Ice as radiation shield

[jhoblik]

Do you know if ice has same or different shielding characteristic as water?

 

[CalliArcale]

You mean water ice, right? Well, two main things come to mind for me:<br /><br />* H2O is one of those rare chemicals that actually takes up more space as a solid than as a liquid, due to its hexagonal crystal shape (which is what makes snowflakes six-sided); it would be more efficient space-wise if you could keep it liquid. It might also make better shielding when its liquid and therefore denser.<br /><br />* Water might be more useful if it were liquid; if you keep it in tanks, you can actually make use of the water, drawing some off to use it, and then pumping cleaned wastewater back in.<br /><br />You will also have to deal with freezing/thawing issues regardless of which phase you prefer to use, which could present structural problems at some point (as anybody knows who has put a full bottle of juice in the freezer to cool and then forgotten about it). <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[spacelifejunkie]

There is a lot of fuss about shielding in space and water is a wonderfully simple solution. The weight makes it positively impracticle, however. What would it take, about 1 meter thickness to adequately protect our DNA in orbit? Long trips to and from Mars? On the moon? A 1 meter shell around a space station the size of a Bigelow inflatable would be about 325 m^3 and at 1000 kg/m^3 makes about 325,000 kg of shielding! Give or take on the cylindrical dimensions. If SpaceX delivers on its promise of an HLV in coming years, at $1000/kg the shielding on a small space station would cost $325 million dollars. That does not include the cost of the engineering required to pump that much fluid into its proper places successfully. As far as I know, nothing like this has ever been done in space. A large (hundreds of meters in diameter), spinning station's water shielding would be astronomical, if not impossible to supply. It might be cheaper to send it from the astroid belt by then. Not to mention the extra amount of rocket fuel the stations will need to move the thing and adjust it's orbit. If it were a transport ship, the water shielding would make interplanetary travel impossible. <br /><br />SLJ

 

[JonClarke]

Currently a shield of about 50g/cm2 mass is supposed to to be adequate for deep space or lunar surface applications during solar storms, 20 g/cm2 for Mars surface. By the time you have subtracted thermal and acoustic insulation, tank walls pressure hulls and other equipment you need about water tanks about 15 cm deep. These can be readily fitted in the space between the inner and outer hull. Propellant tanks containing fuels such as hydrazine would work even better.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[scottb50]

If you look at the other side of the situatio it will take a lot of water to support humans in Space. I think the minimum density quantity would probably be much lower than the amount actually needed. <div class="Discussion_UserSignature"> </div>

 

[shyningnight]

I think that the most reasonable solution, given the weight of water relative to better sheilding materials would be;<br />"If you're going to use water anyway, place your tanks to make them provide extra shielding"<br /><br />If you can put your few hundred gallons of water AND some lead (or whatever) shielding between a solar flare and your crew, it's not going to hurt anything!<br /><br />Paul F.<br /><br />

 

[nacnud]

No need for lead, polythene is more mass efficient.<br /><br />

 

[CalliArcale]

Lead's actually a bad idea anyway; lead atoms are pretty heavy, so if it gets hit by particle radiation (as opposed to just gamma rays), you've got big lead atoms zinging around the spacecraft. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[spacester]

(General comment)<br /><br />When I tried to research radiation shielding on the web 4 years ago, it was hard to find much. I did some basic googling last night and wow, there's lots of good info out there.<br /><br />Google is your friend, folks, the info is out there . . . <br /><br />Having said that, I did not find anything about the difference between water and ice as a shield, which I think is a very good question.<br /><br />Note that the two most mass-efficient materials known are polyethylene and water. In all my space research, I do not know of a result that is simpler and more obviously leads to an Engineering solution.<br /><br />Having said that, there is definitely some engineering to be done in terms of tailoring the material properties of your plastic, as it will be surely serving other functions than as a shield. <br /><br />UHMWPE (Ultra High Molecular Weight PolyEthylene) is a very very common and rather cheap engineering material (e.g. plastic cutting boards for the kitchen) but from a radiation shield standpoint, the ideal would be VMWPE (Variable Molecular Weight PE - dang it's fun making up acronyms). If the first material contacted is high density, you get excellent splitting of the particles, but then the ideal would be to have a low density section, followed by another high density layer.<br /><br />Having said that <img src="/images/icons/smile.gif" /> it does not seem to me to be worth the trouble to develop VMWPE as the gains per pound would be low. <div class="Discussion_UserSignature"> </div>

 

[mlorrey]

actually, its amazing what people are now putting up on the web. there are searches I've done recently that are repeats of ones I did less than a year ago, on google, and the depth is just getting fantastic on so many things. <br /><br />As for radiation:<br />lead shielding not only puts heavy atoms zinging around your capsule, but dangerous velocity neutron radiation as well. When radiation strikes the polyethylene, it absorbs the energy better.<br /><br />Surrounding your capsule in any fuel: LH2, H20, LOX, etc is always a good idea. This is one idea that interstellar probe ideas like Daedelus are unrealistic: the best place to put your probes instruments, guidance, comm, and any payload, when travelling at a few percent or more of c, is inside a big fat hydrogen tank.

 

[mlorrey]

<blockquote><font class="small">In reply to:</font><hr /><p>H2O is one of those rare chemicals that actually takes up more space as a solid than as a liquid, due to its hexagonal crystal shape (which is what makes snowflakes six-sided); it would be more efficient space-wise if you could keep it liquid. It might also make better shielding when its liquid and therefore denser. <p><hr /></p></p></blockquote><br /><br />Actually, not quite. Water reaches its highest density at about 4 C. Below that the density drops until it transitions to ice with a rather sudden change in density between liquid and solid water at 0 degrees:<br />http://www.simetric.co.uk/si_water.htm<br /><br />It should also be noted that this particular behavior is ONLY applicable at Earth standard pressure (1 atm). See the following for lots of stuff on very odd phases of water at various pressures and temperatures:<br />http://www.lsbu.ac.uk/water/phase.html<br /><br />

 

[JonClarke]

A commonly quoted figures for human missions is about 25L per day per person. This is actually quite a lot, and you could probably get away with about half that, iof you had to. <br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>