3. The space shuttle Discovery hitches a ride on a modified Boeing 747 carrier aircraft from California to the Kennedy Space Center in Cape Canaveral, Fla., in August 2005. Discovery's 2005 mission was the first flight for the shuttle since Columbia broke up on re-entry in February 2003.

4. The recently remodeled space shuttle external fuel tank for the next mission is transported past the huge Vehicle Assembly Building after arriving by barge at the Kennedy Space Center March 1, 2006.

5. Mission specialist on STS-121 Piers J. Sellers is wearing a training version of the Extravehicular Mobility Unit space suit. He's participating in a space walk simulation while anchored on the end of the training version of the space shuttle's robotic arm at Johnson Space Center. The robotic arm has an extension attached that is used to reach tiles underneath the shuttle.

6. Workers observe the space shuttle Discovery before it begins it's six-hour trek from the vehicle assembly building to pad 39B at the Kennedy Space Center May 19. Its move to the pad is a major step toward liftoff sometime between July 1 and July 19.

7. A security helicopter hovers as the space shuttle Discovery rolls out of the Vehicle Assembly Building on it way to the launch pad at Kennedy Space Center.

8. Kennedy Space Center security checks camera gear before the media leaves for the launch pad to meet with the STS-121 NASA flight crew June 14.

9. STS-121 mission specialist Thomas Reiter from Germany suits up in a staging area during a dress rehearsal at the launch pad June 15. Reiter represents the European Space Agency.

10. The STS-121 NASA flight crew commander Steven W. Lindsey talks with the media at Kennedy Space Center June 16 after the launch dress rehearsal that occurs before each shuttle mission.

11. NASA photo analyst Tom Rieckhoff poses for a portrait in his Marshall Space Flight Center office June 22 in Huntsville, Ala. Rieckhoff leads the photo analysis team at Marshall, one of three NASA centers where experts pore over hundreds of video and still images after a shuttle launch looking for potential problems.

12. Discovery crew from left: Mission specialists Michael Fossum and Thomas Reiter, pilot Mark Kelly, commander Steven Lindsey, and mission specialists Lisa Nowak, Stephanie Wilson and Piers Sellers.

13. The space shuttle Discovery's nose landing gear door was photographed by the crew on the international space station July 28, 2005, as it did a pitch maneuver for tile inspection before docking. The crew of Discovery moved onto the station after carrying out new damage checks on the shuttle. NASA decided to halt the program again after Discovery's return because of debris that fell off during its July 26 launch.

14. STS-121 mission specialists Thomas Reiter of Germany, foreground, Piers Sellers and Stephanie Wilson participate in a training session in one of the full-scale trainers in the Space Vehicle Mockup Facility at NASA's Johnson Space Center.