Nasa shared some poignant pictures taken from space to mark the 16<sup>th anniversary of the deadliest terrorist attack on US soil. Remembering the devastating 9/11 attacks, the space agency also released a letter written by astronaut Frank Culbertson, who was the only American in space, aboard the International Space Station (ISS) during the attacks.

Nasa says that as the ISS was flying directly over New York City, Culbertson began photographing the attacks as soon as he became aware of it, capturing "incredible images in the minutes and hours following the event".

"Other than the emotional impact of our country being attacked and thousands of our citizens and maybe some friends being killed, the most overwhelming feeling being where I am is one of isolation," Culbertson wrote in a letter, which was published just a day after the attacks. "It's horrible to see smoke pouring from wounds in your own country from such a fantastic vantage point. The dichotomy of being on a spacecraft dedicated to improving life on the earth and watching life being destroyed by such willful, terrible acts is jolting to the psyche, no matter who you are."

Culbertson photographed the massive billowy smoke and dust rising from Manhattan, where the Twin Towers were located. Nasa also shared new images of New York and the Pentagon in Washington DC, taken by ISS astronauts earlier this year.

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A month after the attacks, Nasa flew 6,000 American flags, including one that was recovered from the debris of the World Trade Center (WTC) into orbit, in efforts to honour the men and women who assisted in relief and recovery efforts. Alongside the flags, 23 replicas of shields and 91 patches of the New York Police Department, as well as a huge New York Fire Department flag was also flown into space.

"It's difficult to describe how it feels to be the only American completely off the planet at a time such as this. The feeling that I should be there with all of you, dealing with this, helping in some way, is overwhelming. I know that we are on the threshold (or beyond) of a terrible shift in the history of the world. Many things will never be the same again after September 11, 2001," Culbertson said in his letter. "Not just for the thousands and thousands of people directly affected by these horrendous acts of terrorism, but probably for all of us. We will find ourselves feeling differently about dozens of things."