Lunar Foxhole

Rereading some of the older posts on Lunar exploration, I ran into a lot of discussion on short term vs permanent outposts or bases. The assumption seems to be that short sortie missions will have minimal or even no radiation protection.

A quick thought is that a foxhole approach might be worth looking into for the short sortie or light mobile base concepts. Troops in the field that are likely to get shot at often dig or blast a small hole for shelter. Nothing is assumed to come from below, horizontal incoming is eliminated, and danger is reduced to vertical from above. Then the danger from above is often reduced with logs, sandbags, or even bodies in extreme cases.

With the foxhole model, it seems possible that a small hole can be created in the lower section of a crater to provide radiation protection from 80% of the sky not already covered by the planet. The hab section is lowered into the hole. Then the lander or wheeled vehicle can be parked over the top of the hole to help shield the remaining exposed directions from cosmic radiation. Solar radiation can be almost entirely eliminated from hitting the hab module.

With no high value real estate to destroy, or neighbors to annoy, the hole could be impact from a trans lunar projectile at 2,300 m/s. It could also be explosive, mechanically dug, or pneumatic  as Jon has posted about.

It seems to me that radiation protection for sorties or mobile exploration should be fairly simple except for time in transit.hab

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I do construction for a living and aerospace as an occasional hobby. I am an inventor and a bit of an entrepreneur. I've been self employed since the 1980s and working in concrete since the 1970s. When I grow up, I want to work with rockets and spacecraft. I did a stupid rocket trick a few decades back and decided not to try another hot fire without adult supervision. Haven't located much of that as we are all big kids when working with our passions.

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About johnhare

I do construction for a living and aerospace as an occasional hobby. I am an inventor and a bit of an entrepreneur. I've been self employed since the 1980s and working in concrete since the 1970s. When I grow up, I want to work with rockets and spacecraft. I did a stupid rocket trick a few decades back and decided not to try another hot fire without adult supervision. Haven't located much of that as we are all big kids when working with our passions.
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23 Responses to Lunar Foxhole

  1. Paul451 says:

    “the hole could be impact from a trans lunar projectile at 2,300 m/s.”

    An impactor will produce a crater… obviously, since that’s how craters were formed.

    Hence the hole produced by an impactor will be roughly the same proportions as a crater. Low and wide. Not suitable for what you intend (or at least no more suitable than an existing crater anyway.)

    (Explosive craters wouldn’t be much different. Most of the blast material falls back into the whole, making it shallow. To dig out a hole deep enough for a hab, plus shielding-or-vehicle on top, you’d need a hell of a lot of explosives.)

    But there might be existing features you can use (such as unusually steep-sided craters or rilles).

    The problem would be the instability of steep walls. For sortie missions, you’re dealing with NASA safety mentality. They’d rather deal with the known danger from radiation than have to plan around the harder to predict risk of side-wall collapse. Especially when trying to lower the habitat into the hole. Plus getting safely from the habitat to the surrounding terrain, and back, over and over.

  2. ken anthony says:

    The usefulness of landscaping is pretty obvious however it’s done. With the right implements a dozer the mass and size of former lunar rovers should be plenty to do the job.

    All it would take is to be serious about a moon base.

  3. DougSpace says:

    I think that permanent bases should be set up (inflated) and covered telerobotically prior to crew arrival. Sorties away from the permanent base could (should) be done with a rover in which the cab is shielded with at least 20 gm/cm2. For polyethylene, this would be about 12 cm thick on 5/6 sides. For a crew of two, I estimate that this would be about 2.14 tonnes of polyethylene cabin shielding which would be a reasonable portion of the overall vehicle mass. NASA considers 20 g/cm enough for solar flares and it cuts GCR exposure by about half. The same vehicle with the same shielding could be used by different crew at different times.

    I generally don’t like sortie missions. The focus going forward should be on development and a permanent base / small settlement. The base should produce propellant from local resources and scientific sorties should be suborbital hops to different locations and then return to base for refueling.

    We should try to minimize the risk to crew by minimizing the amount of crew rotations. And also, telerobots could do a lot of the geology field work and sample collection. So, instead of a launch, land, ascent, and re-entry for each sortie, we should do multiple sorties on each mission.

  4. ken anthony says:

    On the moon, I imagine rovers on the surface with people mostly tunneling. I see very few permanent residents because it’s too easy to rotate personnel and because of not being self sufficient the crew will always be limited in number. I don’t see the moon producing anything that would promote growth. Mars has no such limit and people going there would have a great incentive to stay.

  5. john hare says:

    I think early on there will be a need for exploration and prospecting. A crew of one or two spending several days out checking behind the robots and looking for what they may have missed. It would be a shame to spend billions on a permanent base for resource extraction, when a bit more prospecting is likely to find better locations. A poorly located permanent base could be one of the most expensive ghost towns in history.

    I could see a long (Earth) day of driving followed by a good nights sleep before a series of short EVAs in a likely location. It seems possible that an excursion of one Lunar day could have a rover checking a dozen sites over a several hundred kilometer radius with the radiation exposure in the 30-50 hour range. given a minimal shelter at the stops.

    Given the issues Paul brought up, it seems likely that natural features would play a prominent part in the protection with some mechanical digging in at each stop. If there is a type of shaped charge that would clear out an appropriate shelter under Lunar conditions, that might be an option. I can’t see NASA working this model. It would more likely be some corporation in prospector mode.

  6. DougSpace says:

    Hi Ken. Tunneling requires much more digging of compacted regolith than simply pushing the fluffy ‘topsoil’ onto a habitat before inflating. As a starting point, it seems to me that the later is easier with a fair less risk of breakdown.

    I don’t think that it’s easy to rotate crew. Typically it would cost in the hundreds of millions for each crew rotation and each crew rotation would involve considerable risk to the lives of the crew. Loss of crew could endanger the program. So I advocate extending crew stay by monitoring certain biomedical indicators as return criteria.

    Here’s my AIAA paper on the topic:

    And here’s my Space Show on the topic:

    Self-sufficiency is not an all or nothing thing. I think that the right criteria is how much payload mass does not have to be launched from Earth due to taking certain measures. So, extending crew stay can significantly cut the number of launches necessary. Producing in situ propellant would be up there too. Then water for consumption and food. Just those things would reduce the mass needing to be delivered substantially.

    We shouldn’t look at the Moon or Mars as needing to produce something in order to be economically viable. Retirement communities don’t mine anything and yet they get established and grow for decades. Elon’s model of the overlap between those who can afford to go and those who want to go is the right model for economic sustainability. Later, secondary services, and local products would grow in support of the initial inhabitants.

    The Moon has the distinct advantages over Mars in that it would cost less to get to and people living there could be telepresent in an interactive manner at family events on Earth. If going to Mars, one has to cut family ties much more. I believe that studies show that this will be a significant factor. The incentive to stay on the Moon will be strong because one spent so much money to go. Going & returning such as with space tourism will be a small portion of the space economy compared with going to stay. Few people spend as much on their tourism as they do on their retirement.

  7. DougSpace says:

    For an initial habitat, 30 cm of regolith piled on top of an inflatable habitat would provide a 50% reduction in GCR radiation providing a typical crew member (e.g. 47 y/o male) with about 5.7 years before they meet their radiation career limits.

    However, if one were to dig down far enough to provide that same amount of protection, one would have to dig a footprint of about 2.8 meters. That’s nearly 10 times the volume. And when considering the greater difficulty of excavating compacted dirt and the greater time for wearing out equipment, it would probably be about 20 times more difficult to dig under ground rather than just to push regolith onto a habitat before inflating.

  8. Johnhare says:

    I guess working with dirt for a living doing foundations and other concrete work, I tend to seem regolith handling as the easy part.

  9. gbaikie says:

    Paul451 says:
    “December 26, 2016 at 7:35 am

    “the hole could be impact from a trans lunar projectile at 2,300 m/s.”

    An impactor will produce a crater… obviously, since that’s how craters were formed.

    Hence the hole produced by an impactor will be roughly the same proportions as a crater. Low and wide. Not suitable for what you intend (or at least no more suitable than an existing crater anyway.)”

    One can design a projectile to make deep holes [aiming it to hit a existing crater, is another matter]. Natural craters may occur in which an impactor hits the middle of existing crater. And different natural impactor can make deeper craters, compared average crater by average impactors- also the age of the impact crater could affect how deep it it. I would tend to towards looking for a deep hole rather than making one- unless I had very specific requirements for some hole.

    It seems to me that GCR is not much of problem in regards the Moon- or solar flares would be more of a concern. I don’t think GCR are much of problem if you can get to Mars in 3 months or less.
    GCR are twice as much during solar minimum as compared to Solar Maximum- we currently in a solar minimum- or recently have been entering it, and will be in it’s “depths” for several years. And a quieter Sun might more common in coming decade or two or three.
    A part of going to Moon or Mars will related to how well we can predict solar activity- I think we a bit better at this than compared to the times of Apollo, but not much better.
    Roughly, in terms of GCR, the Moon is like ISS’s problem with GCR, but the effects of solar storm is worst on the lunar surface as compared to ISS. And roughly in free space [traveling to Mars] GCR would about twice the amount per month as one gets on ISS.
    GCR comes from all directions- though there are specific directions that one could expect more or less from. But like solar activity- little is know about what direction one can predict where get more or less GCR in the future [a problem of predicting future].
    But basically GCR comes from all direction, and if one hemisphere is blocked, than you get 1/2 as much [particularly if in orbit- traveling in circle or the planet is rotating].
    So one talking about the geometry of sphere or one talking about how much of the total sky you can see [if on planetary surface or in orbit].
    So if in a hole, one sees less sky as compared to being on top of a mountain and being surrounded by mountains [which are near you] that also limits the view.
    But anyhow, in terms human exploration of the Moon vs rather staying on the Moon for months and years, GCR is not much of problem. And in terms of Mars human exploration, GCR are mostly about traveling to Mars and whether it’s solar Min or Max.
    If going to stay on the Moon, it seems one should find lava tubes- this also applicable to staying on Mars.
    With the Moon, it seems we have to find out, whether we should stay on the Moon for any significant amount of time [this also applies to Mars].
    With the Moon, it seems to me there is only a small region which needs to be explored- the lunar polar region. And of particular interest is area near the peak of eternal light- this would very small area compared the surface of Mars, or compared the State of Oregon.
    If we find minable water on the Moon, and if lunar water can be profitably mined, then we will get more exploration of the Moon- both by government and private interest. Or if we find minable lunar water, we will stay for longer periods on the Moon- people will stay for month or will stay permanently- in sense you could move to Georgia and you might stay there for rest of your life, or move somewhere else in a few years or be the third generation that has lived there.

  10. Jonathan Goff Jonathan Goff says:

    Any chance I could get a copy of that AIAA paper from you? I’ve been making a similar point for years (re: extended stays on the Moon), but would like to see what details you came up with.

  11. ken anthony says:

    Doug, great points, well said. My experience is that people are filtering out your most salient point about growth. Certainly a slower rotation rate lowers both mission cost and risk. Economics (growth in particular) seems to be the weakest understood feature of exploration and colonization.

    The other is strategy, which Zubrin gets right regarding surface mobility, but with perhaps a further refinement. The farther you explore from your base camp the less intense it will be for any particular spot. Stuff will get missed (regardless of strategy actually.) Optimum strategy will of course depend on the geology which isn’t known.

    While tunneling is more difficult (on mars I recommend trenching rather than tunneling) I believe it results in better mobility and habitat space because…

    While slower than throwing dirt on an inflatable habitat it has no stopping point. When you run out of inflatables you run out of volume. Tunnels have no volume restriction and the minerals removed have additional value. You are protected from radiation while tunneling. The inflatable habitat provides a relatively quickly built entrance to your tunnels (which will not all be connected at first, if ever.)

    An additional advantage of tunnels over inflatables is the gracious failure of life support. The larger the life support volume the more time you have to fix different levels of failure.

    Basically I’m saying a hybrid strategy is best.

  12. Peterh says:

    A tunnel, if you do nothing to the interior, is going to leak through natural fissures. And more if blasting it used as part of the tunneling process. But those fissures could be sealed with a non-structural coating with much less mass than inflatable that needs to hold pressure against the diameter. A process I’ve considered for Mars, where working fluid can be had for the pumping, involves a colloid of soft particles in a tunnel being pulled by the leaks into fissures.

  13. The radiation exposure on the lunar surface is actually not too different than the exposure experienced at LEO.

    11 to 38 Rem exposure on the Moon per year and 20 to 40 Rem experienced at LEO per year. But there is one– deadly difference– between the two and that’s the heavy nuclei component of cosmic radiation beyond the Earth’s magnetosphere. Long term exposure to heavy ions could cause brain damage and heavy ions have apparently significantly increased the rate of heart disease in the Apollo astronauts even though they were only exposed to heavy ions for less than two weeks.

    However, shielding against heavy ions only requires about 20 gm of mass per cm2. So you could easily thicken helmets and visors and pressure suits with dense metallic materials (iron, tungsten, lead, etc.) only a few centimeters thick to protect astronauts from heavy ions. Even with the extra heavy pressure suit, an astronaut would still not weigh more than he or she would on Earth with no clothes on at all thanks to the Moon’s 1/6 gravity.

  14. DougSpace says:

    Hi Jon. Here is a paper I submitted for a NASA challenge. It led to my AIAA paper which I think is better. I’ll email you the AIAA paper and anyone else that wishes my AIAA paper just request that of me at my gmail account: DougSpace007.

  15. DougSpace says:

    I would also like to point out that extending crew stay really blurs the line between what is a base and what is a settlement. I maintain that the real definition of settlement is when people are settling down. If people are settling down then that is a settlement. Settlements are not necessarily determined by size, economic independence, economic productivity, or the ability to have children. In particular, if retirees are moving away from Earth to stay, their settlement may start with a few people, the money for their settlement comes from their savings not from mining, and they will have no children with them. Yet, as the off-Earth retirement community grows, it will become increasingly obvious that it is a real settlement – Private housing, life support production, growing their own food, community meetings, perhaps it’s own governance structures, etc.

    By way of historic analogy, consider a Mormon couple being sent to some distant valley to settle down, build their home, start growing their own food, raising animals, and preparing for the arrival for others. There may be no ore in the area and they may grow food for themselves. Relatives in the city might occasionally send them manufactured items that they couldn’t produce themselves. But they are settling and could rightly be recognized as being the first settlers for that area. Same with settling off Earth.

    So, what does it take to do this initial type of settlement off Earth? It takes a habitat, adequate, ongoing life support including maintaining equipment, long-term protection from radiation and insufficient gravity amongst other things. These things are already needed for a permanent base. So, really, the only difference is that a base is a worksite and an initial settlement is a home. And a home is where you have a family. And a family can be as small as a husband and wife.

    So, I for one think that the start of settlement doesn’t have to be many decades, trillions of dollars, nor need new, super massive rockets. Additionally, since a base can have a public (government) value and a base could be an initial settlement then a public-private program (e.g. Lunar COTS) could be funded largely by government funds yet also achieve the space advocacy goal of starting settlement.

    I believe that this is very doable, I think that we should do it as a priority, and I think that it best that a free country, in particular the US, should do it before someone else finds out that the historic step of starting humanity’s first off-Earth settlement is as much a matter of choosing to do so rather than some huge technical or financial obstacle.

  16. Paul451 says:

    “I guess working with dirt for a living doing foundations and other concrete work, I tend to seem regolith handling as the easy part.”

    Below a few inches, regolith vacuum cements together. It’s not rock, but it ain’t dirt either. Digging in frozen ground would probably be a good analogy.

    (Throw in the fact that even the loose stuff is fine sharps. No weathering. Mixed with glass and metal. Nightmare fuel for mechanical joints. (And lungs.))

    “and if one hemisphere is blocked, than you get 1/2 as much”

    Not quite. Secondaries produced by GCRs will backscatter off the surface. So less than half the dose is blocked by blocking half the sky.

  17. Doug,

    Great comment on what settlement is. Could I repost that as a blog post (credited to you)?


  18. DougSpace says:

    Sure, go ahead. Thx, Doug

  19. gbaikie says:

    DougSpace: “I believe that this is very doable, I think that we should do it as a priority, and I think that it best that a free country, in particular the US, should do it before someone else finds out that the historic step of starting humanity’s first off-Earth settlement is as much a matter of choosing to do so rather than some huge technical or financial obstacle.”

    I think settlement in space are doable, BUT one needs exploration first. With Utah there was exploration AND with settlement efforts more exploration was done- and exploration continues to present today.

    I would say settlements are generally associated with markets-and towns are market places. So settlements may not be same as towns, but settlements tend to have some access to town[s] or village[s].
    The difference of a base and and settlement or town, is with base one goes thru a bureaucracy to get supplies. Or as example a company run town is more like a base than a town. Or also a military base can allow “independent retailers” to operate which can provide things soldiers may want which the government doesn’t provide.

    With retirees there is the obvious real estate market, and various other services such medical, security, or entertainment activities are part of value of this real estate.
    Retiree also want friends and relatives to be able to visit them and/or them being being able to visit friends and relatives [not in retirement community].
    So roughly settlements need access to rest of the world.
    Or how would create settlements on the continental shelf of the coastal of the oceans- main thing is make cheap and fast access to them. So for example, some kind of ferry system.
    One also needs to technology to cheaply live on “open ocean” and legal issues, but would say “right” access could way to get the other stuff done. Or I think of we had flying cars [which could used to get to continental shelf location] we would soon get such settlements. And it’s mostly real estate market.

    With the Moon and Mars the main thing is that Moon and Mars are better than Earth- not that they are similar to Earth. The Moon and Mars are better for number of reasons- low gravity would have to be one of the reasons.
    One reason could related to vertical living- or one’s environment is more 3 D . Or related to idea that on Moon and Mars you “have to” live in caves.
    There are advantages to living on low gravity world and there are advantages of living underground [plus also living high above the ground level].
    Or on earth we limited to in the depth and height to live at- water table and geothermal heat limits depth and gravity and other factors limit height.
    High population density conditions [which isn’t crowded] has advantages.
    Of course one could say that we should live in some orbit rather on any the planets- in terms of 3 D or less gravity and what I talking about with Mars and/or Moon is more of distant future rather near term advantages.
    I think near term advantage of Mars and/or the Moon is cheaper access to space. And the main advantage of cheaper access to space is the most beneficial for Earthlings.
    The present advantage of access to space is using Earth’s orbits. And the most critical or compelling advantage relates to military security. Or due to security concerns US must have access to space. This also applies to all nations. In this regard space access is not an options, it’s a necessity.
    And of course there other aspect other than security [only or strictly speaking] about access to space being necessity rather than option. And boil it down to access to space allows one to the ability to do things cheaper- or on could do everything done using satellites without using satellites but this would cost a lot more [and generally be more much more dangerous in terms of human lives and simply cost so much one have to “make do” without it].
    So as saying using the Moon and/or Mars would increase our access to earth’s orbits and with enough of this improved access to space we could do things like having Space Power Satellites- but SPS are long term thing rather than short term thing.
    Or before we think about making SPS so they provide enough electrical power for cities on Earth, we MUST have electrical market in space. Or have places beyond earth surface in which one buy as much electrical as you need rather having to make the powerplants to get this electrical power.
    Btw, having access to an electrical market on the continent shelves would also be something needed for settlements there.
    The Moon is quite a favorable location in terms of starting a electrical market in space.
    And rocket fuel is a kind of a portable electrical energy- LH2 and LOX are a needed part of fuel cell battery. So lunar water mining uses lots of electrical power and this electrical power could sold for other consumers of electrical power – and the rocket fuel can be used to power fuel cells to make electrical power. Or with this chemical energy one get a surge of a lot kw watt of power and at some remote location- ie, beamed propulsion or mass drivers.

  20. Andrew Swallow says:

    The USA will have unmanned lunar landers several years before it has manned landers. If you want several sites investigated design small robotic rovers. To cover large distances they will need large solar panels to acquire the power. Built to survive the hot lunar days and cold lunar nights.

  21. DougSpace says:

    Andrew, the lander-rover system is smart. One could not only investigate a number of sites but collect samples and then cache them as well. But I actually think that we should hold off on scientific, geologic, robotic exploration. I think that when we get to the point where the human landers can be fully refueled from lunar polar ice, there will be a long line of nations that would like to conduct their own, inexpensive, “Apollo program” by doing a (5-6, 10 degree) series of suborbital hops before needing to return to the poles to refuel. So, we need to leave some of the best sites for them to have fun at. Yes it will delay the science a bit but the science isn’t that urgent. Having great, unexplored places for astronauts to go to would be an important anchor business to transition from pure NASA support to pure market support (e.g. retiree settlement).

    I suspect that one could plan when the various sites are visited such that you always have sunlight there before you conduct the next suborbital hop to the next sunlit site.

  22. DougSpace says:

    Hi gbaikie. We need to be careful when making historic analogies. They are often misleading. True, most towns served as a market place. Does this therefore mean that if one cannot figure out something that’s more profitable in space than investing the same money in some venture on Earth that space settlement definitely cannot happen?

    I think that the key to understanding this is that certain people want to go to Mars or the Moon themselves for reasons that have nothing to do with making a profit. Look at all of those Mars One candidates. Probably none of them is doing it because they think that it would be more profitable than pursuing a career on Earth. Rather, as subjective a reason that it is, the people who want to go to Mars or the Moon do so because they think that it would be cool. So it really does come down to Elon’s concept that the people who would pay to go to Mars are the intersection of those able (financially) to do so and those who want to (for whatever reason they have).

    Then one could say, “OK, that explains how people could get to the Moon or Mars but how will such a settlement be sustained? Who would pay”?

    The answer lies with a historic analogy that does work — retirement communities. How many retirement communities sustain themselves by mining, or reality TV shows, or inventing things? Practically none. So then, how can they sustain themselves much less grow? The answer is simple and it’s the same answer as to how the residents got there in the first place. It’s the accumulated wealth of the retirees that sustains these communities. Accumulated wealth is what will initially connect the markets of Earth with space settlements. This resolves the recurring question of “What’s the market” and “Who will pay for it”?

    Sure, there will be people within the community growing and selling food, providing medical services, constructing and selling new habs from local resources, etc. But it will be the accumulated wealth of the retirees that will form the economic basis of these early settlements.

  23. Ben says:

    Hi Doug

    Loved reading this thread, and your post got my mind whirring.

    The retirement home is an excellent analogy.
    But I wonder whether (assuming we don’t even have to be talking about actual retirees) that is a viable form for a community given that in order to continue to exist and progress successfully the community as a whole would require a common direction.

    That aim in a space settlement could be to grow the community, or to provide a retreat for a select few, or to become self sufficient or profitable, or even to aim to be a future base for science/further landings – I mean the ultimate aim could be almost literally anything and would most probably something in between all of these things.

    A community of retirees in a retirement home have a relatively common set of goals for the retirement home. In most cases they want it to be a relaxing place to spend the remainder of their days where there are other similarly-minded people and for their subscriptions they know they will be fed, have regular entertainment nights available, medical care, trips to town etc. There certainly aren’t residents there who wish to start profiteering from being there, or are urging others to allow a new wing to be built so their friends can come live there too, or to close a wing if they feel it’s too big or there is someone they don’t like living there.

    A community like this is ultimately managed by a management company so that all continues in relative harmony and marketing and selling is performed to ensure there will always be a steady stream of new residents and new money coming in the door.
    A lot of this is applicable on of consideration to a space settlement but a community funded solely by individuals who are not similarly-minded retirees is immediately going to be beset by a host of problems relating to where that funding should be spent. Without an over-arching governing system (ie one that at the current time can only be provided for by a government or a massive corporation) these conflicts will be extremely hard to avoid and provide additional obstacles on top of those already existing from the environment and sustainability point of view that once they have a sufficient number of different opinions on what is the next step/aim/goal they are doomed to failure.
    You may say I have a pretty bleak view of what people are like and of course I can think of similar settlements like communes which operate with great success on Earth – these have townhalls and votes etc to decide where the community is going to build/spend and who can come or who has to leave and have a certain perhaps even large element of autonomy. This would be a viable self-governing model, but on Earth if there is conflict within a group like this it is not so far for someone to relocate. In an early space settlement everybody is going to have be PRETTY certain they are all like-minded before starting any kind of venture together.

    That leads me finally to the argument that if you are going to live on a settlement not on this planet and avoid the issues I outline above you are going to need to be given a direction or directions by another body. Sure it’d still be great to go but if you are not always going to be able to have a direct say in the direction the settlement is going then you are also not going to want to fund it entirely yourself. A government or corporation will need to fund at least a very large portion and the residents will ultimately be working for them to some extent as it is then the managing body’s aim that everyone is working towards.

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