Research On Small Satellite Attitude Control By Fluid Momentum Loops

This paper presents the design study of a multifunctional actuator of attitude control,thermal control and mass trim for small satellite. First, based on the principle that theannular flow variation in a fluid loop will exert torques on the satellite, absorb wasteheat by circulation and reallocate fluid mass of reservoirs, a combined system scheme ofattitude control/thermal control/mass trim based on a multifunctional actuator (i.e. FluidMomentum Loops, or FML for short) is designed. Then in view of the scheme design ofthe combined system, FML is designed into three feasible configuration schemes in Pumpmode, Valve mode and Pump-Valve Collaborative mode.Based on the scheme designs of FML, the mathmatical model of the Pump modeFML is established by deriving the equations of the electromagnetic torque and the fluidpressure with the motor speed as the independent variable; the mathmatical model of theValve mode FML is established on the transform function of electro-hydraulic servo valvewith the valve opening as the independent variable; the mathematical model of the Pump-Valve Collaborative mode FML is established by combining the mathematical models inPump mode and Valve mode. Meanwhile, the heat model of FML is also built since theheat dissipation varies with the flow rate. Then, in regard of the advantages of FML andthe features of the configurations, the amplification efects of FML-based attitude controlsystem (ACS) the are analyzed, and the influence on the flow resistance and the systemperformance are studied with respect to the flow rates.Combining the mathematical models of FML with the features of the loop configura-tions and driving modes, algorithms are designed to partially decouple the multi-functionsand prolong the period of the velocity saturation. Based on PID control theory, an attitudecontrol law is designed for the FML-based ACS for small satellite, and the computer sim-ulation model of the closed-loop attitude/thermal control system based on diferent FMLconfigurations are established for a certain small satellite. Similarities and diferences inattitude control ability among diferent FML configurations are analyzed. Simulationsare performed to demonstrate the efectiveness of FML as a multifunctional actuator forattitude control and thermal control simultaneously.Furthermore, considering the uncertain factors in the FML-based ACS of smallsatellite, the mathematical models with uncertainties of FML-based ACS are established. Based on robust control theory, an H∞control law is designed and simulated in the com-puter simulation model of the FML-based ACS. Similarities and diferences in attitudecontrol ability between diferent control laws and among diferent FML configurationsare analyzed. Simulations are performed to demonstrate the efectiveness and robustnessof the H∞control law for FML-based ACS.