If the two pieces of metal to attach to each other in vacuum, they "grow together"
A curious process called cold welding, allows you to connect the metal parts, without using heat and any chemical reactions.
Prominent American scientist Richard Feynman in his work "The Feynman Lectures on Physics" explains the essence of the phenomenon:
«The reason for the unusual" behavior "of atoms is the fact that when the vacuum is one piece of metal in contact with another object of the same material, the atoms no longer" understand "that they are in two different pieces of metal. If between the two contacting surfaces are present in any other atoms, metal particles "know" that they belong to a certain structure, so normally there is no cold welding ».
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No need to be Feynman, to realize that cold welding may result in serious trouble for astronauts - for example, if the edge of the door lock chamber "prikipyat" to the skin. Cold welding has been the cause of problems - say, the spacecraft "Galileo" during the flight tightly "grown together" parts of the antenna. To prevent something like this, designers have to go to various tricks: to reduce the number of moving parts to make them out of different materials, or cover them with a protective surface layer.
via factroom.ru
