killing all seven crew members, on February 1, 2003. The ultimate cause of the accident was a piece of foam separating from the external tank moments after liftoff and striking the leading edge of the orbiter's left wing, puncturing one of the reinforced carbon-carbon (RCC) panels that covered the wing edge and protected it during reentry. As Columbia reentered the atmosphere at the end of an otherwise normal mission, hot gas penetrated the wing and destroyed it from the inside out, causing the orbiter to lose control and disintegrate. After the Columbia disaster, the International Space Station operated on a skeleton crew of two for more than two years and was serviced primarily by Russian spacecraft. While the "Return to Flight" mission STS-114 in 2005 was successful, a similar piece of foam from a different portion of the tank was shed. Although the debris did not strike Discovery, the program was grounded once again for this reason. The second "Return to Flight" mission, STS-121 launched on July 4, 2006, at 14:37 (EDT). Two previous launches were scrubbed because of lingering thunderstorms and high winds around the launch pad, and the launch took place despite objections from its chief engineer and safety head. A five-inch (13 cm) crack in the foam insulation of the external tank gave cause for concern; however, the Mission Management Team gave the go for launch. This mission increased the ISS crew to three. Discovery touched down successfully on July 17, 2006 at 09:14 (EDT) on Runway 15 at Kennedy Space Center. Following the success of STS-121, all subsequent missions were completed without major foam problems, and the construction of the ISS was completed (during the STS-118 mission in August 2007, the orbiter was again struck by a foam fragment on liftoff, but this damage was minimal compared to the damage sustained by Columbia). The Columbia Accident Investigation Board, in its report, noted the reduced risk to the crew when a Shuttle flew to the International Space Station (ISS), as the station could be used as a safe haven for the crew awaiting rescue in the event that damage to the orbiter on ascent made it unsafe for reentry. The board recommended that for the remaining flights, the Shuttle always orbit with the station. Prior to STS-114, NASA Administrator Sean O'Keefe declared that all future flights of the Space Shuttle would go to the ISS, precluding the