Impact analysis of the transponder time delay on radio-tracking observables

TL;DR

This paper investigates how the transponder delay affects radio-tracking measurements and spacecraft orbit calculations, emphasizing its importance for high-precision future missions and re-analysis of past data.

Contribution

It introduces a formulation to account for transponder delay effects on tracking observables, which are often neglected in standard models.

Findings

Transponder delay can significantly impact tracking accuracy.

Standard models partially neglect transponder delay effects.

Application to real missions demonstrates the importance of including this delay.

Abstract

Accurate tracking of probes is one of the key points of space exploration. Range and Doppler techniques are the most commonly used. In this paper we analyze the impact of the transponder delay, $i.e.$ the processing time between reception and re-emission of a two-way tracking link at the satellite, on tracking observables and on spacecraft orbits. We show that this term, only partially accounted for in the standard formulation of computed space observables, can actually be relevant for future missions with high nominal tracking accuracies or for the re-processing of old missions. We present several applications of our formulation to Earth flybys, the NASA GRAIL and the ESA BepiColombo missions.