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Subject Matter Expert: Charles W. Lloyd, Pharm D, Dr. Steven Platts, and Dr. Walter Sipes

Blast off! What a thrill it is to see and explore new worlds. Trading Earth’s environment for the environment of space is exciting. But, an “Earth-normal” environment is very different from a “space-normal” world. Space is one of the most hostile environments we will ever explore. As the environment changes, so will an astronaut’s body change.

Less gravity is one of the major changes of living in space. Traveling to Mars and, perhaps into deep space, will involve living in space for months or years. How will an astronaut’s body change and adapt as a result of living in a reduced gravity environment for that long?

Which way is up? Which way is down? In space, there is no physical sensation to let you know when you are upside down. Astronauts can easily become disoriented. On Earth, a small organ inside your inner ear helps you know when you are right-side up or upside down. This organ works because gravity pulls on the fluid and small particles inside your inner ear. In less gravity, the organ gets mixed messages. The only way to know “up” and “down” is to rely on what you see. The ceiling of your spacecraft can just as easily be your floor. You can float upside down without blood rushing to your head. All of these changes can lead to a feeling of space sickness – something like feeling carsick or seasick. A few hours after reaching orbit, one in three astronauts will experience this sensation. For most, these feelings will stop as the astronauts become used to their new space environment.

While on Earth, gravity causes most of the body’s fluids to be distributed below the heart. In contrast, living in space with less gravity allows fluids in the body to spread equally throughout the body. When astronauts first travel into space, they feel as if they have a cold and their faces look puffy. Many astronauts talk about not feeling thirsty because of this fluid shift. The body records this shift as an increase in blood volume. It adjusts by eliminating what it thinks are extra fluids as it would normally – that’s right – through the kidneys -- resulting in visits to the restroom. Once this “extra fluid” is flushed from the body, astronauts adjust to space and usually feel fine.

Puffy faces and feeling space sickness are short-term changes that astronauts feel. Within three days of returning to Earth, the astronauts return to normal fluid levels and the body is “back to normal.” Some other effects are more long-term. Reduced gravity will lead to a loss of calcium in the bones and weaker muscles. During the space mission, resistive exercises and good nutrition can help offset some of these changes. Once they return to Earth, astronauts continue to exercise to strengthen their weakened bones and muscles. Scientists keep a careful watch on astronauts before, during, and after flights in space.

Space environments also affect an astronaut’s sense of time. While traveling around the Earth, astronauts orbit the Earth once every 90 minutes. This means that they see the sun rise and set every 90 minutes. Although a beautiful sight, this can be confusing for the body and could interrupt sleep. To help limit this disruption, covers over windows help block the sunlight. Our “internal body clock” is usually set for a 24-hour light and dark cycle. This internal clock is a circadian rhythm and is usually reset by daily exposure to light. Circadian rhythms are closely linked to the light/dark cycle. They help set sleeping and eating patterns for all living things, including people.

Changing the body’s circadian rhythms usually results in other changes for the body. Many travelers that go across time zones complain of jet lag with its feelings of fatigue, disorientation and insomnia. Have you ever experienced jet lag? You probably felt out-of-sorts and grumpy. Imagine how astronauts must feel when their sleep cycles are changed for long space flights. They usually stay on the Greenwich Mean Time (GMT) while they orbit Earth, but will shift to Houston time and Moscow time for certain activities such as docking with the supply ship and Extravehicular Activities. Once these are finished, the astronauts return to GMT.

Some signs of aging parallel changes in the body caused by living in a reduced gravity environment. Changes in sleep cycles and weakened bones and muscles are found in both cases. While studying ways to reverse the effects of living in a reduced gravity environment, scientists are also learning more about what happens to the body as it ages.

Clearly, the body is amazing as it adapts and changes to its environment. Some of the changes are short-term and easily reversed. Other changes, such as reduced bone mass and weaker muscles, take much longer to return to their original form. Scientists are working to find out all that they can about how the body adapts to new environments to make space travel as safe and comfortable as possible.

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National Science Education Standards (NSES)

The following National Education Standards are addressed in this educational package.

Science (NSTA/NRC)
Mathematics (NCTM)
Health (AAHPERD)

For an alignment see the Educator Section.