Author Topic: Radiation mitigation strategies for early SpaceX Mars missions  (Read 35071 times)

Offline CuddlyRocket

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.

Online guckyfan

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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.

Offline philw1776

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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.
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Offline the_other_Doug

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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.
-Doug  (With my shield, not yet upon it)

Offline philw1776

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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.
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Offline john smith 19

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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
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Online guckyfan

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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.

Offline Nathan2go

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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.

Offline gospacex

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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.

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.

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.

Online Robotbeat

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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.
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Offline whitelancer64

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?
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Online guckyfan

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

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

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

Offline philw1776

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That's depressing.  It will be nearly impossible to get rid of any mice that make it to Mars.   :(
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Offline Nathan2go

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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.

Offline Impaler

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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.

Online Robotbeat

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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...
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Offline DAZ

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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.



Online Robotbeat

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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.
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Online Robotbeat

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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.
« Last Edit: 06/19/2016 03:42 AM by Robotbeat »
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Online Eric Hedman

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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.

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