Author Topic: NASA & Georgetown University study on Cosmic Ray dangers to space travelers  (Read 2347 times)

Offline Eric Hedman

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I found this article on a study about the dangers from cosmic rays on long duration spaceflight beyond LEO.  It is here: https://www.independent.co.uk/news/science/nasa-mars-deep-space-journey-guts-gi-digestive-animal-study-gastrointestinal-health-a8563926.html

The title of the article sounds a bit over dramatic.  Does anyone know more details on this study?
« Last Edit: 10/02/2018 06:00 AM by Eric Hedman »

Offline WBY1984

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The Independent is a trash website generally, they've just copy-pasted the entire article from the Georgetown website, but at least what they've said is not misreporting as a consequence:
https://gumc.georgetown.edu/news/Animal-Study-Suggests-Deep-Space-Travel-May-Significantly-Damage-GI-Function-in-Astronauts

From a brief google, it sounds like Proceedings of the National Academy of Sciences of the United States of America is a widely cited and respected journal. Other news articles are likewise parroting the Georgetown press release, not quoting from the actual study/authors. Sorry I can't find any more details on the actual study. It does, however, seem to fall in line with a growing body of work that says the space environment is going to be as much as, if not more serious an issue as the actual engineering of a spacecraft.
« Last Edit: 10/02/2018 06:36 AM by WBY1984 »

Offline speedevil

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It does, however, seem to fall in line with a growing body of work that says the space environment is going to be as much as, if not more serious an issue as the actual engineering of a spacecraft.
It says '“With the current shielding technology, it is difficult to protect astronauts from the adverse effects of heavy ion radiation." - this does however get easier if you throw mass at it.
A half meter of polythene or methane, or a bit more than a meter of water, for example, cuts your GCR dose to a third.
This is quite a large a lot of mass, but in the further term, in the context of cyclers, and large transfer spacecraft >>8m in diameter, it gets less important.
An 8m*8m inside rounded cylinder, 50cm deep, filled with water, about halves GCR for a 100 ton cost, or several more launches of propellant on BFR.

Also, arguments about GCR being dangerous have to be looked at in the context of ISS astronauts.
They are minimally shielded against GCR, and do not, as a group, have huge health impacts that lead to the worst outcomes.
(May they be subtly affected, sure)

Online RonM

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It does, however, seem to fall in line with a growing body of work that says the space environment is going to be as much as, if not more serious an issue as the actual engineering of a spacecraft.
It says '“With the current shielding technology, it is difficult to protect astronauts from the adverse effects of heavy ion radiation." - this does however get easier if you throw mass at it.
A half meter of polythene or methane, or a bit more than a meter of water, for example, cuts your GCR dose to a third.
This is quite a large a lot of mass, but in the further term, in the context of cyclers, and large transfer spacecraft >>8m in diameter, it gets less important.
An 8m*8m inside rounded cylinder, 50cm deep, filled with water, about halves GCR for a 100 ton cost, or several more launches of propellant on BFR.

Shielding sleeping quarters would help if shielding the entire crew compartment is not feasible. Have the crew do some of their work on computers in their sleeping quarters. Eight to twelve hours per day in the smaller shielded compartment would help.

Also, arguments about GCR being dangerous have to be looked at in the context of ISS astronauts.
They are minimally shielded against GCR, and do not, as a group, have huge health impacts that lead to the worst outcomes.
(May they be subtly affected, sure)

Since ISS is in LEO, the Earth blocks about half GCR exposure. With shielded sleeping quarters as mentioned above, an interplanetary ship would have about the same crew GCR exposure as ISS today.

Online envy887

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The full paper is here: http://www.pnas.org/content/pnas/early/2018/09/26/1807522115.full.pdf

Some caveats: they hit mice with 10 Sv of heavy ions in a very short time (they don't specify the irradiation time but in previous papers they used 20 Sv/minute). This compares unfavorably with the estimated 1 Sv total dose (mostly from protons, not heavy ions) for a 860 day Mars mission, of which only 0.3 Sv results from a moderately shielded to unshielded 500-day surface stay. The 180-day transit each way makes up the other 0.6+ Sv, and this is linearly proportional to transit time.

Even without adding shielding to the transit ship, the total dose can be reduced dramatically below the 1 Sv level by ~100 day transits and heavy surface shielding (e.g. underground sleeping and work quarters). In principal, the radiation dose for a 860-day Mars trip can be reduced below that received in ~14 months on ISS.

Between the heavy dose, the extremely high dose rate, the extremely high fraction of heavy ions, and the disregard for surface shielding, this study probably overestimates the radiation effect by at least 10 times. And that's before any spacecraft shielding is accounted for.

Offline Russel

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I put forward an idea in a different context that is worth repeating here.

Personal wearable shielding, probably focused on the torso. The original context was that in a 0.2-0.4g environment, the extra mass is beneficial for exercise. So in a 0.2g environment you coild wear maybe 300Kg of shielding mass.

I'm well aware that there is a limit to heavy ion shielding by this method. But it would be part of a multi-layered defrnse.

Here's an interesting question. Strong magnetic fields will deflect heavy ions or cause them to spiral. Now instead of a uniform external magnetic field, Imagine a material with numerous zones of high intensity magnetic fields (passive or active).  A heavy ion forced to follow a longer path will see more of the material. In other words making the material effectively thicker. Can this be done for a spacecraft hull? Can this be scaled down to personal protection?

Online Robotbeat

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It'd be useful for solar flares.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Online KelvinZero

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Personal wearable shielding, probably focused on the torso. The original context was that in a 0.2-0.4g environment, the extra mass is beneficial for exercise. So in a 0.2g environment you coild wear maybe 300Kg of shielding mass.
The astronauts of tomorrow :) :



But seriously, it could be worth some extra coverage especially if certain organs turn out to be a particular risk.. and it could cost next to nothing to have some sort of water-bag suit so individuals can leave the solar shelter if they really needed to. The water would just be part of general stores.

Online ChrisWilson68

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Between the heavy dose, the extremely high dose rate, the extremely high fraction of heavy ions, and the disregard for surface shielding, this study probably overestimates the radiation effect by at least 10 times. And that's before any spacecraft shielding is accounted for.

I really want to emphasize this point.  This study is really not very useful because what it studies is so much different from what a real space explorer would experience, and because we have much better data.

The much better data comes from flight crews of airliners.  They get much higher doses of this kind of radiation. than people who stay on the Earth's surface.  And the data shows that space travelers can expect some moderate increased risk from these particles, but not a huge amount.  Certainly for the current generation and the next couple of generations the other risks of space travel will outweigh the small risks from cosmic rays.  This new study does nothing to change that assessment.

Offline niwax

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Personal wearable shielding, probably focused on the torso. The original context was that in a 0.2-0.4g environment, the extra mass is beneficial for exercise. So in a 0.2g environment you coild wear maybe 300Kg of shielding mass.
Don't forget about inertia. Even in no gravity getting going and stopping in a 300kg suit will not be fun.

Here's an interesting question. Strong magnetic fields will deflect heavy ions or cause them to spiral. Now instead of a uniform external magnetic field, Imagine a material with numerous zones of high intensity magnetic fields (passive or active).  A heavy ion forced to follow a longer path will see more of the material. In other words making the material effectively thicker. Can this be done for a spacecraft hull? Can this be scaled down to personal protection?
There are threads on here about protecting Mars colonies with an artificial magnetic field (and some startups claiming to offer the same). It's slightly scifi for now but not impossible, especially when you have ample nuclear power to play with.

Online envy887

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Personal wearable shielding, probably focused on the torso. The original context was that in a 0.2-0.4g environment, the extra mass is beneficial for exercise. So in a 0.2g environment you coild wear maybe 300Kg of shielding mass.
Don't forget about inertia. Even in no gravity getting going and stopping in a 300kg suit will not be fun.

Here's an interesting question. Strong magnetic fields will deflect heavy ions or cause them to spiral. Now instead of a uniform external magnetic field, Imagine a material with numerous zones of high intensity magnetic fields (passive or active).  A heavy ion forced to follow a longer path will see more of the material. In other words making the material effectively thicker. Can this be done for a spacecraft hull? Can this be scaled down to personal protection?
There are threads on here about protecting Mars colonies with an artificial magnetic field (and some startups claiming to offer the same). It's slightly scifi for now but not impossible, especially when you have ample nuclear power to play with.

With superconductors the required power levels to maintain a high magnetic field strength are quite low, since the losses are fairly small.

Offline Russel

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Thanks Kelvin. Best laugh I've had all day :)

The bulkiness of personal radiation protection is the reason I think its limited to the torso. Just how thick is another interesting question.

In terms of a purely passive suit I wonder what the best materials are. There is probably a need for denser materials.

I get the point about inertia. Perhaps 300Kg is over the top.

On the issue of magnetics. The distinction I'm making is between fields generated in free space and fields generated within an ion absorbing material. The field isn't there to totally deflect the particles but instead to lengthen their path. That means you increase the effective thickness of the material.
« Last Edit: 10/11/2018 04:34 AM by Russel »

Offline LMT

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The full paper is here: http://www.pnas.org/content/pnas/early/2018/09/26/1807522115.full.pdf

they hit mice with 10 Sv of heavy ions... This compares unfavorably with the estimated 1 Sv total dose (mostly from protons, not heavy ions) for a 860 day Mars mission...

Looking at their reasoning and method:

Quote
While protons are the major component of space radiation, energetic heavy ions such as 56Fe, 28Si, and 12C contribute significantly toward the dose equivalent, and ∼30% of astronauts’ cells are predicted to be hit by heavy ions during a round trip to Mars...

Since the estimated radiation dose for a 1,000-d Mars mission is about 0.42 Gy (21), with an estimate of an 860-d Mars mission dose equivalent of ∼1.01 Sv (22) so doses of 0.5 Gy or less are more relevant, we have used 0.5 Gy to study IEC migration, which is important for intestinal homeostasis.

Wild-type mice... were irradiated (dose: 0.5 Gy) using a simulated space radiation source at the NASA Space Radiation Laboratory (NSRL), Brookhaven National Laboratory for iron (56Fe; energy: 1,000 MeV per nucleon; LET: 148 keV/μm) irradiation, and a 137Cs source was used for γ-ray (LET: 0.8 keV/μm) whole-body irradiation of mice.

How did you calculate 10x overdose?

Offline LMT

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Personal wearable shielding, probably focused on the torso. The original context was that in a 0.2-0.4g environment, the extra mass is beneficial for exercise. So in a 0.2g environment you coild wear maybe 300Kg of shielding mass.
Don't forget about inertia. Even in no gravity getting going and stopping in a 300kg suit will not be fun.

Here's an interesting question. Strong magnetic fields will deflect heavy ions or cause them to spiral. Now instead of a uniform external magnetic field, Imagine a material with numerous zones of high intensity magnetic fields (passive or active).  A heavy ion forced to follow a longer path will see more of the material. In other words making the material effectively thicker. Can this be done for a spacecraft hull? Can this be scaled down to personal protection?
There are threads on here about protecting Mars colonies with an artificial magnetic field (and some startups claiming to offer the same). It's slightly scifi for now but not impossible, especially when you have ample nuclear power to play with.

With superconductors the required power levels to maintain a high magnetic field strength are quite low, since the losses are fairly small.

Yes, negligible losses in, say, our suggested superconducting cables for the Omaha Field design.  Most power goes to refrigeration of coolant, as in Motojima & Yanagi 2008.  In our case, < 80 kW to shield the floor of a 9 km crater.

Refs.

Motojima, O., & Yanagi, N. (2008). Feasibility of Artificial Geomagnetic Field Generation by a Superconducting Ring Network. Research Report NIFS-Series.

Offline LMT

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On the issue of magnetics. The distinction I'm making is between fields generated in free space and fields generated within an ion absorbing material. The field isn't there to totally deflect the particles but instead to lengthen their path. That means you increase the effective thickness of the material.

Unfortunately, a GCR proton deflects at kilometer scale in a superconductor's strong magnetostatic field.  It's a leisurely turn, even with field exceeding 0.1 T at the cable surface, as below.



[Omaha Field.  9 km crater (red ellipse), field measured 6.5 km above crater rim, 500 MeV proton deflection tracks in black.]

And you don't want that superconducting field generator on your person.  0.1 T is far above the common human safety limit of 5E-4 T.
« Last Edit: 10/12/2018 04:53 AM by LMT »

Online Robotbeat

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Humans can be exposed to 0.1 Tesla without any harm. A good neodymium magnet (pretty common nowadays) is like 0.5 Tesla on the surface, and there's no problem. I'd be more concerned with tools and equipment.

But anyway, there are field configurations that null out the field in the center.
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Offline LMT

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Humans can be exposed to 0.1 Tesla without any harm...  I'd be more concerned with tools and equipment.

Hence the safety limit, yes.
« Last Edit: 10/14/2018 12:23 PM by LMT »

Offline LMT

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The full paper is here: http://www.pnas.org/content/pnas/early/2018/09/26/1807522115.full.pdf

they hit mice with 10 Sv of heavy ions... This compares unfavorably with the estimated 1 Sv total dose (mostly from protons, not heavy ions) for a 860 day Mars mission...

Looking at their reasoning and method:

Quote
While protons are the major component of space radiation, energetic heavy ions such as 56Fe, 28Si, and 12C contribute significantly toward the dose equivalent, and ∼30% of astronauts’ cells are predicted to be hit by heavy ions during a round trip to Mars...

Since the estimated radiation dose for a 1,000-d Mars mission is about 0.42 Gy (21), with an estimate of an 860-d Mars mission dose equivalent of ∼1.01 Sv (22) so doses of 0.5 Gy or less are more relevant, we have used 0.5 Gy to study IEC migration, which is important for intestinal homeostasis.

Wild-type mice... were irradiated (dose: 0.5 Gy) using a simulated space radiation source at the NASA Space Radiation Laboratory (NSRL), Brookhaven National Laboratory for iron (56Fe; energy: 1,000 MeV per nucleon; LET: 148 keV/μm) irradiation, and a 137Cs source was used for γ-ray (LET: 0.8 keV/μm) whole-body irradiation of mice.

How did you calculate 10x overdose?

If useful for calcs, NSRL publishes its Beam Ion Species and Energies, including data on each species' energy, LET, range and intensity.  The NSRL simulated SPE beam spectrum is also characterized.

The simulated GCR beam is detailed in Slaba et al. 2015.

Refs.

Slaba, T. C., Blattnig, S. R., Norbury, J. W., Rusek, A., La Tessa, C., & Walker, S. A. (2015). GCR simulator reference field and a spectral approach for laboratory simulation.

Offline ThinkerX

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It does, however, seem to fall in line with a growing body of work that says the space environment is going to be as much as, if not more serious an issue as the actual engineering of a spacecraft.
It says '“With the current shielding technology, it is difficult to protect astronauts from the adverse effects of heavy ion radiation." - this does however get easier if you throw mass at it.
A half meter of polythene or methane, or a bit more than a meter of water, for example, cuts your GCR dose to a third.
This is quite a large a lot of mass, but in the further term, in the context of cyclers, and large transfer spacecraft >>8m in diameter, it gets less important.
An 8m*8m inside rounded cylinder, 50cm deep, filled with water, about halves GCR for a 100 ton cost, or several more launches of propellant on BFR.

Also, arguments about GCR being dangerous have to be looked at in the context of ISS astronauts.
They are minimally shielded against GCR, and do not, as a group, have huge health impacts that lead to the worst outcomes.
(May they be subtly affected, sure)

Put the living quarters inside the fuel tank?  most propulsion schemes seem to involve substantial amounts of fuel.

Offline Russel

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Does anyone know roughly what the radius of curvature is for heavy ions (and protons) in a much stronger field - say 5 Tesla?

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