Wet tiles put damper on shuttle launch

The space shuttle Atlantis after landing February 20 at Edwards

(CNN) -- Soggy tiles are delaying the launch of the space shuttle Atlantis.

The shuttle was scheduled to go up on June 14, but now will launch no earlier than June 20, according to NASA spokesman James Hartsfield.

"We're drying out tiles that still have some moisture in them," Hartsfield told CNN.com on Thursday. He said dozens of heat lamps are being used to bake the moisture out of the tiles.

Atlantis was caught in a rare desert downpour after landing at Edwards Air Force Base in the Mojave Desert on February 20. Shuttles often are rained on while sitting on the launch pad in Florida, but waterproofing protects the tiles.

The waterproofing burns off during the shuttle's fiery re-entry into Earth's atmosphere, Hartsfield said, leaving the tile-encrusted spacecraft vulnerable to the elements after landing.

Shuttle technicians already dried the tiles once and added waterproofing, but subsequent testing in the last couple of days indicated about 500 of the orbiter's 22,000 heat protection tiles still are damp, according to Hartsfield.

"It's taking us a little longer," he said.

Water on the tiles could freeze as the shuttle reaches orbit, and could cause the tiles to come off.

"For safety we want every tile as dry it can be," Hartsfield said.

The tiles shield the shuttle from the 3000-degree Fahrenheit temperatures the orbiter encounters as it passes through Earth's atmosphere to land.

Atlantis currently is in the orbiter processing facility at Kennedy Space Center. It will be moved to the Vehicle Assembly Building for mating with its solid rocket boosters and external fuel tank in about a week.

When the shuttle goes up, it will carry a crew of five to deliver a new U.S.-built airlock to international space station Alpha. The airlock will allow the space station crew to conduct spacewalks. Construction and work on the space station now is done by crewmembers operating out of docked space shuttles.

The space station currently is staffed by Russian commander Yury Usachev and U.S. astronauts Jim Voss and Susan Helms.

On June 8, Usachev and Voss will do an "internal spacewalk." The pair will work inside the space station, but with the hatch open. They will move a docking mechanism in the Zvezda module to prepare for the arrival of a Russian docking module later this summer.