Rajan Wilcox
The amount of fuel a space shuttle carries internally depends on the stage of the shuttle's journey. The space shuttle's main engine, which must work above the atmosphere, uses 385,000 gallons of liquid hydrogen and 143,000 gallons of liquid oxygen. The two solid rocket boosters used roughly 500,000 kg of Ammonium Perchlorate Composite Propellant (APCP), providing 124 seconds of burn time. The external tank that came in three different configurations had a capacity of 629,340 kg of liquid oxygen and 106,261 kg of liquid hydrogen.
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What You'll Learn
The space shuttle's main engine uses liquid hydrogen and liquid oxygen
The space shuttle's main engine, which must work above the atmosphere, uses liquid hydrogen and liquid oxygen. The RS-25, also known as the Space Shuttle Main Engine (SSME), is a liquid-fuel cryogenic rocket engine that was used on NASA's Space Shuttle and is now used on the Space Launch System. The RS-25 burns cryogenic liquid hydrogen and liquid oxygen propellants, with each engine producing 1,859 kN (418,000 lbf) of thrust at liftoff.
The Space Shuttle's external tank (ET) 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 jettisoned just over 10 seconds after main engine cut-off and re-entered the Earth's atmosphere. The ET was the largest and heaviest component of the Space Shuttle when loaded.
Liquid hydrogen is transmitted from the tank through a 17-inch (430 mm) line to the left aft umbilical, with a flow rate of 465 lb/s (12,700 kg/min) at 104% engine power. The ET thermal protection system consists of spray-on foam insulation (SOFI), preformed foam pieces, and premolded ablator materials. Thermal isolators are required for liquid hydrogen tank attachments to prevent the liquefaction of air on exposed metal and reduce heat flow into the liquid hydrogen.
The main oxidizer and fuel bleed valves are used to dump any residual propellant after engine shutdown, with residual liquid oxygen venting through the engine and residual liquid hydrogen venting through the liquid hydrogen fill and drain valves. The RS-25 nozzle has an unusually large expansion ratio of about 69:1 for chamber pressure. To prevent flow separation, Rocketdyne engineers varied the angle of the nozzle walls, reducing pressure near the exit. The inner surface of each nozzle is cooled by liquid hydrogen flowing through brazed stainless steel tube wall coolant passages.
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Solid rocket boosters are used to launch the shuttle
The Space Shuttle's main engine uses 385,000 gallons of liquid hydrogen and 143,000 gallons of liquid oxygen. However, solid rocket boosters (SRBs) are also used to launch the shuttle. SRBs are solid propellant motors that provide thrust for spacecraft launches from initial launch through the first ascent. The Space Shuttle used two SRBs, which were the largest solid propellant motors ever built until the Space Launch System. The propellant for each solid rocket motor on the Space Shuttle weighed approximately 500,000 kilograms.
SRBs provide several advantages for spacecraft launches. They give launch vehicles much of the thrust required to place the vehicle into orbit. In the case of the Space Shuttle, a pair of SRBs provided 85% of the shuttle's thrust at liftoff and for the first two minutes of ascent. SRBs also reduce the amount of liquid propellant needed and lower the launch rig mass. They are cheaper to design, test, and produce compared to liquid propellant boosters, and their reusability decreases hardware costs.
The Space Shuttle SRBs were the most powerful solid rocket motors ever used to launch humans. Each SRB provided a maximum of 14.7 MN (3,300,000 lbf) of thrust, roughly double the most powerful single-combustion chamber liquid-propellant rocket engine ever flown. After burnout, the SRBs were jettisoned and parachuted into the Atlantic Ocean for recovery, examination, refurbishment, and reuse.
The design of the Space Shuttle SRBs has evolved over time. The original SRBs were four-segment boosters, but later versions, such as the Space Launch System, used five-segment boosters. The five-segment SRBs provide approximately 25% more total impulse than the four-segment SRBs and are not recovered after use. The first test of a five-segment SRB for the Space Launch System was completed in early 2015, and the second test was performed in mid-2016.
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External fuel tanks are not reused
The Space Shuttle's main engine uses 385,000 gallons of liquid hydrogen and 143,000 gallons of liquid oxygen. The 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 largest element of the Space Shuttle, and when loaded, it was also the heaviest. 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.
Although the external tanks were always discarded, it may have been possible to reuse them in orbit. Plans for reuse ranged from incorporation into a space station as extra living or research space to using them as rocket fuel tanks for interplanetary missions. However, unlike the Solid Rocket Boosters, the external tanks were not reused. They broke up before impact in the Indian Ocean or the Pacific Ocean, away from shipping lanes, and were not recovered. Each launch required a new external tank, making it the only component of the shuttle stack that was not reusable.
The external tank detached about 70 miles (113 kilometers) above the Earth's surface. After detaching, the tank fell back towards Earth, with almost all of it disintegrating in the atmosphere on the way down. The external tank was covered with spray-on foam to prevent ice from forming on the outside skin and to insulate the propellants inside. However, this foam could cause problems during launch. For example, during the lift-off of STS-107 in 2003, a piece of foam insulation detached from the tank and struck the wing of the Space Shuttle Columbia, causing catastrophic damage to the shuttle.
The external tank ET-94, completed in 2001, was one of three types of external tanks used in the shuttle program. It was a lightweight tank intended to propel the shuttle into low-Earth orbit. ET-94 was donated by NASA to the California Science Center in Los Angeles, where it is on permanent display with the space shuttle Endeavour. With the addition of ET-94, the California Science Center's Samuel Oschin Air and Space Center became the only place in the world where people can see a complete shuttle stack, including the orbiter, external tank, and solid rocket boosters.
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The shuttle glides back to Earth unpowered
A space shuttle returns to Earth as an unpowered glider, without any propellants available to its Space Shuttle Main Engines (SSMEs). During the shuttle's ascent, thrust is provided by the three SSMEs at the base of the orbiter and two Solid Rocket Boosters (SRBs) that are joined to the external fuel tank. The SRBs are jettisoned about two minutes into the ascent, and the external fuel tank is jettisoned as the shuttle enters Earth orbit. As a result, the shuttle has no propellants available to the SSMEs during its descent, so it glides back to Earth unpowered.
The shuttle's re-entry path from orbit consists of long S-shaped curves to help the vehicle slow down and make the landing "take longer" due to the curved path at the edge of the atmosphere. The shuttle then descends through the atmosphere like a glider. The atmosphere helps slow the shuttle down, but the craft is travelling much faster during its descent than during its launch, so heat and friction are more significant problems. To address this, the leading surface of the craft is sheathed in a heat shield, which dissipates the accumulating heat.
Compared to a normal passenger plane landing, the shuttle's speed is much greater, and the descent is much steeper. Parachutes are deployed from the back of the shuttle upon touchdown to help slow the vehicle down. The shuttle also requires a longer runway than a passenger plane due to its speed—about 4.5 km long, compared to about 2.5 km or less for passenger planes.
The space shuttle's main engine uses 385,000 gallons of liquid hydrogen and 143,000 gallons of liquid oxygen as fuel. The multistage vehicle was invented to address the problem of needing to boost "excess" mass in the form of fuel, most of which is the fuel required for transporting the fuel it will burn later in the journey. As a result, the craft gets progressively smaller and lighter, so that the remaining fuel can do more with less.
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The shuttle's fuel load is heavier than an airplane's
The space shuttle's main engine, which must work above the atmosphere, uses 385,000 gallons of liquid hydrogen and 143,000 gallons of liquid oxygen. This is because any craft with an agenda to leave the atmosphere must carry a much heavier fuel load than an airplane. This is due to the need to boost "excess" mass in the form of fuel, most of which is the fuel required for transporting the fuel it will burn later in the journey. This problem is mitigated by multistage vehicles, where smaller payloads are launched by huge, powerful rockets that drop away sequentially when their fuel supplies are exhausted.
In contrast, a Boeing 747 uses approximately 1 gallon of fuel every second, burning around 36,000 gallons of fuel over a 10-hour flight. A Boeing 747-400 burns around 10-11 tons (approximately 22,000-24,000 pounds) of jet fuel per hour. Smaller aircraft, such as regional jets or single-engine planes, have much lower fuel consumption rates, making them ideal for shorter, domestic routes.
The weight of the fuel itself plays a significant role in fuel planning for airplanes. Heavier aircraft require more fuel to achieve and maintain cruising altitude, creating a complex balancing act where airlines aim to carry just enough fuel without adding unnecessary weight. Commercial aircraft use precise fuel calculations to optimize efficiency and ensure enough reserve fuel is available for delays, reroutes, or emergencies. International flights often require additional reserve fuel to account for unexpected situations.
While specific fuel consumption rates vary depending on the aircraft type and flight duration, large commercial jet airliners like the Boeing 747 and Airbus A380 burn thousands of gallons of jet fuel per hour. In comparison, the space shuttle's fuel load is significantly heavier, requiring liquid hydrogen and oxygen to propel it beyond the atmosphere. Therefore, the shuttle's fuel load is designed to carry a much heavier fuel load than an airplane to achieve its mission objectives.
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Frequently asked questions
A space shuttle does not carry any fuel internally. All the fuel is stored in an external tank (ET) that is discarded after use.
The external tank is the "backbone" of the shuttle during launch. It provides structural support for attachment with the Space Shuttle Solid Rocket Boosters (SRBs) and the orbiter. The tank is connected to the orbiter at several attachment points and supplies fuel and oxidizer under pressure to the three RS-25 main engines in the orbiter.
The external tank carries liquid hydrogen fuel and liquid oxygen oxidizer. The two solid rocket boosters use a mixture of ammonium perchlorate, aluminium, iron oxide, PBAN or HTPB polymers, and an epoxy curing agent.
