Live at KSC: Preps continue for tanking test

Kennedy Space Center workers are preparing for an 8:30 p.m. call to stations in advance of a crucial space shuttle fueling test Wednesday morning.

The outcome of the test could determine whether shuttle Endeavour can proceed with a planned July 11 launch or else face a lengthy mission delay.

Starting at 7 a.m. Wednesday, NASA will fill the shuttle's orange external fuel tank with more than 500,000 gallons of liquid hydrogen and liquid oxygen, hoping to avoid the kind of gas leak that scrubbed two Endeavour launch attempts earlier this month.

Engineers determined that the plate where a seven-inch vent line attaches to the tank was slightly misaligned, allowing a tiny but dangerous leak of highly flammable hydrogen gas outside the tank.

New two-piece Teflon seals were installed in the plate at launch pad 39A on Friday. On Sunday, workers reconnected the vent line and a quick disconnect valve to the tank, adding washers intended to keep the line from twisting when an explosive bolt is tightened in place.

Today's tasks include final tightening of vent line bolts and leak checks using helium at ambient temperature.

The vent line routes hydrogen gas boiling off inside the tank to a flare stack near the launch pad so it burns safely and maintains proper pressure in the tank.

The bolt explodes as the shuttle lifts off, allowing the vent line to fall out of the way.

After the test Wednesday, NASA managers plan to hold a press conference around 1 p.m. to discuss the results. You'll be able to watch the test and the press conference live here.

Endeavour had planned to launch June 13 when the first leak sprang during fueling. It was similar to a leak that stalled Discovery's first launch attempt in March.

But the replacement of seals that worked for Discovery was unsuccessful when Endeavour tried to refuel on June 17.

If the tanking test fails, NASA would swap Endeavour's tank for another one, requiring the shuttle to roll back to the Vehicle Assembly Building and a delay of weeks.

For now, Endeavour's planned 16-day mission to the International Space Station is targeted to launch July 11. The mission will complete assembly of Japan's Kibo science lab complex.

IMAGE NOTE: Above is a live video feed from launch pad 39A at Kennedy Space Center that automatically refreshes every 30 seconds. It shows the gaseous hydrogen vent line connected to shuttle Endeavour's external tank that workers are preparing for a tanking test Wednesday morning. Last Wednesday, a worker removed the seal from the Ground Umbilical Carrier Plate, or GUCP, on the external tank. A hydrogen leak at the location during tanking for the STS-127 mission caused the launch attempts to be scrubbed on June 13 and June 17. The GUCP is the overboard vent to the pad and the flame stack where the vented hydrogen is burned off. Endeavour's next launch attempt is targeted for July 11 at 7:39 p.m. EDT. Photo credit: NASA/Jack Pfaller