Estimation of satellite attitude dynamics and external torques via mixed Kalman/H-infinity filter under inertia uncertainties

Abstract

In this work, a mixed Kalman/H-infinity filter is designed for the attitude estimation of a low Earth orbit microsatellite and the external disturbance torques acting on it. The state vector will be formed by satellite's attitude along with angular rates and the external disturbances. An improved external disturbance modeled as a random walk acting (slowly varying) around three axis attitude was proposed. This external disturbance is mainly generated by the aerodynamic torque, the residual magnetic moment and the gravity gradient torque. The satellite has only magnetometer on board as the attitude sensor. The proposed algorithm is tested using simulated data for a microsatellite, and the results of this study are tested in different scenarios. The first two scenarios are the cases with and without uncertainty in the satellite’s inertia. The last scenario is extensive Monte Carlo simulations with uniformly distributed initial conditions of the Euler angle and angular rate. The major purpose of this work is to demonstrate that we can estimate external disturbances and attitude dynamic parameters of a satellite using a simple filter that combines the best features of Kalman and \({\mathrm{H}}_{\infty }\) filters. The simulation results show that the attitude RMS error is less than \(\pm 1\) deg (acceptable accuracy). Also, Monte Carlo simulation gives good results of the proposed filter. This latter estimates the attitude with accuracy less than 0.8 deg, the rate order is 1 milli-deg/s and the external disturbances around 1.5 μNm.