[KevinDavis]

T-minus 5 minutes, 30 seconds. APU pre-start is complete and the units are ready for activation. The orbiters flight data recorders have gone into the record mode to collect measurements of shuttle systems performance during flight.

[KevinDavis]

T-minus 5 minutes. The "go" has been given for for Auxiliary Power Unit start. Pilot Bill Oefelein is now flipping three switches in Discovery's cockpit to start each of the three APU's. The units, located in the aft compartment of Discovery, provide the pressure needed to power the hydraulic systems of the shuttle. The units will be used during the launch and landing phases of the mission for such events as moving the orbiter's aerosurfaces, gimbaling the main engine nozzles and deploying the landing gear.

Over the course of the next minute, the orbiter's heaters will be configured for launch by commander Mark Polansky, the fuel valve heaters on the main engines will be turned off in preparation for engine ignition at T-6.6 seconds and the external tank and solid rocket booster safe and arm devices will be armed.