NASA has scrubbed the second-to-last space shuttle launch due to problems with an auxiliary power unit (APU), approximately 4h before the scheduled launch. The launch of shuttle Endeavour on STS-134 will be delayed at least two additional days as technicians attempt to fix the problem.
In a statement on its website, NASA cited an "issue associated with Auxiliary Power Unit 1 heaters". Justin Ray of the Spaceflight Now blog, reporting comments by Shuttle launch director Mike Leinbach, said the issue may be due to an electrical short in or around the load control assembly, which routes power to the APU.
To troubleshoot the problem, technicians must access the shuttle itself, and to work safely around the shuttle it must be purged of its highly combustible fuel. To defuel and refuel can take up to two full days.
Delays are routine for space shuttle launches. The highly complex and delicate systems onboard often produce minor faults, and NASA's goal is to take no unnecessary risks.
NASA had earlier announced an expected crowd of 750,000 people to view this second-to-last launch of the iconic shuttle program, including President Obama, who had not arrived as of the delay, but apparently still plans to visit.