An Application of Fuzzy Technique to Thruster Control System of Spacecraft.

Thruster assignment to generate ideal forces and torques is important for a chaser spacecraft approaching another spacecraft (a target spacecraft), for example, during rendezvous and docking operations. The thruster selection is more important in the proximity area of the target spacecraft where the chaser spacecraft controls both relative position and attitude. The conventional method is based on a table look-up. It is easy to execute (calculation time minimum) but tends to generate a wasteful pattern of thruster select. Two new methods based on fuzzy logic are proposed: one removes such wasteful patterns using fuzzy pattern matching and the other selects thrusters one by one while it reduces the residual control forces and torques with smaller fuel consumption using fuzzy inference. Numerical simulations are given to compare the conventional method, the proposed fuzzy methods and the linear programming (fuel minimum). The results show that the proposed fuzzy methods realize a thruster select logic with low fuel-consumption in allowable calculation time and that they provide a flexibility in the trade off between calculation time and fuel consumption.