ROOM
46
Space Environment
Moving off Earth
Protection provided by Earth’s magnetic field and
atmosphere means that in general people living
on the surface are not exposed to the damaging
effects of radiation exposure.
Today, however, as future plans are being
developed for people to move and live away from
Earth in orbiting colonies or on the Moon or Mars,
exposure to space radiation will be a serious hazard.
Scientists and engineers will have to find
creative ways to deal with this danger. One of the
greatest concerns when planning a permanent
settlement, for example, must ultimately be that
of successful reproduction. If humans cannot
conceive and produce healthy children away from
Earth it will become impossible for a colony to
expand and grow naturally.
The first question to answer is how much
radiation someone will be exposed to as they
travel through space from Earth orbit to their
destination on the Moon, Mars or elsewhere.
On Earth we are protected from radiation by the
mass of the Earth itself, then by the magnetic field and
finally the atmosphere. Low Earth orbit (LEO), where
the International Space Station is located, is protected
by Earth’s magnetic field but not its atmosphere.
Mars on the other hand has no strong magnetic
field to shield us from ions, no ozone layer to
stop ultraviolet rays and only a thin atmosphere
to absorb radiation. On the Moon there is no
magnetic field, insignificant atmosphere and only
the Moon’s rocky mass to block some radiation.
Once the first crews leave Earth orbit they will
be hit from all sides - by solar radiation from the
direction of the Sun and by galactic radiation.
Measuring radiation
Radiation doses can be measured in Sieverts (Sv), which
is a measure of radiation absorption by the human
body equal to 10 ergs of energy of gamma radiation
delivered to one gramof living tissue. It is adjusted to
take into account the relative biological effectiveness of
ionizing radiation of all types - therefore, one Sievert of
X-ray radiation would have the same danger to a living
thing as one Sievert of gamma radiation.
A worldwide average of radiation exposure on
Earth is about 3 millisieverts (1 Sv=1000 mSv).
Table 1 shows that the average annual radiation
exposure in open space is 219 times more than on
Earth while that on the Moon is 146 times more.
The surface of Mars would be a little more than 81
times the average annual exposure rate of Earth
The Apollo astronauts, the only humans so far
to travel outside of LEO, received from about 1.6
mSv to 5.8 mSv - with Apollo 14 receiving 11.4 mSv
from solar storms which occur when the Sun
releases a huge burst of plasma that travels at
high speed out into space. The astronauts’ lunar
Table 1: Annual ambient radiation levels for the Earth, Mars, the Moon and space.
EARTH
MARS
MOON
SPACE
Annual Total
3 mSv
245 mSv
438 mSv
657 mSv
Daily Average
0.0082 mSv
0.67 mSv
1.2 mSv
1.8 mSv
The different categories
of radiation experienced
on Earth, Mars, on the
Moon and in open space
The Mars One habitat
plan includes using
landing capsules as living
space and inflating large
greenhouses and other
structures. The inflatable
structures would then be
buried under soil to
provide radiation
protection, a task
requiring a considerable
number of unshielded
hours to accomplish.
Mars One
