The hail-damaged space shuttle Atlantis on Sunday began a slow trek from the launch pad back to a hangar so technicians can inspect the impact of a hail storm and determine what kind of repairs should be made.

The 3.4-mile journey aboard the massive crawler-transporter started at 8:47 a.m. EST and was expected to last about seven hours.

It was the 17th time in the 26-year-old shuttle program that one of the vehicles had to be moved back to the Vehicle Assembly Building from the launch pad.

Last week's hail storm caused thousands of dings in the insulating foam covering Atlantis' external fuel tank and forced NASA to postpone the space shuttle's launch from March 15 to at least late April.

• Click here to visit FOXNews.com's Space Center.

Once Atlantis is back inside, technicians will be able to assess whether the repairs to the tank can be made at the Kennedy Space Center or if the tank needs to be shipped back to its manufacturer near New Orleans, which likely would push back the launch to June.

The insulating foam is of special concern to NASA since a chunk of it flew off during space shuttle Columbia's launch in 2003 and struck the orbiter. The damage allowed fiery gases to penetrate Columbia during re-entry, breaking up the craft and killing its seven astronauts.

NASA redesigned the external tank, removing large amounts of foam, before last year's three successful shuttle missions. The space agency plans another design change to the tank before the shuttle program ends in 2010.

NASA managers still hope to fly five shuttle missions in 2007, the most ambitious schedule in five years. Atlantis' flight is set to be the first of the year.