NASA Unveils Discovery At Kennedy Space Center Launch Pad

NASA unveiled shuttle Discovery at its Kennedy Space Center launch pad today as countdown clocks ticked toward a predawn liftoff early Monday.

The 18-story shuttle and its seven-member crew are scheduled to blast off from launch pad 39A at 6:21 a.m. -- the middle of a 10-minute window to put the spaceship on course for a two-day trip to the International Space Station.

Air Force meteorologists say there is an 80 percent chance the weather will be good enough to give Discovery and its crew a green light for flight.

Forecasters say there is a slight concern that moisture building in the atmosphere might yield early-morning fog, conditions could create low visibility and a violation to launch rules.

Range safety officers must be able to see the shuttle during the critical early parts of flight, and a mission commander also must be able to eyeball the shuttle runway on final approach in the event a systems failure forces an unprecedented emergency landing attempt after launch.

The weather on Tuesday is expected to be about the same. On Wednesday, there chance of a low cloud ceiling is expected to increase, so there is a 70 percent chances conditions would be good enough to proceed with launch that day.

The massive Rotating Service Structure at the launch pad was backed away from the shuttle at the pad earlier today, a key milestone in preparations for propellant-loading operations.

The RSS provides protected access to the orbiter for installation and servicing of payloads at the pad, as well as servicing access to certain systems on the orbiter. Discovery's payload was hauled out to the pad in a large canister that was hoisted into the payload changeout room within the RSS and ultimately into the cargo bay of the spaceship.

A NASA primer on the RSS says the structure is 102 feet long, 50 feet wide, and 130 feet high. It is supported by a rotating bridge that pivots about a vertical axis on the west side of the pad's flame trench.

The structure rotates through 120 degrees -- one third of a circle -- on a radius of 160 feet. Its hinged column rests on the pad surface and is braced against the fixed service structure.

You can click to enlarge any in this series of NASA TV screen grabs that show the RSS as it was backed away from Discovery just after 9:30 a.m. The move took less than a half-hour to complete.

You can watch live launch coverage here in The Flame Trench and at both www.floridatoday.com and www.usatoday.com.