Modelling the long-term evolution of orbital debris

Current space missions around the earth have to deal with a problem mostly ignored just 25 years ago: man-made orbital debris. Besides the more than 9,000 objects (50% of which are break-up fragments) routinely tracked by the U.S. Space Surveillance Network, typically larger than 10-20 cm and with a combined mass exceeding 5,000 metric tons, the circum-terrestrial space is populated by a very large amount of smaller particles, down to sub-millimetre sizes, which is continually being replenished by international space activities.