Your muscles shrink. Your bones degenerate. Your brain doesn't know which way is up. Working onboard ISS is challenging because the environment in space is hostile. Research aboard the ISS can help us understand the long-term effects of space travel on people, and overcome the obstacles that limit human exploration.

Your body functions differently in space. Muscles and bones lose mass at one-millionth the gravity of Earth because in space they don't encounter the same resistance. Bones atrophy about 1 percent a month. Muscle mass can deteriorate at a rate of 5 percent a week. To mitigate microgravity's effects astronauts who stay in space for more than a few weeks work out at least two hours a day. Still, some astronauts who return from long-term space missions must be carried away in stretchers.

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The Body in Space
Spaces Research Office

The ECLSS Water Recycling System reclaims wastewater from the Space Shuttle's fuel cells, from urine, from oral hygiene and hand washing, and by condensing humidity from the air. Without recycling, 40,000 pounds of water from Earth each year would be required to supply a minimum of four crewmembers for the life of the station.

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Water on the Station
Advanced Life Support
Station Life Support

On Earth gravity tells us which way is up. Sensors in the inner ear can feel the pull of gravity. They signal the brain with information about our body's orientation. Nerves in the body's joints and muscles tell us where our arms and legs are, but can be fooled without the stresses in the joints caused by the pull of gravity. While floating in space some astronauts report feelings of motion sickness, which is triggered by a mismatch between what the eyes see and what the body feels.

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The Vestibular System in Space
The Effects of Space Travel

Life support systems on the station must not only support oxygen and remove carbon dioxide from the cabin's atmosphere, but also prevent gases like ammonia and acetone, which people emit in small quantities, from accumulating. Vaporous chemicals from science experiments are a potential hazard too, if they combine in unforeseen ways with the other elements in the air supply.

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Breathing in Space

Overall, astronauts in space need about the same number of calories and the same vitamins and minerals as they need on Earth, with a couple of exceptions: vitamin D and iron. On Earth the body makes vitamin D when the skin is exposed to sunlight, but on the ISS astronauts are shielded from the sun. In space, because the body produces fewer red blood cells astronauts should take in less iron.

Before flight an astronaut samples food and beverages to make a menu, which will repeat about every eight days when in space. On the ISS the food is prepared at a galley that contains a water dispenser to rehydrate food and beverages, and an oven for warming the food. Foods packaged in rehydratable containers include soups, casseroles, bacon and eggs. Thermostabilized foods are heat processed before flight to destroy microorganisms and enzymes. These foods include tomatoes, eggplant and mushrooms. Beverages such as coffee, tea and orange juice come in powdered form.

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Space Food
Food for Space Flight

Spacewalkers wear spacesuits that have pressures much lower than the ambient cabin pressure of a spacecraft. This makes spacewalkers subject to decompression sickness, the "bends," which results from nitrogen bubbles forming in the tissues or blood stream and moving to other areas of the body. Before a spacewalk or Extravehicular Activity (EVA), crewmembers wash excess nitrogen from their bodies with 10 minutes of vigorous exercise followed by two hours and 20 minutes breathing pure oxygen.

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Spacewalk!
Space Station EVA
The Effects of EVA

Astronauts are weightless and can sleep in any orientation. However, they usually attach themselves to something or zip inside a sleeping bag in a wall-mounted sleep station. Astronauts are scheduled for eight hours of sleep at the end of each mission day. Motion sickness can disrupt an astronaut's sleep pattern.

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Space Sleep

An astronaut's training involves working underwater to prepare for microgravity. At the Neutral Buoyancy Laboratory, located at the Sonny Carter Training Facility in Houston, astronauts wear suits that weigh 280 pounds while training under water for space walks. The neutral buoyancy of water is used to simulate the weightlessness of space. The pool holds 6.2 million gallons of water that is recycled every 19 1/2 hours. Groups of astronauts have trained up to a week in an undersea laboratory owned by the National Oceanic and Atmospheric Administration that are 62 feet deep, 3 1/2 miles off the Florida Keys coast.

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Becoming an Astronaut
Selection and Training
Neutral Buoyancy Lab