Also crucial is how well candidates think and act on their feet when a lot of activity is going on around them – or in the galley. The ability to improvise is a trait that uncovers secrets that formal training manuals don't cover: Like the incredible versatility of tortillas, or the importance of duct tape in gourmet cooking – seemingly mundane innovations that make life on orbit more enjoyable.
More candidates are signing up to try their hand. In 2007, NASA hung out the help-wanted sign for a new class of astronauts. The agency received slightly more than 3,500 applications. It's expected to announce the class of 2009 soon, adding 15 to 20 newcomers to its corps of some 90 astronauts. Last month the European Space Agency (ESA) tapped six new astronauts from 8,400 applications, bringing its list of active astronauts to 14. Canada and Japan have also added astronauts recently.
The most promising and adaptable candidates become apparent during two years of basic training, which includes two-week sessions of outdoor leadership training and shorter stints in the field during survival training. By the end, the new crop of astronauts can decide if they want to aim for the shuttle or the space station.
Some people – like astronauts with children – simply don't have the time to spend six months circling Earth.
But other factors come into play as well: such as whether the crew members will drive one another crazy.
"Clearly, as people, we get along with some people better than others," says Sandra Magnus, who returned to Earth March 28 after spending 4-1/2 months on the space station. "You certainly take that into account for a long-duration mission. You don't want to put people together who might not get along as well as you might like."