External Tank Stats
Empty: 78,100 pounds
Gross: 1,667,677 pounds
Propellant Weight *
Gross: 1,585,379 pounds
Propellant Volume *
Liquid oxygen tank:
Liquid hydrogen tank:
Gross: 526,126 gallons
* Liquid oxygen is 16 times heavier than liquid hydrogen.
+ More NASA Facts...
|Liquid Oxygen (LOX) Feedline Bellows|
There is a large pipe, known as the feedline, which runs from the liquid oxygen tank at the top of the External Tank to an umbilical at the bottom of the tank, which is connected to the Orbiter. |
Image left: The LOX Feedline Bellows on the Shuttle's External Tank. Photo credit: NASA/Marshall Space Flight Center.
During tanking and in flight, the ET expands and contracts by small amounts. There is a need for this liquid oxygen feedline to also expand and contract. The feedline bellows, or expansion joints, allow for this movement without stressing the feedline. The liquid oxygen feedline bellows are not insulated with foam, because they allow for movement of the feedline.
This lack of insulation means ice can form on the bellows end and rain shields during pre-launch fueling of the ET, when moisture in the outside air contacts the cold surface. The cold bellows shield surfaces are caused by the near minus-297 degree liquid oxygen in the feedline. As the ice forms, it eventually can migrate to the foam surrounding the feedline bellows.
For the STS-114 mission, NASA decided that installation of a foam "drip-lip" on the bellows cover (rain shield) would sufficiently decrease the amount of ice that could develop. Depending upon the outside temperature and humidity of the day, the drip-lip could reduce the amount of ice by as much as 40 percent in a worst case environment (a very hot and humid Florida day). The "drip-lip" is squared at its bottom end. It has a slight 10 degree angle, so the condensate drips off the cover. The original design was angled toward the tip of the rain-shield, which allowed the water to contact the shield and freeze.
New debris studies showed ice (even soft ice) poses an unacceptable debris concern to the Orbiter. Though it was originally decided the drip-lip configuration would be flown on STS-114, the External Tank Project Office continued to pursue the option of a heater for the bellows, planning on installation of that heater on future External Tanks to eliminate ice from the area. Shuttle managers have now decided to retrofit the tanks already undergoing processing at the Kennedy Space Center and have the heaters in place before the Shuttle returns to flight.
The heater is a copper-nickel alloy metal strip heater, similar to the heaters used on the Solid Rocket Motor joints. The two heater strips are covered and joined by a silicone gasket that allows the heater to be inserted between the bellows rain shield and end shield. It has tabs placed at intervals that assist in the placement of the heater. They are used to perform pull tests that verify the strength of the adhesive bond.