The crew of space shuttle Endeavour, including teacher-turned-astronaut Barbara Morgan, climbed aboard Thursday in a dress rehearsal for next month's launch.

Just as they will on liftoff day, now set for Aug. 7, the seven spacesuited astronauts strapped into their seats inside the recently refurbished Endeavour. The spacecraft hasn't flown since December 2002.

After the countdown clock ticked down to four seconds, the seven astronauts climbed out in an emergency escape drill.

"It was as smooth as it could have been," NASA spokesman George Diller said. "It did exactly what the countdown dress rehearsal is supposed to do."

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The practice countdown capped three days of launch training by the crew at Kennedy Space Center. The astronauts headed back to Houston later Thursday.

Shuttle commander Scott Kelly told reporters on Wednesday that Endeavour had no major technical issues which could delay a launch.

"There are always minor things they work up through launch, but so far there is nothing that concerns me," Kelly said.

After the Columbia disaster, the three remaining shuttles were grounded for almost 2 1/2 years. During that time, Endeavour had an extensive refurbishment that is done every three to four years.

"This is the first time that all of us are together with Endeavour on the pad," Kelly told reporters.

Morgan was the back-up to teacher-in-space Christa McAuliffe, who died with six astronauts when Challenger blew apart 73 seconds into lift-off in 1986. Morgan said she was reminded that Endeavour had replaced Challenger.

She has been waiting 22 years to fly into space. She returned to teaching at an Idaho elementary school after the Challenger accident but represented the space agency as the teacher in space designee in the following years.

In 1998, NASA selected her as a full-fledged astronaut.

"I have thought of Christa and the Challenger crew," Morgan said Wednesday. "Those folks are with us and they have been with us every single day of training."