Attitude State Evolution of Space Debris Determined from Optical Light Curve Observations

Space debris population increased drastically during the last years. One of the contributing factors is the incidental collisions involving massive objects which are predicted to be more pronounced in the future. The removal of large, massive space debris is considered necessary to stabilize the population. In this respect, not only precise orbits, but also more detailed information about their attitude states such as spin period and spin axis orientation is required. Non-resolving optical observations of the magnitude variations, so-called light curves, are a promising technique to determine the tumbling rates and the orientations of the actual objects' rotational axis, as well as their temporal changes. For this purpose, we use the 1-meter telescope ZIMLAT at the Astronomical Institute of the University of Bern (AIUB) to collect light curves of selected LEO, MEO and GEO objects on a regular basis. We have acquired more than 3,000 light curves from 512 objects in various types since January 2007. By analysing the light curve in the AIUB light curve database we could determine that most of the objects in the database were rotators (with known or unknown periods) . They were located in all orbital regions unlike stable objects which were not found in high elliptical orbit. In addition, rotators, slow rotators (rotators but with unknown periods) , and stable objects consist of all object types which include payloads, rocket bodies, and debris. Slow rotators and stable objects mostly located in low earth orbits while rotators mostly located in other orbital regions. Periods of rotation in the database ranged from less than 1 sec to nearly 900 sec. We identified three patterns in spin rate evolution of the rotating objects in the database which showed oscillating, increasing, or decreasing trends. There were 36 oscillating rotators, 10 increasing rotators, and 18 decreasing rotators. All the oscillating rotators were GLONASS satellites while increasing and decreasing rotators were distributed among payloads and rocket bodies in various orbital regions.