The Mothods Of X-Ray Pulsar Navigation And Its Applications In Orbit Estimation

X-ray pulsar based navigation (XNAV) is a newly developed space basednavigation method, it utilizes the pulsed signals emitted from over thousands oflight years away for positioning and time keeping. The orbit estimation of earthorbiting satellites and the deep space navigation of spacecraft are the two mainfields of XNAV applications.XNAV is studied in this dissertation with the application background oforbit estimation, and new XNAV methods are developed. Observability analysisalgorithm are developed to analyze the minimal requirement of XNAV basedintegrated navigation plans and to analyze the observability of clock error. Withthe simulation of GNSS system orbit estimation, the works and results of thisdissertation are proven right and effective, and the main purpose of thisdissertation is to provide a navigation solution with high accuracy, highautonomy and low requirements in orbit estimation.The works in this dissertation are as follows:First, based on the preexisting standard XNAV mode, two new XNAV mode:incremental XNAV and relative XNAV are given, and the navigationrequirements and measurement noise of the three XNAV modes are analyzed, andcomparison simulations are conducted to examine the three XNAV modes’performances. Results indicate that standard XNAV is affected by clock errorwhile incremental XNAV and relative XNAV are insensitive to clock error, andboth XNAV modes have similar accuracy as standard XNAV, they are moresuitable in orbit estimations.Second, to provide orbit estimation with a theoretical analysis method, twoobservability evaluation algorithm are given: globe observability evaluationmethod--EAF, and local observability evaluation method--EAFE. EAF canquantify a navigation plan’s observability, judging whether a plan is observable,and also can compare the observabilities amongst multiple plans. EAFE canevaluate the observability status of each orbit element, and it is very helpful inanalyzing a specific state such as clock error. Simulation results prove the twoanalysis tools are effective. Third, the minimal requirements for total observability when using XNAVunder various navigation situations are given to reduce spacecraft weight andnavigation cost. With the help of EAF and simulations, the results are given asfollows: in single spacecraft navigation, only2pulsars with1X-ray detector canachieve total observability; in multiple spacecraft navigation, only1pulsar canachieve total observability, and the navigation accuracy is within10meters. Amethod of using single detector observing multiple pulsars in turn is developed,and simulation results indicated that this method is most suitable for spacecraftformation navigation.Fourth, based on pulsar’s highly accurate timing ability, the observability ofclock error in orbit estimation using XNAV is studied with EAFE. Analysisresults indicate that clock error cannot be observed using incremental XNAV andrelative XNAV, but when using standard XNAV the clock error can be observed.Theoretical analysis and simulation results indicate that with only1pulsar XNAV,the clock error can be estimated with a fine accuracy within50ns, even thoughthe navigation cannot achieve total observability; when the observability leveland the positioning accuracy of the navigation plan improve, the accuracy ofclock error improves to15ns, which meets the timing requirement of GPSconstellation.Finally, using the analytical algorithm derived and research findingsconcluded in this dissertation as navigation plan designing guideline, settingGNSS as the application scenario, a systematic navigation architecture isdesigned with the consideration of minimize navigation requirements and cost toachieve best navigation results. The source of estimation error is analyzed, andan iteration algorithm is designed to achieve best navigation results withreasonable computing cost. Simulation results prove that in full autonomousGNSS orbit estimation, using only1pulsar XNAV and a well planed navigationalgorithm structure and integrated navigation plan, all the spacecraft in theconstellation can achieve an accuracy within3meters.