Design of Attitude Determination and Control System for Autonomous Docking of Small Satellites

摘要

A robust and reliable Attitude Determination and Control System (ADCS) is necessary to satisfy the stringent requirements for docking of small satellites due to low error tolerances imposed by their small sizes. It has to make sure that the docking happens in the right orientation and there is no final relative angular velocity. Attitude determination for such a mission type can be divided into two phases - absolute and relative. Absolute attitude determination is performed before the final phases of rendezvous and uses conventional sensors such as star tracker, sun sensors etc. Relative attitude determination is performed during the final phases of docking using cameras, etc. Attitude Control should provide good pointing accuracy and stability even in the presence of various disturbance torques. It should also provide 3-axis control of the combined spacecraft considering changes in the inertia tensor and center of mass. The work here addresses the challenges involved in the design of ADCS for autonomous docking of small satellites. It addresses the selection of sensors for absolute and relative determination methods as well as the switching between them. It also addresses the selection of determination and estimation algorithms based on their accuracy, complexity, computational time, etc. It includes the selection of suitable actuators and their placement to achieve efficient 3-axis attitude control. The implementation of the control algorithm is simulated. The mission profile of a conceptual small satellite docking of two spacecraft - SRMSAT-3A & 3B is considered for design and simulation and the results are presented.