Spacecraft attitude determination using a decoupling filter

In this paper, an algorithm for real-time attitude estimation of spacecraft motion is investigated. For efficient computation, the decoupling filter p resented in this paper is accomplished by a derived pseudo-measurement from the given measurement and the decoupled state in the original system. Howe ver, the proposed decoupling filter contains model errors due to coupling t erms in the system. Therefore, we develope an attitude determination algori thm in which coupling terms are compensated through an error analysis. The attitude estimation algorithm using the state decoupling technique for real -time processing provides accurate attitude determination capability under a highly maneuvering dynamic environment, because the algorithm does not ha ve any bias errors from a truncation, and the covariance of the estimator i s compensated by nonlinear terms in the system. To verify the performance o f the proposed algorithm vis-a-vis the EKF (extended Kalman filter), and th e nonlinear filter, simulations have been performed by varying the initial values of the state and covariance, and measurement covariance. Results sho w that the proposed algorithm has consistently better performance than the EKF in all of the ranges of initial state values and covariance values of m easurement, and it is as accurate as the nonlinear filter. However, the con vergence speed of the nonlinear filter is faster than the proposed algorith m because of the pseudo-measurement model errors in the proposed algorithm. We show that the computational time of the proposed algorithm is improved by about 23% over the nonlinear filter.