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SpaceX Vehicles and Missions => SpaceX Starship Program => Topic started by: CuddlyRocket on 06/18/2016 12:24 pm

Title: Radiation mitigation strategies for early SpaceX Mars missions
Post by: CuddlyRocket on 06/18/2016 12:24 pm
Higher radiation levels have long been identified as a problem for human Mars missions, both in transit and on the surface, so I thought it might be useful to have a thread focusing on how to reduce – if not entirely eliminate – the additional risk to human health. I propose we concentrate on early missions, including initial colonisation efforts, as later strategies will be greatly influenced by practical experience and advancements in technology, whereas SpaceX will need to confront this issue from the start with what we know now.

I propose to consider transit and surface scenarios together both because there will be common design solutions but also because the lander/return vehicle will be sat on the surface for considerable periods - radiation is damaging to the vehicle’s structure, especially electronics, and it may have to act as a habitat for periods, for example in an emergency.

As this is a SpaceX section, any mitigation scenarios need to be consistent with SpaceX’s design architecture (so far as we understand it!).

There seems to me to be three main classes of mitigation scenarios: A) Characterisation of the problem; B) design of equipment, especially the LRV and any habitats, and C) Use of the environment, including the site of any base or colony and the use of local resources, such as the proposal to use regolith as shielding. A few thoughts to get things started :) :-

A) It’s important to establish both the amount and nature of the radiation environment before designing any protection. There’s a big difference between protecting from galactic cosmic rays and UV, for instance. SpaceX should send the appropriate measuring equipment on its proposed Red Dragon missions, and experiment with potential shielding materials. Interplanetary space is more uniform and better understood than the Martian surface, but any equipment designed for the latter will probably be sufficient for the former.

As for the surface, I understand that the Curiosity rover found the surface radiation load to be ~50% of that in space. But that’s probably an average; what types of radiation were reduced by how much? It also seems to have discovered that the surface is itself radioactive (probably due to eons of GCR bombardment), but how radioactive and what type of radioactivity? One may need to be cautious about piling radioactive regolith against the skin of a habitat!

Then there’s the question of how much this varies from place to place. A younger surface might be less radioactive than an older one (less GCR bombardment). Also, atmosphere pressure, and therefore its radiation shielding, is greater at some places than others.

Any human missions should have radiation measuring equipment with them.

B) This includes choice of material (high hydrogen-content plastics, for instance) and layout. It’s probably not a good idea to have sleeping quarters on the outside, or at least rotate the crew/passengers between inside and outside quarters. In general, the design should keep the humans on the inside and any equipment, consumables, cargo etc on the outside. Also, orient the craft so that the engines and propellant are between the Sun and the humans. Liquid methane should be a good shielding material (hydrogen!), so one possibility worth considering is a facility to draw some from the main tank to a space surrounding a (possibly chilly!) storm shelter.

Designs for habitats etc on the surface should incorporate use of local materials. And designs for a base/colony as a whole should have habitation areas near the centre, with working and storage spaces on the outside.

Part of the design is reducing the time spent in transit. Also, the overall mission duration for any individual astronaut. This is moot for a colonist of course, but initially crew should be on rotation, starting short and gradually increasing the length of time as confidence in understanding the problem and dealing with it grows.

C) This includes choosing an initial site for a base/colony in an area of lower natural radiation; at a lower elevation, for instance. Also, hilly or mountainous terrain is preferable over a plain, as the hills etc will provide additional shielding against radiation coming from the sky. Nestling against a cliff or even under an overhang will maximise this, but radiation is not the only environmental danger!

A site with easily accessible resources utilisable as radiation shielding – regolith, rock, even ice – is desirable. If you propose burying any habitat, then probably best not site your base/colony on solid rock.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 06/18/2016 12:51 pm
I suggest to add thougts on research, how dangerous GCR really is. Present rules are based on maximum assumptions which may turn out to be way pessimistic. I see the need for animal tests over generations on the surface of Mars to get better data. Maybe include plants too, but I doubt that is even necessary.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: philw1776 on 06/18/2016 02:48 pm

C) This includes choosing an initial site for a base/colony in an area of lower natural radiation; at a lower elevation, for instance. Also, hilly or mountainous terrain is preferable over a plain, as the hills etc will provide additional shielding against radiation coming from the sky. Nestling against a cliff or even under an overhang will maximise this, but radiation is not the only environmental danger!


Another reason I like various Vallis Marinaris potential base sites.  Possibility of far less than 180 degree exposure to GCR sky, etc because of surrounding smaller side canyon walls raising the horizon angle.  It's over 2Km below the 0 Mars datum so added atmospheric protection too.  Knockout factor could be lack of subsurface ice.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: the_other_Doug on 06/18/2016 03:54 pm

C) This includes choosing an initial site for a base/colony in an area of lower natural radiation; at a lower elevation, for instance. Also, hilly or mountainous terrain is preferable over a plain, as the hills etc will provide additional shielding against radiation coming from the sky. Nestling against a cliff or even under an overhang will maximise this, but radiation is not the only environmental danger!


Another reason I like various Vallis Marinaris potential base sites.  Possibility of far less than 180 degree exposure to GCR sky, etc because of surrounding smaller side canyon walls raising the horizon angle.  It's over 2Km below the 0 Mars datum so added atmospheric protection too.  Knockout factor could be lack of subsurface ice.

Another possible knockout factor in re valley floors in general, throughout the Vallis Marineris complex, is that the canyon floors tend to be covered by debris that has come down off the canyon walls over billions of years.  It's unknown how deep this talus/debris layer is, and how well consolidated it is.

In other words, a lot of the canyon floors may be covered by tens of meters of loose, unconsolidated dust, rocks and soil.  Thermal inertia as seen by MO indicates a dust cover over these areas -- but it can't give a lot of feel for how deep that layer is.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: philw1776 on 06/18/2016 04:54 pm

C) This includes choosing an initial site for a base/colony in an area of lower natural radiation; at a lower elevation, for instance. Also, hilly or mountainous terrain is preferable over a plain, as the hills etc will provide additional shielding against radiation coming from the sky. Nestling against a cliff or even under an overhang will maximise this, but radiation is not the only environmental danger!


Another reason I like various Vallis Marinaris potential base sites.  Possibility of far less than 180 degree exposure to GCR sky, etc because of surrounding smaller side canyon walls raising the horizon angle.  It's over 2Km below the 0 Mars datum so added atmospheric protection too.  Knockout factor could be lack of subsurface ice.

Another possible knockout factor in re valley floors in general, throughout the Vallis Marineris complex, is that the canyon floors tend to be covered by debris that has come down off the canyon walls over billions of years.  It's unknown how deep this talus/debris layer is, and how well consolidated it is.

In other words, a lot of the canyon floors may be covered by tens of meters of loose, unconsolidated dust, rocks and soil.  Thermal inertia as seen by MO indicates a dust cover over these areas -- but it can't give a lot of feel for how deep that layer is.

Yes, plus the fogs & winds (q.v. sand dunes)  in MV may be a problem as well.
Back to the interesting radiation mitigation topic.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: john smith 19 on 06/18/2016 05:44 pm
Keep in mind that Mar's sea level atmospheric pressure is 1/169 that of Earth. Earth's atmosphere is about 1030Kg/m^2 of protection over the surface.

Your housing doesn't just have to handle average it has to handle a Coronal Mass Ejection event from the Sun that hits it full on, as nothing else will.

This page gives some rough numbers

http://www.swri.org/9what/releases/2013/mars-measurements.htm
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 06/18/2016 06:36 pm
Your housing doesn't just have to handle average it has to handle a Coronal Mass Ejection event from the Sun that hits it full on, as nothing else will.

Really not. Radiation shelters will do for extreme events. No real need to have everything permanently sheltered.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Nathan2go on 06/18/2016 07:55 pm
Keep in mind that Mar's sea level atmospheric pressure is 1/169 that of Earth. Earth's atmosphere is about 1030Kg/m^2 of protection over the surface.
Earth's atmosphere has a mass equal to 32 feet of water (see any SCUBA book).  That's ten tons/m^2.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: gospacex on 06/18/2016 08:28 pm
because the lander/return vehicle will be sat on the surface for considerable periods - radiation is damaging to the vehicle’s structure, especially electronics, and it may have to act as a habitat for periods, for example in an emergency.

Remember the first rule of a galactic traveller? "DONT PANIC!"  :)

"Damage to vehicle structure"... please. Radiation levels which really can damage vehicle structure to a noticeable degree - those are nearly instantly lethal to humans.

Rad-hard electronics is not a new field.

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establish both the amount and nature of the radiation environment before designing any protection. There’s a big difference between protecting from galactic cosmic rays and UV, for instance. SpaceX should send the appropriate measuring equipment on its proposed Red Dragon missions

I would try simply asking NASA for already collected data on Mars and elsewhere. Some 60 years of it.

Quote
C) This includes choosing an initial site for a base/colony in an area of lower natural radiation; at a lower elevation, for instance. Also, hilly or mountainous terrain is preferable over a plain, as the hills etc will provide additional shielding against radiation coming from the sky. Nestling against a cliff or even under an overhang will maximise this, but radiation is not the only environmental danger!
A site with easily accessible resources utilisable as radiation shielding – regolith, rock, even ice – is desirable. If you propose burying any habitat, then probably best not site your base/colony on solid rock.

Buried habitats are likely anyway because they don't require pressure hulls - a rocky roof ~10 meters thick would provide about one atm of pressure - and incidentally, about Earth-grade radiation protection.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/18/2016 08:40 pm
The atmosphere of Mars in a place like Valles Marineris (a good place to settle... Made up problems about being "unconsolidated" notwithstanding) is enough reduce even the worst flares to non-lethal levels.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: whitelancer64 on 06/18/2016 08:46 pm
the Curiosity rover ... seems to have discovered that the surface is itself radioactive (probably due to eons of GCR bombardment), but how radioactive and what type of radioactivity? One may need to be cautious about piling radioactive regolith against the skin of a habitat!

Is there any more information on this?
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 06/18/2016 09:16 pm
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.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: philw1776 on 06/18/2016 09:32 pm
That's depressing.  It will be nearly impossible to get rid of any mice that make it to Mars.   :(
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Nathan2go on 06/18/2016 11:48 pm
Here's an article on (Spacenews http://spacenews.com/curiosity-finds-fairly-benign-radiation-environment-on-mars/ ) which basically says that Mars radiation is not a big deal.  Levels measured by the Curiosity rover on Mars are about the same as in LEO.

And here (http://spacenews.com/35865curiositys-radiation-results/) is Robert Zubrin's even stronger assertion that radiation will not stop us from safely going to Mars. 

Radiophobio is keeping us from fully enjoying the benefits of nuclear power and helping prolong our fossil fuel addictions.  We should not also let it keep us from exploring Mars.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Impaler on 06/19/2016 01:34 am
Long term animal studies on 'synthetic' (aka particle accelerated protons and other nuclei with a similar energy profile) are being done right now.  Indications are that GCR is worse then has been previously suspected, contrary to popular belief NASA's past estimates were optimistic, it is reality which is pessimistic.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/19/2016 01:43 am
Long term animal studies on 'synthetic' (aka particle accelerated protons and other nuclei with a similar energy profile) are being done right now.  Indications are that GCR is worse then has been previously suspected, contrary to popular belief NASA's past estimates were optimistic, it is reality which is pessimistic.
That's not what I heard...
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: DAZ on 06/19/2016 02:45 am
As the subject of discussion is radiation mitigation, some information on radiation risk might be helpful.  This 1st link provides some information on how the NRC looks at it for radiation exposure to industrial workers.

http://oehs.vcu.edu/radiation/risk.PDF

The next link is to some models the NASA uses for planning purposes.

https://spaceradiation.jsc.nasa.gov/irModels/

The NRC, most of the medical community and NASA uses the linear 0 threshold (sometimes also called the linear no threshold LNT) risk model.  There is some evidence that is building at the linear quadratic no threshold model or possibly even a threshold model is more realistic.  The reason the LNT model is mostly used as it is the most conservative, not because there is the most evidence to support it.  Which model you use can have a huge difference on your acceptable dose limits.  It also can have huge political ramifications.  The LNT model was used to help convince the various nuclear powers to sign on to the open-air nuclear test ban Treaty.  As there is no threshold as in the graph always goes to 0 then some amount of radiation released into the air will always result in some deaths.  But if there is a threshold, which does appear to be more likely, then some low level of exposure from bomb tests would be acceptable and the various powers would not of signed on to the treaty.  This same sort of issue could raise its head when you’re talking about colonizing Mars.  Not everybody is exactly bought off on the LNT model though as you can see from the next link.

http://www.rrjournal.org/doi/pdf/10.1667/RR4029.1

Some additional thoughts and considerations:

In most of the studies all ionizing radiation is pretty much lumped together but there is a growing body of evidence that not all of these ionizing radiation’s have precisely the same carcinogen risk factors.  For example GCR has not been well studied but there is some indications that it might have a higher long-term carcinogenic risk factor than some other ionizing radiations.  But the studies are very limited so it could also possibly turn out to be lower.

Long-term chronic radiation exposure may also not be just about how the cancer risks change with exposure.  There is some evidence that it can result an increase in circulatory diseases or damage to the central nervous system. GCR may be more likely to increase the damage to the central nervous system and less of a carcinogen for example.

Fetal exposure limits to ionizing radiation are much lower than for adult humans.  Not a whole lot is known about chronic exposure before birth as the examples are few and far between and great efforts are made to avoid it.  It is known that there appears to be an increase in birth defects the exact cause of this is not known.  It could possibly be carcinogenic or mutagenic in nature but it could also be teratonesis.  If it is the latter then limiting exposure to a critical period (the 1st 3 to 4 months for example) could be all that is necessary.  Unfortunately the only way to find out the answers to this would be to perform forbidden experiments.

With the above in mind there could be other mitigation strategies that could be used other than dose limits.  For example for the 1st missions until things are well-established only send older people and especially non-childbearing women.  Eventually you would obviously have to send the younger people and women will have to have children in order to establish a colony but for the 1st early missions that is not necessary nor possibly even desirable for other reasons.

Another possible mitigation strategy is that we are learning much more about cancer and its genetic causes.  It is probably possible to screen, at least for the earlier missions, those who are less likely to develop cancer problems later in life.

My personal opinion is other than for acute radiation exposure this will all ultimately end up to be a non-problem.  The long-term fight against cancer is finally starting to bear the fruits of this effort.  It is quite possible, in fact very likely, that within the next 10 to 20 years cancer will likely be a non-issue.  There are still the other possible problems from chronic radiation exposure but medicine may eventually also render them a non-issue also.


Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/19/2016 03:24 am
Keep in mind that sun exposure is ALSO (conservatively) considered to follow the linear no-threshold model.

Do we talk about never going outside while the Sun is up? Nearly half of everyone gets skin cancer (and about 2% get the often-fatal melanoma), but we haven't decided to live as vampires.

I think that Mars settlers will take precautions, like pumping water into reservoirs above sleeping quarters or building underground dwellings, but I do not think they'll live in constant fear of radiation all the time.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/19/2016 03:38 am
And there's also drug countermeasures.

For acute doses, Amifostine has been shown to reduce carcinogenic effects of radiation, including a reduction in resultant DNA damage. In this study, for instance, Amifostine reduced odds of developing tumors in mice exposed to radiation to just 1/3 the odds of mice not receiving Amifostine: http://www.ncbi.nlm.nih.gov/pubmed/6093999

Chronic, low doses of radiation are incredibly hard to study since the statistical power is so low, thus we don't know if Amifostine helps for that. But for the very occasional extremely powerful solar flare that occurs with radiation coming in from the zenith, then Amifostine would provide a nice countermeasure.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Eric Hedman on 06/19/2016 05:09 am
And there's also drug countermeasures.

For acute doses, Amifostine has been shown to reduce carcinogenic effects of radiation, including a reduction in resultant DNA damage. In this study, for instance, Amifostine reduced odds of developing tumors in mice exposed to radiation to just 1/3 the odds of mice not receiving Amifostine: http://www.ncbi.nlm.nih.gov/pubmed/6093999

Chronic, low doses of radiation are incredibly hard to study since the statistical power is so low, thus we don't know if Amifostine helps for that. But for the very occasional extremely powerful solar flare that occurs with radiation coming in from the zenith, then Amifostine would provide a nice countermeasure.
This brings up the next complication.  One of the factors that cause drugs to breakdown and lose effectiveness over time is exposure to background radiation.  It might be necessary to be able to manufacture the drugs on the journey.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Dalhousie on 06/19/2016 05:39 am
Long term animal studies on 'synthetic' (aka particle accelerated protons and other nuclei with a similar energy profile) are being done right now.  Indications are that GCR is worse then has been previously suspected, contrary to popular belief NASA's past estimates were optimistic, it is reality which is pessimistic.

Real world studies of areas with high natural radiation would suggest the opposite.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 06/19/2016 05:43 am
Long term animal studies on 'synthetic' (aka particle accelerated protons and other nuclei with a similar energy profile) are being done right now.  Indications are that GCR is worse then has been previously suspected, contrary to popular belief NASA's past estimates were optimistic, it is reality which is pessimistic.
That's not what I heard...

I am not sure but what I understand from tests being performed they cannot use a constant low radiation and apply it in pulses which would not be a valid test IMO. It runs contrary to the Chernobyl observations. The radiation in chernobyl is not high energy particles but it suggests that only constant low radiation levels are a valid tests, not radiation applied in pulses.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 06/19/2016 05:47 am
But for the very occasional extremely powerful solar flare that occurs with radiation coming in from the zenith, then Amifostine would provide a nice countermeasure.
This brings up the next complication.  One of the factors that cause drugs to breakdown and lose effectiveness over time is exposure to background radiation.  It might be necessary to be able to manufacture the drugs on the journey.

Source? GCR is high energy but really low doses. I just cannot believe they have such a strong effect on medication.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: docmordrid on 06/19/2016 07:10 am
And there's also drug countermeasures.

For acute doses, Amifostine has been shown to reduce carcinogenic effects of radiation, including a reduction in resultant DNA damage. In this study, for instance, Amifostine reduced odds of developing tumors in mice exposed to radiation to just 1/3 the odds of mice not receiving Amifostine: http://www.ncbi.nlm.nih.gov/pubmed/6093999

Chronic, low doses of radiation are incredibly hard to study since the statistical power is so low, thus we don't know if Amifostine helps for that. But for the very occasional extremely powerful solar flare that occurs with radiation coming in from the zenith, then Amifostine would provide a nice countermeasure.
This brings up the next complication.  One of the factors that cause drugs to breakdown and lose effectiveness over time is exposure to background radiation.  It might be necessary to be able to manufacture the drugs on the journey.

Portable pharmaceutical factory at your service. Reconfigurable, 1K doses in 24 hours.

http://news.mit.edu/2016/portable-pharmacy-on-demand-0331
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: CuddlyRocket on 06/19/2016 08:43 am
I suggest to add thougts on research, how dangerous GCR really is. Present rules are based on maximum assumptions which may turn out to be way pessimistic. I see the need for animal tests over generations on the surface of Mars to get better data. Maybe include plants too, but I doubt that is even necessary.
It is quite possible, in fact very likely, that within the next 10 to 20 years cancer will likely be a non-issue.  There are still the other possible problems from chronic radiation exposure but medicine may eventually also render them a non-issue also.

Both these may well be true. Unfortunately, SpaceX will have to make its designs in the light of the present rules and medical techniques if it aims to get there by 2024 (ish).

No doubt there will be strong scientific and medical interest in the response of test animals and planets (and the human crew) to the Martian radiation environment and SpaceX will no doubt sell the opportunity to conduct those experiments (or have them conducted). Future iterations of the designs can then take those results and advancing medical techniques into account.

Keep in mind that Mar's sea level atmospheric pressure is 1/169 that of Earth. Earth's atmosphere is about 1030Kg/m^2 of protection over the surface.
Earth's atmosphere has a mass equal to 32 feet of water (see any SCUBA book).  That's ten tons/m^2.

Atmospheric pressure is based on the weight of the atmosphere whereas its shielding effect depends on its mass, so an adjustment has to be made for Mars' lower gravity. That suggests a shielding mass of 155 kg/m^2 (if my arithmetic is correct :) ). That's not to be sneezed at, especially if you're in a thin EVA suit on the surface.

The pressure at the bottom of Hellas Planitia is twice the average surface pressure. One reason why location, location, location, is going to be one of the most significant early decisions!

because the lander/return vehicle will be sat on the surface for considerable periods - radiation is damaging to the vehicle’s structure, especially electronics, and it may have to act as a habitat for periods, for example in an emergency.

Remember the first rule of a galactic traveller? "DONT PANIC!"  :)

Sound advice. :)

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"Damage to vehicle structure"... please. Radiation levels which really can damage vehicle structure to a noticeable degree - those are nearly instantly lethal to humans.

I wasn't really thinking of bulk damage, but minor flaws - and we all know how tiny flaws in components can bring down a rocket - but I'm happy to be reassured if that isn't a problem!

Quote
Rad-hard electronics is not a new field.

But SpaceX doesn't use rad-hard electronics, relying instead of built in redundancy. The Dragon has only had to cope with similar radiation levels in LEO for a few months. Will SpaceX have to reconsider?

Quote
Quote
establish both the amount and nature of the radiation environment before designing any protection. There’s a big difference between protecting from galactic cosmic rays and UV, for instance. SpaceX should send the appropriate measuring equipment on its proposed Red Dragon missions

I would try simply asking NASA for already collected data on Mars and elsewhere. Some 60 years of it.

I certainly would ask! However, 60 years of effort didn't stop Curiosity's radiation measurements being the first conducted on the Martian surface - and then only at that particular location - and nor did it measure the effect of different shielding materials etc. NASA has primarily measured the radiation environment for scientific research purposes, whereas SpaceX should be primarily interested in its engineering implications.

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Quote
A site with easily accessible resources utilisable as radiation shielding – regolith, rock, even ice – is desirable. If you propose burying any habitat, then probably best not site your base/colony on solid rock.

Buried habitats are likely anyway because they don't require pressure hulls - a rocky roof ~10 meters thick would provide about one atm of pressure - and incidentally, about Earth-grade radiation protection.

Are you thinking of a roof made of rock(s), or a solid rock roof? Although I agree on the likelihood of buried habitats, I think excavating solid rock to be a not-inconsiderable effort for early missions! Especially when set against using regolith, for example.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Impaler on 06/19/2016 09:03 am
Long term animal studies on 'synthetic' (aka particle accelerated protons and other nuclei with a similar energy profile) are being done right now.  Indications are that GCR is worse then has been previously suspected, contrary to popular belief NASA's past estimates were optimistic, it is reality which is pessimistic.

Real world studies of areas with high natural radiation would suggest the opposite.

I'm talking about the 'quality factor' of radiation, aka how damaging it is per unit of energy.  GCR is not photons, it is atomic nuclei at near light speed, physically very different and not an apples to apples comparison with radiation from nuclear fission processes.

This thread is devolving into denial of radiation risk rather then actual mitigation strategy.

The most efficient mitigation is to get to mars quickly and then immediate into habitats buried under 3-6 m of regolith and then to explore only from within a very large rover with a 1m thick slab of polyethylene shielding on top.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 06/19/2016 09:13 am
Unfortunately, SpaceX will have to make its designs in the light of the present rules and medical techniques if it aims to get there by 2024 (ish).

For a 2 year trip NASA seems not to consider GCR as a problem. They plan for shielding solar flares, which is well known territory and certainly SpaceX has planned for it. 2 years on they will have plenty of data from at least lab mice and plants. The risk that plants may be affected are remote, to say the least.


I wasn't really thinking of bulk damage, but minor flaws - and we all know how tiny flaws in components can bring down a rocket - but I'm happy to be reassured if that isn't a problem!

GCR is simply not on a level where that can be a concern.

But SpaceX doesn't use rad-hard electronics, relying instead of built in redundancy. The Dragon has only had to cope with similar radiation levels in LEO for a few months. Will SpaceX have to reconsider?

Do you think it is possible that SpaceX has neglected to consider GCR in their designs? They have planned Dragon to be capable for Mars from the beginning.  They will send several Red Dragon and gather data. Then they will know if their design is safe enough for longer missions with BFS. Still plenty of time to implement results. They already have data from their cargo Dragon missions.

Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 06/19/2016 09:19 am
This thread is devolving into denial of radiation risk rather then actual mitigation strategy.

No it isn't. NASA does not think GCR without effective shielding is a showstopper for a 2 year mission. NASA is not known for being reckless. All their estimates contain huge margins of safety. SpaceX is planning for a much shorter transfer time, which gives them a much longer stay time on the surface before the NASA accepted radiation level is reached. Some people just don't subscribe to do long term planning on that basis. I suggest go there, find out. It does not take decades to establish radiation risks on populations with short reproduction cycles, like mice.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 06/19/2016 09:37 am
A question about GCR. My understanding so far was, that it goes through the earth magnetic field, especially the high energy component. It is the atmosphere that stops it. Is that true? It would mean that LEO gives good data on the effect of GCR on electronics.

Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: jjwaDal on 06/19/2016 10:57 am
About radiation we know you receive in space about 1,8 mSv/day which is 200x daily average dose at sea level and 2000x GCR. One has to have numbers and statistics before saying its trivial.
You do receive less than that in ISS (the Earth is pretty close) but... Most crews stayed about 6 months before getting down at sea level and a few ones stayed one year. They didn't have cancer within months but nobody expected that.
For Mars missions we are talking about one year in space and two on the surface of Mars (but  the crew may remain far more to prepare a settlement and long duration stays must be taken into account).
You get 0,67 mSv/day on Mars (say in a spacesuit or a rover), which is 75x average Earth dose and 744x for GCR.
There's too much difference to bet a crew's long term health on the simple idea that they can make it. We're talking about life expectancy and health expectancy not imminent cancer of course.
A buried modular base is an easy solution for a long term stay. 2,5m underground you are at sea level for all radiations and you avoid thermal cycling, have insulation and protection for impacts. A thick water ceiling can be a bonus when your begin ISRU. 5m underground you'd get half daily dose on Earth and be protected from solar flares too.
We won't know the radiation risk before taking it so if we can reduce it to Earth level why take it ?
Assemble your base close to a mesa or at the bottom of a suitable crater and bury it. Everything anyhow will be better underground to avoid dust, UVs, radiation, and so on.
Any sortie will give them much more mSv than they will get on Earth anyhow and in spite of teleoperation there will have some I guess.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: TaurusLittrow on 06/19/2016 11:32 am
I realize that SpaceX is targeting the Mars surface, but the floor of Stickney crater on Phobos provides natural protection from 90% of radiation encountered in interplanetary space. Mars overhead, the bulk of Phobos, and the walls of the crater provide shielding.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: MikeAtkinson on 06/19/2016 11:43 am
NASA's Evolvable Mars Campaign envisages 1100 days round trips, for the Phobos expeditions almost entirely in space. That is about 3 years. On Mars the ground, atmosphere and cliffs etc. reduce cosmic rays to about a third. It is pretty easy to shield habs to arbitrarily low levels, so we really only have to worry about the trip to Mars (make it short), EVAs and time spent in rovers. Over the course of a 40 year working life it is unlikely that anyone will spend more than 1/5 of their time doing EVAs and in rovers.

So in the course of a 40 year working life for a young colonist we have (space equivalent dose of cosmic rays):
0.25 years (trip) + 40*0.33*0.2 years (EVA) = 2.9 years.

This is about what NASA consider acceptable for the EMC astronauts and has been estimated (using LNT model) to give about a 5% extra chance of dying from cancer.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: gospacex on 06/19/2016 12:19 pm
The most efficient mitigation is to get to mars quickly and then immediate into habitats buried under 3-6 m of regolith...

3 meters of regolith is quite enough for rad protection, but not enough for stopping your habitat's roof from wanting to fly upwards :) under internal pressure. I imagine it would be beneficial to know that your base is *statically* structurally stable, I think ceilings will have more than 3 meters of rocks on top. ~10m if we'd go with 1.0 atm air pressure, a bit less if we settle for 0.8.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: gospacex on 06/19/2016 12:27 pm
Quote
Rad-hard electronics is not a new field.

But SpaceX doesn't use rad-hard electronics, relying instead of built in redundancy. The Dragon has only had to cope with similar radiation levels in LEO for a few months. Will SpaceX have to reconsider?

They need to look into that.

Quote
Quote
Buried habitats are likely anyway because they don't require pressure hulls - a rocky roof ~10 meters thick would provide about one atm of pressure - and incidentally, about Earth-grade radiation protection.

Are you thinking of a roof made of rock(s), or a solid rock roof? Although I agree on the likelihood of buried habitats, I think excavating solid rock to be a not-inconsiderable effort for early missions! Especially when set against using regolith, for example.

I'm not an expert in mining or even above-ground construction. Solid rock roof is not necessary and I agree with you, way too work-intensive. Might be a compacted gravel+dust bed; or base can be excavated laterally into an inclined surface, creating "roof" from undisturbed material above.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: TaurusLittrow on 06/19/2016 12:29 pm
So in the course of a 40 year working life for a young colonist we have (space equivalent dose of cosmic rays):
0.25 years (trip) + 40*0.33*0.2 years (EVA) = 2.9 years.

What does the 0.33 factor represent in the equation?
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 06/19/2016 12:30 pm
Stopping your habitat from exploding cannot be done by regolith at the top. The pressure is going sideways as well.Using weight sideways does not work.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: oldAtlas_Eguy on 06/19/2016 02:32 pm
For such manufactured habitats using regolith. I am thinking of a redolith 3D printer that takes regolith and applying specific microwave frequencies to cook small amounts of regolith and fusing it to the already fused regolith into a solid and even a pressure vessel like structure that is structurally sound even without internal pressure.

http://www.hou.usra.edu/meetings/lpsc2014/pdf/1137.pdf (http://www.hou.usra.edu/meetings/lpsc2014/pdf/1137.pdf)

Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: gospacex on 06/19/2016 02:39 pm
Stopping your habitat from exploding cannot be done by regolith at the top. The pressure is going sideways as well.Using weight sideways does not work.

You must be picturing a house with a thick layer of rocks atop it. That's not how it looks. Picture the entire "house" underground.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: oldAtlas_Eguy on 06/19/2016 03:01 pm
Stopping your habitat from exploding cannot be done by regolith at the top. The pressure is going sideways as well.Using weight sideways does not work.

You must be picturing a house with a thick layer of rocks atop it. That's not how it looks. Picture the entire "house" underground.
Easier to manufacture the large habitat on a flat surface than to dig a deep trench/pit.

For the initial habitat a regular set of habitat/containers tightly arranged so that a sheet of Mylar or similar covering that then the loose regolith is piled onto (at least 3m) and then a Quonset hut like S curved access to the set of huts on at least four sides so that the sides are fully protected as well. The surrounding area of the huts have structure that creates a open area with roofing to enable travel on the outside but under the rad shield for hab work or for work on surface equipment (EVA) but still under the rad shield. It is something quick requiring only an ability to dig up regolith from the surrounding surface, pile around the sides in an hill slope and on top.

The reason for the sheet is to protect the hab and structures from the abrasive and corrosive regolith.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: SpacedX on 06/19/2016 03:09 pm
This interactive link is on Radiation and other health effects of living in space.
It's from AlJazeera which is hardly a technology or space resource. But it's really well done:

http://interactive.aljazeera.com/aje/2016/space-astronauts-iss-return-peake-malenchenko-kopra/index.html

We're on the cusp of cheap(er) human access to space. Zero and Lo G and radiation effects are the elephant in the room too many enthusiasts dismiss.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/19/2016 03:39 pm
This interactive link is on Radiation and other health effects of living in space.
It's from AlJazeera which is hardly a technology or space resource. But it's really well done:

http://interactive.aljazeera.com/aje/2016/space-astronauts-iss-return-peake-malenchenko-kopra/index.html

We're on the cusp of cheap(er) human access to space. Zero and Lo G and radiation effects are the elephant in the room too many enthusiasts dismiss.
Elephant in the room??? Are you kidding? We talk about those things CONSTANTLY on this forum. They're the objects on the coffee table that we've been arguing about, analyzing, and testing with real flight data for the better part of a century, now.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 06/19/2016 03:45 pm
Elephant in the room??? Are you kidding? We talk about those things CONSTANTLY on this forum. They're the objects on the coffee table that we've been arguing about, analyzing, and testing with real flight data for the better part of a century, now.

As long as we don't abandon Mars, we are probably just downplaying the risks.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/19/2016 04:12 pm
Elephant in the room??? Are you kidding? We talk about those things CONSTANTLY on this forum. They're the objects on the coffee table that we've been arguing about, analyzing, and testing with real flight data for the better part of a century, now.

As long as we don't abandon Mars, we are probably just downplaying the risks.
I don't think so. I think this is about differences in risk tolerance, not about downplaying risks which are quantified, well-established, and empirically verified.

Quantified is a key point, there.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: gospacex on 06/19/2016 04:37 pm
Stopping your habitat from exploding cannot be done by regolith at the top. The pressure is going sideways as well.Using weight sideways does not work.

You must be picturing a house with a thick layer of rocks atop it. That's not how it looks. Picture the entire "house" underground.

Easier to manufacture the large habitat on a flat surface than to dig a deep trench/pit.

For the initial habitat a regular set of habitat/containers tightly arranged so that a sheet of Mylar or similar covering that then the loose regolith is piled onto (at least 3m) and then a Quonset hut like S curved access to the set of huts on at least four sides so that the sides are fully protected as well. The surrounding area of the huts have structure that creates a open area with roofing to enable travel on the outside but under the rad shield for hab work or for work on surface equipment (EVA) but still under the rad shield. It is something quick requiring only an ability to dig up regolith from the surrounding surface, pile around the sides in an hill slope and on top.

The reason for the sheet is to protect the hab and structures from the abrasive and corrosive regolith.

What's difficult about digging trenches and putting habitats in them with backhoe?

Here ordinary people, not highly skilled engineers, do it on Earth with poor man's "prefab habitat" in a form of a shipping container:

https://www.youtube.com/watch?v=A3EAJex1RVo
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: gospacex on 06/19/2016 04:54 pm
A buried modular base is an easy solution for a long term stay. 2,5m underground you are at sea level for all radiations and you avoid thermal cycling, have insulation and protection for impacts. A thick water ceiling can be a bonus when your begin ISRU. 5m underground you'd get half daily dose on Earth and be protected from solar flares too.
We won't know the radiation risk before taking it so if we can reduce it to Earth level why take it?

Because reducing it to Earth level, no exceptions, would make other aspects of life much harder.

Regolith shielding - yes, why not?

But "thick water ceiling"? I can imagine a few problems with that. Such as "what would happen if it leaks?".

"Teleoperation"? Try to teleoperate a simple task such as bricklaying, car repair or geological prospecting. In a few weeks of such sadism upon yourself, you will *gladly* go and do it yourself in an EVA suit, despite slight cancer risk increase. There are other forms of suffering, not only cancer. Sadistically slow work is one.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 06/19/2016 05:12 pm
Stopping your habitat from exploding cannot be done by regolith at the top. The pressure is going sideways as well.Using weight sideways does not work.

You must be picturing a house with a thick layer of rocks atop it. That's not how it looks. Picture the entire "house" underground.

That works to some extent with a flexible habitat and inflexible surroundings. There needs to be something that takes horizontal forces. And that's really hard to do unless you drill into something very inflexible. You don't want that surrounding giving in to pressure but also not exerting pressure horizontally to the habitat.

Edit: lose regolith would not do that. You need something like solid rock.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: the_other_Doug on 06/19/2016 06:50 pm
In re covering things with regolith, there was a study on building a lunar surface base back in the 70s which envisioned an automated process that basically filled sandbags with regolith.  The sandbags are then simply layered over the hab modules.  Simple, lends itself to automation, and not as messy as trying to dump loose regolith on top of things, or dig trenches, move your habs into them, then bury them.  Doesn't require nearly as much heavy equipment, either.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: gospacex on 06/19/2016 06:55 pm
Stopping your habitat from exploding cannot be done by regolith at the top. The pressure is going sideways as well.Using weight sideways does not work.

You must be picturing a house with a thick layer of rocks atop it. That's not how it looks. Picture the entire "house" underground.

That works to some extent with a flexible habitat and inflexible surroundings. There needs to be something that takes horizontal forces. And that's really hard to do unless you drill into something very inflexible. You don't want that surrounding giving in to pressure but also not exerting pressure horizontally to the habitat.

Edit: lose regolith would not do that. You need something like solid rock.

Agree. A R&D program is clearly in order here. How to make something like "Martian concrete", using as little as possible of imported materials/additives from Earth. Earthly building industry experience will be useful, but you'd need to constantly remind them "no, we can't order superplasticizer from vendor X. Polyurethane sealer vendors are scarce on this planet as well."
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 06/19/2016 09:14 pm
In re covering things with regolith, there was a study on building a lunar surface base back in the 70s which envisioned an automated process that basically filled sandbags with regolith.  The sandbags are then simply layered over the hab modules.  Simple, lends itself to automation, and not as messy as trying to dump loose regolith on top of things, or dig trenches, move your habs into them, then bury them.  Doesn't require nearly as much heavy equipment, either.

Agree, that is doable. As long as the cover is for radiation protection and its weight is not required to give the habitat stability.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/19/2016 10:36 pm
A lot of things that look daunting for single-family homes on Mars are far more viable if done with multi-story buildings. Let's say you want 1m of polyethylene. A big deal with a single level, seems absurd. But if you have a 20 story building, that's just a couple inches average per level (all on top), and the radiation level drops even further just from structure on the lower levels.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Impaler on 06/20/2016 01:40 am
The most efficient mitigation is to get to mars quickly and then immediate into habitats buried under 3-6 m of regolith...

3 meters of regolith is quite enough for rad protection, but not enough for stopping your habitat's roof from wanting to fly upwards :) under internal pressure. I imagine it would be beneficial to know that your base is *statically* structurally stable, I think ceilings will have more than 3 meters of rocks on top. ~10m if we'd go with 1.0 atm air pressure, a bit less if we settle for 0.8.

That idea is totally unfeasible, the structure would either collapse or explode if the internal pressure changed even slightly.  Any habitat structure will need to be a fully self-contained pressure vessel in it's own right and would normally designed to handle 2-3 times the normal operating pressure, an regolith covering is just that a covering with no structural property.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/20/2016 01:52 am
Stopping your habitat from exploding cannot be done by regolith at the top. The pressure is going sideways as well.Using weight sideways does not work.

You must be picturing a house with a thick layer of rocks atop it. That's not how it looks. Picture the entire "house" underground.

That works to some extent with a flexible habitat and inflexible surroundings. There needs to be something that takes horizontal forces. And that's really hard to do unless you drill into something very inflexible. You don't want that surrounding giving in to pressure but also not exerting pressure horizontally to the habitat.

Edit: lose regolith would not do that. You need something like solid rock.

Agree. A R&D program is clearly in order here. How to make something like "Martian concrete", using as little as possible of imported materials/additives from Earth. Earthly building industry experience will be useful, but you'd need to constantly remind them "no, we can't order superplasticizer from vendor X. Polyurethane sealer vendors are scarce on this planet as well."
There were a bunch of ISRU-related SBIR Phase Ones this year. Some even were about making a concrete using regolith.

Here's the list, look in subtopic H1:
http://sbir.nasa.gov/award_topic_list/selection_nid/56319

Here's one: http://sbir.nasa.gov/SBIR/abstracts/16/sbir/phase1/SBIR-16-1-H1.01-7981.html
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Exastro on 06/20/2016 04:05 am
Why not consider using a composite of water ice and basalt fiber as building material?

It seems to me that this would have a lot of advantages.  Both water and basalt are believed to be widespread, and perhaps omnipresent, on or near the surface of Mars.  It's nearly inevitable that any Martian ISRU will be mining and purifying water ice in large quantities for other purposes, so not much additional R&D or infrastructure would be needed to use it for building material.  And given the -60 C mean surface temperature, melting is not likely to be an insurmountable problem (though you'd probably have to insulate the ice from the warm interior air.)

Basalt fiber is literally made by crushing, washing, and melting (at 1400C) basalt, and extruding it.  Little or no additional material is needed.  And the stuff is very strong, with a tensile strength of 4.4 GPa, which is almost an order of magnitude higher than steel re-bar.  The Martian surface is thought to consist mostly of basalt.  (Caveat: the high tensile strength may require careful selection of the raw material.  But we probably don't need anything like 4.4 GPa anyway).

What should we do with this composite?  I'd suggest building something like an igloo: a circular domed building with a rim wall.  A 3 meter thickness should be adequate to provide a safe radiation environment, provided that the composite is mainly water by mass.  The weight of 3 meters of this material should be around 10^4 Pascal, which is about 0.1 atmospheres.  So the stress on this structure will be dominated by tension when the interior is pressurized.  Suppose we arbitrarily choose a 100 meter radius for the building, with a 100 meter radius of curvature for the dome, and Earth sea-level pressure (10^5 Pascal) inside.  Make it a hemisphere.  Then the hoop stress is 1.7 MPa, which suggests that something like 0.1% of the composite (increase that for margin) has to be basalt fiber.  If the water is pure, the dome might even be transparent.

The floor of the dome would have an area of 3e4 square meters (7.8 acres).  Of course you'd want to use more than just the floor, so you'd probably construct multiple levels inside it.  But even if everybody lives on the ground level there's room for about 200 people at the population density of Tokyo.  Taking advantage of stacked floors would allow the population to reach on the order of 1000.  So a dome this size can house a village.

The total mass of the dome would be around 2e5 tons.  So you probably DO need to invest in infrastructure to get the ice.

I picked the size of the dome arbitrarily.  It probably wouldn't make sense to make it much smaller than 10 meters in diameter since at that point the area of the floor isn't much bigger than the cross-sectional area of the ice at floor level.    The upper limit on the size of the dome is the point at which the hoop stress approaches the strength of the basalt fiber; above that it's necessary to thicken the dome beyond what's needed for radiation protection.  This occurs at a radius somewhere below 250 km, big enough for a major metropolis. 

NB: I'm writing while tired, so it's possible I blew a calculation or overlooked something important.  Kudos to anybody who finds a mistake in the above.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 06/20/2016 06:11 am
The Mars ice house.

http://www.marsicehouse.com/

Something needs to be done to avoid the ice sublimating but it seems there are solutions.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Chris_Pi on 06/20/2016 06:21 am
I did a very quick-and-dirty estimate and figure the load on the foundation supporting this thing is going to be 50 tons weight load (I'm probably low) per meter of the dome perimeter. Can't dig anything up quick on what construction here demands but I'm thinking the foundation is going to be a pretty substantial project on it's own.

Also, Heating: How warm is it going to get inside? If the warm atmosphere pooling in the top gets above freezing then it's going to need constant refrigeration to prevent melting. Insulating slows heat transfer but long-term it still soaks through. Lose cooling and you lose the dome. If it's transparent it will act like a greenhouse. People/equipment inside will also add significant heat.

Sublimation is going to eat away at the exterior unless it's covered with something else. Although an opaque cover layer would help with the greenhouse heat issue.

Exposed ice tends to sublimate away if left uncovered out on the surface. Done on a smaller scale this might be useful to support a layer of regolith that does some/most of the shielding work. Maybe this is more useful for longer-term but still temporary shielding around work areas that move around every so often? It's going to creep under it's own weight and probably (eventually) deform enough to collapse.

I do recall kicking around basalt/water pykrete as a material for easy to build landing pads. Flat slabs poured straight onto the ground and maybe some centimeters of regolith cover layer to cut down on sublimation. Temporary and needing repair between uses, But easy to repair and tolerant of damage until it is. A quick search for the word brings up nine threads for that and other uses. It's a bit late early for me to read through it all, But there's probably a lot already covered in those.

Added - guckyfan beat me to posting. Probably some stuff there that makes some of what I just wrote outdated...
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: MikeAtkinson on 06/20/2016 07:28 am
I did a very quick-and-dirty estimate and figure the load on the foundation supporting this thing is going to be 50 tons weight load (I'm probably low) per meter of the dome perimeter. Can't dig anything up quick on what construction here demands but I'm thinking the foundation is going to be a pretty substantial project on it's own.

Worse than that. During building (no air pressure) we have the weight of the dome on the foundation. After presurisation the air pressure would have a net upward force and there would need to be large anchors holding the dome down.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 06/20/2016 07:38 am
It is purely a gut feeling I cannot substantiate. I don't like the idea of achoring at all. I much prefer self contained pressure vessels.

With a pool at the top that doubles as radiation shielding like on some high rise buildings where the pool doubles as feed for fire fighting. The children will love it. Which would mean vertical cylinders like the mock habitats of the Mars Society and some NASA depictions.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/20/2016 12:42 pm
The reason you don't like it is because it's hard to analyze whether or not anchoring would work without a lot more analysis. At least, that's the reason I usually just assume a self-contained pressure vessel. It makes the analysis a lot more straightforward.

That doesn't mean it won't work. We do anchoring all the time at Earth. But it might not be a good idea for early missions.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: gospacex on 06/20/2016 12:48 pm
Why not consider using a composite of water ice and basalt fiber as building material?

It seems to me that this would have a lot of advantages.  Both water and basalt are believed to be widespread, and perhaps omnipresent, on or near the surface of Mars.  It's nearly inevitable that any Martian ISRU will be mining and purifying water ice in large quantities for other purposes, so not much additional R&D or infrastructure would be needed to use it for building material.  And given the -60 C mean surface temperature, melting is not likely to be an insurmountable problem (though you'd probably have to insulate the ice from the warm interior air.)

Basalt fiber is literally made by crushing, washing, and melting (at 1400C) basalt, and extruding it.  Little or no additional material is needed.  And the stuff is very strong, with a tensile strength of 4.4 GPa, which is almost an order of magnitude higher than steel re-bar.  The Martian surface is thought to consist mostly of basalt.  (Caveat: the high tensile strength may require careful selection of the raw material.  But we probably don't need anything like 4.4 GPa anyway).

Why do you need ice in the composite? Just basalt should work. Fiber, bricks, slabs, etc...
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: gospacex on 06/20/2016 12:50 pm
The most efficient mitigation is to get to mars quickly and then immediate into habitats buried under 3-6 m of regolith...

3 meters of regolith is quite enough for rad protection, but not enough for stopping your habitat's roof from wanting to fly upwards :) under internal pressure. I imagine it would be beneficial to know that your base is *statically* structurally stable, I think ceilings will have more than 3 meters of rocks on top. ~10m if we'd go with 1.0 atm air pressure, a bit less if we settle for 0.8.

That idea is totally unfeasible, the structure would either collapse or explode if the internal pressure changed even slightly.

Why?
Do mines on Earth routinely collapse or explode?
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Exastro on 06/20/2016 01:29 pm
I did a quick search on sublimation of water under Martian conditions.  It looks like the rate for water ice under a meter of regolith is around 1 mm/year.  It's substantially faster without the regolith.  The reference is Chevrier et al., GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L02203, 2007.  So I conclude that it's a significant issue but probably not a show-stopper.  I don't like the idea of putting a meter of regolith on the outside for various reasons: it would convert the living space from an airy greenhouse to a cave, for one thing, and might turn out to be challenging to mechanically stabilize it.

One solution might be to encase the ice in tiles of glass a few millimeters thick.  You'd still lose a little ice through the gaps between the tiles, but I bet the rate could be made tolerable. 

I really like the idea that the dome will work as a greenhouse.  That'll significantly reduce the power requirement to maintain the interior temperature.  At 1 AU the Sun gives around 1.5 kW/m^2 if memory serves.  Roughly accounting for the orbital radius of Mars and the day/night cycle it'll be something like 300 W/m^2, or around 10 MW over the area of the dome.

Another quick search didn't turn up the thermal conductivity of ice.  If we had that, it'd be straightforward to estimate the equilibrium temperature.

One way to build the dome might be to start with a thin layer of basalt-fiber cloth.  Seal it with something (a few microns of Mylar, say) so it holds pressure, and inflate it to size with CO2, using enough pressure to get the shape about right (but well below atmospheric, since it's too weak).  Now apply alternating layers of ice and cloth from the inside.  The ice can be sprayed on; you'll get deposition all over the inside of the dome including the floor, so you'll probably need to scrape the floor periodically to recover that. 

Not sure on the anchoring issue.  One obvious alternative would be to build a complete sphere.  But you'd probably want to excavate so that a significant portion of it is underground -- not a small job.  On the other hand, if I did the math right it'd take a rim anchor roughly 3 meters thick and 150 meters deep to hold the dome down against the internal air pressure, if you're relying on gravity to produce the force.  Probably it'd be easier to anchor to bedrock, but still not a trivial job.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: envy887 on 06/20/2016 01:44 pm
The thermal conductivity of ice is about 1.6 to 2.2 W/m-K

http://hyperphysics.phy-astr.gsu.edu/hbase/tables/thrcn.html A good physics or heat transfer textbook should also have this.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/20/2016 02:59 pm
Thick plastic on the outside, thick enough to insulate the water. Put salts in the water to keep it liquid.

It'd be like living in an aquarium bubble. :)

Interestingly, water thick enough to shield you from radiation would provide a markedly blue tint to the interior.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 06/20/2016 03:11 pm
Do mines on Earth routinely collapse or explode?

Yes they certainly do that when the cover is not solid enough.

I strongly believe any structure built on Mars should be stable with and without internal pressure which are two conflicting goals.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/20/2016 03:15 pm
Do mines on Earth routinely collapse or explode?

Yes they certainly do that when the cover is not solid enough.

I strongly believe any structure built on Mars should be stable with and without internal pressure which are two conflicting goals.
Doesn't have to be stable without internal pressure, just has to not be damaged when without internal pressure.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: whitelancer64 on 06/20/2016 03:18 pm
Do mines on Earth routinely collapse or explode?

Yes they certainly do that when the cover is not solid enough.

I strongly believe any structure built on Mars should be stable with and without internal pressure which are two conflicting goals.

How are those conflicting? Most structures don't need internal pressure to prevent collapse. Virtually every building, bridge, tunnel, etc. I can think of would stand just as well in a vacuum (or the very low pressure on Mars) as it does in the air on Earth.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 06/20/2016 03:24 pm
Do mines on Earth routinely collapse or explode?

Yes they certainly do that when the cover is not solid enough.

I strongly believe any structure built on Mars should be stable with and without internal pressure which are two conflicting goals.

How are those conflicting? Most structures don't need internal pressure to prevent collapse. Virtually every building, bridge, tunnel, etc. I can think of would stand just as well in a vacuum (or the very low pressure on Mars) as it does in the air on Earth.

We are talking about a regolith cover. That does not provide any stability and would collapse without internal pressure. In fact it would collapse if the habitat structure does not support its full weight.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: gospacex on 06/20/2016 03:35 pm
Do mines on Earth routinely collapse or explode?

Yes they certainly do that when the cover is not solid enough.

I strongly believe any structure built on Mars should be stable with and without internal pressure which are two conflicting goals.

How are those conflicting? Most structures don't need internal pressure to prevent collapse. Virtually every building, bridge, tunnel, etc. I can think of would stand just as well in a vacuum (or the very low pressure on Mars) as it does in the air on Earth.

On Earth, most of our buildings never have significant pressure difference between "inside" and "outside".

On Mars, during normal operation base must be at 0.7-1.0 atm. Outside is effectively 0 atm.
And yet, you cannot count on your base to *never, ever* depressurize. IOW: you want it to be able to lose pressure and not collapse.

Earth surface building practices not suitable for this.

We have two developed technologies how to build something like that: pressure hulls (submarines, space stations) and mining.

Mining: on Earth mines are built to withstand external pressures (rock pressure quickly rises to many atm). We have technologies how to bore underground tunnels and secure ceilings and walls, even in fractured loose rock, sand, etc.

A similar mine on Mars can be depressurized from 1 atm to 0 and not collapse: for a rather shallow mine, say, 100 meters deep such depressurization event would amount to ceiling pressure increase by 10% (on Mars. On Earth, it's ~3%). Even if this hypothetical mine wasn't designed with depressurization in mind, standard safety factors in construction are usually much higher than 10%.

This makes mine/tunnel construction technologies worth looking for Mars.

That's not saying that underground habitats *must* literally look like mines. They can be cut-and-cover: dig a hole, put habitat load bearing structure there, fill the hole with concrete or equivalent material, pile regolith on top. Mars even provides you with plentiful ready-made holes :D
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: whitelancer64 on 06/20/2016 03:42 pm
Do mines on Earth routinely collapse or explode?

Yes they certainly do that when the cover is not solid enough.

I strongly believe any structure built on Mars should be stable with and without internal pressure which are two conflicting goals.

How are those conflicting? Most structures don't need internal pressure to prevent collapse. Virtually every building, bridge, tunnel, etc. I can think of would stand just as well in a vacuum (or the very low pressure on Mars) as it does in the air on Earth.

We are talking about a regolith cover. That does not provide any stability and would collapse without internal pressure. In fact it would collapse if the habitat structure does not support its full weight.

If the habitat is buried, then the regolith is just piled on top of it. It doesn't need to be self-supporting!

However, it could easily be made to do so, for example, if you wanted to have space around it to inspect the habitat or make external repairs. You'd just need to make the regolith into bricks and build walls with a roof or an arch of the bricks.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Chris_Pi on 06/20/2016 11:52 pm
Worse than that. During building (no air pressure) we have the weight of the dome on the foundation. After presurisation the air pressure would have a net upward force and there would need to be large anchors holding the dome down.
It went right past me somehow that it would be pressurized. Very low pressure (Hopefully enough to not need a pressure suit) could avoid the problem of lifting the dome if thick walls added enough weight. Having the foundation work with heavy compression loads unpressurized and then tensile loads pressurized is a complication that might be best to avoid.

Why do you need ice in the composite? Just basalt should work. Fiber, bricks, slabs, etc...
Ice+binder (sawdust for pykrete) is wonderfully tough stuff. It's also mostly water ice so it's easy to build with really large volumes. Radiation shielding is going to need really large volume/mass anyways. Working with it is more like cast concrete than brick or smaller parts. Pump large volumes into forms and let it freeze VS lots of individually-placed pieces and special martian mortar. Much less labor or specialized machinery and less manufacturing work too. Step one in any basalt-fiber material is make basalt fiber, Step 2 is mix with water and done. No forming and firing to make brick/block/fiber matting or whatever.

Of course it definitely has it's downsides - sublimation, limited temperature range, maybe creep under it's own weight depending on size and age and probably more. If only there was someplace people could get together and talk about that stuff...  ;)
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: mvpel on 06/21/2016 12:06 am
https://m.youtube.com/watch?v=MVWayhNpHr0
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Impaler on 06/21/2016 01:59 am
The most efficient mitigation is to get to mars quickly and then immediate into habitats buried under 3-6 m of regolith...

3 meters of regolith is quite enough for rad protection, but not enough for stopping your habitat's roof from wanting to fly upwards :) under internal pressure. I imagine it would be beneficial to know that your base is *statically* structurally stable, I think ceilings will have more than 3 meters of rocks on top. ~10m if we'd go with 1.0 atm air pressure, a bit less if we settle for 0.8.

That idea is totally unfeasible, the structure would either collapse or explode if the internal pressure changed even slightly.

Why?
Do mines on Earth routinely collapse or explode?

Mines on Earth are not supported by internal pressure, but turn of the century bridge and tunnel building canons under rivers WERE and they DID and killed lots of people in the process.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Dalhousie on 06/21/2016 02:55 am
The most efficient mitigation is to get to mars quickly and then immediate into habitats buried under 3-6 m of regolith...

3 meters of regolith is quite enough for rad protection, but not enough for stopping your habitat's roof from wanting to fly upwards :) under internal pressure. I imagine it would be beneficial to know that your base is *statically* structurally stable, I think ceilings will have more than 3 meters of rocks on top. ~10m if we'd go with 1.0 atm air pressure, a bit less if we settle for 0.8.

That idea is totally unfeasible, the structure would either collapse or explode if the internal pressure changed even slightly.

Why?
Do mines on Earth routinely collapse or explode?

Mines on Earth are not supported by internal pressure, but turn of the century bridge and tunnel building canons under rivers WERE and they DID and killed lots of people in the process.

Internal pressure in caissons was not to provide support but to keep the water out.  Generally they were not more dangerous than mines of the time, except for the fact that initially people were unaware of compression sickness after workers had spent a shift working under pressure. 
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Impaler on 06/21/2016 03:00 am
The short term protection for first landing astronauts would be to put rigid or inflatable Bigelow type habitat complete with internal furnishings on its side in a trench and cover it with lose regolith.  This is the simplest fastest solution when time is important for initial missions and a decent shelter can be created in a few days.


Mid term solution for around a thousand people is likely to construct a wide long roman arch made of a high comppresive strength material and then covered with additional loose materials, the ends are either capped with vertical walls or extend far enough that any radiation path is so tangential to the ground that the atmosphere blocks it sufficiently.  Inside the arch a thinner pressure vessel can be inflated (as it dose not need micro-meteroid protection) and then furnished from the outside.  Two or more floors may be possible this way to make more efficient use of the cover materials.


Long term for a city size habitat an arcade of Gothic arches would be the most efficient solution, pillars of high compression strength can be made by packing regolith into a sleeve with high tensile strength hoops.  These pillars support groin vault made of the aforementioned compressive materials and on top of this the loose regolith is placed.  Underneath you have a high ceiling supported a forest of widely spaced pillars, again large inflated pressure vessels are used in a cellular arrangement between the pillars.  Ten floors can exist in the vertical space (30 m) that would be like that of a medieval cathedral, each floor supported on joists beams running between and through the pillars, the lower most levels on ground level hold transportation systems (hyper-loop?) and the arcade can be expanded on all sides by adding more pillars and groin vaults until the whole city is miles across, the outer edges naturally being the parking areas for vehicles and storage of bulk materials that are insensitive to radiation.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Exastro on 06/21/2016 03:27 am
The thermal conductivity of ice is about 1.6 to 2.2 W/m-K

http://hyperphysics.phy-astr.gsu.edu/hbase/tables/thrcn.html A good physics or heat transfer textbook should also have this.

Thanks!  Taking 2 Watt/(m*Kelvin) and assuming a temperature difference of 40 Kelvin (outer surface at -60C ambient, inner surface at -20C, since it's insulated from the +20C interior air) gives a heat flux of just 1.7 MW if I did my math right.  Too tired to work out the equilibrium temperature right now, but given that the thermal conductivity of the ice (plus the insulation on the inner surface) is low enough to hold the loss to a small fraction of the mean sunlight input, it's a fair bet that keeping the interior warm won't be too hard.  If anything, it might be necessary to install radiators, or perhaps a system to collect the heat and use it for something useful, like melting more ice for ISRU.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Exastro on 06/21/2016 04:34 am
It's probably worth pointing out that any large habitat on Mars is going to be an inflated structure in the sense that the pressure inside will be higher than the gravitational force per unit area on its roof, unless the walls and roof are very thick or the internal pressure is well below an atmosphere.

One atmosphere is around 1e5 Pascal.  A sheet of water (or water ice) that produces this pressure under Martian gravity is 27 meters thick.  For basalt the thickness is still 9 meters. 

If I recall correctly, a radiation shield made of water needs to be around 3 meters thick to get the radiation down to typical Earth surface levels.  For rock (still from vague memory) the corresponding thickness is around 10 meters, the difference being due mainly to the difference in the density of hydrogen atoms and the tendency of rock to produce secondary radiation.

So in a sense the rock is more ideal: building the roof thick enough to shield against radiation also means its weight is approximately supported by the internal air pressure.

If you're worried about the habitat collapsing on your head if the air leaks out, rock is the poorer choice.  The net weight on the supporting structure goes positive as soon as the internal pressure falls significantly.  If you want the habitat to be able to survive full decompression you're forced to build a structure able to hold up about 30 tons per square meter.   

In contrast, for an ice-composite dome the air pressure can support the weight until around 90% of the air leaks out.  If you want to build a supporting structure to keep it up even at near vacuum, that structure can be about an order of magnitude lighter than would be required for rock.  And any chunks of composite that fall to the surface as the dome settles will likely be significantly less dangerous than rock.

So what does a pressure failure look like?  These big structures are pretty tough.  They're not going to pop like balloons, unless they're designed really badly.  Punch a hole in the pressure vessel and the air leaks out through the hole, but the hole doesn't grow much in the process.

It's hard to see what kind of accident can make a big enough hole to allow a significant fraction of the air to leak out before somebody notices and repairs it.  Back a big rover into a 3-meter thick wall of durable composite, or a 10-meter thick rock wall?  Might make a scratch.  Crash a lander onto it?  Maybe...

But never mind.  Suppose a 1-meter hole appeared in the pressure vessel.  I made a very crude estimate of the flow rate through the hole: 170 m^3/sec.  (NB: this just assumes that successive slugs of air at 1.2 kg/m^3 are accelerated through 1 m by the pressure differential).  A 100 m radius hemisphere has a volume of 2e6 cubic meters, so the time constant for pressure loss is over 3 hours... long enough for emergency measures (patches applied, population gotten to shelter).  It's still a pretty bad day, and the people are in trouble if repairs can't be made in the first hour or so... kind of like what I imagine a similarly sized hole might do to the passengers on a small ship at sea.

The rock shelter might be safer than ice composite, but so far I'm not seeing it.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Chris_Pi on 06/21/2016 06:28 am
Just stumbled into this: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.487.7074 (http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.487.7074)

Some more info on ice sublimation rates under regolith of varying thicknesses. If i'm not horribly misreading it even a pretty thin cover layer does quite well. Planning on a century of working life without any replacement of lost ice looks pretty workable. Exposed windows look like they'd run about 1mm/hr loss which could work if there's enough water supply for regular resurfacing on the top. That would need a couple hundred liters per m2 of window weekly.

I've got half an idea about a multi-layer structure with sintered block, ice/basalt mix and regolith that might go up easy and have a long working life. Going to have to poke at some numbers to figure out wall thicknesses and such to get reasonable strength and enough weight to hold it down with pressure inside and still have reasonable loads on the foundation when unpressurized. If all that can even happen at the same time!

mvpel - I see your bricklaying robot and raise a concrete pump!
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/21/2016 01:29 pm
It's probably worth pointing out that any large habitat on Mars is going to be an inflated structure in the sense that the pressure inside will be higher than the gravitational force per unit area on its roof, unless the walls and roof are very thick or the internal pressure is well below an atmosphere.

One atmosphere is around 1e5 Pascal.  A sheet of water (or water ice) that produces this pressure under Martian gravity is 27 meters thick.  For basalt the thickness is still 9 meters. 

If I recall correctly, a radiation shield made of water needs to be around 3 meters thick to get the radiation down to typical Earth surface levels.  For rock (still from vague memory) the corresponding thickness is around 10 meters, the difference being due mainly to the difference in the density of hydrogen atoms and the tendency of rock to produce secondary radiation.

So in a sense the rock is more ideal: building the roof thick enough to shield against radiation also means its weight is approximately supported by the internal air pressure.

If you're worried about the habitat collapsing on your head if the air leaks out, rock is the poorer choice.  The net weight on the supporting structure goes positive as soon as the internal pressure falls significantly.  If you want the habitat to be able to survive full decompression you're forced to build a structure able to hold up about 30 tons per square meter.   

In contrast, for an ice-composite dome the air pressure can support the weight until around 90% of the air leaks out.  If you want to build a supporting structure to keep it up even at near vacuum, that structure can be about an order of magnitude lighter than would be required for rock.  And any chunks of composite that fall to the surface as the dome settles will likely be significantly less dangerous than rock.

So what does a pressure failure look like?  These big structures are pretty tough.  They're not going to pop like balloons, unless they're designed really badly.  Punch a hole in the pressure vessel and the air leaks out through the hole, but the hole doesn't grow much in the process.

It's hard to see what kind of accident can make a big enough hole to allow a significant fraction of the air to leak out before somebody notices and repairs it.  Back a big rover into a 3-meter thick wall of durable composite, or a 10-meter thick rock wall?  Might make a scratch.  Crash a lander onto it?  Maybe...

But never mind.  Suppose a 1-meter hole appeared in the pressure vessel.  I made a very crude estimate of the flow rate through the hole: 170 m^3/sec.  (NB: this just assumes that successive slugs of air at 1.2 kg/m^3 are accelerated through 1 m by the pressure differential).  A 100 m radius hemisphere has a volume of 2e6 cubic meters, so the time constant for pressure loss is over 3 hours... long enough for emergency measures (patches applied, population gotten to shelter).  It's still a pretty bad day, and the people are in trouble if repairs can't be made in the first hour or so... kind of like what I imagine a similarly sized hole might do to the passengers on a small ship at sea.

The rock shelter might be safer than ice composite, but so far I'm not seeing it.
I really like your reasoning but I think much of it is incorrect (though close). :)

3m  is about enough water to get radiation levels to about half of the limit for radiation workers, ie you'd be down to ~25 mSv/year.  This is good enough. But you might want to do better. Earth is 3mSv/year except in some places.

Also, your estimate of pressure leak is too optimistic. The air is going to be traveling through the hole at about the speed of sound, so you have minutes, not hours.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/21/2016 01:53 pm
Also, air pressure need not be a full 100kPa. With training, adaption, and pure oxygen, you can get down to 10kPa. So 30-50kPa is also feasible.

What's possible is you'd have a huge dome at low pressure, say 20-30kPa, and dwellings inside at another 20-30kPa on top of that. That way, most time is spent at higher pressures (and thus you get the health benefits of higher oxygen), but structural mass is much lower, you're less likely to get the bends from rapid decompression, and you have layers of redundancy built in.

I imagine large pressurized dome tents might be used for construction (keep dust out and wind down) at 10kPa, with workers in modest pressure suits (more flexible/comfortable than at full pressure). If pressure is lost in the suits, you won't die, and if pressure is lost in the dome, the workers wouldn't die.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: gospacex on 06/21/2016 01:54 pm
The most efficient mitigation is to get to mars quickly and then immediate into habitats buried under 3-6 m of regolith...

3 meters of regolith is quite enough for rad protection, but not enough for stopping your habitat's roof from wanting to fly upwards :) under internal pressure. I imagine it would be beneficial to know that your base is *statically* structurally stable, I think ceilings will have more than 3 meters of rocks on top. ~10m if we'd go with 1.0 atm air pressure, a bit less if we settle for 0.8.

That idea is totally unfeasible, the structure would either collapse or explode if the internal pressure changed even slightly.

Why?
Do mines on Earth routinely collapse or explode?

Mines on Earth are not supported by internal pressure, but turn of the century bridge and tunnel building canons under rivers WERE and they DID and killed lots of people in the process.

Mines on Earth (specifically tunnels) *have to* withstand the weight (=pressure) of the rocks in places where rocks are loose and fragmented. Underground infrastructure projects have no luxury of building *only* in rock stratas which are stable enough to be self-supporting (even though they do prefer that). They dig where they have to.

Pressure of overhead rocks in a tunnel only 3 meters below ground is already ~1 atm.

Eiksund Tunnel is −287 m.
Seikan Tunnel is 100 meters below seabed and 240 meters below sea level.
Gotthard tunnel is 2.3 km below ground level (under mountains). 57 km long in total.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: envy887 on 06/21/2016 02:37 pm
...Suppose a 1-meter hole appeared in the pressure vessel.  I made a very crude estimate of the flow rate through the hole: 170 m^3/sec.  (NB: this just assumes that successive slugs of air at 1.2 kg/m^3 are accelerated through 1 m by the pressure differential).  A 100 m radius hemisphere has a volume of 2e6 cubic meters, so the time constant for pressure loss is over 3 hours...

...The air is going to be traveling through the hole at about the speed of sound, so you have minutes, not hours.

He estimated a velocity of about Mach 0.65 (volume rate per CS area = velocity), so the fact that flow will be sonicly choked, while true, doesn't give a result 2 orders of magnitude lower. Also, volume flow isn't important. Mass flow is important, and mass flow decreases with density. As the pressure vessel empties itself, the gas density inside decreases, so it can't push as much mass through the opening.

For a 2e6 m3 volume at 1 atm venting to near vacuum through a 1m hole, the pressure will drop 10% about every 13 minutes. So it takes 30 minutes to get to Denver pressures, an hour to ~12k ft altitude equivalent, and 90 minutes to get to 20k ft equivalent. At that point you definitely want more than 20% oxygen, but there's no need for a pressure suit.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/21/2016 03:20 pm
...Suppose a 1-meter hole appeared in the pressure vessel.  I made a very crude estimate of the flow rate through the hole: 170 m^3/sec.  (NB: this just assumes that successive slugs of air at 1.2 kg/m^3 are accelerated through 1 m by the pressure differential).  A 100 m radius hemisphere has a volume of 2e6 cubic meters, so the time constant for pressure loss is over 3 hours...

...The air is going to be traveling through the hole at about the speed of sound, so you have minutes, not hours.

He estimated a velocity of about Mach 0.65 (volume rate per CS area = velocity), so the fact that flow will be sonicly choked, while true, doesn't give a result 2 orders of magnitude lower. Also, volume flow isn't important. Mass flow is important, and mass flow decreases with density. As the pressure vessel empties itself, the gas density inside decreases, so it can't push as much mass through the opening.

For a 2e6 m3 volume at 1 atm venting to near vacuum through a 1m hole, the pressure will drop 10% about every 13 minutes. So it takes 30 minutes to get to Denver pressures, an hour to ~12k ft altitude equivalent, and 90 minutes to get to 20k ft equivalent. At that point you definitely want more than 20% oxygen, but there's no need for a pressure suit.
I concede the point. You are right! My estimate was way offf.

Here's a good approximation:
http://www.geoffreylandis.com/higgins.html
I get roughly 2 hours for the pressure to halve.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Exastro on 06/21/2016 05:56 pm
...Suppose a 1-meter hole appeared in the pressure vessel.  I made a very crude estimate of the flow rate through the hole: 170 m^3/sec.  (NB: this just assumes that successive slugs of air at 1.2 kg/m^3 are accelerated through 1 m by the pressure differential).  A 100 m radius hemisphere has a volume of 2e6 cubic meters, so the time constant for pressure loss is over 3 hours...

...The air is going to be traveling through the hole at about the speed of sound, so you have minutes, not hours.

He estimated a velocity of about Mach 0.65 (volume rate per CS area = velocity), so the fact that flow will be sonicly choked, while true, doesn't give a result 2 orders of magnitude lower. Also, volume flow isn't important. Mass flow is important, and mass flow decreases with density. As the pressure vessel empties itself, the gas density inside decreases, so it can't push as much mass through the opening.

For a 2e6 m3 volume at 1 atm venting to near vacuum through a 1m hole, the pressure will drop 10% about every 13 minutes. So it takes 30 minutes to get to Denver pressures, an hour to ~12k ft altitude equivalent, and 90 minutes to get to 20k ft equivalent. At that point you definitely want more than 20% oxygen, but there's no need for a pressure suit.
I concede the point. You are right! My estimate was way offf.

Here's a good approximation:
http://www.geoffreylandis.com/higgins.html
I get roughly 2 hours for the pressure to halve.

Cool, and thanks to Robotbeat for correcting my vaguely remembered radiation shielding requirement. 

So this ice-composite dome concept seems to be mostly holding together.  There are a few things I'm still somewhat worried about (haven't been able to confirm they aren't serious issues):

1) Sublimation.  I found the paper that Chris_Pi linked, and it does give a sublimation rate which is very high, but the temperatures they studied were between ~255-273 Kelvin, which is not much below melting and well above the -60C mean surface temperature.  So it's still not clear to me whether or not an outer sealing layer is needed to keep the ice from disappearing on human-relevant timescales.

2) Creep.  I'm not sure where to find the data to compute for this.  If it's a problem, i wonder if the basalt fibers can be arranged to arrest it before it gets too far.

3) Solubility of basalt in water.  I saw somewhere that crushed basalt does dissolve to a significant degree in room-temperature water.  Could 10-micron thick fibers be degraded over time by contact with water ice?  If so, can they be coated with something (readily available on Mars) to protect them?

4) Anchoring.  This is an issue almost regardless of what you build with, if you maintain an Earth sea-level atmosphere inside.  I speculate that if anchoring the rim isn't judged secure enough, then multiple columns (normally under tension and reinforced by more basalt fiber) would be anchored to the bedrock and branch out like trees to multiple attachment points on the dome.

I did kick around the idea of going to a ~10 kPa pure-oxygen atmosphere, but I don't know what the long-term health impact would be.  Using a big low-pressure dome to create a somewhat less-than-lethal semi-outdoor work environment is a really interesting idea.  Maybe tweaking it a little could make it better.  Raising the pressure to, say, 20 kPa and adding a bit of inert gas (5 kPa of argon?) would allow the people inside to live almost normally without adding too much cost or risk to the structure and making the higher-pressure buildings inside less necessary.  This is worth thinking about.

Thanks for the cool comments.

Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: the_other_Doug on 06/21/2016 06:01 pm
1) Sublimation.  I found the paper that Chris_Pi linked, and it does give a sublimation rate which is very high, but the temperatures they studied were between ~255-273 Kelvin, which is not much below melting and well above the -60C mean surface temperature.  So it's still not clear to me whether or not an outer sealing layer is needed to keep the ice from disappearing on human-relevant timescales.

The Phoenix lander found a strata of permafrost, including what appeared to layerings of pure water ice, within the first few centimeters of the surface at its polar landing site.  They scooped up a bunch of ice into their sample delivery scoop, and it all sublimated before it could be delivered to the analysis receiving hoppers.  And all of the exposed ice in the trenches Phoenix dug disappeared to sublimation within a few days.

And that was at polar air temperatures.

I think that ice exposed directly to the air on Mars will sublimate within days, not centuries...

Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Exastro on 06/21/2016 06:08 pm
1) Sublimation.  I found the paper that Chris_Pi linked, and it does give a sublimation rate which is very high, but the temperatures they studied were between ~255-273 Kelvin, which is not much below melting and well above the -60C mean surface temperature.  So it's still not clear to me whether or not an outer sealing layer is needed to keep the ice from disappearing on human-relevant timescales.

The Phoenix lander found a strata of permafrost, including what appeared to layerings of pure water ice, within the first few centimeters of the surface at its polar landing site.  They scooped up a bunch of ice into their sample delivery scoop, and it all sublimated before it could be delivered to the analysis receiving hoppers.  And all of the exposed ice in the trenches Phoenix dug disappeared to sublimation within a few days.

And that was at polar air temperatures.

I think that ice exposed directly to the air on Mars will sublimate within days, not centuries...

That's disturbing.  It seems inconsistent with the results of the Chevrier paper, which predicts something like 170 microns/hour at 255K.  Perhaps the polar layers were very porous, with a much higher surface to volume ratio than a flat sheet?
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: envy887 on 06/21/2016 06:35 pm
Ice structures would be a lot easier to construct with some type of lining that would prevent sublimation anyway.

Perhaps something like a polyetheylene quilt that can be inflated to shape, then filled with liquid water (or a water-fiber mix for better strength), and allowed to freeze.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/21/2016 06:47 pm
Ice composite is an idea, but I prefer a clear dome (rigid or flexible, I haven't entirely decided) filled with water. The dome would be made of clear plastic, would be capable of withstanding some internal pressure by itself (enough for survival), but would utilize the weight of the water to counteract internal pressure, or at least to improve the factor of safety of the dome. (I.e. You'd get a FoS of, say, 6 if the dome has water in it, and 1.5-2 if it's empty.) This increase in factor of safety would have the benefit of, say, eliminating reducing creep over long lengths of time.

(UHMWPE could be fairly easily made out of ISRU materials on Mars, has amazing strength, but can have a problem of creep if always maintained at its limiting stress.... so by balancing the weight of the water shielding with the force of the internal pressure underneath, you would eliminate creep without being in danger of failure of full mechanical failure in case of loss of pressure.)

This way, you still get sunlight, although in a pleasant bluish hue. :) If you had sufficiently clear plastic, you could even have great, 360 degree views of the Martian landscape while being fully shielded. And the vast majority of the shielding mass would still be just water, with the structural strength being provided mostly by, say, ISRU-produced UHMWPE. In the early days (before you have a full chemical infrastructure), you might need to import the optical-clarity plastic used for windows, but that'd be a small fraction of the overall mass.

High strength UHMWPE and translucent/somewhat-transparent polypropylene could be fairly easily produced using methane, however. And there's no better non-cryogenic shielding material per unit mass than polyethylene and polypropylene.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/21/2016 06:49 pm
Ice structures would be a lot easier to construct with some type of lining that would prevent sublimation anyway.

Perhaps something like a polyetheylene quilt that can be inflated to shape, then filled with liquid water (or a water-fiber mix for better strength), and allowed to freeze.
Ha! We had the same idea. I was in the middle of writing my post when you posted this.

...except maybe you'd be better off in the liquid phase for water.

And if you wanted to keep the interior warm, you'll have to insulate the inside. To keep water liquid, you can either use salts or you can use some insulation on the outside.

Either way, I think that an at least /partially/ transparent dome should be done, as long as it's not too difficult.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: envy887 on 06/21/2016 07:55 pm
Large liquid domes will have an enormous pressure head, even under Martian gravity. The internal atmosphere pressure won't help counter the pressure head, because they have greatest effect on different parts of the dome - the upper 1/3 or so will be mostly supported by air, but have almost no water pressure, while the lower 1/3 will have  the air pressure will be pushing outward, but very high water pressure pushing inward.

For a 50m hemispherical dome, the inner wall would be taking 380kPa head pressure in compression at the base. Polyethylene sheets would not work well for that.

Maybe it could have liquid (salted) water at the top, where head pressure is low and air pressure mostly directly opposes it, like a 30 meter skylight. The rest could be ice with quilted polyethylene sheeting with cellular baffles filled with air for insulation on the inside.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: gospacex on 06/22/2016 12:22 am
But why bother with ice in the walls/roof at all, with the attendant volatility and melting problems? Pure basalt fiber / basalt bricks/beams/slabs have none of those problems. If you need lower density than "rocks", various kinds of porous bricks are already in use on Earth.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/22/2016 12:26 am
But why bother with ice in the walls/roof at all, with the attendant volatility and melting problems? Pure basalt fiber / basalt bricks/beams/slabs have none of those problems. If you need lower density than "rocks", various kinds of porous bricks are already in use on Earth.
Because water is a MUCH better shielding material per unit mass and may require lower energy to produce than melting rock.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Chris_Pi on 06/22/2016 01:31 am
But why bother with ice in the walls/roof at all, with the attendant volatility and melting problems? Pure basalt fiber / basalt bricks/beams/slabs have none of those problems. If you need lower density than "rocks", various kinds of porous bricks are already in use on Earth.
Because water is a MUCH better shielding material per unit mass and may require lower energy to produce than melting rock.

That, And assembling a 10 meter thick masonry dome is going to be much more labor-intensive than a minimum-thickness form that supports just the topmost layer of water until it freezes and becomes self-supporting. Then the next layer, and the next. And all the shielding mass is delivered in tanker trucks, mixed with bales of chopped basalt fiber and moved into position with not much more than a pump and a hose. Even with a bricklaying robot doing the formwork there's much less of it to be done.

That's disturbing.  It seems inconsistent with the results of the Chevrier paper, which predicts something like 170 microns/hour at 255K.  Perhaps the polar layers were very porous, with a much higher surface to volume ratio than a flat sheet?
Maybe I'm a bit dense today, But what's your concern here? Chevrier looked at ice at ground temperatures and under various thicknesses of cover layers.  The thickness of that layer had a large effect on the sublimation rate. Anything Phoenix saw was possibly quite a bit warmer in the scoop and all of it was completely exposed. It's going to sublimate much faster because of that. Very small volumes in the scoop  to start with, And the ice in the dug out trenches could create it's own thin cover layer and disappear underneath it if it isn't quite a clean as it looked. There's photos of fresh craters that did the same thing relatively quickly - Bright white to start, Looked like every other crater around a few months later.

I'm thinking that it's time to sit down and put together a spreadsheet to play around with some numbers on dome size/thickness/pressure loads to see what's possible to actually build. I'm hoping to get something that has a heavy enough regolith cover layer to not lift itself off it's foundation with pressure inside and simultaneously be strong enough not to collapse without it.

Does anyone have any idea how strong an ice/basalt mix might actually be? I've really got nothing there and am planning on using the (WWII era) sawdust pykrete info off Wikipedia as a likely worst-case starting point.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/22/2016 01:45 am
I think basalt fiber rope is a good material for large structures on Mars. I just don't think it's a good shielding material. If water is as plentiful as is supposed, it's great for shielding.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Aussie_Space_Nut on 06/22/2016 05:57 am
http://www.marsicehouse.com/

http://www.cloudsao.com/MARS-ICE-HOUSE
A transparent ETFE membrane keeps the 3d printed (ice) shells from sublimating into the Martian atmosphere
An integral spiral rib allows printing robots to navigate the interior surface of the ice shells

http://www.cnet.com/au/news/3d-printable-ice-house-could-be-our-home-on-mars/
Theoretically, when the ice is exposed to the thin, low-pressure Martian atmosphere, it would immediately sublimate, or turn into a gas. The idea would be to capture this gas and use the sun's radiation to heat it, turning it into a liquid. This liquid would then be pumped through a robot that climbs the walls and sprays a composite of

(Take Note!)
water, fibre and aerogel
(Take Note!)

along the layered ring structure of the habitat, using a low-volume, close-range nozzle that ensures that any water that freezes mid-trajectory will melt and refreeze upon impact with the wall. The team has successfully demonstrated this technique on Earth.

In order to protect the ice structure from sublimating, a membrane of Dyneema-reinforced EFTE plastic, manufactured on Earth and deployed by the Mars lander, would coat the exterior. An artificial interior atmosphere with higher pressure would keep the ice inside from sublimating too.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: gospacex on 06/22/2016 12:10 pm
But why bother with ice in the walls/roof at all, with the attendant volatility and melting problems? Pure basalt fiber / basalt bricks/beams/slabs have none of those problems. If you need lower density than "rocks", various kinds of porous bricks are already in use on Earth.
Because water is a MUCH better shielding material per unit mass and may require lower energy to produce than melting rock.

That, And assembling a 10 meter thick masonry dome is going to be much more labor-intensive than a minimum-thickness form that supports just the topmost layer of water until it freezes and becomes self-supporting. Then the next layer, and the next. And all the shielding mass is delivered in tanker trucks, mixed with bales of chopped basalt fiber and moved into position with not much more than a pump and a hose. Even with a bricklaying robot doing the formwork there's much less of it to be done.

"Assemble a 10 meter thick masonry dome" would be a VERY stupid plan.

Why not "put a ~0.5 meter thick airtight ceiling made of basalt slabs and bulldoze several meters of regolith over it" plan instead? Even easier than water/ice plan - you do not need to produce water. And when done, you never need to worry that your ceiling can melt, leak or sublimate. I see that as important features of my ceilings.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/22/2016 04:38 pm
What if you built a pyramid on Mars...

Plenty of radiation shielding, and it'd last forever.

...of course, pyramids are a pretty labor-intensive way of building a house. Even with modern equipment, building the Great Giza pyramid would be expected to cost $5 billion.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Chris_Pi on 06/23/2016 01:03 am
"Assemble a 10 meter thick masonry dome" would be a VERY stupid plan.

Why not "put a ~0.5 meter thick airtight ceiling made of basalt slabs and bulldoze several meters of regolith over it" plan instead? Even easier than water/ice plan - you do not need to produce water. And when done, you never need to worry that your ceiling can melt, leak or sublimate. I see that as important features of my ceilings.

Using regolith as radiation shielding instead of water is, using thicknesses earlier in this thread much heavier. 10 meters vs 3, and much denser. Ice still needs a cover layer but 1/2-1 meter is probably enough to cut down sublimation. The roof ends up around a quarter the weight and the basalt support doesn't need nearly as much strength or to be pressure tight. It might end up needing to be anyways to support enough weight that the roof doesn't blow off, But I haven't gotten to working that out yet. And for low/no pressure interiors lighter weight means less support structure.

I haven't gotten very far with it yet, But I had a spreadsheet around previously for some O'Neill Cylinder stuff that I chopped up and used to do a quick first estimate at what size/wall thickness is needed to hold pressure.

Using the strength info for sawdust pykrete off Wikipedia:
Mechanical properties    Ice    Concrete    Pykrete
Crushing strength [MPa]    3.447    17.240    7.584
Tensile strength [MPa]    1.103    1.724    4.826
Density [kg/m³]    910    2500    980

Converted to PSI for my existing spreadsheet:
Crushing 1099.92
Tensile 699.927

And assuming a 3 meter wall thickness simply because that's what would be minimum for radiation shielding anyways and a tensile load safety factor of 1.5 (Low, but the strength probably is too.) goal seek spits out a internal diameter of 190.098 meters  :o for 1 BAR pressure.

Anyone mind doing a quick sanity check on this just to see if I'm in roughly the right ballpark and haven't screwed up the strength conversions or misplaced a decimal point or something? I was kind of hoping for half that diameter, maybe. So I'm sitting here scratching my head and wondering if I got something wrong. Because this looks surprisingly workable.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/23/2016 01:35 am
I comes down to how easily available water is. If it's gushing from the ground or in vast, easily accessible glaciers, then yeah, just use water for shielding because it's far more effective per unit mass than regolith/rock (or air, for that matter).

But if it's in hydrolyzed minerals, then don't use water for mass shielding unless you have very large-scale water mining equipment and a lot of power.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Coastal Ron on 06/23/2016 11:21 pm
What if you built a pyramid on Mars...

Plenty of radiation shielding, and it'd last forever.

...of course, pyramids are a pretty labor-intensive way of building a house. Even with modern equipment, building the Great Giza pyramid would be expected to cost $5 billion.

Likely the cost would go down though if automated or tele-operated equipment was used.

And in any case, for some reason I just don't see humans having a job driving trucks across the surface of Mars...
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/24/2016 12:57 am
What if you built a pyramid on Mars...

Plenty of radiation shielding, and it'd last forever.

...of course, pyramids are a pretty labor-intensive way of building a house. Even with modern equipment, building the Great Giza pyramid would be expected to cost $5 billion.

Likely the cost would go down though if automated or tele-operated equipment was used.

And in any case, for some reason I just don't see humans having a job driving trucks across the surface of Mars...
Agreed. Self-driving trucks on paths in the desert (on Mars) seems to be one of the easiest things to automate.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: BobHk on 06/24/2016 08:42 pm
Simplicity.

Ice is nice but digging a hole is so much simpler. 

I'd prefer using an inflatable structure with inflatable internal bracing (inflatable in the sense that blowers would hold the structure upright while the majority of the 'walls and ceiling' are filled with earth - inflate the 'braces').  The structure would be inflatable so that you can access it from above to pour in scooped up dirt into he walls and braces.  A dome with braces from ceiling to floor in the form of coned pillars would push out and into the ground.  The thickness required at the roof apex would inform how thick the base and walls need to be.  Once you fill it with native dirt you can turn off the carnival air blower (whatever kind of blower you need) and work on the next building.  Access could be via cargo and suitback ports built into the inflatable so martian soils don't intrude on living/working areas.

The simplest solution is using a lot of dirt.  Preserve your water where an accident can't deprive you of it. 

Resources required: 1 Dome infaltable with suit and cargo ports, inflator, shovels, Martian Dirt.  Duct tape for rip repairs.

Even simpler is digging into the ground but we don't know whats there just yet and might need above ground habitats to start.

The material of the dome, though we could use some hotshot radiation proof plastics, should be durable more than anything else.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/24/2016 09:41 pm
Water is much easier to move than dirt, if you have a lot of water.

Imagine a big multi-celled blow-up structure, but filled with water instead. The water could freeze, and there you have it. Instant highly-shielded, transparent structure.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Aussie_Space_Nut on 06/25/2016 05:33 am
And if you mix the water with other ingrediants to form a slurry that freezes as it is applied such that the ice itself is both reinforced and in part self insulated.........

Like the Mars Ice House  :)
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/25/2016 05:55 pm
And if you mix the water with other ingrediants to form a slurry that freezes as it is applied such that the ice itself is both reinforced and in part self insulated.........

Like the Mars Ice House  :)
The Mars Ice House is supposed to be 3D printed with like little robots and also applying like an ETFE film to keep the ice from sublimating. I was talking about something different, where you can skip the 3D printing altogether just by using an inflatable design. A lot simpler. You can pack up the inflatable plastic in a very small, lightweight volume, then simply pump in water and wait for it to freeze.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: BobHk on 06/25/2016 06:02 pm
And if you mix the water with other ingrediants to form a slurry that freezes as it is applied such that the ice itself is both reinforced and in part self insulated.........

Like the Mars Ice House  :)
The Mars Ice House is supposed to be 3D printed with like little robots and also applying like an ETFE film to keep the ice from sublimating. I was talking about something different, where you can skip the 3D printing altogether just by using an inflatable design. A lot simpler. You can pack up the inflatable plastic in a very small, lightweight volume, then simply pump in water and wait for it to freeze.

I'm fond of inflatables for the simplicity - the first time I saw a inflatable shelter that has a concrete mix in the wall that hardens into a permanent building I fell in love with them.  I like 3d printing for buildings but the more i'd have to depend on machines not breaking down the better. 
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/25/2016 06:48 pm
I do 3D printing all the time for my day job. The process is not a quick one. The idea of being able to simply "inflate" a building with water is pretty interesting.

EDIT: Here's a patent on the idea from 1975, I guess we're not the only ones to think of it:
"Inflatable ice igloo"
http://www.google.com/patents/US3909992
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Aussie_Space_Nut on 06/26/2016 04:18 am
And if you mix the water with other ingrediants to form a slurry that freezes as it is applied such that the ice itself is both reinforced and in part self insulated.........

Like the Mars Ice House  :)
The Mars Ice House is supposed to be 3D printed with like little robots and also applying like an ETFE film to keep the ice from sublimating. I was talking about something different, where you can skip the 3D printing altogether just by using an inflatable design. A lot simpler. You can pack up the inflatable plastic in a very small, lightweight volume, then simply pump in water and wait for it to freeze.

I'm fond of inflatables for the simplicity - the first time I saw a inflatable shelter that has a concrete mix in the wall that hardens into a permanent building I fell in love with them.  I like 3d printing for buildings but the more i'd have to depend on machines not breaking down the better.

The Mars Ice House is an inflatable.

Inside the skin is a form that spirals up. The printer grips this form and spirals up accordingly while printing the wall.

Using a mix of fibre, aerogel & water creates a stronger better insulated wall.

Now if you could use a double skinned inflatable as you say, do away with the printer and still be able to pump in the water, aerogel & fibre mix without those ingrediants settling out, then perhaps you have the best of both worlds.

I believe pure water ice is less resilient than the water, aerogel & fibre ice.

I want resilience in case someone hits it with a Rover etc.  :)
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Impaler on 06/26/2016 04:53 am
People need to specify what phase of development they thing their solutions are good for.

Were not going to have water available in that kind of quantity on an initial human landing, any water that you can make will be going into fuel so you can actually return.  Building with water is a mid to long term concept usable only after a super abundance of water is available, and I'm very doubtful any such super abundance will ever be available.

We all agree that on the Mars surface you shield yourself using some kind of local derived material, this is a no brainier and not at all the difficult part of the problem and were just arguing over architectural and building material merits at this point and that can't be resolved without figuring out the entire ISRU scheme and the relative cost of different local materials.



In space transit is where better solutions are needed.  I'll throw out an idea, hibernation type sleep systems allowing passengers to be stacked into very tight well shielded spaces and then to accelerate them at a more modest speed.

http://www.nasa.gov/sites/default/files/files/NIAC_Torpor_Habitat_for_Human_Stasis.pdf

Suppose a cylinder 6 m long and 7 m in diameter, internal volume is 230 m^3, covered in 30 cm of polyethylene and the dosage would be 1 mili sev/day in space at a mass 70 tons of shielding.  Yes that is a lot of shielding mass but it's not prohibitive considering the expected payload masses involved and if it is left in orbit to use during the return transit.  A 5 month transit time each way would thus yield an acceptable radiation dose without cranking up speed to things like 3 months which is likely to require a lot more then 70 tons of additional propellant to do.

Because both increasing propellant mass to shorten duration and adding shielding mass experience strong diminishing marginal utility the optimum solution for any desired radiation level is to mix speed and shielding strategies rather then relying on one exclusively.  The sweet spot between them always moves towards more shielding mass as the vehicle size and payload increase because the surface area to volume ratio makes shielding more efficient while propellant requirements scale linearly with total vehicle mass for any given DeltaV.  Hibernation makes the protected volume much smaller and likewise amplifies the efficiency of shielding, note that only the actual people in transit need to be shielded, life-support equipment and consumables can be outside the shielded zone.

In addition Hydrogenated Boron Nitride nanotubue fiber is being investigated as a material that could serve as both structure and shielding, it may be able to provide shielding very nearly equal to polyethylene and would make an excellent skin for an inflatable Hab.

http://waset.org/publications/9997248/simulation-of-hydrogenated-boron-nitride-nanotube-s-mechanical-properties-for-radiation-shielding-applications
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: john smith 19 on 06/26/2016 07:52 am

Suppose a cylinder 6 m long and 7 m in diameter, internal volume is 230 m^3, covered in 30 cm of polyethylene and the dosage would be 1 mili sev/day in space at a mass 70 tons of shielding.  Yes that is a lot of shielding mass but it's not prohibitive considering the expected payload masses involved and if it is left in orbit to use during the return transit.  A 5 month transit time each way would thus yield an acceptable radiation dose without cranking up speed to things like 3 months which is likely to require a lot more then 70 tons of additional propellant to do.
Or capture an asteroid and get 3m thick rock walls at (relatively) low cost.
Quote
Because both increasing propellant mass to shorten duration and adding shielding mass experience strong diminishing marginal utility the optimum solution for any desired radiation level is to mix speed and shielding strategies rather then relying on one exclusively.  The sweet spot between them always moves towards more shielding mass as the vehicle size and payload increase because the surface area to volume ratio makes shielding more efficient while propellant requirements scale linearly with total vehicle mass for any given DeltaV.  Hibernation makes the protected volume much smaller and likewise amplifies the efficiency of shielding, note that only the actual people in transit need to be shielded, life-support equipment and consumables can be outside the shielded zone.
Good points.

This discussion shows there are in fact multiple possible ways to handle radiation on the Martian surface. Water based solutions do seem to be (sub-consciously ?)  reflecting Earth based thinking, where water is both abundant and available in large quantities on demand. For that to happen early you're going to need to hit an ice strata and have plenty of heat available to melt it. Piling up rock (or sand) seems much more viable as an early stage strategy.

A shorter transit time is always a good idea (fewer consumables, less exposure to GCR and CME, lower MTBF for the ECLSS target etc) but the question is how good an idea compared to simply adding more shielding?
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Oersted on 06/26/2016 08:13 am
It is necessary not just to rethink material availability in the early stages but also equipment availability. What needs to be built must be built using 95% locally-sourced materials but also using small equipment. No backhoes or bulldozers will be going to Mars in the first long while.

I think we need to focus more on iterative processes. Small little repeatable increments that can grow into something big and solid. Bricks are a good example ( Look up "catalan vaults" on youtube). In the Far West they used local materials and on Mars it will be the same story. Basically all we bring along is human ingenuity and very small-scale machinery. However, if we get brick-and-mortar-making machinery going (mixers, oven, formers) we can make lots of building materials in a repeated, iterative manner.

It is really important to keep the materials and equipment constraints in mind and realise that human ingenuity will have to compensate for those constraints in that crucial initial period were we move beyond brought-along habs and are not yet capable of major city-building. 
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Aussie_Space_Nut on 06/26/2016 10:13 am
What about frozen bricks of mud individually covered in plastic?

Then glue them together?
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Hotblack Desiato on 06/26/2016 11:55 am
Simplicity.

Ice is nice but digging a hole is so much simpler. 

I'd prefer using an inflatable structure with inflatable internal bracing (inflatable in the sense that blowers would hold the structure upright while the majority of the 'walls and ceiling' are filled with earth - inflate the 'braces').  The structure would be inflatable so that you can access it from above to pour in scooped up dirt into he walls and braces.  A dome with braces from ceiling to floor in the form of coned pillars would push out and into the ground.  The thickness required at the roof apex would inform how thick the base and walls need to be.  Once you fill it with native dirt you can turn off the carnival air blower (whatever kind of blower you need) and work on the next building.  Access could be via cargo and suitback ports built into the inflatable so martian soils don't intrude on living/working areas.

The simplest solution is using a lot of dirt.  Preserve your water where an accident can't deprive you of it. 

Resources required: 1 Dome infaltable with suit and cargo ports, inflator, shovels, Martian Dirt.  Duct tape for rip repairs.

Even simpler is digging into the ground but we don't know whats there just yet and might need above ground habitats to start.

The material of the dome, though we could use some hotshot radiation proof plastics, should be durable more than anything else.

That posting deserves more attention (especially the dig a hole part).

How about this: have prefabricated inflateable parts, but they should not form a cylindrical module (yes, I know, cylinders offer the second best surface to volume ratio, after spheres), but a D-shaped profile.

Dig a trench (a bit longer and wider than the inflatable module), place the inflatable module inside it, and inflate it.

It just needs a good radiation protection for the ceiling, the side walls are protected by the trenchs walls. Even without any rad-protection on the ceiling, the radiation inside the module should be 1/2 to 1/3 of the regular surface radiation.

If they can make the inflated ceiling rigid enough, the next step would be sand bags. Regolith inside bags, and pile them up on top of that module. The bags will keep the regolith in place, as long as they don't rupture.

For an evolved colony, I would drill tunnels and set up everything inside of them. Underground domes could be interesting.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/26/2016 01:14 pm
...A shorter transit time is always a good idea (fewer consumables, less exposure to GCR and CME, lower MTBF for the ECLSS target etc) but the question is how good an idea compared to simply adding more shielding?
Shorter transit and shielding are two orthogonal ways of reducing radiation dose. Increasing shielding reaches diminishing returns quickly, and trying to reduce GCR dose is a losing battle unless you're on the surface of something. Reducing transit gets exponentially harder, but it doesn't face such diminishing returns and reduces both GCR and expected average solar flare radiation (although still allows possibility of large solar flares).

So I suggest a small amount of shielding to eliminate the vast majority of the solar radiation (and this could include repositioning of supplies and/or propellant... it doesn't have to be mass that is entered/landed) and a twice-as-fast transit that will halve the rest of the dose.

If the fast transit means you need a little more propellant to slow down, you can actually use that propellant for shielding, so there are ways in which a fast transit and shielding can work together.

Instead of solid polyethylene, you can also use ethylene (or propylene or "olifins", which refers to both propylene and ethylene) as liquid shields if kept under pressure. They are significantly more effective than just water (although not DRAMATICALLY so), so if you're going to be launching that mass from Earth, might as well use the more effect liquid olifin shield, either dumping it before aerobrake/capture/entry or, even better, dumping it through the engines as added thrust.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/26/2016 01:16 pm
However: the only things that work better than olifins or polyolifins is hydrogen and methane. Methane is much denser and easier to store than hydrogen, plus SpaceX will already need it for landing and entry.

...so I suspect SpaceX will utilize their fuel for shielding. Methane is almost the most effect possible shielding material, and can also allow faster transit. And they'll need to solve the methane storage problem anyway.

So I suspect that's what they'll use. It's synergistic between fast transit and shielding and fits with the rest of the architecture like a glove.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: gospacex on 06/26/2016 03:34 pm
"Assemble a 10 meter thick masonry dome" would be a VERY stupid plan.

Why not "put a ~0.5 meter thick airtight ceiling made of basalt slabs and bulldoze several meters of regolith over it" plan instead? Even easier than water/ice plan - you do not need to produce water. And when done, you never need to worry that your ceiling can melt, leak or sublimate. I see that as important features of my ceilings.

Using regolith as radiation shielding instead of water is, using thicknesses earlier in this thread much heavier. 10 meters vs 3, and much denser. Ice still needs a cover layer but 1/2-1 meter is probably enough to cut down sublimation. The roof ends up around a quarter the weight

The "much denser" and "4x lighter" parts are wrong.
Surface rocks (as opposed to mean density of the planet) are only 2 to 3 times denser than water. That's solid rocks, with zero porosity. Regolith cover can have any porosity you design into it. For example, pumice is made of rock, but is even lighter than water.

Quote
It might end up needing to be anyways to support enough weight that the roof doesn't blow off, But I haven't gotten to working that out yet.

The math is: you need about 10 meters of rock, in Mars gravity, to counteract 1 atm of internal pressure of the buried habitat.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: gospacex on 06/26/2016 03:38 pm
It is necessary not just to rethink material availability in the early stages but also equipment availability. What needs to be built must be built using 95% locally-sourced materials but also using small equipment.

Absolutely.

Quote
No backhoes or bulldozers will be going to Mars in the first long while.

But they surely can be built there. Technology base needs to be bootstrapped. I remember reading cases where people were forced to do it here on Earth, unfortunately I forgot where... You need to know in which order it's best to do that. If you do it right, it works surprisingly fast. First a shovel, then a kiln, then a lathe, then all sorts of stuff.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/26/2016 09:20 pm
People need to specify what phase of development they thing their solutions are good for.

Were not going to have water available in that kind of quantity on an initial human landing, any water that you can make will be going into fuel so you can actually return.  Building with water is a mid to long term concept usable only after a super abundance of water is available, and I'm very doubtful any such super abundance will ever be available.
Hundreds of tons of water will need to be mined /anyway/ for propellant for each MCT trip. That implies a certain abundance from the very beginning.

Thus, I suspect that while regolith may well be used to shield early habitats, by the time the first habs are actually BUILT on-site (vs habs from Earth covered with regolith), water will NECESSARILY be plentiful.

I suspect water availability will be one of the prime requirements for base location, if not THE prime requirement.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Impaler on 06/27/2016 01:26 am
First I don't believe that BFS will hold the propellant you imagine or that it will need to volumes of water your anticipating and the cost and slow speed of acquiring water will preclude it from being used for anything but propellant and life-support topping off.

Just because a resource is critical dose not mean it is abundant, their are many resources on Earth that are critical to industry such as copper but homes are built out of brick and wood because they are so much cheaper.  The long term building material in almost every time period and every culture is the cheapest local material that will do the job and water is never going to be the cheapest material available on Mars.

The volume of water needed to build a single igloo shelter is likely to be greater then or equal too that needed to make the propellant to return a single BFS, so the trade off to making an ice shelter is to forfeit an entire BFS delivery due to not having the propellant to return the vehicle to Earth.  The additional payload will always be preferable because it can contain regolith moving equipment that can trench and cover more habitats and keep doing so for years on to come.  If the actual habitat to be buried is made on Earth or Mars doesn't change the trade off.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/27/2016 04:37 am
First I don't believe that BFS will hold the propellant you imagine or that it will need to volumes of water your anticipating and the cost and slow speed of acquiring water will preclude it from being used for anything but propellant and life-support topping off....
What you believe is somewhat irrelevant. In order to accomplish what Musk said the vehicle will accomplish, hundreds of tons of water will be required.

Propellant production requirements for MCT necessitates finding a way to acquire water relatively quickly and in vast quantities. Even for the first crewed missions (i.e. before you're really building large structures from purely ISRU materials).

As far as an igloo... let's say we have a building 1m thick and it is hemispherical with a volume of 250m^3 (5m in radius). That will require 150t of water, less than what a single BFS will need (150t of water makes roughly 300t of stoich methane/oxygen... the balance comes from CO2 in the atmosphere... but it's likely the BFS will run a little fuel-rich... BFS will need more than 300t of propellant)
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Exastro on 06/27/2016 04:49 am
The volume of water needed to build a single igloo shelter is likely to be greater then or equal too that needed to make the propellant to return a single BFS, so the trade off to making an ice shelter is to forfeit an entire BFS delivery due to not having the propellant to return the vehicle to Earth.  The additional payload will always be preferable because it can contain regolith moving equipment that can trench and cover more habitats and keep doing so for years on to come.

The point that use of ice as building material competes with using it for propellant is well taken, but I think you have stated it too strongly. 

A quick look at the Wikipedia page https://en.wikipedia.org/wiki/Water_on_Mars#Present_water_ice (https://en.wikipedia.org/wiki/Water_on_Mars#Present_water_ice) offers reason for optimism about the availability of water at the site of a potential colony: the global mean equivalent depth of water ice is around 35 meters.  That's strongly concentrated toward the poles, but even so there appear to be substantial mid-latitude patches of ice.  One patch (at 70 deg latitude) is around 200 meters deep and tens of kilometers wide.  It seems reasonable that availability of such valuable resources would be a strong driver for choosing the site of the colony.  In that case, it's likely that raw ice will be a plentiful natural resource.

Water won't be BFS propellent; at most it'll be part of the feedstock for making propellant.  If the production process involves electrolyzing it, the energy cost is going to be pretty high: it takes around 60 times as much energy to produce a given mass of H2 than it does to melt the water it came from (just counting the heat of fusion).  If the availability of electrical energy is a major constraint, then water will be cheap compared to hydrogen propellant.  If you're assuming methane propellant made by reacting the H2 with CO2 from the atmosphere then each kg of H2 gets you 4 kg of CH4 and 8 kg of O2.  So the energy cost per unit mass of propellant produced this way is about 6 times as high as the energy cost to melt the ice.  That ratio could get somewhat better if you capture and use some of the energy released as heat during the reaction, or worse if you consider that producing electricity is generally less efficiently than producing heat.

Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/27/2016 04:56 am
Heat of fusion of water (0.3MJ/kg) is nearly least 2 orders of magnitude greater than the typical energy required to split water with electrolysis (15MJ/kg to 30MJ/kg when you include realistic efficiency for electrolysis). Plus, as you say, you can use low-quality heat (i.e. waste heat from, say, the exothermic Sabatier reaction or from a nuclear reactor) which is much cheaper than electrical energy. Not just 6 times lower but 50-100 times lower (unless you want to go all the way and vaporize the water, too).

...additionally, salty liquid aquifers may also exist, feeding the linaea that we see all the time with MRO.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: CuddlyRocket on 06/27/2016 06:32 am
It is necessary not just to rethink material availability in the early stages but also equipment availability. What needs to be built must be built using 95% locally-sourced materials but also using small equipment. No backhoes or bulldozers will be going to Mars in the first long while.

Large ones, no. But if you can send a vehicle to Mars you can send a backhoe or bulldozer, especially ones you don't have to sit in (google mini-excavator). This would limit the size of construction task you could undertake, but certainly not as much as doing it by hand!

Quote
I think we need to focus more on iterative processes. Small little repeatable increments that can grow into something big and solid. Bricks are a good example ( Look up "catalan vaults" on youtube). In the Far West they used local materials and on Mars it will be the same story. Basically all we bring along is human ingenuity and very small-scale machinery. However, if we get brick-and-mortar-making machinery going (mixers, oven, formers) we can make lots of building materials in a repeated, iterative manner.

An alternative to brick is dressed stone. One thing Mars does not appear to be short of is rock so it might be useful to send a stonemason along!

Radiation screening need not be in contact with the habitat. Use of local topography is an obvious example, but you could also build a wall (two screen walls with an aggregate centre?) as an alternative or supplement (to fill a gap between large boulders for instance). If you build a dry stone wall (common in areas with lots of rocks), you don't even need mortar. Such a wall can protect more than one habitat at once, and as it's not in contact with the habitats they could be moved around if desired (much harder if you've buried it!). And not just habitats; workspaces and even crew on the surface. Of course, it doesn't help with radiation coming from above, but we don't need a single solution.

The very earliest habitats are either going to have to have radiation screening built in or to use the local environment in as straightforward a manner as possible. You'll need to get something in place relatively quickly and you'll have limited resources of crew and machinery available. Again, local topography fits the bill, but the humble sandbag will probably come into its own!
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 06/27/2016 10:39 am
Horizontal shielding will be of limited use. The atmosphere will already provide some. Shielding as a roof will be much more effective.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/27/2016 12:14 pm
Horizontal shielding will be of limited use. The atmosphere will already provide some. Shielding as a roof will be much more effective.
Or, said another way, as long as you shield above the habitat to like 10-15 degrees above the horizon, you don't need really any horizontal shielding because the path through the atmosphere is so long. That means that panoramic views are still most certainly possible while remaining fully shielded.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Impaler on 06/27/2016 11:33 pm
First I don't believe that BFS will hold the propellant you imagine or that it will need to volumes of water your anticipating and the cost and slow speed of acquiring water will preclude it from being used for anything but propellant and life-support topping off....
What you believe is somewhat irrelevant. In order to accomplish what Musk said the vehicle will accomplish, hundreds of tons of water will be required.

Propellant production requirements for MCT necessitates finding a way to acquire water relatively quickly and in vast quantities. Even for the first crewed missions (i.e. before you're really building large structures from purely ISRU materials).

As far as an igloo... let's say we have a building 1m thick and it is hemispherical with a volume of 250m^3 (5m in radius). That will require 150t of water, less than what a single BFS will need (150t of water makes roughly 300t of stoich methane/oxygen... the balance comes from CO2 in the atmosphere... but it's likely the BFS will run a little fuel-rich... BFS will need more than 300t of propellant)

300 mt of Propellant is exactly what I think BFS would launch from Mars with as Mars orbital rendezvous refueling for crewed missions is the profile I find most reasonable and likely.

So you basically confirmed my point that these igloo's consume an amount of ice equal to an entire BFS propellant load.  Even your assumed propellant loads which are 3-4 times as much still puts the igloo construction in significant competition with propellant production.

Your logic seems to be to assume water will be cheap and plentiful because your architecture depends on it, and your architecture makes no attempt to conserve water because it is assumed to be abundant.

Note that the most water rich region of Mars, the north pole would be a very bad place to build an igloo because the summer temperatures of close to 0 degrees Celsius their and long sunlight hours are more then adequate to rapidly sublimate ice as the whole north pole can be seen to rapidly sublimate off some of it's layers in summer.  The place with maximum water availability thus may be in conflict with building with water.

Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: CuddlyRocket on 06/28/2016 03:48 am
Horizontal shielding will be of limited use. The atmosphere will already provide some. Shielding as a roof will be much more effective.
Or, said another way, as long as you shield above the habitat to like 10-15 degrees above the horizon, you don't need really any horizontal shielding because the path through the atmosphere is so long. That means that panoramic views are still most certainly possible while remaining fully shielded.

I'm not so sure about that - the distance to the horizon is ~4 km on Mars, whereas the scale height for the atmosphere is 11 km. Also, Curiosity measured radiation levels on the surface to be ~50% of those in space - as the planet itself blocks half the sky this suggests the radiation screening effect of the atmosphere is limited to start with.

What this does show is that we need better characterisation of the radiation environment on Mars, including how it changes with angle above the horizon.

As for walls, there's no requirement that they be on the same level as the habitat. They could be used to raise the effective height of some local topography, for instance; especially if there's just a gap.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/28/2016 11:36 am
I am. It's not the distance to the horizon but the distance through the atmosphere to space. If you're an inch high on a perfect sphere, the distance to your horizon is very close, but that has little to do with your radiation shielding level.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: QuantumG on 06/28/2016 10:06 pm
It makes sense that you'd have less radiation exposure inside a deep canyon as the angles at which you can see the sky are less. Of course, if you're trying to use solar power or grow crops, you'll also have less sunlight for that. So then you start looking at mirrors, and at that point you might as well be underground.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: KelvinZero on 06/28/2016 11:28 pm
I accept the various arguments that the MCT will not look like this, but I have always liked the idea of an MCT that could take off leaving a cargo compartment (which is also a landing pad) behind. This would also solve the shielding problem especially if one MCT is fully fuelled before the crew arrive.

Maybe there is still some way by which crew would spend all their sleeping hours in the shadow of the MCT's full tanks?


It makes sense that you'd have less radiation exposure inside a deep canyon as the angles at which you can see the sky are less. Of course, if you're trying to use solar power or grow crops, you'll also have less sunlight for that. So then you start looking at mirrors, and at that point you might as well be underground.
Random idea: For a spherical cow canyon aligned east-west, you can dig into one side while having all your reflectors on the other, angled nicely to stay fairly free of dust. This could give you earth levels of light. As a tweek, what if these reflectors only reflect wavelengths suitable for photosynthesis to avoid baking your garden and use the rest for conventional solar power?

In general I don't think we want to use freak configurations of canyons or caves to dictate our location. It might be ok because I think good potential sites of water near the equator are in canyons which probably come adorned in many frilly bits giving us a lot of choice.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: QuantumG on 06/28/2016 11:37 pm
Random idea: For a spherical cow canyon aligned east-west, you can dig into one side while having all your reflectors on the other, angled nicely to stay fairly free of dust. This could give you earth levels of light.

That's probably the best idea I've heard for a Mars settlement in a while.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/29/2016 12:32 am
Any place not near the poles is going to have more average sunlight than northern Germany or, say, Seattle.

Also, a nice thing about canyons is you can place the solar panels on the plateau far above.

But I don't think you'd get much radiation benefit in a canyon unless right against a wall because most of your radiation comes from a cone 30-40 degrees above the horizon since near the horizon you have a very long path through the atmosphere.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: john smith 19 on 06/29/2016 07:16 am
But I don't think you'd get much radiation benefit in a canyon unless right against a wall because most of your radiation comes from a cone 30-40 degrees above the horizon since near the horizon you have a very long path through the atmosphere.
Since this thread is about radiation mitigation putting your habitat against a canyon wall (ideal inside the wall) would be the logical place. I'd think you'd want it end on to sun rise as well in case of CME's.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/29/2016 12:54 pm
But I don't think you'd get much radiation benefit in a canyon unless right against a wall because most of your radiation comes from a cone 30-40 degrees above the horizon since near the horizon you have a very long path through the atmosphere.
Since this thread is about radiation mitigation putting your habitat against a canyon wall (ideal inside the wall) would be the logical place.
Right, but then you have other hazards like rocks falling down. It's not entirely a free lunch, though still is a good idea.
Quote
I'd think you'd want it end on to sun rise as well in case of CME's.
That's not a concern because the Martian atmosphere at low altitudes already shields you from solar particle events to a level that they don't present any threat to immediate health and don't contribute much at all to your long duration dose. Additionally, if the angle of radiation is near the horizon, you'll have a LOT more effective atmosphere depth and thus virtually no dose at all.

(for the record, radiation from solar particle events doesn't exactly line up with the Sun's rays. The radiation follows the Sun's magnetic field lines, which curve in a spiral away from the Sun. Plus the radiation also doesn't go in a straight line even then because it gyrates around the magnetic field of the Sun, thus coming it at large angles from even the average direction of the radiation...)
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: BobHk on 06/29/2016 07:58 pm
If you are going to have something as manufactured as a solar panel, why not use it as part of your radiation shielding over the habitat?  Two birds one stone. 

As simple as pentagon/hexagon panels (there are CLEAR solar panels now so you can see through it if you want) in a dome made of struts or far less elaborate: roll of solar film over a poly substrate that is rad resistant et cetera.  Placing them away from the habitat seems a bit odd unless you are in a deep area of shadow, like a valley.

Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/29/2016 08:00 pm
Because solar panels are super thin and thus add very little extra shielding. Mars' atmosphere adds like 400kg per square meter, while an optimized solar panel is like a few pounds per square meter at most.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: BobHk on 06/29/2016 08:17 pm
Because solar panels are super thin and thus add very little extra shielding. Mars' atmosphere adds like 400kg per square meter, while an optimized solar panel is like a few pounds per square meter at most.

Lets start thinking thicker then, like these layered cells.  http://engineering.illinois.edu/news/article/7958

I'm a fan of multi function and simply driving a pole into the ground and plopping a solar cell on it seems a waste of a panel unless its doing something else, like also being a panel in my dome or has a layer of poly rad shielding on the bottom too so it can do three things and not just sit there doing one.

Thats just me though.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 06/29/2016 09:28 pm
Oh sure, if your dome/habitat doesn't have a transparent roof, you might as well plop a solar panel on top of it.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Impaler on 06/30/2016 06:29 am
Continuing my calculations on shielding of hibernating astronauts.  A standard fancy casket is 1 cubic meter external volume as measured by it's maximum length width and height, also ISS racks which are used as the current crew sleeping compartments are 1.5 cubic meters and have a considerable amount of room to float in and folks sleep with arms extended and even spend their private time in them.

Thus I conclude that 1 m^3 is a reasonable volume for a pod/chamber/bed to hold 1 person in a medically induced torpor/hibernation and this will account for padding and the immediately adjacent medical monitoring equipment.  Other equipment and systems for life support can be placed a meter or two away on the other side of the shielding wall and penetrate through it by small tubes and holes which negligibly compromise the radiation shielding.

Now take a cylinder just 6 meters long (3 pods lengths), and 5 meters in diameter and the internal volume is 117 m^3, a 30 cm thick shell of polyethylene around this cylinder would mass 43.6 mt, because the pods need to be packed very tightly I see the cylinder opening radially into several wedge shaped sections from a central spindle, this opens up the pods for egress and allows sections of the passengers to be cycled while minimizing disturbance to the rest.  The whole cylinder is housed inside of a Bigelow style inflatable where it forms the central axis.

The shielding mass is a very reasonable total at 436 kg per person to carry along and likely less then the mass saved by having reduced volume, consumables and power needs due to the hibernation process, the SpaceWorks hibernation study estimated savings of nearly 50% on habitat mass for a hibernation system much more spacious then this.  In essence we can give back saved mass for a very efficient shield made possible by high density packing, the GCR dosage is cut to only 1 mili sivert a day which is comparable to ISS dosage rates which we have well characterized and feel confident exposing people to for multiple 6 month tours.

So with that level of shielding we would feel no need to make a fast transit to Mars unless the hibernation process itself is the limiting factor.  Naturally hibernation is highly speculative and I'm doubtful SpaceX is either working on it or betting on it, but it has interesting ramifications for radiation mitigation and solving the general problem of how to accommodate passengers during transit.

Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: CuddlyRocket on 07/02/2016 03:06 am
I thought it useful to perform some actual calculations on the shielding mass given by the Martian atmosphere. Most of the data I'm using comes from this NASA Mars Fact Sheet (http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html).

First, consider the mass of a vertical column of Martian atmosphere with a 1 m^2 cross-section. Mars atmospheric pressure at mean radius is 6.36 millibar, which is therefore 636 Pascals (as 1 bar = 100,000 Pa) or 636 Newtons/m^2. Thus the column of Martian atmosphere has a weight of 636 Newtons. Weight is mass times acceleration due to gravity, which on Mars is 3.70 m/s^2 at the surface. Thus the column of atmosphere has a mass of ~170 kg.

This is the shielding mass for radiation coming from directly overhead. Radiation coming from an oblique angle will have a longer path through the atmosphere and the longest such path is when it grazes the horizon. The distance to the horizon obviously depends on the local topography, but for ease of calculation we can consider a perfectly spherical Mars. The distance d to the horizon on Mars at a height h above the surface is a simple application of Pythagoras' Theorem (derivation here (http://spacemath.gsfc.nasa.gov/Insight/Insight16.pdf)) and simplifies when h << radius of Mars (R=3390 km) to d=SQRT(2Rh).

For h=3m, d is 4.51 km. Surface density of the Martian atmosphere is ~0.02 kg/m^3, so with a 1 m^2 cross-section this is a mass of ~90 kg. To this we have to add on the mass of the atmosphere the radiation had to pass through before it grazed the horizon. To get a handle on this let's consider radiation passing through a point at the scale height of the Martian atmosphere. This is the height at which atmospheric pressure drops by a factor of e=2.71828... and for Mars is 11.1 km. The distance from this height to graze the horizon is obviously the distance to the horizon at this height, which is 274 km - 25 times the scale height. As density varies with height the same way as for the vertical column, we can estimate the mass passed through as being 25 times that of the vertical column case - i.e. ~4,250 kg. Add on the 90 kg, we get a total of ~4,340 kg.

(Charged particle radiation doesn't always travel in straight lines, but there's no reason to think that particles are any more likely to have a longer path than a shorter one, so let's assume this averages out.)

So, we can estimate the average shielding mass of the Martian atmosphere to vary from ~170 kg vertically to 4,340 kg horizontally per square metre. As 1 m^3 of water or ice has a mass of 1,000 kg, this is the same mass as a depth or thickness of water or ice of 17 cm and 4.34 m, respectively.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/02/2016 03:31 am
NASA has a public radiation shielding online calculator that people can use if they sign up (For free) here:

oltaris.nasa.gov

I've used it a few times. Works great! I typically use an altitude of -5km, i.e. Valles Marineris. Could use -7 or even -8km for Hellas Basin, but I think -5km gives you a lot more options.

Works for free space, too.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Impaler on 07/02/2016 04:04 am
Recommend people state shielding in g/cm^2 as this is what most of the literature uses.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Torbjorn Larsson, OM on 07/02/2016 02:08 pm
Seems CMEs are pesky critters, they hit Earth more than once a week during calm periods. [ http://solar.physics.montana.edu/press/faq.html ]

This means the MCT needs to weather some 10s of events at the initial 3 month transit times. (If Elon's architecture delivers what he claims.) I like the methane storm shelter. Interplanetary crafts weather CMEs by shutting high-voltage systems off [ibid], and I don't see why the MCT couldn't do the same if it needs to, so there may be a need for low power emergency environmental air conditioning, water, bibs, snacks, et cetera - info and in-shelter amusement will be streaming to pads, surely?

As for the initial colonization period, I doubt there will be lack of ideas and idiosyncratic solutions fitting the needs and the local environment. [/Captain Obvious, but I have nothing else not already mentioned]

One thing I noticed in the early discussion was the reliance on rodent experiments. Except for establishing general principles (say, of no threshold/threshold dose response models), I wouldn't trust them without primate/ape experiments. The more we study them, the more biological differences between Rodentia and Primate pops up, despite our close ancestry. Evolution is a harsh mistress.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/02/2016 02:37 pm
Primate reproduction in hypogravity might indeed be something we can't just rely on rodents for.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: BobHk on 07/02/2016 03:49 pm
Oh sure, if your dome/habitat doesn't have a transparent roof, you might as well plop a solar panel on top of it.

:) if it has a transparent roof the transparent roof can ALSO be a solar cell...
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: CuddlyRocket on 07/03/2016 02:25 pm
Recommend people state shielding in g/cm^2 as this is what most of the literature uses.

'We can estimate the average shielding mass of the Martian atmosphere to vary from ~17 g vertically to ~434 g horizontally per square centimetre. As 1 cm^3 of water or ice has a mass of 1 g, this is the same mass as a depth or thickness of water or ice of 17 cm and 434 cm, respectively.' :)

Of course, these are rough estimates and shouldn't be taken too precisely. I carried out the calculations because I had my doubts as to Robotbeat's assertion that the Martian atmosphere is a much better radiation shield against sources at angles close to the horizon than those directly overhead. However, it appears that he's right! :) Which does suggest that we don't need to bury habitats etc to provide adequate radiation protection (though there may be other construction reasons to do so).

One caveat is that this doesn't take account of radiation from the surface as detected by Curiosity. However, I expect that this is probably mainly beta or alpha radiation, both of which are relatively easily shielded against.

SpaceX should not rely on theoretical calculations but data and I reiterate that it should make it a priority to fully characterise the radiation environment (amount, type, source, direction etc), especially at any proposed landing or colony sites. Alternatively, they should design their radiation shielding on a modular basis so that it can be simply increased on an ad hoc basis as required.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: RonM on 07/03/2016 03:55 pm
SpaceX should not rely on theoretical calculations but data and I reiterate that it should make it a priority to fully characterise the radiation environment (amount, type, source, direction etc), especially at any proposed landing or colony sites. Alternatively, they should design their radiation shielding on a modular basis so that it can be simply increased on an ad hoc basis as required.

Good point. SpaceX needs good data and local options on radiation shielding. If not, image the morale of the first crew when they get the message, "About that radiation problem, we have a fix for you and it should arrive in two years."
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 07/03/2016 04:40 pm
Please remember we are talking about a potential maximum of 3% increase of cancer risk over their lifetime as a worst case, assuming maximum radiation damage and no advances in cancer treatments. I am sure this would not keep people from flying. What is needed is protection from solar flares during transit and that is possible.

NASA seems to have accepted that risk, even with an orbital mission in the beginning with much higher exposure than a surface mission. It would be much smaller with SpaceX flights and their short transit time at least on the way out. Again it seems safety demands on SpaceX far exceed those on NASA.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/03/2016 05:59 pm
SpaceX should not rely on theoretical calculations but data and I reiterate that it should make it a priority to fully characterise the radiation environment (amount, type, source, direction etc), especially at any proposed landing or colony sites. Alternatively, they should design their radiation shielding on a modular basis so that it can be simply increased on an ad hoc basis as required.

Good point. SpaceX needs good data and local options on radiation shielding. If not, image the morale of the first crew when they get the message, "About that radiation problem, we have a fix for you and it should arrive in two years."
Posts like this and the one it's replying to imply that we know less about radiation than we actually do.

Radiation is already well-characterized on Mars through MSL Curiosity's instruments. Blocking radiation is about putting as many atoms between you and the sky as possible (hydrogen being the lightest atom means less hydrogen by mass is needed for a given number of atoms). So if colonists want lower radiation doses (though I'm sure they'll be about as inured to it as a fisherman is to UV), then they already know what to do.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: philw1776 on 07/03/2016 11:01 pm
Please remember we are talking about a potential maximum of 3% increase of cancer risk over their lifetime as a worst case, assuming maximum radiation damage and no advances in cancer treatments. I am sure this would not keep people from flying. What is needed is protection from solar flares during transit and that is possible.

NASA seems to have accepted that risk, even with an orbital mission in the beginning with much higher exposure than a surface mission. It would be much smaller with SpaceX flights and their short transit time at least on the way out. Again it seems safety demands on SpaceX far exceed those on NASA.

What's ironic is that most folks here have little problem imagining incredible advances in aerospace technology leading to BFRs and BFSs with advanced capabilities over the next decade or two but somehow cannot imagine that genetic engineering and cancer treatments will not advance much over the next couple decades.  Far, far more $ are invested in these rapidly advancing technologies than SpaceX's few billion$ in Mars transport R&D.  I expect remediation of cancers and genetic injury to advance greatly in the next 10-20 years. 
Why will this exponentially expanding field of knowledge suddenly stop???

Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: stoker5432 on 07/04/2016 12:13 am
Please remember we are talking about a potential maximum of 3% increase of cancer risk over their lifetime as a worst case, assuming maximum radiation damage and no advances in cancer treatments. I am sure this would not keep people from flying. What is needed is protection from solar flares during transit and that is possible.

NASA seems to have accepted that risk, even with an orbital mission in the beginning with much higher exposure than a surface mission. It would be much smaller with SpaceX flights and their short transit time at least on the way out. Again it seems safety demands on SpaceX far exceed those on NASA.

What's ironic is that most folks here have little problem imagining incredible advances in aerospace technology leading to BFRs and BFSs with advanced capabilities over the next decade or two but somehow cannot imagine that genetic engineering and cancer treatments will not advance much over the next couple decades.  Far, far more $ are invested in these rapidly advancing technologies than SpaceX's few billion$ in Mars transport R&D.  I expect remediation of cancers and genetic injury to advance greatly in the next 10-20 years. 
Why will this exponentially expanding field of knowledge suddenly stop???

Probably because a lot of us have experienced generations of are loved ones dieing of cancer. Sorry but the human body is vastly more complex than a future BFR or BFS.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: QuantumG on 07/04/2016 12:27 am
If current trends continue, deaths from cancer will be eliminated by 2050. It's actually more likely that the trend will accelerate and cancer deaths will be eliminated in the early 2030s.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/04/2016 01:03 am
Please remember we are talking about a potential maximum of 3% increase of cancer risk over their lifetime as a worst case, assuming maximum radiation damage and no advances in cancer treatments. I am sure this would not keep people from flying. What is needed is protection from solar flares during transit and that is possible.

NASA seems to have accepted that risk, even with an orbital mission in the beginning with much higher exposure than a surface mission. It would be much smaller with SpaceX flights and their short transit time at least on the way out. Again it seems safety demands on SpaceX far exceed those on NASA.

What's ironic is that most folks here have little problem imagining incredible advances in aerospace technology leading to BFRs and BFSs with advanced capabilities over the next decade or two but somehow cannot imagine that genetic engineering and cancer treatments will not advance much over the next couple decades.  Far, far more $ are invested in these rapidly advancing technologies than SpaceX's few billion$ in Mars transport R&D.  I expect remediation of cancers and genetic injury to advance greatly in the next 10-20 years. 
Why will this exponentially expanding field of knowledge suddenly stop???

Probably because a lot of us have experienced generations of are loved ones dieing of cancer. Sorry but the human body is vastly more complex than a future BFR or BFS.

A lot of us have experienced generations of our loved ones living exclusively on Earth. That alone doesn't preclude the situation changing in the future. Things change. We are, indeed, making huge improvements in both genetic engineering (CRISPR) and cancer treatment (able to basically cure some forms of leukemia by programming the body's immune system). It's certainly plausible that large steps will be made over the next few decades given the advancements of the last decade.

Edit/Lar: PoliteJim3000 stalled without finding a good reword.... so I just nuked the whole sentence... no need for excessive snark.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: RonM on 07/04/2016 02:46 am
Elon Musk is talking about landing people on Mars in 8 years. That will take equipment designed and built for testing in the next couple of years.

While there is good reason to believe in medical advances, you can't count on them occurring on your schedule. Medical research takes years, sometimes decades of development and testing. Hoping that there will be a cure for cancer is not a radiation mitigation strategy, it is wishful thinking. Especially in such a short timeframe that SpaceX is discussing. Remember this thread is about early SpaceX Mars missions, not ones decades from now.

Let's get back to talking about current engineering.

Also, what's wrong with testing radiation levels at the landing site before sending people? Isn't more data a good thing?
 
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/04/2016 05:25 am
Elon Musk is talking about landing people on Mars in 8 years. That will take equipment designed and built for testing in the next couple of years.

While there is good reason to believe in medical advances, you can't count on them occurring on your schedule. Medical research takes years, sometimes decades of development and testing....
And cancer from space radiation is likely to take decades to develop. It's as relevant as everything else.

But I suspect the first explorers will laugh at the radiation. Far greater and more immediate dangers await them on the journey.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/04/2016 05:30 am
...
Also, what's wrong with testing radiation levels at the landing site before sending people? Isn't more data a good thing?
We already have with MSL Curiosity. Knowing the actual on-site radiation level to better than 10% accuracy is not going to make a noticeable difference in radiation mitigation strategies versus what we currently know (which bounds the radiation levels that will be received). I wouldn't be surprised if they did measure radiation data anyway, but it's not in any way required nor really all that helpful.

It's exactly analogous to taking a UV meter with you to the beach when you already know the UV exposure to within 10%. You're going to wear sunscreen, a hat, or not regardless of a reading of high precision. Remember the conservative model says there's no threshold, so exact dose (i.e. within 10%) makes almost no difference on your likely behavior.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: john smith 19 on 07/04/2016 08:51 am
We already have with MSL Curiosity. Knowing the actual on-site radiation level to better than 10% accuracy is not going to make a noticeable difference in radiation mitigation strategies versus what we currently know (which bounds the radiation levels that will be received). I wouldn't be surprised if they did measure radiation data anyway, but it's not in any way required nor really all that helpful.

It's exactly analogous to taking a UV meter with you to the beach when you already know the UV exposure to within 10%. You're going to wear sunscreen, a hat, or not regardless of a reading of high precision. Remember the conservative model says there's no threshold, so exact dose (i.e. within 10%) makes almost no difference on your likely behavior.
Wouldn't a more accurate be analogy be where you know the average radiation level not having a radiation alarm suggests you'll get caught short if there's a sudden rise, say from GCR's.

The obvious mitigation remains getting inside or under a thickish layer of Martian regolith.

But here's a tricky question. Any likely lander will deliver maybe 1% of the Earths atmosphere level of 1030g/cm^2 of mass (from Dr Logan's presentation, although IIRC the LM delivered about 1/2that) and a suit maybe   0.1% of Earth.

So what happens if you land a crew and the rad level starts to rise a lot and you need lots of EVA to put the regolith round the lander?

The cold equations suggest a)Sit tight in the lander and hope it's enough b)Divide the work among all crew to limit exposure and get it covered ASAP c) One or more crew will die.

That's a worst case scenario. I have no sense of how likely that situation will be once surface operations start. Maybe it's a once in a millennia event and beneath worry. Maybe remote control earth moving equipment that can be run from the MCT's on their way to Mars (as the time lag drops) would be a very sensible investment?

Earth's atmosphere is so effective we only notice it when it's protection is not there anymore.

Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: philw1776 on 07/04/2016 12:33 pm
Please remember we are talking about a potential maximum of 3% increase of cancer risk over their lifetime as a worst case, assuming maximum radiation damage and no advances in cancer treatments. I am sure this would not keep people from flying. What is needed is protection from solar flares during transit and that is possible.

NASA seems to have accepted that risk, even with an orbital mission in the beginning with much higher exposure than a surface mission. It would be much smaller with SpaceX flights and their short transit time at least on the way out. Again it seems safety demands on SpaceX far exceed those on NASA.

What's ironic is that most folks here have little problem imagining incredible advances in aerospace technology leading to BFRs and BFSs with advanced capabilities over the next decade or two but somehow cannot imagine that genetic engineering and cancer treatments will not advance much over the next couple decades.  Far, far more $ are invested in these rapidly advancing technologies than SpaceX's few billion$ in Mars transport R&D.  I expect remediation of cancers and genetic injury to advance greatly in the next 10-20 years. 
Why will this exponentially expanding field of knowledge suddenly stop???

Probably because a lot of us have experienced generations of are loved ones dieing of cancer. Sorry but the human body is vastly more complex than a future BFR or BFS.

Lost several family members to cancers that I've survived.  Had two very different types.  21st century tech saved my ass and other body parts twice.  As this was BEFORE any of the more fundamental cell & genetic based therapies now in development, there is valid reason to extrapolate that greatly improved radiation mitigation therapies may arise in a couple decades.  Don't know why this somehow confounds folks.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: RonM on 07/04/2016 02:39 pm
One solution to early exploration radiation issues would be to use an unmanned flight to drop off a habitat over engineered to protect against radiation. It can be used during the first mission while other structures are being deployed, buried under regolith, tanks filled with water, etc.

If early explorers are the typical middle-aged astronauts and the increased risk of cancer is not too high, it should be reasonable. Depending on the complexity of future cancer treatments, these first astronauts might have to fly back to Earth for treatment, assuming they get to stay on Mars in the first place.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: BobHk on 07/04/2016 02:44 pm
We already have with MSL Curiosity. Knowing the actual on-site radiation level to better than 10% accuracy is not going to make a noticeable difference in radiation mitigation strategies versus what we currently know (which bounds the radiation levels that will be received). I wouldn't be surprised if they did measure radiation data anyway, but it's not in any way required nor really all that helpful.

It's exactly analogous to taking a UV meter with you to the beach when you already know the UV exposure to within 10%. You're going to wear sunscreen, a hat, or not regardless of a reading of high precision. Remember the conservative model says there's no threshold, so exact dose (i.e. within 10%) makes almost no difference on your likely behavior.
Wouldn't a more accurate be analogy be where you know the average radiation level not having a radiation alarm suggests you'll get caught short if there's a sudden rise, say from GCR's.

The obvious mitigation remains getting inside or under a thickish layer of Martian regolith.

But here's a tricky question. Any likely lander will deliver maybe 1% of the Earths atmosphere level of 1030g/cm^2 of mass (from Dr Logan's presentation, although IIRC the LM delivered about 1/2that) and a suit maybe   0.1% of Earth.

So what happens if you land a crew and the rad level starts to rise a lot and you need lots of EVA to put the regolith round the lander?

The cold equations suggest a)Sit tight in the lander and hope it's enough b)Divide the work among all crew to limit exposure and get it covered ASAP c) One or more crew will die.

That's a worst case scenario. I have no sense of how likely that situation will be once surface operations start. Maybe it's a once in a millennia event and beneath worry. Maybe remote control earth moving equipment that can be run from the MCT's on their way to Mars (as the time lag drops) would be a very sensible investment?

Earth's atmosphere is so effective we only notice it when it's protection is not there anymore.

Heres a solution that is both small footprint and cheap...

THICK Plastic parkas for exterior work in high radiation situations. 

Small and easily carried, of use even in normal rad day work on Mars but if you need three put on three and send that one guy out into it for the job...

It might suck and make you less nimble and photogenic but its simple and you get to carry your rad barrier with you assembling the permanent shelter. 
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/04/2016 05:21 pm
We already have with MSL Curiosity. Knowing the actual on-site radiation level to better than 10% accuracy is not going to make a noticeable difference in radiation mitigation strategies versus what we currently know (which bounds the radiation levels that will be received). I wouldn't be surprised if they did measure radiation data anyway, but it's not in any way required nor really all that helpful.

It's exactly analogous to taking a UV meter with you to the beach when you already know the UV exposure to within 10%. You're going to wear sunscreen, a hat, or not regardless of a reading of high precision. Remember the conservative model says there's no threshold, so exact dose (i.e. within 10%) makes almost no difference on your likely behavior.
Wouldn't a more accurate be analogy be where you know the average radiation level not having a radiation alarm suggests you'll get caught short if there's a sudden rise, say from GCR's.....
GCRs don't cause a sudden rise. You're thinking of SPEs, solar particle events.

But actually, it's not a concern once you're on the surface of any of the likely landing areas. The atmosphere makes all such events quite mild by the time the radiation gets to the surface.

40g/cm^2 average shielding does a lot for SPEs. It doesn't stop all GCRs, but it does a great job against SPEs.

(SPEs are not very anisotropic... they don't come in straight from the Sun, and they also don't come in from the same direction... More like they generally come stronger from one hemisphere of the sky than the other.)


But anyway, we have instruments that measure such events well before they get to Mars so the astronauts will have adequate warning anyway.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/04/2016 05:23 pm
We already have with MSL Curiosity. Knowing the actual on-site radiation level to better than 10% accuracy is not going to make a noticeable difference in radiation mitigation strategies versus what we currently know (which bounds the radiation levels that will be received). I wouldn't be surprised if they did measure radiation data anyway, but it's not in any way required nor really all that helpful.

It's exactly analogous to taking a UV meter with you to the beach when you already know the UV exposure to within 10%. You're going to wear sunscreen, a hat, or not regardless of a reading of high precision. Remember the conservative model says there's no threshold, so exact dose (i.e. within 10%) makes almost no difference on your likely behavior.
Wouldn't a more accurate be analogy be where you know the average radiation level not having a radiation alarm suggests you'll get caught short if there's a sudden rise, say from GCR's.

The obvious mitigation remains getting inside or under a thickish layer of Martian regolith.

But here's a tricky question. Any likely lander will deliver maybe 1% of the Earths atmosphere level of 1030g/cm^2 of mass (from Dr Logan's presentation, although IIRC the LM delivered about 1/2that) and a suit maybe   0.1% of Earth.

So what happens if you land a crew and the rad level starts to rise a lot and you need lots of EVA to put the regolith round the lander?

The cold equations suggest a)Sit tight in the lander and hope it's enough b)Divide the work among all crew to limit exposure and get it covered ASAP c) One or more crew will die.

That's a worst case scenario. I have no sense of how likely that situation will be once surface operations start. Maybe it's a once in a millennia event and beneath worry. Maybe remote control earth moving equipment that can be run from the MCT's on their way to Mars (as the time lag drops) would be a very sensible investment?

Earth's atmosphere is so effective we only notice it when it's protection is not there anymore.

Heres a solution that is both small footprint and cheap...

THICK Plastic parkas for exterior work in high radiation situations. 

Small and easily carried, of use even in normal rad day work on Mars but if you need three put on three and send that one guy out into it for the job...

It might suck and make you less nimble and photogenic but its simple and you get to carry your rad barrier with you assembling the permanent shelter.
That'd be worth it in deep space, but on the planet's surface, you already have like a foot's worth of shielding. A thick parka wouldn't really make any difference and neither would it really be necessary.

(but NASA Langley does have mockups of such garments for radiation protection, so it's not a bad idea! just more relevant for deep space than Mars surface)
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: IntoTheVoid on 07/05/2016 04:42 am
But anyway, we have instruments that measure such events well before they get to Mars so the astronauts will have adequate warning anyway.

What instruments? Instruments for earth warning are out of position for Mars (or in-transit) warning.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/05/2016 10:54 am
But anyway, we have instruments that measure such events well before they get to Mars so the astronauts will have adequate warning anyway.

What instruments? Instruments for earth warning are out of position for Mars (or in-transit) warning.
We have instruments around the Sun. It's possible we may need more in coming years for transit, but it's really a concern primarily for transit where you don't have natural shielding and also when you're closer to the Sun.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 07/05/2016 12:23 pm
We have instruments around the Sun. It's possible we may need more in coming years for transit, but it's really a concern primarily for transit where you don't have natural shielding and also when you're closer to the Sun.

That's one thing I wondered about. Should solar flare radiation not be half as strong near Mars as it is near earth? Reducing risk as well as the atmosphere of Mars?
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: JasonAW3 on 07/05/2016 04:20 pm
We have instruments around the Sun. It's possible we may need more in coming years for transit, but it's really a concern primarily for transit where you don't have natural shielding and also when you're closer to the Sun.

That's one thing I wondered about. Should solar flare radiation not be half as strong near Mars as it is near earth? Reducing risk as well as the atmosphere of Mars?

As I seem to remember, radiation is reduced by the square of the distance from the source.

     That said, lacking a magnetic field and having an atmosphere only 1% as dense as Earth's, one would still receive a massive dose of radiation on Mars, less than one would on the Moon, assuming similar solar flare activty, but still enough to hit your lifetime dosage in a fairly quick manner.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/05/2016 04:32 pm
...

     That said, lacking a magnetic field and having an atmosphere only 1% as dense as Earth's, one would still receive a massive dose of radiation on Mars, less than one would on the Moon, assuming similar solar flare activty, but still enough to hit your lifetime dosage in a fairly quick manner.
Incorrect. Low pressure doesn't mean low shielding. Again, the radiation dose is reduced DRAMATICALLY by the ~400kg per square meter average of CO2 (40g/cm^2). It's equivalent to about a FOOT of shielding, enough to reduce solar flares until they're not relevant to your lifetime dose.

This meme that Mars' atmosphere is basically nothing is continually misleading to these discussions, and I wish people would back up such claims with actual analysis, because if they did bother to do any analysis, it'd show they are false.


Compare to this slide:
http://www.bioedonline.org/slides/content-slides/space-life-sciences/radiation-effects/?pageaction=displaySlideDetails&tk=56&dpg=13

CO2 is a much better shield per unit mass than aluminum AND Mars' 40g/cm^2 of CO2 (sky weighted average at human landing sites) is higher than the 30g/cm^2 shielding shown in the blue line, the greatest amount of shielding considered in that graph.

Even with the WORST flare recorded here (in half a century of recording), Mars would shield you to levels WELL below your 30-day limit, let alone annual or lifetime limit. And every other flare would likewise be shielded to levels not much exceeding the background level of 0.67mSv/day.

And 0.67mSv/day is low enough to be outside nearly constantly during the work week (~35 hours per day) without exceeding US radiation worker guidelines (and astronauts are usually allowed about twice that).

EDIT:Slight a-hole reduction editing.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: oldAtlas_Eguy on 07/05/2016 06:28 pm
...

     That said, lacking a magnetic field and having an atmosphere only 1% as dense as Earth's, one would still receive a massive dose of radiation on Mars, less than one would on the Moon, assuming similar solar flare activty, but still enough to hit your lifetime dosage in a fairly quick manner.
Wrong. Low pressure doesn't mean low shielding. As I KEEP repeating, the radiation dose is reduced DRAMATICALLY by the ~400kg per square meter average of CO2 (40g/cm^2). It's equivalent to about a FOOT of shielding, enough to reduce solar flares until they're not relevant to your lifetime dose.

This meme that Mars' atmosphere is basically nothing is continually misleading to these discussions, and I wish people would back up such claims with actual analysis, because if they did bother to do any analysis, it'd show they are false.


Compare to this slide:
http://www.bioedonline.org/slides/content-slides/space-life-sciences/radiation-effects/?pageaction=displaySlideDetails&tk=56&dpg=13

CO2 is a much better shield per unit mass than aluminum AND Mars' 40g/cm^2 of CO2 (sky weighted average at human landing sites) is higher than the 30g/cm^2 shielding shown in the blue line, the greatest amount of shielding considered in that graph.

Even with the WORST flare recorded here (in half a century of recording), Mars would shield you to levels WELL below your 30-day limit, let alone annual or lifetime limit. And every other flare would likewise be shielded to levels not much exceeding the background level of 0.67mSv/day.

And 0.67mSv/day is low enough to be outside nearly constantly during the work week (~35 hours per day) without exceeding US radiation worker guidelines (and astronauts are usually allowed about twice that).

Hmmm...

So policy would be something like once a flare is detected to go to a higher shielded area when outside ASAP but not a critical drop and run type of policy. Plus there could be unpressurized umbrella like structures put up so that shields could be readily available while they wait on faster shielded transport back to the colony/base.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: envy887 on 07/05/2016 06:40 pm
Wouldn't a more accurate be analogy be where you know the average radiation level not having a radiation alarm suggests you'll get caught short if there's a sudden rise, say from GCR's.
...
The cold equations suggest a)Sit tight in the lander and hope it's enough b)Divide the work among all crew to limit exposure and get it covered ASAP c) One or more crew will die.
...

GCRs don't suddenly rise. GCR radiation is actually mitigated during coronal mass ejections, and otherwise have an approximate permanent ceiling. SPE radiation is harder to predict, but the Mars atmosphere significantly reduces it. During 500 days of surface data collection, MSL only saw a single SPE peak which rose to about 20% above Mars background levels, whereas in deep space it saw SPE peaks 3000% over than the already much higher background.

Nobody's going to die on the Mars surface from acute exposure to SPE radiation, so none of those scenarios are remotely realistic. If the data from MSL is anywhere near typical, there is likely not even a need for extra shelter during SPEs.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: JasonAW3 on 07/05/2016 06:50 pm
...

     That said, lacking a magnetic field and having an atmosphere only 1% as dense as Earth's, one would still receive a massive dose of radiation on Mars, less than one would on the Moon, assuming similar solar flare activty, but still enough to hit your lifetime dosage in a fairly quick manner.
Wrong. Low pressure doesn't mean low shielding. As I KEEP repeating, the radiation dose is reduced DRAMATICALLY by the ~400kg per square meter average of CO2 (40g/cm^2). It's equivalent to about a FOOT of shielding, enough to reduce solar flares until they're not relevant to your lifetime dose.

This meme that Mars' atmosphere is basically nothing is continually misleading to these discussions, and I wish people would back up such claims with actual analysis, because if they did bother to do any analysis, it'd show they are false.


Compare to this slide:
http://www.bioedonline.org/slides/content-slides/space-life-sciences/radiation-effects/?pageaction=displaySlideDetails&tk=56&dpg=13

CO2 is a much better shield per unit mass than aluminum AND Mars' 40g/cm^2 of CO2 (sky weighted average at human landing sites) is higher than the 30g/cm^2 shielding shown in the blue line, the greatest amount of shielding considered in that graph.

Even with the WORST flare recorded here (in half a century of recording), Mars would shield you to levels WELL below your 30-day limit, let alone annual or lifetime limit. And every other flare would likewise be shielded to levels not much exceeding the background level of 0.67mSv/day.

And 0.67mSv/day is low enough to be outside nearly constantly during the work week (~35 hours per day) without exceeding US radiation worker guidelines (and astronauts are usually allowed about twice that).

Ok, so what you're saying is that no radiation shielding is really needed? 

BTW; that "Myth" has been something that has been more or less been drilled into my head by educators and other supposedly well educated people.  So, please don't jump down my throat for simply repeating what has been ground into my head for a good portion of my life.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: envy887 on 07/05/2016 07:29 pm
...

     That said, lacking a magnetic field and having an atmosphere only 1% as dense as Earth's, one would still receive a massive dose of radiation on Mars, less than one would on the Moon, assuming similar solar flare activty, but still enough to hit your lifetime dosage in a fairly quick manner.
Wrong. Low pressure doesn't mean low shielding. As I KEEP repeating, the radiation dose is reduced DRAMATICALLY by the ~400kg per square meter average of CO2 (40g/cm^2). It's equivalent to about a FOOT of shielding, enough to reduce solar flares until they're not relevant to your lifetime dose.

This meme that Mars' atmosphere is basically nothing is continually misleading to these discussions, and I wish people would back up such claims with actual analysis, because if they did bother to do any analysis, it'd show they are false.


Compare to this slide:
http://www.bioedonline.org/slides/content-slides/space-life-sciences/radiation-effects/?pageaction=displaySlideDetails&tk=56&dpg=13

CO2 is a much better shield per unit mass than aluminum AND Mars' 40g/cm^2 of CO2 (sky weighted average at human landing sites) is higher than the 30g/cm^2 shielding shown in the blue line, the greatest amount of shielding considered in that graph.

Even with the WORST flare recorded here (in half a century of recording), Mars would shield you to levels WELL below your 30-day limit, let alone annual or lifetime limit. And every other flare would likewise be shielded to levels not much exceeding the background level of 0.67mSv/day.

And 0.67mSv/day is low enough to be outside nearly constantly during the work week (~35 hours per day) without exceeding US radiation worker guidelines (and astronauts are usually allowed about twice that).

Ok, so what you're saying is that no radiation shielding is really needed? 

BTW; that "Myth" has been something that has been more or less been drilled into my head by educators and other supposedly well educated people.  So, please don't jump down my throat for simply repeating what has been ground into my head for a good portion of my life.

As Robotbeat noted, it's important to put real numbers in these discussions. If you're standing on the surface of Mars every day with just atmospheric shielding, you're getting a similar dosage per day as the astronauts on ISS, and the variation due to SPE's is small - on the order of 50%.

Obviously that's not ideal, but it's not a immediate death sentence either. These dosage rates are far to small to cause acute effects, and it would take some 10 years to reach 1 Sv of exposure (which raises the lifetime risk of getting cancer by about 5%).
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/05/2016 08:32 pm
It's definitely true that educated people also have big misconceptions about these issues. Radiation especially is one of those areas where there are a lot of counter-intuitive effects, or at least things that don't quite mesh with the zeroth-order assumptions even an educated person might naively bring into the discussion.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: stoker5432 on 07/06/2016 04:03 am
A lot of us have experienced generations of our loved ones living exclusively on Earth. That alone doesn't preclude the situation changing in the future. Things change. We are, indeed, making huge improvements in both genetic engineering (CRISPR) and cancer treatment (able to basically cure some forms of leukemia by programming the body's immune system). It's certainly plausible that large steps will be made over the next few decades given the advancements of the last decade.

I'm not doubting that cancer treatment will improve. It's the comparison of building the BFR and BFS to curing cancer I find questionable. There will never be a 100% cure rate for cancer or complete elimination of the long list of side affects of the treatments. BFR and BFS will be marvels of engineering, but not in the same league.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: QuantumG on 07/06/2016 04:22 am
Never is a long time.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: stoker5432 on 07/06/2016 04:37 am
Never is a long time.

Yes never was too strong of word. I hope I'm very wrong. Watching my mother fight and than die from cancer is something that I would very much like to spare my children from experiencing.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: tleski on 07/06/2016 05:41 pm
I would not bet on cancer therapies as a radiation mitigation strategy. The progress in medicine is far from linear. A good example is infectious diseases. After the spectacular successes of antibiotics and vaccination campaigns in the 70s, it was assumed that these diseases are the thing of the past. Almost 50 years later we are facing a mounting crisis with increasing number of multi-drug resistant bacterial pathogens with very few new antibiotics in the pipeline and a slew of emerging viral diseases. And treating infectious diseases is relatively simple comparing to cancer. The problem is not in the mastering of engineering technologies (genetic engineering in this case) but in the understanding of the extremely complex and heterogenous systems which we want to fix.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: JasonAW3 on 07/06/2016 06:57 pm

CO2 is a much better shield per unit mass than aluminum AND Mars' 40g/cm^2 of CO2 (sky weighted average at human landing sites) is higher than the 30g/cm^2 shielding shown in the blue line, the greatest amount of shielding considered in that graph.

Even with the WORST flare recorded here (in half a century of recording), Mars would shield you to levels WELL below your 30-day limit, let alone annual or lifetime limit. And every other flare would likewise be shielded to levels not much exceeding the background level of 0.67mSv/day.

And 0.67mSv/day is low enough to be outside nearly constantly during the work week (~35 hours per day) without exceeding US radiation worker guidelines (and astronauts are usually allowed about twice that).

Interesting...  So how would dry ice compare to polyethylchloride as a radiation shield?

    Perhaps a layered approach of water ice and dry ice contained in shells of polyethylchloride could work as an acceptable radiation shield system on spacecraft.  Keeping the whole thing cool could be a trick, but not so much as trying to keep cryogenic fuels cold in space.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Eric Hedman on 07/06/2016 07:44 pm
I would not bet on cancer therapies as a radiation mitigation strategy. The progress in medicine is far from linear. A good example is infectious diseases. After the spectacular successes of antibiotics and vaccination campaigns in the 70s, it was assumed that these diseases are the thing of the past. Almost 50 years later we are facing a mounting crisis with increasing number of multi-drug resistant bacterial pathogens with very few new antibiotics in the pipeline and a slew of emerging viral diseases. And treating infectious diseases is relatively simple comparing to cancer. The problem is not in the mastering of engineering technologies (genetic engineering in this case) but in the understanding of the extremely complex and heterogenous systems which we want to fix.
I agree that medicine, especially cancer treatments, has advanced non-linearly so counting on advances in cancer treatment is not a slam dunk.  The most common form of cancer from ionizing radiation is leukemia which has had the best gains in treatment over recent years.  Using CRISPR to reprogram white cells to go after the cancer cells is going into clinical trials in the near future.  Monoclonal antibodies to light up cancer cells for  the immune system to find is also showing great promise.  We have some fairly effective existing, but rough, chemo therapies for leukemia (my brother recently went through the treatment).  With the other things in the pipeline we may know before too many years that we have effective treatments that can handle the most likely radiation induced cancers fairly effectively.

https://en.wikipedia.org/wiki/Radiation-induced_cancer (https://en.wikipedia.org/wiki/Radiation-induced_cancer)
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: envy887 on 07/06/2016 07:53 pm
I'm not sure why that much effort (layered ice, plastic, and dry ice) is required to build a radiation shield on a spacecraft. Background radiation is too high to live for years, but far from an acute issue. A fast transit is much better than dedicated shielding mass. Solar Particles are the real concern, but that flux is highly anisotropic.

BFS will always have EDL fuel in its tanks. Collect that methalox in the bottom of a domed tank with a little ullage thrust, and hide behind it. Then your shielding mass is 2 thicknesses of tank wall, plus 1 thickness of pressure vessel (at least 5g/cm^2 of Al-Li total) plus ~40 tonnes of methalox spread over a ~10m average diameter circle (or ~50 g/cm^2). That ~5 g/cm^2 of Al-Li alloy skin, plus ~50 g/cm^2 of methalox, will reduce even the worst SPEs to levels that are within an order of magnitude of Mars surface levels. That's acceptable for a 4-month transit, since SPEs only last a few days.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/06/2016 07:53 pm

CO2 is a much better shield per unit mass than aluminum AND Mars' 40g/cm^2 of CO2 (sky weighted average at human landing sites) is higher than the 30g/cm^2 shielding shown in the blue line, the greatest amount of shielding considered in that graph.

Even with the WORST flare recorded here (in half a century of recording), Mars would shield you to levels WELL below your 30-day limit, let alone annual or lifetime limit. And every other flare would likewise be shielded to levels not much exceeding the background level of 0.67mSv/day.

And 0.67mSv/day is low enough to be outside nearly constantly during the work week (~35 hours per day) without exceeding US radiation worker guidelines (and astronauts are usually allowed about twice that).

Interesting...  So how would dry ice compare to polyethylchloride as a radiation shield?

    Perhaps a layered approach of water ice and dry ice contained in shells of polyethylchloride could work as an acceptable radiation shield system on spacecraft.  Keeping the whole thing cool could be a trick, but not so much as trying to keep cryogenic fuels cold in space.
You mean polyethylene?

CO2 is not as good as polyethylene or water, it's comparable with carbon (graphite), but it's much better than aluminum.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Impaler on 07/06/2016 08:31 pm
CO2 is inferior to H2O, it is better then aluminum because aluminum it just about the worst shielding material commonly considered for aerospace applications.  Polyethylene not PVC is the preferred plastic shielding material and it is second only to water, their is thus no reason to bring CO2 on a spacecraft as shielding as it is inferior to much easier to handle materials.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: stoker5432 on 07/06/2016 09:30 pm
With the other things in the pipeline we may know before too many years that we have effective treatments that can handle the most likely radiation induced cancers fairly effectively.

So are we assuming there will be a robust health care system on Mars to administer those treatments? Seems like accessiblity and cost are both being ignored with this kind of strategy.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/07/2016 01:25 am
CO2 is inferior to H2O, it is better then aluminum because aluminum it just about the worst shielding material commonly considered for aerospace applications.  Polyethylene not PVC is the preferred plastic shielding material and it is second only to water, their is thus no reason to bring CO2 on a spacecraft as shielding as it is inferior to much easier to handle materials.
Right, but CO2 may be a good shielding material on Mars because it's literally ubiquitous on the surface. All you need is a compressor and a tank.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 07/07/2016 03:51 am
With the other things in the pipeline we may know before too many years that we have effective treatments that can handle the most likely radiation induced cancers fairly effectively.

So are we assuming there will be a robust health care system on Mars to administer those treatments? Seems like accessiblity and cost are both being ignored with this kind of strategy.

And here I am and have thought this is about the early flights where people come back to earth and can be treated here decades later.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: jpo234 on 07/07/2016 07:13 am
Maybe just for giggles: I vaguely remember that I read that Inspiration Mars considered (carefully bagged!!!!) human waste as radiation shielding in the craft. They would surround the crew with water and food and put it back there "after use".

Edit: Found it: Mars trip to use astronaut poo as radiation shield (https://www.newscientist.com/article/dn23230-mars-trip-to-use-astronaut-poo-as-radiation-shield/)
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: envy887 on 07/07/2016 11:34 am
Maybe just for giggles: I vaguely remember that I read that Inspiration Mars considered (carefully bagged!!!!) human waste as radiation shielding in the craft. They would surround the crew with water and food and put it back there "after use".

Edit: Found it: Mars trip to use astronaut poo as radiation shield (https://www.newscientist.com/article/dn23230-mars-trip-to-use-astronaut-poo-as-radiation-shield/)

That's not strictly necessary on a 100 day transit, but not a bad idea if keeping waste onboard.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: GORDAP on 07/07/2016 12:41 pm
It seems that all of the discussion regarding radiation mitigation at Mars surface has revolved around protection from SPEs.  And the conclusion is that the CO2 in the martian atmosphere makes this pretty much not a concern, correct?

So what about GCRs?  Does that not remain a long term concern for Mars surface occupation?  Does the CO2 mitigate this at all and, if not, what height of protective regolith or water etc. would be required to make surface occupation acceptable?
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: whitelancer64 on 07/07/2016 02:51 pm
It seems that all of the discussion regarding radiation mitigation at Mars surface has revolved around protection from SPEs.  And the conclusion is that the CO2 in the martian atmosphere makes this pretty much not a concern, correct?

So what about GCRs?  Does that not remain a long term concern for Mars surface occupation?  Does the CO2 mitigate this at all and, if not, what height of protective regolith or water etc. would be required to make surface occupation acceptable?

About 2-3 meters of Mars' regolith piled on top of the habitat will protect against GCRs and will also absorb secondary radiation.

There's a lot of information on the internet about radiation protection, a good place to start is to look up the halving-thicknesses of various materials.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/07/2016 02:57 pm
It seems that all of the discussion regarding radiation mitigation at Mars surface has revolved around protection from SPEs.  And the conclusion is that the CO2 in the martian atmosphere makes this pretty much not a concern, correct?

So what about GCRs?  Does that not remain a long term concern for Mars surface occupation?  Does the CO2 mitigate this at all and, if not, what height of protective regolith or water etc. would be required to make surface occupation acceptable?

About 2-3 meters of Mars' regolith piled on top of the habitat will protect against GCRs and will also absorb secondary radiation.

There's a lot of information on the internet about radiation protection, a good place to start is to look up the halving-thicknesses of various materials.
Halving thickness is not a good approximation when talking about GCR because it implies the adding more material is going to reduce the relative dose by the same relative amount when in reality you hit diminishing returns pretty quickly and start needing a lot more material to get a good relative effect.

Halving thickness works for x-rays, etc. But not well for GCR.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: JasonAW3 on 07/07/2016 05:09 pm

CO2 is a much better shield per unit mass than aluminum AND Mars' 40g/cm^2 of CO2 (sky weighted average at human landing sites) is higher than the 30g/cm^2 shielding shown in the blue line, the greatest amount of shielding considered in that graph.

Even with the WORST flare recorded here (in half a century of recording), Mars would shield you to levels WELL below your 30-day limit, let alone annual or lifetime limit. And every other flare would likewise be shielded to levels not much exceeding the background level of 0.67mSv/day.

And 0.67mSv/day is low enough to be outside nearly constantly during the work week (~35 hours per day) without exceeding US radiation worker guidelines (and astronauts are usually allowed about twice that).

Interesting...  So how would dry ice compare to polyethylchloride as a radiation shield?

    Perhaps a layered approach of water ice and dry ice contained in shells of polyethylchloride could work as an acceptable radiation shield system on spacecraft.  Keeping the whole thing cool could be a trick, but not so much as trying to keep cryogenic fuels cold in space.
You mean polyethylene?

CO2 is not as good as polyethylene or water, it's comparable with carbon (graphite), but it's much better than aluminum.

Thanks for the correction.  I think I may have misremembered the particular plastic that was recommended as shielding.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: JasonAW3 on 07/07/2016 05:12 pm
CO2 is inferior to H2O, it is better then aluminum because aluminum it just about the worst shielding material commonly considered for aerospace applications.  Polyethylene not PVC is the preferred plastic shielding material and it is second only to water, their is thus no reason to bring CO2 on a spacecraft as shielding as it is inferior to much easier to handle materials.

So a shell of water sandwiched between two layers of polyethylene would be an effective shield?  This could prove useful, as the water could be used to help with waste heat distribution and dissipation for space craft.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/07/2016 05:20 pm
The best materials (per unit mass) for GCR radiation shielding are, in order:

1) hydrogen
2) methane
3) polyethylene/polypropylene
4) other plastics with high hydrogen content, oils, etc.
5) water, lower hydrogen plastics
6) carbon/graphite/CO2/O2
7) regolith
...
n+1) Aluminum
n+2) steel
n+3) lead


The difference between items 3-6 is small. There's a big difference between 1 & 2 (and 6 & 7), and a smaller but not insignificant difference between 2 & 3.

There's also the separate question of radiation effectiveness per unit /thickness/, in which case hydrogen does poorly (since it has SUCH ridiculously low density, even when a deeply cryogenic liquid) but items 2 through 7 work out to roughly the same effectiveness.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 07/07/2016 05:45 pm
5) water,

Build cylindrical habitats, like the ones of the planetary society. Put pools in the top storey.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/07/2016 05:47 pm
5) water,

Build cylindrical habitats, like the ones of the planetary society. Put pools in the top storey.
Or methane fuel tanks. You need lots of fuel storage anyway.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: whitelancer64 on 07/07/2016 05:50 pm
It seems that all of the discussion regarding radiation mitigation at Mars surface has revolved around protection from SPEs.  And the conclusion is that the CO2 in the martian atmosphere makes this pretty much not a concern, correct?

So what about GCRs?  Does that not remain a long term concern for Mars surface occupation?  Does the CO2 mitigate this at all and, if not, what height of protective regolith or water etc. would be required to make surface occupation acceptable?

About 2-3 meters of Mars' regolith piled on top of the habitat will protect against GCRs and will also absorb secondary radiation.

There's a lot of information on the internet about radiation protection, a good place to start is to look up the halving-thicknesses of various materials.
Halving thickness is not a good approximation when talking about GCR because it implies the adding more material is going to reduce the relative dose by the same relative amount when in reality you hit diminishing returns pretty quickly and start needing a lot more material to get a good relative effect.

Halving thickness works for x-rays, etc. But not well for GCR.

I gave a simple answer to a simple question, and halving thicknesses are a good place to start research on radiation protection.

It's true you get diminishing returns with more dirt, that's also why I wouldn't suggest complex things like tunneling into Mars or only putting habitats in caves, etc. 2-3 meters of regolith is more than sufficient.

Number of halving thicknesses to protection factor:
1   2
2   4
3   8
4   16
5   32
6   64
7   128
8   256
9   512
10   1,024
15   32,768
20   a million
30   a billion
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/07/2016 05:54 pm
It seems that all of the discussion regarding radiation mitigation at Mars surface has revolved around protection from SPEs.  And the conclusion is that the CO2 in the martian atmosphere makes this pretty much not a concern, correct?

So what about GCRs?  Does that not remain a long term concern for Mars surface occupation?  Does the CO2 mitigate this at all and, if not, what height of protective regolith or water etc. would be required to make surface occupation acceptable?

About 2-3 meters of Mars' regolith piled on top of the habitat will protect against GCRs and will also absorb secondary radiation.

There's a lot of information on the internet about radiation protection, a good place to start is to look up the halving-thicknesses of various materials.
Halving thickness is not a good approximation when talking about GCR because it implies the adding more material is going to reduce the relative dose by the same relative amount when in reality you hit diminishing returns pretty quickly and start needing a lot more material to get a good relative effect.

Halving thickness works for x-rays, etc. But not well for GCR.

I gave a simple answer to a simple question, and halving thicknesses are a good place to start research on radiation protection.
...
No, it's not at all a good place to start for GCR. It gives totally the wrong impression. Even from the very beginning, if you look at the "halving thickness" for a very thin shield for GCR, it's actually NEGATIVE in most materials (in free space) due to secondary generation. And even after you start getting a positive benefit from shielding, you very quickly get diminishing returns.

It's just not a good start for this broad-spectrum, very high energy heavy charged particle radiation. Halving thickness works great for EM radiation of all sorts, but is incredibly wrong for GCR.

A better place to start, a better first-order estimate of effectiveness for GCR shielding materials is average atomic mass. The lower, the better it'll be per unit mass.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: whitelancer64 on 07/07/2016 05:57 pm
It seems that all of the discussion regarding radiation mitigation at Mars surface has revolved around protection from SPEs.  And the conclusion is that the CO2 in the martian atmosphere makes this pretty much not a concern, correct?

So what about GCRs?  Does that not remain a long term concern for Mars surface occupation?  Does the CO2 mitigate this at all and, if not, what height of protective regolith or water etc. would be required to make surface occupation acceptable?

About 2-3 meters of Mars' regolith piled on top of the habitat will protect against GCRs and will also absorb secondary radiation.

There's a lot of information on the internet about radiation protection, a good place to start is to look up the halving-thicknesses of various materials.
Halving thickness is not a good approximation when talking about GCR because it implies the adding more material is going to reduce the relative dose by the same relative amount when in reality you hit diminishing returns pretty quickly and start needing a lot more material to get a good relative effect.

Halving thickness works for x-rays, etc. But not well for GCR.

I gave a simple answer to a simple question, and halving thicknesses are a good place to start research on radiation protection.
...
No, it's not at all a good place to start for GCR. It gives totally the wrong impression. Even from the very beginning, if you look at the "halving thickness" for a very thin shield for GCR, it's actually NEGATIVE in most materials (in free space) due to secondary generation.

It's just not a good start.

A better place to start, a better first-order estimate of effectiveness is average atomic mass. The lower, the better it'll be per unit mass.

Fine, consider it like this: a meter of dirt for the GCR, another meter for the secondary radiation, and perhaps a third if you're worried about tertiary radiation / for safety's sake / peace of mind.

2-3 meters of regolith.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/07/2016 05:59 pm
It seems that all of the discussion regarding radiation mitigation at Mars surface has revolved around protection from SPEs.  And the conclusion is that the CO2 in the martian atmosphere makes this pretty much not a concern, correct?

So what about GCRs?  Does that not remain a long term concern for Mars surface occupation?  Does the CO2 mitigate this at all and, if not, what height of protective regolith or water etc. would be required to make surface occupation acceptable?

About 2-3 meters of Mars' regolith piled on top of the habitat will protect against GCRs and will also absorb secondary radiation.

There's a lot of information on the internet about radiation protection, a good place to start is to look up the halving-thicknesses of various materials.
Halving thickness is not a good approximation when talking about GCR because it implies the adding more material is going to reduce the relative dose by the same relative amount when in reality you hit diminishing returns pretty quickly and start needing a lot more material to get a good relative effect.

Halving thickness works for x-rays, etc. But not well for GCR.

I gave a simple answer to a simple question, and halving thicknesses are a good place to start research on radiation protection.
...
No, it's not at all a good place to start for GCR. It gives totally the wrong impression. Even from the very beginning, if you look at the "halving thickness" for a very thin shield for GCR, it's actually NEGATIVE in most materials (in free space) due to secondary generation.

It's just not a good start.

A better place to start, a better first-order estimate of effectiveness is average atomic mass. The lower, the better it'll be per unit mass.

Fine, consider it like this: a meter of dirt for the GCR, another meter for the secondary radiation, and perhaps a third if you're worried about tertiary radiation / for safety's sake / peace of mind.

2-3 meters of regolith.
Except you'll still get significant levels of radiation even under 2-3 meters of regolith. If you want "piece of mind" (i.e. so time inside doesn't count against your dosage, just outside), you need more like 10m.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: whitelancer64 on 07/07/2016 06:06 pm
It seems that all of the discussion regarding radiation mitigation at Mars surface has revolved around protection from SPEs.  And the conclusion is that the CO2 in the martian atmosphere makes this pretty much not a concern, correct?

So what about GCRs?  Does that not remain a long term concern for Mars surface occupation?  Does the CO2 mitigate this at all and, if not, what height of protective regolith or water etc. would be required to make surface occupation acceptable?

About 2-3 meters of Mars' regolith piled on top of the habitat will protect against GCRs and will also absorb secondary radiation.

There's a lot of information on the internet about radiation protection, a good place to start is to look up the halving-thicknesses of various materials.
Halving thickness is not a good approximation when talking about GCR because it implies the adding more material is going to reduce the relative dose by the same relative amount when in reality you hit diminishing returns pretty quickly and start needing a lot more material to get a good relative effect.

Halving thickness works for x-rays, etc. But not well for GCR.

I gave a simple answer to a simple question, and halving thicknesses are a good place to start research on radiation protection.
...
No, it's not at all a good place to start for GCR. It gives totally the wrong impression. Even from the very beginning, if you look at the "halving thickness" for a very thin shield for GCR, it's actually NEGATIVE in most materials (in free space) due to secondary generation.

It's just not a good start.

A better place to start, a better first-order estimate of effectiveness is average atomic mass. The lower, the better it'll be per unit mass.

Fine, consider it like this: a meter of dirt for the GCR, another meter for the secondary radiation, and perhaps a third if you're worried about tertiary radiation / for safety's sake / peace of mind.

2-3 meters of regolith.
Except you'll still get significant levels of radiation even under 2-3 meters of regolith. If you want "piece of mind" (i.e. so time inside doesn't count against your dosage, just outside), you need more like 10m.

based on what?
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/07/2016 06:32 pm
http://oltaris.nasa.gov/
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: JasonAW3 on 07/07/2016 07:06 pm
Ok, here's a thought;

      Assuming that polyethylene can handle a low pressure, nearly pure CO2 atmosphere, what about pumping bags of of polyethylene full of water, covering the initial habitats, and then covering those with about 3 or so meters. of regolith?

     While the bags would be thin, the water, extracted from the Martian sources, would be bearing the bulk of the radiation absorption.  It would all depend on how much water would be required to provide sufficent radiation protection.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: whitelancer64 on 07/07/2016 07:13 pm
Ok, here's a thought;

      Assuming that polyethylene can handle a low pressure, nearly pure CO2 atmosphere, what about pumping bags of of polyethylene full of water, covering the initial habitats, and then covering those with about 3 or so meters. of regolith?

     While the bags would be thin, the water, extracted from the Martian sources, would be bearing the bulk of the radiation absorption.  It would all depend on how much water would be required to provide sufficent radiation protection.

According to Robotbeat, you need 10 meters of it.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/07/2016 07:28 pm
Ok, here's a thought;

      Assuming that polyethylene can handle a low pressure, nearly pure CO2 atmosphere, what about pumping bags of of polyethylene full of water, covering the initial habitats, and then covering those with about 3 or so meters. of regolith?

     While the bags would be thin, the water, extracted from the Martian sources, would be bearing the bulk of the radiation absorption.  It would all depend on how much water would be required to provide sufficent radiation protection.

According to Robotbeat, you need 10 meters of it.
Water is a more effective shield. Fewer secondaries.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: envy887 on 07/07/2016 07:30 pm
Ok, here's a thought;

      Assuming that polyethylene can handle a low pressure, nearly pure CO2 atmosphere, what about pumping bags of of polyethylene full of water, covering the initial habitats, and then covering those with about 3 or so meters. of regolith?

     While the bags would be thin, the water, extracted from the Martian sources, would be bearing the bulk of the radiation absorption.  It would all depend on how much water would be required to provide sufficent radiation protection.

According to Robotbeat, you need 10 meters of it.

Is that to get to average Earth background levels, or to the DOE occupational annual limit?

A lot of people on Earth live with much higher than average natural background levels, and actually in some places on Earth the natural background radiation is on the same order as the Mars surface.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: whitelancer64 on 07/07/2016 07:32 pm
Ok, here's a thought;

      Assuming that polyethylene can handle a low pressure, nearly pure CO2 atmosphere, what about pumping bags of of polyethylene full of water, covering the initial habitats, and then covering those with about 3 or so meters. of regolith?

     While the bags would be thin, the water, extracted from the Martian sources, would be bearing the bulk of the radiation absorption.  It would all depend on how much water would be required to provide sufficent radiation protection.

According to Robotbeat, you need 10 meters of it.
Water is a more effective shield. Fewer secondaries.

Then how many meters of water are needed?
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: BobHk on 07/07/2016 07:36 pm
Ok, here's a thought;

      Assuming that polyethylene can handle a low pressure, nearly pure CO2 atmosphere, what about pumping bags of of polyethylene full of water, covering the initial habitats, and then covering those with about 3 or so meters. of regolith?

     While the bags would be thin, the water, extracted from the Martian sources, would be bearing the bulk of the radiation absorption.  It would all depend on how much water would be required to provide sufficent radiation protection.

According to Robotbeat, you need 10 meters of it.

Quote
hielding test results
[26]
indicate that two layers of Demron,
with a density of 3.14 g/cm
3
and a thickness of 0.4 mm each,
act as an effective radiation shield against a variety of sources.
This  would  have  equivalent  shielding  power  as  lead  with  a
density of 11.3 g/cm
3
and a thickness of 0.2 mm. For adequate
shielding  effectiveness  against  highly  energetic  sources,  as
much as 4 mm of Demron would be required. This covers the
range of radiation types that would be similar to those expected
on  Mars.  The  lower  thickness  of  0.8  mm  would  result  in  an
overall mass of 5.024 kg, which seems reasonable when com-
pared with the estimated mass of the overall suit, 20.88 kg. For
a thickness of 4 mm, the mass contribution would be 25.12 kg
to  the  overall  suit,  a  considerable  mass  addition  that  would
present significant weight and possible mobility problems.
Other  materials  used  in  the  Mars  suit  offer  radiation  pro-
tection; for example, Kapton, Teflon, Nylon, and Mylar offer
some  protective  value.  This  additive  effect  may  lessen  the
amount of Demron required if implemented

source: http://www.ae.utexas.edu/courses/ase324_huang/Mars.pdf

So Demron, if your clothes and suits have a layer of it do your shelters outermost areas need to be THAT heavily shielded?

by the way the paper is an interesting read.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: whitelancer64 on 07/07/2016 08:03 pm
Ok, here's a thought;

      Assuming that polyethylene can handle a low pressure, nearly pure CO2 atmosphere, what about pumping bags of of polyethylene full of water, covering the initial habitats, and then covering those with about 3 or so meters. of regolith?

     While the bags would be thin, the water, extracted from the Martian sources, would be bearing the bulk of the radiation absorption.  It would all depend on how much water would be required to provide sufficent radiation protection.

According to Robotbeat, you need 10 meters of it.

Quote
hielding test results
[26]
indicate that two layers of Demron,
with a density of 3.14 g/cm
3
and a thickness of 0.4 mm each,
act as an effective radiation shield against a variety of sources.
This  would  have  equivalent  shielding  power  as  lead  with  a
density of 11.3 g/cm
3
and a thickness of 0.2 mm. For adequate
shielding  effectiveness  against  highly  energetic  sources,  as
much as 4 mm of Demron would be required. This covers the
range of radiation types that would be similar to those expected
on  Mars.  The  lower  thickness  of  0.8  mm  would  result  in  an
overall mass of 5.024 kg, which seems reasonable when com-
pared with the estimated mass of the overall suit, 20.88 kg. For
a thickness of 4 mm, the mass contribution would be 25.12 kg
to  the  overall  suit,  a  considerable  mass  addition  that  would
present significant weight and possible mobility problems.
Other  materials  used  in  the  Mars  suit  offer  radiation  pro-
tection; for example, Kapton, Teflon, Nylon, and Mylar offer
some  protective  value.  This  additive  effect  may  lessen  the
amount of Demron required if implemented

source: http://www.ae.utexas.edu/courses/ase324_huang/Mars.pdf

So Demron, if your clothes and suits have a layer of it do your shelters outermost areas need to be THAT heavily shielded?

by the way the paper is an interesting read.

Lead of 0.2 mm thickness would block about 1% of gamma radiation. It's not much protection.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: BobHk on 07/07/2016 08:07 pm
Ok, here's a thought;

      Assuming that polyethylene can handle a low pressure, nearly pure CO2 atmosphere, what about pumping bags of of polyethylene full of water, covering the initial habitats, and then covering those with about 3 or so meters. of regolith?

     While the bags would be thin, the water, extracted from the Martian sources, would be bearing the bulk of the radiation absorption.  It would all depend on how much water would be required to provide sufficent radiation protection.

According to Robotbeat, you need 10 meters of it.

Quote
hielding test results
[26]
indicate that two layers of Demron,
with a density of 3.14 g/cm
3
and a thickness of 0.4 mm each,
act as an effective radiation shield against a variety of sources.
This  would  have  equivalent  shielding  power  as  lead  with  a
density of 11.3 g/cm
3
and a thickness of 0.2 mm. For adequate
shielding  effectiveness  against  highly  energetic  sources,  as
much as 4 mm of Demron would be required. This covers the
range of radiation types that would be similar to those expected
on  Mars.  The  lower  thickness  of  0.8  mm  would  result  in  an
overall mass of 5.024 kg, which seems reasonable when com-
pared with the estimated mass of the overall suit, 20.88 kg. For
a thickness of 4 mm, the mass contribution would be 25.12 kg
to  the  overall  suit,  a  considerable  mass  addition  that  would
present significant weight and possible mobility problems.
Other  materials  used  in  the  Mars  suit  offer  radiation  pro-
tection; for example, Kapton, Teflon, Nylon, and Mylar offer
some  protective  value.  This  additive  effect  may  lessen  the
amount of Demron required if implemented

source: http://www.ae.utexas.edu/courses/ase324_huang/Mars.pdf

So Demron, if your clothes and suits have a layer of it do your shelters outermost areas need to be THAT heavily shielded?

by the way the paper is an interesting read.

Lead of 0.2 mm thickness would block about 1% of gamma radiation. It's not much protection.

So naked martians that stray outside can get their dose, i'd prefer to be in a suit when I left the habitat.

You gonna import that lead?
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/07/2016 08:11 pm
Ok, here's a thought;

      Assuming that polyethylene can handle a low pressure, nearly pure CO2 atmosphere, what about pumping bags of of polyethylene full of water, covering the initial habitats, and then covering those with about 3 or so meters. of regolith?

     While the bags would be thin, the water, extracted from the Martian sources, would be bearing the bulk of the radiation absorption.  It would all depend on how much water would be required to provide sufficent radiation protection.

According to Robotbeat, you need 10 meters of it.

Is that to get to average Earth background levels, or to the DOE occupational annual limit?

A lot of people on Earth live with much higher than average natural background levels, and actually in some places on Earth the natural background radiation is on the same order as the Mars surface.
Now THAT is the key question.

I think we want somewhere in between. People are going to be living their whole lives on Mars (or at least a decade or two) at a colony. So while US radiation worker limit of 50mSv/year is overly conservative for explorers, it's probably a good rough limit for colonists and something you'd want to stay well under for habitat design (especially for the young). Because you DON'T want to be stuck inside all the time, you want to allot, say, 25-30mSv so you can be outside 15-20 hours a week for workers. That means the habitat should probably be 10-20mSv. But if you want to spend 35 hours a week outside, then you'll want about the same as US total background levels, i.e. 5-10mSv or so (although half of the US 6mSv/year is due to medical sources of radiation).

If we're talking early SpaceX missions, then very little shielding is needed, however. The Mars atmosphere itself provides a LOT of shielding, and the transits will be quick.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: JasonAW3 on 07/07/2016 08:25 pm
It seems that all of the discussion regarding radiation mitigation at Mars surface has revolved around protection from SPEs.  And the conclusion is that the CO2 in the martian atmosphere makes this pretty much not a concern, correct?

So what about GCRs?  Does that not remain a long term concern for Mars surface occupation?  Does the CO2 mitigate this at all and, if not, what height of protective regolith or water etc. would be required to make surface occupation acceptable?

About 2-3 meters of Mars' regolith piled on top of the habitat will protect against GCRs and will also absorb secondary radiation.

There's a lot of information on the internet about radiation protection, a good place to start is to look up the halving-thicknesses of various materials.
Halving thickness is not a good approximation when talking about GCR because it implies the adding more material is going to reduce the relative dose by the same relative amount when in reality you hit diminishing returns pretty quickly and start needing a lot more material to get a good relative effect.

Halving thickness works for x-rays, etc. But not well for GCR.

Actually, as water is a better shield for radiation, I was thinking of the reagolith cover as more of a way to keep the water shield in place, rather than as a primary cover.  The polyethylene is also more to hold the water, but every bit of cover and material helps, even if only fractional
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: whitelancer64 on 07/07/2016 08:36 pm
Lead of 0.2 mm thickness would block about 1% of gamma radiation. It's not much protection.

So naked martians that stray outside can get their dose, i'd prefer to be in a suit when I left the habitat.

You gonna import that lead?

Every little bit helps, but your habitat is still going to need the most protection it can get. That's going to be true even if you have a magic spacesuit that blocks 100% of all radiation.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/07/2016 08:42 pm
Lead might actually make GCR worse. And it'd slow you down, so probably would increase your dose.

Mars' atmosphere already does a good job of reducing your dose on the surface of Mars. In order to do anything significantly better, you'll need more shielding than would ever be practical in a suit.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: envy887 on 07/07/2016 08:46 pm
Lead might actually make GCR worse. And it'd slow you down, so probably would increase your dose.

Mars' atmosphere already does a good job of reducing your dose on the surface of Mars. In order to do anything significantly better, you'll need more shielding than would ever be practical in a suit.

Half a meter of polyethylene on the roof of your rover would work  ;D
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/07/2016 08:50 pm
Lead might actually make GCR worse. And it'd slow you down, so probably would increase your dose.

Mars' atmosphere already does a good job of reducing your dose on the surface of Mars. In order to do anything significantly better, you'll need more shielding than would ever be practical in a suit.

Half a meter of polyethylene on the roof of your rover would work  ;D
It'd help, but that's parasitic mass. Better to put your batteries and supplies on the roof. How about half a meter of lithium-ion batteries on the roof?
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: BobHk on 07/07/2016 08:55 pm
Lead might actually make GCR worse. And it'd slow you down, so probably would increase your dose.

Mars' atmosphere already does a good job of reducing your dose on the surface of Mars. In order to do anything significantly better, you'll need more shielding than would ever be practical in a suit.

Mars heats up/has weather, so doesn't that mean the atmosphere would be thinner on the dayside than the night side?  Wouldn't we have to base any atmospheric protection on the thinnest it gets at the elevation you're on?
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/07/2016 08:57 pm
Lead might actually make GCR worse. And it'd slow you down, so probably would increase your dose.

Mars' atmosphere already does a good job of reducing your dose on the surface of Mars. In order to do anything significantly better, you'll need more shielding than would ever be practical in a suit.

Mars heats up/has weather, so doesn't that mean the atmosphere would be thinner on the dayside than the night side?  Wouldn't we have to base any atmospheric protection on the thinnest it gets at the elevation you're on?
No, because we're talking about a stochastic effect, not an acute effect. Mars' atmosphere at any of the likely human landing sites is always thick enough to defend against acute effects.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: scienceguy on 07/07/2016 09:55 pm
Looking at the International Commission on Radiation Units and Measurements’ 1993 paper (ICRU 1993), we see that water actually stops protons very well if they are in the MeV range.

A 4 MeV proton is stopped by just 0.25 mm of water. However, galactic cosmic rays can have up to 10^21 eV or 10^15 MeV of energy.

https://en.wikipedia.org/wiki/Cosmic_ray

Fortunately, only very few GCR’s actually have that much energy. Most GCR’s hitting Earth (and presumably Mars) are in the 10^11 to 10^13 eV range, or 10^5 to 10^7 MeV range.

Please see attached a graph of values from the ICRU paper that show centimeters of water required to stop various MeV energy protons.

If you extrapolate from the graph, you can see that a 10^5 MeV proton requires 1810 cm, or 18.1 m to stop most GCR’s. The more energetic GCR’s can probably be diverted by a magnetic field or some of them may be stopped by Mars’ atmosphere.

Reference
International Commission on Radiation Units (1993). Stopping Powers and Ranges for Protons and Alpha Particles. ICRU report 49. P. 180
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Impaler on 07/07/2016 10:50 pm
10 m thickness of regolith at 1.5 g/cm^3 would be 1500 g/cm^2 of shielding which is massive overkill, you would have Earth surface levels of protection under that kind of mass.

Regolith is mostly Oxygen and Silicon with heavier elements like Iron and Calcium, it's poorer then Aluminum but not by this much, it's about half way between the shielding value of Aluminum and Water and is comparable to pure Carbon or CO2.

Also the secondary radiation effects causing an increase in dosage are being exaggerated, that's a phenomenon that occurs in the first 5 g/cm^2 and almost exclusively in heavy metals, but even with thouse materials the radiation behind the shielding is less then without the shielding once it's got any decent thickness.  Secondary radiation is only a concern on spacecraft where it makes the traditional thin aluminum skin ineffective as a shield, the Mars surface is an environment in which abundant mass is available for shielding and were arguing between the number of METERS of shielding to use, secondary radiation is a read-hearing in that discussion.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: envy887 on 07/07/2016 11:19 pm
Lead might actually make GCR worse. And it'd slow you down, so probably would increase your dose.

Mars' atmosphere already does a good job of reducing your dose on the surface of Mars. In order to do anything significantly better, you'll need more shielding than would ever be practical in a suit.

Half a meter of polyethylene on the roof of your rover would work  ;D
It'd help, but that's parasitic mass. Better to put your batteries and supplies on the roof. How about half a meter of lithium-ion batteries on the roof?

Just tack a Tesla Powerwall on top of a golf cart, and you're good to go  8) Rad-safe and power for miles  :D
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: docmordrid on 07/08/2016 12:26 am
I would like to point out that the dose "limits" discussed were developed under a doctrine established after Hiroshima known as  Linear No-Threshold. Basically, there is no "safe dose."

This doctrine has been in dispute for many years because of the discovery of DNA repair mechanisms and studies showing there likely are (individual) "safer" thresholds.

A continuing foodnight, with the bureaucrats and regulators, as usual, behind the curve.

In 2014 the United Nations Scientific Committee on the Effects of Atomic Radiation bucked LNT, doing a 180° from previous recommendations.

Radiologic Society of North America 'Radiology' (2009)
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2663584/

"The Linear No-Threshold Relationship Is Inconsistent with Radiation Biologic and Experimental Data"
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/08/2016 01:03 am
10 m thickness of regolith at 1.5 g/cm^3 would be 1500 g/cm^2 of shielding which is massive overkill, you would have Earth surface levels of protection under that kind of mass.
...
Yes, and that's what I was saying: in order to get levels such that time spent in your habitat doesn't really take away from time that you can spend on the surface, you need 10m of shielding.

And, just as I said, this is overkill for early missions which will be made of explorers, not "colonists." (Or if they are colonists, they will be early ones and not children.)
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: stoker5432 on 07/08/2016 01:10 am
10 m thickness of regolith at 1.5 g/cm^3 would be 1500 g/cm^2 of shielding which is massive overkill, you would have Earth surface levels of protection under that kind of mass.
...
Yes, and that's what I was saying: in order to get levels such that time spent in your habitat doesn't really take away from time that you can spend on the surface, you need 10m of shielding.

And, just as I said, this is overkill for early missions which will be made of explorers, not "colonists." (Or if they are colonists, they will be early ones and not children.)

The author of the discussion clearly said "including initial colonization efforts". Wouldn't that include colonists or am I misinterpreting would he posted?
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/08/2016 01:10 am
I would like to point out that the dose "limits" discussed were developed under a doctrine established after Hiroshima known as  Linear No-Threshold. Basically, there is no "safe dose."

This doctrine has been in dispute for many years because of the discovery of DNA repair mechanisms and studies showing there likely are (individual) "safer" thresholds.

A continuing foodnight, with the bureaucrats and regulators, as usual, behind the curve.

In 2014 the United Nations Scientific Committee on the Effects of Atomic Radiation bucked LNT, doing a 180° from previous recommendations.

Radiologic Society of North America 'Radiology' (2009)
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2663584/

"The Linear No-Threshold Relationship Is Inconsistent with Radiation Biologic and Experimental Data"
Oh certainly, but that doesn't mean you wouldn't want to reduce the dose received by children to well below the limit for US Radiation workers.

I completely agree that the LNT model is probably not valid if extrapolated all the way to low doses. But the doses we're talking about on Mars are on the order of 50-150mSv/year, where there IS some evidence of effect.

I think that long-term we'll be able to beat the effect down with drugs and the body's own defense mechanisms, but remember SpaceX is trying to build a city on Mars. That means a million people, and tens of thousands of children, who will be exposed to the environment that we're creating there. It's reasonable to try to reduce the dose if it can be done fairly easily.

And the flip side is that full shielding allows you more time on the surface without any added shielding (for the same overall risk).
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: CuddlyRocket on 07/16/2016 03:08 am
And the flip side is that full shielding allows you more time on the surface without any added shielding (for the same overall risk).

Are there any radiation mitigation strategies for those conducting EVAs? (Of course, the simplest such strategy is to not go out at all - but let's assume the need and/or desire ...)

There would seem to be limited scope in design of the suit given you probably don't want to be carrying a lot of additional mass. Though you'll need to ensure it will block UV and possibly any alpha or beta radiation from ground sources - this should be straightforward.

As mentioned earlier in the thread, the bulk of the radiation exposure will come from overhead so there'll be little scope from utilising the environment (though if there happens to be a convenient cliff overhang ... !), which seems to reduce the options to hats, parasols and awnings. None of these are likely to stop a GCR that makes it to the surface, but they might cut down the radiation from cosmic-ray air showers formed by a GCR hitting an atom high in the atmosphere.

I chose a hat rather than built in head screening as it's removable. The disadvantage is the limited mass and the fact that it's relatively close. The same applies to parasols. Awnings, however, could be much more sturdy. You should definitely consider one over the cab of an unpressurised vehicle; and you might want to stow a portable one on the side of any pressurised exploration rover for occasions when you're outside the vehicle examining an item of interest for any length of time.

It might also be worthwhile building a porch over any airlock. It's one place you know people will be standing, even if not for particularly long on any single occasion. None of these strategies are likely to make a significant reduction to radiation exposure, but every little helps!
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: KelvinZero on 07/16/2016 07:14 am
It might also be worthwhile building a porch over any airlock. It's one place you know people will be standing, even if not for particularly long on any single occasion. None of these strategies are likely to make a significant reduction to radiation exposure, but every little helps!
I can see this becoming a tradition on Mars: people standing around chatting under the water cooler. :)
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Eric Hedman on 07/28/2016 05:39 pm
Here's another study to throw in the mix about Cosmic rays causing heart disease and what they did to Apollo astronauts:

http://news.trust.org/item/20160728130118-h1ptb/ (http://news.trust.org/item/20160728130118-h1ptb/)
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/28/2016 08:25 pm
Here's another study to throw in the mix about Cosmic rays causing heart disease and what they did to Apollo astronauts:

http://news.trust.org/item/20160728130118-h1ptb/ (http://news.trust.org/item/20160728130118-h1ptb/)
Interestingly, it doesn't say it was caused by cosmic rays. For instance, ISS astronauts over 6 months are exposed to far more cosmic rays than an Apollo mission, so it's unlikely to be caused by cosmic rays. Sample size is small and there are huge confounding factors. For instance, maybe eating cheeseburgers was really popular among guys who went to the Moon. Or perhaps they avoided other common causes of death.

Drawing real conclusions from these sorts of studies is really, really hard.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: BobHk on 07/28/2016 09:16 pm
Here's another study to throw in the mix about Cosmic rays causing heart disease and what they did to Apollo astronauts:

http://news.trust.org/item/20160728130118-h1ptb/ (http://news.trust.org/item/20160728130118-h1ptb/)
Interestingly, it doesn't say it was caused by cosmic rays. For instance, ISS astronauts over 6 months are exposed to far more cosmic rays than an Apollo mission, so it's unlikely to be caused by cosmic rays. Sample size is small and there are huge confounding factors. For instance, maybe eating cheeseburgers was really popular among guys who went to the Moon. Or perhaps they avoided other common causes of death.

Drawing real conclusions from these sorts of studies is really, really hard.

On the face of it the sample size is too dang small.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/28/2016 09:57 pm
Here's another study to throw in the mix about Cosmic rays causing heart disease and what they did to Apollo astronauts:

http://news.trust.org/item/20160728130118-h1ptb/ (http://news.trust.org/item/20160728130118-h1ptb/)
Interestingly, it doesn't say it was caused by cosmic rays. For instance, ISS astronauts over 6 months are exposed to far more cosmic rays than an Apollo mission, so it's unlikely to be caused by cosmic rays. Sample size is small and there are huge confounding factors. For instance, maybe eating cheeseburgers was really popular among guys who went to the Moon. Or perhaps they avoided other common causes of death.

Drawing real conclusions from these sorts of studies is really, really hard.

On the face of it the sample size is too dang small.
That's also true. However, if the effect were large enough and the experiment more effectively controlled, the sample size is big enough.

But the effect is much TOO big to likely be caused by cosmic rays, since ISS astronauts are exposed to greater doses of cosmic rays (due to much longer mission) and don't see a significant effect.

But consider that only 8 astronauts who went out to the Moon and back have died. That's a TINY sample size, and just a single astronaut dying or not dying of heart failure would screw up the result. You're right. That's just too small.

...now if ALL the returned astronauts had died of heart failure, that'd be a different story. But since just a few of them did, the effect isn't big enough to reliably detect with such a small sample size.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: JamesH65 on 07/29/2016 09:35 am
Here's another study to throw in the mix about Cosmic rays causing heart disease and what they did to Apollo astronauts:

http://news.trust.org/item/20160728130118-h1ptb/ (http://news.trust.org/item/20160728130118-h1ptb/)
Interestingly, it doesn't say it was caused by cosmic rays. For instance, ISS astronauts over 6 months are exposed to far more cosmic rays than an Apollo mission, so it's unlikely to be caused by cosmic rays. Sample size is small and there are huge confounding factors. For instance, maybe eating cheeseburgers was really popular among guys who went to the Moon. Or perhaps they avoided other common causes of death.

Drawing real conclusions from these sorts of studies is really, really hard.

On the face of it the sample size is too dang small.
That's also true. However, if the effect were large enough and the experiment more effectively controlled, the sample size is big enough.

But the effect is much TOO big to likely be caused by cosmic rays, since ISS astronauts are exposed to greater doses of cosmic rays (due to much longer mission) and don't see a significant effect.

But consider that only 8 astronauts who went out to the Moon and back have died. That's a TINY sample size, and just a single astronaut dying or not dying of heart failure would screw up the result. You're right. That's just too small.

...now if ALL the returned astronauts had died of heart failure, that'd be a different story. But since just a few of them did, the effect isn't big enough to reliably detect with such a small sample size.

In the US 1 in 4 people die of heart disease. It's the biggest cause fo death. Given the high proportion in the population anyway, and the small sample size, I don't think anything can be made of this.

24 people Apollo astronauts went to the moon. If 1 in 4 of them died of heart disease that would be 6 people. However, only 8 have died, and of those, 3 were from cardiovascular disease. Which is only very slightly higher than the general population, and in this sample size, insignificant. Even waiting for them all the die and determining the cause, the sample size if still too small.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: mikelepage on 07/29/2016 09:59 am
Out of curiosity, has anyone ever watched an Antlion dig its conical trap pit, and thought about how it could apply to radiation protection on mars?  :D

(https://whyevolutionistrue.files.wordpress.com/2013/12/180e0-sandpittrapofanantlionlarva.jpg?w=510&h=340)

Just thinking, it may be more efficient to design specialised habitats (broad and spade shaped) that replicate this ability, each one capable of burrowing itself under the ground instead of needing earthmoving equipment (ahem) to pile sand/regolith up on top of the module, or alternatively having to bore tunnels.  The low gravity of Mars would also mean that much higher slope angles could be tolerated, and the obvious lack or rain would mean that only token slope stablizing measures would be required for safety.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: JamesH65 on 07/29/2016 12:41 pm
Out of curiosity, has anyone ever watched an Antlion dig its conical trap pit, and thought about how it could apply to radiation protection on mars?  :D

(https://whyevolutionistrue.files.wordpress.com/2013/12/180e0-sandpittrapofanantlionlarva.jpg?w=510&h=340)

Just thinking, it may be more efficient to design specialised habitats (broad and spade shaped) that replicate this ability, each one capable of burrowing itself under the ground instead of needing earthmoving equipment (ahem) to pile sand/regolith up on top of the module, or alternatively having to bore tunnels.  The low gravity of Mars would also mean that much higher slope angles could be tolerated, and the obvious lack or rain would mean that only token slope stablizing measures would be required for safety.

One big problem, the Sarlacc.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: docmordrid on 07/29/2016 03:38 pm
This Boston Globe reprint of a NY Times article does a nice slice 'n dice on this "study"

Link.... (https://www.bostonglobe.com/news/nation/2016/07/28/study-asks-going-moon-came-with-downside-heart-risks/RYmpDw8ZerjhAMsNa97dEJ/story.html)
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: inventodoc on 07/29/2016 11:54 pm
Here's another study to throw in the mix about Cosmic rays causing heart disease and what they did to Apollo astronauts:

http://news.trust.org/item/20160728130118-h1ptb/ (http://news.trust.org/item/20160728130118-h1ptb/)
Interestingly, it doesn't say it was caused by cosmic rays. For instance, ISS astronauts over 6 months are exposed to far more cosmic rays than an Apollo mission, so it's unlikely to be caused by cosmic rays. Sample size is small and there are huge confounding factors. For instance, maybe eating cheeseburgers was really popular among guys who went to the Moon. Or perhaps they avoided other common causes of death.

Drawing real conclusions from these sorts of studies is really, really hard.

On the face of it the sample size is too dang small.

That stupid report makes me so angry.   They are talking about 7 people - of whom 3 had cardiovascular disease.  That's not an adequate sample size.    As a medical doctor, I don't like misinformation spreading all over the internet, which this story is certainly doing. 

I would note that those astronauts, at least the ones I can think of, had normal life expectancy.  That's a more important measure than what they died from 45 years later.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: MP99 on 07/31/2016 08:27 am


Just stumbled into this: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.487.7074 (http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.487.7074)

Some more info on ice sublimation rates under regolith of varying thicknesses. If i'm not horribly misreading it even a pretty thin cover layer does quite well. Planning on a century of working life without any replacement of lost ice looks pretty workable. Exposed windows look like they'd run about 1mm/hr loss which could work if there's enough water supply for regular resurfacing on the top. That would need a couple hundred liters per m2 of window weekly.

I'm just catching up on this thread, so someone may have suggested this already...

A thin plastic film over the outside of the window could recover the water vapour. Operating at Martian atmospheric pressure, a thin tube could go from each window to a centralised pump (outside the hab) that would pressurise / condense the recovered water.

Since this is distilled water, it might even make good drinking water.

Cheers, Martin
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Eric Hedman on 07/31/2016 04:47 pm
This Boston Globe reprint of a NY Times article does a nice slice 'n dice on this "study"

Link.... (https://www.bostonglobe.com/news/nation/2016/07/28/study-asks-going-moon-came-with-downside-heart-risks/RYmpDw8ZerjhAMsNa97dEJ/story.html)
The key part of this article is that the Apollo astronauts are such a small sample size that they are an anecdote at best.  It does continue to say:

"In their study, Delp and his colleagues exposed mice to simulated conditions of anti-gravity, cosmic radiation, or both effects combined. After half a year (the equivalent of 20 human years), they found that only the mice that had been exposed to radiation had sustained damage to their blood vessels. In particular, the researchers found damage to the lining of the blood vessels."

Anecdotal evidence is best used to trigger real studies.  I think the mice experiment is the more relevant part of the study.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: docmordrid on 07/31/2016 04:57 pm
The big dose at once to the mice screams Linear No Threshold, which is falling out of favor because of mounting evidence there is a low dose threshold. LNT doesn't sufficiently take into account DNA repair mechanisms which were unknown when LNT was thought up after WW-2.

Unfortunately, many US govt. agencies are slow on the uptake.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 07/31/2016 05:54 pm
The big dose at once to the mice screams Linear No Threshold, which is falling out of favor because of mounting evidence there is a low dose threshold. LNT doesn't sufficiently take into account DNA repair mechanisms which were unknown when LNT was thought up after WW-2.

Unfortunately, many US govt. agencies are slow on the uptake.

Sometimes I have the impression that scientists hesitate to question LNT. They may be afraid of being accused of supporting the nuclear industry by diminishing radiation risks. I could be completely wrong of course and scientists are totally above such considerations.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: docmordrid on 07/31/2016 05:57 pm
You're not wrong, but also add in bureaucratic inertia and careers built on fifedoms. Scientists are no less prone to politics; office, govt, or environmental,  than everyone else.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: meekGee on 07/31/2016 06:05 pm
The big dose at once to the mice screams Linear No Threshold, which is falling out of favor because of mounting evidence there is a low dose threshold. LNT doesn't sufficiently take into account DNA repair mechanisms which were unknown when LNT was thought up after WW-2.

Unfortunately, many US govt. agencies are slow on the uptake.

I never understood that LNT assumption.  At best it's just odd.

The body has many defense mechanisms and they are all rate-limited...  I mean, take the total background radiation a person receive over a lifetime, and deliver it in 2 minutes to a 3-years-old.  That's not going to work, right?

Would you do the same for chemical exposure?






Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: docmordrid on 07/31/2016 07:19 pm
This 2009ish Radiology* article lays out the LNT issue, and the reasons why it's obsolete. NIH server,

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2663584/

* Radiological Society of North America (RSNA)

Quote
Summary

Biologic data demonstrate that the defense mechanisms against radiation-induced carcinogenesis are powerful and diverse (Figure) (10,16,78,95,96). This is not surprising, because organisms have been subjected to reactive oxygen species from physiologic processes and environmental insults during evolution. Life is characterized by the ability to build defenses against toxic agents, whether internal or environmental. The defenses are overwhelmed at high doses and are stimulated at low doses, which is incompatible with the LNT model.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: BobHk on 07/31/2016 07:39 pm
The big dose at once to the mice screams Linear No Threshold, which is falling out of favor because of mounting evidence there is a low dose threshold. LNT doesn't sufficiently take into account DNA repair mechanisms which were unknown when LNT was thought up after WW-2.

Unfortunately, many US govt. agencies are slow on the uptake.

Sometimes I have the impression that scientists hesitate to question LNT. They may be afraid of being accused of supporting the nuclear industry by diminishing radiation risks. I could be completely wrong of course and scientists are totally above such considerations.

A lot of them question it:

https://www.sciencedaily.com/releases/2016/02/160203134456.htm (https://www.sciencedaily.com/releases/2016/02/160203134456.htm)

The slow uptake of the US govt and scientists in general is not surprising...a cynic might ask who makes money off of radiation mitigation?

Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 07/31/2016 07:44 pm
Sometimes I have the impression that scientists hesitate to question LNT. They may be afraid of being accused of supporting the nuclear industry by diminishing radiation risks. I could be completely wrong of course and scientists are totally above such considerations.

A lot of them question it:

Good to hear.

Edit: Fixed quote
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 08/01/2016 12:07 am
Also, it bears repeating: LEO astronauts on 6 month stints experience FAR more radiation overall, including cosmic ray radiation (*gasp* "but what about the magnetic field?!!!1!" Well, it's only a filter and doesn't block the highest energy rays), than the <2 week stints to the Moon.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Proponent on 08/01/2016 01:57 am
Has anyone listened to the 13 July FISO telecon on martian radiation risks (http://spirit.as.utexas.edu/%7Efiso/telecon/Cucinotta_7-13-16/)?  It's on my list of things to do, but I haven't got there yet.

P.S.  A word to the wise if you're going to download the files:  the webmaster of the FISO archive runs a tight ship and does take kindly to people downloading a file multiple times.  Be sure to click each download link just once, or your IP address might just get banned!
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: ThereIWas3 on 08/02/2016 12:59 pm
Recently there has been news about increased risk of heart problems in Apollo astronauts (http://www.nbcnews.com/health/heart-health/deep-space-radiation-caused-heart-problems-apollo-astronauts-n618116) that bears investigating.

Quote
The number of deaths due to heart disease among the Apollo lunar astronauts is almost five times greater than that in non-flight astronauts, or astronauts who never flew missions in space, researchers from Florida State University found. Compared to astronauts who flew only in low Earth orbit (LEO), the heart risk among Apollo astronauts is four times higher. There were no differences between LEO and non-flight astronauts.

And the Apollo astronauts wre only outside the Earth's shielding for a week or so.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 08/02/2016 01:20 pm
Recently there has been news about increased risk of heart problems in Apollo astronauts (http://www.nbcnews.com/health/heart-health/deep-space-radiation-caused-heart-problems-apollo-astronauts-n618116) that bears investigating.

Quote
The number of deaths due to heart disease among the Apollo lunar astronauts is almost five times greater than that in non-flight astronauts, or astronauts who never flew missions in space, researchers from Florida State University found. Compared to astronauts who flew only in low Earth orbit (LEO), the heart risk among Apollo astronauts is four times higher. There were no differences between LEO and non-flight astronauts.

And the Apollo astronauts wre only outside the Earth's shielding for a week or so.
...which means the heart issue weren't caused by radiation. ISS astronauts in LEO were exposed to FAR more radiation (yes, INCLUDING more cosmic radiation) and this issue didn't develop.

The article is dumb and the sample size is about an order of magnitude too small to support any of these claims.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: CuddlyRocket on 08/02/2016 07:03 pm
I'm interested in the design of early habitats, which I suspect will be built on Earth and erected (or inflated) on the surface, with buried habitats or those constructed on Mars coming later.

Most of the designs I've seen are multi-storey with living (including sleeping) quarters on upper stories and with workshops and equipment bays on lower stories. I'm not sure this is the right way round! As we've established, the main source of radiation comes from above, so you should design your habitats so that those areas the crew will be in the most (which would include sleeping quarters) are on lower stories and those where they spend the least time on upper stories. Also, you should put equipment and stores - including food, water and air tanks etc - in upper stories.

Granted most people envisage regolith or other local mass resource being piled on the roof as a radiation shield. However, even in Mars gravity such materials are heavy and there's a limit to how much can be used before the structural integrity is compromised (see the potential effects of a similar material - volcanic ash - on structures on Earth). You can always build in structural support, but this eats into the mass budget and you may be better off using clever design to reduce the thickness of shield required. Perhaps you could vary the thickness of the roof covering, with that over the sleeping quarters thicker than that over areas the crew spend less time in?

Thinking about work and living space design. On Earth, all equipment, storage space etc in our living and working areas is arranged laterally around where the humans will be standing, sitting, lying down etc., with very little overhead. On Mars, given the source of radiation and the lower gravity, it might make sense to shift as much as possible overhead. It is possible, though uncommon, to get ceiling, including pull-down, storage here on Earth. Rooms on Mars may be narrower and taller!

Finally, how many radiation sensors should be incorporated? None; one per habitat, or one in every room?
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 08/02/2016 07:22 pm
None; one per habitat, or one in every room?

None, they are good for nothing. The design will determine, how much radiation there is. Why measure, except possibly for new habitats, before they are commissioned?

There would be warning systems for solar flare events. People would know where safe places are. People working in areas where they may not be able to seek adequate shelter may have dosimeter like workers in nuclear facilities on earth.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Survtech on 08/15/2016 03:56 am
Why not just utilize the lava tubes from extinct Martian volcanoes?  (https://marsed.mars.asu.edu/sites/default/files/images_mep/skylight1.jpg)
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 08/15/2016 05:01 am
High altitude, not as much water, harder to land near, and more radiation on the surface.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: woods170 on 08/15/2016 07:52 am
Recently there has been news about increased risk of heart problems in Apollo astronauts (http://www.nbcnews.com/health/heart-health/deep-space-radiation-caused-heart-problems-apollo-astronauts-n618116) that bears investigating.

Quote
The number of deaths due to heart disease among the Apollo lunar astronauts is almost five times greater than that in non-flight astronauts, or astronauts who never flew missions in space, researchers from Florida State University found. Compared to astronauts who flew only in low Earth orbit (LEO), the heart risk among Apollo astronauts is four times higher. There were no differences between LEO and non-flight astronauts.

And the Apollo astronauts wre only outside the Earth's shielding for a week or so.
...which means the heart issue weren't caused by radiation. ISS astronauts in LEO were exposed to FAR more radiation (yes, INCLUDING more cosmic radiation) and this issue didn't develop.

The article is dumb and the sample size is about an order of magnitude too small to support any of these claims.
Well, I would not have voiced as strongly as you did, but I agree with your basic conclusion. The sample size is indeed too small to come to any conclusion.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: mikelepage on 08/15/2016 08:12 am
This 2009ish Radiology* article lays out the LNT issue, and the reasons why it's obsolete. NIH server,

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2663584/

* Radiological Society of North America (RSNA)

Quote
Summary

Biologic data demonstrate that the defense mechanisms against radiation-induced carcinogenesis are powerful and diverse (Figure) (10,16,78,95,96). This is not surprising, because organisms have been subjected to reactive oxygen species from physiologic processes and environmental insults during evolution. Life is characterized by the ability to build defenses against toxic agents, whether internal or environmental. The defenses are overwhelmed at high doses and are stimulated at low doses, which is incompatible with the LNT model.

Interesting paper.  Having a quick read I noticed a few things (for context we have 0.64mSv total radiation Martian daily dose):

1) No intrachromosomal inversions/deletions (the particularly nasty ones) observed from single doses <100mSv
2) No chromosomal abberations observed from single doses <20mSv
3) No activation of DNA repair mechanisms at single doses <5mSv

Additionally, one alternative to LNT appears to be called the Radiation Hormesis model:
http://scholarworks.umass.edu/cgi/viewcontent.cgi?article=1049&context=dose_response&sei-redir=1&referer=http%3A%2F%2Fwww.bing.com%2Fsearch%3Fq%3Dalternative%2Bto%2Blinear%2Bno%2Bthreshold%2Bradiation%2Bmodel%26src%3DIE-TopResult%26FORM%3DIE11TR%26conversationid%3D#search=%22alternative%20linear%20no%20threshold%20radiation%20model%22 (http://scholarworks.umass.edu/cgi/viewcontent.cgi?article=1049&context=dose_response&sei-redir=1&referer=http%3A%2F%2Fwww.bing.com%2Fsearch%3Fq%3Dalternative%2Bto%2Blinear%2Bno%2Bthreshold%2Bradiation%2Bmodel%26src%3DIE-TopResult%26FORM%3DIE11TR%26conversationid%3D#search=%22alternative%20linear%20no%20threshold%20radiation%20model%22)

which if I'm reading this right, finds that small single doses may actually decrease cancer rates, apparently due to activation of certain cellular repair mechanisms.

This is all single dose data, which may manifest different symptoms from the ongoing radiation experienced on Mars, but it did get me (very loosely) speculating about what the threshold might actually be:

I worked with NK cells during my phd, and they are probably a pretty good candidate for the type of immune cell that might actually effect the sort of killing required to detect and destroy damaged cells.  They can do certain killing functions immediately, but in in vitro culture they take 10-14 (call it 12) days to go from resting to activation with IL-2.  Doing a quick pubmed search suggests it takes another 12 days to generate NK cells from bone-marrow derived stem cells. 

If we estimate at least somewhat conservatively that an average person with a normal immune system can repair up to 10 mSv of damage given in a single dose (5 CT scans), my guess would be that the max threshold for ongoing exposure may be 10 mSv over a 24 day period - averaging 0.42 mSv/day (you'd probably want to break it up into "exposure" and "rest" periods so you give your body the best chance at recovering from each hit) and this brings you in at just under 160 mSv in a 365 day period. 

So many caveats here I shouldn't have to mention that this is little more than an educated guess.  But yes, it does make the Mars daily radiation level of 0.64mSv does look slightly more manageable.  I'm thinking you'd probably want to have at least one module much more heavily shielded than the others, and you spend 2 weeks in/2 weeks out.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: launchwatcher on 08/15/2016 07:20 pm
So many caveats here I shouldn't have to mention that this is little more than an educated guess.  But yes, it does make the Mars daily radiation level of 0.64mSv does look slightly more manageable.  I'm thinking you'd probably want to have at least one module much more heavily shielded than the others, and you spend 2 weeks in/2 weeks out.
What prevents the body from continuously producing these immune cells -- or at least having several batches going at once -- so you're stuck cycling like this?

Another paper on hormesis is here:  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2477686/
"Radiation Hormesis: The Good, the Bad, and the Ugly".   The author seems passionately committed to his result (perhaps a red flag?) but a bunch of the cited cases which appear to show hormesis involve continual or at least daily exposure - things like occupational exposures and even "lung cancer deaths decreased with increased radon concentration in homes" (as an aside, it also mentions that the original case for a link between cancer and radon exposure was made with data from underground miners, who are exposed to a lot of other things besides radon..).




Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: docmordrid on 08/15/2016 08:19 pm
So many caveats here I shouldn't have to mention that this is little more than an educated guess.  But yes, it does make the Mars daily radiation level of 0.64mSv does look slightly more manageable.  I'm thinking you'd probably want to have at least one module much more heavily shielded than the others, and you spend 2 weeks in/2 weeks out.
What prevents the body from continuously producing these immune cells -- or at least having several batches going at once -- so you're stuck cycling like this?
>

They are replenished. NK (natural killer) cells are a type of lymphocyte, the others being T (thymus) and B (bone marrow) cells. NK's generally make up about 13% of lymphocytes, and are multi-use; once they attack and cause a defective, infected, cancerous etc. cell to die and the DNA within (cellular and any invaders) to fragment they can move on to attack others.

Think: a gang of Woody Harrelsons.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: mikelepage on 08/16/2016 04:30 am
So many caveats here I shouldn't have to mention that this is little more than an educated guess.  But yes, it does make the Mars daily radiation level of 0.64mSv does look slightly more manageable.  I'm thinking you'd probably want to have at least one module much more heavily shielded than the others, and you spend 2 weeks in/2 weeks out.
What prevents the body from continuously producing these immune cells -- or at least having several batches going at once -- so you're stuck cycling like this?

Sorry, that was unclear yes they are replenished on a continuous basis in the body - there is no "batching" in real life. 

I brought up the cycling idea because we're talking about a "threshold" beyond which the body has less capacity to cope.

Using tiredness/sleep as an analogy (not my area, but interesting), the way I understand it is that there are a number of processes (eg. osmotic pressures across cell membranes, or in the ears balance organ) that function in a periodic rather than continuous sense.  So basically you have mechanisms where they either deplete a gradient or store waste over the course of the day, and become less functional as they are reset to their starting values, and we've evolved to sleep while that happens.

The hunch is that the added burden of DNA repair and defective cell elimination (if there is a threshold below which we can deal, and above which we can't) would be a similarly periodic process.  If true, the time length of the period would presumably be proportional to the life-cycle of the effector cells (NK?) and since the NK cells themselves are subject to the same radiation damage as everything else, it would probably be a good idea to minimise exposure whilst they are maturing.   
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 08/16/2016 06:51 am
I found some reported results from Chernobyl research quite interesting. They found that local animal populations were mostly unaffected, when they had expected severe effects. But they found that migratory birds that  arrive exhausted after long travel were a lot more affected with more birth defects, indicating that their low immune status makes them unable to cope.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: mikelepage on 08/16/2016 07:52 am
Yes, good point about the Chernobyl research: it's really not that surprising that all cellular life would have mechanisms to deal with periods of increased ionising radiation.  We know that the Earth's magnetic poles have flipped numerous times, presumably meaning that the ancestors of every living thing on Earth have at some point had to tolerate multiple generations of being hammered by GCRs.  That's not to say humans will be fine on Mars (we might have lost those particular mutations since the last time), but it mightn't be so problematic, either.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: philw1776 on 08/16/2016 03:01 pm
It may be that AIDS research on immune systems leads to immunity boost treatments a decade or 2 from now useful to cope with GCR flux.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: mikelepage on 08/18/2016 07:14 am
It may be that AIDS research on immune systems leads to immunity boost treatments a decade or 2 from now useful to cope with GCR flux.

I hear what you're saying, but to be pedantic, the immune system as we know it currently (as far as I'm aware) doesn't have any role in DNA repair, and that is left up to the damaged cell individually - because repairing radiation damage is a process that seems to have evolved prior to the advent of multicellular life (which immune systems are unique to).  Immune cells work on the assumption that no cell is irreplacable, so if it's not functioning correctly after DNA damage, it's their job to detect and kill it.

So, with apologies to nursery rhymes everywhere, Humpty Dumpty has to do what he can to put himself back together, because the King's men and horses are a murdery lot.

The question is whether we can find the drugs that assist the repair process, before the cells become irrepairably damaged, but because it's in the nucleus of the cell, this is much harder to do (I don't know if any such drugs exist yet). If you imagine that DNA is a hard drive, there's only so much the data can be corrupted by bit-flips/overwrites before it becomes impossible to figure out what was where originally.  Much better to shield the DNA from being damaged in the first place.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: guckyfan on 08/18/2016 09:18 am
Killing off damaged cells is not a bad strategy. So the immune system can do its part. The problem with cancerous cells is they don't kill themselves. The immune system needs to do that and usually does before it gets out of hand.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: john smith 19 on 08/18/2016 09:53 am
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. 
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: docmordrid on 08/18/2016 05:41 pm
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.... (http://sservi.nasa.gov/articles/next-solar-maximum-may-be-safest-time-for-manned-missions-to-mars/)
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Semmel on 08/18/2016 07:34 pm
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.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 08/18/2016 07:51 pm
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.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: docmordrid on 08/18/2016 08:05 pm
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.)
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Semmel on 08/19/2016 06:59 am
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.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 08/19/2016 12:46 pm
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.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 08/19/2016 12:56 pm
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.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Oli on 08/19/2016 01:54 pm
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?
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 08/19/2016 03:00 pm
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
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: CuddlyRocket on 08/19/2016 06:04 pm
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!
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: AncientU on 08/19/2016 07:56 pm
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.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: envy887 on 06/08/2017 06:23 pm
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
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: ZachF on 06/08/2017 06:47 pm
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.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: CuddlyRocket on 06/10/2017 01:38 am
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!
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: mikelepage on 07/02/2017 08:38 am
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.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: gospacex on 07/02/2017 09:00 am
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.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: CuddlyRocket on 07/03/2017 04:15 am
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.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: mikelepage on 07/03/2017 09:46 am
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.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/03/2017 10:21 am
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?
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: alexterrell on 07/03/2017 11:01 am
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.

If the crew spent most of their time in a "hotel style cubicle" 2mx1mx2m - perhaps 8 hours sleeping, 10 hours computer work and reading, and then maybe 6 hours outside, exercising and meeting. With a cubicle next to it, the front, back, top and bottom have 8m2.

5cm of water would be 400kg.  Less if these units are stacked on top of each other. No need for your own water, it would be pumped through.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: alexterrell on 07/03/2017 11:05 am
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.

Good graphs. They say that radiation shielding is going to be pretty much zero in space (5cm of water is still a lot of mass), and not really a problem in Mars accommodation units, where metres of regolith can be used.

The exception would be if propellant was used as shielding, but that is a design difficulty, and most of the propellant is used at the start of the mission.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: livingjw on 07/03/2017 11:56 am
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?
I think he means subatomic particles created by the collision.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: jpo234 on 07/03/2017 01:44 pm
What bits?

Quarks: (https://www.i2u2.org/elab/cms/graphics/PonP.png)
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/03/2017 01:48 pm
What bits?

Quarks: (https://www.i2u2.org/elab/cms/graphics/PonP.png)
You still aren't going to end up with free quarks. You'll still have hydrogen by the end.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: gospacex on 07/03/2017 02:10 pm
What bits?

Quarks: (https://www.i2u2.org/elab/cms/graphics/PonP.png)
You still aren't going to end up with free quarks.

Who said you would?

Quote
You'll still have hydrogen by the end.

Or neutrons, which would transmute some nearby atoms.

Or even lambda-hyperons, which also can merge into some nearby atoms. Such things as Helium-5-Lambda exist (briefly). Even double-Lambda nuclei were observed!

https://arxiv.org/pdf/1111.5748.pdf
"Formation of double-Λ hypernuclei at PANDA"

http://www.sciencedirect.com/science/article/pii/0370269382910310
"The hypernuclei Σ6H and Σ16C were observed..."
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: jpo234 on 07/03/2017 02:20 pm
What bits?

Quarks: (https://www.i2u2.org/elab/cms/graphics/PonP.png)
You still aren't going to end up with free quarks. You'll still have hydrogen by the end.

Yup. There are no free quarks (https://medium.com/starts-with-a-bang/there-are-no-free-quarks-ddec8cb831ea)
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: gospacex on 07/03/2017 02:36 pm
Yup. There are no free quarks (https://medium.com/starts-with-a-bang/there-are-no-free-quarks-ddec8cb831ea)

Note of caution: pop-sci articles tend to have errors. This one, for example, says:

"First off, there’s no longer one type of charge, nor even two [referring to electric], but three."

Wrong. if you count + and - electric charges as "two types of charge", then you should likewise count red and anti-red colors as two types of charge. Which leads to "six types of charge" overall for color interaction, not three. Yes, antiquarks have "negative" colors: anti-red/green/blue. Moreover, gluons carry a pair of color and anti-color charge (actually it's a bit more weird than that for gluons, but that would be way too much to explain in pop-sci).

Later, pictures of antiquarks within mesons have wrong colors.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/03/2017 09:00 pm
The hydrogen (by which I mean proton) itself doesn't get blown to bits. If it defies all odds and gets transmuted into a neutron (which decays to a proton, thus back to hydrogen, if it doesn't hit anything), that's not blown to bits. If it gets somehow incorporated into a larger nucleus, that's not blown to bits either.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: CuddlyRocket on 07/04/2017 02:50 am
The Large Hadron Collider collides protons with other protons. Actually, it's their constituent quarks and gluons that collide, but in any event the result is a shower of sometimes hundreds of particles. The details are somewhat complex, but effectively kinetic energy is converted into mass.

Changing the subject:

Team invention may help to protect astronauts from radiation in space (phys.org) (https://phys.org/news/2017-07-team-astronauts-space.html)

Quote
Scientists at The Australian National University (ANU) have designed a new nano material that can reflect or transmit light on demand with temperature control, opening the door to technology that protects astronauts in space from harmful radiation.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/04/2017 03:24 am
The Large Hadron Collider collides protons with other protons. Actually, it's their constituent quarks and gluons that collide, but in any event the result is a shower of sometimes hundreds of particles. The details are somewhat complex, but effectively kinetic energy is converted into mass.

...
And yet... https://en.m.wikipedia.org/wiki/Baryon_number#Conservation
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: jpo234 on 07/04/2017 08:09 am
Team invention may help to protect astronauts from radiation in space (phys.org) (https://phys.org/news/2017-07-team-astronauts-space.html)

This doesn't do anything about GCR.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: CuddlyRocket on 07/04/2017 09:22 pm
And yet... https://en.m.wikipedia.org/wiki/Baryon_number#Conservation

What is conserved is the arithmetic sum of all the baryon numbers in an assemblage of particles, both before and after any collision. Protons and neutrons have a baryon number of +1. Their anti-matter equivalents have -1. Any particle without quarks has 0 as does any meson (quark + anti-quark). Two protons colliding have a baryon number of +2 - there are quite a few ways to combine varying numbers of +1s, -1s and 0s to end up with a sum of +2.

This doesn't do anything about GCR.

True. But, GCRs are not the only radiation hazard.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: jpo234 on 07/04/2017 09:26 pm



True. But, GCRs are not the only radiation hazard.

But GCRs are the hardest problem because of their high energy.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: CuddlyRocket on 07/05/2017 10:43 pm
True. But, GCRs are not the only radiation hazard.

But GCRs are the hardest problem because of their high energy.

Again true. But even the easier problems are still problems that need solving. Or, at least, solving more efficiently.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: scienceguy on 07/05/2017 10:54 pm
10 m of water will stop pretty much everything. And there are places with lots of water on Mars.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/05/2017 11:14 pm
True. But, GCRs are not the only radiation hazard.

But GCRs are the hardest problem because of their high energy.

Again true. But even the easier problems are still problems that need solving. Or, at least, solving more efficiently.
Except not even that is true. This invention targets UV and thermal. It's not relevant to anything you get if you're inside even a spacesuit let alone a spacecraft.

I guess this highlights the persistent misunderstanding of even basic space radiation knowledge even among scientists and engineers.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: CuddlyRocket on 07/07/2017 05:16 am
10 m of water will stop pretty much everything. And there are places with lots of water on Mars.

It won't stop GCRs.

10m thick water shielding has a mass of 10 tonnes per m^2. This probably has structural implications for habitats and is unlikely to be practical for rovers and EVAs. :) In other words, it's unlikely to be a panacea. Radiation mitigation is likely to involve a number of strategies and technologies.

But even the easier problems are still problems that need solving. Or, at least, solving more efficiently.

Except not even that is true. This invention targets UV and thermal. It's not relevant to anything you get if you're inside even a spacesuit let alone a spacecraft.

Yes, we have effective solutions for spacecraft and spacesuits. But are they the most efficient solutions? As the authors say: "Our technology significantly increases the resistance threshold against harmful radiation compared to today's technologies..." They also say that their invention could be tailored for other light spectrums including visible light ..." Apart from making lighter window shades, might it work for X-rays and Gamma rays?
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/07/2017 06:02 am
No, it won't help x-ray and gamma ray. Way too short of wavelength.

Look, space radiation is basically all very fast charged particles with a few secondary neutrons and x-rays (which go right through this material). Their claims to the contrary, it simply isn't going to help shield astronauts from space radiation.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Bynaus on 07/07/2017 06:24 am
10 m of water will stop pretty much everything. And there are places with lots of water on Mars.

It won't stop GCRs.

Yes it would, at least down to the level of the radiation environment on Earth's surface. 10 m of water is just 1 bar, so 10 m of water will shield you just as well as the Earth's atmosphere (because to first order, radiation shielding is mass between the part to be shielded an the radiation source; to second order, it is the hydrogen content of the shielding material, which likely makes 10 m of water an even better shield than the Earth's atmosphere).

EDIT: regarding the phys.org article linked above, I agree with Robotbeat - this will do nothing against GCRs, SCRs, gamma rays, etc. A material which can screen out certain wavelengths at will should have many potential applications, but a full protection from cosmic rays is not among them.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Robotbeat on 07/07/2017 06:29 am
...and before anyone says "but magnetosphere," remember that the magnetosphere isn't NEARLY as important for shielding from radiation as the atmosphere is, and the magnetosphere doesn't even shield the REALLY high energy GCRs beyond the geomagnetic cutoff...
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: scienceguy on 07/07/2017 06:14 pm
I just wanted to point out, that in a paper by Sanin et. al. (2015), it says that Galactic Cosmic Rays hitting Mars’ surface have an energy of greater than 100 MeV (p. 117), and that these are all stopped by the atmosphere and turned into energetic neutrons.

The actual wording in the paper is as follows:

Besides the pulsing DAN PNG, there are two other permanent sources of neutrons in the vicinity of the rover: the secondary emission of the soil due to irradiation by MSL MMRTG and the secondary emission of the soil due to bombardment by energetic particles of Galactic Cosmic rays (GCRs). The GCR flux varies in time due to solar activity. These variations are generally slow and smooth with 11-year period or fast during Solar Particle Events with time scales from minutes to days. The GCR particles are primarily protons with energies > 100 MeV. They generate neutrons in the Martian atmosphere and regolith by spallation reactions. Most of these secondary neutrons have initially high energy (>20 MeV) and are able to produce additional charged particles and next generation of neutrons by nuclear interactions with the regolith and rover material.

Perhaps I missed it or am not reading the paper correctly, but it seems to say that GCR’s do not even make it to the surface of Mars: they are just turned into energetic neutrons which can be stopped by water or any other hydrogen rich material (or borosilicate glass).

https://en.wikipedia.org/wiki/Neutron_radiation

Reference
Sanin, A. B. et. al. (2015) Data processing of the active neutron experiment DAN for a Martian Regolith investigation. Nuclear Instruments and Methods in Physics Research A. 789: 114-127

edit: oops I realized the paper says that some GCR's reach the regolith
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: Bynaus on 07/11/2017 10:43 pm
I just wanted to point out, that in a paper by Sanin et. al. (2015), it says that Galactic Cosmic Rays hitting Mars’ surface have an energy of greater than 100 MeV (p. 117), and that these are all stopped by the atmosphere and turned into energetic neutrons.

The actual wording in the paper is as follows:

Besides the pulsing DAN PNG, there are two other permanent sources of neutrons in the vicinity of the rover: the secondary emission of the soil due to irradiation by MSL MMRTG and the secondary emission of the soil due to bombardment by energetic particles of Galactic Cosmic rays (GCRs). The GCR flux varies in time due to solar activity. These variations are generally slow and smooth with 11-year period or fast during Solar Particle Events with time scales from minutes to days. The GCR particles are primarily protons with energies > 100 MeV. They generate neutrons in the Martian atmosphere and regolith by spallation reactions. Most of these secondary neutrons have initially high energy (>20 MeV) and are able to produce additional charged particles and next generation of neutrons by nuclear interactions with the regolith and rover material.

Perhaps I missed it or am not reading the paper correctly, but it seems to say that GCR’s do not even make it to the surface of Mars: they are just turned into energetic neutrons which can be stopped by water or any other hydrogen rich material (or borosilicate glass).

https://en.wikipedia.org/wiki/Neutron_radiation

Reference
Sanin, A. B. et. al. (2015) Data processing of the active neutron experiment DAN for a Martian Regolith investigation. Nuclear Instruments and Methods in Physics Research A. 789: 114-127

edit: oops I realized the paper says that some GCR's reach the regolith

Yes, most of them actually. See e.g. this paper:

http://science.sciencemag.org/content/343/6169/1244797
(paywalled, but google the title)

As I mentioned above, radiation shielding is to first order the amount of matter between the radiation source and the target. On the martian surface, shielding amounts to about 20 g/cm2 (you can imagine a column with a mass of 20 g above each square centimeter - if the material is water, then the column would thus be 20 cm high, and about 13 cm if it is CO2; note that this shielding also varies with atmospheric pressure, with the height of the ground, and with solar activity). This is enough to shield some GCRs and SCRs (with energies <150 MeV/nucleon), and to produce some secondary neutrons, but the shielding is still far from the one provided by the Earths atmosphere (which corresponds to about ~1000 g/cm2 or 10 m of water).

In the paper, they find that the radiation level on the martian surface is at about 44% of the value in interplanetary space. The bulk mass of Mars provides most of the additional shielding (89% of the total reduction), with the rest being due to the martian atmosphere.
Title: Re: Radiation mitigation strategies for early SpaceX Mars missions
Post by: LMT on 11/17/2017 06:58 pm
I just wanted to point out, that in a paper by Sanin et. al. (2015), it says that Galactic Cosmic Rays hitting Mars’ surface have an energy of greater than 100 MeV (p. 117), and that these are all stopped by the atmosphere and turned into energetic neutrons.

The actual wording in the paper is as follows:

Besides the pulsing DAN PNG, there are two other permanent sources of neutrons in the vicinity of the rover: the secondary emission of the soil due to irradiation by MSL MMRTG and the secondary emission of the soil due to bombardment by energetic particles of Galactic Cosmic rays (GCRs). The GCR flux varies in time due to solar activity. These variations are generally slow and smooth with 11-year period or fast during Solar Particle Events with time scales from minutes to days. The GCR particles are primarily protons with energies > 100 MeV. They generate neutrons in the Martian atmosphere and regolith by spallation reactions. Most of these secondary neutrons have initially high energy (>20 MeV) and are able to produce additional charged particles and next generation of neutrons by nuclear interactions with the regolith and rover material.

Perhaps I missed it or am not reading the paper correctly, but it seems to say that GCR’s do not even make it to the surface of Mars: they are just turned into energetic neutrons which can be stopped by water or any other hydrogen rich material (or borosilicate glass).

https://en.wikipedia.org/wiki/Neutron_radiation

Reference
Sanin, A. B. et. al. (2015) Data processing of the active neutron experiment DAN for a Martian Regolith investigation. Nuclear Instruments and Methods in Physics Research A. 789: 114-127

edit: oops I realized the paper says that some GCR's reach the regolith

Yes, most of them actually. See e.g. this paper:

http://science.sciencemag.org/content/343/6169/1244797
(paywalled, but google the title)

As I mentioned above, radiation shielding is to first order the amount of matter between the radiation source and the target. On the martian surface, shielding amounts to about 20 g/cm2 (you can imagine a column with a mass of 20 g above each square centimeter - if the material is water, then the column would thus be 20 cm high, and about 13 cm if it is CO2; note that this shielding also varies with atmospheric pressure, with the height of the ground, and with solar activity). This is enough to shield some GCRs and SCRs (with energies <150 MeV/nucleon), and to produce some secondary neutrons, but the shielding is still far from the one provided by the Earths atmosphere (which corresponds to about ~1000 g/cm2 or 10 m of water).

In the paper, they find that the radiation level on the martian surface is at about 44% of the value in interplanetary space. The bulk mass of Mars provides most of the additional shielding (89% of the total reduction), with the rest being due to the martian atmosphere.

The cosmic ray spectrum is certainly a key to shielding.  For a modeled spectrum of cosmic rays at the martian surface, see for example:

Wilson, J. W., Kim, M. Y., Clowdsley, M. S., Heinbockel, J. H., Tripathi, R. K., Singleterry, R. C., ... & Suggs, R. (1999, January). Mars surface ionizing radiation environment: Need for validation. In Workshop on MARS 2001: Integrated Science in Preparation for Sample Return and Human Exploration (p. 112).

That GCR proton flux peaks around 70 MeV, and the SPE proton flux peaks around 100 MeV.  Fortunately, magnetostatic shielding can deflect at higher energies.  Our simple artificial geomagnetic field design deflects 500 MeV protons well, and 1 GeV protons partially.  It can't block all cosmic rays, but it can block solar storms and even solar flares, apparently.

Quote
The Urbanization of Mars

HP Mars Home Planet Urbanization Concept Challenge

Artificial Geomagnetic Field to Protect a Crewed Mars Facility from Cosmic Rays (https://launchforth.io/LakeMatthewTeam/artificial-geomagnetic-field-to-protect-a-crewed-mars-facility-from-cosmic-rays/overview/)

(http://www.lakematthew.com/wp-content/uploads/2017/11/Fig5.png)

(http://www.lakematthew.com/wp-content/uploads/2017/11/Fig7.png)