The crew patch for STS-101. Photo: NASA

The original 2A.2 crew was made up of Halsell, pilot Scott Horowitz, flight engineer Jeffrey Williams, Mary Ellen Weber, Ed Lu and two cosmonauts - Yuri Malenchenko and Boris Morukov - assigned to the flight to help activate and outfit the service module.

After the 2A.2 mission was broken into two parts, however, NASA managers and their Russian counterparts decided to reassign Lu, Malenchenko and Morukov to the 2A.2b mission later this year. Joining them will be commander Terrence Wilcutt, pilot Scott Altman, Daniel Burbank and Richard Mastracchio.

To fill out the 2A.2a crew, the one scheduled for launch April 24, NASA added the three-member crew already in training to spend six months aboard the international space station as the lab's second full-time crew: Russian commander Yuri Usachev, Susan Helms and James Voss.

Changing crews and flight plans so late in a shuttle flow is unprecedented. But Halsell said last-minute changes will be the rule in future space station flights, not the exception.

"We've had to learn to deal with those changes," Halsell said. "We have agreed among ourselves as a crew to train for the equivalent of two or three different flights. That way it gives the international space station program and the shuttle program management the flexibility to basically, right here at the end, to decide which of those items we're already trained for they want to pull off the shelf and have us go do.

The STS-101 astronauts pose for a portrait. Photo: NASA

"It has been an issue. We have learned how to deal with it and I think in some ways we're pioneering the way we're going to have to do business in the future. That is, be more flexible, perhaps train for a greater number of tasks than we really have time to do on orbit, perhaps train in a more generic fashion, that is, arm ourselves with the skills so at the last minute we're able to focus in on exactly the task they want us to do.

"I think we're going to prove this is a successful, safe and productive way of doing business," Halsell said. "And in fact, it's where we're headed in the future."

But that does not mean it will be easy. Halsell, Horowitz, Williams and Weber found it especially difficult to say farewell to three crew mates who had spent the past year training for a mission they will not conduct.

"It was hard," Weber said in an interview. "I would be lying if I told you it was easy to give up Ed Lu, Yuri Malenchenko and Boris Morukov. We were a crew. It was almost like going through a death in the family."