Seventeen years ago, President Ronald Reagan said the seven astronauts killed in the 1986 shuttle Challenger explosion, "slipped the surly bonds of earth and touched the face of God." Saturday, seven more astronauts made the very same trip.

Shortly after 8 a.m. (CST) the space shuttle Columbia, broke apart, exploded and scattered debris across much of east Texas, killing all seven astronauts on board.

The tragedy was the third such accident in NASA's history where astronauts were killed, and the second since the space shuttle program began in 1981.

"I assure you. We will find out what happened. Fix it. And move on," said Capt. Bill Readdy, Assistant Administrator of Space Flight at NASA's Kennedy Space Center. "We owe that to those men and women who died today and their families."

President Bush, who returned to Washington early from a weekend trip to Camp David, addressed the nation Saturday afternoon.

"The Columbia's lost. There are no survivors," Bush said. "These men and women assumed great risk in this service to all humanity. In an age when space flight has come to seem almost routine, it is easy to overlook the dangers of travel by rocket and the difficulties of navigating the fierce outer atmosphere of the earth."

On board Columbia were: Col. Rick Husband, Lt. Col. Michael Anderson, Commander Laurel Clark, Capt. David Brown, Commander William McCool, Dr. Kalpana Chawla and Ilan Ramon a colonel in the Israeli air force - the first Israeli astronaut.

With family members awaiting their return at a site close to the Kennedy Space Center landing strip in Florida, Columbia was scheduled to land at 8:16 a.m. (CST) - a landing they would never make.

"Our thoughts and prayers are with the families and this brave and dedicated professional crew who accepted the challenges and were running a flawless mission," said Sen. Jeff Sessions. "I know Sam O'Keefe and his field center directors are conducting a thorough investigation so we can correct the problems that led to this tragedy. Space flight is a risky endeavor and these astronauts gave their lives bravely performing a scientific mission for the good of mankind. We grieve today for their crew and their families, but we are a nation of explorers, it is our destiny. We will overcome this tragedy."

"Our thoughts and prayers are with the astronauts and their families," said U.S. Rep. Spencer Bachus, R-Ala., said from his home Saturday. "Today's tragedy again should remind us of the bravery and sacrifice of the men and women confronting these dangers daily in the service of our nation."

"The loss of the crew of the space shuttle Columbia us a national tragedy," said U.S. Sen. Richard Shelby. "I join with the Bush Administration and the entire nation in offering my sincerest condolences to the families and friends of Rick Husband, William McCool, Ilan Ramon, Michael Anderson, Laurel Clark, David Brown, and Kapulna Chawla. These brave astronauts and al their grieving loved ones are in our thoughts and prayers."

With the loss of Columbia, which was concluding a 16-day science mission, NASA's fleet of shuttles is now down to three. Before the Challenger explosion in 1986, the fleet had been as many as five.

Following the Challenger tragedy, shuttle flights were discontinued for nearly three years, it is unclear just how long the program will be delayed now, but Bush promised the mission will continue.

"The cause in which they died will continue. Mankind is led into the darkness beyond our world by the inspiration of discovery and the longing to understand," Bush said. "Our journey into space will continue."

Bush also worked to comfort the families of those lost.

"The same creator who names the starts also knows the names of the seven souls we mourn today," Bush said. "The crew of the shuttle Columbia did not return safely to Earth, yet we can pray that all are safely home."

Mary Reeves contributed to this report.