68 th International Astronautical Congress (IAC), Adelaide, Australia, 25-29 September 2017. Copyright ©2017 by the International Astronautical Federation (IAF). All rights reserved. IAC-17-F1.2.3 Page 1 of 6 IAC-17-F1.2.3 Attitude State Evolution of Space Debris Determined from Optical Light Curve Observations Abdul Rachman a *, Thomas Schildknecht a , Jiri Silha a , Jean-Noel Pittet a , Alessandro Vananti a a Astronomical Institute University of Bern (AIUB), Switzerland, abdul.rachman@aiub.unibe.ch * Corresponding Author Abstract 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. Keywords: space debris, optical observation, light curves, spin rate evolution 1. Introduction Space debris population which threatens the sustainability of space activity keeps growing. This trend still prevails despite the existence of mitigation guidelines since 1995. The main reason for this is the substantial increase of breakup debris due to collisions between large objects. This type of debris contributes more than 53% of the current catalogued in-orbit Earth satellite population [1]. Even worst, it is predicted that the number of incidental collisions will be more pronounced in the future. This will happen after man- made satellite population density is high enough to trigger the collisional cascading event (the Kessler syndrome). It is a common agreement that the mitigation measures should be accompanied by the so called Active Debris Removal (ADR) to stabilize the future population of space debris. This is conducted by nudging the large debris into a safer orbit or forcing it to prematurely reenter the atmosphere [2]. For the mission to be successful, sufficient knowledge about the attitude of the debris is mandatory. The information can be obtained using optical observations, satellite laser ranging (SLR), and other means. By observing debris using optical telescope, we can measure its attitude by analysing the change of brightness over time. This variation which is represented in a so called light curve is obtained by using astronomical photometry. Compared with other methods, the light curve method has several advantages. First, generally it is the most cost effective method. Second, we can benefit from the long history of astronomical photometry in the study of natural objects especially asteroid. In fact, in the space debris domain, light curves are the major source of information to the attitude state of non-controlled objects [3]. Using light curves, we can determine whether the objects are stable or tumbling and measure the apparent periods (and thus the spin rates) as well as the orientations of the actual objects' rotational axis. Periodic observations can reveal the temporal changes. Light curves can also be used to validate other attitude determination techniques like radar or SLR measurements and forward modelling refinement [4]. In this paper we will present spin rates and their temporal evolution for a large set of selected decommissioned LEO, MEO, HEO, and GEO spacecraft and upper stages, including more than 60 abandoned GLONASS satellites. All of them are