Author Topic: Radiation mitigation strategies for early SpaceX Mars missions  (Read 40935 times)

Offline Robotbeat

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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.
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.
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Online guckyfan

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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.

Offline Robotbeat

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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.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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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.

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:


Offline gospacex

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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.

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.

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.
« Last Edit: 06/19/2016 05:12 PM by guckyfan »

Offline the_other_Doug

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

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.

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."

Online guckyfan

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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.

Offline Robotbeat

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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.
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To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Impaler

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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.

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.

Offline Robotbeat

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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.

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
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To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Exastro

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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.

Online guckyfan

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The Mars ice house.

http://www.marsicehouse.com/

Something needs to be done to avoid the ice sublimating but it seems there are solutions.

Offline Chris_Pi

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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...

Online MikeAtkinson

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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.

Online guckyfan

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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.

Offline Robotbeat

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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.
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Offline gospacex

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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...

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.

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?

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