When the towers of the World Trade Center fell on September 11, 2001, one American was not on the planet.
Astronaut Frank Culbertson had been aboard the International Space Station for a month when the 9/11 attacks occurred, joined only by two Russian cosmonaut crew mates. He could only monitor the events of the day from 300 miles above the Earth.
On Friday, NASA released letters Culbertson wrote and images he took as the space station passed over the New York City area after the 9/11 attacks.
Full story: 9/11 from space: Astronaut shares pictures and thoughts