to their final position at the port end of the truss. Outreach STS-120 carried the signatures of over 500,000 students that participated in the 2007 Student Signatures in Space program, jointly sponsored by NASA and Lockheed Martin. In celebration of Space Day in May 2007, students from over 500 schools around the world signed giant posters. Their signatures were scanned onto a disk, and the disk was manifested on the STS-120 mission. Also during STS-120, the lightsaber used by actor Mark Hamill in the 1983 film Return of the Jedi was flown to the station and returned to Earth. Stowed on-board Discovery for the length of the mission, the prop was flown in honor of the 30th anniversary of the Star Wars franchise. On August 28, 2007, Chewbacca from the Star Wars films presented the lightsaber to NASA officials from Space Center Houston, in an official ceremony at Oakland International Airport. The lightsaber was then flown to Houston, where it was greeted by Stormtroopers. The lightsaber will be displayed at Space Center Houston. Mission background At the time of the Columbia disaster, STS-120 was scheduled for early 2004. It was delayed repeatedly until October 23, 2007. NASA originally scheduled the launch for October 20, 2007, but due to the International Space Station program requirement, launch was delayed to October 23, 2007. In light of the small gouge to the underside of Endeavour that occurred on STS-118, in August 2007, NASA managers announced that they expected to add a fifth spacewalk to the STS-120 mission, designed to test a heat-shield repair tool. The repair technique was originally scheduled for a flight in 2008, but following STS-118, it was decided to move up the testing. The repair tool, called a TPS (thermal protection system) repair ablator dispenser (T-RAD), has never been tested in space, so the spacewalk would have allowed managers to evaluate its effectiveness in low gravity environments. During the course of the mission, issues with the S4 starboard Solar Alpha Rotary Joint (SARJ), and P6 Solar Array, deferred this test objective to a future mission. The mission marked: 151st NASA crewed spaceflight 120th Space Shuttle flight since STS-1 34th flight of Discovery 95th post-Challenger mission 7th post-Columbia mission Mission timeline Launch preparations Following STS-118 in August 2007, NASA managers decided to make modifications to the external tank to be used on STS-120, and modify the liquid oxygen feed-line brackets. The