Design of an Acceleration Sensor Assembly for Estimation of Mechanical Asteroid Surface Properties

Abstract

In this thesis, a tetrahedral acceleration sensor assembly carried by the MASCOT-2 asteroid lander is verified for feasibility and designed in terms of mechanical implementation. This includes understanding of the sensor itself and its application during the mission, initial tests and the CAD-Design of the assembly. MASCOT-2 belongs to the Asteroid Impact Deflection Assessment (AIDA) mission,planned by the European Space Agency, commencing in 2020. Besides the lander's main operations on the asteroid's surface, the sensor assembly's particular goal is to measure elastic stiffness and strength of the target asteroid's surface material during touchdown and relocation. The introduction gives an understanding of the lander's role during the AIDA Mission, especially regarding the acceleration sensor's tasks. Furthermore, the particular sensor type available for testing is described in terms of actual application in the tetrahedral assembly for data acquisition, stating requirements and constraints due to its function principle. Nearly all the requirements are to be easily fulfilled by the miniature MEMS Sensor,yet other sensor types are considered to be used at present. In the second chapter (regarding sensor properties) the general sensor capabilities as well as its suggested electrical operation as given by the manufacturer are described. The sensor's operation is simple, each sensor needs a stable SV source as weil as two output lanes, one of them combining the differential acceleration output using a differential OP-AMP. As an additional feature, temperature can be measured by the sensor directly. The third chapter regards actual conducted sensor tests and calibration approaches related to the in-mission occurrences. lts results are sketched and summarised. Known influences like temperature and radiation on microelectromechani cal systems (MEMS), especially for the particular type of sensor, are also described and tested, if possible. In the fourth chapter, the technical approach and actual design of two possible sensor assemblies is described, leading to a functional mechanical solution, only covering fundamental electrics.A relatively simple, lightweight construction built around the PCB decouples the sensors from oscillations of the more flexible PCB that serves as housing for all sensor related electronics. A detailed summary shows that the particular sensor type is technically capable of measuring the desired mechanical surface property factors using the stiff support structure. An additional highly stiffening support structure was designed briefly for applications on earth or less mass-restrictive missions