For long-distance manned missions, such as a mission to Mars, we are inevitably going to have to shield astronauts from cosmic radiation, especially in the event of a solar flare or SEP. What materials provide the best protection from the kinds of high-energy cosmic radiation astronauts would be exposed to on these journeys?

  • $\begingroup$ From my understanding Mars has no iron core and thus no magnetic shield so getting there would be just part of the problem.. Sustain habitation seems to be impossible. $\endgroup$
    – user17324
    Oct 18, 2016 at 18:33
  • $\begingroup$ @Rick Shielding from radiation is not an unsolvable problem. Maybe you're thinking about terraforming? If so, there are potential solutions there as well, but certainly beyond our current capabilities. $\endgroup$
    – called2voyage
    Oct 18, 2016 at 18:38

5 Answers 5


There's a pretty good Wikipedia page about it, which lists a couple of options:

  • Water makes for fairly good radiation shielding (also discussed with land based radiation here), but is relatively heavy and is consumed during flight.
  • Liquid hydrogen is also good, and is used as fuel, so it will already be on board. However, this too is consumed during flight.
  • We could change the materials that spacecraft are made out of. Since hydrogen rich materials work well to shield the most common types of cosmic radiation, some plastics could work. However, this would require some reengineering to be practical.
  • Like JKor said, human waste works well, but has "grossness" problems. However, this is unique in that it increases instead of decreases as flight goes on, so it could supplement liquid hydrogen and water.

One of the largest problems with bringing up extra shielding is that it tends to be heavy, and more weight == more cost.

The Wikipedia page mentions active magnetic shielding, but that is at this point mostly a theoretical idea.

Shielding is important for unmanned missions as well (though not as much), as radiation can have effects on computer systems by interfering with magnetic storage - see this National Geographic article and this NASA press release for an instance of such an event happening on Voyager 2.


With respect to potential travel in our own solar system there are two general types of radiation that have our concern!

The first type of radiation is solar radiation, which mostly consists of low- to intermediate-energy protons, electrons and x-rays from our own star. We would shield against the protons with low molecular mass materials. Typically hydrogen-bearing materials such as Lithium-Hydride are used for this because of how effective they are at stopping the protons as well as neutrons that might come from future reactors and because of how light they are. The electrons and photons (x-rays) are best stopped with high-Z materials. High-Z materials are comprised of elements that have many electrons per atom. While high-Z materials are used to stop electrons and photons, they are also useful in stopping other charged particles to include assisting with protons.

The second type of radiation is Galactic Cosmic Rays (GCRs). GCRs are typically very high energy massive particles such as carbon, and iron atoms. Due to their energetic nature and how massive these particles are, they are very hard to stop. Stopping GCRs requires thick layers of high-Z materials, which are typically dense and heavy. Heavy shielding is expensive and difficult to get into space. I will not go so far as to say that we cannot shield against GCRs, but I will say that the weight of contemporary shielding materials makes it seem as if current approaches to GCR shielding are not practical.

Our star is a type-G main sequence star, which produces Helium through proton-proton fusion at its core. Because of the dynamics of fusion in our star, ionized Helium nuclides are the primary product of this fusion. However, some of the Helium produced from proton-proton fusion is itself fused, which produces carbon. As stars become more massive they start fusing heavier elements, which can be ejected into space. Iron-56 is the heaviest element that can be produced from traditional stars, with the heaviest elements being produced by much more energetic events such as a supernova.

The energy produced from the fusion of these isotopes ionizes gases near the edge of our star, producing copious quantities of protons and electrons, which are flung into space during coronal mass ejections. Numerically speaking the majority of radiation from our star as well as other stars are in the form of protons, electrons and photons, with lesser quantities of heavy nuclides. Statistically speaking, the heavier the nuclides, the rarer it is to find them streaming in space. While I am mainly speaking about our star, the same is true of other stars, regardless of their mass.

Other stars do indeed produce protons, electrons and photons that stream into our solar sphere of influence; however, these other stars eject radiation in all directions, with only a very small fraction of them being ejected in the narrow cone angle to make it to our solar system. Much of the charged radiation from other stars is also deflected by the sun's magnetic field. As a result, the vast majority of protons and electrons in our solar system were ejected from our star and not other stars and the ones that are not are mostly of the same energy as the protons and electrons ejected from our own star. Because of this we essentially neglect non-solar protons and electrons from our radiation exposure calculations because they are negligible in their effect on absorbed dose.

However, the heavy elements ejected from super-energetic events such as supernova are traveling at near light speeds and as a result, have a profound effect on biological tissue and electronics that they encounter. Even though they make up a very small fraction of the total particle count per unit volume in space, the effects that they can have on absorbed dose is not negligible. Therefore when we talk about galactic cosmic rays, we generally are talking about the energetic heavy ions from extra-solar energetic events and not the protons and electrons from normal, everyday extrasolar sources.

  • 1
    $\begingroup$ This is a good answer but GCRs are still mostly protons and alpha particles. en.wikipedia.org/wiki/Cosmic_ray#Types $\endgroup$
    – kim holder
    Jun 2, 2015 at 23:14
  • $\begingroup$ Not sure I agree in a practical sense. Alpha particles are considered heavy particles, so I think that is in the context of the definition I provided The fraction of extra-solar protons in our own solar system is negligible compared to solar protons, to the point of being below background MDA depending on solar conditions. However, the effect of Helium, Carbon and Iron CGRs is very noticeable in dose calculations and relative to background levels. $\endgroup$
    – Jon
    Jun 2, 2015 at 23:37
  • $\begingroup$ The Wikipedia article I referenced gives me a different understanding. Is it accurate when it says 99% of GCRs are protons and He nuclei? If so I don't understand how the (even) heavier particles could be more important. I have searched before for better explanations online without success. Your input could perhaps also be valuable on this section: space.stackexchange.com/a/8666/4660 $\endgroup$
    – kim holder
    Jun 3, 2015 at 1:18
  • $\begingroup$ I will expand my post to best answer this without running into character space limitations. $\endgroup$
    – Jon
    Jun 3, 2015 at 21:05
  • 1
    $\begingroup$ In short this is a science vs. engineering definition. Protons and electrons are the most copious product of all stars, with lower mass ions being the next most. However, if you could add up all the particles in our system, most (>99%) came from our star, so we neglect extra solar particles in calcs. However, super heavy ions from super-nova cannot be neglected, so we typically save the GCR definition to describe those particles and not protons and electrons from traditional solar emissions. $\endgroup$
    – Jon
    Jun 3, 2015 at 21:26

One possible material that was mentioned in Scientific American is fecal matter. The hydrocarbons in it can absorb the radiation safely.
However, most of the general public would reject this possibility because of the grossness factor (just like recycling water by purifying and sanitizing urine).

  • 1
    $\begingroup$ If that works shouldn't ordinary hydrocarbons also do the trick, instead of having to come from fecal matter? $\endgroup$
    – Gwen
    Jul 18, 2013 at 16:35
  • 2
    $\begingroup$ It is more viable to use fecal matter because then you don't have to bring up more mass for the hydrocarbons. The idea mentioned in Scientific American was "go out padded with food, come back padded with fecal matter". $\endgroup$
    – JKor
    Jul 18, 2013 at 16:40
  • $\begingroup$ General public seems ok with ISS people drinking recycled sweat and urine (cannot dig out where I read that :-( An article that mentioned the public was not interested in the ISS achievements, and mostly ignored it). $\endgroup$ Feb 5, 2015 at 1:35
  • 3
    $\begingroup$ There will be fecal matter on board the vehicle whether it is used for shielding or not. It must be stored somehow. Why not in void spaces in the walls? Same for drinking water and 'gray' water. There would still be need for other shielding, but I at least this saves internal volume in the spacecraft - and possibly the mass separate tanks too. Maybe. $\endgroup$ Jun 24, 2016 at 14:42

There is talk that it might be possible to use magnets as a shield from cosmic radiation:

Astronauts travelling to the International Space Station are protected from much of this radiation by the Earth’s atmosphere as well as by its “magnetosphere”, the magnetized bubble of plasma surrounding the Earth created by its magnetic field. However, people on longer flights will not have this natural shielding and are therefore at greater risk.


injecting a supersonic plasma into a 1.5 m long vacuum vessel lined with magnetic coils, with a target magnet placed at the far end of the vessel. Using both optical imaging and an electromagnetic probe, Bamford’s team showed that the target magnet deflected the plasma such that the volume of space surrounding the magnet was almost entirely free of plasma particles.

-- physicsworld.com

An image showing how Earth's magnetic field takes care of this:

enter image description here


  • $\begingroup$ That sounds awesome! But wouldn't that be too energy-intensive to be practical for a long-range mission? $\endgroup$
    – Gwen
    Jul 18, 2013 at 16:37
  • 1
    $\begingroup$ @Gwenn Well, we would probably need some kind of crazy-powerful engine in the first place, right? Also, you need to consider the energy implications of launching a spacecraft coated with lead, too. $\endgroup$
    – Undo
    Jul 18, 2013 at 16:38
  • $\begingroup$ @Undo are you aware of anything more recent that you could add here? $\endgroup$
    – uhoh
    Mar 11, 2017 at 13:35
  • 1
    $\begingroup$ @uhoh I'm not, sorry! $\endgroup$
    – Undo
    Mar 11, 2017 at 17:07
  • $\begingroup$ @Undo OK, you are welcome to add this information there as a supplemental answer. I'm looking for something recent, but this is interesting background. Just a thought. $\endgroup$
    – uhoh
    Mar 11, 2017 at 17:08

I know this is not as good as an answer than most here. I would say that a blimp could be inflated around the ship and the gas electrified to create electromagnetic shielding. This method is light weight.


  • $\begingroup$ What is an electrified gas? Do you mean ionized? The Van Allen Belts of Earth work with the magnetic field of the Earth but are outside its atmosphere. $\endgroup$
    – Uwe
    Apr 4, 2018 at 15:46
  • $\begingroup$ @Uwe a Neon or florescent light is a good example, but maybe there is a gas that does not light up staying transparent when ionized that will emit an EM field that can block radiation? $\endgroup$
    – Muze
    Apr 4, 2018 at 16:05

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