Cosmic Rays Could Kill Astronauts Visiting Mars

jvchamary writes "Given the recent stream of reports of 10th planets and the relative success of the NASA Discovery mission, it might again be time to get excited at the prospect of visiting the Red Planet. Unfortunately, New Scientist reports that Astronauts traveling to Mars would be exposed to so much cosmic radiation that 10% would die of cancer."

Is this news?

[pcmanjon]

We've known this for quite a while.

I think they'd also have to go through the Van Allen radiation belts which could also be a concern. Conspiracy theorists have argued that space travel to the moon was impossible because the Van Allen radiation would kill or incapacitate an astronaut who made the trip. In practice, even at the peak of the belts, one could live for several months without receiving a lethal dose.

Apollo had timed things however to make it accross while radiation was at a minimum. However, if they'd be on such a long trip -- timing will have to be a lot more precise.

Short of hauling up lead plates, I don't know what they'll do.

What kind of propulsion?

[RevRigel]

If they're talking about current chemical propulsion technologies, then yes, they'll be out there for the better part of a year. If we get dig out nuclear propulsion technology that's already been developed, such as NERVA, and other things such as gas core nuclear rockets, it's simple to cut the trip down to weeks while simultaneously packing dozens of tons of extra shielding.

Re:Is this news?

[Cheerio Boy]

However, if they'd be on such a long trip -- timing will have to be a lot more precise.

I didn't understand half the math in The Case for Mars [amazon.com] but the author explains in detail how the route could be planned to be both low cost and safe from radiation.

I need to read that again...

Re:Anyone Know this Number?

[BlackCobra43]

You have a 33% chance of contracting cancer at some point in your life, assuming you live an "average", complete, life. Let's ballpark an estimate 40% average survival rate for cancer (a good deal of them are treatable if detected in time) and we get 13.2%

Send me up there.

Re:Whoa, that's gotta suck

[drudd]

While clearly not susceptible to ovarian cancer (perhaps comparable to prostate and testicular cancers), men do suffer from breast cancer, albeit at a lower rate than women.

Doug

uhm, I don't think there will be much ping-pong

[slew]

I don't want to get into a particle vs wave debate, but at the energy level of gamma rays (photon-like particles), I don't think you have to worry about changing their momentum much so they "bounce" with a some weak lead shielding resulting in a ping-pong game...

If the gamma photon gets through the lead (and it usually's got lot of momentum/energy), it'll get to the person and have some probablity of hitting one of the atoms in the person (resulting in the atom decaying and causing ionizing radiation damage). Since a person is usually thicker than the shield, the probability of hitting an atom in the person's body is much higher than hitting an atom in the lead shield. For alpha and beta radiation, they are charged and also usually have lower energy/momentum and as you mentioned can be mostly stopped with thin layers of material...

And cosmic rays (which mostly originate outside the solar system, but some come from the sun) are about 10-1000x more energetic than typical gamma rays (since both cosmic and gamma rays are techically photons they are only distinguished by energy level anyhow, a rose is a rose).

As for slowing down these highly energetic photons, well, there's not much a lead plate in a space-suit (or in a space-ship) is gonna do about that. Particles with that much energy/momentum aren't easy to stop with a few inches of any material, but if a "peice of radiation decided to stop", the photon would have zero rest mass and you wouldn't notice it (except for the residual path of damage it made in the attempt to stop)...

For current astronauts "near" earth, they of course have this big shield that protects us from about 1/2 of this radiation (the technical name of the shield is called earth), for someone far away from a big planetary body to shield them, they'll get at least a double dose of cosmic rays. For those of us on earth we get protection from both the earth on one side and atmosphere on the other, but of course mars's atmosphere is thinner (and doesn't have any ozone, although there may be some other thing there that helps)...

Re:Easy Solution

[Rei]

The situation is a lot more complicated than that. High atomic mass elements are great at causing collisions with the particles composing the radiation that you're trying to shield against. However, a direct collision isn't always the best thing.

Case and point: The best way to shield against solar radiation is high atomic mass materials. Even moderate materials, such as aluminum, should work quite well if you plate it on thick enough.

But what happens when GCR (Galactic Cosmic Radiation) strikes that shielding? You often get bremsstrahlung ("braking radiation") - the single particle is instead replaced with a shower of much more dangerous particles. Even worse, these particles are released partway or even all the way through the shielding.

The best way to shield against GCR is hydrogen in huge quantities to decelerate the particles - this generally means either your fuel or plastics in the skin. But that doesn't shield well against solar radiation. In short, what you end up needing is a complex layered system. The exact design? That's still a wide-open question. We know we can pack enough aluminium to stop solar-radiation-only (including a small shelter for storms) without having too heavy shielding requirements. Factor in bremsstrahlung, however, and it's a wide-open question.

By the way, to those who suggest "active shielding" (creating a magnetic field around the craft to deflect radiation) - studies show that it won't work to stop GCR (only solar).

It's a conspiracy, I tells ya!

[Mr. Cancelled]

Seriously, this is one of the same arguements from those who don't believe we ever visited the moon: The cosmic rays would kill you.

It's an interesting theory, but also one which must be answered before long term/distance space travel will be possible. Or even short term travel, if the conspiracy theorists are to be believed.

Men get breast cancer too.

[douglips]

http://www.menstuff.org/issues/byissue/breastcance r.html [menstuff.org]

Re:Whoa, that's gotta suck

[budgenator]

OK on ovarian, but men get testcular CA that women don't and BOTH get breast CA but it's more common in women, male breast CA patients are more likely to be fatal, much less early detection with men. It's been a while since I had Oncology, so anybody that's current should feel free to chime in.

Re:Easy Solution

[twiddlingbits]

You often get bremsstrahlung ("braking radiation") - the single particle is instead replaced with a shower of much more dangerous particles. Most galactic cosmic rays have energies between 100 MeV (corresponding to a velocity for protons of 43% of the speed of light) and 10 GeV (corresponding to 99.6% of the speed of light). The number of cosmic rays with energies beyond 1 GeV decreases by about a factor of 50 for every factor of 10 increase in energy. Over a wide energy range the number of particles per m2 per steradian per second with energy greater than E (measured in GeV) is given approximately by N(>E) = k(E + 1)-a, where k ~ 5000 per m2 per steradian per second and a ~1.6. The highest energy cosmic rays measured to date have had more than 1020 eV, equivalent to the kinetic energy of a baseball traveling at approximately 100 mph! (So should shielding be wood? ;)) Note that 100MeV is about 30X Gamma Ray Energy so even with the loss of energy in the collision (it's not 100% transfer of energy) with the shielding there is a lot of energy left over to cause havoc in the material used as the shielding.

Re:Easy Solution

[mOdQuArK!]

Dunno how dangerous "ionized" water is - certainly not as dangerous as letting the radiation hit the water in your body, and I believe that there are standard techniques for creating "deionized" water or bleeding off the extra charge from arriving beta particles.

As far as radiation goes, I believe you are talking about the radioactive particles from space that are left in the water after they have been slowed down, or perhaps the creation of deuterium & tritium from high-energy collisions? Again, I believe that the results are pretty low level - hydrogen & oxygen don't exactly fission into radioactive particles easily (unlike stuff like uranium).

I think the primary byproduct of the captured particles from space will probably be alpha (bare helium nuclei) and beta (high-energy electronics) particles, so you could probably harvest the resultant accumulated helium gas over time.

As far as gamma rays are concerned, I don't think they can fission hydrogen & oxygen atoms (unless you're talking energy levels high enough to reduce basic particles to quarks, in which case your spaceship/spacestation has bigger problems), so a thick enough wall of water with an inner wall of lead or something similarly dense should be enough to protect against almost anything. (I guess it would be a bad idea to have your water in direct contact with lead :-)

Of course, there's always the possibility of a neutrino blast (like when a star goes nova or supernova), but we don't really have any way of defending against that whether we are in a spaceship/station or on a planet.