Space debris surface characterization through BVRcIc photometry

Abstract

The increasing population of space debris orbiting the Earth, poses a significant threat to operational and future missions. The follow-up observations of space objects can help to estimate their rotational states, albedo, shape, size, and to characterize surface properties of the object and its composition. Such field is known as object characterization and uses all kinds of photometric and spectroscopic methods to investigate object’s physical properties. The 70 cm newton reflector (AGO70) operated by the Faculty of mathematics, physics and informatics of the Comenius University Bratislava, Slovakia focuses mainly on the follow-up observations of man-made space debris population. One of the photometric methods is color - specifically BVRcIc photometry. It uses different photometric passbands of the visible light to estimate how much sunlight the object reflects in particular channels. Each material has reflective signatures, which enable us to distinguish different features on the object’s surface and provide information about the object’s attitude or utilize the categorization into the population or material groups. The study presents a detailed description of methods that must be utilized to be able to extract the standard color indices of space debris objects, as well as our implementation and understanding of these methods. Moreover, color index dependencies on the phase angle, object’s rotational state, and attitude state are discussed step-by-step in specific examples. Our complete pipeline from target selection, observation planning, data acquisition, data processing, and interpretation is demonstrated on the extensive observations of the CZ-3B third upper stage which was used as a test case in this study. In this study, we define what features of the rotating objects can be seen by the BVRcIc photometry, furthermore, we discuss the materials that are the main drivers of reflection. Finally, we describe ways how to interpret these data for space debris characterization.