Lucía Ayala Fernández, Technische Universität Braunschweig; Carsten Wiedemann, Technische Universität Braunschweig; Vitali Braun, IMS Space Consultancy @ ESA/ESOC; Stijn Lemmens, ESA/ESOC Space Debris Office
Keywords: post-mission disposal, orbital lifetime, orbit propagation, space debris mitigation
Abstract:
One of the essential aspects of space debris mitigation is the performance of Post-Mission Disposal (PMD) once the mission of a space vehicle has concluded. The main goal of the PMD is to avoid the creation of further space debris, especially mitigating the risk of on-orbit collisions or explosions that would cause a fragmentation and potentially contribute to the collisional cascading effect known as the Kessler syndrome. An integral part of the PMD is the clearance from the protected regions, as it is stated in the IADC space debris mitigation guidelines. For the Low Earth Orbit (LEO) protected region, this implies the re-entry into Earths atmosphere within 25 years after the end of the mission.
In this context, orbital lifetime estimations are crucial to assess the compliance of new missions to be launched. Different standards provide guidance in the methodologies that can be applied for the orbit propagation leading to such estimates. This paper assesses the accuracy of the estimated orbital lifetime of rocket bodies following the standard procedures and tools from the European Space Agency (ESA). The impact of the solar and geomagnetic activity scenario chosen is analyzed, as well as the drag coefficient used for the propagations.
The dataset used for this purpose was extracted from ESAs DISCOS database. It comprises all the rocket bodies in the database that have already re-entered, and whose initial orbits cross the LEO-protected region. The dataset is therefore composed of 363 objects resident in LEO and 408 objects in High Eccentric Orbits (HEO). These objects were propagated with the OSCAR (Orbital SpaCecraft Active Removal) tool from the DRAMA (Debris Risk Assessment and Mitigation Analysis) software for 3 of the available 5 different solar and geomagnetic activity scenarios. These scenarios include the latest updated prediction, Monte Carlo sampling, and repeated cycle, which are recommended in the ESA Handbook for Space Debris Mitigation practices. The re-entry epochs obtained with this propagation were then compared with the observed re-entry epoch of each rocket stage, and the errors obtained for each scenario and for each orbital region were analyzed in detail. It was found that OSCAR tends to underestimate the orbital lifetime in all solar activity scenarios for the objects resident in LEO. On the other hand, the high dispersion of the error for objects in HEO shows the challenges associated with the orbital lifetime estimation of these objects and their high sensitivity to the initial conditions and other parameters used for the propagation.
In this first analysis, the ballistic coefficient was computed using the mass and the average cross-section of each rocket stage as available in DISCOS. Two cases were analyzed for the drag coefficient: a default drag coefficient of 2.2 for all objects, and an estimated drag coefficient for each object based on the available diameter and length, assuming a cylindric shape. However, the information in the database is not always completely accurate. The results in LEO show a significant improvement for the second case, suggesting that a more refined approach to estimating the ballistic coefficient of the objects could lead to even further improvement.
Moreover, specific examples are described in the paper, for both LEO and HEO objects. The goal of these examples is to show the most important dynamics affecting the lifetime estimations in each orbital region, and the magnitude of the errors that they can lead to.
Date of Conference: September 19-22, 2023
Track: Space Debris