Fri, Apr 29, 2011
APU Heaters Malfunctioned About Three Hours Before Launch
ANN Realtime Update 1410 EDT 04.29.2011:
Shuttle launch director Mike Leinbach stated that Endeavour's
launch will be no earlier than Monday at 1433 EDT. Engineers
need that time to troubleshoot an issue that resulted in Friday's
launch scrub.
Lightning Strikes Thursday Near Endeavour. Weather has not
been associated with Friday's launch scrub.
During today's countdown, engineers detected a failure in one of
two heater circuits associated with Auxiliary Power Unit (APU) 1.
Heaters are required to keep the APUs' hydrazine from freezing on
orbit. Attempts to activate the heater were not successful and
engineers now believe the problem might be associated with a Load
Control Assembly, which is a switchbox, located in the aft end of
Endeavour, or an electrical short in the wires leading into or out
of the switchbox.
Endeavour's external tank will be drained, technicians will
enter Endeavour's aft compartment overnight and by tomorrow
afternoon, will put in a platform to gain access to the avionics
bay where the Load Control Assembly is located. Once there, they
will assess whether they need to remove and replace the switchbox,
or fix an electrical wiring short.
Because of this, Leinbach said there will be a minimum 72-hour
scrub turnaround.
Engineers and managers will meet Friday afternoon to further
refine their troubleshooting plan. NASA has scheduled a news
conference at 1600 to discuss today's scrub and the plan.
BREAKING NEWS Update: 1330
EDT. Shuttle Endeavour's launch now no earlier than
Monday at 1433 EDT. A news conference is scheduled for 1600
Friday.
Original Story: 4.29.2011 1340 EDT: The launch
of space shuttle Endeavour has been scrubbed for at least 48 hours.
NASA announced the scrub via Twitter about 1230 EDT. They cite
problems with two of the heaters associated with
the spacecraft's Auxiliary Power Unit (APU) 1 as the reason
for postponing the launch.
The shuttles three APUs provide hydraulic power to steer the
shuttle's aerosurfaces during ascent and entry.
Additional information will be posted as it becomes
available.
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