2.2 Lunar Radiation Environment
25
Table 2.2 Basic parameters
of the solar wind
Basic parameter Value Basic parameter Value
Average
energy/(keV/u)
1
Average
velocity/(km/s)
450
Density of
particle/cm −3
1~20
Energy of
electron
Several electron
volts
Density of
electron/cm −3
7.1
Energy of
proton/keV
0.21~3.3
Density of
proton/cm −3
6.6
Magnetic
field/nT
7
1. Solar Wind
The solar wind is rare plasma originated in high temperature corona. When the
temperature (kinetic energy) of high temperature corona is over the control of solar
gravity, the solar wind emits in all direction. On average, the solar wind particles are
composed of about 95% of protons, 4% of α particles and about 1% of heavy ions.
Among the heavy ions, the abundance of carbon, nitrogen, oxygen, neon, magnesium,
silicon and ferrum is relatively high. The basic parameters of solar wind are shown
in Table 2.2.
Since the energy of proton in the solar wind is only a few thousand electron volts,
and its penetrating range inside the material of spacecraft is only about 0.1 μm, it
does not have any effect on spacecraft beside that the very thin optical coating suffers
a certain amount of damage caused by total ionizing dose [7].
In the space plasma environment, electrons and ions have similar density and
energy (in electroneutral state). However, the mass of ion is 1000 times of the mass
of electron, therefore its speed is far lower than that of electron. The electronic
current is in leading role and the negative current is larger than positive current. In
other words, the charging effect in spacecraft is mainly triggered by electron. It is
shown that the energy of electrons in solar wind is as low as a few electron volts in
the Table 2.2. Its influence on the charging effect in spacecraft can be ignored.
2. Plasma in Magnetic Tail
The Moon passes the remote magnetic tail region of the Earth magnetic field while
orbiting the Earth. In each revolution period, the Moon stays in the magnetic tail of
Earth for about 4 days (before and after the full moon). While passing the magnetic
tail, the Moon encounters two plasma regions that have very different properties. The
two regions are plasma sheet and plasma mantle (which is also called tail lobe). The
density of plasma in plasma sheet is very low and is usually lower than 0.1 cm
−3 . The
energy of plasma is lower than several electron volts in general. Therefore, its effect
on spacecraft can be ignored. Plasma mantle distributes over the magnetic equator
of Earth with a thickness of about 4Re (Re is radius of the Earth). It is primarily
composed of thermal plasma with thousand electron volts of energy.
25
Table 2.2 Basic parameters
of the solar wind
Basic parameter Value Basic parameter Value
Average
energy/(keV/u)
1
Average
velocity/(km/s)
450
Density of
particle/cm −3
1~20
Energy of
electron
Several electron
volts
Density of
electron/cm −3
7.1
Energy of
proton/keV
0.21~3.3
Density of
proton/cm −3
6.6
Magnetic
field/nT
7
1. Solar Wind
The solar wind is rare plasma originated in high temperature corona. When the
temperature (kinetic energy) of high temperature corona is over the control of solar
gravity, the solar wind emits in all direction. On average, the solar wind particles are
composed of about 95% of protons, 4% of α particles and about 1% of heavy ions.
Among the heavy ions, the abundance of carbon, nitrogen, oxygen, neon, magnesium,
silicon and ferrum is relatively high. The basic parameters of solar wind are shown
in Table 2.2.
Since the energy of proton in the solar wind is only a few thousand electron volts,
and its penetrating range inside the material of spacecraft is only about 0.1 μm, it
does not have any effect on spacecraft beside that the very thin optical coating suffers
a certain amount of damage caused by total ionizing dose [7].
In the space plasma environment, electrons and ions have similar density and
energy (in electroneutral state). However, the mass of ion is 1000 times of the mass
of electron, therefore its speed is far lower than that of electron. The electronic
current is in leading role and the negative current is larger than positive current. In
other words, the charging effect in spacecraft is mainly triggered by electron. It is
shown that the energy of electrons in solar wind is as low as a few electron volts in
the Table 2.2. Its influence on the charging effect in spacecraft can be ignored.
2. Plasma in Magnetic Tail
The Moon passes the remote magnetic tail region of the Earth magnetic field while
orbiting the Earth. In each revolution period, the Moon stays in the magnetic tail of
Earth for about 4 days (before and after the full moon). While passing the magnetic
tail, the Moon encounters two plasma regions that have very different properties. The
two regions are plasma sheet and plasma mantle (which is also called tail lobe). The
density of plasma in plasma sheet is very low and is usually lower than 0.1 cm
−3 . The
energy of plasma is lower than several electron volts in general. Therefore, its effect
on spacecraft can be ignored. Plasma mantle distributes over the magnetic equator
of Earth with a thickness of about 4Re (Re is radius of the Earth). It is primarily
composed of thermal plasma with thousand electron volts of energy.