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How the International Space Station Works

Sustaining a Permanent Environment in Space

International Space Station
NASA astronaut Jessica Meir waters plant pillows where Mizuna mustard greens are raised as part of the Veg-04B botany experiment. NASA

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Sustaining a permanent environment in space requires things many of us take for granted here on Earth: fresh air, water, food, a comfortable (and habitable) climate — even waste removal and fire protection.

First, let's talk air. We all need oxygen, so the ISS has several methods of providing it. One technique is to have oxygen delivered from Earth via spacecraft. Supply shuttles periodically arrive with fresh oxygen in tow; the life-giving element is deposited into pressurized tanks aboard the ISS [source: Starr].

The ISS also has systems that make breathable oxygen from recycled water. Using electrolysis, some of these devices split water into hydrogen and oxygen gas. Then, the former is combined with an undesirable compound: carbon dioxide (CO2). Humans naturally exhale this colorless gas, but breathing in too much of it is hazardous to your health.

On Earth that usually isn't a problem because plants absorb CO2. Yet gardening space is limited on the ISS, which forced engineers to devise other means of removing excess carbon dioxide. After the electrolysis process kicks in, some of the hydrogen reacts with the accumulating CO2. A byproduct of this interaction is methane gas, which gets vented into space. Meanwhile, reclaimed oxygen enters the ISS air supply [source: Starr].

While that's going on, drinking water gets recycled as some of these very mechanisms repackage exhaled air. Water is also reclaimed by collecting sweat, condensation and urine. (Plus, some crew-members get water from reusing toilet and shower water.) As astronaut Douglas H. Wheelock told The New York Timesin 2015, when you're aboard the ISS, "Yesterday's coffee is tomorrow's coffee" [source: Schwartz].

According to the European Space Agency, as much as 80 percent of the water aboard the ISS is recycled. Right now, the ESA and NASA are tinkering with closed-loop life support systems that — if perfected — might totally eliminate the need for water and oxygen shipments to the ISS. Cracking this technology could become the key to long-distance space travel in the future [source: ESA].

OK, so what about food? Well, apart from some edible plants that are grown onboard, the crew depends on routine deliveries for most of its food supply. Lots of menu items come in specially-designed packets that get affixed to dining surfaces with Velcro, lest they float away in the low-gravity environment [sources: Lemonick and Preston].

Maintaining a habitable temperature is another big concern. The ISS has to withstand temperatures of -128 degrees Celsius (-200 degrees Fahrenheit) and 93 degrees Celsius (200 degrees Fahrenheit) on the dark and sunlit sides of our planet, respectively.

Among other things, the ISS uses heaters, insulation and liquid ammonia-circulating loops to regulate the internal temperature. Radiators help release excess heat generated by some of the machinery aboard the station [source: NASA].

Like any home, the ISS must be kept clean. This is especially important in space, where floating dirt and debris could present a hazard. Astronauts use various wipes, detergents and vacuums to clean surfaces, filters and themselves. Trash is collected in bags, stowed in a supply ship and returned to Earth or incinerated [sources: Anderson and NASA].

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