Two U.S. astronauts will step out into space at 9:20 a.m. for a two-and-a-half hour spacewalk on Wednesday. Steve Swanson and Rick Mastracchio will install a backup computer on the exterior of the International Space Station, and remove a broken one. This is the fifth spacewalk for Swanson. Its the ninth for Mastracchio. Mastracchio is EV 1, and his suit has red stripes.