Positioning Of Spacecraft With VLBI Inverse Phase Reference

The Deep Space exploration is a kind detection which is from the earth's gravitational field into the solar system space and cosmic space.It mainly includes the exploration of the moon and the planets,and the astronomical observation.It's one of the key technologies to realize the high precision positioning and orbit determination of space detectors.In the positioning about Deep space probe,VLBI technology has developed a stage of delta VLBI technology,detla DOR technology and phase-referenced technology.The precision is becoming more and more high.The ability to measure the depth of the deep space probe has been increased from a few hundred milliarcseconds(mas)to a few milliarcseconds(mas),which is now up to the level of sub-milliarcseconds(mas).For positioning of spacecraft with VLBI phase-reference,an extragalactic radio source was usually served as phase reference.After fringe fitting on the radio source,the solutions including delays and rates mainly from the propagation media were adapted to calibrate the observed phase of the spacecraft.The common phase errors of the nearby source pair were significantly reduced in their differential phases,allowing accurate relative position measurement.However,this traditional phase-reference method requires strong and nearby extragalactic radio source,which is hard to fulfill due to the lack of strong calibrators on the sky.Since the radio flux density from the spacecraft is much stronger than that of the extragalactic radio source,it is possible to use the spacecraft as phase reference.In this paper,we investigated the feasibility and advantages of this so called inverse phase reference method,based on real VLBI observations.We compared the data analysis results using the two phase reference methods,it proved that the inverse phase reference is capable to measure accurate relative positions,and could achieve better results that the traditional methods,especially when the extragalactic radio source was weak.The main works are as the following:1.This paper systematically expounds the basic principle of VLBI astrometry,and explains the two types of VLBI astrometry—absolute and relative.Based on the brief introduction of the basic principle of VLBI,this paper introduces the basic principle,the observation mode and the main influence factors of the VLBI phase reference method.2.In order to overcome the shortcomings of the traditional VLBI phase reference method,we proposed an inverse phase reference method and analyzed the advantages and applicable conditions of inverse phase reference method.According to the measured data of the CASINI detector based on the VLBA,we described the data processing flow of the two methods in detail,including the use of AIPS software and Parsel Tongue software for the CASSINI detector phase reference map data processing.Compared with the previous results,it proved that the inverse phase reference is capable to measure accurate relative positions.3.In order to study the inverse phase reference in the advantage of weak source,based on the measured data to simulate the weak source,that is,According to the success rate about fringe fitting is related to the number of channels used,We adopt the method of selecting fewer channels to simulate the weak River source.By comparing the results of the two methods to the weak source,the advantage of the inverse phase reference is verified.