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The countless stars in Earth’s night sky
represent just a small fraction of our home
galaxy - a vast stellar pinwheel of more than
100 billion stars known as the Milky Way.
When viewed from a distance, our galaxy appears
immense, a teeming mass of tiny, glittering
points of light, gas, and dust.
Every morning, the closest star in our galaxy
rises majestically above the horizon
of our own planet.
The sun.
Located just 93 million miles from Earth,
our sun is a 1.4 million kilometer ball of
exploding gas, blasting out massive amounts of
radiation at all wavelengths.
This radiation - as well as radiation from
other stars and from interstellar space -
bombards our planet constantly.
Fortunately, Earth’s magnetic field and
the ozone in our atmosphere form a protective
cocoon around our planet that insulates us from
most solar and cosmic radiation.
Even with the protection of our atmosphere and
magnetosphere, the effect of radiation on our
bodies is apparent to anyone who has spent
too much time outdoors.
But what happens to our bodies when we leave
the surface of Earth to travel in space or
visit the International Space Station?
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Radiation and Human Space Exploration
Just outside the protective layer of Earth’s
atmosphere and magnetosphere,
a few hundred miles above the surface,
is a universe full of radiation.
In addition to the solar radiation, x-rays,
and gamma rays that we experience here on Earth,
astronauts are exposed to even more dangerous
forms of radiation once they leave our planet.
(Cucinotta) 'What we’re concerned with
for the astronauts is space radiation, which is
cosmic rays that originate either from the sun
or from all the stars in our galaxy -
they’re called galactic cosmic rays.'
Galactic cosmic rays are bare atomic nuclei,
some as heavy as iron atoms, accelerated to
nearly the speed of light as they hurtle
through interstellar space.
Because of their high velocity, high mass, and
positive electric charge, galactic cosmic rays
can cause tremendous damage to human cells.
That’s because when a particle of ionizing
radiation penetrates the human body, it knocks
electrons off of the atoms it encounters on
its path though the body.
(Cucinotta) 'Wherever the particle goes,
those cells are going to be highly damaged,
which is different from other types of radiation.'
Ionized radiation can also damage DNA, most
often destroying both strands of the helix.
The resulting damage and mutation of human cells
and DNA can lead to future health problems
like cataracts, cancer, and damage to the
central nervous system.
We are still learning about space radiation
and its damaging effects on the human body.
Until we know more about how human biology is
affected, we do not know how many days humans
can remain in space or how to protect them,
especially during extended stays on the moon or
long-duration flights to Mars and other planets.
One of the most valuable resource we have for
studying the effects of radiation in space is
the International Space Station.
Research into the effects of radiation has
been conducted on the station for several years.
Some of the experiments that have been performed
include studies on how radiation affects cells
and tissue, medicines, and food.
Before experiments can be flown in space,
scientists on Earth must be able to
conceptualize, create baselines, and develop
models to test their theories.
The Brookhaven National Laboratory in
Long Island New York is the Earth-based analog
of the International Space Station.
(Lowenstein) 'We can supply the kind of
environment - not microgravity, not vacuum -
of space, but it’s the closest you can get on
Earth to mimic the sort of radiation environment
that exists in space.'
The Brookhaven National Laboratory includes a
suite of particle accelerators and colliders.
The facility is also home to the
NASA Space Radiation Laboratory, or NSRL.
(Sivertz) 'We take a particle beam that is
either proton or heavy ion and we accelerate it
up to energies that are characteristic of the
cosmic rays, and we use that particle beam to
irradiate samples of cells and instrumentation
and we see what the effects of that space
radiation is likely to be.'
The types of radiation we experience on Earth -
such as gamma rays and x-rays - are relatively
low energy forms of radiation.
Although dangerous, they are not as difficult
to shield against as high energy radiation
galactic cosmic rays which can penetrate not
only human skin and tissue, but also
space suits and spacecraft.
Radiation exposure on the moon is very different
from that in low Earth orbit.
When astronauts travel to the moon,
they will leave behind the relative safety of
the Earth’s magnetosphere.
Astronauts on the lunar surface face
even greater risks from the effects of galactic
cosmic rays and solar particle events.
(Cucinotta) 'On the moon, you have no
protection of the magnetic field,
and you also have very short warning
- maybe just a few hours warning -
so the solar particle events become the major
concern for the astronauts.'
Scientists and engineers can partially shield
astronauts from low to medium levels of
radiation while they are inside vehicles and
habitats on the lunar surface.
Fifty years of NASA research has shown that
effective shielding from radiation consists of
at least ten to fifteen centimeters of materials
like water or polyethylene.
But nothing can stop high-energy radiation
like galactic cosmic rays.
The challenge then becomes two-fold
- understanding the risks involved and finding
ways to keep the risks as low as possible.
In order to better understand these risks,
researchers are studying the long-term effects
of radiation on the human body.
Astronauts currently spend an average of
six months at a time living and working on
the space station. To minimize radiation
exposure, engineers and scientists have
developed new types of shielding in the most
frequently used locations.
Materials that have high hydrogen content
can reduce radiation exposure better than
metals such as aluminum.
(Cucinotta) 'On the space station what
we’ve done is implemented polyethylene shielding
in the crew quarters of the astronauts, and this
really reduces the dose from the trapped
radiation and when you do have a solar particle
event it would reduce those doses.'
NASA is continuing to research different types
of shielding for longer duration missions,
such as flights to an asteroid or
the surface of Mars.
To be effective, the shielding must have enough
mass to prevent the majority of radiation from
entering the protected area.
Shielding is only one element that will
protect both current and future astronauts.
Nutrition - such as antioxidants from fruit
and vegetables - as well as medicines
may also play an important role.
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In order to protect astronauts and future space
explorers, we must continue to learn more about
the effects of space radiation on the human body.
Understanding space radiation will not only
help us protect the crew on the space station,
but also those first humans that will take
the next steps in the continued exploration
of our solar system.
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