Rajan Wilcox
The Space Shuttle External Tank (ET) is an integral component of the Space Shuttle launch vehicle, providing structural support and housing the liquid hydrogen fuel and liquid oxygen oxidizer required for lift-off and ascent. Over the years, NASA has worked to enhance the ET's efficiency by reducing its weight and modifying the insulating foam to prevent shedding during launch. Despite these improvements, the ET is not reusable and breaks up before impact in the Indian or Pacific Ocean. The arrival of NASA's last space shuttle external fuel tank, ET-94, in Los Angeles in 2016 marked the end of an era, with the production plant responsible for building these giants shutting down.
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What You'll Learn
- The Space Shuttle external tank (ET) is the component that contains liquid hydrogen fuel and liquid oxygen
- The ET is the largest and heaviest element of the Space Shuttle
- The ET is not reused and breaks up before impact in the ocean
- The ET provides structural support for attachment with the Space Shuttle Solid Rocket Boosters (SRBs)
- The ET has electrical umbilicals that carry power and information between the orbiter and the tank
The Space Shuttle external tank (ET) is the component that contains liquid hydrogen fuel and liquid oxygen
The ET is jettisoned just over 10 seconds after the main engine cut-off (MECO) and re-enters the Earth's atmosphere. Unlike the Solid Rocket Boosters, the external tanks are not re-used. They break up before impact in the Indian Ocean (or the Pacific Ocean in the case of direct-insertion launch trajectories), away from shipping lanes, and are not recovered. The ET is the largest element of the Space Shuttle, and when loaded, it is also the heaviest.
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 original ET, informally known as the Standard Weight Tank (SWT), was fabricated from 2219 aluminium alloy, a high-strength aluminium-copper alloy used for many aerospace applications. The SWT weighed approximately 77,000 pounds (35,000 kg) inert. The weight reduction was accomplished by eliminating portions of stringers (structural stiffeners running the length of the hydrogen tank), using fewer stiffener rings, and modifying major frames in the hydrogen tank.
The liquid oxygen sensors allow the maximum amount of oxidiser to be consumed in the engines while allowing sufficient time to shut down the engines before the oxidiser pumps cavitate (run dry). In addition, 1,100 pounds (500 kg) of liquid hydrogen are loaded over and above that required by the 6:1 oxidiser-fuel engine mixture ratio. This ensures that cutoff from the depletion sensors is fuel-rich; oxidiser-rich engine shutdowns can cause burning and severe erosion of engine components, potentially leading to the loss of the vehicle and crew. Each propellant tank has a vent and relief valve at its forward end, which can be opened during prelaunch and during flight when the ullage (empty space) pressure reaches a certain level.
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The ET is the largest and heaviest element of the Space Shuttle
The Space Shuttle External Tank (ET) was the largest and heaviest element of the Space Shuttle. It 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 it re-entered the Earth's atmosphere. Unlike the Solid Rocket Boosters, the external tanks were not reused. They broke up before impact in the Indian Ocean or the Pacific Ocean in the case of direct-insertion launch trajectories, away from shipping lanes.
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 tank was connected to each SRB at one forward attachment point (using a crossbeam through the intertank) and one aft bracket. It was connected to the orbiter at one forward attachment bipod and two aft bipods. In the aft attachment area, there were also umbilicals that carried fluids, gases, electrical signals, and electrical power between the tank and the orbiter. Electrical signals and controls between the orbiter and the two solid rocket boosters were also routed through those umbilicals.
The ET also had two electrical umbilicals that carried electrical power from the orbiter to the tank and the two SRBs and provided information from the SRBs and ET to the orbiter. The ET had external cameras mounted in the brackets attached to the shuttle, along with transmitters that could continue to send video data long after the shuttle and the ET had separated. The LOX tank is located at the top of the ET and has an ogive shape to reduce aerodynamic drag and aerothermodynamic heating. The ogive nose section is capped by a flat removable cover plate and a nose cone. The nose cone serves as an aerodynamic fairing for the propulsion and electrical system components.
Over the years, NASA worked to reduce the weight of the ET to increase overall efficiency. The weight reduction in the ET resulted in an almost equal increase in the cargo-carrying capability of the Space Shuttle. The external tank's orange colour is the colour of the spray-on foam insulation. 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 that the shuttle spent on the launch pad before launch. However, NASA engineer Farouk Huneidi stated that the paint did not actually protect the foam.
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The ET is not reused and breaks up before impact in the ocean
The Space Shuttle External Tank (ET) is not designed for reuse and is always discarded. During lift-off, the ET provides structural support for attachment with the Space Shuttle Solid Rocket Boosters (SRBs) and the orbiter. It also supplies fuel and oxidizer to the RS-25 main engines. Just over 10 seconds after the main engine cut-off, the ET is jettisoned and re-enters the Earth's atmosphere.
The ET is the largest and heaviest element of the Space Shuttle. It consists of three major components: the forward liquid oxygen (LO2) tank, the aft liquid hydrogen (LH2) tank, and the intertank that connects them. The LH2 tank is the largest component of the ET, but it is relatively light due to liquid hydrogen's low density.
Over the years, NASA worked with Lockheed Martin to reduce the weight of the ET to increase the cargo-carrying capability of the Space Shuttle. The original ET, informally known as the Standard Weight Tank (SWT), was fabricated from 2219 aluminum alloy. The current super-lightweight version debuted in 1998, and the tanks have undergone significant weight reductions, allowing shuttles to carry more payload.
After being jettisoned, the ET breaks up before impact in the Indian Ocean or the Pacific Ocean, away from shipping lanes, and is not recovered. The external fuel tank for the space shuttle's last scheduled mission was delivered to NASA's Kennedy Space Center in Florida in September 2010. The production plant responsible for building the giant external fuel tanks has since shut down.
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The ET provides structural support for attachment with the Space Shuttle Solid Rocket Boosters (SRBs)
The Space Shuttle External Tank (ET) is an essential component of the Space Shuttle launch vehicle, serving as the "backbone" of the shuttle during its launch. It provides structural support for the attachment of the Space Shuttle Solid Rocket Boosters (SRBs) and the orbiter. The ET is connected to each SRB at specific attachment points, including a forward attachment point utilizing a crossbeam through the intertank and an aft bracket. The intertank is a critical structural connection within the ET, bridging the LOX and LH2 tanks and facilitating the distribution of thrust loads from the SRBs.
The SRBs are massive solid-propellant motors, each weighing approximately 1,300,000 pounds (590 tonnes) at launch. They provide the primary thrust required to lift the shuttle off the launch pad, carrying the entire weight of the external tank and orbiter. The SRBs are connected to the ET through attachment rings, which have been redesigned to encircle the motor case completely for enhanced structural integrity. The attachment process also involves struts with bolts and NSD pressure cartridges, ensuring a secure connection.
The ET and SRBs work in tandem during the critical launch phase. The ET supplies fuel and oxidizer to the orbiter's engines, while the SRBs provide the necessary thrust for lift-off. The SRBs are ignited under the command of onboard computers, and their separation is initiated through explosive bolts. The ET is jettisoned after main engine cut-off and re-enters the Earth's atmosphere, breaking up before impact in the Indian or Pacific Ocean. Unlike the SRBs, the external tanks are not reused, although there have been proposals for their incorporation into space stations or as rocket fuel tanks for interplanetary missions.
The weight of the ET has been a significant focus for NASA, as reducing its weight directly increases the cargo-carrying capability of the Space Shuttle. Over time, NASA employed stronger yet lighter materials, such as titanium and aluminium-lithium alloys, in the construction of the ET to achieve weight reduction. The Super Lightweight Tank (SLWT) design, first flown in 1998, significantly reduced tank weight compared to the previous Lightweight Tank (LWT) design.
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The ET has electrical umbilicals that carry power and information between the orbiter and the tank
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. During lift-off and ascent, it supplies fuel and oxidizer under pressure to the three RS-25 main engines in the orbiter. The ET 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 has two electrical umbilicals that carry electrical power and information between the orbiter and the tank. These umbilicals also connect with the two SRBs.
Umbilicals are used to allow the flow of liquids, gases, electrical power, and signals to a spacecraft. They are typically detached at or before launch to allow the craft to move freely. In the context of the Space Shuttle ET, the electrical umbilicals provide power from the orbiter to the tank and the SRBs, and they transmit information from the SRBs and ET back to the orbiter. This includes data from the external cameras mounted on the ET, which can continue to send video data even after the ET and shuttle have separated.
The ET also features a range safety system that can disperse tank propellants if necessary. This system includes a battery power source, a receiver/decoder, antennas, and ordnance. However, starting with STS-79, this system was disabled, and it was completely removed for STS-88 and subsequent flights. The ET has undergone design changes over the years, including reductions in weight to increase overall efficiency and changes in colour to protect the tank from ultraviolet light during the time spent on the launch pad before launch.
The ET is jettisoned just over 10 seconds after main engine cut-off (MECO) and re-enters the Earth's atmosphere. Unlike the Solid Rocket Boosters, the ETs are not reused. They break up before impact in the Indian Ocean or the Pacific Ocean, away from shipping lanes, and are not recovered. Despite always being discarded, there have been proposals to reuse ETs in orbit, such as incorporating them into a space station or using them as rocket fuel tanks for interplanetary missions.
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Frequently asked questions
The ET is the component of the Space Shuttle launch vehicle 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 always discarded after use and breaks up before impact in the Indian Ocean or the Pacific Ocean, away from shipping lanes. Unlike the Solid Rocket Boosters, they are not reused.
The ET is made of spray-on foam insulation, which is rust-coloured. The original ET was fabricated from 2219 aluminum alloy, a high-strength aluminum-copper alloy used for many aerospace applications.
