Laser altimeter for the deep space mission aster modeling and simulation of the instrument operation above a surface with crater

Abstract

The 1st Brazilian deep space mission, ASTER, will carry onboard a laser altimeter to assist in the investigation of the triple asteroid system 2001-SN263. The instrument was named ALR and its development is now in progress. A series of studies was conducted with a view to the creation of the instrument control software. These studies involved the modeling of the instrument and its operation and resulted in the creation of a package of computer programs to simulate the operation of a pulsed laser altimeter with operating principle based on the measurement of the time of flight of the travelling pulse. The software Simulator was called ${ALR{\_}Sim}^{\textregistered }$, and the results obtained with its use represent what should be expected as return signal when laser pulses are fired toward a target, reflect on it and return to be detected by the instrument. The program was successfully tested with regard to some of the most common situations expected. It constitutes now the main workbench dedicated to the creation and testing of control software to embark in the ALR. In addition, the Simulator constitutes also an important tool to assist the creation of software to be used on Earth, in the processing and analysis of the data received from the instrument. The main focus of this work is the special case which involves the modeling of a surface with crater, along with the simulation of the instrument operation above this type of terrain. The approach used here was the comparison of the return signal obtained from the crater with the expected return signal in case of a flat and homogeneous surface. This method proved to be useful in the extraction of details of the terrain with crater and is recommended for the analysis of the return signal of any surface.