Galileo POD using optical inter-satellite links: A simulation study

Abstract

In this simulation study the benefit of optical two-way inter-satellite links (OISL) between the Galileo satellites for orbit determination is discussed. Different link scenarios are analyzed in combination with Global Navigation Satellite System (GNSS) observations and a ground station network of seven or 16 stations, respectively. Great importance was attributed to the simulation of systematic effects in the different measurement techniques as realistically as possible. For GNSS observations this is multipath, errors in tropospheric delays and phase center variations on transmitter and receiver side as well as variable biases. For ISL this is colored link noise, a variable offset in the phase lock loop and a distance dependent noise. Modelling errors also have to be considered to avoid unexpectedly good orbit solutions in all scenarios. We study formal errors together with the influence of the systematic errors and the weighting of the measurement techniques relative to each other. The main focus lays on the comparison between the different inter-satellite link scenarios and only secondarily we looked on the gain these additional measurements have on the precise orbit determination of Galileo satellites. Inter-satellite links can be used for different purposes, such as data transfer, increasing autonomy, reducing costs and higher accuracy in orbit determination and clock synchronization. Especially for optical inter-satellite links data transfer capabilities rise and the scenarios preferring stable link configuration are discussed more and more. The question answered by this study is whether or not closed link topologies have a valuable contribution to precise orbit determination. In different sub-scenarios the precision of Galileo processing is increased from worst case to unexpected precision, and the benefit of the additional optical tracking is analyzed.