Gold foil

In many photographs of space agencies, whether NASA or Roskosmos, parts often wrapped in gold-colored foil often appear in the preparation of spacecraft. Obviously, it serves to isolate, but why gold? And how does it work?

As is known, there is solar radiation, which affects the Earth’s atmosphere and is the main source of energy for all the natural processes of the planet. From the graph, where the intensity is visually presented, it is clear that the peak falls on the visible spectrum, although a large proportion of the radiation is in the IR and UV ranges (for more information on the phenomenon, see Wikipedia, the article " Solar Radiation "):
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Therefore, the equipment that should work in space, it is necessary to protect as much as possible from exposure to IR radiation. To do this, some parts of the spacecraft are wrapped in metal insulating "foil". Conventional such "reflectors" are made of aluminum, silver, copper or gold. But in the space industry is widely used gold. The graph below shows the change in reflection coefficient for each of the metals, depending on the wavelength:



All four metals do well with the reflection of infrared radiation, the coefficient is close to 100% for waves longer than 700 nm. So why exactly is gold used? Because, unlike copper or silver, gold does not give in to corrosion (for the same reason it is widely used in the manufacture of printed circuit boards), and it is easier to work with gold than with aluminum (Remember what happens with aluminum foil if crumpled and then deploy again).

In general, the "golden foil" is far from only gold. This is a multi-layer metallized film, and different parts of the spacecraft are wrapped in different types of films, depending on the needs. There is such a PDF from NASA, which tells in detail about this, with pictures!



Often Kapton is used as a material for the film, which in turn is applied a thin layer of gold, aluminum, and silver. The last two metals can give a golden color with a very thin coating.

Modern spacesuit technologies are a good example of the use of gold plating: helmets filters are made of polycarbonate-based plastics (UV protection), which are also covered with a sufficiently thick layer of gold to protect the cosmonaut from solar radiation. As a result, the filter transmits no more than 35% of the light, which completely protects the eyes from external exposure to IR radiation, which is outside the visible spectrum, and therefore can imperceptibly cause irreparable damage to the astronaut's vision. The "golden filter" stops almost all UV and IR radiation and about 60% of the radiation in the visible spectrum.



PS Another use of gold foil: