UNDER-ACTUATED SPACE ROBOTS: PHYSICAL and ALGORITHMIC CONSTRAINTS in SMOOTH MOTION PLANNING

Space manipulator systems having spacecraft actuators turned off, operate in free-floating mode, and exhibit nonholonomic behaviour due to angular momentum conservation. The system is underactuated and a challenging problem is to control both the location of the end effector and the attitude of the base, using manipulator actuators only. A developed path planning method that perform this task is briefly presented and the constraints of motion, both physical and algorithmic, are examined. The physical limitations are imposed by system’s dynamic parameters. Lower and upper bounds for base rotation, due to manipulator motions, are estimated. Smooth functions such as polynomials are employed in the planning scheme, leading to smooth configuration changes in finite and prescribed time, and avoiding many small cyclical motions. Algorithmic limitations of the method in reaching arbitrary final configurations are discussed and examples are presented.