radiation shielding for a habitat

How much is needed and of what type?

It seems obvious to me that the earth has enough radiation shielding
at sea level or even at say 12,000 feet above sea level to protect
people from pretty much the worst that we can expect. That implys
about 10-14.7 pounds-mass per square inch of surface area of the
habitat in light elements like Oxygen and Nitrogen or Hydrogen, and
perhaps more of other materials.

H2O ice, or perhaps liquid water, or perhaps various plastics might
make good materials for this with perhaps nickle steel or aluminum
structural backing.

This winds up being about 23.1 to 33.92 foot thick ( 7.03-10.34 meters)
of liquid water.

Is this a reasonable approximation? Or does someone have a better
reference with hopefully less massy shielding ideas?

I am aware that this much will not be needed all the time, but even for
a radiation shelter this is pretty heavy.

On 14 Mar 2005 23:33:55 -0800
"Alfred Montestruc" wrote:

This winds up being about 23.1 to 33.92 foot thick ( 7.03-10.34
meters) of liquid water.

Is this a reasonable approximation? Or does someone have a better
reference with hopefully less massy shielding ideas?

I am aware that this much will not be needed all the time, but even
for a radiation shelter this is pretty heavy.

I have seen suggestions from other people that 10cm of water is
sufficent for shielding against radiation in space. I think you would
want more than that if you were in a high radiation environment like the
Van Allen belts.

Remember that the mass of your shield scales with the surface area of
the habitat, but the overall worth of the habitat scales with the
volume. So if your habitat was 1km wide a radiation shield 10 metres
deep wouldn't represent much of a cost overall.
--
Michael Smith
Network Applications
www.netapps.com.au | +61 (0) 416 062 898
Web Hosting | Internet Services

Alfred Montestruc wrote:
How much is needed and of what type?

It seems obvious to me that the earth has enough radiation shielding
at sea level or even at say 12,000 feet above sea level to protect
people from pretty much the worst that we can expect. That implys
about 10-14.7 pounds-mass per square inch of surface area of the
habitat in light elements like Oxygen and Nitrogen or Hydrogen, and
perhaps more of other materials.

Is this a reasonable approximation? Or does someone have a better
reference with hopefully less massy shielding ideas?

Not quite.
A big bit of the shielding is hundred Km or so extent of the atmosphere.
Energetic particles hit stuff high up in the atmosphere, and the resultant
spray of particles all hit other stuff slightly lower in the atmosphere,
until very little gets through, as the hot stuff has time to interact
or even decay.
With a less extensive shield of the same mass, you don't get quite the
same shielding, some of the shorter lived particles hit your shield and
carry right on through, depositing energy in the people inside.
In general the higher the atomic number your shield, the worse the problem
with secondary radiation is.
You want incoming particles to react with something light first, so that
the resultant particles are again light, and easily absorbed, and not
heavy hard to stop particles.

Hydrogen is best, but is hard to store.
Water is OK, as it's gots lots of hydrogen, and isn't too hard to store.
Something like lithium hydride would probably be ideal for the first layer,
bit is a bit expensive.
You want a thick enough layer of this first material of low atomic mass
that it slows down most of the secondary fragments enough that when it reaches
your higher atomic weight backstop they are absorbed, rather than
spalling off particles to cut through the crew.

Alfred Montestruc wrote:
How much is needed and of what type?

As a rule of thumb: a lot of mass.

This winds up being about 23.1 to 33.92 foot thick ( 7.03-10.34
meters)
of liquid water.

That's about correct. 14.7 pounds of mass per square inch should give
you radiation shielding on par with Earth's atmosphere.

Is this a reasonable approximation?

Yes.

Or does someone have a better reference with hopefully
less massy shielding ideas?

You could use thinner shields of denser materials, and some layered
multi-material shields have certain advantages against different types
of penetrating radiation, but a ~30ft thick wall of water is a good
start.

I am aware that this much will not be needed all the time, but even
for
a radiation shelter this is pretty heavy.

I believe you can get substantial protection from most radiation
threats with, say, a meter or two of water. If you want a temporary
storm shelter, a big tank of water reaction mass is a good start. You
need the water for the engines, and it can serve as shielding, too.

Mike Miller, Materials Engineer

"Alfred Montestruc" wrote in message
ups.com...
How much is needed and of what type?

Have a look at
http://lifesci3.arc.nasa.gov/SpaceSe...dy/Design.html where
it's recommended that we use slag (which will be producing anyway) for
shielding.

http://lifesci3.arc.nasa.gov/SpaceSe...html#Shielding

--


Regards,
Mike Combs
----------------------------------------------------------------------
Member of the National Non-sequitur Society. We may not make
much sense, but we do like pizza.

"Alfred Montestruc" wrote in
ups.com:

How much is needed and of what type?

It seems obvious to me that the earth has enough radiation shielding
at sea level or even at say 12,000 feet above sea level to protect
people from pretty much the worst that we can expect. That implys
about 10-14.7 pounds-mass per square inch of surface area of the
habitat in light elements like Oxygen and Nitrogen or Hydrogen, and
perhaps more of other materials.

H2O ice, or perhaps liquid water, or perhaps various plastics might
make good materials for this with perhaps nickle steel or aluminum
structural backing.

This winds up being about 23.1 to 33.92 foot thick ( 7.03-10.34 meters)
of liquid water.

Is this a reasonable approximation? Or does someone have a better
reference with hopefully less massy shielding ideas?

I am aware that this much will not be needed all the time, but even for
a radiation shelter this is pretty heavy.


If I'm correct, a lot of the (harmful) radiation from the sun is trapped by
earth's magnetic field, even before it gets to the atmosphere.
Maybe it would be possible to also produce a magnetic field around the
spaceship, in addition to the above mentioned water/plastics. (I have no
idea how strong the magnetic field is, this might not be possible at all).