Battered by an intense hail storm six days earlier, space shuttle Atlantis retreated off launch pad 39A and returned to the cavernous Vehicle Assembly Building on Sunday to undergo thorough inspections and repairs.

Atlantis rolls back from pad 39A. Photo credit: Justin Ray/Spaceflight Now

Perched atop a mobile launching platform, the shuttle was hauled three-and-a-half miles back to the 52-story building by an Apollo-era transporter. The trip began at 8:47 a.m. and was considered complete at 5:49 p.m. EST when the platform was placed on pedestals in the VAB.

Crews immediately began work to place access platforms around the shuttle for an upclose examination of the hail strikes. The methods for fixing the pitted insulating foam on the external fuel tank and the time needed to carry out such work will be determined in the coming days.

A severe storm swept over pad 39A around 5 p.m. Monday and dropped hail the size of golf balls, causing thousands of chips and divots in the orange foam covering the tank.

The heatshield on the orbiter's left wing also experienced wind-blown hail impacts. Initial examinations at the pad revealed more than two dozen of the ship's black tiles sustained surface damage.

"This constitutes, in our evaluation, the worst damage that we have ever seen from hail on the external tank foam," said Wayne Hale, the shuttle program manager. "We have had hail a number of times in the past, hail is not unusual in Florida. ... But usually the hail is quite small and rarely causes damage.

"This was large, wind-driven, damaging hail. It is very clear a number of these areas need to be repaired."

The lack of adequate access to the widespread damage at the launch pad meant NASA had no choice but return the shuttle to the Vehicle Assembly Building.

Atlantis heads into the VAB. Photo credit: Justin Ray/Spaceflight Now

Atlantis had been slated for launch just before sunrise March 15 to deliver and install a 17.5-ton power truss module at the International Space Station. But the trip back to the VAB will cause the shuttle to miss its window to fly before previously-scheduled Russian Soyuz spacecraft traffic at the station.

A Russian Soyuz capsule with the Expedition 15 long-duration resident crew is scheduled for blastoff from Kazakhstan on April 7. The outgoing Expedition 14 crew returns to Earth aboard its Soyuz on April 19.

Since station controllers require at least a few days between the departure of one craft and the arrival of the next, Atlantis won't launch before late April. An official target launch date has not been established.

Rollbacks have been relatively rare occurrences over the life of the shuttle program. NASA said that Sunday's move was the 18th since 1983, with the majority caused by technical problems. A handful were prompted due to the threat of tropical weather and hurricanes.

Two previous rollbacks were required to repair external tank foam. Woodpeckers drilled nearly 200 holes on the tank for shuttle Discovery's STS-70 mission in 1995 and hail caused damage before Discovery's STS-96 flight in 1999.

A complete list of rollbacks is available here.

Additional coverage for subscribers:
VIDEO: TIME-LAPSE MOVIE FROM SUNDAY'S ROLLBACK PLAY
VIDEO: NASA BRIEFING ON LAUNCH DELAY AND ROLLBACK PLANS PLAY
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