This is awesome! According to wikipedia:
"During STS-120, the lightsaber used by actor Mark Hamill in the 1983 film Star Wars Episode VI: Return of the Jedi will be flown to the station, and then returned to Earth. Stowed on-board Discovery for the length of the mission, the fictional Jedi weapon is being flown in honor of the 30th anniversary of director George Lucas' Star Wars franchise.
The initial shuttle launch time was set at 11:38 (EST), a possible homage to George Lucas, whose first film's name THX 1138 often appears in his later scripts.
On 28 August 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. After STS-120, the lightsaber will be on display at Space Center Houston."