In the vacuum of outer space, similar metal pieces can fuse together due to the phenomenon of cold welding, causing significant issues.
Humans have mined and utilized metals for thousands of years. In modern times, we have learned how to make these materials more resilient to environmental effects. Many might think that in the vacuum of space, metals would perform better without rusting or degrading. However, in reality, the vacuum environment also presents numerous challenges that can even lead to serious consequences for space missions.
In the vacuum of space, metal pieces can fuse together due to cold welding. (Photo: SimoneN).
Joining metal pieces together can be very beneficial. Long ago, humans joined metals through welding. This process requires high temperatures, melting one or both metal pieces, fusing them together, and then allowing them to cool.
Today, the world has discovered many alternative methods for welding metals. Chemicals, pressure, and molecular techniques can also assist in joining metals. Notably, there is a method that can occur in the vacuum of space: cold welding.
In cold welding, the welder does not need to melt the metals to join them. However, this technique has certain requirements. For instance, the metals must be of the same type. They also need to be clean, flat, and placed in a vacuum. As the metals come close to each other, the Van der Waals forces between the atoms become stronger. This force is not as strong as a chemical bond, but it can help pull the metals together. When the surfaces make contact, they will weld together.
Take two pieces of gold as an example. They are placed together in a vacuum, with nothing in between. The gold atoms on the surface of one piece will come into contact with the gold atoms on the surface of the other piece. These atoms will sense the interaction with the other piece of gold while also feeling the interaction with the gold atoms deeper within their own piece. They cannot distinguish between the first and second pieces, so they will bond together through metallic bonds.
In many cases, at a larger scale, it is not enough to simply have the metal pieces touch for them to be cold welded. The reality is more complex and challenging than the theory suggests. A certain level of pressure is required for cold welding to occur. However, at the nanoscale, welders can create fairly strong gold nanowires, making it hard to believe they were once different pieces.
Despite the challenges, cold welding at a larger scale is still possible in real-world situations. Moreover, unintentional cold welding can pose significant problems for space missions, such as an airtight compartment door suddenly closing.
According to a report from the European Space Agency (ESA), the Galileo spacecraft, which flew to Jupiter in the 1990s, was unable to deploy its directional antenna due to cold welding. The interaction between the antenna’s arms, which were locked during launch, caused them to fuse together. Fortunately, this did not end the mission, as the spacecraft had a smaller backup antenna that successfully deployed. However, Galileo was unable to collect as much data as expected.
This type of malfunction can have even more serious consequences for space missions, especially those with crew members. Therefore, cold welding is a phenomenon that space agencies must always consider. The more we understand this phenomenon, the safer space missions will become.
