A Time Delay/Star Angle Integrated Navigation Method Based on the Event-Triggered Implicit Unscented Kalman Filter

Time delay is a novel celestial navigation measurement that can provide the distance information of the spacecraft relative to the nearby celestial body. Combining time delay measurement with traditional star angle measurement can greatly improve navigation performance. However, the navigation accuracy will be affected by the ephemeris error of the nearby celestial body. To solve this problem, this article adds the position and velocity of the nearby celestial body to the state vector and estimates them online. The estimated values are used to replace the ephemeris data of the nearby celestial body in the measurement model. Besides, an event-triggered implicit unscented Kalman filter (IUKF) is proposed to reduce unnecessary calculation and shorten the running time. Simulation results indicate that the position error and velocity error of the proposed method are reduced by about 61% and 67% compared with that of the traditional time delay/star angle integrated navigation method (TDSA), respectively. The running time of the proposed method is reduced by about 88% compared with that of the TDSA with the augmented state (AS). In a word, the proposed method can greatly reduce the running time while maintaining high navigation accuracy.