The BepiColombo solar conjunction experiments revisited

TL;DR

This paper revisits the BepiColombo mission's solar conjunction experiments, analyzing how solar radiation variability affects the precision of tests of general relativity during spacecraft tracking near the Sun.

Contribution

It introduces a numerical method to account for solar irradiance fluctuations in the dynamical model, improving the accuracy of relativistic parameter estimation.

Findings

Estimated accuracy of gamma between 6 and 13 x 10^-6

Inclusion of solar irradiance variability impacts measurement precision

Method enhances the reliability of gravity tests during solar conjunctions

Abstract

BepiColombo ESA/JAXA mission is currently in its 7 year cruise phase towards Mercury. The Mercury orbiter radioscience experiment (MORE), one of the 16 experiments of the mission, will start its scientific investigation during the superior solar conjunction (SSC) in March 2021 with a test of general relativity (GR). Other solar conjunctions will follow during the cruise phase, providing several opportunities to improve the results of the first experiment. MORE radio tracking system allows to establish precise ranging and Doppler measurements almost at all solar elongation angles (up to 7-8 solar radii), thus providing an accurate measurement of the relativistic time delay and frequency shift experienced by a radio signal during an SSC. The final objective of the experiment is to place new limits to the accuracy of the GR as a theory of gravity in the weak-field limit. As in all gravity experiments, non-gravitational accelerations acting on the spacecraft are a major concern. Because of the proximity to the Sun, the spacecraft will undergo severe solar radiation pressure acceleration, and the effect of the random fluctuations of the solar irradiance may become a significant source of spacecraft buffeting. In this paper we address the problem of a realistic estimate of the outcome of the SSC experiments of BepiColombo, by including in the dynamical model the effects of random variations in the solar irradiance. We propose a numerical method to mitigate the impact of the variable solar radiation pressure on the outcome of the experiment. Our simulations show that, with different assumptions on the solar activity and observation coverage, the accuracy attainable in the estimation of $\gamma$ lays in the range $[6, 13]\cdot10^{-6}$.