Angular rate and attitude estimation for satellites using vector observation only

Abstract

During last decades gyros have been used for attitude determination of communication satellites. However, gyros have certain disadvantages such as short lifetime and tendency to fail. Accordingly, the issue of changing gyros as a means of orientation is become important. It should be noted, that current topic can be apply for general satellite when gyro failed as well for satellite with gyro-less design a priori. Traditionally, vector observation is used for attitude estimation; however, in this paper vector observation is applied for angular rates determination too. In this case, a necessity of using gyro stands no longer. As the basis of Vector Observation one would take any vectors: Sun vector, Earth`s vector, Earth`s magnetic field vector. In this work applicable and reconstructed algorithm is proposed for purpose of satellite angular rate and attitude estimation without gyro sensor. For the later one in real life we need set of observation vectors and reference vectors set as a requirement. Next step is taking the well-known QUEST algorithm for determination of spacecraft orientation. And for angular rate estimation here is shown the point of using more than two of vectors` sequences. From the unit-vector measurement model observation vectors are taken at successive time intervals and used in spacecraft kinematics equations. Finally, angular velocity is determined from measurements through a weighted least-square approach. There are advantages such as independence of attitude information and freedom from the bias of gyro in this method.