Low-cost stellar sensor for attitude control of small satellites

The paper describes the design and development of an autonomous, low-cost, lowpower, low-mass attitude sensor, that requires no computational resources from the On-Board Computer. Application domain is small satellites (micro- and nano-satellites) the vast majority of which does not have a precision attitude determination and control, due to excessive cost, weight, volume and energy demand requirements, hard to meet in general when satellites have such small dimensions. We propose the integration of two sensors, specifically an APS-based (Active Pixels Sensor) Star Tracker and a MEMS-based (Micro Electro-Mechanical Systems) Rate Gyroscope, integrate into a single unit that can operate in single or combined mode. The star sensor allows to determine both relative and absolute satellite attitude, operating as the dominant sensor at low angular rate, while for high angular rates, the gyroscope will be used. Special care has been made to optimize the attitude data computation by the data fusion from the two sensors, aiming to obtain an accuracy of 0.1◦ of resolution in real-time attitude determination. The work has been divided into three phases. The first phase concerned the definition of project characteristics and requirements, in particular the selection of main components. The main building blocks for the project are the MEMS piezoelectric gyroscope, the APS CMOS image sensor, the optical system to form the field of view for the image sensor, and a 32-bits microcontroller (PIC32MZEF by Microchip Technology Inc.), for data processing data. The second phase concerned the development of a breadboard PCBs for implementation of evaluation tests. The third phase implemented an algorithm for image noise reduction, recognition and tracking of bright stars and determination of relative sensor axis orientation from the movement of stars on the image plane. Algorithms for attitude determination have been also defined in this study.