Dynamic Model and Variable Structure Control for Flexible Fuel-filled Spacecraft

The present paper deals with dynamics modeling and controller designing for a large flexible spacecraft, such as tracking and data relay satellite (TDRS) with several flexible appendages and a liquid fuel tank. The basic parameters for the equivalent mechanical model under low-gravity are given when the pendulum motion of the tank is small enough such that it can be approximated linearly. Hybrid coordinate is used to describe the configuration of the large flexible liquid-filled spacecraft, and the D´ Alembert principle in virtual work is employed to derive the dynamics equations. The equations obtained are simple and common, which can be applied to describe many complicated open-chain spacecraft systems. A controller is designed using the variable structure control strategy. The control mission consists of maneuvering the large antennas to track the pre-selected motion laws, stabilizing the spacecraft in an inertial space and suppressing the elastic vibration of the appendages. A numerical example is given to prove the validity of the control laws.