Delusions of a Mars Colonist

Abracadabra! We turn Mars into a second Earth (National Geographic Society)

Abracadabra! We turn Mars into a second Earth (National Geographic Society)

A perennial talking point promoted by the space media is the belief that to save humanity, we must make a beeline to Mars. Supposedly, Mars is so “Earth-like” that it is the natural second home for humanity in space, a place to assure species survival in the event of some planetary catastrophe (such as a large meteorite impact). Because Mars could be “terraformed” to become even more Earth-like, we must focus our principal space efforts on undertaking human missions to Mars – ASAP (for the last 45 years).

For any sustainable human presence off-Earth to be successful, one must develop the means to arrive, survive and thrive. Most commentary on human Mars missions has focused entirely on the requirement to arrive because many of the technical problems associated with this must-accomplish first task remain unresolved. Presently, we don’t know how to build fault-tolerant, in-space serviceable systems necessary to support human life over the course of a multiple-year-long Mars mission. Protecting the crew from exposure to constant high-energy cosmic rays and sporadic solar particle events requires some means of shielding the vehicle – a daunting prospect in terms of mass and power. The means of a safe entry, descent and landing of a spacecraft (having mass of tens-of-tones) onto the martian surface must be developed, as these are currently completely unknown “details.” And if it the trip is to be more than one-way, then provisioning, refueling and launching for the return home must be sorted out too. These issues must be resolved before a crewed mission to Mars can take place.

For the moment, I’ll ignore these non-trivial “arrival” issues and focus instead on the two remaining objectives – “survive and thrive.” Only rudimentary attention has been given to how humans will survive on the martian surface. Certainly, additional problems will come up that we cannot know now, but the ones we do understand are formidable enough. In contrast to the press it receives, the martian surface is a cold, alien, hostile environment – much more dangerous than free space or even, in some respects, the lunar surface. Although Mars does have an atmosphere, it is composed almost entirely of carbon dioxide and has less than one-hundredth the surface pressure of Earth. While this thin atmosphere protects the surface from the smallest micrometeoroids, it does not shield it from the highest energy cosmic rays or solar ultraviolet (UV) radiation. In addition, because Mars has no global magnetic field (and we cannot create one), galactic cosmic rays will always shower the surface, making underground dwellings a must – not in transparent domed cities on the surface, as portrayed in science fiction novels and films.

Like the Moon, the surface of Mars is covered with a fine dust, but unlike lunar soil, martian dust is chemically reactive – a toxic mix of perchlorates and peroxides that, combined with the high flux of solar UV and galactic cosmic rays to which the surface is exposed, makes for an almost completely sterilizing environment. The Viking landers flown 50 years ago could not find any organic matter (i.e., compounds made of carbon, nitrogen and hydrogen) in martian soil in any concentration at the parts-per-billion sensitivity level. The scenes in the recent film The Martian (held up by NASA as a model of scientific veracity and prediction) in which the astronaut fertilizes the martian soil and grows potatoes, is complete fantasy – we simply do not know how to alter the soil chemistry of Mars, fertilize it with organic matter, and then grow radiation-tolerant plants quickly enough to support a human community, let alone a single astronaut.

Water is thought to be present on Mars, so clearly supplying water would be no problem. Or would it? The upper surface of Mars is covered by rock and dust, but ground ice is present in many locations at depths between a few meters to several tens of meters. Subsurface ice could be reached by drilling or by setting off an explosive charge. Martian water is likely to be saline, which will necessitate its distillation for human consumption or agriculture, requiring more electrical power and adding complexity to surface systems.

Human communities need energy to do almost anything and energy production on Mars is a significant issue. Mars is farther from the Sun than the Earth is, so solar panels will generate only about half the energy (so at least twice the collection area will be needed). Because there are frequent dust storms on Mars, solar panels will require regular cleaning to assure peak power production; such a task is challenging for very large areas (thousands of square meters) of solar arrays. The gravity of Mars (0.38 of Earth) is more than twice that of the Moon (0.16 of Earth) and landing large masses of supplies and infrastructure on Mars is difficult. Perhaps solar arrays can be manufactured from local materials on the martian surface but as we do not know the surface chemical composition of different localities in detail, we do not know how difficult this might be. The obvious solution to these difficulties in energy production is to deploy a nuclear fission reactor; the problem is that no reactor of suitable size for use in space exists.

So aside from the inconvenient facts that we don’t know how to safely make the voyage, how to land on the planet, what the detailed chemistry of the soil is, or if we can access potable water, whether we can then grow food locally, or how to build habitats to shield us from the numbing cold and hostile surface environment, don’t know what protection is needed due to the toxic soil chemistry, or how to generate enough electrical power to build and operate an outpost or settlement – in spite of these annoying details that make this idea prohibitive, the creation of a Mars colony within a decade is marketed to the public as if the plans had already been drawn up.

But let us say for the sake of argument that we have addressed the first two tasks adequately – we have arrived and survived. How do we “thrive” on Mars? Of all the notions promulgated in the media about future Mars colonization, this last element is the one that is always ignored. With flashy artwork depicting futuristic cities, sleek flying cars, and lush green fields resplendent under transparent crystal domes (in startling contrast to the red-hued surrounding desert of the martian surface) it is simply assumed that a human colony on Mars will evolve into some kind of off-Earth utopia.

But how will these future Mars inhabitants make a living? And by that, I mean what product or service will they offer that anybody on Earth will want? If you think that the answer is autarky (complete economic isolation and self-sufficiency), then you are imagining an economy (and likely, a political state) in which North Korea is a free market, pluralistic paradise by comparison. People who migrate to Mars need more than food and shelter – they will need imports from Earth, material and intellectual products designed to enrich and refine life on the frontier. What will they have of value to trade or to sell for these imports?

We do not know if Mars contains anything that would have economic value on Earth. Mars has had a complex geological evolution, so we might expect the formation of ore deposits, possibly of substantial value. But even if this is true, we have no idea where these deposits occur or if they are accessible for mining and refining. Martian products must be of sufficient worth so as to merit their transportation back to terrestrial markets, which would require their launch out of the substantial Mars gravity well and back into the even greater gravity well of the Earth. Much is made of the possible economic value of “information,” but it is not clear that Mars is particularly rich in factual data marketable to those back on Earth, although a martian pioneer might have desperate need of it – which would make them their own “customers” and exacerbate the economic disparity of the colony to an even greater degree.

Colonies are not founded in some far-off land because they “look cool” or because some plutocrat wants to retire there. They are established primarily for two reasons: power projection and/or wealth creation. Small, barren islands or isolated localities might not offer much in the way of wealth, but their strategic value might be immense (e.g., Gibraltar). On the other hand, the New World was often more trouble than profit to most European states in the immediate aftermath of Columbus’ discovery. But once the gold and silver started flowing, colonists soon followed and pursued profitable and sustainable endeavors once they arrived and survived. The idea of a sustainable space settlement requires the creation of some kind of market – either economic or strategic – for whatever they find or produce there. Such might be achievable in free space (e.g., the generation and sale of space solar power) or on the Moon (e.g., the production of water to fuel a permanent space transportation system). Mars is too far away and relatively inaccessible to serve strategic ends, and an economic driver has not been identified – other than reality TV to observe any surviving arrivals as if they were zoo creatures (“Mars Survivor!” Who gets voted out of the airlock this week?).

Of all the “thrive” concepts yet advanced for space settlements, the idea of “terraforming” Mars (i.e., making the martian surface conditions like those of the Earth) is the most unbelievable. In essence, this is a proposal to manufacture an Earth-like environment on a planetary scale – a technical task we can barely manage within the confines of a single, small spacecraft. Yet some blithely speak of altering a planet’s atmosphere, hydrosphere and crust to make a “second Eden” where humans can roam free and settle widely. The unknowns involved in such an undertaking are not simply monumental, they are literally inestimable – to borrow a phrase, “we don’t know what we don’t know.” We are still uncertain about all of the factors that control and influence Earth’s climate and habitability, let alone know enough to manipulate the evolution of an alien planet toward some desired end. Spurring imaginations, this fantasy future is always depicted in beautiful artwork, where colonists inhabiting the ancient, parched red planet, see a world gradually being overtaken by shades of blue and green. We just need to go! This is science fiction indeed.

This new delusion – Mars as the New World – illustrates better than almost anything else the anemic state of the American space program. This debilitating condition allows for patent nonsense to be seriously peddled to a credulous, compliant and negligent media who will eagerly print virtually any headline or story.   The space community needs to rethink how they communicate the truth about our space future to the public (and to future engineers and scientists) if they seriously plan to go anywhere in the future.

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34 Responses to Delusions of a Mars Colonist

  1. Joe says:

    More than a bit out of my area of expertise, so this is a real (as opposed to rhetorical) question.

    Have read that Mars is thought in the past to have had a significantly more substantial atmosphere, but this was lost to space due to various causes (less gravity/no magnetic field etc.).

    Even if it were somehow possible to terreform Mars, would not the same processes begin to immediately un-terraform it?

    • Paul Spudis says:

      Yes, the lack of a global magnetosphere is the most serious issue. First, it would enable high-energy cosmic rays to reach the surface, making it a hard radiation environment. Second, the solar wind would directly impinge upon the upper atmosphere, eroding it away over time.

      In response, terraforming proponents claim this process occurs on geological time scales and if they can modify the planet’s atmosphere globally, they can tweak it on occasion as needed.

      Your mileage may vary.

      • Joe says:

        “…. they can tweak it on occasion as needed.”

        Musk’s version of terraforming seems to involve detonating thermonuclear bombs at the Martian Poles.

        However practical (or – more likely – impractical) that may be, “tweaking” it would presumably involve setting off more nukes.

        Mileage may indeed vary.

        • I believe in a Red Mars.

          Nothing wrong with exploiting up to 1% of the surface of Mars (1.4 million square kilometers) for colonization and commercial exploitation, IMO. But nuking Mars in an attempt to make it marginally earth-like would be a very bad idea.

          Marcel

          • Joe says:

            Hi Marcel,

            If I seemed to be endorsing terraforming by thermonuclear bomb to you, I was not.

            Musk did not originate the “instant” terraforming by nuke concept, it has been around for a while. It has, however, never made sense to me.

            I am just an engineer not an environmental scientist, but it doesn’t seemed likely that by blowing a bunch of indiscriminate material into the sky it would somehow distribute itself in the exact way required to make Mars more Earth like.

  2. The trade issue is relatively simple to solve. Mars needs to be able, without any Earth resources, to ship from Mars surface to Earth Surface. If that is achieved for zero Earth dollars then dirt could be sold to Earth at a profit in terms of Earth dollars.

    Minimum tech to do that is mars energy source, mass Launcher on Mars, solar sail based transit shipping, aero-brake and potentially parachute all sourced from Mars or off Earth.

    A coil-gun was demonstrated in 1970s that used 1 cm of track to reach 5000 m/s so the physics is possible for metals at a much reduced launcher mass compared to 1G launchers that need 1000+ km track.

    They won’t be rich by any means but they will be able to trade physical goods.
    Obviously most of the value will need to be intellectual property which could compete much more attractively with Earth.

    Martian jewelry will probably be the first physical export product.

    SpaceX and Mars One are banking on the Earth funding mars colonization at the same levels that the moon program was funded once its proven. I think this is probably a valid assumption. The decade after landing on Mars is likely to be dominated by Mars news and culture like the moon dominated.

    All of the technology for this approach would also help a moon colony so there isn’t really a need to get one or the other we can have both.

    • Paul Spudis says:

      If that is achieved for zero Earth dollars then dirt could be sold to Earth at a profit in terms of Earth dollars.

      Aside from the novelty value, who wants and/or needs such a product?

      Your scenario is far-fetched, to say the least.

  3. I believe Mars is a more habitable location than the moon in terms of supplying 1 million people.

    If that turns out to be true then Mars will be the future military capital of the solar system as it will be the cheapest manufacturer/launcher of spacecraft tonnage.

    Other locations can launch cheaper but until humans are obsolete they will be needed in the manufacturing and testing phases.

    That is my argument for strategic importance.

    • Paul Spudis says:

      That is my argument for strategic importance.

      More of a rationalization than an argument. We simply don’t know what Mars possesses in terms of resources that have value beyond its own surface.

  4. Grand Lunar says:

    Excellent writing here, as always.

    Comments on other sites show how far the delusions of Martian colonization go.
    Quite often, of course, is the idea that SpaceX will take us to Mars, using NASA’s money and Musk’s.
    No one seems to bother with the fact that the path is based on a paper rocket (the MCT) that is supposed to be up and ready in about a decade or so, despite the fact SpaceX hasn’t even managed to fly the Falcon Heavy. Nor does anyone consider the problems of getting all material from Earth.
    I find it sad. If we do manage to take the path of Cislunar development with the nation’s space program, NASA will be on top of the game.

    On colonization, I believe we should be builders of artificial worlds, not terraformers.
    What I mean is something like an L5 colony, a Bishop Ring, or an Orbital (from the sci-fi novels “Culture”).

    Yet another reason to create wealth from material in space.

  5. J Fincannon says:

    “Because there are frequent dust storms on Mars, solar panels will require regular cleaning to assure peak power production; such a task is challenging for very large areas (thousands of square meters) of solar arrays.”

    I think this is not such a showstopper. There are a number of methods to remove dust off solar array surfaces and, if you don’t want to use them, even setting up the solar array at a tilt of 45 deg is likely enough to minimize the dust accumulation problem.

    “… because Mars has no global magnetic field (and we cannot create one), galactic cosmic rays will always shower the surface, making underground dwellings a must …”

    You are likely correct, but I do recall reading about work in the area of active radiation shielding (either electrostatic, magnetic or plasma). Whether they are mass and power competitive with being underground is yet to be proven.

    • Joe says:

      “… the area of active radiation shielding (either electrostatic, magnetic or plasma). Whether they are mass and power competitive with being underground is yet to be proven.”

      Would be nice if it were to work out, but such affordable active shielding would be just as useful on the Moon as on Mars and so it would not be a discriminator between Lunar and Martian activities.

      • I really don’t understand all of the concern over protecting humans from cosmic radiation on the surface of the Moon and Mars.

        It only requires about 1.5 meters of lunar or martian regolith or 3 meters of water to lower radiation levels inside of a habitat below those required for nuclear and air flight workers on Earth (5 Rem). And its still not clear if even 10 Rem per year is actually harmful to humans. There are populations on Earth that have lived in areas for thousands of years where they experience 1 to 26 Rem per year of background radiation– with no ill effects.

        And it only requires about 10 centimeters of regolith or 20 centimeters of water to protect astronaut’s from potentially brain damaging heavy nuclei.

        Does mass shielding work? Well it certainly does for the humans living under the atmospherically mass shielded Earth.

        Marcel

        • Joe says:

          Agreed on all counts.

          My point about “Would be nice if it were to work out” about practical active radiation shielding was based on two points (there are probably others):

          (1) If local “bubbles” could be produced it would make surface EVA activities easier.

          (2) Aesthetically, if active shielding can be used, the view out your window would be nicer.

          • Interesting comments Joe:-)

            Since you don’t have to worry about micrometeorites on Mars, you could deploy transparent inflatable Kevlar biodomes (actually biospheres with one hemisphere beneath ground level) to the martian surface.

            Layered on top, a transparent biodome inflated with at least three meters of water could protect the top habitat habitat hemisphere from excessive radiation. Another, thin layer, of UV protective transparent material could be placed on top of that to protect the dome from ultraviolet radiation and from dust storms. And if the thin top layers gets too dirty, it could be periodically replaced with a new thin top layer.

            The maximum size for a biodome (biosphere) manufactured on Earth and deployed to the martian surface would probably be about 40 meters in diameter– if pressurized to the safest level for its human occupants.

            Much larger biodome diameters would probably require the deployment of much thinner biospheres that are subsequently internally layered with more layers of Kevlar until the appropriate safety levels are reached.

            Marcel

        • J Fincannon says:

          Just like for the solar array dust removal, there is a simple solution, for radiation it is mass shielding. But it is aesthetically pleasing to have more openness. Also, one does not want to be forced to limit one’s time on the surface in a suit (this would be a lifetime limit, so for “colonists” its pretty critical). You can’t carry an umbrella of thick shielding around when you go for a walk!

          “There are populations on Earth that have lived in areas for thousands of years where they experience 1 to 26 Rem per year of background radiation– with no ill effects.”

          As to what level of Rem is “harmful”, this has bothered me. Cancer and other personal biological degradation is one thing, but genetic damage leading to mutations in subsequent generations is another. If one is really intending long term living on Mars, genetic mutations need to be carefully screened in any progeny (can this be done?).

          • Joe says:

            Exactly what long term levels of radiation exposure/protection are allowable/required in the long term are currently unknown.

            The same is true for minimum gravity levels and maximum rotation rates to produce them (if centripetal force is to be used to supply gravity).

            Those are among the reasons it is too soon to make Mars an immediate goal.

            The development of Cis-Lunar Space (including Lunar resources) can produce useful products/services for Earth and at the same time answer the long term habitation questions safely (only a few days from Earth).

            When Cis-Lunar Space development is well under way and those questions have been answered it will then be time to move out into the rest of the Solar System (including, but not limited to, Mars).

          • billgamesh says:

            “-it will then be time to move out into the rest of the Solar System (including, but not limited to, Mars).”

            We do know what level of Rem is “acceptable” and what level of gravity and the rotation rates.

            If you mean to settle colonies on other natural bodies when you write “move out” then I have to disagree.

            Much of what is being discussed here are just the dead ends explored and left behind by the early 1970’s work of Gerard K. O’Neill and his students at Princeton. Nothing less or more than Earth radiation and gravity is acceptable. Mega-structures created with lunar material make rotation rates a non-issue.

          • Joe says:

            “We do know what level of Rem is “acceptable” and what level of gravity and the rotation rates.”

            No we do not.

            To pick just one example, several years ago I had the good fortune (at a human factors conference) to meet and have an extended conversation with Dr. Joseph Kerwin (medical doctor Skylab Astronaut).

            The current rotation rate conventional wisdom (essentially a maximum of 1 to 2 RPM) is based on ground based tests run in the 1960’s. Kerwin said based on testing run on Skylab he believed the actual maximum to be 5 RPM. Since the centripetal force increases with the square of the RPM that would reduce the required spin diameter for any desired gravity level by a factor of 6.25 even if you use the previous maximum 2 RPM as a base (by 25 if you use 1 RPM).

            You seem to want all issues to be completely settled and they are not. In fact many issues may well be resolved in a positive way for any one truly interested in space development.

        • Those of you who are interested in more details about the relative effectiveness of various types of cosmic radiation shielding materials (including secondary radiation) should read the 2011 US Department of Energy Study which can be found at:

          http://www.pnnl.gov/main/publications/external/technical_reports/PNNL-20693.pdf

          • Joe says:

            Eighty Six information dense pages. Always interested in a “little lite reading”. 🙂

            Thanks for the link.

  6. It think its pretty obvious that the Moon will be the economic titan of the solar system. And the most important economic relationship future colonies on Mars will have will probably be with future colonies on the Earth’s moon.

    Mars will probably depend on the Moon for most of its energy. Thorium mined from thorium rich areas on the lunar surface could be exported to Mars to be used in nuclear power plants on the martian surface.

    While it seems probable that the Moon should have substantial quantities of hydrogen, carbon and nitrogen at its poles, its possible that rapid population growth on the lunar surface could eventually require the import of some hydrogen, carbon, and nitrogen resources before the end of the century. This might be especially true if future scientist and conservationist want to protect at least 90% of the volatiles at the lunar poles from commercial exploitation.

    Mars could supply hydrogen, carbon, nitrogen to the lunar surface. But it seems more likely that the atmosphere of Venus might be a more economical resource for imported carbon and nitrogen if nuclear powered PROFAC units are used to mine the atmosphere and then transport these commodities by light sail back to cis-lunar space.

    Hydrogen, carbon, and nitrogen might also be economically exploited from the poles of Mercury if— light sails— are used to transport these commodities from low Mercury orbit to cis-lunar space.

    Sodium chloride and the chlorine derived from martian salt would probably be an extremely valuable chemical needed to be imported to the Moon for industrial manufacturing and marine food production on the lunar surface. So sodium chloride might be the most valuable export to cis-lunar space from the surface of Mars. The salt mines of Mars!

    I would also guess that oxygen exported to cis-lunar space from the martian moons, Deimos and Phobos, might be competitive with oxygen exported to the Earth-Moon Lagrange points from the lunar surface— if light sails— are used to transport these commodities from Mars orbit to cis-lunar space.

    Marcel

    • billgamesh says:

      “-future colonies on Mars-”

      There are not going to be any colonies. The most glaringly obvious fact you are completely ignoring is the one that was the genesis of the space colonization movement of the 70’s: there are not natural bodies besides Earth suitable for human colonization.

      Humans evolved in a 1 gravity environment and that is what is required. Mars is a scam.

  7. Seb says:

    A very few points:
    – not going there because we don’t really know what’s there is a lame excuse for not exploring; not saying there are plenty of other reasons for not doing so
    – the bio-medical envelope is in itself worth pushing to extremes, i.e., in my experience pushing biology to extremes creates more often interesting and near magic things to occur, say, opportunities
    – that this is a deluded fools paradise for some is crystal clear. I think, if these guys have the metal to live like mole-rats then okay go hard. Otherwise, I can take them on a tour of hell right here on Earth that makes the South Pole or some lava field look like a veritable 5-star holiday. I think, based on personal experience, a real-world reality check is high time in order. No saying, again, it shouldn’t be done, just not led by people who play with rocket-equations and don’t get out of the office for real and often enough. Talk about not seeing the forest of the trees.

    Since the vast majority of these people are clearly not stupid, just lost in big picture, one can only conclude this at the top this is a geopolitical driven power-play distraction for kudos and national prestige, a bit like playing football and cheering when all around you is going to sh*ts …. seen that before. I would have thought, hoped, that we’d moved well above the last bar of ultra-nationalistic consciousness to something loftier,like higher level consciousness, but apparently not. Maybe a reading of Voltaire and a few others might be in order.

  8. billgamesh says:

    “It only requires about 1.5 meters of lunar or martian regolith or 3 meters of water to lower radiation levels inside of a habitat below those required for nuclear and air flight workers on Earth (5 Rem).”

    You keep citing this figure in your comments on radiation and I keep citing Eugene Parker- “the world’s leading expert on interplanetary gas and magnetic fields.” The amount of shielding you propose is inadequate and since water is superior to regolith how can half as much provide the same protection?
    From Shielding Space Travelers, 2006:

    “A spherical shell of water five meters thick provides the same protection that Earth’s atmosphere offers at an altitude of 5,500 meters (18,000 feet).”

    “-to match the protection offered by Earth’s atmosphere takes the same one kilogram of shielding material per square centimeter, although astronauts could comfortably make do with 500 grams, which is equivalent to the air mass above an altitude of 5,500 meters. Any less would begin to be
    counterproductive, because the shielding material would fail to absorb the shrapnel.If the material is water, it has to be five meters deep. So a spherical water tank encasing a small capsule would have a mass of about 500 tons.”

    Radiation is the dirty little secret, the elephant in the room, that NASA and NewSpace will not talk about. The radiation problem is square one and makes space travel far more difficult than the media is portraying it. Not impossible, but certain realities must be accepted.

    “I really don’t understand all of the concern over protecting humans from cosmic radiation-” is the problem because everyone is in denial over the facts. We have to get past denial to the solution.

    • Joe says:

      Since we seem to have to do this regularly, here is a link (for anyone interested) to the article by Dr. Parker being referenced.

      https://engineering.dartmouth.edu/~d76205x/research/Shielding/docs/Parker_06.pdf

      Note that is a popular science article (not peer reviewed) and that the good doctor uses a lot of emotionally loaded language like:

      (1) It is not as bad as venturing inside a nuclear reactor, but traveling through space…
      (2) Mar’s pitiful atmosphere…
      (3) Etc.

      Then on the last page squeezes in this interesting disclaimer:

      “But on the bright side, researchers are only beginning to explore the biomedical side of the problem. Natural healing processes in the cell may be able to handle radiation doses that accumulate over an extended period, and some people’s bodies may be better at it than others’. If so, the present estimates of the cancer incidence, all based on short, intense bursts of radiation, may overestimate the danger.”

      Before returning to his real message to close:

      “Capable people might be willing to go to the moon or Mars just for the adventure, come what may. Even so, the radiation hazard would take the luster off the idea of human space travel, let alone full-scale colonization.”

      It can be left to the individual reader as to whether Dr. Parker is (in this case) acting as a dispassionate scientist or an anti-human space flight political advocate.

    • The lack of neutrons in hydrogen is what gives water its radiation shielding advantages. But this is limited since water is only about 11% hydrogen. Water loses its— thickness advantage— over denser materials such as lunar regolith beyond 80 centimeters.

      You could easily shield a lunar habitat with 5 meters of lunar regolith to equal the mass of radiation shielding on Earth. And you could easily shield a martian habitat with 10 meters of water to equal that of the Earth’s atmosphere. But, again, we still don’t know if that’s really necessary.

      • billgamesh says:

        Regolith is not denser than water. You are not making a bit of sense. What I suspect you have done is become confused with the GCR exposure on the surface of the Moon, which is half of open space (because the mass of the Moon blocks out half).

        • Paul Spudis says:

          Sorry, Bill — regolith (unpacked – 1400-1800 kg/m^3) IS denser than water (1000 kg/m^3).

          • billgamesh says:

            I stand corrected.

          • Paul Spudis says:

            The advantage of water over regolith for radiation shielding is that for comparable levels of protection, you need less water than you do using regolith. When high-energy gamma- and cosmic rays interact with regolith, they induce reactions in the heavy atoms, which can cascade and shower down as secondary radiation. This problem is lessened with water because, as mentioned above in the comment by Marcel, it has fewer neutrons on a mass per mass basis. However, it was assumed in early lunar base studies that there was no water to be had on the Moon, thus those scenarios showed using regolith exclusively as regolith shielding. It will work, but you need several meters of it to absorb the secondary radiation.

  9. John E Bowen says:

    Great article, Paul. I love science fiction, but I have a pretty clear idea of the distinctions between it and reality. I like my non-fiction reading to be, well, factual. I too, find the low level of level-headedness among “journalists” annoying. Beyond the writers themselves, the audience wants to believe in a gee-whiz future just 20 years away, so it’s not all the fault of the media. I wanted it too, but time and facts have convinced me it’s not going to happen that way. The way it will happen, I think, is with those small steps. Less glamorous, more certain.

  10. Shannon says:

    Structures, use of glass on Mars’ surface: My query in the Mars Society’s Facebook Group on 18 March 2016 reads: “According to this site (http://marshield.com/medical-shielding/lead-glass/), lead glass ‘2.0 mm Pb offers the same protective effect as a 2 mm thick lead wall.’ So, since Curiosity rover detected surface radiation to be 300 mSv, roughly 24 CAT scans …. What thickness of glass would be necessary to provide adequate radiation shielding on the surface of Mars?” The post generated 95 comments. It turns, “glass has a density of 2.7, so 10 g/cm2 = 3.7 cm, 20 g/cm2 = 5.4 cm, 10 g/cm2 =8.1 cm” thick. This suggestion was the best alternative: “Polycarbonates like lexan have densities of about 1.2, so 10 provide 10 g/cm2 shielding you would need 0.83 cm of lexan.”–both were provided by Johnathan Clarke.

    Plants and soil: see article, “Farming on Mars: How Could Martian Soil be Cultivated?” aka “Evolution of Soil on Mars” (Astronomy & Geophysics academic journal) –
    http://astrogeo.oxfordjournals.org/content/57/2/2.18.full?keytype=ref&ijkey=NWL0rzGK5CzJJOM

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