Astronaut Sidney Gutierrez changing a lithium hydroxide canister in the mid-deck of Shuttle Columbia. Gutierez was pilot of Columbia during the STS-40 mission of 5-14 June 1991. The canisters of lithium hydroxide are used to remove carbon dioxde form the Shuttle's air system during flight. With seven crew members on the flight, canisters had to be changed every six to seven hours. Mission STS-40 carried the Spacelab Life Sciences SLS-1 module in its cargo bay. After return from this mission, Columbia has been transfered for major alterations, allowing it to operate as the first Extended Duration Orbiter (up to 16-day missions) from 1992.