Attitude Dynamics/Control of Dual-Body Spacecraft with Variable-Speed Control Moment Gyros

The dynamics equations of a spacecraft consisting of two bodies mutually rotating around a common gimbal axis are derived by the use of the Newton‐Euler approach. One of the bodies contains a cluster of single-gimbal variable-speed control moment gyros. The equations include all of the inertia terms and are written in a general form, valid for any cluster configurations and any number of actuators in the cluster. A guidance algorithm has been developed under the assumtion that the two bodies of the spacecraft are optically coupled telescopes that relay laser signals. The reference maneuver is found by the imposition of the connectivity between the source and the target on the ground. A new nonlinear control law is designed for the spacecraft attitude and joint rotation by the use of Lyapunov’s direct method. An acceleration-based steering law is used for the variable-speed control moment gyros. The analytical results are tested by numerical simulations conducted for both regulation and tracking cases. I. Introduction T HE dynamics and control of multibody spacecraft are a challenging problem because of the complexity of the dynamics equations and the time-varying inertia of the system. The problem becomes even more interesting when gimbaled momentum exchange devices are considered to control attitude. Control moment gyros (CMGs) are unique among attitude control actuators because they can provide high output torque without using expendable fuels and can provide a level of precision and continuity unachievable with jet thrusters. Indeed, CMGs have been used for decades on space stations and on military spacecraft when fast slewing capability and high pointing accuracy were required. The use of CMGs is also currently under consideration for several future civil spacecraft requiring high agility (as in Refs. 1 and 2). A main drawback to the use of CMGs is the presence of singular gimbal-angle configurations at which the CMG cluster is unable to produce the required torque, or, in some cases, any torque at all. 3−5 Many previous studies have considered the problem of the dynamics and control of spacecraft by the use of single-gimbal CMGs.