An improvised “letter box” helped Apollo 13 breathe

After an oxygen tank exploded, the crew of Apollo 13 used the lunar module as a refuge. Carbon dioxide must also be removed from the breathing air. Absorbent cartridge reserves of this module are limited. Other cartridges exist on board, in the control module, with a shape that is not directly suitable.

The so-called "letter box" solution allows to connect these incompatible equipment. Engineers design and test it on the ground before offering it to astronauts. They make the adapter with the available materials, including adhesive tape. The photographs of the interior show this montage far removed from the usual appearance of space hardware.

The ribbon did not make oxygen. It helped operate a device that used lithium hydroxide to remove carbon dioxide. This framed DIY answered a specific problem among the difficulties of the return. The ingenuity was as much in the assembly as in the work between the teams on the ground and the men locked up in their refuge.