Updated at 5:19 p.m. ET (2119 GMT)
"We simply ran out of time," said NASA spokesperson George Diller here at KSC of the tasks needed to prepare the orbiter for its wayward journey.
Endeavour and its seven-astronaut crew are now set to launch Wednesday, Aug. 8 at about 6:36 p.m. ET (2236 GMT) on NASA's STS-118 mission to continue assembly of the International Space Station (ISS).
Shortly after the crew arrived at KSC via a private jet today, crew commander and veteran spaceflyer Scott Kelly approved of the delay from the tarmac.
"We understand the decision to delay until Wednesday, and we agree with it completely," Kelly said on behalf of the entire crew.
A series of time-consuming preparation tasks contributed to postponing the mission, Diller said.
Technicians spent this week tracking a crew cabin leak aboard Endeavour. The problem was eventually traced to a pressure-releasing valve in the crew's cabin, which allows excess air to vent from the shuttle to prevent over-pressurization. The faulty valve, however, let off too much air during the tests.
"We assumed we had leak test equipment problems, but the more we tested it in other ways, we found that we really did have a leak," Diller said.
By Friday morning, shuttle engineers had repaired and successfully retested the leak, but making the fix cost NASA precious time leading up to the original Tuesday launch window.
With extra time to go over Endeavour with a fine-toothed comb this weekend, officials are confident they can launch the shuttle on Wednesday. Following liftoff, the shuttle and its seven-astronaut STS-118 crew are expected to dock at the orbital laboratory two days later.
Once there, Endeavour's crew will deliver a fresh load of cargo, spare parts and a new starboard-side piece of the ISS during an 11-to-14-day mission.
The flight also marks the first launch for teacher-turned-astronaut Barbara Morgan, who first joined NASA's ranks in 1985 as the backup for Teacher in Space Christa McAuliffe. McAuliffe and six NASA astronauts died in January 1986 when their space shuttle Challenger broke apart just after launch.
"I thank … my colleagues in education all across the country," Morgan said of her opportunity to become an astronaut.
- VIDEO: Teaching the Future: Teacher-Astronaut Barbara Morgan
- Complete Space Shuttle Mission Coverage
- IMAGES: NASA's STS-117 Shuttle Mission in Pictures