NASA has a mission protocol which says if
a low-earth orbit mission increases the
life time risk of the crew getting
cancer by more than 3% then
they won't go ahead with it but the
upcoming Mars missions may expose the
crews to levels which will be beyond
that limit and two other hazards,
so how dangerous is deep space travel to
Mars and Beyond. With Ellen musk pushing
to get men onto Mars by the mid-2020s
and NASA looking to do the same for
the 2013 just how much we learned since
Apollo and from space stations. 50 years
on from the beginning of the Apollo
missions and we have yet to send any man
back to the moon let alone on the much
more arduous journey to our nearest
viable planet Mars. Now whilst much of
this as being down to the lack of
political will in the face of our own
man-made problems here on earth
it's also down to be increasing
sophistication of robotic probes and
Landers that are much cheaper to make
launch, can go where no man could go and
continue working for years of the time.
The Voyager probes for example are still
going 40 years after their launch. If we
relied upon man discovery only we would
know a fraction of what we know now. With
data from probes that we have sent
around solar system since then we have
built up a picture which is far from
the vision of just whizzing through
interplanetary space that along with the
joint NASA-Russian experiment of having
been in space for a year on board the
International Space Station, we now have
a much better understanding of what they
may experience from the two-and-a-half
year round trip tomorrow. We humans
evolved on earth and our bodies are
adapted from moving around under the
effects of 1g of gravity, take that away
and problem start to arise our
physiology. We often forget what a
sheltered life we all leave here on our
little blue dot in the harshness of space.
We are protected from 99.9% of
harmful radiation not only from the Sun
but also from other galactic sources by
our atmosphere the Earth's magnetic
field and the Van Allen belt,
yes they make a pain for space travel
but they do protect us from further
radiation on earth. Get beyond the
shelter of these and open space is far
from empty, it's teeming with not only
radiation from our Sun but also much
more powerful radiation from outside our
solar system in a form of galactic
cosmic rays and gamma rays. Most of the
hard data we have about the levels of
radiation in deep space comes from the
radiation assessment detector instrument
which was aboard Mars rover Curiosity,
part of the bar science laboratory which
was launched in November 2011. The
radiation assessment detector was turned
on for about 220 out of 253 day journey
to Mars and showed that the radiation
levels were between 100 and 1000 times
higher than that on the earth for an
unshielded occupant but it was highly
variable and depended a lot on the
solar activity at the time. Experiments done on
earth with Beam accelerators, computer
modeling and confirmation from the
cosmic-ray scope on the lunar
reconnaissance orbiter as it goes around
the moon has shown that plastics with a high hydrogen
content are more effective than the same
weight of aluminium at stopping particle
radiation from both the Sun and galactic
cosmic rays and this has been
incorporated into the latest spacecraft
design like the NASA Orion and the SpaceX Dragon 2. Galactic cosmic rays are
protons and nuclei of atoms which have
been expelled from supernovas and other
violent cosmic events and have been
accelerated to near the speed of light.
Because of this
they have a much greater energy level
and can right through space craft
and the crew.
Shielding helps but it's a compromise
between thickness of the shield the
extra weight involved which makes it more
difficult then to get into space from
Earth. To contend with solar flares, a
radiation shelter in the craft where
there is extra shielding has been
proposed with SpaceX Mars mission. Liquid
hydrogen or water storage tanks around
the crew areas provide a good shield
against particle radiation and creating
a strong magnetic shield around the crew
areas are all possible but don't protect
well against electromagnetic wave
radiation gamma-rays. Using the curiosity
data has been calculated that the
radiation risk of a return journey to
Mars will be about 600 millisieverts
equivalent to about 50 full-body CT
scans over that period or being on the
International Space Station for 4 years
straight.
This is also about 30 times the yearly
allowance for a radiation worker and
that doesn't include stay on Mars itself.
A dose of one sievert or 1000 millisieverts
is associated with a lifetime increase in
fatal cancers by about 5%,
which is near the level of the whole
mission including stay on Mars. This
would be a career limit any of the crew
and young women are at a higher risk of
cancer from radiation compared to older
men so that could affect the crew make
up. Along with the cancer risk there's
also be increased chance of developing
cataracts as the radiation passes
through the eye.
Recent research has also suggested that
the effects of galactic cosmic rays
damaging brain cells at the molecular
level could cause brain damage
similar to the onset of dementia which
could show within the duration of the
journey. Away from the radiation risks
they're also physiological effects of
microgravity on the human body.
NASA astronaut Scott Kelly spent 340
days in space on the International Space
Station and even with a tough
two-and-a-half-hour exercise regime each
day, he still experience problems
with circulation, eye sight as well as a
loss of bone and muscle mass. Once in space
the fluids in the body no longer have
gravity to pull them into the lower
extremities and are equally distributed
around the body. One of the effects of
this is to make the back of the eye
swell up and alter their shape which effects
vision. Stays on the International
Space Station  of about a week were quickly
reversed when back on earth but lasted
for much longer after several months in
microgravity. On earth the heart pumps
blood around the body and the veins in
the legs squeeze the blood back to the
heart. In space the same amount of blood
is being pumped by the heart but there
is much less effort required to return it
to the body
this allows cardio muscular system in
the legs to weaken over time again. When
returning to a gravity environment this
can cause extreme dizziness and fainting
due to the lack of blood been returned
to the upper body and brain which could
occur the when they reach Mars. Within five
months of being in a microgravity
environment, astronauts can lose up
40% of their muscle mass and
12% of bone mass, this increases the
risk of bone fractures when returning to
a gravity environment and it's like
turning a 20 year-old into a
60-year-old in just a few months.
Psychological issues are also a problem
to people in isolated areas for long
periods. Some scientists that worked all
year round in Antarctica suffer mental
health disorder called "Winter Over  Syndrome"
which is characterized by symptoms such
as depression, irritability, aggressive
behavior, insomnia and memory problems
all the sort of things you don't want to
happen when trying to perform mission
critical tasks in space or on Mars.
Humans traveling in open space is always
going to be a risky business and in the
end some say the risk is worth the
reward of getting men to Mars and they can
do much more than a robot in a short
space of time and they are much better
at handling unexpected situations. But dead
or dying crew is something no one wants
to see beamed back to earth so it's in
all our interests
to make sure the risks are minimized as much as
possible. It will be over 50 years since
the last Apollo flight by the time the
earliest Mars  missions come around, so
even just take a little bit longer than
expected, it won't make that much
difference to make sure that we get it
right.
What do you think of the Mars mission
and the risk of traveling in deep space?
let me know in the comments below and
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