John Grunsfeld arrives at the Shuttle Landing Facility at NASA's Kennedy Space Center for Terminal Countdown Demonstration Test or TCDT activities.

STS-125 mission specialist John Grunsfeld arrives at the Shuttle Landing Facility at NASA’s Kennedy Space Center in Florida for Terminal Countdown Demonstration Test, or TCDT, activities. To his left is mission specialist Megan McArthur. During TCDT, space shuttle Atlantis’ STS-125 crew members will participate in a simulated launch countdown, practice emergency egress procedures at the launch pad and continue to familiarize themselves with the mission payload and hardware. STS-125 is the fifth and final shuttle Hubble Space Telescope servicing mission. Launch is targeted for Oct. 10. Photo credit: NASA/Kim Shiflett