"The number of pieces of space debris has risen by 40 per cent in the past four years alone. The US air force Space Command now tracks 19,000 orbiting objects that are 10 centimetres or more across – including around 800 working satellites – and estimates that there are 500,000 smaller fragments in orbit. Lewis wondered what effect this growing debris field would have on managing future satellite operations. How much more often will mission controllers have to track debris and consider taking evasive action? To find out, he used data from an industry database called Socrates to correlate the change over time in the quantity of debris with the number of occasions on which objects come within 5 kilometres of each other. Then, using the predicted growth in the debris population over the next 50 years, he estimated the number of close approaches that are set to occur." - Steven Perez from Bookmarklet