Shuttle Discovery's launch pad at Kennedy Space Center will reeopen this afternoon and NASA managers will meet late today to set a course of action for troubleshooting work the agency hopes will lead to a launch attempt Sunday.
The U.S. Air Force and United Launch Alliance, meanwhile, are continuing to step toward an already scheduled Saturday night launch of an Atlas V rocket with a new-generation military communications satellite.
But ULA is willing to forego their launch opportunity Saturday if NASA can put itself in position to pick up a countdown and try to send up Discovery and seven astronauts at 7:43 p.m. Sunday.
"We're pressing ahead with preparations to launch on Saturday. But there's not a national imperative that we launch on that day, so we can adjust," said ULA spokesman Mike Rein.
As it stands, an Atlas V and its payload -- a Wideband Global SATCOM spacecraft -- are scheduled to blast off from Launch Complex 41 at Cape Canaveral Air Force Station at 9:25 p.m. Saturday. The launch window that night will extend until 10:03 p.m.
NASA is facing a Tuesday deadline to launch Discovery. After that, the agency would have to stand down for an already scheduled crew rotation and change-of-command at the International Space Station. In that case, the Discovery launch would be pushed back to about April 7.
If NASA presses ahead with a launch attempt Sunday, then the Atlas launch would be postponed until the middle of next week.
The reason: It typically takes about 48 hours to reset Eastern Range tracking and range safety systems between the launches of different vehicles flying different flight profiles. Range users typically are allowed a back-up launch date in case weather or a minor technical problem prompts a scrub.
So NASA would be allotted launch attempts on Sunday and Monday, and in this case, the agency probably would be given an opportunity on Tuesday if need be. The earliest the Atlas could launch then would be next Wednesday or Thursday.
An initial attempt to launch Discovery on Wednesday was scrapped when a gaseous hydrogen leak was detected near the end of fuel-loading operations.
The leak was traced to a quick-disconnect valve that links a gaseous hydrogen vent line with the shuttle's external tank. The vent line is designed to route excess gaseous hydrogen from the liquid hydrogen tank within the ET to a flare stack in the pad 39A area. The flare stack burns off the hydrogen.
NASA drained the external tank Wednesday and the pad will be reopened about 3 p.m. this afternoon. Technicians with United Space Alliance then will extend a work platform from the Fixed Service Structure at the pad to the area where the leaking gaseous hydrogen line connects to the tank's Gaseous Umbilical Carrier Plate. The suspect quick-disconnect valve links the gaseous hydrogen line and the carrier plate. Scaffolding then will have to be built up on the extended work platform to emable technicians to reach the valve.
The general plan calls for technicians to remove the valve so that it can be inspected. Of paricular interest will be two seals within the valve. The seals might be the source of the leak. Or the quick-disconnect valve might be misaligned.
NASA mission managers will meet at 4 p.m. to go over a more refined troubleshooting plan. Once the plan is okayed, then the technicians will begin the troubleshooting work. NASA will reveiew the results of the troubleshooting work and decide Friday whether to press ahead with a launch attempt Sunday.
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