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#241
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Questions about "The High Frontier"
On Oct 18, 10:44 pm, Pat Flannery wrote:
Troy wrote: Dock an ion drive to a Bigelow module and you would have a manned asteroid expedition. I don't know how radiation proof those synthetic fabric walls are going to be. Pat They'd have to be uprated for interplanetary space, that's for sure. A 5cm layer of water is supposed to be sufficient shielding - and synthetic fabric's a lot safer than the radiation bath you'd get from an aluminium hull. |
#242
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Questions about "The High Frontier"
On Oct 18, 11:45 pm, Quadibloc wrote:
On Oct 17, 12:56 pm, Hop David wrote: I agree moon habs will have lower start up costs. But why would Martian habs be less expensive than NEO based habs? There are NEOs that can be reached with less delta vee than Mars and with launch windows of comparable frequency. The start up cost of a small Martian habitat would be larger, since initial supplies would be launched from Earth. But the cost of expanding the habitat, while it would still be larger than costs of Earth habitats - they would have to be airtight - doesn't involve gallivanting around the Solar System to pick up asteroids for metals and comets for volatiles. Surface transport will do. John Savard In zero-g, you could probably use some kind of Venetian glass-blowing technique to inflate a large pressure vessel from molten steel. A little axial rotation would get you a disc shape, a little tug on the ends would get you an ellipsoid. O'Neill suggested a magnetised steel spray. Yes, getting materials from other asteroids is trickier than scooping them up with a rover but it can be done. Raw materials could be supplied by unmanned solar sail craft scooping it off other asteroids, if absolutely necessary. However, I believe the idea is to go prospecting for one with the right mix of materials. Sure, Mars and NEO are different, but I don't see them as having to necessarily compete. But somebody, sooner or later will start to utilise NEOs. NASA can go off and set up Mars colonies (actually the Russkies are more apt to do that), Japan can build SPS, ESA can develop the moon and India or China or private companies can go haring after space rocks. |
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Questions about "The High Frontier"
"Pat Flannery" wrote in message
... The winds will help to some extent. Yeah, but think about putting an electric fan into a bell jar and pumping out 99% of the air. It wouldn't surprise me if the fan didn't seriously overheat, even with the added air movement. You can drill down into the surface, and used a closed-loop system to cycle something through a heat exchanger that dumps internal eat into the bedrock where it migrates away via conduction. Eh, maybe. I'm still concerned that that bedrock is covered by regolith, so I'm thinking you'd quickly get into diminishing returns. It's not like the bedrock is like a big slab of iron or aluminum. On the other hand, radiators might not be that big a problem in orbit. One thing you could do in weightless which you could never do under gravity is have a heat radiator 3 inches thick but 3 square miles in area which moreover can radiate heat away from both sides. You are probably going to want the base primarily underground, or at least have soil covering it for radiation protection, and that will be easier to do with some gravity on your side to keep it in place. The old space colony studies recommended fusing the slag left over from the ore refinement process into 6-foot thick slabs which would then be assembled into a radiation shield surrounding the habitat. I don't see much of a problem with that approach. Molds could be heated at the focus of a big solar mirror. That strikes me as uncomplicated and inexpensive. Transparent inflatable domes might be tough though; there's unfiltered high-UV sunlight to deal with, as well as radiation degrading of the dome's material. I'd agree. I'm more optimistic about glass windows set in steel or aluminum frames than transparent, inflatable material. -- Regards, Mike Combs ---------------------------------------------------------------------- By all that you hold dear on this good Earth I bid you stand, Men of the West! Aragorn |
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Questions about "The High Frontier"
"Hop David" wrote in message
... We don't know what gravity's needed to stay healthy. This argument also works against orbital habs. So long as mammoth O'Neill cylinders are perceived as entry level orbital habs, people will dismiss them as implausible science fiction. But they most certainly should NOT view the O'Neill Cylinder as the entry level orbital hab (though Zubrin, in trying to bias the argument, may frequently pretend to think this is the case). An O'Neill Cylinder might mass 1 billion tons. A Stanford Torus would mass 10 million tons, a Bernal Sphere would come in at under 4 million tons, and a simple Space Manufacturing Facility (even one with a rotating, radiation-shielded section for housing) would mass much less still. -- Regards, Mike Combs ---------------------------------------------------------------------- By all that you hold dear on this good Earth I bid you stand, Men of the West! Aragorn |
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Questions about "The High Frontier"
"Hop David" wrote in message
... Pat Flannery wrote: We don't know what gravity's needed to stay healthy. A question which the centrifuge module on the ISS might have answered, so of course we canceled that. ISTR that a centrifuge module would cost nearly as much as the ISS itself. I think Pat was refering to a small centrifuge (fitting inside a work area) which might have been good for white-mice type experiments. -- Regards, Mike Combs ---------------------------------------------------------------------- By all that you hold dear on this good Earth I bid you stand, Men of the West! Aragorn |
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Questions about "The High Frontier"
"John Schilling" wrote in message
... But it's probably going to be a *lot* less expensive if you allow for the inhabitants to build, provision, and resupply their habitat using local resources. And there's every reason in the world to expect an asteroidal settlement to be doing this. And Mars has a much broader range of useful resources than any NEO. Than all NEOs combined, probably. I'm not sure why you would say this. What resources would be available on the surface of Mars that you couldn't find in a well-selected CC-type asteroid? Mars also has gravity, which is quite useful if you want your inhabitants to remain, like, alive and stuff. Providing gravity on or near an NEO is rather hard, especially at small scales. I wouldn't so much say "hard" as "requiring a certain minimal scale". If one has two counter-rotating structures of equal mass, nothing is required to spin them up and keep them spinning other than an electric motor between them. On the other hand, 1/3 G may turn out to be too little gravity to remain healthy. If so, a rotating structure in close orbit of an asteroid could provide a full 1-G. Right, so, settling Greenland is likely to be less expensive for hypothetical European explorers than settling North America or the Carribean? I think you would find the magnitude of the relative energy differences to be very large. -- Regards, Mike Combs ---------------------------------------------------------------------- By all that you hold dear on this good Earth I bid you stand, Men of the West! Aragorn |
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Questions about "The High Frontier"
John Schilling wrote:
On Wed, 17 Oct 2007 11:56:44 -0700, Hop David wrote: Quadibloc wrote: Mike Combs wrote: We won't build orbital habitats because someone has forbidden the moon or Mars. We'll build orbital habitats because there are significant advantages to them over same-scale habitats built on either the moon or Mars. People who insist on living on other planetary bodies will find themselves unable to economically compete with those located in free orbit. Yes, asteroids are good sources of mineral resources, and not being in a gravity well is an advantage. I think, though, that the Moon and Mars still have a place, because start-up costs are going to be way lower. I agree moon habs will have lower start up costs. But why would Martian habs be less expensive than NEO based habs? There are NEOs that can be reached with less delta vee than Mars and with launch windows of comparable frequency. That's fine if all you're planning to do is send prefabricated habs by rocket from Earth, with periodic resupply shipments. But it's probably going to be a *lot* less expensive if you allow for the inhabitants to build, provision, and resupply their habitat using local resources. And Mars has a much broader range of useful resources than any NEO. Than all NEOs combined, probably. http://clowder.net/hop/railroad/asteroidresources.html Mars also has gravity, which is quite useful if you want your inhabitants to remain, like, alive and stuff. Is Mars gravity sufficient to maintain health? Moon gravity? This is an open question so far as I know. Providing gravity on or near an NEO is rather hard, especially at small scales. If Lunar gravity is sufficient, that substantially changes the mission requirements and constraints. Nyrath has said recent research suggests workers can tolerate higher angular velocity if they're gradually acclimated. If this is true that also reduces the mission requirements. The difficulty of providing sufficient gravity at small scales is still unknown. Here's a graphic I made showing relative delta vee distances for assorted "low hanging fruit": http://clowder.net/hop/railroad/deltaveemap.html Right, so, settling Greenland is likely to be less expensive for hypothetical European explorers than settling North America or the Carribean? See the asteroid resources page I gave above. When you demonstrate the relative poverty of NEOs vs Mars, I'll buy the Greenland vs North America analogy. Myself, I'd like the the Moon, NEOS _and_ Mars-Deimos-Phobos developed. Hop |
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Questions about "The High Frontier"
Mike Combs wrote:. I think Pat was refering to a small centrifuge (fitting inside a work area) which might have been good for white-mice type experiments. This thing: http://en.wikipedia.org/wiki/Centrif...dations_Module Pat |
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Questions about "The High Frontier"
Mike Combs wrote:
"Troy" wrote in message oups.com... Try telling that to politicians and hysterical anti-asteroid campaign groups! I'd have to allow that public education would be a hurtle to overcome. Similarly, I think SBSP is the best long-term energy solution (and might lead to space settlement), but that will require extensive public education that no, there's no cause for concern from the microwave beams. I think what we might call "Deep Impact hysteria" might rule out aerobraking asteroids through Earth's atmosphere, but I would hope we won't be prevented from depositing a fragment of an asteroid perhaps the size of an apartment building into either L-4 or L-5. It's desirable to have a near earth perigee not only for aerobraking but to exploit the Oberth effect. I don't think hysteria is the right word. Large payloads would be harder to control and a tiny error could change aerobraking to lithobraking. I would call it "Deep Impact sensible fear". Again, I advocate payload mass ceilings well below Tunguska size. Given plausible methods of delivering payloads, we won't be bumping into that ceiling for some time to come anyway. Isn't there a big fight between the L5 crowd and the Zubrinites? Yeah, and I find it significant that we L5'ers tend to emphasize things like servable markets, exports, balance of trade, and return on investment, while the Zubrinites say things like "those who colonize Mars will go for hope, not for cash". But I think they say that because they have to. You'll probably wind up with both. Yeah. I've decided it would be wrongfully dogmatic for me to say that Mars will never be settled by anybody. Some will do it out of nothing other than a stubborn love of the planet. I believe colonization of Mars will come as naturally from the development of Phobos and Deimos. The Martian moon colonies will probably need resources that are more easily supplied by Mars than other sources. The inhabitants of the Martian moons will want to explore and enjoy their neighbor. Phobos and Deimos enjoy substantial advantages over most other small objects. Their proximity to Mars reduces the delta vee budget - aerobraking and the Oberth effect can be used. There's a nice launch window to Phobos and Deimos every 2+ years. Given an eccentric elliptic orbit (as most NEOs have), a nice, low delta vee Hohmann transfer launch window only opens up when the NEO has a near earth perihelion. If the NEO's orbital period isn't resonant with the earth, such launch windows will occur very rarely. Some examples: Given an asteroid with a 3/2 year period, it's possible to have a near earth perihelion every 3 years. An asteroid with a 5/4 year period can have a near earth perihelion every 5 years. Given an earth resonant asteroid with periodic near earth perihelions, high delta vee but very short duration sprint trajectories between the earth and the asteroid are also possible. http://clowder.net/hop/railroad/HohmSprin.jpg These considerations make earth resonant asteroids much more amenable to human bases, in my opinion. But, sadly, resonant NEOs with near earth perihelions are a small fraction of the total population. Non resonant asteroids may be exploited by one shot missions (possibly Kuck mosquitos) but they don't lend themselves to human settlement. So, after the Moon and the Earth-Moon Lagrange points, Phobos and Deimos hold spots near the top of my list. Hop |
#250
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Questions about "The High Frontier"
On Oct 19, 10:52 am, "Mike Combs"
wrote: But they most certainly should NOT view the O'Neill Cylinder as the entry level orbital hab (though Zubrin, in trying to bias the argument, may frequently pretend to think this is the case). An O'Neill Cylinder might mass 1 billion tons. A Stanford Torus would mass 10 million tons, a Bernal Sphere would come in at under 4 million tons, and a simple Space Manufacturing Facility (even one with a rotating, radiation-shielded section for housing) would mass much less still. OK. Then why bother with the O'Neill Cylinder? Or, for that matter, the Stanford Torus or the Bernal Sphere? If they all produce the same product (whatever that product may be), and the Space Manufacturing Facility is orders of magnitude cheaper, then there's no point in building million-plus-ton behemoths in space. |
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