Impact of End-of-Life manoeuvres on the collision risk in protected regions
Introduction
The collision between the operational Iridium 33 and the defunct Cosmos −2251, that resulted in the creation of over 2000 observable fragments [1], [2] highlighted the dangers originating from objects left in space, in particular in already crowded regimes. The Space Debris Mitigation Guidelines, issued by the Inter-Agency Space Debris Coordination Committee (IADC) in 2002, and revised in 2007, define two protected regions: the Low Earth Orbit (LEO) protected region, up to 2000 km, and the Geostationary Orbit (GEO) protected region at an altitude range of hgeo ± 200 km and a declination range of ±15°, where hgeo = 35786 km [3].
In order to protect these regions, the guidelines recommend the prevention of on-orbit collisions and to limit the debris released during normal operations. They further recommend to passivate stored energy to minimise potential break-up and to perform Post-Mission Disposal (PMD) upon reaching mission End-of-Life (EOL). For LEO, the spacecraft, subsequently called Payload (PL), or the Rocket Body (RB) should be left in an orbit, such that the remaining lifetime does not exceed 25 years. For GEO, the PL should be re-orbited into an orbit sufficiently above the protected region, such that it remains cleared from the region, taking into account solar radiation pressure, luni-solar and geopotential perturbations.
Hundreds of objects have already performed such an EOL-manoeuvre. The contribution of this work is to quantify the effect of these manoeuvres on the cumulative number of collisions with space debris in the protected regions. The collision probability is analysed by calculating the debris flux the manoeuvering object is exposed to for its remaining lifetime, or up to 1 January 2055. Estimated for both the evolution of the pre-EOL-manoeuvre orbit as well as the post-EOL-manoeuvre orbit enable a comparison between the two scenarios. The results are presented statistically.
Section snippets
Methodology
The analysis can be described in three parts, all of which are explained in more detail in the following subsections. In the first, the source and the criteria for the selection of the objects are described. Subsequently, the selection process of the pre- and post-EOL-manoeuvre states is outlined. Lastly, the propagator used for the evolution of those states and the tool and settings to estimate the debris flux the objects are exposed to are presented.
Results
Table 1 summarises the total cumulative number of collisions experienced by all the objects within their respective groups, for the pre- and post-manoeuvre scenarios (marked via the indicespre and post respectively). In addition, the number of objects involved, the total cross sectional area and total dwell time on orbit are listed. The total numbers are driven by a few objects clearing highly populated orbital regions. To give a feeling about the distribution of reduction of collision
Discussion
Previous studies [13], [14], [15] on the evolution of the number of collisions in LEO, involving objects larger than 10 cm and studying PMD levels of 0% and 50%, predict 12–14 collisions (where the number of fragment on fragment collisions - which are not considered in the current study - was found to be small), within the next 50 years. Both types of collisions are included in those studies; catastrophic and non-catastrophic, the former being defined as having a ratio of impactor kinetic
Conclusions
This study shows that the individual benefit of implementing an EOL-manoeuvre in reducing the risk of colliding with space debris is large. It is evident that commercial users (e.g. constellation and GEO satellite operators) are already clearing their operational orbits. Unfortunately, today, from a global perspective, and in particular in LEO, too few objects implement an EOL-manoeuvre compliant with the IADC mitigation guidelines in order to make a significant difference in the number of
References (16)
Spot 1 end of life disposition manoeuvres
Adv. Space Res.
(2005)Collision activities in the future orbital debris environment
Adv. Space Res.
(2006)- et al.
Analysis of the consequences in low earth orbit of the collision between Cosmos 2251 and Iridium 33
- et al.
DISCOS - current status and future developments
IADC Space Debris Mitigation Guidelines
(2007)- et al.
Two-line-elements-based maneuver detection methods for satellites in low earth orbit
J. Guid. Control Dyn.
(2014) - et al.
Classification of Geosynchronous Objects
(2016) - et al.
Maintenance of the ESA MASTER-model
(2010)