The ET (External Tank) is the largest element of the space shuttle, and when loaded, it is also the heaviest. It consists of three major components: the forward liquid oxygen (LOX) tank an unpressurized intertank that contains most of the electrical components the aft liquid hydrogen (LH2) tank; this is the largest part, but it is relatively light, due to hydrogen's very low density. Those 2 chemicals funnel out of the engine and when combined energy is released.
Anna Fisher - chemist and NASA astronaut (1979) Currently one of the oldest active American astronauts, in her long career at NASA she has been involved with three major programs: the Space Shuttle, the International Space Station and the Orion project.
As if soaring through the heavens, space shuttle Discovery launches through rolling clouds of smoke and steam, embarking on its final scheduled mission, STS-133, to the International Space Station. Liftoff from launch Pad 39A at NASA's Kennedy Space Center in Florida occurred at 4:53 p.m. EST on Feb. 24, 2011.