What does it take for humans to survive the dangerous environment of space?
A complex network of systems supports astronauts in their everyday lives on the International Space Station. These include air revitalization, water recovery, and oxygen generation.
“Three seconds is about how long you can survive with no pressure around you,” said Grant Anderson, president and CEO of Paragon Space Development Corporation. “Despite what all the science fiction movies show you, you can’t go out and then come back a minute later. Three minutes is about how long you can go without oxygen. Then there’s the three days, which is about how long you can go without water. Three weeks is how long you can go without food.”
Outside the spacecraft, the environment is a space vacuum with radiation exposure.
“When in sunlight, the temperature is about 250°F, and when outside of the sun, the temperature is about -250°F,” said Sandra Jones, public affairs officer for the International Space Station.
The International Space Station provides astronauts with their survival needs in terms of clean air at the right pressure and temperature, drinkable water, personal hygiene, physical fitness, and food, according to Alesha Ridley, Environmental Control and Life Support Systems program manager at the National Aeronautics and Space Administration’s Johnson Space Center.
On a miniature level, spacesuits provide some of those same features — water, oxygen, temperature, and pressure, Ridley said. “We have scrubbers that remove the carbon dioxide to keep that from building up too high and causing toxicity. They’ve got drinking water in their spacesuits. They can drink through a straw. They’ve got coolant running through their suits.”
The International Space Station has reached a milestone where it now recovers 98% of the water onboard, Ridley said.
This was a technology gap that needed to be addressed to make travel to Mars possible.
The water-recovery system consists of the urine processor, the water processor, and the brine processor, Ridley said. The urine is treated with a chemical that prevents microbes from growing in it.
The urine processor uses low pressure to separate the water from everything else that is in the urine, Ridley said. The brine processor assembly takes brine from the urine processor and extracts even more water from it by flowing heat over a bladder. This vapor is collected in the air. The distilled urine from the urine processor goes into the water processor and is combined with water from the humidity in the cabin that comes from sweat, breathing, washing, and the brine processor. The water processor has a series of filters in it. It also has a catalytic oxidizer that uses oxygen to remove volatile organic chemicals and other contaminants.
The astronauts use water from the water processor to fill drink bags or hydrate meals.
”A lot of [the] food gets shipped to space dehydrated, just like a camping meal,” Anderson said. “You buy those things, you put in hot water and mix it around, you've got macaroni and cheese or risotto or whatever. The same thing gets done in space.”
The astronauts on the International Space Station can choose from a vast menu where they can select from many different cuisines, Ridley said. “There’s a lot of dehydrated food. Then when we fly cargo vehicles, we fly fresh food as well. They can get fresh fruit and stuff like that. We’ve been developing the capacity to grow food on the space station. They’re, I think, almost always in the process of growing some types of vegetables or fruits… and to my knowledge, they get to eat that when they’re harvesting it.”
To conserve water, the astronauts do not take showers, Ridley said. They use washcloths with small amounts of water. Overall, astronauts get less dirty in space than they would on the ground. They use no-rinse shampoos, according to a video from the International Space Station.
Some of the clean water also goes into the oxygen generator for electrolysis, Ridley said. The oxygen generator uses a cell sac that is similar to what is used in submarines. Membranes inside the cell sac separate the water into hydrogen and oxygen. The oxygen goes into the cabin. Oxygen levels can be adjusted by changing the amount of power that is sent to the sac. A hydrogen-and-water mixture comes out of the sac and is separated. Currently, the hydrogen is vented outside the spacecraft and the water is reused.
The air revitalization system monitors the pressure of oxygen, the pressure of nitrogen, and the amount of carbon dioxide, Ridley said. It also keeps an eye on trace gases. Humans emit a small amount of methane, along with ammonia and carbon monoxide.
Plastics and adhesives in space and on Earth emit chemicals through offgassing. The designers of spacecraft have a list of materials they can and cannot use, Anderson said. “In a microgravity environment, some materials do offgas even more. The toxicity depends on exposure.”
“We have to keep the oxygen at a breathable amount, which is generally between 2.8 and 3.2 pounds per square inch partial pressure,” Anderson said. “That's just to provide you with enough oxygen to operate. Then we have to scrub out the carbon dioxide. The carbon dioxide turns toxic after a certain level. You always have to have the air flowing around you. So the fans are life-critical.”
The crew aboard the space station exercises two to 2.5 hours a day to maintain their bone density and muscle mass. On the U.S. side of the station, Ridley said, they use a bicycle, a treadmill, and a weight machine.
In the long run, a disturbingly large number of health conditions can occur due to space travel.
Astronauts can experience higher risks of cancer, heart disease, cataracts, psychiatric problems, bone loss, muscle loss, and kidney stones, according to NASA. The publication ”NASA Technology Roadmaps TA 6: Human Health, Life Support, and Habitation Systems (2015 report)” says that central nervous system and degenerative tissue effects may also occur.
Astronauts may also age prematurely, experience immune or endocrine problems, or have difficulties with hand-eye coordination or spatial perception, according to the report “Review of NASA’s Evidence Reports on Human Health Risks (2016).”
Without the International Space Station, humanity would have almost no way of knowing what the body experiences in long-duration spaceflight and its permanent effects. This critical data is needed for human missions to Mars and long-term settlement on the moon.