The countdown is under way for the launch of the Shuttle Discovery on the Return to Flight mission. Launch is set for no earlier than 10:39 a.m. EDT on Tuesday, July 26.

At noon today, countdown clocks at NASA’s Kennedy Space Center in Florida came to life at the T-43 hour mark and immediately began counting down toward a liftoff Tuesday at 10:39 a.m. EDT.

Space Shuttle Discovery is in great shape for the Return to Flight launch, NASA Test Director Pete Nickolenko announced during a briefing Saturday morning. “We believe our flight systems and ground support systems are ready,” Nickolenko explained. “We are looking forward to a successful launch and mission.” Due to concerns about the early development of showers and cumulus clouds, the chance of Kennedy weather prohibiting launch is 40 percent, according to Shuttle Weather Officer Kathy Winters. There are also concerns about crosswinds at all three Trans-Atlantic Landing sites, located in Spain and France. The flight crew, led by Commander Eileen Collins, returned to Kennedy on Friday to begin final preparations for their flight to the International Space Station.