The Saturn V rockets that launched astronauts to the Lunar surface had over three million moving parts constructed from various materials. We take a closer look at the different materials used in a modern orbital rocket.
An orbital rocket’s structure primarily consists of strong, lightweight materials like aluminum, stainless steel, titanium, and carbon composites. Its propulsion system typically consists of heat-resistant materials with high thermal conductivity, like copper alloys, niobium, and Inconel.
The various materials used in the construction of a rocket need to be strong enough to hold the vehicle together and withstand all the dynamic forces put on it during launch and ascent but also be light enough to assist it in escaping Earth’s gravity and achieving orbit.
As a result, strong, lightweight materials like titanium, aluminum, and carbon composites are typically used to build the most critical parts of an orbital rocket. These materials are typically used for the construction of a launch vehicle’s structural system.
However, an orbital rocket consists of more than just its structural system. It also consists of the propulsion, guidance, and payload system. (You can learn more about the four primary components/systems that make up an orbital rocket in this article.)
The materials used in the electronic equipment for the guidance system is very similar to the ones used on the planet’s surface and in modern aircraft, apart from being strengthened and adapted to withstand the harsh conditions in an orbital rocket and the vacuum of space.
As a result, the following section will focus primarily on the materials used in the structural, propulsion, and payload systems of modern orbital rockets.
Materials Used In An Orbital Rocket’s Structural System
A number of materials are used in an orbital launch vehicle’s structural system, depending on the type of rocket and where on the vehicle a specific material is needed. However, most modern orbital rockets use one or a combination of the following materials:
- Aluminum
- Stainless Steel
- Titanium
- Silica (Ceramic) Fibers
- Carbon Composites
The different types of aluminum alloy (specifically aircraft grade 6061 aluminum) are the primary metal used in the construction of a rocket’s structural system. Various compounds of this metal exist, each with its own benefits and drawbacks.
For example, duraluminum (which is a combination of aluminum, copper, and manganese) is harder and stronger than aluminum but is hard to weld, and the parts are typically riveted or bolted together.
Aluminum-magnesium alloys are more widely used in the space industry since it is more easily deformed and welded, while aluminum-lithium alloy (a combination of aluminum and lithium) turned out to be the strongest and lightest combination.
Launch vehicles whose structures are primarily constructed of aluminum include the iconic Saturn V (using 2014T6 Aluminum plates) and the Falcon 9 rocket, which primarily used AlLi 2198 (an Aluminum-Lithium-Copper alloy) to construct its outer shell.
Although it is much heavier than aluminum, stainless steel is also commonly used in rocket manufacturing and is used for the construction of the world’s largest launch vehicle, SpaceX’s Starship, currently in development at its Boca Chica launch facility in Texas.
It is much cheaper than carbon fiber (which was originally proposed), and manufacturing advancements allow it to be more durable, not prone to cracking, and can also withstand large temperature drops.
Titanium is a very strong metal that is also commonly used in the Space industry but is not as widely used as often perceived. In a spacecraft’s structure, it is used specifically in components & areas where high strength and additional protection are critical.
(In the Juno spacecraft that orbited and studied Jupiter, a radiation vault was used that had walls made from 1 cm thick titanium to protect the electronics from the planet’s strong radiation belts.)
Silica (ceramic) fibers and reinforced carbon-carbon are used to create the heat shields that protect the vehicles that need to return to Earth’s surface, which experience temperatures of up to 1600° Celsius (3000° Fahrenheit) during the critical reentry process.
Carbon composites have been used for several years in various parts of orbital rockets. However, their use in the development of their structural system is on the increase, especially among small launch vehicle manufacturers like Rocket Lab, based in New Zealand.
The main structure of its small satellite launch vehicle, the Electron, is almost entirely made from carbon fiber, which is 3D printed in only 12 hours.
Materials Used In An Orbital Rocket’s Propulsion System
The materials used in a rocket’s propulsion system need to withstand extreme temperatures. These temperatures range from cryogenic temperatures colder than any natural environment on Earth to scorching temperatures hot enough to melt most metals.
Materials that can typically be found in a rocket’s propulsion system include:
- Stainless Steel (Propellent Storage)
- Aluminum-Lithium Alloy (Propellent Storage)
- Copper Alloys (Combustion Chamber & Nozzle)
- Inconel (Combustion Chamber & Nozzle)
- Niobium (Nozzle)
Cryogenic fuels like liquid hydrogen, the fuel source for many launch vehicles, need to be stored below -253° Celsius (-423° Fahrenheit) to remain in liquid form. Liquid oxygen that serves as the oxidizer needs to be stored below -183° Celsius (-297° Fahrenheit).
(The fuels orbital launch vehicles use can primarily be divided into liquid and solid propellants. Learn more about the different fuels rockets use, their characteristics, and each one’s advantages and drawbacks in this article.)
The internal propellant tanks of a rocket are primarily made out of stainless steel. It is a harder/more rigid metal than aluminum and, in general, more suitable for storing liquid fuel and oxidizers.
However, many launch vehicle manufacturers also make use of aluminum-lithium alloy to manufacture their rockets’ propellant tanks since this metal is not only much lighter than stainless steel, it also has a higher tensile and yield strength than conventional aluminum.
The final version of the Space Shuttle’s external fuel tank consisted of aluminum-lithium alloy, and the material is also used for the SpaceX Falcon 9 rocket’s fuel and oxidizer tanks.
On the other side of the scale, the temperatures inside a liquid-fueled rocket’s engine can exceed 6000° Celsius (3300° Fahrenheit), which will melt most metals in seconds. As a result, the materials used to manufacture rocket engines need to be highly heat resistant.
(Even the most heat-resistant metals can not withstand the heat generated by a rocket engine for sustained periods. As a result, various cooling methods are utilized to keep the engine & nozzle cool and prevent them from melting, which are explained in this article.)
For the inside of rocket engines, especially the combustion chamber and nozzle, copper alloys (specifically chromium copper) are typically used, not only because they have high heat resistance but also due to their thermal conductivity.
A heat-resistant alloy called Inconel is often combined with copper to form the walls of a rocket engine’s combustion chamber, which are regeneratively cooled by cryogenic fuels pumped through channels running through the inside of the chamber & upper nozzle walls.
In Space, radiative cooling is used to reduce heat. Niobium, a metal with a high melting point that can also conduct heat well, was used for the nozzle extensions of the Apollo Service Module and is currently used for the Falcon 9 vacuum-optimized Merlin engine nozzle.
Materials Used In A Orbital Rocket’s Payload System
When one refers to the payload system of an orbital rocket part, it is essentially the front part of the rocket, including the nose, which is typically covered by the payload fairings.
The payload itself may consist of several different items. Most launch vehicles carry a type of satellite deployed at different orbits. It can also include resupplies for the International Space Station, exploratory spacecraft, and astronauts/cosmonauts, amongst others.
This means the materials used vary substantially and include a wide range of alloys and compounds, too numerous to list. A common characteristic of all these materials, though, is that they need to withstand the stress of a rocket launch & the hostile environment of space.
The payload fairing (which covers the front and forms the nose of a rocket) is a standard part of any launch vehicle’s payload system, though. It must be both light and strong enough to withstand the stresses put on an orbital rocket during launch & also protect the payload.
Carbon fiber composites are the chosen material that fulfills all these requirements and is widely used by most modern orbital rockets. Modern vehicles that use these materials for their respective payload fairings include the Atlas V, Falcon 9, and Ariane 5 rockets.
Another universal component in most payload systems is the forward adapter that connects the launch vehicle’s upper stage to the payload. A strong, lightweight material with high tensile strength is required for this section, making aluminum-lithium alloy an ideal choice.
The forward section of the Centaur Upper Stage (a cryogenic upper stage rocket used on several orbital launch vehicles) primarily consists of aluminum-lithium alloy.
Conclusion
An orbital rocket is subjected to a tremendous amount of force and stress during and after liftoff from the thrust generated by its thrusters, the stresses put on it as it accelerates through our thick atmosphere and the harsh, hostile environment of space.
As a result, the materials used in these spacecraft must be strong, light, resistant to stress and vibrations, heat tolerant, as well as being able to withstand extreme cold temperatures. This is a tough ask, explaining why so many different materials are used in an orbital rocket.
This article highlighted some of the primary materials used in these launch vehicles, their characteristics, and the specific areas where they are implemented. It is not an exhaustive list of all materials used by any means, but it does underline the most commonly used ones.
This article was originally published on headedforspace.com. If it is now published on any other site, it was done without permission from the copyright owner.
