May 10 the Earliest for Endeavour Launch
May 2, 2011 — The shuttle Endeavor, whose scheduled April 29 launch was scrubbed due to a failure in a heater circuit associated with Endeavour's hydraulic power system, won’t launch before Tuesday, May 10, according to NASA managers. A new launch date is expected early this week. Meanwhile, Endeavour's six astronauts have returned to NASA's Johnson Space Center in Houston for several days of additional training.
After Friday's launch scrub, technicians found the problem in a power circuit in a switchbox in the shuttle's aft compartment, and a schedule is being developed to remove, replace, and retest the switchbox.
The shuttle’s three auxiliary power units (APUs) provide hydraulic power to steer the vehicle during ascent and entry. The hydrazine fuel lines on each APU have two heater circuits that prevent the fuel from freezing while the shuttle is in space. NASA launch commit criteria and flight rules require all three APUs and heater circuits to be operational for liftoff.
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