Cold Welding- Story of First Space Walk and Galileo Spacecraft
The two Astronauts Gemini IV, Edward H. White II and command pilot James A. McDivitt, had difficulty first opening and then closing the hatch on 3 June 1965, on the mission of America’s first spacewalk. White found the hatch as hard to push up in zero g as it had been on the ground. They successfully managed to perform both tasks and returned safely to Earth after their successful spacewalk. However, what caused the hatch to stick? Initially, Cold Welding was thought to be the culprit.
Cold welding is a solid-state welding process which requires little or no heat to join two or more metals together. Two surfaces without an interposing oxide layer are brought together, the similar atoms of either side collapse into each other with some pressure. Richard Feynman explains the phenomena in his lectures as:
“The reason for this unexpected behavior is that 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. When there are other atoms, in the oxides and greases and more complicated thin surface layers of contaminants in between, the atoms “know” when they are not on the same part.” — Richard Feynman
On the earth, the surface layers of a metal reacts with oxygen in the air to form an oxide layer which can prevent two pieces of metal from joining together but in space those layers can be worn away from pieces of metal like by sliding over each other and due to lack of any oxygen those layers won’t form again. The pieces of metal can then fuse with a little bit of pressure.
Finally, the Gemini IV mission did not have a cold welding problem; instead, a spring had failed to compress causing all this mess. Although, This problem has not occurred often in missions since it can take a lot of time for dirt and oxygen layer to wear off, The European Space Agency published a paper detailing why cold welding is a significant issue that spacecraft designers need to carefully consider.
The only noticeable problem occurred with “Galileo” spacecraft. NASA launched “Galileo” spacecraft into space with the main aim of gathering data about Jupiter on October 9, 1989. Its high gain antenna was made to be opened like an Umbrella. When Galileo spacecraft reached Jupiter on April 10, 1991, NASA tried to open its high gain antenna but 3 ribs of antenna got cold welded to the body and they wouldn’t open which caused antenna failure. NASA had to use low gain antenna to receive information about Jupiter which reduced the efficiency.
