Study On X-ray Navigation And Communication Integration

With the increasing development of space explorations, deep space missions are turning from short-term, rough detection to detection with features of long-duration, high resolution, strong autonomy, and multi-platform cooperation, which raises the requirements for future navigation and communication. To satisfy the increasing demand for navigation and communication in deep space explorations, navigation and communication integration has become a tendency. X-ray Pulsar-based NAVigation (XPNAV) and X-ray Communication (XCOM) are rising techniques suitable for deep space explorations, both of which show great potential in future development. XPNAV and XCOM show similarities and tight connections in signal, detection equipment, and functions, which provides the possibility of technology integration, i.e., X-ray navigation and communication integration. X-ray navigation and communication integration is implemented by the mutual fusion, complementation, and augmentation of XCOM and XPNAV and their derivative technologies. It aims at providing navigation and communication service of high quality under limited technological resources in deep space. X-ray navigation and communication integration provides a potential solution for the increasing demand for deep space navigation and communication. Focusing on the key technologies of X-ray navigation and communication integration, the dissertation studies the function connections and complementation between XPNAV and XCOM. The main contents of the dissertation include:1. Range is a basic element of deep space navigation, and accurate range information can provide supplementary observation information for XPNAV. Thus, an X-ray Circularly Polarized Ranging (XCPolR) method based on XCOM is proposed, which transmits range information as special "communication data". On the basis of XCOM, the proposed method utilizes circular polarization modulation method to modulate X-ray, and the range information is conveyed by circular polarization states. Strokes vector is adopted to model the ranging signal and the signal processing flow is described based on the signal model. Besides, the impact of the Doppler effect, the signal differential detection, and the ranging signal correlation on the proposed method is analyzed both theoretically and numerically. Simulation results demonstrate that XCPolR could provide high-accuracy range measure results.2. Deep space missions are far away from the Earth and operate in complex and changeable space circumstances, which results in low link availability. To raise link efficiency under low link availability, an X-ray communication and ranging integration method is proposed. On the basis of the communication capability of XCOM, the proposed method realizes simultaneous communication and ranging in a single X-ray link. The proposed method not only shows advantages in enhancing the link efficiency, but also indicates the concept of technology integration, which provides reference for the realization of X-ray navigation and communication integration. The dissertation designs the signal structure of X-ray communication and ranging, and describes the signal processing flow in detail. Besides, the parameters for assessing the performance of the proposed method, including the ranging repeat rate, the data transmission rate, the bit error rate, the ranging jitter, etc., are analyzed by both theoretical derivation and numerical simulation. Simulation results demonstrate the feasibility of the proposed method. The simulation results also indicate that parameters like the signal acquisition property, the bit error rate, and the ranging jitter, are mainly influenced by the Signal-to-Noise Ratio (SNR) of the signal.3. XPNAV is a new celestial navigation method realized by observing the periodic pulse signals emitted by pulsars, which is an essential part of X-ray navigation and communication integration. Influenced by various factors, the positioning accuracy of XPNAV shows difficulty in improvement, which hinders its further study and application. An XCOM based XPNAV augmentation method is proposed, which utilizes the derivative technology of XCOM, i.e. X-ray ranging, to provide supplementary range information for XPNAV augmentation. The observation models of pulsar timing and X-ray ranging are established. The states of the spacecraft are estimated based on the orbital dynamics models and the established observation models. Furthermore, numerical experiments are utilized to analyze the impact of the pulsar observation time, the SNR of the ranging signal, and the operation orbits on the proposed augmentation method. Simulation results indicate that, compared with XPNAV method, the proposed augmentation method can effectively improve the positioning performance of XPNAV.4. Time is a basic parameter in deep space exploration, which is the life-line for deep space navigation and communication. To provide accurate timing service for X-ray navigation and communication integration, a deep space autonomous timekeeping method based on pulsar timing observation is proposed. The proposed timekeeping method originates from XPNAV and utilizes the observation of pulsar signals to correct clock error of a spacecraft. In the dissertation, a colored noise model is adopted to model the timing noise in pulsar timing observation. Based on the timing observation model and the clock revolution model, a Kalman filtering method is utilized to estimate the clock states. Numerical experiments are utilized to evaluate the performance of the proposed method, and the impact of the pulsar observation time and the selection of pulsars on the proposed method. Simulation results indicate that the proposed timekeeping method can effectively restrain the clock error and implement deep space autonomous timekeeping.