A model of geometric delay in Space VLBI

Abstract

A relativistic delay model for space very long baseline interferometry (hereafter SVLBI) observation of sources at infinite distance is derived. In SVLBI, where one station is on a spacecraft, the orbiting station's maximum speed in an elliptical Earth orbit is much bigger than the ground VLBI (here after GVLBI), leading to a higher delay rate . The delay models inside the VLBI correlators are usually expressed as fifth-order polynomials in time that good for a limited time interval, which are evaluated by the correlator firmware and track the interferometer delays over a limited time interval. The higher SVLBI delay rate requires more accurate polynomial fitting and evaluation, more frequent model updates.

A Stellar Ranging Scheme Based on the Second-order Correlation Measurement

“…When the star's position is fully determined, the remaining independent time delay can also be added to the calculation to reduce the uncertainty in the position. Similar methods of position calculation relying on time delays are widely employed in very long baseline interferometry (VLBI, Sekido & Fukushima 2006;Liao et al 2014) and other astronomical observations.…”