Research On Spacecraft Autonomous Navigation Using X-Ray Pulsars

Pulsars provided by nature for humanity are like natural lighthouses. It is hopeful to get rid of the restriction of artificial beacons by using pulsars in spacecraft navigation, which can be a real sense of spacecraft autonomous navigation in the large temporal and spatial range. Researches on pulsar based navigation have been carried out in recent years and this field has become a hotspot in the space technology. Thereupon, plans of pulsar based navigation have been put on the agenda. This thesis, based upon the investigation and analysis of the existing research progress, taking into account the engineering implementation, systematically studies a new method of pulsar based navigation. The effectiveness of the proposed work is validated by simulating most of the principles and algorithms using RXTE satellite measured data and orbit information.In the aspect of pulsar based navigation principle, pulsar based relative navigation scheme is proposed, and its bases are the definitive direction vector of pulsar and accurate pulse period. The scheme, based on fact that the solar system can be considered as a weak gravitational field, deduces the pulsar signal period predicted model in GCRS and establishes the function between pulsar signal phase difference and spacecraft displacement increment in pulsar direction vector in the J2000 coordinate. Compared with the existed pulsar based navigation schemes by numerical simulation, the new scheme with the position error less than one millimeter when the period of pulse signal updates in seconds, and can calculate the projection of spacecraft orbit in pulsar direction vector by utilizing Crab’s observed data, which is consistent with RXTE real orbit. The pulsar based relative navigation scheme also has the advantages of low computational complexity, intuitionistic measurement, as well as irrespective of pulsar signal phase forecast and integer ambiguity.In the aspect of X-ray detector, a small volume, low power dissipation CMOS technology X-ray detector is designed considering the changeover of the X-ray detector from test load to satellite platform load in pulsar based navigation system. The detector adopts reverse bias diode with high W/L value as sensitive area, applies Not-gate cascade amplifier to boost the micro weak voltage signal caused by X-ray photons, and designs feedback mechanism to regulate states of the Not-gate dynamically, also compensate the effect of the dark current on sensitive area. This thesis, through semiconductor process simulation, verifies the feasibility of the X-ray detector.In the aspect of pulsar signal processing, based upon analyzing the existing algorithm, Walsh transform based signal recognition and multiple harmonic time-delay estimation algorithm are proposed to realize the synchronization of pulsar signal recognition and phase estimation. To evaluate the algorithm, the Cramer-Rao Bound of pulsar signal phase estimation is introduced. Utilizing the RXTE observed data and orbit information to verify the algorithm, the results show that the algorithm could greatly reach the Cramer-Rao Lower Bound on the estimation of pulsar signal time-delay when the time of signal integration is over 300 s. While there is hysteretic nature when the estimation of pulsar signal phase is obtained by integration signal, thus, reconstructed Gauss twice resampling algorithm based on particle filter, which is a real time estimation of time-delay for pulsar signal is put forward. The premise of the algorithm is high SNR pulsar signal obtained by enlarging the detector area, and in order to avoid the particle degradation of the standard particle filter, the algorithm modifies the particle distribution strategy in particle filter.In the aspect of pulsar based integrated navigation, firstly, in respect to the most common situation that only one pulsar can be observed in engineering applications, pulsar/astronomical integrated navigation scheme is proposed and studied. Secondly,considering the hysteretic nature in the process of phase information acquisition, as well as the real time signal of starlight angle, this paper proposes an improved Kalman predicted filtering algorithm, which makes the research be closer to the real situation of pulsar based navigation. Finally, the thesis conducts comprehensive simulation on the method of pulsar based relative navigation, improved Kalman predicted filtering algorithm and pulsar/astronomical integrated navigation scheme.