Abstract: To maintain the three axis attitude of the underactuated nadir-pointing spacecraft, an attitude hold control method based on the pitch-axis bias momentum wheel and roll-axis thruster was proposed.The method was based on coupling between the roll and yaw axes of biased-momentum spacecraft, and could avoid the problem that zero momentum spacecraft′s underactuated axis and actuated axis were almost decoupled. Spacecraft attitude dynamics was divided into long period dynamics and short period dynamics, and the control laws were designed by the pole assignment method. The scale of control parameters was confirmed, and the stable state error of the control system was obtained. The simulation results show that the designed controller can eliminate initial attitude error of the spacecraft and resist the external disturbance, and the spacecraft attitude is maintained at the equilibrium point.

Key words: Bias momentum wheel, Thruster, Underactuated, Attitude hold control, Spacecraft