Preparing for spacewalk. Astronauts Bernard A. Harris Jnr., payload commander (top), and C. Michael Foale, mission specialist, float in their spacesuits in the airlock of the Space Shuttle Discovery while preparing for a spacewalk. Before leaving the airlock they must breathe pure oxygen for 3.5 hours to avoid getting the bends. This photograph was taken during mission STS-63 (3-11 February 1995), when Discovery made a close rendezvous with the Russian space station Mir in rehearsal for the first shuttle-Mir docking in June 1995.