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Onboard orbit determination using GPS observations based on the unscented Kalman filter
Authors:Eun-Jung Choi  Jae-Cheol Yoon  Byoung-Sun Lee  Sang-Young Park  Kyu-Hong Choi
Affiliation:1. Space Development Division, Satrec Initiative, Daejeon 305-811, Republic of Korea;2. KOMPSAT-5 System Engineering and Integration Team, Korea Aerospace Research Institute, Daejeon 305-333, Republic of Korea;3. Satellite Control and Navigation Research Team, Electronics and Telecommunications Research Institute, Daejeon 305-700, Republic of Korea;4. Astrodynamics and Control Laboratory, Department of Astronomy, Yonsei University, Seoul 120-749, Republic of Korea
Abstract:Spaceborne GPS receivers are used for real-time navigation by most low Earth orbit (LEO) satellites. In general, the position and velocity accuracy of GPS navigation solutions without a dynamic filter are 25 m (1σ) and 0.5 m/s (1σ), respectively. However, GPS navigation solutions, which consist of position, velocity, and GPS receiver clock bias, have many abnormal excursions from the normal error range for space operation. These excursions lessen the accuracy of attitude control and onboard time synchronization. In this research, a new onboard orbit determination algorithm designed with the unscented Kalman filter (UKF) was developed to improve the performance. Because the UKF is able to obtain the posterior mean and covariance accurately by using the second-order Taylor series expansion through the sampled sigma points that are propagated by using the true nonlinear system, its performance can be better than that of the extended Kalman filter (EKF), which uses the linearized state transition matrix to predict the covariance. The dynamic models for orbit propagation applied perturbations due to the 40 × 40 geo-potential, the gravity of the Sun and Moon, solar radiation pressure, and atmospheric drag. The 7(8)th-order Runge–Kutta numerical integration was applied for orbit propagation. Two types of observations, navigation solutions and C/A code pseudorange, can be used at the user’s discretion. The performances of the onboard orbit determination were verified using real GPS data of the CHAMP and KOMPSAT-2 satellites. The results of the orbit determination were compared with the precision orbit ephemeris (POE) of the CHAMP and KOMPSAT-2 satellites.
Keywords:Onboard orbit determination   Navigation solutions   GPS C/A code pseudorange   Unscented Kalman filter   Extended Kalman filter   Spaceborne GPS receiver
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