A Path Planning Method for Underactuated Space Robots

In free-floating mode, space manipulator systems have their thrusters off, and exhibit nonholonomic behavior due to angular momentum conservation. The system is underactuated and a challenging problem is to control both the end effector location and the base attitude, using manipulator actuators only. Here, a path planning methodology satisfying this double goal is presented. The key idea is to use high order polynomials as arguments in cosines, specifying a desired path directly in joint-space, drastically extending configuration accessibility. The initial problem is converted to one of satisfying the motion integrals by optimization techniques. This approach always leads to a path, provided that the desired change in configuration lies between physically permissible limits. The method is presented for 3D systems. The resulting paths are smooth, avoid the need for small cyclical motions, and lead to smooth changes in finite and prescribed time.