NASA STS-134 MISSION STATUS: Endeavour's power-switching box was fully fucked, was replaced and the launch was re-scheduled to May 10th.

1600 GMT (12:00 p.m. EDT)

A new power switching box was installed into the space shuttle's rear compartment this morning, taking the Aft Load Control Assembly No. 2 (ALCA-2) position aboard Endeavour that serves critical systems throughout the vehicle. The team is awaiting further data from the old box's failure analysis before fully plugging in the replacement, however.

Positioned in the overhead avionics bay just inside the right-aft entrance doorway on Endeavour, technicians manhandled the 45-pound device into its slot with the help of guide rails.

"The work itself to replace the box is really quite easy, relatively speaking. Access is good," shuttle launch director Mike Leinbach told reporters Sunday. "It's standard work. It's just unfortunate it happened to us in (the) countdown and it's getting all this attention."

The replacement was ordered after a string of fuel line heaters on Auxiliary Power Unit No. 1 failed during last Friday's launch attempt for Endeavour's final spaceflight. Troubleshooting indicated power wasn't reaching the heaters because of a faulty component in the ALCA-2. The old box, which was removed Monday night, is undergoing full forensics at the malfunction laboratory to figure out exactly what went wrong.

There's three such Load Control Assemblies in the shuttle's aft that switch electrical feeds to various systems from the main power buses. They also enable the power paths to be changed as needed and take alternate courses for redundancy sake.

The ALCA-2 box that's been replaced controls approximately 75 functions in 9 different parts of the shuttle including the auxiliary power units, environmental control and life support, electric power distribution, solid rocket booster electronics, the water spray boilers, the main propulsion system, the main engines, orbital maneuvering system and flight controls, Leinbach said(...)