Wich is the best Radiation Hull or Shield we can build for a spacecraft?

wrote in message ...

Yes. Complicated stuff. What you end up with is a "sandwich
shielding", a set of layers, each with a specific function. We do it
already. When you want to shield against fast neutrons, you need a
sandwich of moderator-neutron_absorber_gamma absorber. You can think
up more complex configurations.

Yes. And you need a sandwich for spallation neutrons which are 20% of
the radiation in some cases, and which come off of 30 or 40 heavy ion
species at a very wide range of energies.

No simple answers to any of this. On doing a little research I find
that much of the needed data and analysis hasn't even been collected
or done.

Its not that bad. Most if not all of the information required exists,
you just need to put it together into a design.

COMMENT

Nope you underestimate this. Truely. There are monte carlo quantum
codes for heavy ion radiation transport in solid matter. But that's
just the beginning. You have to know the input flux of heavy ions not
only in interplanetary space, but also on the Martian surface, where
the atmosphere has greatly screwed things up and changed the character
of the radiation (more neutrons!) but not blocked very many rads. We
know this muchy, but we know too little of the character of radiation
on the Martian surface to model effects on humans that well, yet.
It's a major question on future Mars robotic missions.

Then you have the problem that heavy ion biological effects are the
most poorly studied of all known radiation effects, and here they're a
major player.

For every phase you have that 3-element neutron sheild design, but you
have to do it THREE times, and in three separate ways.

The reason is that a decent Mars mission involves two 1-yr cruise legs
and a year and half on the surface (alternative is two 1-yr cruise
legs and a couple of months on the surface for payoff, which is really
ridiculous.)

Cruise phase is easiest-- we know a lot about interplanetary space
radiation, and can model it. We know what we'll be sending. Only
problem: it's hard to predict solar activity and how much fast-proton
"solar storm cellar" stuff we have. Guess wrong, get unlucky, and
you're dead.

Surface phase is complicated since you really don't want to use the
fuel to send down all that sheilding, when you're going to a place of
rock and sand that can be used instead. But now the landing is in two
phases:

1) A frantic foxhole phase where astronauts have to get our of their
lander and dig in before they are fried.

2) A long duration phase where they've added enough H-rich plasticized
concrete to their habitat that they're okay. Impossible to calculate
this, since they'll just have to keep adding layers until it's enough.
But how about calculations for phase 1 to make sure they don't fry
UNTIL they can add enough? Very hard.

Mars habitats I suppose will be like those concrete domes on Earth
made by putting a balloon on the ground, pouring concrete on it, and
inflating it as the concrete sets. On Mars, inflate with CO2 and of
course make the concrete out of soil and whatever else you bring
(maybe if you bring only hydrogen, you can make polyethylene-graphite
composite out of CO2 and energy from you reactor?). There are going to
have to be some very wierd concrete-making robots sent to Mars to test
this out. I wonder if robotics will get good enough to blow a couple
of preliminary domes before the humans arrive? In any case, success of
this venture will mean the difference between a 1 month or 18 month
stay on the surface. If you ever had any mental pictures of Mars
astronauts spending their entire surface time in their titanium
landers, forget it. Spallation neutrons would fry them good.

For just a hint at the difficulties still to be solved, I suggest:

http://sd.msfc.nasa.gov/cosmicray/DS...RSMR_final.pdf

SBH


SBH

In article , (Steve Harris ) writes:
wrote in message ...

Yes. Complicated stuff. What you end up with is a "sandwich
shielding", a set of layers, each with a specific function. We do it
already. When you want to shield against fast neutrons, you need a
sandwich of moderator-neutron_absorber_gamma absorber. You can think
up more complex configurations.

Yes. And you need a sandwich for spallation neutrons which are 20% of
the radiation in some cases, and which come off of 30 or 40 heavy ion
species at a very wide range of energies.

No simple answers to any of this. On doing a little research I find
that much of the needed data and analysis hasn't even been collected
or done.

Its not that bad. Most if not all of the information required exists,
you just need to put it together into a design.

COMMENT

Nope you underestimate this. Truely. There are monte carlo quantum
codes for heavy ion radiation transport in solid matter.

There is much more than just this. Heavy ions, protons,
ultra-relativistic electrons, gammas, neutrons and all possible mixes.
How much you'll find in the open literature, that's another story.

But that's
just the beginning. You have to know the input flux of heavy ions not
only in interplanetary space, but also on the Martian surface, where
the atmosphere has greatly screwed things up and changed the character
of the radiation (more neutrons!) but not blocked very many rads. We
know this muchy, but we know too little of the character of radiation
on the Martian surface to model effects on humans that well, yet.
It's a major question on future Mars robotic missions.

Then you have the problem that heavy ion biological effects are the
most poorly studied of all known radiation effects, and here they're a
major player.

Only if you shield very poorly. The reason heavy ion biological
effects are the most poorly studied, is because heavy ions are the
easiest to block. It is only when their kinetic energy, per nucleon,
exceeds their binding energy (again, per nucleon), that spallation
effects become a bitch. But you don't encounter many heavy ions in
this range.

For every phase you have that 3-element neutron sheild design, but you
have to do it THREE times, and in three separate ways.

Not really. A neutron shield is a neutron shield. One which is
designed for the highest energy neutrons you expect to face is good
for all the rest, as well. The problem with neutron shields is that
there is really no way to make them compact. You need sufficient
thickness for moderation.

So, basically, you've to plan on sufficient thickness to stop the fast
protons, followed by a sufficient thickness, from this point, to
moderate the neutrons. And the you've to absorb the thermal neutrons
and provide sufficient thickness, from this point, to absorb most of
the resulting gammas. That's quite bulky.

Mati Meron | "When you argue with a fool,
| chances are he is doing just the same"

Personally, I was thinking from the NASA Ames Summer Study 1975, wherein the
participants were charged to build a permament Space City. This can
correlate to building the initial Martian, or Lunar, Settlement.

One of the problems The Summer Study faced was the issue of Radiation in the
Colony Station. The participants solved it through use of a six feet thick
shield, consisting of lunar regolith, between the double hulls. A reduced
version could be used in the interplanetary spacecraft. Unfortunately, the
regolith is deadweight mass, and requires fuel to transport it between Earth
and Mars (as well as vice versa).

Comments?

--
Leonard C Robinson
"The Historian Remembers, and speculates on what might have been.
"The Visionary Remembers, and speculates on what may yet be."

wrote in message ...
Then you have the problem that heavy ion biological effects are the
most poorly studied of all known radiation effects, and here they're a
major player.

Only if you shield very poorly. The reason heavy ion biological
effects are the most poorly studied, is because heavy ions are the
easiest to block. It is only when their kinetic energy, per nucleon,
exceeds their binding energy (again, per nucleon), that spallation
effects become a bitch. But you don't encounter many heavy ions in
this range.

COMMENT:

You do in interplanetary space and on the Martian surface---that's the
whole point. The fraction of hadron radiation in space goes down as
some power loaw, but it's not absolute fractions that are important as
energy fluxes (fluences). For (extra galactic) cosmic rays (which will
cause more radiation than a quiet sun), in order to look at all
significant biological dosing, you have to integrate all the way up
from channels of 10 MeV per nucleon to 100 GeV per nucleon. All above
binding energy. As I said, 20% of your total radiation dose on the
Martian surface is spallation neutrons.


For every phase you have that 3-element neutron sheild design, but you
have to do it THREE times, and in three separate ways.

Not really. A neutron shield is a neutron shield. One which is
designed for the highest energy neutrons you expect to face is good
for all the rest, as well. The problem with neutron shields is that
there is really no way to make them compact. You need sufficient
thickness for moderation.

So, basically, you've to plan on sufficient thickness to stop the fast
protons, followed by a sufficient thickness, from this point, to
moderate the neutrons. And the you've to absorb the thermal neutrons
and provide sufficient thickness, from this point, to absorb most of
the resulting gammas. That's quite bulky.

COMMENT:

Reread my message. You need three neutron sheilds because you need to
make them out of three different sets of materials, and they need to
do the job against two different radiation environments. In space you
have one shield. For that you can use all the hydrogen you're taking
with you for reaction mass to Mars orbit and to get you home again.
Plus drinking water and urine for the voyage out. And you don't have
as many neutrons to worry about, since a lot of your shield is
hydrogen (giving you proton-proton collisions for a lot of cosmic
rays) and not Mars atmospheric CO2 or Martian SiO2.

On the Martian surface you get the hot neutrons made in the
atmosphere, and you're stuck with those. And you here have two
sheilds, one lousy and temporary, and the other better and for the 18
mo surface stay. The lousy one is probably going to be your temporary
crew capsule of your lander, tipped on its side, with a supported roof
designed to hold up a foot of Martian sand which you collect with
electric plows and run up with a conveyor belt where some guy in a
pressure suit trowels it out. You need to figure out how much plastic
under that will keep you from getting fried until you build your
balolon inflated concrete sand domes. Which will be yet a third
shield, maybe with the hydrogen in the plasticizer. Who knows? Maybe
hydrogen is rare enough on Mars that all of it will have to be landed
as liquid, then quickly turned into water or plastic by reacting it
with air.

SBH

In article , (Steve Harris ) writes:
wrote in message ...
Then you have the problem that heavy ion biological effects are the
most poorly studied of all known radiation effects, and here they're a
major player.

Only if you shield very poorly. The reason heavy ion biological
effects are the most poorly studied, is because heavy ions are the
easiest to block. It is only when their kinetic energy, per nucleon,
exceeds their binding energy (again, per nucleon), that spallation
effects become a bitch. But you don't encounter many heavy ions in
this range.

COMMENT:

You do in interplanetary space and on the Martian surface---that's the
whole point. The fraction of hadron radiation in space goes down as
some power loaw, but it's not absolute fractions that are important as
energy fluxes (fluences). For (extra galactic) cosmic rays (which will
cause more radiation than a quiet sun), in order to look at all
significant biological dosing, you have to integrate all the way up
from channels of 10 MeV per nucleon to 100 GeV per nucleon.

You got some confusion here. There are protons in all possible
energies. There is little if any evidence for any significant amount
of heavy ions at hig energy (heavy ion is an ion with *Z 1*).
Proton at 1000 Gev has an energy of 1000 GeV pre nucleon. This *does
not* mean that you've heavy ions at high energies.

All above
binding energy. As I said, 20% of your total radiation dose on the
Martian surface is spallation neutrons.

Certainly since all protons above 10 MeV or so will give
you spallation. Nothing to do with "heavy ions".

For every phase you have that 3-element neutron sheild design, but you
have to do it THREE times, and in three separate ways.

Not really. A neutron shield is a neutron shield. One which is
designed for the highest energy neutrons you expect to face is good
for all the rest, as well. The problem with neutron shields is that
there is really no way to make them compact. You need sufficient
thickness for moderation.

So, basically, you've to plan on sufficient thickness to stop the fast
protons, followed by a sufficient thickness, from this point, to
moderate the neutrons. And the you've to absorb the thermal neutrons
and provide sufficient thickness, from this point, to absorb most of
the resulting gammas. That's quite bulky.

COMMENT:

Reread my message. You need three neutron sheilds because you need to
make them out of three different sets of materials, and they need to
do the job against two different radiation environments.

No you don't yyou need a primary shield which is thick enough to stop
all (or nearly all) charged particles). Then you need a moderation
layer thick enough to slow all neutrons in generated within the first
layer (or neutrons incoming into the first layer) to thermal or near
thermal velocities. Then you need something to absorb these neutrons
and absorb the gammas generated by the neutron absorption.

Mati Meron | "When you argue with a fool,
| chances are he is doing just the same"

wrote in message ...
In article , (Steve Harris ) writes:
wrote in message ...
Then you have the problem that heavy ion biological effects are the
most poorly studied of all known radiation effects, and here they're a
major player.

Only if you shield very poorly. The reason heavy ion biological
effects are the most poorly studied, is because heavy ions are the
easiest to block. It is only when their kinetic energy, per nucleon,
exceeds their binding energy (again, per nucleon), that spallation
effects become a bitch. But you don't encounter many heavy ions in
this range.

COMMENT:

You do in interplanetary space and on the Martian surface---that's the
whole point. The fraction of hadron radiation in space goes down as
some power loaw, but it's not absolute fractions that are important as
energy fluxes (fluences). For (extra galactic) cosmic rays (which will
cause more radiation than a quiet sun), in order to look at all
significant biological dosing, you have to integrate all the way up
from channels of 10 MeV per nucleon to 100 GeV per nucleon.

You got some confusion here. There are protons in all possible
energies. There is little if any evidence for any significant amount
of heavy ions at hig energy (heavy ion is an ion with *Z 1*).
Proton at 1000 Gev has an energy of 1000 GeV pre nucleon. This *does
not* mean that you've heavy ions at high energies.


Not my confusion. Need for you to read up on the subject, since you're
way out of date. 98% of extragalactic cosmics are H and He, but the
remaining 2% (which is better than our own solar system for
metalicity) are ions all the way up the periodic table, at any energy
you like (and as far up as has been measured). Mostly below Z=30, as
expected, but also going higher. Relative abundances for even elements
look a lot like what we're used to. All evidence for the supernova
shock origin theory.

http://www.wkap.nl/prod/a/ISBN_0-7923-7196-8_29.PDF

Certainly since all protons above 10 MeV or so will give
you spallation. Nothing to do with "heavy ions".


Heavy ions are important to the extent you have to do your shielding
with other than hydrogen. If you're sheilded with a big ball of frozen
H2 on the voyage out, heavy ions are your most important source of
neutrons.


COMMENT:

Reread my message. You need three neutron sheilds because you need to
make them out of three different sets of materials, and they need to
do the job against two different radiation environments.

No you don't yyou need a primary shield which is thick enough to stop
all (or nearly all) charged particles). Then you need a moderation
layer thick enough to slow all neutrons in generated within the first
layer (or neutrons incoming into the first layer) to thermal or near
thermal velocities. Then you need something to absorb these neutrons
and absorb the gammas generated by the neutron absorption.


Yes, and since you have three different sets of materials available to
do some of these jobs. The moderator will be of different thicknesses
depending on how much neutron radiation has to be dealt with, which is
a function of radiation type atmosphere interactions, and type of
primary sheild (how much hydrogen). If you are in space this will be a
lot of hydrogen, so your moderator has to deal with only those
neutrons produced by heavy elements in the primary sheild, and
neutrons produced by high Z cosmics in the primary sheild. But on the
Martian surface things are very different, and you have neutrons
produced by a primary sheild of sand, and in the atmosphere before
that. Neutrons which may need to be moderated, but with only sand
absorption after that.

Remember, with enough sand you not only don't need a gamma sheild
(certainly you dont' need to carry down from orbit whatever you used
in space),you also don't even need a dedicated neutron absorber, and
won't use it any more than one is used in modern power plants. You
don't really think there's a layer of gadolinium or cadmium in
powerplants, do you? Similarly, there's no point in carrying carrying
gadolinium down to the Martian surface, either, except possibly in the
small quantities necessary to protect the lander capsule during the
initial "foxhole digging" or "concrete making" phase of the surface
stay.

SBH

I can see the answer to my question depends in part upon if you are in
a spacecraft somewhere in between Earth / Mars orbits, or on some part
or other of the Moon, or on some part or other of Mars.

My question is, what directions does this radiation come in from; and
if you're on some body, what cyclical variation do you see?

The case for shielding sounds pretty good; but if I were there, I
wouldn't yet know where best to put it.

Thanks -- Martha Adams

In article ,
Martha H Adams wrote:
My question is, what directions does this radiation come in from; and
if you're on some body, what cyclical variation do you see?

Galactic cosmic rays essentially come in from all directions uniformly;
their paths are randomized by interaction with the galactic magnetic
field. The only significant variation in intensity is due to solar
activity: there are fewer of them near solar maximum, presumably because
the stronger solar wind and its associated magnetic fields have some
tendency to fend them off from the inner solar system.

The case for shielding sounds pretty good; but if I were there, I
wouldn't yet know where best to put it.

All over. The only direction in which you don't need shielding is down,
if you are on a planetary surface.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

(Martha H Adams) writes:

I can see the answer to my question depends in part upon if you are in
a spacecraft somewhere in between Earth / Mars orbits, or on some part
or other of the Moon, or on some part or other of Mars.

My question is, what directions does this radiation come in from;

Cosmic radiation has no apparent specific discrete sources in space;
it appears to arrive with equal intensity from all parts of the sky.
It is believed that this is because the galactic magnetic field is
sufficiently "tangled" to effectively randomize the direction
the cosmic ray particles appear to be coming from, on a scale
smaller than the typical distance between sources.


and if you're on some body, what cyclical variation do you see?

You would all the time see lots of cosmic rays coming down from the sky,
and very few coming up out of the ground if it is thick enough to shield you,
with no significant cyclic variation.


The case for shielding sounds pretty good; but if I were there, I
wouldn't yet know where best to put it.

You need to put shielding everywhere between you and naked sky.


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

In article , says...

In article ,
Martha H Adams wrote:
My question is, what directions does this radiation come in from; and
if you're on some body, what cyclical variation do you see?

Galactic cosmic rays essentially come in from all directions uniformly;
their paths are randomized by interaction with the galactic magnetic
field. The only significant variation in intensity is due to solar
activity: there are fewer of them near solar maximum, presumably because
the stronger solar wind and its associated magnetic fields have some
tendency to fend them off from the inner solar system.

The case for shielding sounds pretty good; but if I were there, I
wouldn't yet know where best to put it.

All over. The only direction in which you don't need shielding is down,
if you are on a planetary surface.



So then this configuration might be sufficient?

http://www3.telus.net/webshrinker/wow/marsshot.jpg