The countdown begins Sunday night for NASA’s next space shuttle mission. Endeavour is set for launch of mission STS-118 Wednesday evening.

The launch had to be postponed 24 hours from its originally scheduled liftoff, to allow the shuttle processing team additional time to complete routine work. The new launch is targeted for Wednesday, August 8, at 6:36 p.m. EDT. The additional day will provide time to complete the processing and allow the countdown to begin at 8 p.m. Sunday.

Image above: The Space Shuttle Endeavour on the launchpad. Credit: NASA

Led by Commander Scott Kelly, the STS-118 flight crew is now at Kennedy Space Center’s Shuttle Landing Facility. The seven astronauts will spend the remaining days until launch undergoing final prelaunch preparations, including suit fit checks, briefings, medical exams and landing practice in the shuttle training aircraft.

“I would like to congratulate all the orbiter teams here at the Kennedy Space Center for the really outstanding effort they gave trying to get Endeavour ready to go for a Tuesday launch,” said Commander Scott Kelly upon arriving at the spaceport.

An earlier leak in Endeavour’s crew cabin has been fully resolved. The problem was traced to one of two positive pressure-relief valves that ensure that the cabin does not become over-pressurized. The suspect valve was removed and replaced with a valve from Atlantis. Another round of testing was successfully completed last night, with no leakage detected.

The 22nd flight to the International Space Station, STS-118 will be the first flight for Endeavour since 2002, and the first mission for Mission Specialist Barbara Morgan, the teacher-turned-astronaut whose association with NASA began more than 20 years ago.