Punch a hole in most materials and eventually get around to patching it. NASA and the International Space Station don’t have the luxury of ‘eventually’. So, NASA developed a material that is a sandwich with liquid in the middle. When punctured, the liquid leaks out, and if it hits oxygen, solidifies in seconds. The material isn’t structural (yet) but could act as an inner lining for spacecraft, whether it is the station, crew transfer vehicles, or planetary missions. Seems simple, yet obviously has been difficult to invent. Applications also exist on Earth anywhere we don’t want leaks but do have things flying around, like bullets and glass.
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