Author Topic: Radiation mitigation strategies for early SpaceX Mars missions  (Read 90712 times)

Offline john smith 19

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Just a reminder

The Apollo lander had 0.5% of the protection afforded by Earths atmosphere at sea level.

I would suggest any habitat either needs a thick layer of regolith on it or be underground.

But the real problem is being roasted on the way to Mars, unless you're inside an asteroid. There the issue is doing radioprotection without such a big mass penalty. 
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Online docmordrid

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Your best GCR radiation mitigations are speed of transit and timing. Speed is clear; it gets you from pad into a shielded shelter reducing transit exposure; go propellant rich. Timing is to take advantage of the solar cycle as much as possible;

Solar maximum may be safest for manned missions to Mars....
« Last Edit: 08/18/2016 05:42 pm by docmordrid »
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Offline Semmel

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Also Shielding is a bad idea unless its really massive shielding. We had a talk by R. Wimmer-Schweingruber at our institute about radiation measurements from MSLs RAD instrument. In this talk, he showed among other things, that shielding from cosmic rays is a bad idea. Whenever a cosmic ray is stopped by an atom, it destroys the atoms core of what ever it hit. The shrapnel of that collision are like a shotgun shell, with much more likelihood to hit someone behind the shield than the cosmic ray in the first place. As a result, radiation damage with a shield is actually worse than radiation damage without. Unless of course the shield is truly massive and can stop the shrapnel pieces as well.

Online Robotbeat

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Semmel: Shielding cosmic rays /with aluminum/ is a really bad idea.

MSL was shielded using aluminum.

But even a small shield using plastic is helpful vs cosmic rays (for the most part), although only barely.


Radiation is one of those things which is fractally complex. Each thing you learn is just a crude approximation, with exceptions all the way down, such as:

1) The more mass between you and the radiation, the better
2) Except cosmic rays, in which case shielding is bad
3)... but only if it's high-atomic-mass shielding. Low atomic mass shielding is actually still good if it's thin, though barely does anything to cosmic rays.

...and so on.
« Last Edit: 08/18/2016 07:52 pm by Robotbeat »
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Online docmordrid

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IF you're going to use one graded Z is the way to go; laminated ranging from a high Z element like tantalum to a high hydrogen polymer like polypropylene. Extra points for a borated layer (neutrons.)
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Offline Semmel

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Robitbeat, he did not specify the material of the shield. Also, cosmic rays are fast protons for the most part. Many if them far higher energetic than anything we can produce in particle accelerators. Whatever atom they hit, it's going to be smashed to pieces and creates a particle shower with a much higher chance that one of the parts interacts with your body. If you want protection from cosmetic rays, you need to reduce the shrapnel to below the hit probably of the original proton.

That's as much as he explained. I don't think it depends on the material..  only on the flat out mass thickness of the shield.
« Last Edit: 08/19/2016 07:13 am by Semmel »

Online Robotbeat

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Yeah, it absolutely depends on the composition of the shield.

And VERY few particles are higher energy than can be produced in a particle accelerator here on Earth. For purposes of radiation shielding, you can safely neglect particles over 1TeV because of their extreme rarity.
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Online Robotbeat

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This graph shows it most clearly as it gives a range of materials from hydrogen to lead.

As you can see on the right, even the smallest hydrogen shield reduces the radiation dose. Whereas for aluminum, there's a large portion of the right curve where the aluminum makes you worse off, but eventually helps some as you approach 30g/cm^2. For lead, it's the entire curve to beyond 30grams/cm^2 where it makes the effective dose much worse. Carbon fiber composite would be somewhere near water as far as effectiveness. As you can see, it's better than aluminum.
« Last Edit: 08/19/2016 01:00 pm by Robotbeat »
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Offline Oli

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This graph shows it most clearly as it gives a range of materials from hydrogen to lead.

As you can see on the right, even the smallest hydrogen shield reduces the radiation dose. Whereas for aluminum, there's a large portion of the right curve where the aluminum makes you worse off, but eventually helps some as you approach 30g/cm^2. For lead, it's the entire curve to beyond 30grams/cm^2 where it makes the effective dose much worse. Carbon fiber composite would be somewhere near water as far as effectiveness. As you can see, it's better than aluminum.

Wow, I didn't know liquid hydrogen is such a superior shielding material. Can you post a link to that article?

Online Robotbeat

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This graph shows it most clearly as it gives a range of materials from hydrogen to lead.

As you can see on the right, even the smallest hydrogen shield reduces the radiation dose. Whereas for aluminum, there's a large portion of the right curve where the aluminum makes you worse off, but eventually helps some as you approach 30g/cm^2. For lead, it's the entire curve to beyond 30grams/cm^2 where it makes the effective dose much worse. Carbon fiber composite would be somewhere near water as far as effectiveness. As you can see, it's better than aluminum.

Wow, I didn't know liquid hydrogen is such a superior shielding material. Can you post a link to that article?
http://asgsb.indstate.edu/bulletins/v16n2/v16n2p19-28.pdf
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Offline CuddlyRocket

Also, cosmic rays are fast protons for the most part. Many if them far higher energetic than anything we can produce in particle accelerators. Whatever atom they hit, it's going to be smashed to pieces ...

Unless it's a hydrogen atom, of course!

Offline AncientU

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This graph shows it most clearly as it gives a range of materials from hydrogen to lead.

As you can see on the right, even the smallest hydrogen shield reduces the radiation dose. Whereas for aluminum, there's a large portion of the right curve where the aluminum makes you worse off, but eventually helps some as you approach 30g/cm^2. For lead, it's the entire curve to beyond 30grams/cm^2 where it makes the effective dose much worse. Carbon fiber composite would be somewhere near water as far as effectiveness. As you can see, it's better than aluminum.

Wow, I didn't know liquid hydrogen is such a superior shielding material. Can you post a link to that article?

Maximum energy loss per collision of a high energy proton or neutron is realized when the mass of the atom collided with is equal to that of the proton/neutron.  Think two billiard balls colliding vs billiard ball and bowling ball... the former transfers an average of half of the energy per collision.
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Offline envy887

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Seems like a relevant study:

Non-Targeted Effects Models Predict Significantly Higher Mars Mission Cancer Risk than Targeted Effects Models

Quote
The health risks from galactic cosmic ray (GCR) exposure to astronauts include cancer, central nervous system effects, cataracts circulatory diseases and acute radiation syndromes. Cancer and cataracts are the main concern for space missions in low Earth orbit, while for long-term space missions outside the protection of the Earth’s magnetic field cancer risks are predicted to exceed acceptable risk levels, and non-cancer risks are of concern for the higher organ doses of long-term space missions compared to missions in low Earth orbit. Annual GCR organ absorbed doses and dose equivalents vary over the solar cycle between 0.1 and 0.2 Gy/y and 0.3 and 0.6 Sv/yr, respectively for average spacecraft shielding thicknesses. Protons dominate absorbed doses, while heavy ions, low energy protons and helium particles, and neutrons make important contributions to dose equivalent because of their large quality factors. The high energies of GCR limit practical shielding amounts from providing significant attenuation. The exploration of Mars will require missions of 900 days or longer with more than one year in deep space where exposures to all energies of GCR are unavoidable and doses only modestly decreased by radiation shielding.

https://www.nature.com/articles/s41598-017-02087-3

Offline ZachF

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A while back I saw a documentary about Chernobyl radiation research on TV, so no link. It was quite interesting.

They researched several different populations from mice to wild horses. All at radiation levels that were expected to cause severe issues. The populations were very healthy and had no increased rate of birth defects. With one notable exception. Migratory birds who arrived in the area exhausted and with bad immune status and bred there had an increased number of birth defects. So it seems the immune system plays an important role in fighting radiation related damage.

There was an interesting experiment with lab mice too. They took a batch of mice and exposed half of the batch to Chernobyl radiation for a while, several weeks. Then they exposed both the Chernobyl group and a control group to severe radiation. With present theory it was to be expected that the Chernobyl group pre exposed would fare worse because of their higher total exposure. The opposite happened. The Chernobyl mice fared significantly better. Like they developed an ability to deal with radiation better because of their pre exposure.

Current used standard for radiation damage is the Linear No-Threshold Hypothesis, which honestly hasn't been proven. It basically proposes radiation damage is cumulative with no threshold for damage... ie, if radiation was alcohol drinking a gallon of vodka over the course of a few months would be just as bad as chugging the entire thing at once. Nothing else in nature is like this are far as biological damage goes, and there is has been no proof this is the case, but people stick with it none the less. There is a lot of anti-science politicalization and FUD regarding radiation and radiation damage.
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Offline CuddlyRocket

Quote
The exploration of Mars will require missions of 900 days or longer with more than one year in deep space ...

By 'deep space', I presume they mean interplanetary? If so, a year is a maximum and SpaceX at least are talking shorter journey times.

Quote
Quote
... where exposures to all energies of GCR are unavoidable and doses only modestly decreased by radiation shielding.

I'm not sure if the 'where' applies only to 'deep space' or to the entire mission. If the latter, there's a lot of radiation shielding whilst on the surface of Mars!

Offline mikelepage

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It strikes me that the main question to be solved is, how is water going to be stored on ITS?  You could keep it in big vessels around the rim of the craft, but then you need to cover the entire surface of the crewed section in order for it to be effective (= very massive).

The idea that just occurred to me is that there is probably a better solution if you make a combination water bed/air mattress type unit, that can be moved around the inside of the crew section as needed.  Because of this, you can keep "communal" water to a minimum, and instead make every crew member responsible for their own water store.

Imagine a standardised water bed "mat" that contained a volume of water 2m x 2m x 10 cm = 400kg of water.  It's contained by polyethylene membranes, and has internal polyethylene baffles that stop it from sloshing around too much during launch/landing.  You take/store as many of them as you need, (flat-packed away from the crew during high-g-force maneuvers).

Once in cruise phase, each crew member gets a number of these mats to be used as their own personal water supply.  They drink/bathe using this water, and top them up with recycled water from ship water reclaimers.

Each mat also has an integrated "air-mattress" set of channels that allow air to be pumped in and out of it, for the purpose of changing its shape from flat to various degrees of curvature.  So for example, it could be made into a cylindrical "bed" tube of circumference 2m (so about 64cm in diameter - could even have the air pockets extend over the ends to create acoustic damping). 

The edges of the mat would be able to attach (with velcro or hook&eye, etc) to itself, or others so multiple mats can be joined to create larger enclosures as required.   Mats could also be stacked on each other in multiple layers, or wrapped around each other to create as much water shielding thickness as required.

I'm hoping I'm interpreting the graph upthread correctly, but if in cruise phases, everyone slept in a mat tube two layers (20cm) thick, and spent most of the rest of their time in other such enclosures, I figure you might reduce effective doses down to a third (0.6 mSv/day) which is only marginally higher than ISS astronauts (0.47mSv/day)

TLDR: Instead of shielding the entire crew section, create portable "water-bed" mats, with "air-mattress" channels in them, so it can be shaped to create sleep/work enclosures as needed.

Offline gospacex

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Also, cosmic rays are fast protons for the most part. Many if them far higher energetic than anything we can produce in particle accelerators. Whatever atom they hit, it's going to be smashed to pieces ...

Unless it's a hydrogen atom, of course!

Not at all. High-energy protons (starting with ~300 MeV) "smash to bits" even other individual protons.

Offline CuddlyRocket

The idea that just occurred to me is that there is probably a better solution if you make a combination water bed/air mattress type unit, that can be moved around the inside of the crew section as needed.  Because of this, you can keep "communal" water to a minimum, and instead make every crew member responsible for their own water store.

It's an interesting idea. However, you don't really need a mattress when you're in the interplanetary coast phase, which is when you need the greatest radiation shielding. Where you do need a mattress is on Mars, but it would only protect you from radiation coming from below, and that's straightforwardly dealt with anyway.

Offline mikelepage

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The idea that just occurred to me is that there is probably a better solution if you make a combination water bed/air mattress type unit, that can be moved around the inside of the crew section as needed.  Because of this, you can keep "communal" water to a minimum, and instead make every crew member responsible for their own water store.

It's an interesting idea. However, you don't really need a mattress when you're in the interplanetary coast phase, which is when you need the greatest radiation shielding. Where you do need a mattress is on Mars, but it would only protect you from radiation coming from below, and that's straightforwardly dealt with anyway.

I can see my calling it a "mattress" sent you off on a tangent :P  Flat rectangular prisms are just the easiest way to pack water containers together for storage, and encasing them in flexible polyethylene membranes reminds me of a waterbed/air mattress, but the actual idea was that during interplanetary cruise phase you could pump air into chambers in the water "mattress" that would reshape it into a cylindrical private space (or join multiple mats into a larger enclosed cylindrical space).

The idea is that you feel cradled while sleeping in zero gee, have some of the noise damped out, as well as cutting out some of the radiation.

Online Robotbeat

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Also, cosmic rays are fast protons for the most part. Many if them far higher energetic than anything we can produce in particle accelerators. Whatever atom they hit, it's going to be smashed to pieces ...

Unless it's a hydrogen atom, of course!

Not at all. High-energy protons (starting with ~300 MeV) "smash to bits" even other individual protons.
What bits?
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