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'Space Brain': Mars Explorers May Risk Neural Damage, Study Finds (nbcnews.com)
An anonymous reader quotes a report from NBC News: Astronauts making a years-long voyage to Mars may get bombarded with enough cosmic radiation to seriously damage their brains, researchers reported Monday. The damage might be bad enough to affect memory and, worse, might heighten anxiety, the team at the University of California Irvine said. It's the second study the team has done to show that cosmic radiation causes permanent, and likely untreatable, brain damage. While their experiments involve mice, the brain structures that are damaged are similar, they write in the Nature journal Scientific Reports. NASA knows that astronauts risk physical damage from the radiation encountered in space. Earth is enveloped in a large, protective sheath called the magnetosphere, which deflects a lot of the ionizing radioactive particles that speed through space. Teams aboard the International Space Station are inside that envelope. But moon travelers were not, and this summer a study showed the cosmic radiation may have damaged the hearts of many of the Apollo program astronauts. A trip to Mars would expose astronauts to even more radiation -- enough to cause cancer, for sure, and now this research suggests brain damage, as well. They bombarded mice with the same type of radiation that would be encountered in space, and then looked at what happened to their brains. It did not look good. The changes were seen in the connections between brain cells and in the cells, as well. "Exposure to these particles can lead to a range of potential central nervous system complications that can occur during and persist long after actual space travel -- such as various performance decrements, memory deficits, anxiety, depression and impaired decision-making. Many of these adverse consequences to cognition may continue and progress throughout life."
If they think it's viable then then already have neural damage. A little more won't make much of a difference.
I'm a minority race. Save your vitriol for white people.
Once travelers get to mars the problem is not over, as Mars magnetic field is rather weak, because its dynamo was killed a long time ago
They didn't expose the rats to anything similar to the radiation an astronaut would be subjected to in their travel to Mars: they fried the rats with a short, intense radiation dose, while the astronauts would be exposed to a low dose long term. In fact, in the study they don't even claim that this radiation is anything similar to what one would find in space, they just say it is "space relevant". So what they found out is only that if you fry rats with radiation it impairs their cognition, and this impairment is long-lasting.
Also, TFS says that Scientific Reports is a Nature journal. This is true, Nature the company (or more precisely Holtzbrinck Publishing Group) does own this journal, but it has nothing to do with the Nature journal, editorially or scientifically. This is just a lame attempt to bestow Nature's reputation on Scientific Reports, which is in fact a pretty crappy journal, that does not even try to select papers based on quality, but claims to check only for correctness.
entropy happens
Second sentence true, first sentence false.
The generating equipment does
But requires energy.
It's all a balancing act that I don't think humans will solve until/if they master really compact fusion generators.
"I don't know, therefore Aliens" Wafflebox1
Magnetic shielding (on practical scales) is not effective against GCR, only solar. The article talks about GCR.
IMHO, SpaceX probably has the right solution to radiation: go fast. If you have to bring up extra mass anyway, you might as well make that mass be fuel to shorten the trip rather than inert shielding for a long coast (although there clearly is *some* balancing point; paper-thin walls won't do, even on a short-trip). Also, their solution of "go big" is probably right, as surface area to shield rises propotional to the radius squared but internal volume (and mass / payload capacity of boosters) rises proportional to the radius cubed (assuming proportions are kept roughly the same on all three axes). The bigger your crew transport vehicle, the lower the percentage of its mass that needs to be dedicated to shielding to achieve the same result.
But there's no question that radiation is one of those issues that we really don't have a good "magic bullet" for.
The internet is not a series of tubes. It's more like a net. Or a network of computers. Or an internet.
It's even worse because there's potential compounding factors on Mars that could make psychological issues even worse. For example, here's one that's little studied: deuterium. Mars's deuterium levels are 5-7 times higher than Earth's (nothing like Venus's 150-240x, but still..). Animals and plants certainly can survive rather high deuterium levels, up to 50% (and bacteria can survive 98% deuterated water); in terms of survival, it poses no threat. However, in terms of effects on long-term health effects, it's much less clear. For example, one study found a 1,8% increase in incidence of depression for every 10ppm increase in deuterium in water (Earth mean = ~155ppm). So when you're talking an ~800ppm increase... the issue of long-term deuterium health effects really warrants more study. Furthermore, microbial food sources that may be used on Mars (either for direct consumption or producing feed for, e.g. aquaponics) can concentrate deuterium even further.
Unlike most isotopes, hydrogen isotopes have rather different properties. Deuterated drugs are a new field of interest, for example, as they can have lifetimes in the body an order of magnitude higher than their non-deuterated equivalents. Deuterated plastics are often dramatically more transparent (and significantly more radiation resistant) than non-deuterated plastics. However, mixtures of deuterated and non-deuterated versions of the same plastic, melted together, often yield an opaque result because the two versions have different melting points and densities, yielding an inhomogenous result.
The internet is not a series of tubes. It's more like a net. Or a network of computers. Or an internet.
The magnetosphere does not shield against high energy cosmic rays. You need mass density, and on Earth that shielding is provided by the atmosphere.
There's no point burning fuel rushing to Mars to minimise exposure to cosmic rays, since the atmosphere on Mars is too thin to provide any protection. So the only safe option is to make the entire round trip as short as possible. It just seems so difficult to do with current rocket technology...
http://www.nasa.gov/feature/goddard/real-martians-how-to-protect-astronauts-from-space-radiation-on-mars
:T:R:A:N:S:
Indeed. This effect was described 25 years ago by John Kricfalusi and dubbed Space Madness.
Slashdot's first reaction to VMware
Not exactly. Ideal shielding is relatively thin metal followed by lots of hydrogen-rich material, plus a small amount of neutron absorbers (boron, etc). The hydrogen-rich material should make up the majority of the mass. This can be hydrogen-rich plastics (such as polyethylene), liquid hydrogen propellant (great ISP, although storage is difficult), methane propellant (what SpaceX plans to use, albeit they don't call for much during coast), ammonia (coolant, easy hydrogen store), water (need it anyway, even easier to store), hydrazine (commonly used for RCS thrusters), etc. NASA has been looking at trying to make structural composite materials out of hydrogenated boron nitride nanotubes, which would be killing two birds with one stone (since they're strong as well).
The reason you need lots of hydrogen is that a lot of your high energy impacts will often kick off neutrons, and these are much harder to block than ionized particles (this is particularly of concern with GCR and high-energy solar flare protons). The best way to eliminate neutrons is to moderate them down to the thermal spectrum so that they can be readily absorbed by high cross section absorbers. Hydrogen is by far the best neutron moderator per unit mass; nothing else really even comes close. It has a fairly high scattering cross section to begin with, and scatters far more per event than other compounds due to its low mass (more energy transfers from the neutron to the hydrogen), and presents far more nuclei to scatter from per unit mass than other elements. Liquid hydrogen is even better because you're thermalizing to a very cold temperature, which dramatically increases absorption cross sections (whether from hydrogen itself, or elements specifically used as absorbers such as boron). But again, liquid hydrogen is more difficult to store than other forms....
The internet is not a series of tubes. It's more like a net. Or a network of computers. Or an internet.
They got drunk and decided to test out their interdimensional transportation device and then the green ooze from the other dimension planet caused them. And the producers said "holy shit this movie sucks!" and rushed out an ending in 2 days and released it.
We don't have a state-run media we have a media-run state.
I think you are severely overestimating the danger of radiation. NASA measured the radiation dose received in 180 day trip to Mars to be about 330 mSv. This is probably enough to increase long-term cancer risk, but little else. Check the xkcd about radiation.
entropy happens
Absorbing, not moderating. You have to moderate neutrons down from the MeV range to the thermal range in order to raise the absorption cross sections to reasonable levels - even with high cross section absorbers like boron.
The internet is not a series of tubes. It's more like a net. Or a network of computers. Or an internet.
The estimated exposure for a 400 day round trip transit and 560 days on the surface with 5g/cm2 aluminum shielding is 1070mSv with a 4.2% increase in death rate for men / 5.1% for women, and for 20g/cm2 aluminum it's 960mSv with an increase of 3.4% for men and 4.1% for women. But there's caveats that make this effectively higher, see below. Additionally, both of these are for solar minimum with no solar storms. The big problems however come when you have major charged particle events. If you don't budget for the mass for it, then you're playing dice with your crews' lives, so you pretty much have to. Events that give enough dose to significantly increase the mortality rate (ex. the August 1972 event) are not rare. And while rare, some events are powerful enough to cause acute radiation poisoning and even death in short (30 day) timeframes (4x the August 1972 event). The probability of the former is estimated at 0.2% per week, while the latter is estimated at 0.01% per week.
Re: the comic: XKCD vastly oversimplifies the situation. Radiation risks are not limited to "100mSv: lowest one-year dose clearly proven to increase cancer risk" levels. Radiation is also tied to a wide range of other diseases beyond cancer (cataracts, cognitive decline, lung damage, heart disease, etc), and the level "clearly linked" to cancer does not mean "there is no cancer beyond this point". Specifically concerning cancer: The NCRP-98 / NCRP-132 recommended limits for blood-forming organs are 250mSv/mo, 500/yr, 400-2900/life (depends on age and sex; young and female = less, old and male = more). These limits are based around a calculated excess 3% risk of developing fatal cancer. However, they are misleading because the error bars are large, and the upper end of the error bars is much more likely to kill you than the lower end - so if you want a 95% confidence interval, the risks from such figures are about 3 times higher than the mean suggests. Additionally, wherein the odds of dying from cancer are 3%, the odds of contracting cancer are inherently higher, since - especially in the presence of modern medicine - not all cancer is fatal.
Furthermore, studies with astronauts and animal models keep suggesting more problems from radiation in space than had previously been assumed, and we know little of the effects of the radiation environment beyond LEO. Simplistic radiation models that treat all types of radiation damage from a certain category "grouping" as equivalent appear thusfar to be inaccurate.
You will not find any researchers working in the field of studying the radiation health risks to astronauts who feel that the case is overblown. It is very much considered a significant problem that remains to be solved. Unless you're fine with willingly compromising travelers health and risking their outright survival in the case of a severe solar event, wherein, there's no problem, you can go ahead and launch ;)
The internet is not a series of tubes. It's more like a net. Or a network of computers. Or an internet.
Indeed, most plans call for varying materials - and not just with respect to the inside/outside, but also with where they are on the spacecraft. Even the passengers' own bodies act as shielding for other other passengers and needs to be taken into account. Modeling radiation and health risks on interplanetary missions is not a simple task!
If anyone wants to get more of a sense of how cross sections of different elements / isotopes can vary with different types and energies of radiation, I strongly recommend the Sigma server. Start off with neutrons (although you can change that in the dropdown on the top right), pick an isotope, then look at the options on the right. You'll see lots of entries of the form (n, X). The first part in the parentheses is what the incoming particle is; the second part is what the heaviest outgoing particles are. (n,gamma) for example means that there are no nucleons that result from the collision, only gamma; this is a simple neutron-capture transmutation. (n, total) means the total of all cross sections; (n, elastic) is elastic scattering (the dominant method of moderation at low energies; follows the same sort of energy/angular momentum distribution as elastic collisions between objects on macroscopic scales); (n, inelastic) is inelastic scattering (an additional loss mechanism at high energies where the particle is absorbed and then re-emitted, with a more complex energy distribution), etc. Click on "plot" for any category and it'll show you the result.
For example, here's the (n,alpha) for 10B, a well known neutron absorber. And indeed, these are very high cross sections compared to, say, the odds of elemental carbon doing anything to get rid of the neutron. But note how vastly higher the cross sections are in the thermal (meV) spectrum than they are in the fast (MeV) spectrum. Even with boron, you're unlikely to capture fast neutrons (MeV range or higher) except with a great thickness of absorber. But if you moderate them down - moderation having a high cross section - then they become easy to capture. Remember when looking at these charts that 1H is also 1/10th the molar mass of 10B.
On the other hand, low-Z (light) materials aren't that great at blocking certain types of radiation - if you want to block EM radiation spectrum, for example, you want high-Z materials (that's why there's the standard "lead apron" for getting an x-ray). But the balance of effects in space turns out to favor the need for low-Z materials.
If the terms above like "cross sections" are unfamiliar... picture a particle of any type of radiation like a baseball pitched randomly toward an area where someone has hung a bunch of spheres. What's the odds that the baseball is going to hit one of them? Well, it depends on the cross section that they present to the ball. While a naive expectation might be that it would just simply be proportional to the size of the atoms, in practice different isotopes vary widely in their different effective cross sections to different particles and different reactions. Still, cross sections are measured in "barns", which is a unit scaled to be roughly the size of typical atomic physical cross sections for comparison purposes. Anyway, you can just read nuclear cross sections as "how likely a reaction is per unit traveled through the target".
Oh, and I forgot to mention one other thing: when picking shielding materials, neutron capture or other transmutation reactions alter the isotope that they hit. Often what they produce will be unstable and will decay - sometimes multiple times - releasing more radiation. So it's also important to look
The internet is not a series of tubes. It's more like a net. Or a network of computers. Or an internet.
I checked the last three papers under "magnetic shielding papers" on that page. None of them say anything to suggest that active shielding is an effective means to shield from GCR. They're also all quite old, there's much more recent research on the topic.
They do mention what I wrote - that active shielding is probably mass effective against SCRs (but needs more research). But it's very doubtful that it could be mass effective against GCR. The gyroradius of a particle is proportional to its energy and inversely proportional to the magnetic field strength. GCR is very high energy (commonly hundreds of MeV, up into the tens of GeV range in relevant amounts, with virtually no limit on the extremes), so you have to scale up the size of your magnet proportionally. To oversimplify, if you wanted to take a magnetic shield for the solar wind (commonly a few keV, up to a few dozen) and scale that up to shielding from solar storms protons (hundreds of keV to a few MeV), you'd have to increase it's scale 100fold; and to go from there to GCR would be another hundred-fold increase.
That is of course an oversimplification (even on Earth you can't just scale magnet masses like that, and it's more complex in space because you're actually making a mini-magnetosphere), but you get the gist. It's really hard to shield from GCR-energy particles.
The internet is not a series of tubes. It's more like a net. Or a network of computers. Or an internet.
I said that The Real Dr John specifically was overestimating the danger. He said "until they figure out how to fully shield the spacecraft, this is not practical for humans". And I really don't agree that "~5% increase in death rate" equals "not practical for humans". You have to put things in perspective: just the launch itself has a ~5% probability of killing the astronauts, so while a further 5% increase in the death rate is certainly not welcome, it is one additional danger of an already quite dangerous task. I think you'll find very few astronauts that refuse to take this risk.
That said, of course we need to reduce the radiation exposure as much as we can, because having astronauts who are dead, or with cancer, or with cataracts, or stupid, or with lung problems, or with heart disease is clearly not desirable. Going for extra shielding, as The Real Dr John suggested, is a terrible idea. You need a crazy amount of shielding, on the order of 100 g/cm, to significantly reduce the exposure, so waiting for that to happen is to wait forever. So I think the only plausible solution in the near term is to go fast.
In this respect I find Musk's proposal quite reasonable. He intends to do the trip in 90 days, and rotate the spacecraft to use to fuel tank as a shield during solar flares. NASA calculates that 5% from the 330 mSv in the trip would come from solar flares, so cutting that out and using the shorter trip time already reduces your pessimistic 1070 mSv to 650 mSv, so about 325 mSv per year, already well below the recommended level you quote.
entropy happens
I don't know what kind of battery you're thinking of, but a standard 6V lantern battery has two spring contacts, and that's it, no "screw cap". Here's a Wikipedia article about them that shows a 6V lantern battery in the first picture. They use springs because they work well in a flashlight with poor manufacturing tolerances and which can be subject to a lot of bumping and jostling and being dropped. You might be thinking of the protective plastic caps that are normally found on top of the springs when you first buy the battery. Those are just there so it doesn't get shorted out.
The ISS is above the atmosphere, so its only protection for the hemisphere away from Earth is the magnetic field, and we keep some people there for a year. They aren't in good shape then, but I haven't seen complaints about radiation.
Is there something I'm missing here, or is the ISS a good approximation to an interplanetary spaceship to within a factor of 2?
"When you have eliminated the unacceptable, whatever is left, however improbable, must be the truthiness" - Holmes