scope:

Description of Driving Event:

The portable purge unit supplies conditioned air through ducts to the orbiter to purge and/or pressurize the payload bay's forward and aft compartments. Airflow varies between 50 lbs/min minimum to 100 lbs/min maximum. Vent door observers are always on station when a vent door is repositioned for a test or TPS tile/thermal barrier work. Overpressurization may occur if all the orbiter vent doors (normally in the purge position) for a compartment are closed at one time. Control logic program VAM09 also notifies the firing room engineers if both a right hand and left hand purge vent door set is closed.