Leave footer empty – The Conference footer will be added to the first page of each pap er. ATTITUDE CHARACTERIZATION OFAERODYNAMIC STABLE OBJECTS BASED ON TLE C. Parigini (1) , D. Bonetti (1) , Gonzalo Blanco Arnao (1) , N. Sanchez-Ortiz (1) , S. Lemmens (2) (1) Deimos Space, Tres Cantos, Madrid, 28760, Spain, Email: {cristina.parigini, davide.bonetti, gonzalo.blanco, noelia.sanchez } @ deimos-space.com (2) ESA/ESOC Space Debris Office (OPS-GR), Robert-Bosch-Str. 5, 64293 Darmstadt, Germany, Email: Stijn.Lemmens@esa.int ABSTRACT The problem of reconstructing the body attitude from TLE is difficult due to the accuracy of TLE information and data frequency. However, attitude could be reconstructed when additional information is available, for instance, optical measurements or when additional assumptions could be made (e.g. stable attitude behavior). In this paper we present the main outcomes of the work performed within the Bench-marking Reentry Predictions ESA study, where we analyzed space objects that present similarities with GOCE in terms of aerodynamic stability and geometry. 1 INTRODUCTION In re-entry predictions, drag plays a critical role as it is the main force driving the orbital decay in Low Earth Orbits: according to [1], it is the most significant orbit perturbation that affects the semi-major axis in a secular manner. Other perturbations affect the semi-major axis, but most average out over an orbit cycle due to their periodic character. Some perturbations, however, do cause a secular variation in the semi-major axis, such as the combination of solar radiation pressure and gravity anomalies as a satellite passes in and out of Earth’s shadow. However, these variations are small compared to those produced by drag, and they are neglected in this work. Estimation of the drag is not easy due to the large uncertainties on the atmospheric properties and drag area. Focusing on the latter, attitude knowledge is critical: it has a direct impact not only on the drag coefficient but also on the effective area where the aerodynamic perturbations are exerting the force. Therefore, attitude knowledge reduces the uncertainty on the estimation of drag which means an improvement in the re-entry time estimation. The problem of reconstructing the body attitude from TLE is difficult due to the accuracy of TLE information and data availability frequency: only rough estimations of the BC could be obtained from TLE and with this information it is not possible to reconstruct accurately the attitude. However, attitude could be reconstructed when additional information is available, for instance, when optical measurements are available [2] or when additional assumptions could be made (e.g. stable attitude behavior). In this frame, GOCE attitude behavior presents the ideal case where very small variability in the yaw and pitch angles is observed in the last weeks before entry. In this paper we present the main outcomes of the work done within the Bench-marking Reentry Predictions ESA study, leaded by Deimos Space, where we analyzed space objects that present similarities with GOCE in terms of aerodynamic stability and geometry (e.g. elongated bodies). A preliminary analysis of the critical parameters and ranges that guarantee a stable flight at high altitude is done based on Flying Quality analysis for simple shape objects (e.g. cylinder and box). These results are then used as a filter applied to DISCOS database to select 5 objects among the known debris including both rocket bodies and payloads that re-entered in the past. For such objects, 3-DoF and 6- DoF simulations and TLE analysis are combined to characterize the attitude during the orbital decay. GOCE is used to benchmark the approach followed. 2 APPROACH A schematic overview of the approach followed is shown in Fig. 1. The work has been split in two main parts: - Object analysis and selection, presented in section 3. - Object trajectory simulation, presented in section 4 Concerning the object analysis and selection, the idea is to identify first the conditions under which a stable flight is possible, based on the analysis of the aerodynamics of simple geometric shapes. Once the ranges of feasible conditions for a stable flight are determined, objects compatible with these conditions are searched, also fulfilling other additional criteria (e.g. circular orbit, elongated body). Finally, among the Proc. 7th European Conference on Space Debris, Darmstadt, Germany, 18–21 April 2017, published by the ESA Space Debris Office Ed. T. Flohrer & F. Schmitz, (http://spacedebris2017.sdo.esoc.esa.int, June 2017)