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posted by martyb on Friday December 28 2018, @06:43AM   Printer-friendly
from the ask-Senator-Shelby dept.

Submitted via IRC for takyon

An article at SpaceNews.com asks Is the Gateway the right way to the moon? — the "Gateway" is The Lunar Orbital Platform-Gateway.

This article originally appeared in the Dec. 17, 2018 issue of SpaceNews magazine.

Sometime in 2028, competing for attention alongside a presidential election and the return of the Summer Olympics to Los Angeles, NASA will return humans to the surface of the moon.

A lunar lander will depart the cluster of modules in an elliptical orbit around the moon, called Gateway, and descend. One stage will take the lander to a low lunar orbit and then separate, after which the descent module will handle the rest of the journey to the lunar surface. A crew of up to four will spend days — perhaps up to two weeks — on the surface before boarding the ascent module, which will take them back to the Gateway.

At least that’s NASA’s plan for now. A year after President Donald Trump formally directed NASA to return humans to the moon in Space Policy Directive (SPD) 1, the agency has developed the outlines of a plan to carry that out, while emphasizing the language in the policy to do so in a “sustainable” manner and with international and commercial partners. But as the agency describes two of the biggest elements of the plan, the Gateway and a “human-class” lunar lander, it’s still struggling to sell the proposal to its various stakeholders, including its own advisers.

[The somewhat long article is well worth a read. Notable members of NASA as well as former astronauts weigh in on their views of the pros and cons of such an approach as opposed to direct flights to and from the moon. To my eye, NASA was instructed to make the Deep Space Gateway happen so there was a destination for the Space Launch System (SLS) which currently costs something like $2 billion per year in launch and development costs. By comparison, I recall reading that SpaceX anticipates it can develop its next-generation Big 'Falcon' Rocket (BFR) and Big 'Falcon' spaceship (BFS) — now called "Super Heavy" and "Starship", respectively — for about $2 billion total. --martyb]


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  • (Score: 2) by Immerman on Wednesday January 02 2019, @01:26AM (5 children)

    by Immerman (3985) on Wednesday January 02 2019, @01:26AM (#780822)

    Sounds like the magnetopause distance varies between about 3 and 15 Earth-radii, while the moon is ~60 Earth-radii away. Something interesting may happen around every full moon tough, as it travels through the Earth's wake.

    I've long been a fan of lava tube construction - particularly if we can find some nice long ones (or better yet, a network) that allow for lots of underground expansion without tunneling. Just keep building a nice big airlock in the back wall of each new expansion and grow as resources allow. Also handy for less ambitious early projects - as long as it's stable enough for the equipment vibrations, just assemble your habitats freestanding within it and don't worry about radiation. You could potentially have whole cities in a truly large lunar tube, with experimental greenhouses and perhaps recreational spaces extending out onto the surface as acceptable radiation risks were established.

    I wonder how hard it would be to make a reliably air-and-pressure-tight version of those inflatable concrete-impregnated "tents"?

    Early on, depending on the particular tunnel and landscape, you could actually have a fair sized community all having a nice wide view of the surface, just not of the sky. Just be sure to have that cosmic-ray shadow-line clearly marked, and be mindful of how much time you spend outside it.

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  • (Score: 2) by JoeMerchant on Wednesday January 02 2019, @03:15AM (4 children)

    by JoeMerchant (3937) on Wednesday January 02 2019, @03:15AM (#780862)

    I'm guessing that, even if the lava tubes are structurally sound enough to hold air pressure better than 10psi, they probably leak, a lot, and will need some kind of skin sprayed onto their interior if they are to hold a breathable atmosphere.

    I'm also guessing that there's a more or less standard maximum size of lava tube due to the physical properties of the lava, though in Lunar gravity that size might be quite large. The tubes formed on the big island of Hawaii when hot lava was running through a cooled shell, then the supply stopped and it just ran out the bottom, so they tend to be sloped floors most of the time.

    Definitely easier to use a natural pre-bored tunnel than to dig your own structure. Wonder how long before we run into vacuum tube inhabiting aliens - it's gotta be a common formation throughout the universe, and is quite the natural radiation barrier.

    --
    🌻🌻 [google.com]
    • (Score: 2) by Immerman on Wednesday January 02 2019, @08:07PM (3 children)

      by Immerman (3985) on Wednesday January 02 2019, @08:07PM (#781146)

      They probably do leak on their own, but that's fine.

      Early on you probably wouldn't incorporate the tube itself in your structure - especially if it's a big one. That just complicates the construction process, and your crew needs someplace to sleep while they develop vacuum-friendly construction practices. Plus, while lava tubes typically top out at around 50 feet or so wide on Earth, various analysis put the lunar limit at between 1,600ft and several miles before gravitational instability causes them to collapse, and the near absence of moon-quakes and other weathering should help them approach that. A couple hundred feet for a nice solid one is probably not unreasonable, and even 50' would be quite usable. A large tube could potentially swallow entire cities without scraping the edges.

      For the early outpost, just drive into the mouth of a modest-sized tunnel and erect your free-standing, pressurized but un-shielded habitats there - heck, sturdy inflated "tents" could get the job done (though I'd want at least a double wall to forestall catastrophic leaks) - except for the floor they're already essentially in a giant insulated vacuum thermos. Sloping cave floors do seem likely, but you're going to want your habitats on a raised or well-insulated platform anyway, to avoid conductive heat loss into the perpetually sub-freezing rock, and leveling the surface of such a platform level is trivial. (Strong vacuum-curing foamed insulation poured into a "sandbag dam" form seems like a quick and easy way to do it). Early expansion is similarly easy, just be sure to leave a wide enough path for additional habitats to be transported further into the tunnel.

      When you're ready for a more permanent, less pre-fab habitat, start building a more permanent structure further down the tunnel, making sure to leave lots of unpressurized space near the currently occupied mouth of the tunnel as "garage space" for anything in the future that needs unrestricted access to the surface

      For longer-term (and larger scale) construction, incorporating the existing tube walls is almost certainly the way to go. I'd imagine you'd probably want a multi-layered coating - at least a thick layer of insulation to smooth the surfaces, retain heat, and provide level "stepped" floors, followed by with an air-tight surface to reduce leakage, all covered by a layer of reinforced moon-crete to provide bulk pressure containment and protection for the air boundary skin (plus some insulated thermal mass for comfort). Concrete typically needs to breathe atmospheric CO2 for several years to finish curing, but the rate of airflow through it is generally very low, so that might be enough. A coat of non/low-breathing paint would probably go a long way to further reducing leakage.

      You also don't need 15 psi, or even 10. 7psi (~1/2 atmosphere) is easily adjusted to by most people, especially if it's more oxygen-rich so that the oxygen partial pressure is still close to an Earth-normal 3psi. And it's mostly the partial pressure that determines the fire hazard, not the amount of other inert gasses, so not much worry there.

      • (Score: 2) by JoeMerchant on Wednesday January 02 2019, @08:23PM

        by JoeMerchant (3937) on Wednesday January 02 2019, @08:23PM (#781158)

        Concrete typically needs to breathe atmospheric CO2 for several years to finish curing, but the rate of airflow through it is generally very low, so that might be enough.

        That sounds like an opportunity for your outer layers to outgas CO2 into the concrete from the other side...

        All of this is great, just need to divert the funding from an Aircraft carrier group or two and git'er done.

        --
        🌻🌻 [google.com]
      • (Score: 2) by JoeMerchant on Wednesday January 02 2019, @08:30PM (1 child)

        by JoeMerchant (3937) on Wednesday January 02 2019, @08:30PM (#781161)

        As for 10psi, if I'm reading the charts correctly, that's the pressure at 10,000 feet, and at 10,000+ feet I'm not happy at all doing strenuous activities like snowboarding. Sure, you can increase the oxygen fraction, but I believe that's also increasing the overall flammability. Of course, people can adapt to a lot and you can make 3psi work, though I'd be worried about the boiling point of water getting too close to body temperature...

        --
        🌻🌻 [google.com]
        • (Score: 2) by Immerman on Thursday January 03 2019, @02:03AM

          by Immerman (3985) on Thursday January 03 2019, @02:03AM (#781321)

          As you say, that's not the lack of pressure that's bothering you, it's the lack of oxygen.

          That's where the oxygen partial pressure comes in - it's the pressure the oxygen in the room would be at if you magically removed all the other gasses in the room. Basically it's the total pressure multiplied by the percentage of molecules that are oxygen. So long as that number doesn't change, neither does the amount of oxygen in a breath of air.

          Flammability is also tied very closely to partial pressure (all reactivity is, really). Pressure is basically a measure of how many molecules are hitting a surface per second (and how fast, which depends only on temperature). So long as the number of oxygen molecules hitting a surface in a second is constant, so is the number of potential chemical reactions that could contribute more heat to the flame. Inert gasses would alter the thermo-fluid dynamics of the flames themselves to some extent, but I *think* the effect on fire hazards would be relatively minor.

          Regardless though, if you want a full 1atm of pressure, it's not *that* much more difficult - you only have to double the tensile strength of your walls.

          As for the boiling point of water, no worries. Body temperature is ~40C, if we call 60C a nice wide safety margin, then we can drop the pressure to about 3 psi - or pure oxygen at Earth-normal partial pressure.