A Method Of Spacecraft Velocity Estimation With Using Doppler Frequency Shift Of Pulsar Signals

Spacecraft autonomous navigation is a new type of celestial navigation system,which does not need to rely on the support of ground stations,and it also has strong anti-interference and survivability.Spacecraft velocity estimation is an important part of autonomous navigation,and it is necessary to know the velocity information of the spacecraft in many missions.The X-ray pulsar is a neutron star with high speed,periodically radiates electromagnetic pulse signal,and the pulse signal is stable,with which we can determine the spacecraft's position,velocity and acceleration ect.The Doppler frequency shift is generated when the spacecraft is moving relative to the X ray pulsar.In this paper,the Doppler frequency shift of the X-ray pulsar signal is used to estimate the velocity of the spacecraft.The main research work includes:(1)Introduced the basic theory of X-ray pulsar signal modeling,and analyzed the common time and coordinate system and its conversion relation.At last,describes the structure and application of the ephemeris file(2)Studied a time transformation model with high accuracy(analyzed the influence of all factors in time transformation model in detail and the difference of different ephemeris),based on which we generated photon arrival time series at the spacecraft positively.The results show that the time conversion table with high accuracy is obtained.The photon arrival time series produced by scale transforming method positively contains time correction information,the pulse profile folded out with considering the slow change of frequency has consistent waveform with standard profile waveform,and the Pearson correlation coefficient is 0.9995.It provides a great support for the Doppler frequency estimation and spacecraft velocity estimation.(3)Studied a frequency estimation method with high accuracy——H-test(analyzed a determination method of m value),estimated the observed frequency of spacecraft with simulation data and the measured data of Crab pulsar searched by RXTE satellite and compared with the?~2 statistic.The results show that,compared with the?~2 statistic,the H-test method has higher precision in frequency search and higher with two orders of magnitude.For the measured data of Crab pulsar,the H-test method is more stable and accurate.(4)Established a velocity measurement model of Doppler based on frequency shift,lead the speed prior information into the spacecraft.Discussed and analyzed the main error of velocity estimation based on the measured data of Crab pulsar.The results showed that the H-test method can effectively track the change of spacecraft's velocity.Based on the Crab pulsar data,velocity error of spacecraft in the direction of pulsar is subject to the update time of Doppler frequency shift.The appropriate update time makes the speed estimation error interval is smaller.For the two data packets selected in this paper,the update time of40s is better,and the error interval of velocity estimation is[-18,97]m/s,the acceleration error is around?0.5m/s~2.