\<COLOUR 1> CONSTRUCTION: \<COLOUR 0> Constructed in aluminium alloys, the ET comprises the oxygen tank at front and hydrogen tank aft, with a cylindrical intertank unit linking them; oxygen tank contains slosh baffles to prevent liquid surge; four structural interfaces on each side provide attachment for the solid rocket boosters, three on top provide attachment for the orbiter; the propellant feed lines from the tanks mate with the orbiter feed lines at the two aft ET/orbiter interfaces; a spray-on polyurethane foam (orange-brown) coating, about 2.5 cm thick, covers the ET, providing insulation for the cryogenic propellants (down to -253 degrees) within
\<COLOUR 1> COMMENTS: \<COLOUR 0> Expendable: The ET is the largest single component in the shuttle and provides its structural backbone; the orbiter rides on top of it and the solid rocket boosters are strapped to its sides; it is the only component that is not reusable; it is jettisoned some 8.5 minutes after lift-off and breaks up and falls into the Indian Ocean.