STS-125 Pilot Gregory C. Johnson tries on his helmet for a fit check.

STS-125 Pilot Gregory C. Johnson tries on his helmet for a fit check. Johnson will be making his first shuttle launch. His name patch reflects his military “call sign.” 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