Range Tracking

External Tank Gaseous Oxygen Vent Arm

A piece of Space Shuttle history sits in the overgrown grass of a NASA junkyard at Kennedy Space Center. This is the External Tank Gaseous Oxygen Vent Arm, or more popularly called the “beanie cap”, that used to sit atop Launch Complex 39A and used for all the Space Shuttle launches from that pad. LC-39A is undergoing major modifications to prepare it for launching the SpaceX Falcon 9 Heavy rocket so this piece of equipment is no longer needed at the pad.
A detail from a NASA photograph shows Space Shuttle Endeavour on LC-39A with the “beanie cap”, circled in white, in place atop the External Fuel tank. An excerpt from a NASA publication explains what the device is used for: “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…. Vapors are created as the liquid oxygen in the external tank boil off. The hood vents the gaseous oxygen vapors away from the space shuttle vehicle.

About two-and-a-half minutes before launch, the vent hood is raised to clear the external tank, a 25-second procedure. The arm is retracted against the fixed service structure at about one minute, 45 seconds before liftoff. It is not latched in the event there is a hold, in which case the arm can be re-extended and the beanie cap again lowered onto the external tank.

The arm is latched when the solid rocket booster ignition signal is given at T minus zero minutes.”
The circled vent arm is seen here retracted against the fixed service structure in this photo from a 2012 visit to LC-39A.
A close-up of the vent arm against the fixed service structure taken on the same pad visit seen above.
The vent arm from Launch Complex 39B is on permanent display in the Space Shuttle Atlantis exhibit at the Kennedy Space Center Visitor Complex.
View more images from the Atlantis exhibit at http://www.lunarcabin.com/Shuttle/end_of_shuttle_program_60.html

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