'We've left junk everywhere': why space pollution could be humanity's next big problem

With satellites under threat from collisions, a former lieutenant is now focused on technology that can remove space debris

Jason Held rekindled his love for space while lying in a ditch in Bosnia in 1996, where he was one of 16,500 US troops deployed on a peacekeeping mission at the end of the Bosnian War.

Then a lieutenant, he says he had "nothing to do but to watch the two armies put their guns away". So he signed up for a class in undergraduate biology through an army education program, taking the books to the ditch and passing the hours by studying.