The lithium hydroxide canister was designed as a replaceable filter for the command module's environmental control unit (ECU). The ECU provided cooling, water and breathable oxygen for the astronauts’ suits and cabin. Two canisters were present in the oxygen system at all times and were alternately replaced, one every twelve hours. To maintain a safe pure-oxygen environment, the canisters contained lithium hydroxide (LiOH) and charcoal and were covered by a felt cloth barrier. The LiOH within the canister absorbed carbon dioxide, the charcoal eliminated odors, and the felt trapped particles and debris.
This canister, made by Airesearch, was flown on the final Apollo lunar landing mission (Apollo 17) and was transferred to the Smithsonian in July 1973.