Sending human travelers to Mars would require scientists and engineers to
overcome a range of technological and safety obstacles. One of them is the
grave risk posed by particle radiation from the sun, distant stars and
galaxies.
Answering two key questions would go a long way toward overcoming that
hurdle: Would particle radiation pose too grave a threat to human life
throughout a round trip to the red planet? And, could the very timing of a
mission to Mars help shield astronauts and the spacecraft from the
radiation?
In a new article published in the peer-reviewed journal Space Weather, an
international team of space scientists, including researchers from UCLA,
answers those two questions with a "no" and a "yes."
That is, humans should be able to safely travel to and from Mars, provided
that the spacecraft has sufficient shielding and the round trip is shorter
than approximately four years. And the timing of a human mission to Mars
would indeed make a difference: The scientists determined that the best time
for a flight to leave Earth would be when solar activity is at its peak,
known as the solar maximum.
The scientists' calculations demonstrate that it would be possible to shield
a Mars-bound spacecraft from energetic particles from the sun because,
during solar maximum, the most dangerous and energetic particles from
distant galaxies are deflected by the enhanced solar activity.
A trip of that length would be conceivable. The average flight to Mars takes
about nine months, so depending on the timing of launch and available fuel,
it is plausible that a human mission could reach the planet and return to
Earth in less than two years, according to Yuri Shprits, a UCLA research
geophysicist and co-author of the paper.
"This study shows that while space radiation imposes strict limitations on
how heavy the spacecraft can be and the time of launch, and it presents
technological difficulties for human missions to Mars, such a mission is
viable," said Shprits, who also is head of space physics and space weather
at GFZ Research Centre for Geosciences in Potsdam, Germany.
The researchers recommend a mission not longer than four years because a
longer journey would expose astronauts to a dangerously high amount of
radiation during the round trip—even assuming they went when it was
relatively safer than at other times. They also report that the main danger
to such a flight would be particles from outside of our solar system.
Shprits and colleagues from UCLA, MIT, Moscow's Skolkovo Institute of
Science and Technology and GFZ Potsdam combined geophysical models of
particle radiation for a solar cycle with models for how radiation would
affect both human passengers—including its varying effects on different
bodily organs—and a spacecraft. The modeling determined that having a
spacecraft's shell built out of a relatively thick material could help
protect astronauts from radiation, but that if the shielding is too thick,
it could actually increase the amount of secondary radiation to which they
are exposed.
The two main types of hazardous radiation in space are solar energetic
particles and galactic cosmic rays; the intensity of each depends on solar
activity. Galactic cosmic ray activity is lowest within the six to 12 months
after the peak of solar activity, while solar energetic particles' intensity
is greatest during solar maximum, Shprits said.
Reference:
M.I. Dobynde et al, Beating 1 Sievert: Optimal Radiation Shielding of
Astronauts on a Mission to Mars, Space Weather (2021).
DOI: 10.1029/2021SW002749
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