Opportunities with VLBI Transmitters on Satellites

Abstract

Very Long Baseline Interferometry (VLBI) transmitters on satellites are considered for future satellites of Global Navigation Satellite Systems (GNSS) as well as for the upcoming Genesis mission of the European Space Agency (ESA). In both concepts, VLBI observations to VLBI transmitters on the satellites can contribute to orbit determination, with the geometry of observations to Genesis advantageous compared to GNSS. With Galileo as one of the GNSS, we emphasise the importance of VLBI observations for the estimation of the right ascension of the ascending node , which cannot be determined from GNSS alone. We find that can be estimated with accuracies better than 50 μas from 24 hour sessions with alternate observations to quasars and the Galileo satellite of interest. Station coordinates, on the other hand, can be determined from observations to three Galileo satellites with an accuracy at the centimetre-level or better from 24 hour sessions, again with alternate observations to the satellites and quasars for a better estimation of tropospheric parameters. Station coordinate results with VLBI observations to VLBI transmitters on satellites form the basis for frame tie and local tie determination. The transfer of space ties to local ties on the ground is of particular relevance for Genesis.