Angular velocity observer for space tether exploiting non-singular dynamics and vector measurements

Abstract

This paper aims to develop efficient observers of angular velocity for a space tether system using the measurements of the unit vector along the tether. The presented observers exploit a special formulation of the libration dynamics which inherently avoids the singularities caused by the conventional modeling method with two angular parameters. Two kinds of nonlinear observers are constructed in a progressive manner. The first observer, referred to as a reference observer, takes a simple form similar to an observer design proposed in the literature for estimating the angular velocity of a rigid body. The second observer, referred to as an extended observer, is specially tailored for the space tether system to remove the restrictive assumptions made in the reference observer. Theoretical analysis is made to analytically reveal the stability characteristics of the observers. Moreover, the performance of the observers is evaluated through numerical simulations.