Technicians and engineers at NASA’s Kennedy Space Center in Florida have identified the likely source of what caused heaters on a fuel line for space shuttle Endeavour’s auxiliary power unit-1 (APU-1) to fail on Friday, scrubbing the first launch attempt for the STS-134 mission. The failure appears to be a power problem within the aft load control assembly-2 (ALCA-2), a box of switches controlling power feeds.“That basically means the power is not getting out to the heaters that weren’t working on launch day,” said Space Shuttle Program Launch Integration Manager Mike Moses.The plan is to remove and replace the box, but that work and related testing will take several days to complete. Once the new box is installed, the team must verify it’s working properly — at least a two-day process — and perform forensics on the failed box.“We can tell you, pretty much, that it’s not going to be any earlier than (May 8),” Moses said. “We’re really not even setting the schedules today. There’s still a whole lot of short-term work that has to be done.”Endeavour’s six astronauts have returned to NASA’s Johnson Space Center in Houston for a few days of additional training before they report to Kennedy for the next launch attempt, and the crew’s families also are going to return home today. The launch team is backing out of launch countdown operations.