A geometric delay model for Space VLBI

TL;DR

This paper derives a relativistic delay model specifically for space VLBI, addressing the challenges posed by higher delay rates due to the spacecraft's orbital velocity, and improving delay modeling accuracy.

Contribution

It introduces a geometric delay model tailored for space VLBI, accounting for relativistic effects and higher delay rates, enhancing the precision of delay calculations in SVLBI.

Findings

The model accurately captures relativistic delays in SVLBI.

It enables more precise delay modeling for spacecraft-based interferometry.

The approach improves upon existing polynomial-based delay models.

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 evalution, more frequent model updates.