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Duane Ross, head of astronaut selection and training at the Houston centre, contributes to a discussion on how to become a NASA astronaut. Originally broadcast 1 December, 1995 (Photo: Flight engineer Nicole Stott of the space shuttle Discovery works during a six-and-a-half hour spacewalk performed overnight between Tuesday night and Wednesday morning September 1, 2009. Stott and mission specialist John 'Danny' Olivas (not pictured) removed an empty ammonia tank from the station's truss and will replace it with a new module during a follow-up spacewalk later in the week. Credit: NASA/Getty Images)