Translational and Rotational Maneuvers of an Underactuated Space Robot using Prismatic Actuators

We study the simultaneous control of three dimensional translation and rotation of an underactuated multibody space robot using sliding masses that are configured as ideal prismatic actuators. A crucial assumption is that the total linear and angular momenta of the space robot are zero. The prismatic actuators may be intentional actuation devices or they may be dual-use devices such as retractable booms, tethers, or antennas that can also serve as space robot actuation devices. The paper focuses on the underactuation case, i.e., the space robot has three independent prismatic actuators, which are used to control the six base body degrees of freedom. Controllability results are developed, revealing controllability properties for the base body translation, base body attitude, and actuator displacement. Based on the controllability results, an algorithm for rest-to-rest base body maneuvers is constructed using a Lie bracket expansion. An example of a three dimensional space robot maneuver is presented. The results in the paper demonstrate the importance of “nonholonomy” and related nonlinear control approaches for space robots that satisfy the prismatic actuation assumptions. KEY WORDS—space robots, translational and rotational maneuvers, nonlinear control, underactuated systems, prismatic actuators, nonholonomy