“Space Debris Evolution, Collision risk, and Mitigation” SpaceDebECM
1. PUBLISHABLE SUMMARY
The space surrounding our planet is densely populated by an increasing number of man-made space
debris, most of which have been generated from the break-up of operational satellites, abandoned
spacecraft or upper stages of launchers. Space debris is internationally recognised as a hazard to
current and future space activities and space agencies are currently cooperating to identify
appropriate and sustainable space debris mitigation measures. A number of these challenges were
addressed by the project “Space Debris Evolution, Collision risk, and Mitigation” SpaceDebECM
(webpage: www.spacedebris-ecm.com). An Intra-European Fellowships (IEF) under the framework
FP7-PEOPLE-2011-IEF was awarded to Dr. Camilla Colombo for a two year project (1 June 2013 to 31
May 2015) at the Department of Aerospace Science and Technology at Politecnico di Milano.
The first objective of the SpaceDebECM project is to investigate the orbital dynamics of space debris
through semi-analytical techniques as they allow a deeper insight into the orbit debris evolution under
the effect of natural perturbations in the Earth environment. The second objective of SpaceDebECM
is to design ways for end-of-life removal of space debris and assess the effectiveness of any proposed
mitigation strategy. Finally, the SpaceDebECM project addresses the problem of the modelling of large
clouds of small debris fragments and the computation of the resulting collision probability. The
SpaceDebECM project is organised in the following Tasks.
Task 1. Space debris evolution
The long-term evolution of space debris orbits under the effect of natural perturbations was studied.
As an output, the PlanODyn suite for orbit propagation through averaging techniques was developed.
This allowed identifying orbital regimes characterised by complex dynamics due to the interaction of
different perturbations. It was thus possible to
identify stable and unstable regions in the space
of orbital elements. In the current state of the
art particular focus is given to Geostationary to
Low Earth Orbit regions, as space activities are
mostly concentrated in these areas. In this
research the search was extended to Highly
Elliptical Orbits to investigate the interaction of
luni-solar perturbation with the Earth’s
oblateness. Through the single-averaged
approach derived, the dynamics of HEOs can be
propagated for long time-spans at high
accuracy. This allows the analysis of the
Fig. 1. Space debris evolution: Orbital dynamics of
Highly Elliptical Orbits through a stability map.
dynamical behaviour in terms of long-term
evolution of eccentricity and anomaly of the perigee (see Fig. 1) to identify conditions for quasi-frozen,
or long-lived libration orbits as preliminary design tool for graveyard or frozen orbit or natural re-entry
trajectories at the end-of-life. The effect of orbit perturbations is fundamental when analysing the
long-term evolution and stability of the motion of natural or artificial satellites in a planet-cantered
dynamics. In this project, the computation of transfer maps for repetitive dynamical systems was
performed exploiting Differential Algebra (DA) techniques (based on high order Taylor expansion) as
a novel approach to study the long-term evolution of satellites motion around the Earth.
Task 2. Collision
Many models of the debris population proposed in the literature usually consider only objects larger
than 10 cm as the number of small objects is so large (i.e., 200 million of objects larger than 1 mm)
that the cost of simulations would be prohibitive. However, also small objects can be detrimental to
operative spacecraft and, in particular, objects between 1 and 10 cm are considered extremely critical
because they are too large for current debris shields and too small to be tracked. For this reason,
getting a deeper insight on the small fragment population is of priority. SpaceDebECM developed a
methods to describe the motion of small fragments generated by a collision. The proposed approach
do not consider each single fragment; rather, it focuses on the spatial density of the fragments within
the generated cloud. Two techniques were analysed, one based on the continuity equation and the
solution of the density equation through analytical techniques, the second based on the use of
differential algebra to expand a cloud of initial condition and semi-analytical techniques to propagate
their orbital dynamics.
Task 3. Space debris mitigation through end-of life disposal
No guidelines currently exist for the end-of-life of Libration Point Orbits (LPOs) and Highly Elliptical
Orbit missions; however, as current and future missions are planned to be placed on these orbits, it is
a critical aspect to clear these regions at the end of operations. Methodologies for the design of
optimal transfers to end-of-life disposal were studied. The definition of stable and unstable orbit
conditions developed in Task 1 suggested a novel way of active spacecraft disposal at the end-of
mission by identifying natural long-term stable
graveyard orbits, or fast eccentricity grow
trajectories which lead to Earth re-entry. The
effect of natural perturbations such as luni-solar
perturbation or solar radiation pressure and
artificial low-thrust propulsion or impulsive
manoeuvres were exploited for the disposal
design. In this phase the research was focused
on the disposal of Highly Elliptical Orbits,
Libration Point Orbits and Medium Earth Orbits.
The options analysed are Earth re-entry, or
injection into a graveyard orbit for HEOs, while
Fig. 2. End-of life manoeuvre for Integral mission.
spacecraft on LPOs can be disposed through an
Earth re-entry, or towards the inner or the outer solar system, by means of delta-v manoeuvres or the
enhancement of solar radiation pressure with some deployable light reflective surfaces. In order to
perform a parametric study, different starting dates and conditions for the mission disposal were
considered, while the manoeuvre was optimised considering the constraints on the available fuel at
the end-of-life. Five European Space Agency missions were selected as scenarios: Herschel, GAIA,
SOHO as LPOs, and INTEGRAL (see Fig. 2) and XMM-Newton as HEOs. The robustness of the end-oflife strategies was evaluated by analysing the risk of an uncontrolled re-entry into the Earth’s
atmosphere or the planetary protection compliance for mission at the Libration Point Orbits.
Contact details
Project webpage
Researcher
Scientist in charge
www.spacedebris-ecm.com
Dr. Camilla Colombo (allimac17@gmail.com)
Prof. Franco Bernelli