I'm only just a year into this journey of grieving Evelyn Husband

Evelyn Husband said the families of the dead crew had been engaged in "tough meetings" with the US space agency.

Nasa was criticised in the official accident report for failing to ensure the safety of the orbiter - a finding Mrs Husband said had angered her.

But she told the Everywoman programme the findings were being acted on.

"We've had some very tough meetings, and they have outlined where they are not only taking on board what the accident investigation revealed, but they are implementing the suggestions," she told the BBC World Service series.

"It's not going to happen overnight - you cannot take a giant organisation the size of Nasa and in one week everybody changes the way they do business.

"But they are taking very concrete steps to implement and learn from this tragedy."

No option

Columbia was lost on re-entry on 1 February because of a breach in its left wing. Damage sustained on take-off had opened a hole in the wing through which superhot gases could penetrate and destroy its internal structure.

One criticism in the report held that Nasa's cost-cutting was partly to blame. Management attitudes within the agency were also criticised.

I came to the conclusion that at the end of the day, no matter how angry or bitter I became towards this, it would not bring Rick back Evelyn Husband

However, Mrs Husband, who has written a book, called High Calling, about her experience, said she did not "specifically" hold anyone responsible.

"There are certain individuals that, when the event occurred, were at the wrong place at the wrong time, or making the decisions that they were poorly trained to make," she said.

"But I think the accident investigation report was extremely well done, and highlighted areas that Nasa can improve."

However, she also stated the extent of her anger when the accident report was first published.

"I was incredibly angry because there were so many areas at Nasa that this accident could have been prevented," she said.

"For the first time, I felt very disappointed and aggravated, because Rick was never informed of the magnitude of the impact on the wing on the shuttle. Therefore he was never given the authority to deal with it or do anything.

"He was informed there had been a foam strike, but they informed him it was of absolutely no consequence."

She added that this decision was made worse because two of the crew members had been trained to perform a spacewalk in case of any problem with the shuttle.

"They had spacesuits on board the orbiter and they could visually assess the damage," she said. "They were never given that opportunity. I was incredibly upset about that."

The report also found that a rescue effort would have been possible - although Mrs Husband had thought this was not so. "I found that incredible frustrating as well," she said.

'My best friend'

Mrs Husband said her husband had two dreams: to be an astronaut and to build a strong family.

She continues to look after their children, Laura and Matthew.

"I came to the conclusion that at the end of the day, no matter how angry or bitter I became towards this, it would not bring Rick back," she said.

In depth guide: Columbia's last mission

"My goal is not to raise my children in an atmosphere of bitterness and anger. I have taken that and used it very productively."

But she added that it would still take a long time for her to accept completely what had happened.

"I still cry all the time. I suspect that I will spend the rest of my life mourning the loss of my husband. I met him when I was 18 years old, and I'm 45 years old.

"So it's a huge piece of my life. He was father to my children; he was my best friend.

"So as far as coming to terms with that, I'm only just a year into this journey of grieving.