CAPE CANAVERAL — SpaceX's first demonstration flight for NASA has been delayed to at least Wednesday, as engineers evaluate cracks in a Falcon 9 rocket's upper-stage engine nozzle.

The company initially thought the launch from Cape Canaveral Air Force Station would occur no earlier than Thursday, with a possible slip to Friday or Saturday if the nozzle needed replacing.

SpaceX President Gwynne Shotwell said a review of vehicle closeout photos early Monday spotted "porosity and potential cracking" on a nozzle weld joint.

"We wanted to take some additional steps, certainly, to go ahead and actually look at it," she said during a pre-launch news conference Monday at Kennedy Space Center.

The company later confirmed two small cracks near the end of the nozzle and said the launch would be no sooner than Wednesday while it evaluated options.

SpaceX engineers said the cracks were in a thin, low-stress area that would not cause a flight to fail but must be studied further to ensure there isn't a more serious problem.

The nozzle could be trimmed to remove the cracked area, which helps provide a level of efficiency not required for the upcoming mission

SpaceX is preparing to launch an important demonstration flight, the first of several under a NASA program developing commercial vehicles to deliver cargo to the International Space Station after the shuttle is retired.

The flight will be the first by an active Dragon capsule and the second by a Falcon 9 rocket.

The mission plans to test the Dragon's systems in space for nearly two orbits as it flies 186 miles above Earth. The capsule is scheduled to re-enter the atmosphere and splash down in the Pacific Ocean more than three hours after launch.

Liftoff from Cape Canaveral Air Force Station had been planned for between 9:03 a.m. and 12:22 p.m. today.

The launch window would be the same Wednesday or Thursday, when the forecast improves from a 40 percent chance of favorable weather to a 90 percent chance.

At Launch Complex 40 on Monday, SpaceX teams lowered the 157-foot rocket to a horizontal position for inspections, then raised it again to test engine steering systems. Workers in the afternoon could be seen examining the upper-stage area from a basket hoisted by a crane.

A single Merlin engine with a nine-foot nozzle powers the rocket's upper stage. It is scheduled to light roughly three minutes into flight and burn for nearly six minutes before the Dragon separates.

The rocket on Saturday completed a short test firing of nine first-stage engines on the third attempt.