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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]
(Score: 3, Interesting) by JoeMerchant on Friday December 28 2018, @12:21PM (10 children)
When I was 2 years old, Neil Armstrong took one small step.
When I was 5 years old, Eugene Cernan became the last man to walk on the moon.
The last 46 years feel like paralysis by analysis. Fund a mission, choose a course and follow it, figure out the "best way" by doing something sub-optimal that gives real data to make future decisions on.
If we can afford $5B for a wall, we can afford a sub-optimal lunar program.
🌻🌻 [google.com]
(Score: 3, Interesting) by Immerman on Friday December 28 2018, @07:39PM (9 children)
Quite.
And in a relatively few years SpaceX Starship will likely be a game-changing well-tested, reliable, and cheap vehicle capable of landing on the Moon's surface and returning, while providing more pressurized volume than the ISS - an excellent basis for short-term mission-specific lunar outposts, as well as massive cargo deliveries from Earth for the construction of more permanent lunar facilities.
Seems to me that that should be the foundation of a near-optimal lunar supply line and initial build-out. Funding for space development is so hard to come by, and a lunar base likely to be so expensive, that not incorporating such a massive strategic advantage into the plan seems like a good way to ensure we continue to accomplish nothing much.
As does wasting precious resources recreating the ISS around the moon. If we're going to the moon, let's do it properly and go all the way. Want to scout the surface in person first? Fine, spend a month or three hopping a Starship with an exploration team and equipment around the surface, with possible orbital refueling trips, then back to Earth for refurbishing, leaving a large cache of supplies and equipment behind for future teams. Do that a few times, guided by in-depth orbital maps of promising resources, and we'll have gotten a good idea of the challenges of operating on the Lunar surface for extended periods, as well as having almost certainly identified at least one site that would make an excellent location for a more permanent outpost, and leaving behind a bounty of equipment and supplies accessible by a quick sub-orbital hop to get them started.
(Score: 2) by JoeMerchant on Saturday December 29 2018, @03:19PM (8 children)
The elephant outside the ionosphere (as opposed to in the room) is radiation.
Those 3 years of lunar missions got lucky by not having a crew cooked alive by a solar flare. Worse still, they likely wouldn't have died before getting home, but instead presented on the ground like Nagasaki bombing victims with horrible symptoms for a short time before they finally died.
The last 46 years of tech development means that the bulk of lunar development work can be carried on robotically, and should be so that human crews can dash across the danger zone to well shielded bunkers on the other side.
"Moon" presently streaming on Netflix
I'm still not sure what we could possibly do to ensure a safe journey to Mars, and I'm surprised there's not a public discussion of the probability of missing/surviving solar flare exposure on a typical trip there. I wouldn't be surprised if the first attempted manned trips to Mars do coincide with the predicted solar minimums, nor would I be surprised if they don't make a big deal about that timing in the discussion of why it's a good time to go.
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(Score: 2) by Immerman on Sunday December 30 2018, @05:21PM (7 children)
Quite - though I'd say the magnetosphere rather than ionosphere, though I suppose the ISS lies well within the ionosphere as well.
And yeah, the radiation is one of the big reasons I think it makes a lot more sense to aim straight for the moon's surface - land in a small steep-walled valley or crater and the geology (lunology?) could easily and immediately shield you from a good 75% or more of incoming solar and cosmic radiation, as well as similarly reducing your chances of getting hit by a solar flare. If we can find some conveniently located exposed lava tubes to use as an emergency bunker when needed that would make things even easier.
I'm not sure how big a problem solar flares would actually be for a Mars mission - they're nasty, but the radiation is pretty much all coming from a single direction - point the free-coasting rocket directly away from the sun whenever solar flares are threatening and you'd have the rocket, engines, and all the braking and landing fuel (and the tanks) as shielding. Plus all your supplies, etc stored on the lower levels - my understanding is that both EM and charged particle radiation is rather devastating to living tissue, but generally doesn't cause long-term lingering radioactivity that would contaminate rations and the like. You probably only need a relatively small amount of additional shielding, if any, to bring things down to a safe level - add a bit of a bunker safely sheltered within your water reserves and you'd probably be good to go. Maybe you have to cram in like sardines for a few hours, but that's a small price to pay, and the rest of the time the room would offer the only real privacy available during the journey. Other than spacewalks, which they obviously need to have available at all times because why not? It'd still be a once-in-a-lifetime opportunity (maybe twice, if you ended up returning to Earth)
Obviously, I'd want to see some math on that before I signed up - and ideally a rocket loaded with test animals being exposed to a solar flare for confirmation. Don't see any point in intentionally subjecting people to such a thing by putting them in a long-term station in lunar orbit though.
(Score: 2) by JoeMerchant on Monday December 31 2018, @03:06AM (6 children)
Check on the magnetosphere, though I think the protection doesn't get good until you're pretty deep inside it.
IIRC, they have discovered some probable big-ass lava tubes that are also candidates for significant water-ice deposits. Now, if it's my show to run, I'd demand that the lunar water deposits be used in sustainable fashion, meaning: if there are an estimated X mega-tons of water in a given area, use it by all means, but that estimate had better increase over long time scales and not ever decrease at a rate that could result in total depletion within the next 500 years...
Particle physicists have a fairly good handle on a lot of what goes on between the various charged, uncharged, etc. high energy particles, and they _think_ they have a good idea of what goes on outside the Earth's magnetosphere, but the data is based on a very tiny collection of observations. Think about being deposited in 1000 random locations on Earth and getting to observe what's visible just from the place you appear... after observing 100 locations for 10 years, I don't think you're really prepared to deal with the next 100 locations you'll be placed in - maybe 90 of them, but 10 are going to be some kind of surprise. And, even with 1000 drops onto Earth, what are the odds that one of your observations will tell you about active volcanoes, or strong earthquakes, or extreme lightning or hail or tornadoes, tsunami, mudslide, elephants, copperhead snakes, drop bears, etc.? We think we can see what goes on in space, but compared to the surface of the Earth, space is BIG.
🌻🌻 [google.com]
(Score: 2) by Immerman on Wednesday January 02 2019, @01:26AM (5 children)
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.
(Score: 2) by JoeMerchant on Wednesday January 02 2019, @03:15AM (4 children)
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)
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
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)
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...
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(Score: 2) by Immerman on Thursday January 03 2019, @02:03AM
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.