via The Atlantic: The Story of the Only American Not on Earth on September 11th: 

This tension was particularly poignant on 9/11, when the effects of violence on Earth were actually visible from space, as captured in the photograph above. At the time, three people were not on Earth: Russian astronauts Mikhail Tyurin and Vladimir Dezhurov, and American Frank Culbertson, making Culbertson the only American not on Earth during the 9/11 attacks.