BepiColombo Laser Altimeter (BELA) performance evaluation
BORIS DOI
Subtitle
from laboratory tests to simulations of flight observations
Abstract
The BepiColombo Laser Altimeter [BELA, Thomas et al., 2007] is one of the main instruments on board Mercury Planetary Orbiter (MPO), one of the two spacecrafts of the European Space Agency’s (ESA) BepiColombo mission Benkhoff et al. [2010]. It will arrive at Mercury by 2025 and start its measurements of Mercury’s surface. The main goal of this study is to analyse the laboratory test results in the framework of a comprehensive in-orbit performance model for BELA. We determine the quality of observations and the recovery of surface features.
To determine the in-flight performance, we first use the laser altimetry performance model described in Gardner [1992] as our basis and we implement the end-to-end test results on BELA in the laser altimetry test laboratory of the University of Bern to our modeling of the instrumental noise. We then model the probability of false detection for each observation and based on that, we produce a coverage map over different surface terrains.
At each observation time we use the dynamical model to determine the position of MPO around Mercury and to determine the bouncing time and coordinates of the laser beam on the planet surface. Then, using a synthetic topography model, we determine the surface properties (e.g. local slope, roughness, ...) at that point and calculate the properties of the return signal.
Finally, using the instrument noise model, we determine the time of flight, pulse width and pulse energy measurement errors. This results in a performance map over the surface of Mercury and we study the attainable topography and the expected accuracy of the measurements of surface properties, e.g. local slopes, roughness and albedo, in different conditions and over different terrains.
The second goal of this PhD thesis is to estimate the impact of BELA on the improvement of the orbit of spacecraft and planet geophysical parameters. To achieve this goal, we first perform a Doppler-only orbit determination. We simulate one year of 2-way X-band and K-band Doppler radio-science tracking data, including station and planetary eclipses. These are in turn used to reconstruct MPO orbit and evaluate its accuracy within a closed-loop simulation.
In addition to this, we set-up pseudo-measurements at the crossover points of BELA ground- tracks, based on the nominal orbit and evaluate their potential contribution to the recovery of MPO orbit and of Mercury geophysical parameters.
Finally, we recommend technical settings to improve the pulse detection and the quality of observations. We also suggest potential calibrations and several approaches for the recovery of surface properties, which would enhance the scientific outcome of BELA and, in general, of the BepiColombo mission.
To determine the in-flight performance, we first use the laser altimetry performance model described in Gardner [1992] as our basis and we implement the end-to-end test results on BELA in the laser altimetry test laboratory of the University of Bern to our modeling of the instrumental noise. We then model the probability of false detection for each observation and based on that, we produce a coverage map over different surface terrains.
At each observation time we use the dynamical model to determine the position of MPO around Mercury and to determine the bouncing time and coordinates of the laser beam on the planet surface. Then, using a synthetic topography model, we determine the surface properties (e.g. local slope, roughness, ...) at that point and calculate the properties of the return signal.
Finally, using the instrument noise model, we determine the time of flight, pulse width and pulse energy measurement errors. This results in a performance map over the surface of Mercury and we study the attainable topography and the expected accuracy of the measurements of surface properties, e.g. local slopes, roughness and albedo, in different conditions and over different terrains.
The second goal of this PhD thesis is to estimate the impact of BELA on the improvement of the orbit of spacecraft and planet geophysical parameters. To achieve this goal, we first perform a Doppler-only orbit determination. We simulate one year of 2-way X-band and K-band Doppler radio-science tracking data, including station and planetary eclipses. These are in turn used to reconstruct MPO orbit and evaluate its accuracy within a closed-loop simulation.
In addition to this, we set-up pseudo-measurements at the crossover points of BELA ground- tracks, based on the nominal orbit and evaluate their potential contribution to the recovery of MPO orbit and of Mercury geophysical parameters.
Finally, we recommend technical settings to improve the pulse detection and the quality of observations. We also suggest potential calibrations and several approaches for the recovery of surface properties, which would enhance the scientific outcome of BELA and, in general, of the BepiColombo mission.
Date of Publication
2020
Year of graduation
2020
Theses Type
dissertation
Subject(s)
Language(s)
en
Author(s)
Faculty/Graduate School
Institute
Access(Rights)
open.access
Primary OA Publication
true