The Van Allen Radiation Belt And The Moon Missions.

One of the most hotly contested
procedures during the Apollo missions
was how NASA dealt with the issue of
Van Allen belts. The naturally-occurring
belts of radiation that's surround the
earth both on the journey to the moon
and also returning from it.

Van Allen belts.

To some this just proves the point that NASA never
went to the moon because they contest
that if the crew went through the Van Allen
belts they would have received a lethal
dose of radiation and died during or
shortly afterwards. But as we know that
didn't happen so how did NASA achieve this?

Cutaway drawing of two radiation belts around Earth: the inner belt (red) dominated by protons and the outer one (blue) by electrons. Image Credit: NASA.

Mention the word "radiation" and most
people think of x-ray,s the atom bomb
Hiroshima, Chernobyl and therefore
associated with bad things.

Yes, you do need thick lead shielding to
protect against high-intensity x-rays
but the radiation in the Van Allen belts
is not x-rays, it's charged particles.

Electromagnetic waves.

There are two main types of radiation
the first is electromagnetic waves. This
covers everything from radio waves
through microwaves, infrared which we
feel is heat, visible light on through
ultraviolet light onto x-rays to gamma
rays, that is the electromagnetic
spectrum.

Charged particles.

The second type of radiation is charged
particles. These are the component parts
of atoms such as protons, neutrons and
electrons which had been broken apart by
nuclear reactions or extreme heat in the
Sun.

These particles flow out from the
Sun as the solar wind and because they
have a positive or negative electric
charge they react with the Earth's
magnetic field.

Illustration of the various dynamic and constant solar effects on Earth. The two solar constants, sunlight and solar wind, takes 8 minutes and 4 days, respectively, to reach Earth. Arrival times of dynamic solar events such as Flares, solar energetic particles and CMEs, are approximated and range from immediate effect to several days.

Credits: NASA/Berkley

Some are attracted to the north and
south poles where they enter the
atmosphere and react with the air to
create the northern and southern lights
others are captured into the bands of
magnetic fields around the earth where
they form the Van Allen belts. These
consist of an inner and outer belt and a
temporary third belt which appears when
the Sun has large solar flares.

A close-up of an erupting prominence with Earth inset at the approximate scale of the image. Taken on July 1, 2002.

Credits: ESA&NASA/SOHO

These bands extend from between 1000 and
60,000 miles above the earth surface
with the most active areas centered
around the equatorial area of the earth
but thin out near the poles. This type of
charge particle radiation is also known
as ionizing radiation which means that
it has enough energy to knock electrons
from atoms or molecules that make up
spacecraft and the crew inside, which can
cause tissue damage if there is a high
enough exposure for long enough.

Technological and infrastructure affected by space weather events.

Credits: NASA

The main types of ionizing particles in the Van
Allen belts are high-energy protons and
electrons. The protons can be stopped by
light materials such as the aluminium
skin of craft and also the epoxy resin
Heat shield. Electrons which are also
known as beta particles can penetrate
several inches into living tissue but
because they're very small they don't
tend to do much damage, they can also be
blocked by materials like polyethylene
which contain a lot of hydrogen.

The hydrogen atom.

The hydrogen atoms are very light and absorb
the beta particles as well as the
fibrous insulation material that was
fitted between the inner and outer hulls
of command module should also have been
a good shoot against them.

Alpha radiation consists of helium nuclei and is readily stopped by a sheet of paper. Beta radiation, consisting of electrons or positrons, is stopped by thin aluminum plate, but gamma radiation requires shielding by dense material such as lead, or concrete.

One problem is that when beta particles
interact with large atoms they give off secondary x-rays.
And this is called the bremsstrahlung effect.
So the thick lead shielding but some people
think is needed to protect the crew
against x-rays would ironically make the
problem worse by creating more x-rays.

Bremsstrahlung produced by a high-energy electron deflected in the electric field of an atomic nucleus.

Whereas the lighter metals like
stainless steel and aluminium of command
module would create less x-rays and even
then some of the x-rays would be absorbed
by the inner hull.

So whilst we can shield against the radiation to a degree
provided it's not too strong, there are other things have been NASA
engineers and the mission planners knew
about, and one of these was where the
thickest and most lethal parts of Van Allen
belts were and also how the human body
reacts to radiation.

The effects of radiation are cumulative.

The effects of radiation are cumulative
which means the longer exposed to it the
more damage it causes. Within reason a
short exposure to high levels of
radiation is better tolerated by the
body as it has time to repair the damage
afterwards.

Long exposures to low levels of radiation caused
more problems because the body has to try and repair
itself and contend with a continual
damage while it's doing so.

If you spent an extended period within the Van Allen
belts then the effects would be lethal but
the Apollo Crews only spent about six
hours in total.

Probe data indicated, and actual dosimeters worn by the Apollo crews confirmed, that total exposure due to the Van Allen belt passage would be about the equivalent of a chest X-ray. In other words, nothing to worry about.

Around three and a half hours going two and a half hours
returning several days later, effectively to short bursts
separated by a rest period.

More importantly the course which each
of the Apollo craft took avoided the
most lethal parts of the inner belt
completely and they only went through
the thinnest part of the outer belt.

All the astronauts wore dosimeters to
measure their personal radiation
exposure levels during the flight and
reported results back to NASA at regular
intervals.

This sketch images the inner solar system at the time the light and electrons from solar activity reach the Earth. Fast electrons and the slower ions follow magnetic lines of force.

In total the amount of radiation at the Apollo
Crews received during their flights to and from the
moon from high-energy protons electrons
and x-rays from the bremsstrahlung
effect was much less than that of the
yearly allowed dose for someone working
the nuclear industry and regularly
dealing with radioactive materials.

There was no shortage of threats facing Apollo astronauts on missions to the Moon. Like radiation. Specifically, the dense radiation environment of the Van Allen belts that surround our planet. When it launched Apollo missions through the Van Allen belts on a path to the Moon, NASA didn’t just hope for the best. The agency had studied the “Van Allen problem” as it were, knew the risks, and made the decision to go anyway. And not one astronaut died from passing through the Van Allen Belts.

In the end a simple answer to why Van Allen
radiation belts were not the killer
issue that some people think it was and
how the Apollo missions cut a radiation
exposure from the cruise to between just
1% and 5% of what it could
have been is because the Apollo missions
didn't need to go straight through the
Van Allen belts is because they basically flew
around the most deadly areas and we're
not in the less dangerous areas for long
enough for it to be a showstopper.

This remains true today as it was for any future missions.
Why go through it, when you can just go around it.