics and spacecraft control, offering valuable insights for researchers and engineers in aerospace applications.