The increasing quantity of debris orbiting the Earth is causing concern for space agencies. At the average collision velocity of 10 km s-1, even projectiles 1 cm across can damage satellites. Impacts have a significant chance of occurring, especially for large structures that remain in orbit for a long time 1. Particularly at risk are satellites at altitudes of about 800 and 1,400 km, where there is already a high density of orbiting bodies and atmospheric drag is not effective in removing small fragments.