Satellite & Space Missions

Biography

Biography: Giulio Avanzini

Abstract

A spacecraft is in underactuated conditions when three rotational degrees of freedom need to be controlled by means of actuators, delivering control torque components around two non-collinear axes only. This condition can be the consequence of an actuator failure, when the satellite is equipped with a non-redundant system or multiple failures, for redundant ones. It can also be a natural condition for spacecraft equipped with magnetic actuators, which can deliver a control torque, which lies on a plane perpendicular to the direction of the local geomagnetic field. Since it is not possible to simultaneously control attitude and angular speed of a rigid body with two control torque components by means of a continuous time-invariant feedback, the problem of attitude stabilization and control becomes significantly more difficult.

Discontinuous control approaches (e.g. switching control logics [2, 3]) as well as time-varying controllers [4, 5] has been proposed. In the paper, a review of these techniques will be proposed and a focus will be placed on kinematic approaches, developed by the author in cooperation with Fabrizio Giulietti, from University of Bologna, and other collaborators. The kinematic approach allows for tackling many control problems for underactuated spacecraft by means of controllers, which are at one time very efficient in terms of required computational effort and effective in terms of convergence time. The results for various operational scenarios, such as detumbling by means of magnetic actuators only [6], or pointing of an axis in an arbitrary direction by means of only two reaction wheels will [7] be discussed.