Launch pad 39A this morning is clear of all but essential personnel as workers begin pressurizing propellant tanks inside Endeavour, four days before the shuttle's scheduled launch at 7:55 p.m. Friday.
The tanks hold pressurized helium and nitrogen that help push fuel through the shuttle's main propulsion system, twin maneuvering engines and 44 nose and tail steering thrusters.
The risk of the tanks - called Composite Overwrap Pressure Vessels - rupturing places workers at risk of injury from shrapnel or a fire, so the pad is closed to tours or any unnecessary work.
Managed from the Launch Control Center next to the Vehicle Assembly Building, the pressurization is done in two stages, first to 80 percent and later 100 percent.
NASA will hold its first countdown status briefing at 10 a.m. Tuesday, featuring NASA Test Director Jeff Spaulding, STS-126 Payload Manager Joe Delai and shuttle weather officer Kathy Winters.
You can watch live NASA TV coverage of the briefing here at The Flame Trench, along with the Endeavour crew's arrival at Kennedy Space Center around 4 p.m. Tuesday.
Also today, workers in the assembly building began disconnecting Atlantis from its solid rocket boosters and external tank.
Atlantis was scheduled to launch Oct. 14 on the fifth and final mission to service the Hubble Space Telescope. But the mission was postponed when observatory computers failed in late September.
Once it was determined that backup parts would not be ready in time for a February launch, NASA decided to return Atlantis to its hangar and place Discovery on its mobile launcher platform stack.
Discovery is targeted for a mid-February launch to the International Space Station to delivery a final set of solar wings.
IMAGE NOTE: At left, a Kennedy Space Center camera shows shuttle Endeavour on launch pad 39A. You can click on the image at right to launch a NASA TV viewer. The Flame Trench will be showing live NASA TV coverage of STS-126 briefings starting Tuesday at 10 a.m.
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