COLLISION RISK MITIGATION IN GEOSTATIONARY ORBIT
L. ANSELMO and C. PARDINI
Consiglio Nazionale delle Ricerche (CNR) – CNUCE Institute, Spaceﬂight Dynamics Section,
CNUCE/CNR, Via Moruzzi 1, 56124 Pisa (PI), Italy (Tel.: +39-050-315-2952; Fax: +39-050-313-8091;
(Received 31 October 2001; Accepted 2 March 2002)
Abstract. The short- and long-term effects of spacecraft explosions, as a function of the end-of-life re-orbit
altitude above the geostationary orbit (GEO), were analyzed in terms of their additional contribution to the
debris ﬂux in the GEO ring. The simulated debris clouds were propagated for 72 yrs, taking into account all
the relevant orbital perturbations.
The results obtained show that 6–7 additional explosions in GEO would be sufﬁcient, in the long term, to
double the current collision risk with sizable objects in GEO. Unfortunately, even if spacecraft were to re-orbit
between 300 and 500 km above GEO, this would not signiﬁcantly improve the situation. In fact, an altitude
increase of at least 2000 km would have to be adopted to reduce by one order of magnitude the long-term risk
of collision among geostationary satellites and explosion fragments. The optimal debris mitigation strategy
should be a compromise between the reliability and effectiveness of spacecraft end-of-life passivation, the
re-orbit altitude and the acceptable debris background in the GEO ring. However, for as long as the re-orbit
altitudes currently used are less than 500 km above GEO, new spacecraft explosions must be avoided in order
to preserve the geostationary environment over the long term.
Keywords: collision risk, debris ﬂux, geostationary ring, orbital perturbations, satellite explosions, satellite
Abbreviations: ASAP – Artiﬁcial Satellite Analysis Program; ASI – Agenzia Spaziale
Italiana (Italian Space Agency); CLDSIM – cloud debris simulator; CNUCE – former Centro
Nazionale Universitario di Calcolo Elettronico; CODRM-99 – 1999.0 CNUCE Orbital
Debris Reference Model; GEO – geostationary orbit; IADC – Inter-Agency Space Debris
Coordination Committee; JPL – Jet Propulsion Laboratory; SDIRAT – Space Debris Impact
Risk Analysis Tool; yr – year.
Due to the rapid increase in the number of spacecraft and apogee kick motors in the
geo-synchronous region, there was growing concern in the 1980s regarding the possible
overcrowding of the geostationary orbit (GEO) and the consequent threat to its long-term
utilization and exploitation (Hechler and Van der Ha, 1981; Fusco and Buratti, 1984). The
risk of collision between space objects in GEO was estimated in order to devise affordable
and effective end-of-life disposal measures, such as satellite re-orbiting (Chobotov, 1990).
Space Debris 2, 67–82, 2002.
© 2002 Kluwer Academic Publishers. Printed in the Netherlands.