Author Topic: Radiation mitigation strategies for early SpaceX Mars missions  (Read 37812 times)

Offline Dalhousie

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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.

Real world studies of areas with high natural radiation would suggest the opposite.
"There is nobody who is a bigger fan of sending robots to Mars than me... But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans" Steve Squyres

Online guckyfan

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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...

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.

Online guckyfan

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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.

Offline docmordrid

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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.

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

http://news.mit.edu/2016/portable-pharmacy-on-demand-0331
DM

Offline CuddlyRocket

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!

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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?

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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.

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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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.

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.

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.

Online guckyfan

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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.


Online guckyfan

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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.

Online guckyfan

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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.


Offline jjwaDal

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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.

Offline TaurusLittrow

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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.

Online MikeAtkinson

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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.

Offline gospacex

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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.

Offline gospacex

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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.

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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.
« Last Edit: 06/19/2016 12:28 PM by gospacex »

Offline TaurusLittrow

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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?

Online guckyfan

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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.

Offline oldAtlas_Eguy

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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


Offline gospacex

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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.

Offline oldAtlas_Eguy

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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.

Offline SpacedX

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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.

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