Remembrance services have been held across America

The crew's families attended the ceremony at Arlington National Cemetery, where a bronze replica of the doomed mission's symbol was unveiled.

The service came a year and a day since the shuttle broke up as it re-entered the Earth's atmosphere.

On Sunday, services of remembrance were held across the United States.

'Seven true heroes'

"Today we remember and commemorate the undaunted courage of seven true heroes for our time and for all time," Nasa Administrator Sean O'Keefe said of the Columbia crew.

"They were pilots, engineers and scientists, all motivated by a fire within, a passionate eternal flame that burned in their souls, that compelled them to live lives of distinction and to bring the heavens ever closer to our grasp."

An honour guard of astronauts unveiled the memorial - a stone monument with a bronze replica of the mission patch bearing the names of Columbia's crew.

Mourners placed flowers on the monument and a bagpiper played the hymn Amazing Grace.

The remains of 29 astronauts killed on space missions are buried in Arlington National Cemetery.

Super Bowl tribute

On the anniversary of the Columbia disaster, services were held from Texas to Florida, with tributes paid before Sunday's Super Bowl game in Houston.

Speaking at Cape Canaveral's Space Mirror Memorial, Kennedy Space Center director Jim Kennedy said the astronauts' deaths "will not be in vain".

A more public tribute was paid as thousands gathered in Houston - the city that was home to mission control, and most of the astronauts - for the annual Super Bowl.

In a pre-game interview, President George W Bush said: "Our love and prayers go out to the Nasa family, especially those members from the Columbia family who are still in mourning."

The crew on board were Rick Husband, Willie McCool, Michael Anderson, David Brown, Laurel Clark, Kalpana Chawla and Israel's first astronaut Ilan Ramon.