Author Topic: Radiation mitigation strategies for early SpaceX Mars missions  (Read 90713 times)

Offline BobHk

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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.
« Last Edit: 06/24/2016 08:42 pm by BobHk »

Offline Robotbeat

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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.
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Offline Aussie_Space_Nut

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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  :)

Offline Robotbeat

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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.
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Offline BobHk

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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. 

Offline Robotbeat

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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
« Last Edit: 06/25/2016 06:52 pm by Robotbeat »
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Offline Aussie_Space_Nut

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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.  :)
« Last Edit: 06/26/2016 04:22 am by Aussie_Space_Nut »

Offline Impaler

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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
« Last Edit: 06/26/2016 04:58 am by Impaler »

Offline john smith 19

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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.
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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?
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline Oersted

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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. 

Offline Aussie_Space_Nut

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What about frozen bricks of mud individually covered in plastic?

Then glue them together?

Offline Hotblack Desiato

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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.

Offline Robotbeat

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...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.
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Offline Robotbeat

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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.
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Offline gospacex

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"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.

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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.

Offline gospacex

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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.

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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.

Offline Robotbeat

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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.
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Offline Impaler

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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.

Offline Robotbeat

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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)
« Last Edit: 06/27/2016 04:43 am by Robotbeat »
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Offline Exastro

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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 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.


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