Welding is the use of high heat to melt two metal pieces together so they fuse into one. It’s tricky and not a relaxing hobby done on the sofa while watching TV. It’s something that people take classes for and get certified for. In other words, it’s definitely a skill to be learned.
But sometimes it happens on accident. Let me introduce you to cold welding.
This diagram shows the antenna of Galileo, which NASA launched in 1989 to gather data about Jupiter. Its special high gain antenna would transmit 134 kilobits per second back to Earth, and was tucked into an umbrella structure so it would be small and convenient for transportation. However, once it arrived at Jupiter, the antenna didn’t release as expected. Of the 18 ribs, only 15 released.
When a team went to work trying to figure out what happened, they discovered that some the rods were cold welded. The umbrella shaped antenna was packaged away before take-off, but some of the rods fused once they were in space.
Cold welding was first recognized in the 1940s. It’s the fusing of two pieces of metal without any applied heat, and happens when two flat metal pieces come in contact in a vacuum. It happened on Galileo because space is a vacuum.
“When the atoms in contact are all of the same kind, there is no way for the atoms to “know” that they are in different pieces of copper.” – Richard Feynman
Basically, it happens because the pieces are pressed so closely together that they fuse. Unlike traditional forms of welding, it requires no heat. It also requires the surfaces to be extremely clean. If any dirt, foreign atoms, or air molecules stand in the way, the metal pieces won’t join.
The European Space Agency published a 2009 paper declaring that spacecraft designers must consider this issue while working. There a number of possible preventative measures to take: selecting materials that won’t cold-weld, coating surfaces, lubricating moving materials, and reducing contact surfaces.
It’s a problem that aerospace engineers have to think about, but not anything to lose sleep over. It’s just something that designers have to keep in mind. Either way, it’s pretty cool that space can squeeze things together so hard that they become one!