Optimizing the baffle of a CubeSat Star Tracker using Ray Tracing

Abstract

This thesis arises as a result of a bigger project called CubeSat. The CubeSat is a miniaturized Satellite for space research. The CubeSat uses a system to control the attitude called ADCS. One of the subsystems of the mentioned system is the Star Tracke,r which basically is a camera that take pictures of the stars and compares the information with a database in order to determine its orientation. This device requires high sensitivity and it can be blinded if stray light hits the detector of the camera. The biggest source of light that could affect the star tracker is the Sun and from this problem the main goal of this thesis rises. To limit the effect of stray light it is necessary to design and optimize a device capable to avoid that the stray light punctures the detector of the camera. This device already exists and its name is baffle. As the title of the thesis indicates, this paper deals with the goal of improve the standard baffle using Ray Tracing. The thesis can be divided in 5 parts. The first part is about the research of literature followed in order to understand the physic involved in the problem described above and on the other hand to know more about the background of the baffles. The second part deals with the implementation of a Ray Tracing method in MATLAB® to simulate the specular reflection and scattering of the light when it interacts with an opaque object. The third part discusses the process of optimization used to develop a design that has a better performance than the standard one. The fourth part is related to the process of manufacturing. The prototypes were manufactured by two different techniques. The fifth part presents the two different tests that have been developed in this thesis and all the details of their set up and instrumentation involved. In the first test the surface of study is the exit surface of the baffle. The second test is more realistic and the surface of study is the camera itself, which is placed behind the real star tracker lens. Finally, a comparison between the real results and the simulations has been done and a physic interpretation of them has been proposed. Through this thesis the importance of the process of manufacturing of the prototypes is observed, and also it is observed how imperfections in the prototypes can highly affect to the performance.