Beyond the need for a generalist's hands-on skills, astronauts accustomed to shuttle operations face starkly different conditions as they prepare for space-station work. Those differences can weigh heavily in their decision about whether to remain in the corps.
Mike Fossum, a veteran of two shuttle missions since the Columbia tragedy, heads to the ISS in May. He is in a fairly unique position: Over those two shuttle missions he took part in spacewalks that helped assemble the station; now he's going to live in it.
"I dreamed of living on a space station when I was a kid," he says. Even so, he has had to adjust to a dramatically new training regimen. "A shuttle crew is kind of a sprint crew," he says. During a mission, "You've got a short time – two weeks – to get a lot done. You train together as a really tight unit. Because you train together over the course of about a year, you become really close."
While shuttle training involves some travel and the hours can be long, training is still conducted largely in Houston, near family and friends. Space-station training "came as a little bit of a surprise," he acknowledges. Training for a posting to the space station takes at least 2-1/2 years, "and for a lot of it, you're alone in different corners of the globe."
As a result, a space station assignment can be like a military posting – with long road trips during training and six months out on the job (in this case orbit). A returning astronaut also faces a period of physical rehabilitation after a half year floating weightless in space and, perhaps most important, reintegration into a family that has adapted to living without Mom or Dad.