Materials Used in Rocket Constructions
We will list out the materials and the challenges faced for rocket constructions.
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Modern rockets consist of a combination of metals and advanced technology. In this series, we aim to provide comprehensive information on the construction and components of rockets. In this particular segment, we will focus on the structural element of rockets.
Factors to Consider and Challenges….
Rocket boosters and space vehicles are constructed using a range of materials, including high-density materials for heat absorption and high-strength, lightweight materials to bear flight loads. The primary consideration in selecting these materials is to achieve minimum weight, as each extra pound of material used in construction reduces the useful payload by at least one pound. The ideal material would be a composite of two or more materials, with each component utilized for its best property. For certain applications, it may be preferable to protect conventional structures from severe thermal environments rather than constructing high-temperature materials. The insulation of rocket nozzles and re-entry nose cones is one example where protection may be more advantageous than using high-temperature materials.
To minimize weight, vehicle skin thickness should be as low as possible, but very thin sections of material possess appreciable strength only under tension loads and not in other directions, which creates unique design and handling challenges. One method of using thin-walled structures involves internally pressurizing the structure to prevent buckling of the walls. This is achieved by making the net stretching force due to internal pressure greater than the compressional force due to flight loads. Another method involves using stiffening members (stringers) that are fastened to the skin in the direction of the compressive load, a common practice in the construction of conventional aircraft (Fig. 1).
A single-piece construction with ribs or "waffles" that serve as stringers can also be achieved through chemical milling or machining of a solid sheet. This method involves removing all metal except for the desired ribs or "waffles," as illustrated in Fig 2.
Another method for stabilizing thin sheets against buckling is by using a lightweight supporting core to create a "sandwich" structure. The core could be in the form of honeycomb (as depicted in Fig. 3), corrugation, or a light plastic or metal foam. Sandwich construction is particularly relevant for higher temperature applications and is becoming increasingly important. This method of construction may prove useful in vehicles such as hypersonic gliders.
Best Metal Choices!
The backbone of modern space vehicles is made up of various metals. Aluminum, which was originally used in aviation, was found to be too light and not robust enough for rocket construction. As a result, duralumin, an alloy containing copper and manganese, was developed and became commonly used due to its strength and hardness. However, it has low weldability and is typically riveted or bolted together. The aerospace industry commonly uses aluminum alloys with magnesium content up to 6%, which are deformable and weldable.
Steel is also an indispensable material in the aerospace industry, with stainless steel being the most commonly used. Stainless steel is superior to aluminum alloys in terms of hardness and has proven to be more compact and lightweight while also being cheaper, even in the most exotic grades. Propellant tanks are typically built from stainless steel, which has very thin walls that are maintained by internal pressure to prevent them from collapsing under their own weight. Copper, which is heavy and expensive, is used for the inner walls of rocket engines due to its fantastic thermal conductivity.
Titanium and silver are also used in rockets, but their volumes are insignificant due to their higher weight and cost compared to steel and aluminum alloys. Glass and carbon fiber are also being used in modern space vehicles, including American reusable space shuttles, which have a thermal protection system built from seven different fiber and ceramic materials.
Elon Musk is confident in modern metallurgical technologies, and high-strength non-magnetic steel with chrome-nickel content will help him achieve his goals. In conclusion, steel will remain a key material in the space industry for a long time to come due to its durability, affordability, and resistance to external factors.
In next article we will continue with this and cover another aspect of rocket construction.