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      Endeavour launch date now no earlier than May 16

      Diagram: Auxiliary Power System Components

      / NASA
      Updated May 7, 2011 9:40 PMNASA managers have retargeted space shuttle Endeavour's launch to no earlier than Monday, May 16. After a meeting on Friday, they also extended the length of Endeavour's STS-134 mission to the International Space Station from 14 to 16 days. If Endeavour launches on May 16, liftoff would be at 8:56 a.m. EDT.At 3 p.m. on Monday, May 9, NASA Space Shuttle Program Launch Integration Manager Mike Moses and Shuttle Launch Director Mike Leinbach will hold a news conference at Kennedy Space Center in Florida to discuss the progress of repairs since Endeavour's launch postponement on April 29. The news conference will air live on NASA Television and online at technicians are continuing work to resolve an issue in a heater circuit associated with Endeavour's hydraulic system that resulted in the launch postponement. Technicians determined the failure was inside an aft load control assembly, which is a switchbox in the shuttle's aft compartment, and possibly its associated electrical wiring.Although the root cause of the failure in the switchbox has not been found, technicians are replacing hardware that could have caused the problem. The faulty box was changed Wednesday, and a test of nine shuttle systems powered by the new box is under way.This weekend, technicians will install and check out new wiring that bypasses the suspect electrical wiring connecting the switchbox to the heaters. They also will run the heaters for up to 30 minutes to verify they are working properly and complete retesting of the other systems powered by the switchbox.The shuttle has three Auxiliary Power Units (APUs) that provide hydraulic power to steer the vehicle during ascent and entry. The hydrazine fuel lines on each APU have two heater circuits that prevent the fuel from freezing while the shuttle is in space. NASA launch commit criteria and flight rules require all APUs and heater circuits to be operational for launch. On Endeavour's first launch attempt, one of two heaters for APU-1's fuel line did not work. Engineers confirmed the circuit in the original switchbox that directed power to the heaters was shorted out.Launch attempts are available through May 26. May 21 is the only day a launch is not an option because it would lead to a May 23 docking with the space station. May 23 is when three of the space station's Expedition 27 crew members undock and return home in their Soyuz spacecraft. Managers reviewed the STS-134 mission timeline and determined the Endeavour crew can accomplish all objectives even with the departure of the three station crew members.Updated May 4, 2011 1:40 PM CBS News is reporting that engineers inspecting a suspect electrical distribution box removed from the shuttle Endeavour after a launch scrub last week have found blown internal fusing that could be the result of an external, yet-to-be-identified short circuit somewhere in the ship's complex electrical system, officials said Wednesday. But they cautioned that troubleshooting is not yet complete and a problem with the box itself has not yet been ruled out.Hoping for the best, engineers installed a replacement aft load control assembly switching box in Endeavour's engine compartment, but initial testing has been modified to make sure the new box is not inadvertently damaged by whatever caused the presumed short Friday.Endeavour was grounded when telemetry indicated one of two redundant "strings" of fuel line heaters used by one of the ship's three hydraulic power units had not activated as required. Testing showed no obvious problems upstream of an aft load control assembly switching unit that routes power to the system and no obvious problems with the downstream heaters or thermostats.On Saturday, engineers decided to replace ALCA No. 2 on the assumption that something had failed inside the box, preventing power from reaching the heaters. The box was removed from avionics bay No. 5 in Endeavour's engine compartment Monday, clearing the way for installation of a replacement.The ALCA is one of three in the aft compartment that routes power to nine critical subsystems, including the hydraulic system, from three major circuits, or buses.On the assumption a fault would be found in the suspect power box, NASA managers said Monday Endeavour's launch would be on hold until at least May 10 to give engineers time to install the replacement ALCA, retest downstream systems and to ready the shuttle for another three-day countdown.If additional testing confirms an external short -- and if engineers are not able to quickly find and fix whatever might have caused it -- launch likely will face an additional delay. Endeavour's current launch window extends through May 29. The next available window opens June 19 based on temperature constraints related to the space station's orbit.Only two fights remain on NASA's shuttle manifest, Endeavour's mission and a final flight by the shuttle Atlantis that is currently scheduled for launch June 28. Endeavour's launch delay likely will trigger a slip for Atlantis, but managers have not yet made any official changes.Updated May 4, 2011 12:01 PMTeams on NASA Kennedy Space Center TMs Launch Pad 39A are installing a new power distribution box called a Load Control Assembly-2 (LCA-2) into space shuttle Endeavour.The LCA-2 distributes power to nine various shuttle systems, including heaters on a fuel line for Endeavour's auxiliary power unit-1 (APU-1). The heaters did not work on April 29, prompting the launch team to scrub Endeavour TMs first launch attempt for its STS-134 mission to the International Space Station.After the new LCA-2 is installed, technicians will begin testing it and its power distribution system. Managers will continue to evaluate the repair process and make any additional adjustments before scheduling Endeavour TMs next launch attempt, which remains no earlier than May 10.At NASA's Johnson Space Center in Houston, the STS-134 crew is conducting tag ups today in crew quarters with their Flight Directors and Robotics and Spacewalk Officers.Original StoryWell Endeavour has been removed from her 72 hour scrub turnaround timeline " following the decision to cancel the attempt to launch on Monday, I decided that as much as I would love to stay in Florida to wait it out it would better if I waited it out here. Besides NASA engineers at Pad 39A have been configuring the stack for an extended stay ahead of the next Launch Countdown for STS-134.If you haven TMt yet heard, Friday's launch attempt was scuttled by a bad fuse box aboard the shuttle Endeavour. NASA managers have internally refined Endeavour TMs troubleshooting schedule on Monday, placing STS-134 on a NET (No Earlier Than) launch date of May 10.The schedule continues to be provisional, as engineers continue to work on replacing the Aft Load Control Assembly the likely cause of the Axillary Power Unit TMs 1 heater failure during Friday TMs countdown.This Load Control Assembly box was removed last night. Teams are evaluating data from inspections and will install a new LCA-2 after evaluations and any repairs, if needed, have been made.But still the earliest Endeavour could be launched on the STS-134 mission is Tuesday, May 10.Right now the plan is for managers to reconvene Friday to determine a more definite launch date after the box is removed, replaced and the retest of systems has been completed.The STS-134 crew was in the motion base simulator this morning, conducting refresher ascent and entry simulations prior to their planned return to Kennedy later this week for the second launch attempt.