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Kur T., Kalarus M. (2021). Simulation of Inter-Satellite Link schemes for use in precise orbit determination and clock estimation. Advances in Space Research, Volume 68, Issue 12, 15 December 2021, Pages 4734-4752. doi: 10.1016/j.asr.2021.05.011.

Abstrakt/Abstract: Inter-Satellite Links (ISL) are considered a key technology which might improve the accuracy of the Global Navigation Satellite System (GNSS) and navigation satellites orbit determination. This research aims at evaluation of advantages of the ISLs with special consideration of the Galileo, as a contribution to precise orbit determination and satellite clock estimation. The performed analysis will also pave the way to more advanced processing including more sophisticated modifications of the current orbit determination approach and development of the algorithms for the ISL system.

The study provides a detailed analysis of various ISL connectivity schemes (organisation of the inter-satellite connections). Selected results are then presented in the context of the precise orbit determination (POD) based on weighted least squares adjustment. As there is no Galileo satellite currently equipped with operational ISLs, the analysis is based on simulated measurements. The most promising connectivity schemes are collated according to their influence on POD performance and compared in terms of their accuracy and reliability. The performance of the estimation process was also tested with respect to the different number of GNSS stations and variable ISL measurement sampling interval.

By using ISLs in nominal simulation, the POD is improved by reducing RMS orbit error in along-track by about 8 mm, cross-track components from 2 mm to 7 mm depending on used connectivity scheme, and in radial by about 5 mm. Generally clock estimation errors are smaller with the ISL contribution up to 30%. Furthermore, the ISLs make the constellation more resistant to the reduction of the number of ground stations, however about 30 stations are optimal. For 6 ground stations ISLs help to minimize orbit errors even up to 4 times comparing to a GNSS-only solution. Establishing ISLs more often, with sampling interval on the level of 30 s or less, seems to be the most promising in improving the orbit determination. Using sampling intervals equal to 300 s or 600 s indicates that a very small percentage of ISL observations compared to total number of GNSS measurements is still sufficient to reduce orbit errors in reference to GNSS-only solution from 30% to 40%.

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