How Do Spacecraft Return To Earth Without Burning Up?

Spacecraft can return to Earth safely due to ablation, wherein the shuttle’s outermost layer absorbs the heat of re-entry and erodes.

Man has sought protection from invading elements for millennia, in some form or other. As our adventures took ever-riskier paths, the role of protective equipment also became more critical. Beginning as any kind of barrier between a man’s skin and the external environment, protective equipment has come to play far more active roles in work, travel, industry and survival. One such crucial role is in the flight back home from space!

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What Is Re-entry From Space Like?

Before we look at the evolution of safety materials, we should first attempt to understand the basics of entering Earth’s atmosphere from space. Getting spacecraft to land safely back on Earth is no walk in the park.

2. Charring Ablators

Charring ablation involves material getting burnt to form a porous layer. It is porous due to selective melting or sublimation of the material. The gases derived from the formation of the char layer further add to the insulating properties. Charring ablators are also progressive in nature. This means that more char gets formed as the top layer erodes away, due to aerodynamic shear forces. Due to this, charring ablators are the most effective, and are therefore highly preferred for thermal protection. They are often used in conjunction with sublimating or melting ablators to increase their efficacy.

Carbon fiber-reinforced phenolic composites and resins are examples of charring ablators. They can be used with melting ablators, such as silica or nylon, to enhance their ablative characteristics.

Wood has been used as a low-cost charring ablator in the past, but it was phased out, as the thermal and physical characteristics of wood aren’t uniform throughout.

3. Intumescent Ablators

Intumescent ablators form a foam-like porous structure when exposed to heat. While you can think of them as charring ablators, they are actually the outcome of an exothermic reaction, as opposed to the endothermic reactions that take place in charred ablators. Since exothermic reactions add to the overall exposure to heat, they are usually reinforced with inorganic material that helps consume energy, rather than adding to it.

Intumescent ablators are known for their superior mechanical strength. However, this also means that their structure is detrimental to the aerodynamics of a vehicle as it enters Earth from space. For this reason, they are not used in high-speed re-entry vehicles. They find use in ammunition that is susceptible to fire, and in load-bearing applications, such as beams, pillars, and bridges on oil rigs. Intumescent ablators are easy to install, as they are available in the form of proprietary spray-on coatings, sheets and tapes.

Advancements In Ablator Technology

The process of ablation can be wasteful, given that material gets consumed in the process. Research bodies are looking for reusable ablatives that sacrifice less material. At the same time, scientists want to shift from using organic material to metallic ablators.

The use of such ablators would help to delay the oxidation and decomposition of ablators, especially in low-level orbits of Earth’s atmosphere, where temperatures are generally high, and satellites face prolonged exposure.