NASA engineers think they have pinpointed the cause of dangerous hydrogen leaks that prompted back-to-back launch scrubs for shuttle Endeavour and aim to conduct a fuel-loading test to prove it by the first of July.
Shuttle program managers, meanwhile, say they believe the problem can be repaired in time to proceed with a launch attempt tentatively scheduled on July 11.
"They have good confidence that they know what the problem is and how they can fix it," Kennedy Space Center spokeswoman Candrea Thomas said today.
But Endeavour and its seven astronauts would have to launch no later than July 14 to get to the International Space Station and complete a complex assembly mission before the arrival of a robotic Russian space freighter carrying critical supplies.
A delay past July 14 would push the launch to no earlier than July 27 and have a significant ripple effect on an International Space Station assembly mission set for launch on Discovery on Aug. 18.
"Obviously there would be a downstream impact," said KSC spokesman Allard Beutel.
Significant leaks of gaseous hydrogen from a line that vents the substance from the shuttle's external tank prompted NASA to scrub a June 13 launch attempt as well as a second try last Wednesday.
Some cryogenic liquid hydrogen, which is Minus 423 degrees Fahrenheit, always "boils off" -- or changes to a gaseous state -- during propellant-loading operations. The vent line maintains proper pressure levels within the tank by carrying excess gaseous hydrogen to a flare stack about 1,000 feet away from the shuttle. There, the highly flammable substance is safely burned off.
Thomas said engineers believe a slight misalignment between the line and a carrier plate that connects it to the external tank is causing an internal Teflon seal to pull out of place, creating a leak path for the gaseous hydrogen.
Engineers think technicians can fix the misalignment and install an alternative seal that would provide a tighter fit and stop the leak.
Technicians this weekend are taking exact measurements of the misalignment. Next week they will disassemble the vent line, the carrier plate and a quick disconnect valve that enables the line to separate from the tank at liftoff.
The go-forward plan then calls for technicians to try to correct the misalignment and install an alternative seal before a tanking test that is to be staged right around the end of the month.
Engineers will load more than 500,000 gallons of supercold liquid hydrogen and liquid oxygen into the shuttle's 15-story external tank.
Leak rates will be measured and if they are within engineering specification, then NASA would press ahead with plans to get back into a countdown posture and make another launch attempt on July 11.
"It's a confidence test," Beutel said.
The launch-scrubbing leaks on Endeavour were near-identical to one that caused a delay for a Discovery mission in March. A seal-swap enabled NASA to load Discovery's external tank and proceed with a mission to deliver a fourth and final set of massive American solar wings to the station.
A Russian Progress cargo carrier is slated for launch July 24 on a critical station resupply mission. The unmanned freighter can loiter in orbit for five days but must dock at the orbiting outpost no later than July 29.
Endeavour consequently must launch by July 14 to complete a 16-day mission and depart the station before the Russian resupply ship arrives.
Seven astronauts aboard Endeavour plan to deliver the third and final section of the $1 billion Japanese Kibo science research facility to the station.
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