A view of the billowing smoke as seen by the space station crew flying 250 miles above New York on Tuesday. Photo: NASA TV/Spaceflight Now

The astronauts aboard the international space station reported they saw the rising smoke and dust clouds from the destroyed World Trade Center towers today while flying overhead. With American targets under attack, NASA centers were closed and Air Force bases at Cape Canaveral and Vandenberg were put on high alert.

"As we went over Maine, we could see New York City and the smoke from the fires," Expedition Three commander Frank Culbertson radioed to the ground. "Our prayers and thoughts go out to all the people there and everywhere else."

Culbertson continued, "I hope that the people responsible are caught and brought to justice as soon as possible. But first, our prayers and condolences to everybody involved."

As of 11:45 a.m. EDT (1545 GMT), Force Protection Condition Delta measures had been ordered at Florida's Kennedy Space Center where the entire space shuttle fleet is currently located. All work was halted in an "orderly shutdown" of the spaceport with the thousands of workers sent home. Only personnel needed for security and guarding the site, the so-called "ride-out crew", were to remain. This is similar to the situation during a hurricane threat.

NASA Headquarters in Washington, D.C. and Goddard Space Flight Center in Maryland were also told to close this morning. The other field centers across the country were expected to follow suit.

At Vandenberg Air Force Base in California and Florida's Cape Canaveral Air Force Station, America's primary rocket launch sites, security was being stepped up.

Gen. Ed. Eberhart, commander of Air Force Space Command, directed the base movement. In addition to plane crashes at the World Trade Center in New York City, the Pentagon in the nation's capital was hit by an aircraft this morning.

"As a matter of policy, specific security actions are not disclosed," a statement from Vandenberg's 30th Space Wing said. "While security forces maintain constant vigilance, these measures help reinforce situational awareness for all government employees."