US President George W Bush has hailed the courage of India born Kalpana Chawla and six other astronauts who died when space shuttle Columbia exploded while returning home five years ago.
"They assumed great risk so we could understand what lies beyond the heavens. Americans are grateful for their service, and they will always be cherished," he said in a message to US space agency NASA as it commemorated the fifth anniversary of the tragedy.
"Our nation will forever honour the memory of the fallen crew," he said as space officials, schoolchildren and families of the seven crewmembers gathered in Cape Canaveral, Florida, Sunday to remember them.
"Space exploration is a dream deeply rooted in human history. The seven brave astronauts of Columbia sacrificed their lives so that the rest of mankind could realise this dream," said Bush, sending the first couple's best wishes to the families and friends of the Columbia crew.
"Rick D. Husband, William C. McCool, Michael P. Anderson, David M. Brown, Kalpana Chawla, Laurel Blair Salton Clark and Ilan Ramon all nobly faced the dangers of space travel with courage and idealism," he said.
NASA's top space flight officials joined nearly 200 others at the Kennedy Space Centre's outdoor astronaut memorial to remember the seven who died five years ago as the spaceship with its wing gashed by a chunk of fuel tank foam insulation at lift-off 16 days earlier, shattered high above Texas just minutes from home.
Indian Space Research Organisation (ISRO) chairman G. Madhavan Nair represented India, Chawla's homeland, at the hour-long ceremony. He noted how the loss of Columbia was painful not just for the astronauts' families but also for the entire world.
Each guest received a long-stemmed rose. The flowers were placed in the grating in front of the giant shiny granite marker bearing the names of all NASA's 24 astronauts killed in the line of duty.
"Much more than any physical monument, they're memorialised right here in our hearts," said former shuttle commander Bill Readdy.
On January 31, NASA deputy administrator Shana Dale and other NASA senior management had participated in a wreath laying ceremony at Arlington National Cemetery in Washington as part of NASA's Day of Remembrance.
Wreaths were laid in the memory of those men and women who lost their lives in the quest of space exploration, including the astronaut crews of Columbia, Challenger and Apollo 1.