25 years ago, a NASA astronaut witnessed the tragic 9/11 attacks from space. Here's what he saw.

Frank Culbertson had a birds-eye view of one of the most memorable and tragic events in American history.

The NASA astronaut was the only American off of Earth on Sept. 11, 2001. He was circling the planet aboard the International Space Station (ISS) when terrorists flew commercial jets into the twin towers of the World Trade Center in New York City, killing more than 2,700 people.

The ISS passed over New York shortly after the attacks took place, so Culbertson saw the devastation from an eerie remove. He shared his thoughts with Mission Control at NASA's Johnson Space Center in real time, chronicling the tragedy like no one else could.

"We could see New York City and the smoke from the fires," Culbertson said. "Our prayers and thoughts go out to all the people there and everywhere else here — I'm looking up and down the East Coast to see if I can see anything else — and to the people in Washington."

Terrorists hijacked four commercial planes on 9/11, flying two of them into the World Trade Center and one into the Pentagon in Washington, D.C. Passengers on the fourth plane overpowered the hijackers, forcing it to crash in a field in Pennsylvania rather than hit the terrorists' intended target, which was likely the U.S. Capitol building or the White House.

"I hope that the people responsible are caught and brought to justice as soon as possible," Culbertson added. "But first, our prayers and condolences to all involved. And I just wanted the folks to know that their city still looks very beautiful from space. I know it's very difficult for everybody in America right now, and I know folks are struggling very hard to to deal with this and recover from it. But the country still looks good, and, for New Yorkers, your city still looks great from up here."

Culbertson gave a more complete accounting of his thoughts in an open letter, which he published a day after the attacks.

"The world changed today. What I say or do is very minor compared to the significance of what happened to our country today when it was attacked," he wrote.

"It's horrible to see smoke pouring from wounds in your own country from such a fantastic vantage point," Culbertson added. "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 arrived at the ISS on Aug. 12, 2001 aboard the space shuttle Discovery along with cosmonauts Vladimir Dezhurov and Mikhail Tyurin. The trio comprised Expedition 3, the third-ever crewed mission to the orbiting lab, which ran through December of that year.

We're now up to Expedition 75, and there have been no breaks: The ISS has been continuously staffed by rotating astronaut crews since November 2000.

Expedition 3 was Culbertson's third and final spaceflight. He retired from NASA in August 2002 and went to work in the private sector. Among other roles, he led human spaceflight efforts at Orbital Sciences Corp., which built the Cygnus ISS resupply spacecraft. Cygnus still flies today, for the aerospace giant Northrop Grumman, which bought Orbital Sciences in 2018.

Culbertson, 77, retired from Northrop Grumman in 2018. He currently serves on the board of directors of the nonprofit Space Foundation, among other roles.

You can read more about Culbertson's experiences on NASA's dedicated 9/11 page. That page also outlines how the agency helped emergency managers assess the damage in New York City just after the attacks and discusses some of the ways NASA has honored 9/11 victims and their families over the years.

For example, NASA flew nearly 6,000 small American flags on the STS-108 mission of the space shuttle Endeavour, which launched on Dec. 5, 2001 and landed 12 days later.

"Students working out of Johnson Space Center in Houston assembled commemorative packages that included the space‑flown flags, which were then presented to victims' families," NASA officials wrote about the project. "Distribution began on June 14, 2002 — National Flag Day — during a ceremony at the American Museum of Natural History’s Rose Center for Earth and Space in New York."