NPSAT1 Parameter Estimation Using Unscented Kalman Filtering

Abstract

NPSAT1 is a small satellite being built at the Naval Postgraduate School and scheduled to launch in 2007. It primarily employs magnetic sensing and actuation for attitude control. The nature of the in-house fabrication and assembly of the spacecraft requires reliable computational estimation of the difficult-to-measure parameters of the end-product. The inherent nonlinear dynamics of the system makes the observer design a challenging problem. This paper presents the successful implementation of the unscented Kalman filter (UKF) for the spacecraft parameter estimation. Since a three-axis magnetometer is the only sensor onboard, the UKF algorithm also estimates the system orientation and angular velocity. The unit quaternion constraint is enforced by treating the norm of the quaternions as a dummy measurement. Simulations and ground test experimental results show the superior performance of the UKF in spacecraft dual state-parameter estimation.