KENNEDY SPACE CENTER, FL - NASA was forced to scrub today's launch of space shuttle Endeavour due to a leak of gaseous hydrogen in the umbilical system that vents the flammable gas away from the shuttle on the launch pad. Mission managers will meet this weekend to discuss repairs to the system and set a new launch date which will be no earlier than the June 17.
VIDEO: JUNE 13 POST-SCRUB PRESS CONFERENCE The leak was almost identical to one that occurred two launches ago on STS-119, in the same location and was detected at almost the same time as the previous leak. After the leak was detected, the launch team began draining the external fuel tank at 12:06 a.m. EDT before a launch scrub was officially called at 12:26. Launch officials described the leak as "significant" and something they wouldn't be comfortable launching Endeavour with under any circumstances. "Hydrogen is a commodity you just don't mess with," said NASA Launch Director Mike Leinbach. The leak was detected near the end of the three-hour fueling operation that began at 9:52 p.m. as engineers cycled a vent valve on the liquid hydrogen tank. Just as happened during the STS-119 countdown, the leak cropped up near the Ground Umbilical Carrier Plate where the external side of the vent valve assembly connects with its counterpart on the external tank side. "We got into tanking on time," said NASA Launch Director Mike Leinbach at a post-scrub press conference. "Everything was going perfectly fine, per plan. But, just like on the STS-119 mission, we suffered a leak at the Ground Umbilical Carrier Plate just as soon as we got into the topping part of the sequence on the hydrogen load." As the shuttle sits on the launch pad in the relatively warm air, some of the hydrogen boils off and is released through a vent on the tank and to a ground support a line that routes the gas to a flare stack away from the launch pad where it is harmlessly burned off. "The signature was almost identical to what we had two flows ago," Leinbach said. "The guys on console cycled the valve as they did previously. They cycled the valve four times trying to clear up that leak. In the past, every now and then that'll work for us. This time, again, it didn't work for us. We were out of spec leakage at that disconnect." After the tank was drained, it has to sit for 24 hours and outgas any residual propellants before technicians will be able to get inside and troubleshoot the leak. It will be Sunday morning before workers are able to enter the tank. NASA's current plan calls for replacing what engineers suspect is a leaky seal in the valve. Then the vent line will be re-attached to the external tank and tested for any misalignment between the two sides. If everything checks out, the launch team could then pick up the countdown on Monday for a Wednesday liftoff. However, NASA still doesn't know the root cause for the leak. After the incident on STS-119, subsequent inspection didn't reveal any smoking gun and the replacement hardware worked perfectly. It also performed as expected during Atlantis' launch on STS-125 last month with the same ground support equipment as on this launch. Without root cause, or fix, NASA's only option is to replace all the hardware, fuel up the vehicle and hope the leak doesn't re-occur. "Our plan is going to be pretty much what it was last time, which is just R & R that seal and then we really haveto tank again to see what happens," said Leinbach. If all that work goes well, NASA could launch Endeavour as early as next Wednesday. However, that date is already booked on the Air Force's Eastern Range for the launch of the Lunar Reconnaissance Orbiter spacecraft. It takes 24 hours for the Air Force to reconfigure tracking stations and other range assets to support another launch and NASA previously said that the shuttle would stand down and defer to the LRO launch, on an Atlas 5 rocket, if teh shuttle isn't off the ground by Monday. "Obviously, the 17th is a range problem, there's a conflict out there with LRO/LCROSS," said Shuttle Integration Manager Mike Moses. "We'll start those negotiations tomorrow and see where we get both with the range and with the NASA payload. "We had pretty much agreed ahead of time that we would probably not bump them off the range, but it would all depend on why we needed to scrub in the first place. We didn't really talk about a failure like this. We were mostly thinking weather. So we'll go and re-talk again. But I don't expect that we'll make them go away and we'll take that whole window." The lunar spacecraft faces a challenging launch window. Because of the precise trajectory required to rendezvous with the Moon, it can only launch during a four day period every two weeks. If Endeavour launches on Wednesday, that would leave only two days for LRO to launch before waiting two weeks. "They only have a four-day window," said Moses. "It's a lunar rendezvous, so they have those four days and if they don't make that they have to wait two weeks before they could go again." NASA faces pressure to launch LRO because United Launch Alliance, the company that makes the Atlas 5, has several more Atlas clients backed up waiting for the already-delayed LRO probe to launch. If LRO goes as scheduled, NASA will have only one day, the 20th, to launch Endeavour before facing a delay until July 11 due to the station's solar beta cutout angle which precludes shuttle launch and docking with the station between June 21 and July 10. (The Spacearium / Space Media Corporation)
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