A satellite travels at incredible speeds, encountering atmospheric conditions and temperature fluctuations not experienced within the Earth’s atmosphere. For this reason, the materials used to construct and protect satellite components must be chosen with particular care and consideration.
Thermal and Atmospheric Considerations
Although the sun’s extremely powerful light and heat is absorbed and dispersed by the earth’s atmosphere, this is not the case in the atmospheres in which satellites orbit. For this reason, the satellite must be protected from exposure to light, heat and direct radiation. Additionally, UV radiation in the upper atmosphere produces atomic oxygen when exposed to oxygen atoms. This can result in undesirable oxidation and corrosion.
As satellites orbit, meteoric debris can cause damage to coatings, platings and structures. For this reason, the materials used to coat and plate satellites must be able to resist high impacts and retain their strength. Thermal conditions change rapidly as satellites reach speeds of around seven kilometers per second. These rapid environmental changes can result in coating degradation and insulation challenges.
Popular Materials for Coating and Insulation
Satellite designers commonly use aluminium alloys to insulate satellites. Aluminium is widely admired for its low weight, durability, availability and cost-effectiveness. Multi-layer insulation, for example, contains aluminium in the form of aluminized polyimide. Where insulation requires additional reinforcement with plating, gold is a popular choice for internal components. Designers also use silver for internal plating of satellite components and copper for electronic applications such as circuit boards.
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Multi-Layer Insulation with Aluminium
Multi-layer insulation is, as the name suggests, a combination of layers made from aluminium-coated polyimide that protect a satellite’s instrument controls from thermal or radiation damage. The silver aluminium side faces inwards while the outward-facing polyimide layer appears to be shiny gold, sometimes mistaken for a type of golden foil wrap. In addition to the aluminium-coated polyimide, multi-layer insulation may also include layers of beta cloth, fiberglass, netting spacer and silver.
Not only do the instruments onboard the satellite generate heat, the temperature extremes outside are also formidable, both in terms of heat and cold. Multi-layer insulation consists of around 40 layers with a variety of thicknesses, and these must not come into thermal contact. The insulation is not only heat and radiation reflective, it also reflects visible light and guards against dust and debris.
Metal Satellite Plating with Gold
Where insulation is not sufficient to protect a satellite from radiation, light, heat and impact, plating is used. Gold is a popular, though expensive material for plating, taping and protecting equipment. Despite its price, designers use gold because of its extremely beneficial properties in the vacuum of space. Gold absorbs light well, reflects radiation away from the satellite, does not react to atomic oxygen and conducts heat and electricity extremely well. Additionally, it’s soft and workable during manufacturing and can be vacuum deposited into a film. Gold is also used together with polycarbonate plastic on astronaut visors to protect eyes against visible light and UV radiation. Additionally, it forms electronic components, coats telescope materials and assists collector analysis.
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