End-of-Life of Upper Stages in Geostationary Transfer Orbit

Kurzfassung

This report focusses on four specific topics within the overarching theme of upper stage Geostationary Transfer Orbit (GTO) debris: 1. A review of recent practices in mitigation procedures for GTO Launch Vehicle Upper Stages and intentional mission debris. From 2004-2012, 210 launch vehicles operated by five nations and two international organisations placed satellites in Geostationary Earth Orbit (GEO). Analysis of 185 of these launches found that 294 pieces of debris and upper stages were left in GTO. 43 of these bodies have since decayed and re-entered Earth’s atmosphere with an average decay time of 1.53 years. Of the remaining objects, 4 have perigees sufficiently small enough to ensure orbital decay and re-entry within 25 years of launch, 43 are in orbits which did not cross Low Earth Orbit (LEO) or GEO and 204 bodies are located in orbits that cross LEO and/or GEO. 2. A Monte-Carlo simulation of orbital decay for objects left in GTO to determine what parameters influence decay time. A Monte-Carlo simulation using the European Space Agency’s (ESA) Debris Risk Assessment and Mitigation Analysis (DRAMA) tool analysed the orbital decay of 100,000 upper stages in GTO. It was found that the initial perigee altitude strongly affected whether the upper stage would decay in the requisite 25 years, with a perigee of 200km leading to 80% of debris re-entering. Inclinations closer to 45° and larger apogees also led to higher probabilities of re-entry due to the coupling of orbital perturbations, specifically third body effects and atmospheric drag. The mass/area ratio also had a weak influence, with larger mass/area ratios contributing to lower probabilities of re-entry. 3. Creation of a program to model the controlled de-orbit of an upper stage, including its initial orbit, de-orbit burn and atmospheric re-entry. This program interfaced with ESA’s DRAMA software. A Fortran program was created to model the controlled de-orbit burn of an arbitrary upper stage. Four phases were implemented: an initial coast, an instantaneous, in-plane burn, the unpowered de-orbit trajectory (all modelled directly by the Fortran program) and the re-entry itself, starting at 120km altitude (modelled by DRAMA). The program calculated the footprint for all resultant pieces of debris. 4. Modelling of the controlled de-orbit of the Ariane 5ME Upper Stage using aforementioned software, and an investigation on how the burn parameters (magnitude, angle and time) affect the impact position. Calculations performed by Astrium gave the Ariane 5ME upper stage re-entering in the Pacific Ocean at -5° to 5° latitude and -157° to -130° longitude. The designed program calculated a footprint of 0.74° to 2.38° latitude and -148.81° to -138.54° longitude. The differences arose from the Astrium simulation not considering ablation and melting of debris and the designed program not considering additional breakup velocities due to tank rupture during re-entry. The burn parameters were varied, and it was determined that for the Ariane 5ME, larger de-orbit burns led to a more northern impact position, larger burn angles led to a more south-eastern impact position and longer coast times led to a more north-western impact position.