Session
Technical Session X: Propulsion
Abstract
Sunjammer is a NASA technology demonstration mission that will demonstrate the potential for solar sail propulsion using a 1200 m2 sail. Attitude control of the sail is achieved by changing the four 15m2 boom-tip vanes’ orientation relative to the satellite-Sun vector. A control scheme has been developed that incorporates passive stability about two axes and utilization of equilibrium-trim angles alongside a proportional-derivative (PD) controller. The attitude control system employs predetermined trim vane angles to maneuver the vehicle to a desired attitude. By observing the command history of the PD controller that maintains the desired attitude, these predetermined vane angles are adjusted autonomously. This adjustment allows for errors in sail force and moment characterization to be conducted on-orbit and provides a reduction of the required control effort. This control scheme is shown to be well suited in handling experimentally derived sail force and moment coefficients that do not assume a simplified flat-plate model. System performance is evaluated using test reorientation maneuvers and robustness is checked against various modeling uncertainties. Through simulation, the attitude control algorithm is shown to achieve better than a 2 degree pointing accuracy in the presence of expected environmental disturbances.
Presentation
Attitude Control of the Sunjammer Solar Sail Mission
Sunjammer is a NASA technology demonstration mission that will demonstrate the potential for solar sail propulsion using a 1200 m2 sail. Attitude control of the sail is achieved by changing the four 15m2 boom-tip vanes’ orientation relative to the satellite-Sun vector. A control scheme has been developed that incorporates passive stability about two axes and utilization of equilibrium-trim angles alongside a proportional-derivative (PD) controller. The attitude control system employs predetermined trim vane angles to maneuver the vehicle to a desired attitude. By observing the command history of the PD controller that maintains the desired attitude, these predetermined vane angles are adjusted autonomously. This adjustment allows for errors in sail force and moment characterization to be conducted on-orbit and provides a reduction of the required control effort. This control scheme is shown to be well suited in handling experimentally derived sail force and moment coefficients that do not assume a simplified flat-plate model. System performance is evaluated using test reorientation maneuvers and robustness is checked against various modeling uncertainties. Through simulation, the attitude control algorithm is shown to achieve better than a 2 degree pointing accuracy in the presence of expected environmental disturbances.
