The very large, very orange, object on the Space Shuttle stack is the External Tank (ET) which holds fuel in the form of iquid hydrogen (LH2) fuel and liquid oxygen (LO2) oxidizer which mix in the three Space Shuttle Main Engines (SSME). The ET is the only non-reusable lift object: the ET is jettisoned just over 10 seconds after Main Engine Cut Off (MECO).

Above: the External Tank. The right hand pipe is the LO2 feedline which enters the shuttle near the orbiter LH2 feedline and umbilicals at the aft attachment point.

The ET is covered in foam in order to keep the fuel liquid – this is the same foam which cause the catastrophic loss of the Space Shuttle Columbia when during liftoff a suitcase-size piece of thermal insulation foam broke off from the ET, striking Columbia’s left wing panels. The specific piece of foam which broke off (the Left Bipod Foam Ramp) was designed to reduce aerodynamic stresses around the bipod attachment to the shuttle, and on further missions this piece was removed from design and flight.

There are three main parts to the ET: the iquid hydrogen (LH2) fuel tank (bottom), liquid oxygen (LO2) oxidizer tank (top) and the intertank connecting the two pieces. The large exterior line is the LO2 feedline which is 17″ in diameter which is connected to the space shuttle at the bottom mating points.
The specific ET which is being flown on STS-134 is ET-122 which was refurbished after damage during Hurricane Katrina, being fully certified and flight-worthy. As a NASA manager stated, It might not be pretty, but it is fully flight ready. To mark the return of ET-122 to flight-worthy status, Lockheed Martin created a Return to Flight logo which was applied to the Intertank Access Door at the request of NASA, the first of its kind. The logo is below (courtesy of Lockheed Martin):

Below are photos of the ET, LO2 Feedline, and space shuttle mating section:

ET-122 Rollout to Barge (NASA, 9/20/10) by NASA’s Marshall Space Flight Center:

External tank-shuttle bipod:

17″ O2 Feedline at Top of the External Tank:

LH2 Feedline (O2 Feedline behind) at orbiter aft attachment point:

More information

• Space Shuttle External Tank
• Orbiter propulsion datasheet from NASA
• Solid Rocket Boosters
• Shuttle main engines
• mobile launcher platform

This is another in a series of posts documenting my time around the liftoff of STS-134 Space Shuttle Endeavour. For more posts, check out my STS-134 Launch Page.