Vapor trails look like balls of smoke as the orbiter touches down on Runway 15 at NASA's Shuttle Landing Facility.

Vapor trails from Discovery's wing tips look like balls of smoke as the orbiter touches down on Runway 15 at NASA's Shuttle Landing Facility, completing mission STS-121 to the International Space Station. At touchdown -- nominally about 2,500 ft. beyond the runway threshold -- the orbiter is traveling at a speed ranging from 213 to 226 mph. Discovery traveled 5.3 million miles, landing on orbit 202. Mission elapsed time was 12 days, 18 hours, 37 minutes and 54 seconds. Main gear touchdown occurred on time at 9:14:43 EDT. Wheel stop was at 9:15:49 EDT. The returning crew members aboard are Commander Steven Lindsey, Pilot Mark Kelly and Mission Specialists Piers Sellers, Michael Fossum, Lisa Nowak and Stephanie Wilson. Mission Specialist Thomas Reiter, who launched with the crew on July 4, remained on the station to join the Expedition 13 crew there. The landing is the 62nd at Kennedy Space Center and the 32nd for Discovery. During the mission, the STS-121 crew tested new equipment and procedures to improve shuttle safety, and delivered supplies and made repairs to the International Space Station. Photo credit: NASA/Tony Gray & Tim Powers