STS-125 Mission Specialist John Grunsfeld tries on his helmet to check the fit.

STS-125 Mission Specialist John Grunsfeld tries on his helmet to check the fit. A veteran in space, Grunsfeld will be making his fifth shuttle launch. His name patch reflects the nicknames the crew gave each other. The crew is at NASA's Kennedy Space Center in Florida to take part in terminal countdown demonstration test, or TCDT, activities as preparation before launch on space shuttle Atlantis’ STS-125 mission to service NASA’s Hubble Space Telescope. TCDT provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization, emergency training and a launch countdown. Atlantis is targeted to launch Oct. 14. Photo credit: NASA/Kim Shiflett