Life support in spacecraft

On February 20, 1962, John Glenn orbited the earth three times in a Mercury capsule. During the flight he took only a little applesauce from a squeeze tube. After landing he was five pounds lighter; doctors put it down to heat, humidity, and loss of water.

In Mercury (1961–1963), the cabin held pure oxygen at 5 pounds per square inch, about one-third of the air pressure at sea level. Oxygen came from two high-pressure tanks. In the suit circuit, a compressor pushed the oxygen through a canister of activated charcoal, which took up odors, and lithium hydroxide, a chemical that soaks up the carbon dioxide people breathe out. To cool the cabin and the pilot's suit, water was let boil off into space through heat exchangers. Moisture from the pilot's breath was caught in a sponge and squeezed into a tank.

Longer flights brought new problems. In Gemini (1965–1966), fuel cells made electricity from hydrogen and oxygen, with water as a by-product. On Gemini V in 1965 that water was stored beside the crew's drinking water, divided only by a bladder, and the cells made more of it than planned. On January 27, 1967, a fire in the oxygen-filled cabin of the first Apollo spacecraft killed Virgil Grissom, Edward White, and Roger Chaffee during a ground test. Afterward the Apollo cabin was filled at launch with a mix of 60 percent oxygen and 40 percent nitrogen.

For Skylab's designers, food and waste were the hardest parts. Early space food was compressed, processed, and packed to survive launch. Mercury and Gemini crews did not complain, but Apollo crews did, and a NASA engineer who lived on Apollo food for four days found eating a chore. Skylab (1973–1974) added a freezer, an oven, a wardroom for meals, a shower, and a toilet that used a current of air to draw waste into a bag. Doctors also wanted all urine measured and samples of it, and all feces, brought home, to track how the body lost calcium and nitrogen without weight.

Early writers faced the same questions. In Kepler's The Dream (written about 1609), the spirits who carry a man to the Moon fight the cold of the journey and hold damp sponges to his nostrils so he can breathe. In Tsiolkovsky's Greenhouses in Orbit (1917), plants take up the crew's waste and give back food and oxygen, a closed cycle.