Katerina Swanson
The Space Shuttle's external tank (ET) is the component that contains the liquid hydrogen fuel and liquid oxygen oxidizer. It is 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 is also the largest and heaviest element of the Space Shuttle. There were three variants of the external tank, with capacities of 629,340 kg (1,387,457 lb) of liquid oxygen and 106,261 kg (234,265 lb) of liquid hydrogen. The Space Shuttle originally had a white fuel tank, but they stopped painting it to reduce weight.
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What You'll Learn
- External tank (ET) provides structural support and attachment to Solid Rocket Boosters (SRBs)
- SRBs used 500,000 kg of Ammonium Perchlorate Composite Propellant
- ET is the largest and heaviest element of the Space Shuttle
- ET consists of three components: liquid hydrogen (LH2) tank, liquid oxygen (LOX) tank, and aft bracket
- Fuel tank colour changed from white to save weight
External tank (ET) provides structural support and attachment to Solid Rocket Boosters (SRBs)
The Space Shuttle External Tank (ET) is an integral component of the Space Shuttle, serving as the "backbone" of the shuttle during its launch. Its primary function extends beyond merely storing fuel; it also provides crucial structural support and facilitates the attachment of the Solid Rocket Boosters (SRBs) and the orbiter.
The ET is connected to each SRB at specific attachment points. At the forward end, it utilizes a crossbeam that extends through the intertank structure, while at the aft end, it employs a bracket. This aft attachment area also houses umbilicals that serve multiple purposes, including the transfer of fluids, gases, electrical signals, and power between the tank and the orbiter. These umbilicals are also responsible for routing electrical signals and controls between the orbiter and the SRBs.
The intertank, a critical component within the ET, acts as the structural connection between the liquid oxygen (LOX) and liquid hydrogen (LH2) tanks. It receives and distributes thrust loads from the SRBs and effectively transfers loads between the tanks. The SRB forward attach fittings are positioned 180 degrees apart on the intertank structure, and a beam is mechanically fastened to these fittings. When the SRBs are in operation, the beam flexes due to the high-stress loads, which are then transferred to the fittings.
The attachment points at the aft end of the ET consist of three separate struts: upper, diagonal, and lower. Each strut contains a bolt with an NSD pressure cartridge at each end. Notably, the upper strut facilitates the transfer of the umbilical interface between the SRB and the external tank, and subsequently, to the orbiter. The solid rocket boosters in the SRBs are ignited by firing these NSD pressure cartridges, which are connected to redundant confined detonating fuse manifolds.
The structural integrity and attachment mechanisms provided by the ET are vital for the safe and successful operation of the Space Shuttle. The SRBs provide the main thrust required to lift the shuttle off the launch pad, and the ET plays a crucial role in supporting and connecting these boosters to the rest of the shuttle assembly.
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SRBs used 500,000 kg of Ammonium Perchlorate Composite Propellant
The Space Shuttle Solid Rocket Boosters (SRBs) used 500,000 kg of Ammonium Perchlorate Composite Propellant (APCP). APCP is a solid rocket propellant that differs from traditional rocket propellants in its chemical composition, overall performance, and manufacturing process. It is composed of ammonium perchlorate, an elastomer binder such as hydroxyl-terminated polybutadiene (HTPB) or polybutadiene acrylic acid acrylonitrile prepolymer (PBAN), powdered metal (typically aluminium), and various burn rate catalysts.
The APCP used in the SRBs consisted of 69.6% ammonium perchlorate (as the oxidizer), 16% atomized aluminium powder (as the fuel), 0.4% iron oxide (as a catalyst), 12.04% PBAN (as a binder and additional fuel), and 1.96% of an epoxy curing agent. This mixture provided a specific impulse of 242 seconds (2.37 km/s) at sea level and 268 seconds (2.63 km/s) in a vacuum. The SRBs were ignited after the three RS-25 main engines' thrust level was verified and provided a liftoff thrust of approximately 12 meganewtons (2,800,000 pounds-force) at sea level, increasing shortly after liftoff to 14.7 MN (3,300,000 lbf).
The APCP in the SRBs had a burn time of 124 seconds, producing 12.5 MN of thrust per SRB. The SRBs helped take the Space Shuttle to an altitude of 28 miles (45 km) and a speed of 3,094 mph (4,979 km/h) before being jettisoned and parachuting into the Atlantic Ocean for recovery, examination, refurbishment, and reuse.
The use of APCP in the SRBs offered advantages such as manufacturing regularity and repeatability, as well as simplicity and reliability in aerospace rocket propulsion. The geometry of the APCP inside the rocket motor also influenced overall motor performance, with various geometric configurations employed to achieve the desired thrust curve.
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ET is the largest and heaviest element of the Space Shuttle
The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system that was operated by NASA from 1981 to 2011. The Space Shuttle system consists of the Orbiter Vehicle (OV), which contains the crew and payload, the external tank (ET), and two solid rocket boosters (SRBs). The ET is the largest and heaviest element of the Space Shuttle.
The ET is the "backbone" of the shuttle during launch, providing structural support for attachment with the SRBs and the orbiter. It is 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 ET also contains umbilicals in the aft attachment area that carry fluids, gases, electrical signals, and electrical power between the tank and the orbiter.
The ET consists of three major components: the LOX tank, the intertank, and the aft liquid hydrogen (LH2) tank. The LOX tank is located at the top of the ET and has an ogive shape to reduce aerodynamic drag and aerothermodynamic heating. The LOX tank has a volume of 19,744 cubic feet (559.1 cubic meters) at 22 psi (150 kPa) and −297 °F (90.4 K; −182.8 °C). The LH2 tank is the largest part of the ET, but it is relatively light due to liquid hydrogen's very low density.
Over the years, NASA worked to reduce the weight of the ET to increase overall efficiency. The weight reduction resulted in an almost equal increase in the cargo-carrying capability of the Space Shuttle. The first two tanks, used for STS-1 and STS-2, were painted white to protect them from ultraviolet light during the extended time on the launch pad before launch. However, it was later determined that the paint did not actually provide protection, and the tanks were left unpainted beginning with STS-3, resulting in a weight reduction of approximately 272 kg (600 lb).
The Super Lightweight Tank (SLWT) was first flown in 1998 on STS-91 and was used for all subsequent missions except STS-99 and STS-107. The SLWT used an aluminium-lithium alloy (Al 2195) for a large part of the tank structure, resulting in a significant reduction in weight compared to previous tanks. The reduction in weight allowed the Orbiter to carry more payload to the highly inclined orbit of the International Space Station.
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ET consists of three components: liquid hydrogen (LH2) tank, liquid oxygen (LOX) tank, and aft bracket
The Space Shuttle external tank (ET) is the component of the Space Shuttle launch vehicle that contains 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 ET is the largest and heaviest element of the Space Shuttle when loaded. It is also the only major component of the Space Shuttle system that is not reused. The external tank breaks up before impact in the Indian Ocean or the Pacific Ocean, away from shipping lanes. Over the years, NASA worked to reduce the weight of the ET to increase overall efficiency. The reduction in weight allowed the Orbiter to carry more payload to the highly inclined orbit of the ISS.
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Fuel tank colour changed from white to save weight
The Space Shuttle's external fuel tank was initially painted white for its first two missions. The paint added approximately 600 pounds to the tank's weight, which is a significant amount considering the scale of space machinery. As NASA continued to refine and optimise the shuttle for more efficient space travel, the removal of the white paint was proposed to save weight.
The decision to transition from a white fuel tank to an orange one was driven by engineering pragmatism and a desire for efficiency in space exploration. The white paint was originally chosen for its highly reflective properties, which were thought to protect the tank against the extreme temperatures of space. However, the paint added considerable weight to the shuttle, and its removal allowed for an additional 600 pounds of payload capacity. This weight saving was crucial, as it meant that more scientific equipment, experiments, and other payload enhancements could be carried by the shuttle.
The orange hue associated with the Space Shuttle fuel tank is the natural colour of the spray-on foam insulation that coated the tank. This insulation was vital for shielding the tank's super-cooled liquid hydrogen and oxygen fuel from the intense heat generated during lift-off and the initial climb. The foam also helped to minimise ice formation on the tank's surface, reducing the risk of damage to the shuttle during launch.
The shift from a painted to an unpainted fuel tank was not merely cosmetic but reflected a broader drive for technological efficiency and weight reduction in space exploration. The removal of the paint also decreased the risk of paint flecking off during launch, which could potentially damage the shuttle's thermal protection system. The orange fuel tanks served the Space Shuttle Program faithfully until its conclusion in 2011, becoming an enduring emblem of humanity's endeavour to explore beyond Earth's confines.
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Frequently asked questions
The space shuttle uses liquid hydrogen fuel and liquid oxygen oxidizer. The external tank (ET) supplies the fuel and oxidizer under pressure to the three RS-25 main engines in the orbiter.
The ET is the component of the space shuttle launch vehicle that contains the fuel and oxidizer. It is the largest and heaviest element of the shuttle when loaded.
The ET has a capacity of 629,340 kg (1,387,457 lb) of liquid oxygen and 106,261 kg (234,265 lb) of liquid hydrogen.
The SRBs provide additional thrust to the shuttle during the first two minutes of flight. Each SRB burns around 500,000 kg of solid propellant.
The ET is jettisoned just over 10 seconds after the main engine cuts off. It re-enters the Earth's atmosphere and breaks up over the Indian or Pacific Ocean, away from shipping lanes.
