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How much radiation awaits lunar colonists? A new NASA mission
aims to find out.
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September 8, 2005: On the Moon, many of the things
that can kill you are invisible: breathtaking
vacuum, extreme temperatures and space radiation top the list.
Vacuum
and temperature NASA can handle; spacesuits and habitats provide
plenty of air and insulation. Radiation, though, is trickier.
The
surface of the Moon is baldly exposed to cosmic rays and solar
flares, and some of that radiation is very hard to stop with
shielding. Furthermore, when cosmic rays hit the ground, they
produce a dangerous spray of secondary particles right at your
feet. All this radiation penetrating human flesh can damage
DNA, boosting the risk of cancer and other maladies.
Above:
The surface of the Moon is exposed to space radiation.
According
to the Vision for Space Exploration, NASA plans to send astronauts
back to the Moon by 2020 and, eventually, to set up an outpost.
For people to live and work on the Moon safely, the radiation
problem must be solved.
"We
really need to know more about the radiation environment on
the Moon, especially if people will be staying there for more
than just a few days," says Harlan Spence, a professor
of astronomy at Boston University.
To
carefully measure and map the Moon's radiation environment,
NASA is developing a robotic probe to orbit the Moon beginning
in 2008. Called the Lunar Reconnaissance Orbiter (LRO), this
scout will pave the way for future human missions not only
by measuring space radiation, but also by hunting for frozen
water and mapping the Moon's surface in unprecedented detail.
LRO is a key part of NASA's Robotic Lunar Exploration Program,
managed by the Goddard Space Flight Center.
One
of the instruments onboard LRO is the Cosmic Ray Telescope
for the Effects of Radiation (CRaTER).
"Not
only will we measure the radiation, we will use plastics that
mimic human tissue to look at how these highly energetic particles
penetrate and interact with the human body," says Spence,
who is the Principal Investigator for CRaTER.
 By
placing the radiation detectors in CRaTER behind various thicknesses
of a special plastic that has similar density and composition
to human tissue, Spence and his colleagues will provide much-needed
data: Except for quick trips to the Moon during the Apollo
program, most human spaceflight has occurred near Earth where
our planet's magnetic field provides a natural shield. In
low-Earth orbit, the most dangerous forms of space radiation
are relatively rare. That's good for astronauts, but it leaves
researchers with many unanswered questions about what radiation
does to human tissue. CRaTER will help fill in the gaps.
Right:
The CRaTER telescope consists of silicon radiation detectors
(red) mounted on detector boards (green), separated by pieces
of "tissue-equivalent" plastic (tan). [More]
Out
in deep space, radiation comes from all directions. On the
Moon, you might expect the ground, at least, to provide some
relief, with the solid body of the Moon blocking radiation
from below. Not so.
When
galactic cosmic rays collide with particles in the lunar surface,
they trigger little nuclear reactions that release yet more
radiation in the form of neutrons. The lunar surface itself
is radioactive!
So
which is worse for astronauts: cosmic rays from above or neutrons
from below? Igor Mitrofanov, a scientist at the Institute
for Space Research and the Russian Federal Space Agency, Moscow,
offers a grim answer: "Both are worse."
 Mitrofanov
is Principle Investigator for the other radiation-sensing
instrument on LRO, the Lunar Exploration Neutron Detector
(LEND), which is partially funded by the Russian Federal Space
Agency. By using an isotope of helium that's missing one neutron,
LEND will be able to detect neutron radiation emanating from
the lunar surface and measure how energetic those neutrons
are.
Right:
The distribution of ground-level neutron radiation around
the Moon's south pole. "Hot spots" are red; cool
spots, blue. Credit: Lunar Prospector. [More]
The
first global mapping of neutron radiation from the Moon was
performed by NASA's Lunar Prospector probe in 1998-99. LEND
will improve on the Lunar Prospector data by profiling the
energies of these neutrons, showing what fraction are of high
energy (i.e., the most damaging to people) and what fraction
are of lower energies.
With
such knowledge in hand, scientists can begin designing spacesuits,
lunar habitats, Moon vehicles, and other equipment for NASA's
return to the Moon knowing exactly how much radiation shielding
this equipment must have to keep humans safe.
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Author: Patrick
L. Barry | Editor:
Dr. Tony Phillips | Credit: Science@NASA
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