Mercedes Mullins
The Space Shuttle external tank (ET) was an essential component of the Space Shuttle launch vehicle, providing structural support and housing the liquid hydrogen fuel and liquid oxygen oxidizer required for the shuttle's ascent. Constructed primarily of aluminum, the ET was the largest and heaviest element of the Space Shuttle. While the external tank was crucial for the shuttle's launch, it was not reusable and detached from the shuttle shortly after liftoff, burning up in the Earth's atmosphere. The ET also featured an epoxy layer and a spray-on foam exterior to prevent ice formation and insulate the propellants.
| Characteristics | Values |
|---|---|
| Name | Space Shuttle External Tank (ET) |
| Weight | 66,000 pounds |
| Colour | Orange |
| Material | Aluminium |
| Components | Aft liquid hydrogen (LH2) tank, liquid oxygen oxidizer tank, intertank |
| Sensors | Fuel depletion sensors, hydrogen sensors |
| Cameras | External cameras |
| Foam | Closeout foam (blowing agent was CFC-11) |
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What You'll Learn
The external fuel tank was made of aluminium
The Space Shuttle External Tank (ET) was a vital component of the Space Shuttle launch vehicle, providing the necessary fuel and structural support for the shuttle's journey into space. The ET was the largest element of the Space Shuttle and, when loaded, also the heaviest.
The aluminium construction of the ET contributed to its structural integrity, ensuring it could maintain its shape and stability even when empty. The internal pressure of the fuel also played a crucial role in maintaining the tank's structural integrity.
To protect the aluminium structure and insulate the propellants, the external tank was covered with spray-on foam. This foam skin experienced extreme temperature variations during launch, with the outside facing several hundred degrees and the inside reaching several hundred degrees below zero.
The external fuel tank was not reused and detached from the shuttle shortly after liftoff, burning up in the Earth's atmosphere.
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The tank was covered in spray-on foam insulation
The Space Shuttle External Tank (ET) was the component of the Space Shuttle launch vehicle that contained the liquid hydrogen fuel and liquid oxygen oxidizer. The ET was the "backbone" of the shuttle during launch, providing structural support for attachment with the Space Shuttle Solid Rocket Boosters (SRBs) and the orbiter. The external tank was one of three main sources of fuel for the space shuttle, along with twin solid rocket boosters.
The external tank was the largest element of the Space Shuttle, and when loaded, it was also the heaviest. The tank held up to 1.6 million pounds of liquid hydrogen and liquid oxygen. The aluminum tank flexed and vibrated while being pushed by aerodynamic forces of thousands of miles per hour. To prevent ice from forming on the outside skin and to insulate the propellants inside, the tanks were covered with spray-on foam insulation. During launch, the foam skin could be several hundred degrees on the outside and several hundred degrees below zero on the inside.
The ET also had a crucial role in providing electrical connections and structural support. It had two electrical umbilicals that carried electrical power from the orbiter to the tank and the two SRBs, and it provided information from the SRBs and ET to the orbiter. The ET was connected to each SRB at one forward attachment point and one aft bracket and to the orbiter at one forward attachment bipod and two aft bipods.
The external tanks were always discarded and broke up before impact in the Indian or Pacific Ocean, away from shipping lanes. They were not reused, and each launch required a new tank. The ET was jettisoned just over 10 seconds after the main engine cut-off.
The external fuel tanks were initially painted white but were left unpainted after the first two launches as it was found that the paint added several hundred kilograms of weight and was unnecessary. The tanks were then left in their natural orange color.
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The tank was painted orange, not white, to save weight
The Space Shuttle external tank (ET) was the component of the Space Shuttle launch vehicle that contained the liquid hydrogen fuel and liquid oxygen oxidizer. During lift-off and ascent, it supplied the fuel and oxidizer under pressure to the three RS-25 main engines in the orbiter. The ET was the largest element of the Space Shuttle, and when loaded, it was also the heaviest. The ET was the "backbone" of the shuttle during launch, providing structural support for attachment with the Space Shuttle Solid Rocket Boosters (SRBs) and the orbiter.
The external tank was made of aluminum. The first two tanks, used for STS-1 and STS-2, were painted white to protect the tanks from ultraviolet light during the extended time the shuttle spent on the launchpad before launch. However, it was later determined that the paint did not actually protect the foam.
Beginning with STS-3, Martin Marietta (now part of Lockheed Martin) reduced weight by leaving the rust-colored spray-on insulation unpainted, saving approximately 272 kg (600 lb). The tank's orange color is the color of the spray-on foam insulation. This foam also helped to maintain the tank's temperature and prevent ice from forming on its surface, which could potentially damage the orbiter's heat shield.
By not painting the external fuel tanks, weight was reduced, resulting in an almost equal increase in the cargo-carrying capability of the Space Shuttle. This weight reduction was a significant factor in the decision to leave the tanks unpainted, as it allowed for greater efficiency and payload capacity.
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The tank was the backbone of the shuttle during launch
The Space Shuttle External Tank (ET) was an integral component of the Space Shuttle launch vehicle. It was the backbone of the shuttle during launch, providing structural support for attachment with the Space Shuttle Solid Rocket Boosters (SRBs) and the orbiter. The ET was the largest element of the Space Shuttle and, when loaded, it was also the heaviest. It held up to 1.6 million pounds of liquid hydrogen and liquid oxygen, which fuelled and oxidised the three RS-25 main engines in the orbiter.
The ET was connected to each SRB at one forward attachment point and one aft bracket. It was also connected to the orbiter at one forward attachment bipod and two aft bipods. The aft attachment area also contained umbilicals that carried fluids, gases, electrical signals, and power between the tank and the orbiter. These umbilicals also routed electrical signals and controls between the orbiter and the two solid rocket boosters.
The external tanks were not reused. They were jettisoned just over 10 seconds after the main engine cut-off and broke up before impact in the Indian or Pacific Ocean, away from shipping lanes. The tanks were covered with spray-on foam to prevent ice from forming on the outside skin and to insulate the propellants inside. The foam skin could be several hundred degrees on the outside and several hundred degrees below zero on the inside.
The external tanks were originally painted white but were kept unpainted in their signature orange colour, as painting them added 600 lbs of weight. The ET's structural integrity was maintained by the internal pressure of the fuel, and its walls were quite thin. The pressurization contributed to its ability to withstand flight loads, as is the case for almost all liquid-propellant rocket tanks.
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The ET contained liquid hydrogen and liquid oxygen
The Space Shuttle External Tank (ET) was the component of the Space Shuttle launch vehicle that contained the liquid hydrogen fuel and liquid oxygen oxidizer. During lift-off and ascent, it supplied fuel and oxidizer under pressure to the three RS-25 main engines in the orbiter. The ET was jettisoned just over 10 seconds after the main engine cut-off and re-entered the Earth's atmosphere. The ET was the largest and heaviest element of the Space Shuttle when loaded.
Liquid hydrogen and liquid oxygen are cryogenic liquids, which means they have very low temperatures. Liquid hydrogen, for example, must be cooled to below 33 K to exist as a liquid and to 20.28 K to be in a fully liquid state at atmospheric pressure. Liquid oxygen is warmer than liquid hydrogen but still requires thermal protection to prevent it from freezing. The ET's thermal protection system consisted primarily of spray-on foam insulation (SOFI), as well as preformed foam pieces and premolded ablator materials. The system also included the use of phenolic thermal insulators to prevent air liquefaction and reduce heat flow into the liquid hydrogen.
The ET had five propellant umbilical valves that interfaced with orbiter umbilicals: two for the liquid oxygen tank and three for the liquid hydrogen tank. The liquid oxygen tank umbilical valves were for liquid and gaseous oxygen, while the liquid hydrogen tank umbilical had valves for liquid and gas. The intermediate-diameter liquid hydrogen umbilical was used only during the liquid hydrogen chill-down sequence during prelaunch. Excess gaseous hydrogen was vented through umbilical connections over a large diameter pipe on an arm extended from the fixed service structure.
The ET also had electrical umbilicals that carried electrical power from the orbiter to the tank and provided information from the tank to the orbiter. Sensors were installed to measure hydrogen levels, and there were propellant-depletion sensors for both fuel and oxidizer. These sensors played an important role in ensuring the safe operation of the Space Shuttle, as erroneous readings from fuel depletion sensors have delayed several shuttle launch attempts.
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Frequently asked questions
The external fuel tanks of the shuttles were made of aluminum.
The external fuel tank (ET) was the component of the Space Shuttle launch vehicle that contained the liquid hydrogen fuel and liquid oxygen oxidizer.
The external fuel tanks were always discarded and burned up in the atmosphere shortly after liftoff. Unlike the Solid Rocket Boosters, they were not reused.
The external fuel tank weighed 66,000 pounds.
The external fuel tanks were painted white originally but were later kept in their natural orange colour as the paint added 600 lbs of weight.
