What prevents the shuttles and ISS from getting hit and having hull breaches? From what I understand the Earth gets hit by dozens of these a day and they all burn up. But in the vaccum of space even something the size of a grain of sand is lethal is it not? Every now and then you hear of stories of people finding pieces of meteorites that have made there way through and hit earth. Have we just goten lucky with the shuttle? I know its a small target but with the hours it spends up there i find it hard to beleive. Can we even track and see things that small?