Control of underactuated free floating robots in space

The underactuated free floating robot in space is a nonlinear system where velocity and acceleration constraints are both nonintegrable, therefore it is a second-order nonholonomic system. Some of the existing nonholonomic control methods will not be directly applicable to such systems as it is extremely difficult, if not impossible, to find the control Lie brackets. In this paper, by investigating the system dynamics in depth, we propose a simple velocity-based method to control the unactuated joints and a multistep composite strategy to implement orientation tracking tasks. The proposed algorithm is of significance in controlling of space robots when some joints fail to function, or they are intentionally set to be passive for energy efficiency and safety purposes