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rreppy
2008-Apr-17, 03:12 PM
Lately I've read discussions that the deadly effect of radiation in space may be the ultimate barrier to mankind voyaging between the planets. It is said that the sheer mass of the shielding required to protect astronauts from months and even years of exposure during a mission would make the trips impossible. They say even if it doesn't kill them immediately, they'll all get cancer.
Tell me it ain't so! Are all our dreams of space exploration to be dashed by cosmic rays? Will we be limited to sending out robots instead of going ourselves? Please discuss just how much of a hazard space radiation is, and whether it will keep us Earthbound or not.

logic.exe
2008-Apr-17, 07:43 PM
Don't worry about it, there are plenty of ways to get around the radiation. None of them are very easy or cheap (not right now anyway) but there's no reason to think it's an unsurmountable problem.

One way to get around it is to simply send your ship up into orbit in pieces in multiple launches and assemble the ship in orbit. Of course, all those launches would be ludicrously expensive. We could also just work on manufacturing materials that are lighter and more effective at blocking radiation (like this) (http://www.nasa.gov/vision/space/travelinginspace/radiation_shielding.html).

And then there are the more exotic ideas involving electrostatic fields ((Linky) (http://science.nasa.gov/headlines/y2005/24jun_electrostatics.htm). Of course the downside to those are the fact that they require energy, which means it could be more cost effective to simply reinforce the hull and use your fuel for other things. It depends really on how much extra energy it costs to keep something like this running vs the added costs of launching the extra mass into orbit and then getting that extra mass to move once the ship is assembled. Even if the "shield" is more energy efficient, you could still run into some problems if the system suffers irreparable damage. Something like this would probably be a lot more fragile than a reinforced hull.

So yeah, it's a problem, but not an impossible one.

dcl
2008-Apr-23, 12:22 AM
I do not know the answer with certainty, but it's my very strong impression that rreppy is right, which if true, would seem to make logic.exe's optimism unwaranted. By the very nature of matter and radiation, effective shielding necessarily requires shielding containing significant amounts of mass, usually lead. The stronger the radiation, the greater the need for large amounts of shieding. The only way to provide effective shielding is to place lead or other massive shielding between the radiation source and whatever is to be protected.

Radiation in the solar system is mostly in the form of energetic particles from the sun and in planetary radiation belts. Extrasolar sources may also be dangerous.

In spacecraft, mass needs to be kept to a minimu to conserve fuel requirements, so it's not practical to provide heavy shielding against intense radiation now, and I'm not aware that the situation shows much promise of improving in the foreseeable future.

Kebsis
2008-Apr-23, 12:54 AM
logic.exe, why would assembling a ship in orbit help keep out radiation?

dcl
2008-Apr-23, 01:50 AM
Kebsis: "Most editorials are written by people that love to argue but got kicked off debate team for not making any sense." -Seanbaby".

-- I have not the slightest idea what you are trying to say. Do you or do you not agree with Kebsis, me, or both? Let's not play semantic games.

logic.exe
2008-Apr-23, 03:32 PM
logic.exe, why would assembling a ship in orbit help keep out radiation?

Sorry, I may have been unclear. What I meant was that the heavy components required to block out the radiation can be launched into low earth orbit with multiple launches. While in assembly in low earth orbit the pieces are protected from radiation. Once it's assembled the thick armor plating will protect the interior from radiation once it leaves orbit.

Dcl, yeah you may be right, perhaps I am being a little too optimistic. Like I said in my other post, there are lots of people trying to find a good solution to the problem that avoids having to line the ship with thick heavy lead plating. If we don't and we end up having to line all our ships with lead, well that would probably kill the idea of easy routine space travel and any form of personal space travel would be totally out of the question. It's still within the realm of feasibility though. I do agree though that it would be slow and cumbersome, but that doesn't rule out the possibility of human exploration of our solar system, it just makes it more inconvenient.

This highlights the ever growing importance of robotic probes. Even if we found an easy way to block out the radiation, we'd have to send reconaissance probes anyway, this makes them all the more important if we ever plan on sending humans to other celestial bodies.

Unfortunately, we probably won't ever be taking vacations up to Mars unless magical shields a la Star Trek can be built.

crosscountry
2008-Apr-23, 03:58 PM
The only way to provide effective shielding is to place lead or other massive shielding between the radiation source and whatever is to be protected.



so far anyway. Some of the mass could be useful for other things too. Water containment is necessary, and water also blocks radiation to a degree. People cannot live without water.


but I suspect since mass isn't the only requirement to block radiation there will arise other technologies to solve that problem. First off, thickness and a constant factor inherent in each material are actually what block it. So by finding materials, alloys most likely, that can block different energy radiation we can solve that problem. Thick walls are key too, but again they can be useful for other things as well.

dcl
2008-Apr-23, 04:44 PM
Thank you, logic.exe and crosscountry, for your comments. My response to both of you is the same. It follows:

I believe both of you are grossly unestimating the cost of mass in a spaceship. The more mass a spacecraft contains, the more fuel it will need to consume in changing its speed for any reason. Getting large amounts of mass into orbit for shielding a spaceship would cost a huge expenditure in fuel to launch it into orbit. Once in orbit, it would cost an additional large amount of fuel to acceleratge it to a high enough speed to be practical for traveling even to the moon, much to Mars or beyond. An additional large amount of fuel would need to be brought along to insert the spaceship into orbit at its destination. And this does not include fuel for the return trip to earth.

The probability of finding a way to shield a spaceship against radiation without massive lead shielding is extremely low. There seems to be no hope whatever of stopping radiation other than with mass in the form of lead or other extremely dense materials. New materials, no matter how exotic, will be useless for shielding agaisnt radiation if they are not massive. Only mass can attenuate radiation.

Someone's going to have to do some awfully fast talking to succeed in persuading me to buy a round-trip ticket for a two-week stay in the most popular vacation resort on Mars.

crosscountry
2008-Apr-23, 04:53 PM
no one goes to Mars for a two week stay.

logic.exe
2008-Apr-23, 05:54 PM
Oh man, why do you have to be such a downer dcl? :razz:

The more you get me thinking about it the more I start to realize you may be right. My thought process was that we could take advantage of the different speeds the outsides surface area and internal volume would increase as we built bigger and bigger ships. Assuming we build it big enough we could make something with more than enough room for fuel to make up for the mass, but then I got to thinking about what you could possibly use to actually build a ship that massive.

I was about to post a reply talking about how with enough volume you could counteract all the extra mass, then I scrapped it all when it dawned on me that you'd probably need much stronger materials that what's currently available to build something that large and massive. :doh:

Kebsis
2008-Apr-23, 08:31 PM
Kebsis: "Most editorials are written by people that love to argue but got kicked off debate team for not making any sense." -Seanbaby".

-- I have not the slightest idea what you are trying to say. Do you or do you not agree with Kebsis, me, or both? Let's not play semantic games.

...huh? I didn't say anything to you.

dcl
2008-Apr-23, 08:45 PM
kebsis, I was evidently sleeping peacefully when I said, "I have not the slightest idea ...", etc. I now realize you were merely quoting Seanbaby.

Sorry.

Vanamonde
2008-Apr-26, 06:17 AM
Mmmm - you know, if it is lots of mass you need, maybe inside of launched it from Earth, you send robots to a nice metallic asteroid and install some ion engines or HUGE solar sails and then move it to under the Van Allen belts. It is the Van Allen belts that make the ISS a safer place to live than interplanetary space, right? Then hollow out that asteroid, install an environment for a crew, and trim the excess mass and polish it up. And then, we have a safely shielded spaceship for interplanetary travel! Heavy, but you are not sacrificing yourself to get to Mars. And a whole lot less delta-V than launching lead from earth. It will be mostly nickel and iron, so the hull needs to be thicker than lead but should mass about the same. And it should never touch an atmosphere - unless something goes terriblity wrong. You need landing craft for the planet you are visiting.

Lots of new engineering techniques to learn before we get there, but that's all part of the fun.

dcl
2008-Apr-26, 02:41 PM
The Van Allen belt does not make any region of space safe from radiation. On the contrary, it is an extremely dangerous region surrounding the earth. Traveling through it would subject the traveler to intense radiation. The asteroid belt is not likely to contain bodies with high concentrations of iron. Iron meteorites are believed to come from the Oort Cloud, not from the asteroid belt.

eburacum45
2008-Apr-26, 03:56 PM
The asteroid belt is not likely to contain bodies with high concentrations of iron. Iron meteorites are believed to come from the Oort Cloud, not from the asteroid belt.
Hmm; I'd like to see some more details on that, please.
From here
http://en.wikipedia.org/wiki/Asteroid_belt#Composition

M-type (metal-rich) asteroids form about 10% of the total population; their spectra resemble that of iron-nickel. Is this no longer thought to be the case?

ASEI
2008-Apr-26, 04:29 PM
I think one perspective problem that has never been adequately addressed is the difference between long periods of extremely low level radiation, and a sudden dose all at once (as in a nuclear bomb). We know linear-no-threshhold is wrong. If it were right, none of us would live under prolonged exposure to sunlight - our sunburns would be chronic injuries rather than things that the body heals over time. Yet it is what we use to quantify radiation damage anyway, because it is ludicrously conservative. People who have to cover their butts from lawsuits know that if they use it as a standard, there is no possible way someone within the "safety limit" could develop a problem.

dcl
2008-Apr-26, 10:03 PM
eburacum45: Thanks for waking me up with your reference to http://en.wikipedia.org/wiki/Asteroid_belt#Composition. My reference to the Oort cloud was respect to comets, so it was irrelevant to the present discusssion because we're talking about meteorites, of which I'm under the impression some do in fact have a good probability of having come from the asteroid belt and seem unlikely to have come from the Oort cloud or even from the Kuiper Belt.

Vanamonde
2008-May-02, 09:26 AM
The Van Allen belt does not make any region of space safe from radiation.

It does not protect the space beneath it from the raw exposure of the sun? I mean *under* the belts, not in them. I do realize that radiation at the ISS is above that of sea level but I thought it was less than, say, geo-synchonous orbit, for example. I could have swore I read that polar orbits are more hazardous as well, do to the fact the Van Allen belts don't go that far north. When I have time, I need to hunt down the references...

I WAS WRONG

I discovered at question 41 at this NASA FAQ on the magnetosphere (http://www-spof.gsfc.nasa.gov/Education/FAQs3.html#q41) that is the very rarefied atmosphere in low Earth orbit, not the radiation belts, that provide the extra protection you do not get from Deep Space.

Thank you for making me look this up and unlearn my misconception.

dcl
2008-May-05, 09:14 PM
Vanamonde: It does not protect the space beneath it from the raw exposure of the sun? I mean *under* the belts, not in them. I do realize that radiation at the ISS is above that of sea level but I thought it was less than, say, geo-synchonous orbit, for example. I could have swore I read that polar orbits are more hazardous as well, do to the fact the Van Allen belts don't go that far north. When I have time, I need to hunt down the references...

dcl: What is dangerous about the Van Allen belt is the fact that it consists of high-speed charged partles racing back and forth at high speed between the earth's north and south magnetic poles. Those particles were originally emitted from the sun and subsequently captured by the earth's magnetic field, As long as one stays out of the paths of those protons, a space traveler is in no danger from them.

Vanamonde: I WAS WRONG

dcl: It takes courage to admit one is wrong about something.

drainbread
2008-May-07, 12:41 AM
How about using carbon based aerogel for radiation insulation?

dcl
2008-May-07, 01:24 AM
I know of no reason to expect carbon-based anything to be effective for protection against anything except "slow" neutrons. The only thing I know of for protection against radiation in general is material with heavy nuclei such as lead. The only useI know of involving carbon to affect radiation is in the first nuclear reactor, in which graphite, consisting of amorphous compacted carbon, was used as s "moderator" to slow the neutrons emitted in that reactor because uranium 235 has a much higher nuclear cross section to "slow" neutrons than to the "fast" ones emitted in U-235 fission. I believe that carbon would be totally useless for shielding against any other type of radiation.

Drunk Vegan
2008-May-07, 01:54 AM
Personally I think an iceship would be the most viable design, given that a significant chunk of ice surrounding your ship seriously mitigates the hazard from radiation, and both water and oxygen can be extracted from the "hull" as needed.

DCL:

You seem to be new to using vBulletin forums. I'd point out two things:

1. If you wish to quote someone, you can either use the Quote button located under every post, or if you want to choose one particular segment of someone's post you can copy and paste it into your own post.

Before and after what they've said you should put in :


and at the end
or

and

Also that line you were talking about earlier, "Most editorials are written by people that love to argue but got kicked off debate team for not making any sense."

...is not something that was meant to be a part of the discussion. It's a tagline/signature phrase that is automatically appended to the end of every post that person makes. Anything below the black line at the bottom left of a post is part of that person's signature.

You can make your own in the User Control Panel (the UserCP link at the top of the page).

dcl
2008-May-07, 02:10 PM
Thanks, Drunk Vegan, for your comments. In the following. I respond to them:

You're right about my being a new contributor. I took issue with Dr. Gay's characterization of the shape of hte Universe as doughtnut-like. Fraser Cain urged me to take my beef to the Forum and, after resisting his urging for some time, I finally decided to do so. I submitted my own thread "The Shape of the Universe", and it went on from there.

Regarding an ice ship as the most viable design for a radiation shield, I doubt that ice would provide any protection against radiation at all because it contains very little mass, and it's mass that's needed to block radiation. That's why lead is used to block x-rays and other penetrating radiation.

As for quoting other contributors, I prefer my own way of doing it. I feel that merely preceding quoted statements by the contributors' pseudonyms is less disruptive to the flow than placing them in specially formatted boxes. Others may disagree with me, and they may be right.

Also, "About that line you were talking about earlier...", I may have failed to recognize it as a tagline as opposed to part of the contributor's own statement.

aquitaine
2008-Jun-01, 03:58 AM
The real problem is with gamma rays, since they are hardest to block. Now, it is possible to reflect them although only if the angle of the material is small enough. I suggested in another thread you could possibly do something like this:

-------------------- outer hull

/-\/-\/-\/-\/-\/-\/-\ first inner hull layer
:)/-\/-\/-\/-\/-\/-\/-\ second inner hull layer
--------------------- third inner hull layer

the outer hull and the third inner hull could be made out of more traditional materials while the second and third inner hull layers would be made out of reflective (at least for gamma rays) material. Since only the areas near the tops of the parabolas are able to reflect the rays, the second layer is staggered to provide more complete protection.

EDIT: The smily is so that it aligns somewhat close to the way I wanted it to. Still not exactly what it should be, but hopefully enough for you guys to get the picture.

dcl
2008-Jun-01, 10:59 PM
aquitaine: It appears to me that by invoking "only if the angle of the material is small enough" you are trying to invoke specular reflection by regular crystals at high angles of incidence, an effect used to produce Bragg patterns in x-ray spectroscopy. I believe that the method you describe would be essentially ineffective in affording protection against cosmic rays because cosmic rays come from all directions. In addition, the ice sheath around the spaceship would need to be a monocrystal for any effective Bragg diffraction to occur at all to reflect cosmic rays from even any direction at all.

crosscountry
2008-Jun-02, 01:46 AM
dcl, unless I he mentioned it in the other thread you've made some assumptions that he didn't state.



and aquitaine, we can reflect gamma rays, and that's how a gamma ray telescope works. But it takes more than two reflections to focus them even slightly. Being as it is a round ship, cylindrical often, your design might in effect focus them onto the astronauts.

as dcl mentioned they come from all directions. letting them pass through would be more desirable. With several more layers it may be possible to redirect the gamma rays around the spacecraft.

aquitaine
2008-Jun-02, 05:23 AM
With several more layers it may be possible to redirect the gamma rays around the spacecraft.

Yeah, that's it. How would something like that look?

crosscountry
2008-Jun-02, 02:04 PM
I'm not sure exactly how many, but every point on the spacecraft would have to have all the same layers, and they would start to interfere. Gamma rays are only reflected at very slight angles, so a mirror won't work. something like a hyperbola would do, but it would be difficult to make one that surrounds the ship.

damian1727
2008-Jun-02, 03:05 PM
cant we deflect radiation with a strong magnetic field....like the earth does??

:):):):)

01101001
2008-Jun-02, 03:19 PM
cant we deflect radiation with a strong magnetic field....like the earth does??

Universe Today: Scientists Designing "Ion Shield" To Protect Astronauts From Solar Wind (http://www.universetoday.com/2008/01/27/scientists-design-ion-shield-to-protect-astronauts-from-solar-wind-radiation/)


These are very early results however, and development on any large-scale system will take some work. Lots of energy would be required to create a spaceship-sized magnetic bubble, so there will be energy optimization issues to work into the design.

damian1727
2008-Jun-02, 03:39 PM
great link thanks

makes sense huh ? better than lugging all that lead around....

sure they can make it work....

dcl
2008-Jun-02, 08:32 PM
The real problem is with gamma rays, since they are hardest to block. Now, it is possible to reflect them although only if the angle of the material is small enough. I suggested in another thread you could possibly do something like this:

-------------------- outer hull

/-\/-\/-\/-\/-\/-\/-\ first inner hull layer
:)/-\/-\/-\/-\/-\/-\/-\ second inner hull layer
--------------------- third inner hull layer

the outer hull and the third inner hull could be made out of more traditional materials while the second and third inner hull layers would be made out of reflective (at least for gamma rays) material. Since only the areas near the tops of the parabolas are able to reflect the rays, the second layer is staggered to provide more complete protection.

EDIT: The smily is so that it aligns somewhat close to the way I wanted it to. Still not exactly what it should be, but hopefully enough for you guys to get the picture.

This scheme seems to depend on Bragg diffraction, which works omly for uniform monocrystals, which such a shell of requisite size is practically guaranteed to not be capable of fabrication. Even if it could be made, it would work only for a very small number of discrete incident angles, viz., those that produce Bragg diffraction. This would reflect an almost vanishingly small portion of incoming gamma rays.

crosscountry
2008-Jun-03, 04:31 AM
ah, but it is not Bragg reflection but real reflection.

http://www.mssl.ucl.ac.uk/www_xmm/ukos/onlines/uhb/XMM_UHB/img24.gif

dcl
2008-Jun-03, 05:25 PM
The following responds to remarks by aquitaine on 01-June-2008, 3:58 AM UT, and by crosscountry on 03-June-2008, 04:31 AM UT:

Granted that the reflecting layer is metallic rather than regular monocrystalline, reflection would still be effect only for x-rays incident at very close to 90 degrees. How does this scheme protect against the influx of gamma rays at all other angles?

crosscountry
2008-Jun-03, 05:51 PM
that's what we've been discussing. it would take some creative distribution and angles to make it work. I'm thinking hyperboloid outer shell.

dcl
2008-Jun-03, 10:02 PM
that's what we've been discussing. it would take some creative distribution and angles to make it work. I'm thinking hyperboloid outer shell.

I cannot imagine any array of reflecting surfaces, including hyperbolic, that could intercept and reflect back into space gamma rays incident from all directions.

crosscountry
2008-Jun-04, 05:11 PM
you need a better imagination.

and I didn't say it would be easy to reflect from every direction.

dcl
2008-Jun-04, 08:29 PM
you need a better imagination.

and I didn't say it would be easy to reflect from every direction.

In the long term, you may be right, but I strongly suspect that you do not recognize the immensity of the problem.

crosscountry
2008-Jun-04, 09:43 PM
designing something and constructing it are two different things.

dcl
2008-Jun-05, 10:09 PM
My guess is that no one will be able to design a shielding system providing adequate shielding from cosmic rays from all directions however ingenious its design.

aquitaine
2008-Jun-06, 01:58 AM
something like a hyperbola would do, but it would be difficult to make one that surrounds the ship.

A hyperbola made from what materials?

Maybe it would be difficult, but not impossible. The layers themselves dont need to be very thick, so maybe (correct me if I'm wrong) something like this would reduce the total mass required.


Universe Today: Scientists Designing "Ion Shield" To Protect Astronauts From Solar Wind

How much power is required for something like this? The article doesn't say exactly....



In the long term, you may be right, but I strongly suspect that you do not recognize the immensity of the problem.

No doubt it would require some new manufacturing techniques, but given the major power issues with other ideas (like force fields, magnetic fields) or the mass issues (such as piling on lead), it is probably a better way to go until we can invent some kind of high power portable reactor of some kind.


I will admit that I'm not a physicist or astronautical engineer, so I don't have the know-how to pull something like this off, but that doesn't make it any more or less of a good or bad idea.

crosscountry
2008-Jun-06, 03:43 PM
variations on the definition of adequate may exist.

aquitaine
2008-Jun-06, 04:17 PM
I think it's safe to say adequate==safe

crosscountry
2008-Jun-06, 04:21 PM
what is your definition of safe?

Drunk Vegan
2008-Jun-06, 09:29 PM
As far as cosmic radiation is concerned, I'd say on any non-colonization mission an acceptable level of radiation is that which will cause infertility but not death or serious health problems.

crosscountry
2008-Jun-06, 10:04 PM
I think death is probably undesired. Some people might think infertility is too much to endure.


I bet we find ways to reduce the potential damage to acceptable levels in humans before we send people to Mars.

aquitaine
2008-Jun-06, 11:57 PM
I think safe means no illness, no death, and no cancer.

crosscountry
2008-Jun-07, 03:09 PM
that may be a little more difficult to reach. we'll see what NASA agrees is safe.

dcl
2008-Jun-09, 02:49 PM
Universe Today: Scientists Designing "Ion Shield" To Protect Astronauts From Solar Wind (http://www.universetoday.com/2008/01/27/scientists-design-ion-shield-to-protect-astronauts-from-solar-wind-radiation/)

Magnetic deflection is effective against a collimated beam of particles all of the same kind, speed, and direction of motion. Cosmic rays are nmot all the same. Most are hydrogen nuclei, some are helium nuclei, and so on. Particles of different masses are deflected by different amounts by magnetic fields, so a field that deflects one type of particle away from a given target might deflect particles that would have missed the target without the magnetic field might be made to hit it. But worst of all is the fact that cosmic rays come from all directions. Magnetic fields would merely determine from which directions the rays that hit you will come.

dcl
2008-Jun-09, 02:56 PM
Universe Today: Scientists Designing "Ion Shield" To Protect Astronauts From Solar Wind (http://www.universetoday.com/2008/01/27/scientists-design-ion-shield-to-protect-astronauts-from-solar-wind-radiation/)

Magnetic deflection is effective against a collimated beam of particles all of the same kind. Cosmic rays are nmot all the same. Most are hydrogen nuclei, some are helium nuclei, and so on. Particles of different masses are deflected by different amounts by magnetic fields, so a field that deflects one type of particle away from a given target might deflect particles that would have missed the target without the magnetic field might be made to hit it. But worst of all is the fact that cosmic rays come from all directions. Magnetic fields would merely determine from which directions the rays that hit you will come.

neilzero
2008-Jul-21, 12:47 PM
As far as I know, we have not tested a magnetic shield nor an electrostatic shield in space? Probably because we think we know how it will work = not good with current technology. In theory we can build a monster super conducting loop, diameter 100 kilometers, and shield the space craft as well as earth's magnetic shield protects the equator, which is far from perfect. Earth's atmosphere provides most of the protection. On the plus side the loop would behave like a linear motor with earth's magnetic field. This would provide weak propulsion in some directions, but would be a nusence in other directions. Beyond Earth's magnetosphere, it would still partially protect as a magsail.
Electostatic provides similar protection, except the ground crew and EVA = extravehicular activities would be in danger of electrocution. Dimentions on the order of 100 kilometers are also needed to be as effective as Earth's magnetic field at the Equator.
I've forgotton the details, but a sort of combination plus a very thin atmosphere of ions has been proposed which can also provide a bit of propulsion in some directions. I think this method will be tested in space soon. It has the advantage that it reduces nuetrons a bit, as well as electrically charged particals. None of these methods shied significantly from photons = ultraviolet light, X rays and gamma.
Perhaps we can go to Mar's and return with very few casualties, due to radiation, even if nothing special is done to reduce the radiation exposure. The astronaughts will however be at increased risk of developing cancer. Neil

publiusr
2008-Jul-21, 07:23 PM
This is where mass becomes your friend. Just keep making larger LVs--forget force fields--and put lead shielding on your Sea Dragon assembled Nuke-pulse by the ton.

doggone
2008-Aug-02, 09:23 PM
I understand that the Apollo astronauts were only out there about a week per mission, but did any of them show any signs of radiation damage.?? I don't remember reading anything on this.

cr1t
2008-Aug-14, 10:38 AM
You don't have to shield the entire ship. Just the part where the crew spends most of its time. Also you don't have to block everything Even a foot or two of dirt makes for good blocking of radiation.

aquitaine
2008-Aug-14, 03:02 PM
This is where mass becomes your friend. Just keep making larger LVs--forget force fields--and put lead shielding on your Sea Dragon assembled Nuke-pulse by the ton.


Mass is not your friend for other reasons. The point I was making earlier is that there must be someway of dealing with radiation that doesn't involve piling on the lead. This would allow us to build more flexible ships, spacestations and probably other stuff I haven't thought of yet.

What Max
2008-Aug-14, 05:53 PM
I think one perspective problem that has never been adequately addressed is the difference between long periods of extremely low level radiation, and a sudden dose all at once (as in a nuclear bomb). We know linear-no-threshhold is wrong. If it were right, none of us would live under prolonged exposure to sunlight - our sunburns would be chronic injuries rather than things that the body heals over time. Yet it is what we use to quantify radiation damage anyway, because it is ludicrously conservative. People who have to cover their butts from lawsuits know that if they use it as a standard, there is no possible way someone within the "safety limit" could develop a problem.

Yep. The LNT is meant for a quick approximation of the risk involved. It is not generally considered accurate or precise.

We have little information regarding radiation in outer space. Shielding on the space ship will most likely not fully protect the astronauts inside. The main dose will be a result of secondary radiation due to scattering of shield material.

doma
2008-Aug-15, 02:38 AM
I saw a recent show called The Planets which interviewed nasa scientists re research into radiation protection.

An interesting thing discussed was that the aluminum shell of a spacecrafe is very bad for radiation since incomming cosmic rays hit the aluminum atoms and cause a cascade of radioactive/high energy fragments. Hydrogen was discussed as much safer since cosmic ray strikes don't produce a cascade when hitting hydrogen nucli. Is this because the aluminum atoms are split? Or do the fragments come only from the incomming cosmic ray?

Perhaps this means we'll see something like giant gas bag around the spacecraft? Or ... a shell of liquid hydrogen?

What Max
2008-Aug-15, 03:25 PM
Doma: Yes I've heard this as well. Maybe they will use H2O.

doma
2008-Aug-16, 01:09 AM
Okay, this article (http://en.wikipedia.org/wiki/Cosmic_ray) describes the shower of other particles produced when a cosmic ray hits an atom such as oxygen, nitrogen, (aluminum, etc). Basically, the atom is split.

So, using H2O as a shield would not be good. The Oxygen atom in a water molecule could be split and release a shower of other particles. Hydrogen itself, being a single proton in the simplist isotope of H, can't be split into lessor atoms.

I wonder if a cosmic ray of sufficient power could actually trigger some of the hydrogen to fuse into higher elements/isotopes.

The article also claims that 9% of cosmic rays are He nucli. In that case I would suspect that even with a hydrogen only shield the cosmic ray (a He isotope) could itself be split into hydrogen isotopes thus producing a cosmic ray cascade even with a hydrogen only shield.

What Max
2008-Aug-18, 02:14 PM
Okay, this article (http://en.wikipedia.org/wiki/Cosmic_ray) describes the shower of other particles produced when a cosmic ray hits an atom such as oxygen, nitrogen, (aluminum, etc). Basically, the atom is split.

So, using H2O as a shield would not be good. The Oxygen atom in a water molecule could be split and release a shower of other particles. Hydrogen itself, being a single proton in the simplist isotope of H, can't be split into lessor atoms .

Nope. Protons can be split into pions etc. However, the [p + cosmic ray] interaction is unlikely to produce this effect. Oxygen is a low-atomic-mass constituent and hydrogen is abundant in water. As a result water is a good radiation shielding material. There are weight, specific temperature, and other issues involved with radiation shielding. Currently, there is no clear answer regarding what the preferred material will be.

crosscountry
2008-Aug-22, 05:57 PM
The article also claims that 9% of cosmic rays are He-nuclei. In that case I would suspect that even with a hydrogen only shield the cosmic ray (a He isotope) could itself be split into hydrogen isotopes thus producing a cosmic ray cascade even with a hydrogen only shield.

I think a layer of aluminum foil - or lead-foil would be sufficient to stop a heluim-nuclei. No worries on that front.

doma
2008-Aug-22, 09:06 PM
I think a layer of aluminum foil - or lead-foil would be sufficient to stop a heluim-nuclei. No worries on that front.

Hi. I'd agree that in everyday life on the ground alpha particles (helium nuclei) are easily stopped by aluminum foil, even tissue paper. Their energies are only 5 * 10^6 eV or so (reference (http://en.wikipedia.org/wiki/Alpha_particle)).

But in space cosmic rays come in at around 10^20 eV. At that energy level the atoms may fragment and cause cascades - a problem not see on the ground here on earth. (even our colliders can't produce particles with 10^20 eV energies)

Still, you may be right, perhaps alpha particles at 10^20 eV can be stopped by aluminum or lead foil. But I'd like to see the math or the article; it doesn't seem obvious enough that we can say 'no worries' when we're talking cosmic ray energies.

For example, on earth an alpha particle is absorbed by aluminum foil - no cascade is produced. But in space a 10^20 alpha particle contacting an aluminum atom in your shield would produce pions, gamma rays, and other debris with a count potentially numbering into the billions(reference (http://en.wikipedia.org/wiki/Cosmic_ray)). The remaining aluminum foil certainly couldn't stop the resulting gamma rays?

Here's (http://en.wikipedia.org/wiki/Image:Protonshower.jpg) a cool picture of a debris shower created when a single proton (admittedly not an alpha particle), at cosmic ray energies, hits an atom smaller than aluminum in the upper atmosphere. Much of the radiation reaches all the way through the atmosphere till it strikes the ground. (I think that's Chicago they chose to place under the air shower simulation)

-doma


disclaimer: I've only got a basic understanding of this stuff. I am eager to learn more from you more advanced guys/gals and am glad of the discussion and responses. thanks. ;)

crosscountry
2008-Aug-23, 11:18 PM
10^20eV is significantly more!