8.16 Radiation Hazards of Space Travel
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∼8.6% of the dose at Lunar Reconnaissance Orbiter altitudes (∼50 km) arises from
secondary lunar species, primarily “albedo” protons (3.1%) and electrons (2.2%).
Other lunar-nuclear-evaporation species contributing to the dose rate are positrons
(1.5%), gammas (1.1%), and neutrons (0.7%).
The great solar storm of August 4, 1972, had it occurred during the Apollo lunar
landings in April 1972 and in December 1972, would likely have caused acute
radiation sickness in the astronauts. The galactic cosmic rays consist of protons
p, helium nuclei 4 H e (with a fluence of about 1/4th that of protons), carbon (with a
fluence of about 1/6 that of H e), iron (about 3/8 of carbon) with peak energy at about
1 GeV, dropping off exponentially with a power of about 10 −2 . The dose would have
been: Protons: 6.21 cGy, Helium: 3.02 cGy; Carbon: 0.83 cGy; Oxygen: 1.37 cGy;
Magnesium: 0.66 cGy; Silicon: 0.69 cGy; Iron 1.56 cGy; with a total 14.34 cGy.
The solar particle radiation is dominated by protons, giving about 0.17 Sv per
year at solar sunspot min, 40 Sv per year at solar sunspot max, to exposed astronauts
in space near the Earth.
A Solar Particle Event (SPE) may occur during a solar magnetic storm. For
example, a July 2000 event produced 1.7 Sv in the vicinity of the Earth, and an
August 1972 event made 3.4 Sv. The SPE can last for several hours.
Thin shielding may be worse than none, as secondary radiation by proton
scattering from the shield occurs. However, a thickness of 10 cm of Al shielding to
the Aug 1972 SPE would have reduced the dose from 3.4 cSv to 0.40 Sv. There are
a number of possible shields: Hull shields, deployable water shields, and deployable
high-density polyethylene (HDPE) slabs. Active magnetic or electrostatic shielding
is an untried alternative.
During the Apollo missions, which were 4 day missions to the Moon, the
astronauts experienced flashes in eyes every few minutes. These were caused by
cosmic rays traversing through the vitreous humor in front of retina.
Astronauts on a Moon mission for 6 months would incur 50–2000 mSv. (The
Moon has no significant magnetic field, nor an atmosphere.)
A 3-year Mars mission would incur about 1200 mSv. (1000 mSv makes a 5.5%
increased risk for fatal cancer.) Mars has no significant global magnetic field, and
little atmosphere to protect against solar wind and solar flares.
The Curiosity and Odyssey Mars rovers detected an average of about 240 mSv
per year, compared to a dose on Earth of about 3.5 mSv per year (from both cosmic
and geologic sources), so Mars at its surface has about seventy times more radiation
than the Earth. A human habitat on Mars would have to employ radiation shields
(initially layers of dirt), until a good atmosphere can be manufactured, perhaps by
robots and genetically engineered bacteria, that can take Mars’ radiation.
In addition to solar proton flux, there are energetic heavy ions from the Galaxy.
Galactic High Z Energetic ions (HZE) include carbon, oxygen, magnesium, silicon,
and iron ions. Their mean energy is from 1 to 10 GeV/amu. Damage to tissue is
comparable to solar flare protons from the sun. Galactic cosmic rays are a hazard
due to dosage near and far from the Earth, and near and far from the Sun. In addition,
damage occurs to electronics and solar panels. Strategies are being considered for
321
∼8.6% of the dose at Lunar Reconnaissance Orbiter altitudes (∼50 km) arises from
secondary lunar species, primarily “albedo” protons (3.1%) and electrons (2.2%).
Other lunar-nuclear-evaporation species contributing to the dose rate are positrons
(1.5%), gammas (1.1%), and neutrons (0.7%).
The great solar storm of August 4, 1972, had it occurred during the Apollo lunar
landings in April 1972 and in December 1972, would likely have caused acute
radiation sickness in the astronauts. The galactic cosmic rays consist of protons
p, helium nuclei 4 H e (with a fluence of about 1/4th that of protons), carbon (with a
fluence of about 1/6 that of H e), iron (about 3/8 of carbon) with peak energy at about
1 GeV, dropping off exponentially with a power of about 10 −2 . The dose would have
been: Protons: 6.21 cGy, Helium: 3.02 cGy; Carbon: 0.83 cGy; Oxygen: 1.37 cGy;
Magnesium: 0.66 cGy; Silicon: 0.69 cGy; Iron 1.56 cGy; with a total 14.34 cGy.
The solar particle radiation is dominated by protons, giving about 0.17 Sv per
year at solar sunspot min, 40 Sv per year at solar sunspot max, to exposed astronauts
in space near the Earth.
A Solar Particle Event (SPE) may occur during a solar magnetic storm. For
example, a July 2000 event produced 1.7 Sv in the vicinity of the Earth, and an
August 1972 event made 3.4 Sv. The SPE can last for several hours.
Thin shielding may be worse than none, as secondary radiation by proton
scattering from the shield occurs. However, a thickness of 10 cm of Al shielding to
the Aug 1972 SPE would have reduced the dose from 3.4 cSv to 0.40 Sv. There are
a number of possible shields: Hull shields, deployable water shields, and deployable
high-density polyethylene (HDPE) slabs. Active magnetic or electrostatic shielding
is an untried alternative.
During the Apollo missions, which were 4 day missions to the Moon, the
astronauts experienced flashes in eyes every few minutes. These were caused by
cosmic rays traversing through the vitreous humor in front of retina.
Astronauts on a Moon mission for 6 months would incur 50–2000 mSv. (The
Moon has no significant magnetic field, nor an atmosphere.)
A 3-year Mars mission would incur about 1200 mSv. (1000 mSv makes a 5.5%
increased risk for fatal cancer.) Mars has no significant global magnetic field, and
little atmosphere to protect against solar wind and solar flares.
The Curiosity and Odyssey Mars rovers detected an average of about 240 mSv
per year, compared to a dose on Earth of about 3.5 mSv per year (from both cosmic
and geologic sources), so Mars at its surface has about seventy times more radiation
than the Earth. A human habitat on Mars would have to employ radiation shields
(initially layers of dirt), until a good atmosphere can be manufactured, perhaps by
robots and genetically engineered bacteria, that can take Mars’ radiation.
In addition to solar proton flux, there are energetic heavy ions from the Galaxy.
Galactic High Z Energetic ions (HZE) include carbon, oxygen, magnesium, silicon,
and iron ions. Their mean energy is from 1 to 10 GeV/amu. Damage to tissue is
comparable to solar flare protons from the sun. Galactic cosmic rays are a hazard
due to dosage near and far from the Earth, and near and far from the Sun. In addition,
damage occurs to electronics and solar panels. Strategies are being considered for