Space Shuttle Atlantis is slated to roll out today from the vehicle assembly building for a four-mile journey to Launch Pad 39-B, NASA announced.

The fully assembled space shuttle vehicle, consisting of the orbiter, external tank and twin solid rocket boosters, mounted on a mobile launcher platform, is to be delivered to the pad via a crawler transporter in a six-hour process.

Atlantis will launch in a window beginning Aug. 28 and extending into early September, set to blast off for a mission lasting 11 days..

The shuttle, will carry components to be attached to the International Space Station (ISS), including more solar arrays to boost electrical power for the artificial moon.

ISS will grow in size as further construction work occurs in an ambitious series of 16 space shuttle flights over four year.

There is no room for slipups or delays in the tight flight schedule, and NASA leaders are hoping each shuttle mission goes as well as the most recent flight.

On July 4, Space Shuttle Discovery lifted off for a 12-day mission that was extended to 13 days.

Pre-launch apprehension about the safety of the Discovery flight turned to elation when the shuttle survived the launch unharmed.

It was the second shuttle mission since the fatal flight of Space Shuttle Columbia. A hefty chunk of foam insulation ripped loose from the Columbia external fuel tank and hit the leading edge of a wing on the orbiter.

That opened a hole that, during later reentry, permitted the blazing hot gases of reentry to blast inside the Columbia wing, causing structural failure. The Columbia orbiter vehicle disintegrated in a blazing streak across the sky, and the crew was lost on Feb. 1, 2003.

While changes were made to the Discovery fuel tank and foam insulation application, two senior NASA officers recommended against permitting Discovery to fly, fearing it might still be damaged during liftoff.

But the Discovery flight was picture-perfect, and after the shuttle orbiter safely touched down in Florida, NASA Administrator Michael Griffin said he never saw such a clean, undamaged orbiter post-flight.

What foam insulation broke free from the tank was in tiny bits, and occurred too late in the flight to pose a major danger.

The question for the Atlantis flight: will this mission go as well, with no major foam insulation loss, and no damage to the orbiter?

Before the Atlantis flight, there will be action beginning Thursday by the ISS crew.

This will be extravehicular activity (EVA), or spacewalks, to activate an external cooling system, and perform other work on the ISS to facilitate its continued operation and construction. Multiple component installations will be performed, with two astronauts acting as a construction crew. In some cases, failed units will be replaced with new gear.