© 2015, Editorial Dept. of JA. All right reserved. When a spacecraft moves toward or away from the X-ray pulsars, Doppler effects are present in the pulsar signal measured by onboard X-ray detectors. By measuring the observed pulsar frequency, the speed of the spacecraft along the line of sight of the pulsar can be derived. The mathematical model is established to characterize the spacecraft's velocity estimation by adopting the time of arrival of X-ray photons. To improve the accuracy of Doppler frequency estimation, a robust averaging technique, RANSAC, is introduced to combine with the χ2statistical method. Besides, the priori information of the spacecraft velocity is utilized to improve the computational efficiency. The Crab pulsar data observed by RXTE satellite are applied to validate the presented method and some dominating error factors are analyzed. The results demonstrate that the method can track the spacecraft's velocity effectively. For RXTE satellite with the orbit altitude 570 km, in terms of the obvious changes in spacecraft's acceleration, the velocity estimation error along the line of sight of the pulsar is about ±150 m/s, and the corresponding acceleration estimation error is ±0.5 m/s2.
Sun Hai-Feng;Bao Wei-Min;Xue Meng-Fan;Fang Hai-Yan;Li Xiao-Ping
Yuhang Xuebao Journal of Astronautics