GTO debris mitigation using natural perturbations

Abstract

Objects ingeostationary transfer orbit (GTO) can collide with operative satellites in lowEarth orbit (LEO) and geostationary orbit (GEO). Various organisationshave laid down debris-mitigation guidelines that will be enforced by law forfuture launchers. One of the guidelines entails proving that the generateddebris will re-enter in less than 25 years with a 90% probability. Naturalperturbations can be exploited to meet this requirement without the use ofextra propellant or complex de-orbiting systems, which is especially attractivefrom an economic point of view. Objects in GTO can undergo a resonancetriggered by an interplay between perturbations caused by the Sun’s gravity andthe irregularities in Earth’s gravity field, leading to a sudden re-entryor making the object stay in orbit for decades. This effect is very sensitiveto initial conditions because it depends on the relative positions of theperigee and the Sun when the semi-major axis is close to 15000 km.By simulating the orbital evolution of a representative GTO object—ballistic coefficient of 0.011 m²/kg, initial orbital inclination of 10degrees and initial perigee altitude of 200 km— for several initialepochs, it was found that favourable launch conditions take place twice perday during most part of the year, while for epochs close to the equinoxesof March and September they only happen once per day or not at all. Giventhe high sensitivity to initial conditions, the problem was studied from astatistical perspective, taking into account the uncertainties in thevalues of the relevant parameters. Semi-analytical techniques were used topropagate the mean equinoctial elements instead of the osculatingCartesian elements, which reduced computation times by a factor of 45 whilestill keeping proper levels of accuracy. Current practice for GTO launches fromKourou is to launch at around 6-7 PM. It was found that the launchtime leading to the highest probability of compliance with debris-mitigationguidelines for GEO launches from the European spaceport in Kourou isslightly later, regardless of the day of the year, although the value of theoptimal lifetime does vary slightly throughout the year. Thus, achange in procedures would be required in order to reach a higher degreeof compliance with debris-mitigation guidelines, which was below 10% for GTOlaunches carried out with Ariane 5 from in the period 2004-2012.