Endeavour launch scrubbed at least 72 hours.

The launch of Endeavour on the next-to-last mission in America’s space shuttle program was delayed at least 72 hours due to a problem in one of the craft's auxiliary power units.

Auxiliary power unit No. 1, one of the three units which supply hydraulic power to steer the shuttle's main engines in flight and control flight surfaces and other critical functions during re-entry, developed a problem managers believed could not be resolved in time for the scheduled 3:47 p.m. liftoff.

Two heaters, required to keep the unit's turbine engine thermally conditioned, failed.

The mission of STS-134 will fly no earlier than 2:33 p.m. Monday from Kennedy Space Center Launch Pad 39B on a planned 14-day flight to the International Space Station. Even that date may be too early.

The mission drew intense interest that transcended it being Endeavour's 25th and final flight since President Barack Obama and his family were to attend. Also, Arizona congresswoman Gabrielle Giffords, wife of Endeavour Commander Mark Kelly, was in attendance four months after being critically wounded in a Jan. 8 assassination attempt in Tuscon.

Mission managers immediately gathered to hammer out a solution.

The scrub was announced just as the van carrying the six-member crew to the launch pad was leaving the Launch Control Center after a stopover that observers called the first in the shuttle’s history.

Normally the van stops on the main road leading to the launch pad to drop off the chief astronaut and the pilot who flies the weather reconnaissance aircraft before continuing to the pad. This time, however, the van pulled into the LCC parking lot and stopped for several minutes before leaving and turning left to head back to the crew quarters at the Operations and Checkout facility.

-Mark DeCotis