SPACE-BASED DETECTION OF ORBITING OBJECTS BY USING STAR SENSORS

The increasing number of space activities has led to the growth of the population of resident space objects, i.e. satellites and space debris. The availability of a complete catalogue of orbiting objects is therefore extremely useful for the reliability evaluation of present and future missions. The existing catalogues are essentially based on-ground radars, or optical measurements. The main limitation of this approach is related to the distance between the observer and the orbiting object. Such limitation can be solved by using space-based measurements. Within the framework of this application, the paper proposes the use of star sensors as orbiting observers, profiting from their disseminated optical sensors. In fact, the star sensors are typically mounted on-board of satellites for the attitude determination. The proposed approach provides the opportunity of using them for objects’ detection, thus minimizing the impact in terms of cost and system architecture with respect to dedicated space object observer missions. Usually, star sensors discard information of observed moving objects against the fixed stars, losing many data that could be very useful for the Space Situational Awareness. An orbiting observer of spacecraft and space debris provides the opportunity of continuous operations with the detection of close objects within a range of a few thousands of kilometers. A star sensor in sun-synchronous orbit can observe hundreds or thousands of objects, especially in the regions over the poles. This work presents a preliminary study of the Italian Space Agency project SPOT (Star sensor image on-board Processing for Orbiting objects deTection). The paper focuses on the analysis in using star sensors in LEO to detect space debris. A mission with Multi-Head Star Sensors, could have a star sensor not used for the attitude determination. The idea is to exploit this star sensor to detect moving objects, which appear as streaks in the acquired image. The main factors which affect the visibility have been considered: the sensor characteristics (sensitivity, field of view, exposure time, and boresight direction), the optical properties of the observed objects, the environment influence, and the relative velocity between target and observer. The paper shows the results by selecting up to 12 satellites in LEO as simultaneous observers.