Thomas during training for Expedition 6. Photo: NASA

Astronaut Donald Thomas, veteran of four shuttle flights and more than 43 days in space, trained for more than a year and a half to fly aboard the international space station as a member of its sixth full-time crew, the crew currently en route to the lab complex aboard the shuttle Endeavour.

But on July 26 of this year, NASA announced Thomas had been replaced by backup astronaut Donald Pettit because of what a press release said was "a medical issue that affects Thomas' long-duration space flight qualification." Sources said later the reason was cumulative exposure to radiation during his four shuttle flights.

In the same press release, chief astronaut Charles Precourt said "the demanding nature of long-term space flight requires a conservative approach to crew health issues, especially this early in the program."

Thomas has not granted any known interviews since his removal from the ISS-6 crew and NASA has not provided any additional details, citing medical privacy issues.

But in an interview this evening with The Associated Press, Expedition 6 commander Kenneth Bowersox said Thomas was hurt "pretty bad" by his removal from the station crew and that it will take more time to heal the emotional wounds.

The Expedition 6 crew patch. Photo: NASA

"This emblem that's on our shirt was designed by Don," Bowersox said, floating on the shuttle's lower deck with Pettit and ISS-6 flight engineer Nikolai Budarin. All three wore shirts with the Expedition 6 logo on the left breast.

"So he's with us every minute in spirit and we think about him a lot and we can only wish him the best. We know this has been very, very hard for him, so that's been the toughest thing for us, too. But he's a big part of this mission, everywhere we go we see reminders of him and there's no way we could not think about him."

Bowersox said he was not able to chat with Thomas before Endeavour's launching Saturday, saying "it's still kind of painful and sore for Don, when he talks with us it becomes even more painful."

"We're going to try to connect with him when we get on orbit or after we get home, after he's had a little bit of distance," Bowersox said. "But this is a very, very tough thing, to be so close to accomplishing a dream - going up for a long-duration flight was Don Thomas' dream - and when he wasn't able to do it, it hurt him pretty bad.

"So as the distance and the time heals that wound, then I think it'll be a little bit easier for him to discuss how much fun we're having on orbit."

Before launch, Bowersox said expedition crew members build a bond as training progresses and "when you lose someone from the crew, it rips a little piece of you away as they leave." Pettit, Bowersox said, should simply enjoy "the fact that he's going to be flying."

"But he has to be a little bit sad for his friend Don Thomas," Bowersox said. "And the same thing for me. I'm happy to get to fly with Don Pettit but I was really looking forward to flying with Don Thomas, too, because he's such a great guy."

The Expedition 6 crew plans to remain aboard the station until late March.

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