Regan Brown
The number of fuel tanks in space is unclear, but the topic is an interesting one. Fuel tanks are essential for spacecraft, providing the propellant needed to reach orbit and beyond. The number of tanks varies depending on the spacecraft and its mission. For example, the Dragon spacecraft carries 1380 kg of propellant, which is split across multiple tanks, while the Orion Moon module has four large tanks, each containing about 2000 litres of propellant. The Cassini spacecraft is also notable for its large fuel tank, which makes up a significant proportion of its total mass. The design and materials used for fuel tanks are critical, with insulation and structural strength being key considerations.
| Characteristics | Values |
|---|---|
| Name of fuel tanks | Space Shuttle external tank (ET) |
| Components | Three major components: aft liquid hydrogen (LH2) tank, liquid hydrogen fuel, and liquid oxygen oxidizer |
| Function | Supplied fuel and oxidizer under pressure to the three RS-25 main engines in the orbiter |
| Weight | 77,000 pounds (35,000 kg) |
| Materials | Stainless steel, steel alloys, aluminum alloys |
| Insulation | Foam, multilayered aluminum, shields to block solar radiation |
| Testing methods | Cold shocking, vibration testing, speaker testing |
| Location | One test fuel tank located near St. Johns River in Florida |
| Recent developments | Installation of fuel tanks in the European service module for NASA's Orion Moon module |
| Tank capacity | 2000 litres of propellant |
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What You'll Learn
Fuel tank testing and durability
Fuel tanks in space, such as the Space Shuttle External Tank (ET), are crucial components that supply fuel and oxidizer to engines during lift-off and ascent. These tanks are designed to be lightweight yet sturdy, posing several challenges in their testing and durability.
Testing and Durability:
The durability of fuel tanks is of paramount importance in space missions. In the 1960s, stainless steel and steel alloys were the preferred materials for cryogenic fuel tanks. Over time, the focus shifted to minimizing tank weight while maximizing strength. To achieve this, engineers conducted extensive tests to evaluate the performance and resilience of fuel tanks.
One common method of testing a tank's durability was "cold shocking." This involved filling the tank with liquid nitrogen or other stable cryogenic fluids, followed by emptying it to check for any potential issues with welds, couplings, or lines caused by the extreme temperatures. Additionally, NASA researchers utilized facilities like the Rocket Systems Area to study tank durability, pressurant variations, and insulation systems.
The performance of fuel tanks is closely tied to the effectiveness of turbopumps, which play a critical role in pumping fuel and oxidizer from the tanks to the fuel injectors at high speeds. Hydrogen pumps, in particular, present unique challenges due to the cryogenic fluid's proximity to its boiling point. To address this, engineers designed impellers and inducers (spiral-shaped rotors) to reduce the effects of cavitation, thereby improving turbopump performance and longevity.
Furthermore, insulation is essential for preventing cryogenic fuel from evaporating. NASA researchers examined various methods, including the use of foam, multilayered aluminum, and shields to block solar radiation, to insulate cryogenic propellant tanks. These insulation techniques were crucial for preventing fuel evaporation during launch and long-duration missions, as even minor temperature increases could result in significant fuel loss and mission failure.
In addition to standard testing procedures, NASA also conducts destructive testing on fuel tanks to evaluate their resilience. For instance, during the development of the Space Launch System (SLS), NASA performed tests on an empty fuel tank, subjecting it to extreme compression, twisting, and bending forces until it failed. This allowed engineers to study the tank's durability and identify its failure point.
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Insulating cryogenic propellant tanks
Cryogenic propellant tanks are an integral part of spacecraft, including the Space Shuttle external tank (ET), which supplied the fuel and oxidizer to the main engines. These tanks must be insulated to prevent the cryogenic fuel from evaporating, a phenomenon that can be caused even by minor temperature increases. Insulating these tanks is crucial to mission success, as the evaporation of cryogenic fuel can lead to significant fuel loss.
NASA researchers have explored various methods for insulating cryogenic propellant tanks, including the use of foam insulation and multilayered aluminum for short-term missions. Foam insulation, such as polyurethane foam, is created by mixing liquid constituents that react and expand, forming component cells. This foam has been used in external tanks, providing protection against ultraviolet light and insulating cryogenic propellant tanks.
For long-term missions, NASA has investigated multilayer insulation systems, such as those designed by Linde and Arthur D. Little corporations. These systems may include layers of aluminum, fiberglass, Mylar, gold, and silk mesh, encapsulated in a protective jacket. Another approach is to use multilayer insulation shaped into removable blankets, offering flexibility in insulation coverage.
Additionally, scientists at NASA's Langley Research Center have developed polyimide foam insulation for reusable cryogenic propellant tanks. This high-performance, flame-retardant, and flexible foam has been licensed to a Florida-based company, PolyMAC Inc., for use in various applications, including spacecraft.
The German Aerospace Center's AKIRA project has also proposed a purged gap insulation design, which reduces overall layer thickness. This design successfully met the defined thermal boundary conditions through experimental simulations.
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Fuel tank sensors
There are several types of fuel sensors used in various applications, including floating fuel sensors, capacitive fuel sensors, and ultrasonic fuel sensors. Floating fuel sensors are commonly found in vehicles and provide a gauge of the fuel level on the dashboard. However, they offer only approximate readings with a relative error of 10-20%. Capacitive fuel sensors, on the other hand, are known for their precision, with a significantly lower relative error of 1-2%. The size of the sensor must be slightly larger than the tank's height to ensure it reaches the fuel at the bottom.
Ultrasonic fuel sensors transmit ultrasonic impulses from the bottom of the tank to the fuel surface and back. By measuring the time of flight, the sensor can determine the height of the fuel column. While ultrasonic sensors provide accurate measurements, their installation is typically more complex and requires special epoxy glue or a metal band to secure the sensor to the tank. Additionally, the shape and internal surface of the tank can affect the accuracy of ultrasonic sensors, making it crucial to choose the right spot for sensor placement.
In the context of space exploration, fuel tank sensors play a critical role in ensuring the success of missions. NASA, for example, has encountered challenges with faulty fuel tank sensors, leading to launch delays to address these issues. In 2006, NASA postponed the launch of its space shuttle mission to replace potentially faulty fuel sensors inside the orbiter's external tank. Known as Engine Cutoff (ECO) sensors, these devices monitor fuel tank levels and are designed to shut down the engines before the tank runs dry. Wiring defects in the manufacturing of some sensors can lead to erroneous readings, potentially causing premature engine shutdown.
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Fuel tank materials
Fuel tanks in space need to be lightweight yet sturdy. In the late 1950s and early 1960s, the Lewis Research Center focused on the handling of liquid hydrogen, which is challenging because the cryogenic fluid is often near its boiling point. Cryogenic propellant tanks for space applications must be lightweight but sturdy enough to contain a heavy gas such as helium to naturally push the liquid into the supply line.
In the 1960s, stainless steel and steel alloys were the preferred materials for cryogenic fuel tanks. The most common method of testing a tank’s durability was to fill it with liquid nitrogen or another stable cryogenic fluid. The tank was then emptied to check if the cold temperatures affected any of the welds, couplings, or lines.
By the early 1960s, engineers determined that multilayered aluminium or foam insulation was sufficient for short-term missions. Shields to block solar radiation were found to be key to storage on long-term missions. One such multilayer insulation system consisted of an aluminium and fibreglass layer encapsulated in an aluminium and Mylar jacket. Another system featured a gold, Mylar, and aluminium layer separated by mesh silk layers.
The original Space Shuttle external tank (ET) was fabricated from 2219 aluminium alloy, a high-strength aluminium-copper alloy used for many aerospace applications. The ET's three primary structures are an LOX tank, an intertank, and an LH2 tank. Both tanks are constructed of aluminium alloy skins with support or stability frames as required. The intertank aluminium structure utilises skin stringers with stabilising frames. The primary aluminium materials used for all three structures are 2195 and 2090 alloys. AL 2195 is an Al-Li alloy designed by Lockheed Martin and Reynolds for the storage of cryogenics. AL 2090 is a commercially available Al-Li alloy. The LOX tank is located at the top of the ET and has an ogive shape to reduce aerodynamic drag and aerothermodynamic heating.
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Fuel tank size
The fuel tank size of a spacecraft is a critical aspect of space missions. The size of the fuel tank determines the amount of propellant that can be carried, which in turn influences the duration and range of the mission.
The External Tank (ET) of the Space Shuttle, for example, played a vital role in supplying propellants during lift-off and ascent. It contained liquid hydrogen fuel and liquid oxygen oxidizer, which were fed under pressure to the three RS-25 main engines. The ET was the largest and heaviest component of the Space Shuttle when loaded. It consisted of three major structures: the LOX tank, the intertank, and the LH2 tank. The LH2 tank was the largest in terms of volume, but due to the low density of liquid hydrogen, it contributed relatively less to the overall weight. The LOX tank, on the other hand, was smaller but significantly heavier due to the higher density of liquid oxygen.
The ET's design underwent iterations, with the development of lightweight tanks (LWTs) and super lightweight tanks (SLWTs) to reduce weight and increase efficiency. These newer tanks maintained the external appearance of the standard-weight tanks (SWTs) used in the first six Space Shuttle missions but featured internal construction and material differences.
The size of the fuel tank can also vary depending on the mission's specific requirements. For instance, the Venus orbiter Magellan had a fuel mass fraction of nearly 70%, carrying 2414 kg of propellant out of a total launch mass of 3449 kg. In contrast, the MAVEN Mars orbiter had a fuel mass fraction of 66%, indicating a higher proportion of fuel relative to its total launch mass.
Additionally, the number of fuel tanks within a spacecraft can also vary. For instance, there is speculation that the SpaceX Dragon spacecraft has eight fuel tanks, with four each for MMH and NTO propellants. However, the exact number of tanks and their functions remain unconfirmed.
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Frequently asked questions
I cannot find an exact answer to this question. However, I can tell you that the Space Shuttle External Tank (ET) was the largest element of the Space Shuttle and was jettisoned after each launch. There are also cryogenic propellant tanks, which are used for Centaur, Saturn, and nuclear rocket programs. Furthermore, the spacecraft Cassini, which was sent to Saturn, is described as being composed of two giant things: a giant fuel tank and a giant dish.
Fuel tanks in space are used to store fuel that provides thrust for spacecraft.
The materials used for fuel tanks vary. In the 1960s, stainless steel and steel alloys were the preferred materials for cryogenic fuel tanks. Nowadays, aluminium alloys are used for the external tank of the Space Shuttle, while multilayered aluminium and foam are used for insulating cryogenic propellant tanks.
Fuel tanks have fuel-depletion sensors located at the bottom, and oxidizer sensors in the orbiter liquid oxygen feed line manifold. Turbopumps are required to pump the fuel and oxidizer from the tanks to the fuel injectors at high rates of speed.
