Vacuum welding is a problem in space probes -- how does vacuum welding occur?

Answer 1

Vacuum welding occurs when two flat pieces of material (particularly materials with crystaline molecular structures) are placed in intimate contact. The crystaline matrix literally 'grows' itself together over time. It can even be observed here, on the surface, when a pair of ultra flat guage blocks ('Jo- blocks') are left together for more than an hour or two.

HTH

Doug