Showing papers by "N.H. McClamroch published in 2003"

Dynamics and control of an elastic dumbbell spacecraft in a central gravitational field

Abstract: The dynamics of a dumbbell shaped spacecraft are modeled as two identical mass particles connected by a linear elastic spring. The equations of motion of the spacecraft in a planar orbit in a central gravitational field are presented. The equations of motion characterize orbit, attitude, and shape (or elastic deformation) degrees of freedom and the coupling between them. Relative equilibria, corresponding to circular planar orbits, are obtained from these equations of motion. Linear equations of motion that describe perturbations from these relative equilibria are presented. New dynamics and control problems are introduced for these linear equations. Controllability results are presented for various actuation assumptions, based on the linear equations.

Shape change actuation for precision attitude control

Abstract: This article focuses on an alternative technology for attitude control called shape change actuation and control. The objective is to control the spacecraft attitude by purposefully changing the mass distribution of the spacecraft. Shape change actuation and control is not useful for momentum dumping or storage. Rather, it is intended for efficient, low-authority attitude control, possibly as a backup for thrusters and reaction wheels.

Attitude control of a tethered spacecraft

Abstract: An attitude control problem for a tethered spacecraft is studied. The tethered spacecraft is viewed as a multibody spacecraft consisting of a base body, a massless tether that connects the base body and an end mass, and tether actuator dynamics. Moments about the pitch and roll axes of the base spacecraft arise by control of the point of attachment of the tether to the base spacecraft. The control objective is to stabilize the attitude of the base spacecraft while keeping the perturbations of the tether small. Analysis shows that linear equations of motion for the tethered spacecraft are not completely controllable. We study two different control design approaches: (I) we decouple the attitude dynamics from the tether dynamics and we design a linear feedback to achieve stabilization of the attitude dynamics, and (2) we decouple the controllable modes from the uncontrollable mode using Kalman decomposition and we design a linear feedback to achieve stabilization of the controllable modes. Simulation results show that, although it is difficult to control the tether, the tether motion can be maintained within an acceptable range while subilizing the attitude dynamics of the base spacecraft.

Asymptotic stability of rigid body attitude systems

Abstract: A rigid body, supported by a fixed pivot point, is free to rotate in three dimensions. Two cases are studied: the balanced case, whose dynamics are described by the Euler equations for a free rigid body, and the unbalanced case, whose dynamics are described by the heavy top equations. Both cases include linear passive dissipation effects. For each case, conditions are presented that guarantee asymptotic stability for relevant equilibrium solutions. The developments are based on a careful treatment of nonlinear coupling in applying LaSalle's invariance principle. Emphases are given to the partial damping cases; an approach based on the polynomial structure of the dynamics is used to obtain asymptotic stability conditions for these cases.

Nonlinear control of the air spindle testbed with constraints

Abstract: In this paper we design nonlinear feedback controllers for the air spindle testbed, a multibody attitude testbed consisting of a freely rotating platform and two proof mass actuators. We take into account stroke limits and velocity limits of the proof mass actuators. Two control methods are proposed: one is based on a time-state strategy; the other is based on a hybrid scheme. Detailed design procedures are given; simulations demonstrate the effectiveness of the controllers for this constrained stabilization problem.