Vacuum cementing or vacuum welding is the natural process of solidifying small objects in a hard vacuum.^{[clarification needed]} The most notable example is dust on the surface of the Moon.

This effect was reported to be a problem with the first American and Soviet satellites, as small moving parts would seize together.^{[citation needed]}

In 2009 the European Space Agency published a peer-reviewed paper detailing why cold welding is a significant issue that spacecraft designers need to carefully consider. The paper also cites a documented example from 1991 with the Galileo spacecraft high-gain antenna.^[1][2]

One source of difficulty is that vacuum welding does not exclude relative motion between the surfaces that are to be joined. This allows the broadly defined notions of galling, fretting, sticking, stiction and adhesion to overlap in some instances. For example, it is possible for a joint to be the result of both vacuum welding and galling (and/or fretting and/or impact). Galling and vacuum welding, therefore, are not mutually exclusive.^{[citation needed]}