In April 1970 an oxygen tank exploded on Apollo 13, and the crew had to use the lunar module as a lifeboat. Carbon dioxide began to build up. The spare filters from the command module were square, and the lunar module needed round ones.
Engineers on the ground designed and tested an adapter made from plastic bags, cardboard from the flight plan cover, a spacesuit hose and duct tape. NASA calls it “the mailbox.” The engineer who led the work, Ed Smylie, explained it in a 2021 documentary: “If you’re a Southern boy, if it moves and it’s not supposed to, you use duct tape.”
In his NASA oral history he said: “It was pretty straightforward, even though we got a lot of publicity for it …” He added that “a mechanical engineering sophomore in college could have come up with it.”