Scientific Applications Of Radio Tracking Data From Deep Space Probes

The successful implementations of the Chang'e series orbiting,landing,and return mission are contributing to the development of planetary radio science and scientific applications of tracking data.Planetary gravitational research is one application of radio tracking data that potentially can reveal internal structure of planets.Over the last fourteen years,massive quantities of radio tracking data were collected from the Chang'e series of missions.These rich data can be mined for scientific applications such as generating new lunar gravity field solutions.Recently,the Tianwen-1 mission to Mars was launched,and the China National Space Administration has planned several future gaseous planet exploration missions going forward.These planned missions indicate that Chinese space exploration efforts will gradually penetrate into depths of the Solar System.Although the Cassini and Juno missions have demonstrated enormous scientific value of the recovery of gaseous planet gravity field solutions and studies of the inner structure of Jupiter and Saturn,many open questions remain.This thesis focuses on the applications of radio tracking data and deliveries the following six contributions:(1)The basic theories and related practical models and methods for deep space probe radio data processing and planetary gravity recovery are systematized,especially the time and coordinate reference systems,the light-time calculation algorithm,and the celestial dynamics modeling used for data reduction.Based on these principles,an in-house Precise Orbit Determination(POD)software was developed and introduced.A processing module for the gaseous planet missions was introduced and compared with the well-known GEODYN-II software system on internal and external accuracy,in order to demonstrate architecture in software development.Based on China Deep Space Network(CDSN)and Chinese Very long baseline interferometry Network(CVN),VLBI data were simulated and analyzed to evaluate its potential application for Jupiter gravity field recovery.(2)The Cassini Grand Finale data improved the accuracy of the Saturn gravity field recovery,but the latest results include unknown non-axisymmetric gravity signals.We designed a comprehensive simulation in order to verify the possibility that this unknown signal may induced from the deep convective structure of Saturn.The gravity anomaly induced from the convective dynamo was calculated and a new theoretical gravity model for Saturn was derived.Based on this model,we adopted a Cassini Grand Finale-like orbit in the experiements,simulated the observables,and recovered the simulated convective dynamo gravitational signal.Our results show that the Cassini Grand Finale mission is insufficient for determining the weak non-axisymmetric gravitational moments related to the deep convective dynamo.In addition,a new orbit configuration was provided that the value 0.5 was selected as the optimal orbital eccentricity at a perifocal height of about 6000 km above the top of Saturn.This orbit configuration maintains a 2×10~5 km apoapsis distance.We found this orbit with five month tracking data is able to detect the strong field dynamo.(3)Processing radio tracking data from gaseous planet missions is subject to dynamic uncertainty;this is due to the imperfect Main Belt Asteroid(MBA)model describing Solar System dynamics.Furthermore,the accuracy of orbit estimations for Mars and Jupiter are significantly disrupted by the dynamic effects from these MBA models.Thus we propose a new six-ring model to physically model the effects of MBAs and provide a corresponding numerical calculation method for the acceleration based on a combined elliptical integral.The results indicate that the new model can capture at least 98%of the perturbations caused by MBAs.Meanwhile,the remaining 2%effect is estimated,with less than 0.5 m error in Mars-Earth distance estimations during a ten-year dynamic integration for all eight planets in the Solar System.(4)We reprocessed the tracking data and comprehensively summarized the evolution of POD accuracy and the tracking system precision from the Chang'e 1 to Chang'e 4missions using in-house software.Our results show a progression of the tracking station accuracy,as the first Chang'e 1 mission only reached 0.2?2 mm/s level accuracy in the Doppler measurements and 1?2 m level accuracy for the two-way range measurements.Later on,the accuracy of Chang'e 2 Doppler measurements reached about 0.23 mm/s and two-way range was about 2 m;the accuracy of Chang'e 5T1 Doppler measurements reached about0.35 mm/s and the accuracy of the Chang'e 3 two-way range measurements were below 0.7m.The overlap of Chang'e 1 and Chang'e 2 was about 200 m,the overlap of the Chang'e 3on the 100 km orbit was about 573 m,and for the Chang'e 5T1 mission it was about 115 m.Moreover,the Chang'e 4 relay satellite achieved POD residual RMS(Root Mean Square)values for the two-way range of less than 0.7 m with an orbital accuracy at the 277 m level.(5)We proposed an optimal weighting algorithm based on Helmert-variance component estimation applied to VLBI phase delay data.We validated our algorithm using the Chang'e 3 lander VLBI phase delay data collected from the CVN.The lander positioning accuracy achieved with our new algorithm was at least 53%higher than the previous estimations based on the same observations.The position of the lander based on continuous4-day observations was estimated to be 44.1215°N(±21.9 m),19.5135°E(±4.2 m).(6)We obtained an improved lunar gravity field model up to degree and order 100,termed CEGM03,and a new tidal Love number,estimated to be 0.02430±0.0001(ten times the formal error),using two-year tracking data of the Chang'e 5T1 mission.The gravity spectrum power,post-fit residuals after POD,lunar surface gravity anomalies,correlations between parameters,admittance and coherence with the topography model,and accuracy of POD were analyzed to validate the new CEGM03 model.The error spectrum illustrates that the formal error in CEGM03 was reduced by about twice when below the harmonic degree of20,as compared to the existing CEGM02 model.The admittance and correlation of gravity and topography was also improved when compared to the correlations for the CEGM02model.