The Institute of Space Sciences of Catalonia (IEEC) is developing PhotSat, a 16U CubeSat whose scientific goal is the all-sky observation of the 40 million brightest astronomical sources. As such, the attitude knowledge and control of the satellite is paramount for the correct operation of the mission. This is the main task of the Attitude Determination and Control Subsystem featured in satellites, and its most precise attitude sensor, the star tracker, is a critical instrument. Star trackers are devices that capture an image of the stars and determine the satellite's orientation with respect to a fixed reference frame through a series of algorithms. In this project, we provide an overview of the different algorithms comprising a star tracker and review the literature for existing star tracker algorithms capable of being compliant with stringent accuracy requirements in the arcsecond range, such as in the PhotSat mission. We place special emphasis on the critical lost-in-space case, the first attitude acquisition with no prior information of the satellite's orientation.

9 - Indústria, Innovació i Infraestructura