Monday, February 07, 2011

Techs will replace vent line seal

With all the focus on repairs to cracked support beams on Discovery's external tank in recent months, it was easy to forget the problem that caused the shuttle's Nov. 5 launch scrub.

But Kennedy Space Center technicians will soon be back at work on the hydrogen gas vent line that connects to the tank's mid-section, whose leaking seals have forced multiple launch scrubs since 2009.

A successful tanking test Dec. 17 appeared to show that improvements in the line's alignment had resolved the leak issue.

Managers, however, have decided as a precaution to swap out one of the seals inside the line's seven-inch quick disconnect device. An analysis determined excess pressure may have been applied to the seal when the line was last disconnected, according to a KSC spokesperson, increasing the potential for a leak.

The procedure is not expected to impact Discovery's targeted 4:50 p.m. Feb. 24 launch on an 11-day mission to the International Space Station on Discovery's final flight.

After the shuttle returned to the launch pad early Feb. 1, five contingency days were available to handle unexpected technical issues.

The line in question vents excess hydrogen to a flare stack near the launch pad so the explosive gas burns off at a safe distance while the shuttle is fueled with a half-million gallons of liquid hydrogen and liquid oxygen.

Results from leak checks performed after the vent line was reinstalled last Friday were slightly above normal levels but within allowable limits, and NASA said that was not the reason for swapping the seal.

Shuttle program managers are scheduled to hold a flight readiness review Thursday. Another review including top NASA officials is expected to follow Feb. 18, when an official launch date and time will be set.

If a Feb. 24 launch is confirmed, Discovery's six-person crew would be expected to fly into Kennedy Space Center two days later.

IMAGE: Shuttle Discovery's external fuel tank on Dec. 9, 2010, was being prepared for a tanking test at Kennedy Space Center. A newly replaced ground umbilical carrier plate (GUCP) is shown. Photo credit: NASA/Ben Smegelsky

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