Just like in the movie "Gravity," space junk actually is a real-life threat in space. In March 2012, six astronauts on the International Space Station had to take refuge in the station's lifeboat-like space capsules, after they got an urgent warning that a leftover piece of an old Russian telecommunications satellite was headed their way. Fortunately, the hunk of debris — one of 2,000 pieces that were created when the satellite smashed into a U.S. satellite in 2009—whizzed by the ISS without collision, missing by 6.8 miles (11 kilometers) [source: Malik].
It gets worse: NASA is tracking some 500,000 pieces of debris that are hurtling around Earth at speeds of 17,500 mph (28,164 kph), but there are probably a lot of smaller pieces that it can't detect. It doesn't take a big piece to demolish a spacecraft or knock out an astronaut on a spacewalk. Some space shuttle windows were replaced because of damage from what turned out to be paint flecks floating in space – or hurtling might be more like it [source: NASA].