Attached between the 207-foot and 227-foot levels is a retractable arm and vent hood assembly.
The arm truss section measures 65 feet long from tower hinge to vent hood hinge.
The 13-foot wide vent hood also is known as the "beanie cap." Heated gaseous nitrogen is pumped
into the hood to warm the liquid oxygen vent system at the top of the external tank.
This prevents oxygen vapors that are exiting the vent louvers from condensing water vapor in
the surrounding air into potentially damaging ice. (Source, Nasa)