United States President George W Bush remembered Columbia astronauts Kalpana Chawla and six others in an open-air memorial ceremony at the Johnson Space Centre in Houston, Texas, on Tuesday.

"Their mission was almost complete. And we lost them so close to home," Bush said. "The men and women of the Columbia had journeyed more than six million miles and were minutes away from arrival and reunion.

"The loss was sudden and terrible, and for their families, the grief is heavy.

"None of our astronauts travelled a longer path to space than Kalpana Chawla. She left India as a student, but she would see the nation of her birth, all of it, from hundreds of miles above."

Kalpana's sister Sunita, father Banarsi Lal and husband Jean-Pierre Harrison sat close to the president and First Lady Laura Bush.

"Kalpana's native country mourns her today, and so does her adopted land," Bush said.

NASA Administrator Sean O'Keefe said there was a moment during the Columbia's last flight that he would always remember.

Kalpana called the flight desk, he said, excited and overwhelmed by the sight of the sun setting on the earth, and how the entire earth was reflecting on her retina. She called everyone on the shuttle to see how the world looked, literally, in her eyes.

O'Keefe said the space agency would investigate the cause of the shuttle's break-up and take corrective steps.

Chief of Astronaut Corps Captain Kent Rominger said Kalpana was admired for her kindness. He mentioned her love for flying and said she had 'a terrific sense of humour'.

The Columbia crew had great respect for her abilities, Rominger said. "[Columbia pilot William] McCool once asked KC, 'May I borrow your brain?'"

And she never got upset about all the delays. "You are training to fly in space, what more could you want?" Rominger quoted her as saying.

US navy bands played devotional tunes while a rabbi and a chaplain recited prayers for the astronauts.

The ceremony ended with NASA T-38 training jets flying in the 'Missing Man' formation.

Indian NASA employees attending the ceremony appreciated the gestures and said they were honoured that the astronauts were remembered in such fashion.

"I was very touched by the service," said Murthy Pinnameneni, an engineer from Boeing who had come from Seattle to pay his respects.

"Seeing the Tricolour, hearing about India being spoke of so highly, I had a great swelling of pride as an Indian," Murthy said.

"This was a big deal for us; to hear the president and others speak about our country and Chawla. I wish her family peace. I can only imagine how they feel."

"Losing the crew of the Columbia was very painful. We were like family," said Ahsen Cheema, an engineer with flight operations.

He had never met Kalpana, but had worked with other members of the shuttle. The day the shuttle disintegrated over Texas, he rushed to his computer, like others, to check the flight data.

"I was so surprised. Nothing has ever happened before in re-entry," he said.

One attendee who did work with Kalpana briefly was Kirit Patel, an engineer in the shuttle avionics integration laboratory.

He said Chawla was hard-working and a perfectionist, who always had a number of questions for him about the shuttle systems.

"We are all proud of her," he said. "I wish that someone will follow her and become the next Indian astronaut."

The Columbia Crash: The Complete Coverage