Limits Of Radiation Shielding

[Spacescifi]

 

I read somewhere online that water is effected by space radiation, and over time will turn acidic or something and cease to offer the protection it once did. That's assuming if it was just water bags with little to no shielding between the bags and the outer hull.

 

As for hydrogen rich plastics abd everything else.... I am not sure.

 

But I have a suspicion that spaceships in real life, unlike those depicted in fiction, will have expiration/planet space dock repair dates based on radiation hull protection.

Likewise any space station would likely need it's hull replaced over time too for the same reasons.

Unless one is expected to simply brave cancer rays like astronauts already do.

 

What do you think? Serious replies only.

 

Edited October 21, 2019 by Spacescifi

[kerbiloid]

That's where idea of armored space battleships makes sense. We need steel armor to protect the water cans from the space radiation. Because why drink it and then recycle by electrolysis.
How much water does a crew need if it's recyclable? Just keep it in _{squared plastic} barrels in a closet next to the room.

40 minutes ago, Spacescifi said:

Likewise any space station would likely need it's hull replaced over time too for the same reasons.

Which means a total replacement of the station and can be much easily provided by a modular construction. Then you scrap the module and replace it with a new one with no "hull" replacement.
(Btw what is the "hull" when it's a several millimeter thin envelope around the trusses?)

40 minutes ago, Spacescifi said:

Unless one is expected to simply brave cancer rays like astronauts already do.

Unless somebody makes thin-skinned pressurized tin can modules, surround them with other equipment and put outer non-pressurized panels/cover around all this.
Btw, if you want an armored space battleship, its armor also should not be a pressurized hull, but separate plates.

40 minutes ago, Spacescifi said:

Serious replies only.

No, seriously.

Edited October 21, 2019 by kerbiloid

[Spacescifi]

23 minutes ago, kerbiloid said:

That's where idea of armored space battleships makes sense. We need steel armor to protect the water cans from the space radiation. Because why drink it and then recycle by electrolysis.
How much water does a crew need if it's recyclable? Just keep it in _{squared plastic} barrels in a closet next to the room.

Which means a total replacement of the station and can be much easily provided by a modular construction. Then you scrap the module and replace it with a new one with no "hull" replacement.
(Btw what is the "hull" when it's a several millimeter thin envelope around the trusses?)

Unless somebody makes thin-skinned pressurized tin can modules, surround them with other equipment and put outer non-pressurized panels/cover around all this.
Btw, if you want an armored space battleship, its armor also should not be a pressurized hull, but separate plates.

No, seriously.

 

In my scifi I do not really need a space battleship.

I am far more interested in space freighters that have the option of shipping passengers too.

Coincidentally, the difference between a space freighter and a space battleship can be quite slim anyway depending on what it's payload is.

[Guest]

11 hours ago, Spacescifi said:

Coincidentally, the difference between a space freighter and a space battleship can be quite slim anyway depending on what it's payload is.

The main difference between a space battleship and a space freighter is hull armor. A freighter can double as a drone carrier or a missile boat, but is going to have much less protection, and what it would have would be geared towards MMOD and radiation damage. A viable warships, but it would fare badly in an encounter with a battleship.

Radiation shielding is an important problem, but it's not as hard as you may think. Water isn't really all that good, its dense, so it works for gammas, but its real advantage is high neutron absorption. If you want that, you want a coating of lithium-6 instead, which is lighter. Yes, it will need replacement (since hitting Li-6 with a neutron makes tritium, which escapes), but it will wear down rather slowly. For protection against gammas, your best hope is to make a thick tungsten or lead plate. It's heavy, but it will work better than water. So lithium-6 on top of a tungsten plate. You don't even need that much of it, if you're not trying to reduce a point-blank nuke explosion to background.

And no, equipment modules would make for extremely poor shielding. They tend to be fairly non-dense, highly variable in their composition, not to mention you don't need that much equipment these days, what with electronics getting smaller.

[DDE]

13 hours ago, Spacescifi said:

I read somewhere online that water is effected by space radiation, and over time will turn acidic

Ionizing radiation creates various reactive oxygen species of water, which can cause considerable damage when ingested - or when they're already inside human cells.

13 hours ago, Spacescifi said:

and cease to offer the protection it once did

Neutrons care not for your chemical bonds.

[KSK]

That information as written mostly sounds like a load of nonsense to me. Would need a link to the original source to tell me otherwise.

I would expect water to ionise when hit by well... ionising radiation. Since it will split into hydrogen ions, hydroxyl ions and/or oxygen ions then, in a sense, it does get more acidic since acidity is a measure of hydrogen ion concentration.

However, I wouldn’t expect that to be a big effect. And I definitely wouldn’t expect it to degrade the performance of that water as a radiation shield. Radiation shielding is a nuclear effect with different masses of nuclei interacting with different radiations in different ways. Ionised water still contains the same number of nuclei as neutral water molecules, so I don’t see where any reduction in radiation shielding is going to come from.

Hydrogen rich plastics will probably break down over time when exposed to ionising radiation. Keep them in suitable packaging (to contain your eventual plastic powder) and they’ll retain most of their shielding efficacy. If they release hydrogen as they degrade (unsure how likely this is) then I would expect them to lose some of their effectiveness over time.

Edited October 21, 2019 by KSK

[Laie]

20 hours ago, Spacescifi said:

But I have a suspicion that spaceships in real life, unlike those depicted in fiction, will have expiration/planet space dock repair dates based on radiation hull protection.

If ionising radiation was the only problem, plastics would be good for decades, and sheet metal ought to last a few millenia. For all practical purposes, it's of no concern.

Boring, I know.

 

[kerbiloid]

11 hours ago, Dragon01 said:

So lithium-6 on top of a tungsten plate.

A giant spaceship covered with tungsten armor with lithium-6... A really good engineering way, indeed.
Buy one and get a tonne of platinum for free. Buy two, and we'll name our shipyard after you.

Any enough thick metal construction will happily protect the habitat together with its puny water tank from gammas without increasing the mass and spending a pyramid of expensive tungsten.
Just don't put the habitat on surface, surround it with other modules.

The lithium-6 cover is obviously better than dull boron they use for ages for neutron protection, if cheap polymers are not enough good.
Why don't they use it for reactors?.. Fools. Or have not enough Li-ion batteries to mine Li-6.
(And yes, space neutrons are very important part to take care about, compared to galactic gammas and solar charged particles.)

Btw, why just tungsten? I insist, it would be thorium, it's denser.

Edited October 22, 2019 by kerbiloid

[Guest]

On 10/21/2019 at 9:49 AM, Spacescifi said:

But I have a suspicion that spaceships in real life, unlike those depicted in fiction, will have expiration/planet space dock repair dates based on radiation hull protection.

I should remind you that everything has an expiration date in real life. Planes need regular maintenance, cars need to be taken to a mechanic for regular check-ups, and even a computer needs to be dusted once in a while. Spaceships will need regular recertifications (and perhaps restoration) of their radiation shielding, but this will be handled together with checking reactor pumps, replacing airlock hatches (only rated for a specific number of cycles), certifying rocket nozzles... Radiation protection will not be the limiting factor here, spaceships have many other systems that will need maintenance first. If nuclear powered, you can also expect refuelling the reactor to be a big job.

5 hours ago, kerbiloid said:

A giant spaceship covered with tungsten armor with lithium-6... A really good engineering way, indeed.

Yes, it is indeed good engineering. Boron works, too, but Lithium-6 also works, and is lighter. It is better engineering than anything you had proposed.

No, surrounding it with other modules will not work. Because guess what, they either don't need to be pressurized, and therefore don't need a thick hull at all (only the crew needs to be armored), or they need, and they need to be, and then they most likely need to be rad-shielded, too. As I already explained, mission modules aren't good at shielding from radiation at all. 

Lead, tungsten, osmium and thorium-232 would all work, but tungsten is the most structurally sound of them all (osmium is no slouch, either, but it's more expensive). A good hull design is a carbon composite Whipple plate, with small spacing, Li-6 filler (to absorb neutrons and the shattered MMOD fragments) and a tungsten backplate for structural integrity. This protects you from radiation, heat and most impacts. 

TL;DR: You're wrong, just take your trolling elsewhere, like onto that bridge you bought recently.  

Edited October 22, 2019 by Guest

[kerbiloid]

54 minutes ago, Dragon01 said:

Boron works, too,

Without "too". Boron just works, and does it everywhere in nuclear plants. Its capture cross-section is several times greater than the lithium's.
Show me an example of a real nuclear plant with lithium protection instead of boron.

And very strange (actually, not) that you haven't mentioned high-molecular polymers with boron atoms which are probably the most perspective rad-protection in foreseable future, not exotic lithium-tungsten armored fighters.

54 minutes ago, Dragon01 said:

No, surrounding it with other modules will not work. Because guess what, they either don't need to be pressurized, and therefore don't need a thick hull at all (only the crew needs to be armored), or they need, and they need to be, and then they most likely need to be rad-shielded, too.

Their ability to absorb gamma-rays has nothing common with pressurization. Only total mass per surface are makes sense (as they are anyway made of same materials).
So, you can surround the core habitat (command center, dormitory, diner, restrooms, medlab) with less necessary rooms (gyms, storehouses, electric stands, etc) as a radiation shelter, surround the whole habitat with rarely visited and non-pressurized modules, then raise thermal insulation screens on top.

You lithium protection will degrade with poor abilities of quick repair, and no sane engineer will do this in real life.
Also the lithium layer will bombard the inner parts of the ship with secondary alpha and gamma when 6Li turns into an alpha-particle and a tritium core.
(Surprise-surprise, that's why they use it in fusion nukes)
Then you have your ship polluted with radioactive tritium and kill the crew.

While a polymer insulation screen (which is also a primary rad-protector and an anti-meteorite screen) will be easily replaced on demand.

54 minutes ago, Dragon01 said:

As I already explained, mission modules aren't good at shielding from radiation at all. 

I'm afraid, you didn't "explained", but just "guessed", and guessed wrong.

54 minutes ago, Dragon01 said:

Lead, tungsten, osmium and thorium-232 would all work, but tungsten is the most structurally sound of them all (osmium is no slouch, either, but it's more expensive).

Any enough "heavy" material would work, including steel. Just needs a twice thicker layer.
And, guess what? We already have a lot of metal in various metal structures surrounding the properly designed habitat.

Let me provide you with some numbers. 27 g/cm² is presumed to be enough to protect a Martian ship crew for 3 years with total dose which won't get them sick. (It is definitely not "safe").
It is ~4 cm of steel or ~10 cm of aluminium.

A typical ISS module is ~15 t heavy and, say, ~4x8 m in cross-section (estimation, as they have different shapes).
I.e. it provides ~40 g/cm². Just put it parallel to the habitat, put batteries outside (that's your lead or lithium, as you wish), put high-molecular-polymer/foil/boron sandwich on top, that's all.
A bonus idea: attach TEI fuel tanks around the habitat, they will protect the crew totally most part of the Martian flight.
Which "tungsten", which "lithium", what is it about at all?

54 minutes ago, Dragon01 said:

You're wrong, just take your trolling elsewhere,

I don't troll you, just you are thinking out various nonsense far from real life engineering, and harshly react on the opponents' argumentation.

Edited October 22, 2019 by kerbiloid

[farmerben]

In space you don't need shielding against any neutrons other than the ones produced aboard the spacecraft itself.  The neutron is unstable, it does not travel great distances before beta decay.  

For shielding we want high scattering and low absorption.  Scattering means dissipating the radiation energy as heat within a volume of the shield.  Absorbtion means transmuting an atom into another isotope, typically leading to secondary radioactive decays. 

In our solar system the radiation we are concerned about are protons, electrons, and alpha particles coming from our sun (and gammas).  The same radiation is particularly concentrated in some planetary magnetic fields.  There is little we can do about high energy cosmic rays.  And no neutrons worth worrying about.  

Lithium, Beryllium, and Boron can absorb low energy protons so we do not want them as shielding (unless they are inside the fuel tank).  Nearly all the elements above that plateau out and will not absorb a proton or an alpha particle less than 25 MeV. 

Scattering of mostly a function of density and also conductivity.  However dumping all the energy fast into a conductor lets off harder X-rays than the more gradual braking in materials like water and plastic.  Where dense elements are good at stopping gamma rays, light elements buffer them down with scattering of weaker and weaker photons.  Carbon and hydrogen are better for this than most other materials.  

Gamma rays do ultimately wear down metal components.  Steel bolts become weaker, etc.  This is largely due to >5 MeV gamma rays creating positron-electron pairs.  It might be better to think of this as more of a continuous maintenance problem than a shielding problem.

[kerbiloid]

10 minutes ago, farmerben said:

Gamma rays do ultimately wear down metal components.  Steel bolts become weaker, etc.

Obviously. But as we can see, orbital station modules of Mir/ISS are still intact after 20+ years (and magnetosphere doesn't weaken the gamma rays).
So, we can presume exactly a periodic maintenance problem, which any ship will face anyway.