Wednesday, May 11, 2011

Tests On Spare Shuttle Switching Box Complete

NASA is pressing ahead with preparations to pick up a second Endeavour launch countdown after finishing up all retesting on a spare power switching box installed after hydraulic power unit heater failures prompted an April 29 launch scrub.

Mission commander Mark Kelly and five crewmates, meanwhile, are taking part in a review of procedures for the final four spacewalks planned during the 30-year-old shuttle program. The astronauts will fly to KSC early Thursday. Their ETA: 9 a.m. You can watch the arrival live here in The Flame Trench. Click the NASA TV box on the right side of the page to launch our NASA TV viewer and live coverage.

NASA contractor technicians installed the spare power switching box in the aft engine compartment of Endeavour after two Auxiliary Power Unit heaters failed during countdown to an April 29 launch. NASA engineers thought a short within the original power switching box might have prevented power from reaching the heaters. The heaters keep hydrazine lines at the proper temperature in orbit. A frozen power line could cause a flammable hydrazine leak.

The power switching box routes electricity to nine critical shuttle systems, including the solid rocket boosters, main engines and life support systems. So a good deal of testing had to be performed after the box swap to make sure the spare is routing electricity to each of the nine systems. That work started last week and was completed late Tuesday.

Endeavour's launch now is scheduled for 8:56 a.m. Monday. A three-day countdown is slated to pick up at 7 a.m. Friday. External tank propellant-loading operations are scheduled to begin at 11:36 p.m. Sunday.

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