You’ve probably noticed that many artificial satellites are covered with what seems to be gold or silver foil. In fact, it’s not just satellites; you can see this in most space-related equipment (i.e., the equipment that actually goes into space).
While they may seem like they are draped in precious metal, it’s usually not gold at all… or even foil! It is actually a material called multi-layer insulation, or MLI.
MLI consists of lightweight reflective films assembled into thin layers that range in thickness. These layers are usually made of polyimide or polyester films (types of plastics) coated with very thin layers of aluminum. This is used over critical spacecraft parts to severely limit effect of surface temperature fluctuations in parts sensitive to thermal changes by limiting the amount of heat transferred between the two sides of the layers.
Depending on its orbit, a
satellite can experience temperatures from below -200°F to well above
300°F, sometimes at the same time! Not to mention the high temperatures
the onboard instruments can produce.MLI is designed to reflect solar
radiation back into space, keeping the instruments cool enough to
operate while in sunlight. It also maintains internal temperatures by
keeping heat in, protecting the instruments from the extreme cold
experienced when the spacecraft moves through Earth’s (or its own)
shadow.
MLI can also provide a layer of defense against dust impacts, protecting delicate internal instruments and sensors from tiny particles of space debris.
