Space junk : a complex challenge

The term space debris is used to characterize all objects (fragments of satellites, rocket parts, remains of explosions or collisions), of all sizes and all chemical compositions, which orbit around the Earth at different altitudes. The number of space debris has dramatically increased in the last decades, the space activities are accelerating with a lowering of the technological costs and the multiplication of the actors.

It was commonly thought that the drag would rapidly bring back to the Earth most of the objects; it is true for the low orbits (LEO) with altitudes smaller between 500 et 900 kilometres, but certainly not for the highest ones, in particular for the geostationary orbits (GEO) situated at 36 000 kilometres of altitude and characterized by periods of exactly 24 hours.

And even if the drag is able to clean progressively the LEO region, the presence of a huge number of debris is responsible for collisions and consequently, generates a continuous re-population of the region.

Even if we stopped all launches, the number of debris would still increase for several years just by collisions and fragmentations of the present objects in orbits.

Our lifestyle is really dependent on the presence of spacecrafts: telecommunications, GPS or cellular phones, TV, Internet, climate watches, ecological studies, catastrophe prevention, or military surveys, ... and a space economy is growing up with the new services. In parallel with a real future politics of respect of the space environment, the technological challenge for ADR has to be supported by a better understanding of the evolution of the present and future debris population and by suitable simulation tools, taking into account all the aspects of the problem.

At the end of the nineties, the space debris population has interested the community of celestial mechanicians, traditionally involved in the dynamics of natural bodies. with uncontrolled objects present for thousands of years. Since 2006, UNamur has contributed to this field, via naXys, through PhD, post-docs and publications.

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