A teacher in Wales has spoken of his shock on learning of the Columbia tragedy and paid tribute to the "caring" nature of one of the astronauts.

Chris Greenfield, head of physics at Ysgol Tregaron in Ceredigion, knew one of the seven person team - Kalpana Chawla.

Mr Greenfield was involved in running the International Space School at Houston and Dr Chawla was involved with fund-raising and talked to children in the school.

Several Welsh schoolchildren who went over to the school for a two-week course will have known her, he said.

Geoff Mules from Penarth

"She was highly intelligent, but very aware of her roots. She was so caring about the students and just a wonderful person to be associated with."

The astronaut even had pupils attending the space school staying with her at her home, he said.

The space school at the Johnson Space Centre is run by businessman Geoffrey Mules, who is originally from Penarth, south Wales.

Pupils from Stanwell School in Penarth have been going to Mr Mules' school for the last ten years and several other educational and personal links have become established.

The Columbia flight, which broke up during descent, was a science mission that would have been overseen by Welsh Canadian Dafydd Rhys Williams, said Mr Mules.

Dr Williams himself flew in Columbia in April 1998, taking up the Welsh flag, a Gareth Edwards rugby cap and several other Welsh mementos.

During the flight, Dr Williams, whose father was from Bargoed in the Rhymney Valley, carried out an interview with BBC Wales television news.

Mr Mules explained that Dr Williams' current job, as Head of Life Sciences at NASA, would have meant he was directing the crew, because they were on a science mission.

He would also, as a physician, have had responsibility for health and fitness, so would have known them extremely well.

Welsh-Canadian astronaut Dafydd Rhys Williams

Mr Mules spoke of the sadness throughout the tight-knit astronaut community in Houston at the loss of friends and colleagues.

"We live in Clear Lake City - the area around the Johnson Space Centre," he said.

"All the people who work at the space centre live here. And this is the third time this community has suffered this type of major tragedy.

"First came Apollo 1 in 1967, then Challenger in 1986 and now this," he said.

According to Mr Mules, Dr Williams was about to embark on astronaut training and had been designated a mission to lead later this year.

It is unclear whether that mission will go ahead, following Saturday's tragedy.