NASA promises a "relentless" review over the next several weeks of a mysterious gas leak problem that has halted three of the last five space shuttle launch countdowns. "We're going to step back and figure out what the problem is and go fix it, and then we'll fly as soon as we're ready to safely go do it," said LeRoy Cain, deputy shuttle program manager.
Endeavour's planned 5:40 a.m. liftoff this morning scrubbed for the same reason as a first attempt on Saturday: hydrogen gas leaking outside the shuttle's external tank during fueling.
Cain said engineers aren't sure what is causing the problem, particularly after the repair that worked for Discovery in March failed for Endeavour this week.
"Obviously we have something here that we didn't understand as well as we thought we may have in terms of our work toward root cause," he said.
It's not clear even if the equipment problem lies with the external tank, or with the launch pad equipment that connects to it.
The leak is occurring where a vent line attaches to the tank and routes excess gas to a flare stack to be burned off.
A quick disconnect valve that hooks the line up to the tank was replaced, along with seals on either side of it, but the problem reappeared.
The size of the leak is about the size of the tip of a pen on a seven-inch diameter valve, said Pete Nickolenko, the mission's launch director. But when dealing with highly flammable hydrogen gas, it presents an unacceptable risk.
Cain said teams would review everything about the system, from the parts and materials and associated vendors to procedures for installing the vent line.
"Our sense is that something has changed, that something is different and we need to go reevaluate," he said.
Early speculation has examined misalignment of seals and the thermal effects of super-cold propellants used during fueling, temperatures not experienced during preliminary leak checks.
Another possible culprit is the process of connecting and reconnecting the vent line more than once - such as when Endeavour was moved from launch pad 39B to pad 39A.
Endeavour is now targeted to fly to the International Space Station in just over three weeks, on July 11.
The STS-127 mission is scheduled to last 16 days and include five spacewalks, with the primary goal to complete construction of Japan's science laboratory.
2 comments:
Dear James:
Has anyone talked about 'Cannibalizing' the H2 loading equipment from Pad 39B and moving it over to Pad 39A?
Perhaps that might solve the leaking H2 problem.
What do you think?
Rick Steele
Sarasota, Florida
Rick: I don't know the answer but will pose the question. They've been swapping out seals and quick disconnect valves at pad A, and I'm not sure what other equipment pad B might have that would help. They haven't filled a tank there for a long time, so pad B gear hasn't really been tested recently under those cryogenic tanking conditions. But I'm sure it's something they're talking about.
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