Space junk hurtles toward Earth: The biggest piece of U.S. space junk to fall in 30 years could hit Earth late Friday or early Saturday, NASA said as it struggled to predict where and when the defunct satellite would crash. Space junk is a growing problem in low-Earth orbit. More than 20,000 pieces of debris, at least 4 inches in diameter, are being tracked on a daily basis. These objects pose a serious threat to the International Space Station. Why has NASA only now decided that space pollution is a problem? Couldn’t they have been more mindful of this and planned not to dump junk in space over the past several decades?