On the effectiveness of end-of-life re-orbiting for debris mitigation in geostationary orbit

The effect of satellite breakups over 72 yr, as a function of the end-of-life re-orbiting altitude (0-2000 km), was analyzed in terms of fragment contribution to the object density in the GEO ring, both short and long-term. On the short-term, the explosions in geostationary orbit are the most detrimental for the GEO ring environment, even though the average fragment density in the ring is never higher than 1/5 of the background, decreasing to less than 1/100 of the existing environment after 4 yr (apart for a density rebound five decades later, due to luni-solar perturbations). Spacecraft end-of-life re-orbiting is a possible mitigation solution. But the re-orbiting altitude is critical if explosions continue to occur. In order to reduce the post-event average density by an order of magnitude with respect to an explosion occurring in GEO, more than 500 km of re-orbiting are needed. Concerning the long-term environmental impact, the re-orbiting strategy supported by IADC seems adequate to guarantee, after 2-3 years, a long-term average density of fragments in the GEO ring at least two orders of magnitude below the existing background. But at least 1000 km of re-orbiting are needed to stay below that threshold also in the short-term. In conclusion, the re-orbiting strategy recommended by IADC is totally adequate in the long-term, but only if satellite passivation is quite extensively carried out.