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