Radiation and Space Travel

[rreppy]

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]

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).

And then there are the more exotic ideas involving electrostatic fields ((Linky). 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]

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]

logic.exe, why would assembling a ship in orbit help keep out radiation?

[dcl]

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]

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]

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]

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]

no one goes to Mars for a two week stay.

[logic.exe]

Oh man, why do you have to be such a downer dcl?

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.

[Kebsis]

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]

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]

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]

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]

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]

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]

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]

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 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]

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]

How about using carbon based aerogel for radiation insulation?

[dcl]

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]

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 :

[QUOTE] and at the end [/QUOTE]
or
[QUOTE=username] and [/QUOTE]

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]

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]

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]

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]

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]

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]

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]

cant we deflect radiation with a strong magnetic field....like the earth does??

[01101001]

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

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.