Research On Timekeeping Ethod Of X-ray Pulsar Autonomous Navigation

The pulsar is a magnetized neutron star with high-speed rotation characteristics,it produces signal radiation in electromagnetic wave bands such as radio,visible light,X-ray,and?-ray.X-rays concentrate most of the capability of X-ray pulsar,making it easier to miniaturize detection equipment.Therefore,X-ray pulsar can be used to achieve spacecraft navigation tasks.X-ray pulsar navigation can provide accurate information including position,time and speed for near-space and deep-space spacecraft.X-ray pulsar navigation has the advantages of strong autonomy,high security and high accuracy.It is an important research direction for human exploration of deep space.This paper focuses on the research of X-ray pulsar navigation and explores the problems encountered by X-ray pulsar navigation.The main tasks are as follows:1)In order to improve navigation precision and clock difference correction ability of long-term navigation of spacecraft,a X-ray pulsar and Doppler difference integrated navigation method with clock difference correction is proposed.In the case of the distorted solar spectrum,Doppler difference navigation is used to eliminate the influence of Doppler velocity error on navigation and ensure the accuracy of Doppler velocity;In order to overcome the influence of clock difference on navigation accuracy,the clock difference is expanded into state variable,a state model considering the clock difference is constructed,and a measurement model of X-ray pulsar navigation is given to ensure long-term spacecraft navigation precision;The federated unscented kalman filter is used to fuse the navigation information of X-ray pulsar navigation and Doppler differential navigation,the simulation results show that this method can restrain the influence of Doppler speed error on navigation,control the satellite clock difference and provide Ihigher navigation precision.2)In order to reduc.e the influence of pulsar direction error and clock difference on navigation,an X-ray pulsar navigation method is proposed to correct the direction error and clock difference.The influence of pulsar direction error on system bias is analyzed;The X-ray pulsar navigation measurement model that takes into account the direction error and the clock difference is given,and the system bias caused by the pulsar direction error and clock difference are extended to the state vector;The state estimation was performed using the unscented kalman filter,the simulation results show that this method can suppress the influence of direction error and clock difference on navigation and provide higher navigation accuracy.