Attitude dynamics and stability of a flexible gravity-gradient stabilized spacecraft in orbit raising maneuvers

This thesis examines the dynamic response of a flexible Gravity-Gradient Stabilized Spacecraft (GOSS) comprising coupled orbital, attitude, and vibrational motions. Highly nonlinear, coupled equations of motion are developed. The fourth order Runge-Kutta numerical scheme is applied to solve these equations. The response of the spacecraft is analyzed in simulations of a multi-stage maneuver from Low Earth Orbit (LEO) to Geosynchronous Earth Orbit (GEO) altitude using the Hohmann transfer method. Three maneuver conditions are considered here. First, the spacecraft attitudes are considered not to be affected by the thruster firing. Second, the thruster firing effects are taken into account. Third, the effects of imperfect thruster firing, which creates parasitic torques, is considered. The results indicate the stability of the response depends on the eccentricity of the transfer orbit. The thruster's impulse effect helps drive the system unstable. The presence of parasitic torques about the roll and yaw axes leads to attitude instability. Parasitic torque about the pitch axis can be tolerated as long as its magnitude is below some value. Flexibility of the linkage does not affect the orbital or attitudinal responses to the maneuver, except when the thruster's impulse is included in the analysis. Inclusion of the thrusting process in the simulation has the potential for exciting high frequency characteristics of the model.