How has spacecraft material evolved over the past several decades?
Material is an essential and interesting part of the design of a spacecraft. Unlike aircraft, which are transportation vehicles that fly in the atmosphere, spacecraft often confront much more extreme conditions, such as low temperatures, cosmic radiation, and low pressure. Therefore, material design plays an important role in spacecraft construction; we must make sure spacecrafts are safe from that dangerous environment.
The development of materials is not completed in one run, instead, it has evolved several times, from concepts to real designs. This also refers to the history of spaceflight is also the history of solving different newly found physical limits. In other words, every major material appeared because engineers faced a serious problem and needed a better way to survive it.
The first thing, which is also the fundamental system used in early spacecraft, was the Whipple shield, which was invented in 1947. In outer space, there are thousands and millions of orbital debris that are flying at a significant high speed, around 7–15km/s. At this scale of velocity, even a tiny piece of a micrometeoroid can destroy the entire machine by simply striking its surface. Solving this difficulty, instead of using only one thick wall, they use a thin outer layer first, so tiny particles break apart before hitting the main wall. This idea is very powerful since it does not simply add more mass, so it does not affect the weight and make the launch more difficult.
From the 1950s, aluminum alloy became a standard structural material for many spacecraft. However, it had already been invented since the 1900s, but the usage in spacecrafts was implemented at that time. It has a lot of advantages over other metals; it is light, strong, and relatively easy to build with. Because of that, although it is not perfect, even today it is still widely used because of its high reliability and the heritage supply chain of it.
Another key material system is multi-layer insulation (MLI), a silver blanket-like cover on spacecraft. The main problem is not limited to the coldness in outer space, but the repeated cycling between hot sunlight and cold shadow. Indeed, MLI helps reduce radiative heat transfer, which keeps spacecraft systems more stable. In real cases, one spacecraft might need multiple thermal materials at the same time. Silica tiles protected many surfaces, while reinforced carbon-carbon (RCC) was used in hotter areas like the leading edges at the same time. They were all invented in the latter half of the 20th century and promoted further development and research in modern Aerospace Materials Science.
After a period of time, a modern material system, PICA (Phenolic-Impregnated Carbon Ablator), was invented, which shows why ablative materials are still essential. For high-speed reentry, some missions need a material that can char and slowly burn away to carry heat away from the vehicle. This development continues in the 21st century, and there are still massive problems waiting for solutions.