Propellant: 719,115 kilograms|
Gross: 719,115 kilograms|
Liquid hydrogen tank:|
Gross: 1,991,604 liters|
Liquid oxygen is 16 times heavier than liquid hydrogen.|
external tank falls back to Earth after exhausting its fuel and
separating from the space shuttle.
tank, or ET, is the "gas tank" for the orbiter; it contains the
propellants used by the space shuttle main engines. The tank is
also the "backbone" of the shuttle during the launch, providing
structural support for attachment with the solid rocket boosters
and orbiter. The tank is the only component of the space shuttle
that is not reused. Approximately 8.5 minutes into the flight, with
its propellant used, the tank is jettisoned.
liftoff, the external tank absorbs the total (7.8 million pounds)
thrust loads of the three main engines and the two solid rocket
motors. When the solid rocket boosters separate at an altitude of
approximately 45 kilometers (28 miles), the orbiter, with the main
engines still burning, carries the external tank piggyback to near
orbital velocity, approximately 113 kilometers (70 miles) above
the Earth. The now nearly empty tank separates and falls in a preplanned
trajectory with the majority of it disintegrating in the atmosphere
and the rest falling into the ocean.
The three main
components of the external tank are an oxygen tank, located in the
forward position, an aft-positioned hydrogen tank, and a collar-like
intertank, which connects the two propellant tanks, houses instrumentation
and processing equipment, and provides the attachment structure
for the forward end of the solid rocket boosters.
tank is 2.5 times larger than the oxygen tank but weighs only one-third
as much when filled to capacity. The reason for the difference in
weight is that liquid oxygen is 16 times heavier than liquid hydrogen.
skin of the external tank is covered with a thermal protection system
that is a 2.5-centimeter (1-inch) thick coating of spray-on polyisocyanurate
foam. The purpose of the thermal protection system is to maintain
the propellants at an acceptable temperature, to protect the skin
surface from aerodynamic heat and to minimize ice formation.
tank includes a propellant feed system to duct the propellants to
the orbiter engines, a pressurization and vent system to regulate
the tank pressure, an environmental conditioning system to regulate
the temperature and render the atmosphere in the intertank area
inert, and an electrical system to distribute power and instrumentation
signals and provide lightning protection. The tank's propellants
are fed to the orbiter through a 43-centimeter (17-inch) diameter
connection that branches inside the orbiter to feed each main engine.