Astrometry of Cassini with the VLBA to Improve the Saturn Ephemeris

TL;DR

This paper reports high-precision VLBA astrometric observations of Cassini, enhancing Saturn's ephemeris accuracy by integrating VLBI data with spacecraft tracking over five years.

Contribution

It introduces an improved method combining VLBA measurements with spacecraft tracking to refine Saturn's position in the solar system.

Findings

Enhanced Saturn ephemeris accuracy.

Improved residuals compared to JPL's ephemeris.

Five additional years of high-precision VLBA data.

Abstract

Planetary ephemerides have been developed and improved over centuries. They are a fundamental tool for understanding solar system dynamics, and essential for planetary and small body mass determinations, occultation predictions, high-precision tests of general relativity, pulsar timing, and interplanetary spacecraft navigation. This paper presents recent results from a continuing program of high-precision astrometric very-long-baseline interferometry (VLBI) observations of the Cassini spacecraft orbiting Saturn, using the Very Long Baseline Array (VLBA). We have previously shown that VLBA measurements can be combined with spacecraft orbit determinations from Doppler and range tracking and VLBI links to the inertial extragalactic reference frame (ICRF) to provide the most accurate barycentric positions currently available for Saturn. Here we report an additional five years of VLBA observations along with improved phase reference source positions, resulting in an improvement in residuals with respect to the Jet Propulsion Laboratory's dynamical ephemeris.