Research On Precise Orbit Determination By Transfer For GEO Navigation Satellites

GEO satellites play significant roles in the space segment of the regionalnavigation and augmentation system, such as WAAS, IRNSS, QZSS, EGNOS, BDSand CAPS. The high precise orbit is essential to high precise navigation, positioningand timing service. Therefore, it will promote the construction of regional navigationand augmentation system to research on theory of POD (Precise Orbit Determination)and Prediction.However, the unique characteristic of GEO satellite such as high altitude andsmall movement make it difficult for POD achievement. Firstly, the geostationarycharacteristic of GEO satellite makes the tracking geometry between stations andGEO being almost unchanged, the difficulty of separating the clock error and stationbiases and so on. Secondly, GEO satellites’ orbit altitude is about36000km, whichmakes the POD precision is poor when tracking geometry of GEO satellite is poor iftracking stations are placed limit in a small area. Moreover, maneuver control isoften performed because of GEO satellites’ particularity to keep pace with Earth,which increases demand for high precision and continuous orbit determination andprediction.The C-Band transfer ranging method developed by NTSC(National TimeService Center) has been widely used in the CAPS, with its advantages of separatingsatellite ranging from time synchronization and being unaffected by weather. Aimingat solving these questions, the research on POD using C-Band，VLBI, SLR and otherkinds of data have been conducted. The detailed work and contribution of thisdissertation are as follows.1．Orbit determination for GEO satellites with the mode receiving timesignals from their own station and differenced ranges between slave stations bytransferIn order to restrict the transverse orbit error more greatly, a new method named“differenced ranges between slave stations bytransfer”, similar to VLBI observation,has beendeveloped in CAPS. In this dissertation, the principle of “differenced rangesbetween slave stations by transfer” has been depicted in detail, with the observationequation, the observation matrix, clock offset between slave stations and systemerror which affect the precision of the differenced ranges observation being discussed.Especially, the problem of clock offset calculating between slave stations beingconquered since there is no direct TWSTFT (Two-Way Satellite Time Frequency Transfer) links between slave stations in CAPS.The differenced observation of the SINOSAT-1satellite with C-Band betweenslave stations from6to13June2005was firstly conducted. Then comparison on theaccuracy of orbit determination and prediction has been conducted betweencombined method and ranging method only. It has been shown that combination ofdifferenced data and pseudo-range receiving the own station-disseminated signal hasa higher accuracy.2．Evaluation of C-Band precise orbit determination of GEO satellitesSince the GEO satellite which CAPS observes has no laser reflector, theprecision of GEO satellite shoud be evaluated and the station biased errors in thesystem should be calibrated. The explicit ranging correction models for the C-Bandtransfer ranging method and the out circle time delay measuring method areintroduced in detail in this dissertation. GEO satellite can be measured by C-Bandtransfer measuring system with high precision.The orbit of the GEO satellite has been evaluated by SLR data from bothdomestic and foreign SLR sites for the first time. The relation between distribution ofCAPS stations and orbit precision has been researched, since all sites in CAPS arenow located in China with low and medium latitudes. It can be seen that the residualRMS in line-of-sight for a SLR site in China is about0.5m, while the RMS for Yarragadeesite in Australia is about3.3m. The distribution of CAPS stations does affect the orbitprecision.3. Research on time-sharing observing model for GEO satellite in CAPSThe normal consecutive observing model in CAPS can only supply observationof one GEO satellite in1d. However, this can’t satisfy the project need for observingmany GEO satellites in1d. Therefore, the time-sharing observing model for GEOsatellite in CAPS needs research. In this dissertation, the principle of time-sharingobserving model is firstly introduced. Then, three kinds of time-sharing observationare created using C-Band consecutive observation in June2005. Finally, thisdissertation gives one time-sharing observing model appropriate for CAPS, withorbit precision better than2m.4. Orbit determination and prediction of GEO satellite duringrepositioning maneuverIn order to have a continuous GEO satellite orbit during repo sitioning maneuverdetermined, a suitable maneuver force model is established with optimal orbit determination method and strategy. The orbit determination method and strategy arethen illuminated, with assessment of orbit being determined and predictedaccordingly. The effect of data before maneuver on the precision duringrepositioning maneuver has been analysised, with the comparison between methodsof short arc orbit determination and repositioning maneuver.5. Combined orbit determination using VLBI data and C-Band dataThe observations after maneuver in short arc are small, and the horizontal orbitprecision is not high using only C-Band data. The combined data of VLBI andC-Band data are processed to support the quick orbit recovery after maneuver. CVN(Chinese VLBI Network) organized the tracing and orbit determination trial lastedfor24hours to GEO navigation satellite, and got VLBI delay and delay rate data.This dissertation has used the VLBI data and C-Band ranging data to determine theGEO satellite’s orbit. The short arc and1day POD precision using C-Bandobservation and VLBI data has been analysed, with effect of different baseline onPOD and prediction precision.