Video footage captures the moment an astronaut watched in horror from space as the South Tower collapsed during the 9/11 terrorist attack in New York City.
Frank Culbertson was the only American off the planet during the attacks on 11 September 2001, having been inside the International Space Station with two Russian cosmonauts at the time, around 250 miles (400km) above Earth.
Looking down from the space station, Culbertson saw smoke billowing from New York, which was coming from the second of the Twin Towers.
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