Comprehensive in-orbit performance evaluation of the BepiColombo Laser Altimeter (BELA)

Abstract

The BepiColombo Laser Altimeter (BELA) is on its way to Mercury on board the Mercury Planetary Orbiter (MPO), one of the two spacecraft of the BepiColombo mission. It will arrive at Mercury in Dec 2025 and start measurements of Mercury's surface and environment. The goal of this study is to analyze the performance of BELA by using a comprehensive in-orbit performance model of the instrument. To determine the in-flight performance, we model the laser altimeter instrument noise based on laboratory tests performed on BELA. In order to obtain the most realistic in-flight performance, we add a realistic instrument degradation model on top of it. We thus obtain the probability of false detection for each simulated observation and based on that, we produce a coverage map over different surface terrains. We show that the pointing uncertainty dominates the range measurement error. Moreover, we compare the predicted working limit using different gain settings and we show that instrument degradation can lower the working limit of the instrument by around 200 km in the worst case scenario. Finally, we produce BELA measurement performance maps over the surface of Mercury, study the attainable quality of topography recovery and determine the expected accuracy of the measurements of surface properties, e.g., local slopes, surface roughness and albedo in different conditions and over different terrains. We also suggest potential improvements to instrument operations by choosing an optimum gain setting and by combining different measurements together when constructing a digital terrain model of Mercury.