Shuttle at pad for planned June launch

CAPE CANAVERAL, Florida (Reuters) - Space shuttle Atlantis returned to its Kennedy Space Center launch pad on Tuesday ahead of a planned June 8 liftoff for the International Space Station.

Atlantis had been due to take off on its construction mission to the space station in March, but a storm a month earlier peppered the shuttle and its fuel tank with hail as they were perched on their seaside launch pad.

Repair work on more than 4,200 areas where hailstones gouged holes in the tank's foam insulation stole valuable time from a tight schedule to finish building the space station before the shuttles -- which are required for assembly of the orbital outpost -- are retired in 2010.

The repairs were complex, and at times unprecedented, with workers temporarily transplanting themselves from the shuttle tank manufacturing facility outside New Orleans to the Florida spaceport to tackle the delicate task of hand-spraying insulation around the top of the massive tank.

The insulation is needed to prevent ice from forming after the shuttle is filled with cryogenic oxygen and hydrogen, which power the ship's main engines for liftoff.

The ice could break off and damage the ship as it climbs toward space.

The foam itself became a serious debris concern after the 2003 Columbia disaster, which killed seven astronauts. A flyaway piece of tank foam fell off Columbia during launch and broke a hole in the spaceship's heat shield. Hot gases snaked into the breach as the shuttle tore through the atmosphere for landing 16 days later, causing it to break apart over Texas.

Instead of being a uniform orange color, Atlantis's fuel tank now has a patchwork of white spots. But NASA managers are confident it is as safe to fly as any of the other tanks redesigned twice after the accident. There have been four shuttle launches since the Columbia accident.

Barring additional problems or lengthy weather-related delays, the agency hopes to dispatch four missions to the space station this year, including a flight to deliver and install the European Space Agency's research laboratory, Columbus.