posted 09-06-2006 03:18 AM               

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SCRUB! Today's launch attempt has been stopped by the fuel cell problem. Another try could come as early as Thursday, with a target liftoff time of 12:03 p.m. EDT.

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When the launch crews started to activate the fuel cells last evening, they got a voltage drop in fuel cell No. 1. That indicates that the unit is not operating properly. Engineers started troubleshooting. The MMT, convening at 1:45 a.m., decided to hold fuel loading operations until they could resolve the problem.

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Engineers are continuing to troubleshoot the issue in hopes of getting Atlantis off the ground Thursday or Friday, the end of the current launch window. But if the powerplant has to be replaced, NASA could be forced to haul Atlantis back to its hangar for repairs, a move that would delay launch several weeks.

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posted 09-06-2006 08:26 AM               

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The suspect fuel cell that prompted NASA to scrub today's Atlantis launch is not believed to have failed. NASA believes the problem lies with an associated freon coolant loop, which prevents the electricity-generating device from overheating.

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posted 09-06-2006 04:23 PM               

Mission managers will hold another meeting Thursday at 1 p.m. EDT to assess the issue. There will be a news conference on NASA Television at the conclusion of that meeting. If the team decides to "go" for launch Friday, lift-off would be at 11:41 a.m. EDT.

Tuesday night as ground teams were preparing for Atlantis' scheduled launch Wednesday, a voltage spike in the motor of Atlantis' fuel cell #1 coolant pump was observed during the activation of the shuttle's three fuel cells. The coolant pump flows Freon through the fuel cell to prevent it from overheating during flights.

During Atlantis' mission, STS-115, astronauts will deliver and install a girder-like structure, known as the P3/P4 truss, aboard the station. The 35,000-pound piece includes a set of giant solar arrays, batteries and associated electronics. The arrays eventually will double the station's power capability.

Atlantis' crew, Commander Brent Jett, Pilot Chris Ferguson and mission specialists Dan Burbank, Heide Stefanyshyn-Piper, Joe Tanner and Steve MacLean, a Canadian Space Agency astronaut, will remain at Kennedy Space Center while the fuel cell evaluation continues.