A tradeoff investigation for the BepiColombo Laser Altimeter design

Abstract

The BepiColombo Laser Altimeter (BELA) is a proposed experiment for the BepiColombo mission to the planet Mercury. BELA is intended to provide payload-to-surface ranging data from a spacecraft in a polar Hermean orbit by measuring the time-of-flight of outgoing laser pulses and their echoes. As proposed, BELA also will provide small-scale surface variation and reflectivity data via characterization of return pulse forms. Primary instrument components include a low frequency pulsed Nd:YAG laser transmitter and a reflective receiver telescope feeding a silicon avalanche photodiode to capture pulse echoes with a direct detection approach. To assist with the evaluation of various design strategies, we have developed a numerical model of the instrument that returns a signal-to-noise-ratio figure of merit, as well as simulated return pulses, according to a diverse set of hardware specifications and viewing geometries as input parameters. An analysis of large sets of simulated pulses assists with the estimation of measurement accuracy. This model has been used to investigate the performance of a variety of instrument configurations, and some tradeoffs leading to the favored design will be described.