This phenomenon, called cold welding, has been a known hazard for spacecraft engineers for a long time. So what's actually happening at the atomic level, and why does space make it so much easier?
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But on Earth, nearly every metal surface is coated in an oxide layer. The layer is just a few atoms thick and forms when metal meets oxygen. "Once the oxide is formed, it's over," Julia Greer, a materials scientist at Caltech, told Live Science. "Then it can't cold weld anymore, because the oxygen basically passivates these bonds."
In space, there's no oxygen to rebuild that layer once it's gone. The cold and the radiation make things worse. Bombardment from solar and ionic radiation in orbit can scour metal surfaces clean, Greer said, leaving freshly exposed atoms primed to bond. "Everything in space is conducive to cold welding," she said.
Pressing two surfaces together, especially with any sliding or vibration, can shear off the oxide layer that formed while the metal was on Earth and flatten those peaks into metal-to-metal contact. "You're breaking up the surface oxide, and you're forming metallurgical bonds," Cordero said.
For example, say you were to add a metal screw to a metal door. After a while, you would not be able to unscrew it because it would have become part of the door.
An illustration of NASA's Galileo spacecraft, whose high-gain antenna never fully deployed during its journey to Jupiter. The failure is widely attributed to cold welding. (Image credit: MARK GARLICK/SCIENCE PHOTO LIBRARY via Getty Images)
Some metals are more troublesome than others. Gold and platinum don't form an oxide layer at all, even on Earth, which makes them notoriously prone to cold welding. "Gold definitely is a very notorious metal for cold welding," Greer said, adding that gold's softness lets it conform easily to whatever surface it touches and it bonds even more easily.
How to prevent cold welding in space
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Before launch, hardware also gets shaken on vibration tables and cycled through extreme hot-and-cold swings inside vacuum chambers, simulating the stresses of liftoff and orbit to catch problems on the ground.
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