Spaceships are a peculiar thing. We've got them in all forms, sizes & colours. They are everywhere and go everywhere else. carrying with them anything from music, over tractors, to foodstuffs and frozen babies... but space is vast and empty actually filled to the brim with all sorts of fancy exotic radiation.

Assuming we have mastered the challenges of creating nigh unlimited amounts of energy in a stable manner, as well as having figured out (smart) solutions to any other hindrance:

Q: What current-day or near-future (potential) materials/technologies can be used to shield our ships from radiation other than wraping them into meter-thick layers of lead (or ice or other stuff)?

• – JDługosz Nov 4 '16 at 13:11
• – CaptClockobob Nov 4 '16 at 17:43
• Actually, to bring cosmic radiation down to Earthly levels you need 5 metres of water or rock as your shielding.....Ref Marshall Savage "The Millennial Project" amazon.com/Millennial-Project-Colonizing-Galaxy-Eight/dp/… – Thucydides Nov 4 '16 at 19:01
• Sadly, I haven't found one (my paper copy is pretty worn out as well....) – Thucydides Nov 4 '16 at 21:24
• Since you don't seem content with my answer summarizing existing research, what more detail are you looking for? – Frostfyre Nov 17 '16 at 13:35

I'll defer to NASA on this one.

With human missions to Mars looming on the horizon, research into how to protect astronauts from radiation is a major field of study. NASA is conducting research into a few potential areas; I'll give a brief overview of each.

## Hydrogen

One of the best ways to protect against high-energy particles is with a particle of a similar size. Guess what? Hydrogen is basically a particle (an atom composed of 1 proton + 1 electron). Even better, it's the most abundant element. Using water as shielding has good potential; it's also necessary for the astronauts, so they're already taking it with them. Additionally, hydrogen is a major component in some plastics, such as shopping bags and water bottles. This kind of plastic isn't structurally feasible for a spacecraft, so it would add mass and make launches harder, but there's good news on this front!

## Hydrogenated BNNTs

This is a new material being developed: hydrogenated boron nitride nanotubes. It has the potential to double as a structural component and protection against radiation. They've even figured out how to make spacesuits out of it.

## Force Fields

Yes, they're looking into this, too. We're nowhere near what we see in fiction (Star Trek, et. al.), but creating an energy-efficient magnetic field (exactly like the Earth does naturally) would be an excellent form of protection. At the moment, though, doing so is prohibitively energy- and material-intensive.

## Medication

One suggested item is also a medication that would actively alleviate the impact by radiation on the astronauts. This one is currently purely theoretical.

• I would be glad if you could provide some hard facts on Force Fields and Hydrogen. I don't really see, how a field of general magnetic radiation would counter alpha rays of nuclear radiation. I would hardly count Hydrogen as particle, as it is an Element, consisting 1 proton and 1 electron together. Astronaut supplies are part of a space mission, but drinking water is one of the most "heavy" material. Using it to absorb radiation is seriously inefficient, drinking pure H2O without vital minerals will build up health issues, and drinking contaminated water is direct exposition to radiation. -1 – Sonic Nov 17 '16 at 8:28
• @Sonic Nuclear reactors actually use H$_2$O as radiation shields, right now. They are effective against gamma radiation. A magnetic field stops an 'alpha ray' because an 'alpha ray' is a a positively charged (+2$e$) helium nucleus that will be deflected by the magnetic field. Radiation exposure in space is largely from charged particles interacting with spacecraft hulls and releasing gammas in the vicinity of human passengers. So stopping the gammas with a water shield or charged particles with a magnetic field are both effective. – kingledion Nov 17 '16 at 12:40
• @kingledion: I still see as false assumption that astronaut supply water is to be used as radiation shield. Here on Earth it may prove to be abundant, but up there it is not, weighs relatively heavy at volume/weight ratio, and to fulfill astronaut proper intake, it must consist minerals. If containing minerals, it is not H2O exclusive. I do not deny that H2O can absorb radiation, but it is seriously misleading to mention radiation shielding water as 'also necessary for astronauts', because it causes direct radiation poisoning. – Sonic Nov 17 '16 at 12:54
• @Sonic I take it you didn't read the linked article? I was just summarizing what NASA said there. – Frostfyre Nov 17 '16 at 13:05
• @Sonic The water shield will not be the normal or 'first-line' defense against radiation. That is the job of the hull; the Apollo astronauts made it to the moon (outside of earth's magnetosphere) with hull of a few inches of aluminum and steel, at most. It is not intended for the drinking water to get irrradiated during regular operation. It exists so that in case of unusual solar activity, the spacecraft can rotate the water shield between the radiation source and the astronauts. It is better to get a low radiation dose in your drinking water than direct acute radiation poisoning. – kingledion Nov 17 '16 at 13:31

Here are some articles discussing the idea of a portable magnetic shield. A pro one and a sorta con one. Using ice or water as a physical shield shouldn't be casually dismissed though, it is likely that the ship and crew NEED lots of water, might as well multi-task large tanks of water if you have to bring it with you anyway!

Another option would be a solar shield/bunker just to block solar flare radiation. This would rely on mass, but would be less massive than wrapping your entire ship in it. The crew/electronics areas would be protected, but just from one direction (or a very confined area). This would require an early warning system for flares and either the ability to maneuver the ship to put the shield in between the ship and the flare or for the ship to operate normally while all the crew huddle in the bunker. This wouldn't help with background cosmic radiation, but perhaps there is a biological solution for that, making human DNA robust enough to resist persistent low levels of gamma rays (probably not a good idea for children or fertile women though).

But if you have a super energy source, then you presumably have access to all sorts of other high tech things. The mag shield is more feasible with tons of power, and travel times would be short enough that cosmic ray exposure could be minimal and solar flares wouldn't be a guaranteed thing every trip. In this case, something like a plasma shield could help. It would lower exposure to cosmic radiation without the need for a strong magnetic field and perhaps in the event of a solar flare, the shield could be "dialed to 11" for a short period of time.

Heck, perhaps the crew spends the entire flight secure in small shielded coffins, living in VR with anthropomorphic drones for when they need to do physical work. This is rather dull for fiction, but probably quite feasible for real world work in an extremely hazardous environment. Bulk cargo carriers and the like would probably be completely automated, so humans would just be around for travel, search and repair missions (for when one of those drone haulers breaks down), and exploration. We are pretty close to being able to do fine detail work with drones so it shouldn't be much of a stretch for an entire space mission to be completed with the crew in VR the entire time.

• "with tons of power, and travel times" for some reason I initially read this as "with tons of power, time travels... " I don't know, you may be right either way :) – Adrian Colomitchi Nov 20 '16 at 14:35

I'll bring out a little idea that's been considered for lunar colonization; while it might work better for a station than a ship, it's still worth considering, I say.

# Water

Turns out, water is a pretty darn good insulator from radiation! They use the same stuff to store old nuclear fission rods, when they go bad. And this useful trait has been considered for a lunar colony. Imagine an inner "safe room", surrounded by water to keep out harmful solar radiation during solar flares. That's basically the idea.

Now don't take this as me saying your spaceships should be water-ships. Far from it, ya don't have to go that far. But consider this: during those longer treks, close to large gas giants and during heavy solar flares, your crew will need a little more protection from radiation.
So a yellow alert sounds, and all staff are sent to the rad-bunkers: special rooms on the ship surrounded by a tank of water, with enough supplies and tools to wait out any high-radiation zones. Then, when the danger is passed, the crew exit, and return to their posts!

Just an idea, but one with some basis in reality. And who knows? It might come in handy!

• Thucydides’s comment on the OP (from Nov 7) quantifies this and gives a link. You ought to follow op on that and give details beyond just “water is goid for that”. I have to note that the comments (which were not considered worthy of a full answer post) contain more information than this Answer. Having a small better-shielded area is general to any shilding approach. – JDługosz Nov 17 '16 at 18:43
• You also need to credit the image source. Why not just link to the page where the image came from, as a reference, anyway? – JDługosz Nov 17 '16 at 18:48
• You have to carry tanks of water anyway, might as well use them to shield the crew. – ventsyv Nov 17 '16 at 20:15
• Image is from XKCD. And sorry, didn't see the bit where we had to provide sources. I believe I first found the theory in a documentary on National Geographic, if that helps. :( – Atlas the Worldbuilder Nov 17 '16 at 21:54
• You beat me to it. The same water that can be used upon arrival at the destination, could be used to block radiation. – Mikey Nov 17 '16 at 22:33

## Major Caveats

Let’s start this discussion by saying that although crazy things are possible we aren’t trying to build for every crazy thing.

For example, the Oh-My-God particle describes a cosmically-sourced particle moving so fast that it hits with the force of a baseball. Despite the enormous power and theoretical possibility of being hit by a barrage of the things, they are so rare that we aren’t going to consider them.

Space dust is another example. The faster you go, the more space dust starts to feel like bullets. I’m leaving it to you to deal with shielding against that sort of debris… we’re only talking about radiation here.

Ultraviolet radiation - the 10-125nm area - ionizes air molecules and is biologically hazardous. On Earth we are generally shielded by our atmosphere, but in space that is not the case.

Fortunately UV radiation is blocked or reflected by any material likely to enshroud your spacecraft. Quoting Wikipedia, “standard summer fabrics have UPF of approximately 6, which means that 20% of UV will pass through”. In contrast, Earth’s atmosphere blocks about 98-99% of UV radiation. The logical extension here is that if your spaceship’s hull were comprised entirely of t-shirts, with just 3 layers you would block more UV than Earth’s atmosphere (99.2% vs 98%), and at 5 layers you could block 99.968%.

To be safe I would probably move up from t-shirts to sweaters… or, you know, pretty much any metal of non-trivial thickness.

Alpha particles consist of two protons and two neutrons. They are charged and so interact with matter strongly, which is both a good and bad thing. On the bad side it means that standing next to an alpha particle emitter can be very hazardous, however on the good side the fact that they do react with matter so readily means they are also blocked very readily.

The standard statement on Alpha radiation is that, in general, a standard piece of paper is sufficient to shield you. So unless you plan on making your spaceship out of ultra-thin paper, I think you are OK on this one.

Beta radiation is basically an energetic electron. Being smaller it can be more penetrating than alpha radiation, and is also capable of causing bodily harm. However, any non-trivial amount of metal shielding (eg. 1-2mm of aluminum) will stop this radiation from penetrating.

Gamma Radiation - How Much Weight Do You Wanna Bring?

Photons less than 3x10^-11 meters. Bad ju-ju.

The trick with gamma radiation is that the type of shielding is almost (but not quite) irrelevant. What matters most is the mass of material that gamma rays pass through, not the makeup of that mass. For example, a lead shield only provides a 20-30% improvement over a lighter metal like aluminum or something like soil on a per-kg basis. Obviously though, lead (or, better, tungsten) is more compact, which may have advantages in terms of ship construction.

To identify how much shielding you need, you’ll need to consult the Half Value Layer index for your target material. This index identifies how thick the layer of material needs to be to reduce the gamma radiation allowed through by half. The HVL for a few materials for gamma radiation from Cobolt-60 are: - Concrete: 60.5mm - Steel: 21.6mm - Lead: 12.5mm - Tungsten: 7.9mm - Uranium: 6.9mm

Next you need to identify what amount of gamma radiation is normal for your environment and what you consider “safe”. To tell the truth I could not find a good number for the amount of normal background radiation in space, nor even good peak estimates. On the safety side though, we do know that when we are talking about short-term exposure anything less than 15rem is basically undetectable and that, discussing long-term exposure norms, the average American receives ~0.62rem.

Not knowing the background radiation amount is a problem, but I have a solution: we cheat. I’m going to make the not-so-wild assumption that a 1.2 megaton nuclear blast releases more gamma radiation at 2km (500 rem / 5sv) than you are going to get from peak background radiation in space. Though I could not find any hard numbers about what background levels are in space, this assumption seems to hold with what I found. So let’s just find out what it would take to protect one against that level of radiation all the time.

To reduce 500rem to <0.62rem, you should plan on 10 HVL’s (takes it down to 0.49rem). More is better though. That would mean shield thicknesses of: - Concrete: 605mm (23.8”) - Steel: 216mm (8.5”) - Lead: 125mm (4.9”) - Tungsten: 79mm (3.1”) - Uranium: 69mm (2.7”)

Personally though, I’d add another layer to be safe.

As a reminder, the key here is MASS. You can use water and only take a 20% performance hit on a per-mass basis, but 1 cubic centimeter of Tungsten weighs a LOT more than 1 cubic centimeter of water. You can choose other materials like water, but you the thickness required will increase sharply when using non-metals or even lighter metals.

This is really a duplicate to Gamma radiation. Effectively, if you elect to block Gamma radiation with a dense metal, it’s going to deal with X-ray radiation as well.

In short, using Concrete as the example, a 1GVp X-ray has the same HVL requirements as gamma radiation from Cobalt-60 decay (44.45mm). Lead, however, goes down from 12.5mm with Gamma radiation to 7.9mm with X-rays.

Here’s where things get interesting.

To protect against Gamma radiation and maintain ship slimness you want a heavy metal shield… but that’s totally inappropriate for a Neutron shield. Heavy nuclei have a very hard time slowing down a neutron, let alone absorb a fast neutron.

At the same time, having no charge they ionize matter only indirectly and have great penetrating power.

Your best bet for Neutron radiation is to use a high concentration of light elements, like hydrogen, which can absorb neutrons quite effectively. Water with Boric Acid is ideal, though probably not useful in constructing a long-term vessel.

To make a long story short here, see the link below from the Space SE, which recommends 1m of water be used for shielding when in Earth’s orbit. It’s either 1m of water or a lot more of something else, when discussing long-term travel.

## Shielding So Far

So far we have identified that to shield the ship you need:

• Alpha Radiation: Literally anything of any thickness
• Beta Radiation: Any non-trivial amount of metal is ideal
• Neutron Radiation: 1m of water

With that summary being stated though, you don’t need both 125mm of lead AND 1m of water; in reality the answer could be a compromise between the two (as long as you compromised on the amount of lead and not on the amount of water).

For the sake of safety factors though, let’s say that you keep both. Presuming that you don’t want the water outside the hull and that you don’t want it uncontained INSIDE your hull either, you could happily get away with an 80mm outside hull of lead, a cavity for 1m of water, and a 45mm internal containment wall.

If you have other material lining your ship (and I presume you would, on average) then you can shave off some additional size that way or leave the measurements as-is and enjoy some additional safety margins.

This section covers visible light, infrared, microwaves, radio waves, VLF and ELF. In general, this is all radiation on the electromagnetic spectrum which your shielding as currently described could handle with ease. Visible light isn’t going to be a substantial problem, and otherwise the ship is going to act like a faraday cage.

One challenge you may have is heat acquisition due to infrared (and the other frequencies to a lesser degree). Object cooling in space can be quite difficult, but how that can be dealt with is really another topic… though one I would suggest looking into.

Planets are shielded from the deadly solar wind (an array of charged particles) through their magnetic fields. I would suggest the same for a spaceship. Basically, you would want to turn your spaceship into a giant electromagnet.

# How it would be done?

This magnetic ability of the spaceship would have to be integrated into its design from the basic level. When you start building the outer shell of the spaceship, you would make it two-layered. The outer layer would be what spaceship shells are usually made of (some alloy of aluminum or titanium), and the inner layer would be Alnico wrapped in insulated electric wire.

When the spaceship is in space, you would turn on the electricity to the coil, turning the alnico layer into a powerful electromagnet. You would want to orient the polarity of your spaceship magnet so that it is the same as the polarity of the solar wind, hence deflecting it away from your spaceship. This can be easily done by simply reversing the polarity of the electric current flowing through alnico's wiring.

• Is alnico “magnetic” in the manner desirable for electromagnets? What is the polarity of the solar wind? I would have thought that it’s neutral in bulk, not blowing electrons and protons out in different streams. – JDługosz Nov 17 '16 at 23:35
• And what does polarity have to do with it? You’re not repelling charged particles; you are deflecting them, and positive and negative charges will be deflected in opposite directions. – JDługosz Nov 17 '16 at 23:36
• IAC, Frostfyre’s answer already states that this is “prohibitively energy- and material-intensive.” You are repeating an existing point without addressing the issues. And look at the very first sentence of Jason’s answer: he gives links to details even though this is not the focus of his own answer. – JDługosz Nov 17 '16 at 23:39

I'd recommend Equipment.

You're going to need lots of big, heavy, reliable equipment on your spaceship. Things like:

• Power sources (probably VERY large - lots of metal and water)
• Pumps and Fans (for heat transfer)
• Refrigeration units (for frozen babies)
• Atmosphere control (for breathing...)
• Spare parts
• Stores (especially water)
• Fuel
• Engines
• Severs and other electronics

So one could imagine a space ship where the people largely live and work in the center of the vessel, and lots of infrequently visited equipment and stores are spread around the exterior.

This equipment is going to be largely unaffected by the high energy particles that are the most dangerous portion of cosmic radiation. A few inches of steel will lower the ionizing radiation level by an order of magnitude.

When personnel need to do maintenance or otherwise interact with this "shielding equipment" they might bring temporary shielding, carefully track their time, and take other preventive measures.

This actually works better with larger spaceships; surface area grows more slowly than volume as you scale up - so the fraction of your equipment that needs to be "infrequently visited" can be smaller.

This is known and used widely in the nuclear industry - portions of the plant immediately adjacent to the reactor are designed to be visited less often, and the further away you get the more all the equipment has soaked up the zoomies.

If we assume that we are so advanced that we can create nigh unlimited amounts of energy, I think you could also assume that we mastered building objects at the molecular level. It doesn't seem crazy to think that we could manufacture some hi tech sandwich polymer of highly radiation resistant material being

1) worn by astronauts all the time

2) used in the hull of the space ship

Passive solutions (things that are "always there") seem to always be better than active solutions (energy shield that needs to be activated)