Unscented Kalman Filtering: NPSAT1 Ground Test Results

NPSAT1 is a small satellite that employs magnetic sensing and actuation for attitude control. The spacecraft orientation and angular velocity should, therefore, be estimated from the magnetometer readings. The inherent nonlinear dynamics of the system poses a challenging problem on the observer design. This paper demonstrates the ground test results of NPSAT1 state estimation using the Unscented Kalman Filter (UKF) - a fairly recent method with inherent appeals of extended Kalman fllter but with no need for linearization; thus more suitable for highly nonlinear flltering and control applications. The quaternion-based modeling constraint that the quaternion has a unit norm is enforced by treating the norm of the quaternion as a dummy measurement. The experimental results show the superior performance of the UKF in practice.