APU Heaters cause of Shuttle launch delay ...

NASA engineers have identified a failure in the power switching box of a primary auxiliary power unit as the culprit of last Friday's scrubbed final launch of the Shuttle Endeavor. The "aft load control assembly," is a box of switches that manages the heating to fuel lines and prevents them from freezing in the cold of space. With it's required replacement and testing, NASA will be unable to resume the launch countdown on Tuesday as the space agency had hoped. It is now expected that the final flight of the Shuttle Endeavor will not occur until at least May 8th.

The reason for such a long delay has to do with the amount of testing required once the assembly is replaced, a procedure which will take several days. The testing requires 48 hours to verify the assembly is working properly and then certify it as flight ready. Workers have already begun the process, starting with draining of the shuttle's external fuel tank. And the crew of STS-134 has returned to Houston for additional training until the next launch attempt.

The launch of the Shuttle Endeavor had attracted great attention since it was the next to the last shuttle flight before NASA undergoes a long dark period with no man rated launch vehicle in it's inventory. NASA had developed the Ares 1X test launch rocket in anticipation of a return to the moon with the Constellation Project. But the Obama Administration canceled that program after just one test launch and directed NASA to design and build a new launch vehicle, a process that's expected to take several years. During which, NASA will have to hitch rides from the Russian Space Agency to ferry crew and material to the International Space Station.

[via NASA Shuttle News]