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#21
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Ok, if we consider a 50 m shell, we get 65,449 cubic meters for a total
volume, and for the inside volume of the inner shell, we get 44,602 cubic meters. Getting it up in one shot is a good goal. But I'm trying to maximize leasable volume, too. A 100 meter sphere give 523,598 cubic meters of internal volume, and 434,892 cubic meters inside the inner shell. I still think the inner and outer shell concept is important for puncture repair, and sheilding augmentation, and general ease of construction. The costs are going to be such to develop any sizable facility that we probably are going to need about 50 tenants, besides the resort/hotel with about 25 guests per week, (eventually), a large "movie set", a repair/maintenance /workshack area for contract projects such as a Mars trip, other larger facilities and so on. I don't think a 50 meter sphere is going to be big enough. to bring in enough income. |
#22
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Mike:
Zylon is just fibers, right? Kapton would be available in film? Harmon |
#23
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What are your figures for getting an initial mass of 40 tons for the
initial shell? Are you still figuring on 3 - 4 cm thick of Zylon? I think it would be easier to bond sheets of Zylon fiber to already existing inflated walls of Kapton in place, rather than trying to patch together pieces of a large sphere while in a small room while weightless. Something like hanging wallpaper, without having to worry particularly about getting the pattern to match, or leftover bits at the top and bottom. That way the initial outer shell would only have to be 5 mil Kapton, which would mass much less. |
#24
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"harmoneverett" wrote:
wrote: You want an environment with enough pressure that construction workers can promptly ditch their space suits, or at least reduce them. That's going to require ~3psi of air pressure (pure oxygen). why pure oxygen? The eventual goal is to be able to breathe in it, but for the moment, an air tank doesn't weigh anything. Because if you're going to be sending gases up to achieve ~3 psi of blood oxygen tension, the minimum IIUC to sustain human life for extended periods, you are money ahead to send oxygen, which is breathable, and thus a money payload, not some inert gas, which is pure waste (but see below) until and if you go on to 1 atmosphere. My hope was that sending a really bare minimum shell, hardly able to constrain 1 or 2 psi would allow workers to then work in a much less bulky pressure suit over the next several years while they pasted on a couple more of the fabric and insulation layers for the main shell. I think you're missing the point that if you put 3 psi of oxygen _inside_ the human body, you have to put 3 psi _outside_ the human body as well, or the person just explodes. Working for long periods of time, like years, in pressure suits in a container with pressure less than the breathing gas pressure, is going to involve too many really unphotogenic industrial accident fatalities from suit failures to be acceptable. The base law of gaskets is, now as ever: gaskets fail. That's from a submariner whose seen far too many such failures in working plumbing, including one leaking radioactive fluids from a running nuclear reactor. You might as well plan for 3 psi, just to start, and the space crew lost on the ground years ago because pure O2 is a hellishly dangerous fire hazard modulo incredible precautions in what you let come in contact with it, impractical for a years-long effort, suggests you plan for a cartload of pressure capability for inerting gases as well, or some safety board somewhere is going to set all your planning efforts to no eventual value. HTH xanthian. -- Posted via Mailgate.ORG Server - http://www.Mailgate.ORG |
#25
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#26
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Tim McDaniel wrote:
In article , Henry Spencer wrote: you want the insulation external, because that lets you use MLI, which is superb insulation but works only in vacuum "MLI"? http://www.acronymfinder.com/ suggests "Multi-Layer Insulation", but not what's so special about insulation having multiple layers (putting on a sweater only works in a vacuum?). It's much, much better than most other sorts of insulation. It depends for its insulative properties on having lots of shiny reflective surfaces through which heat has to radiate. |
#28
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So the argument against working in space suits is that they break and
kill people? Is the same argument valid against the stacking multiple tin cans with space walks concept in developing the ISS? If you are working in a space suit inside a volume with 1/2 psi, with the space suit pressurized to 3 psi, and the space suit develops a leak, are you more likely to get a slow leak, which you can get back to the fully pressurized area and patch, or explosive decompression? |
#29
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Harmon Everett wrote: wrote: wrote: Well, it'd be easier, but the resulting structure isn't something I'd expect to pass any safety inspection, at least not until it was much thicker than a shell made of continuous, woven fibers. I was thinking the additional layers of fibers would be continuous woven fabric. Unless the interior of the sphere is completely empty (of revenue-generating modules), you're not going to be able to install a continuous-fiber fabric shell. You're going to have install patches, which goes right back to the problems of hand lay-ups. The second layer would be thicker and more capable of being pushed against with the squeegee, and so on. Speaking as a materials engineer, I *still* wouldn't trust a composite shell laid up by hand in that fashion even if you could press and roll it firmly. And each layer would add to the radiation protection and micrometeorite puncture protection. No, the micrometeorite protection won't increase noticeably with a slight thickening of the hull. Thick, solid materials are poor means of stopping micrometeorites. Why limited to the strength of the binding resin? Because the fibers would not be interlinked between layers and between patches. The resin would be the only source of strength in those areas. The hand lay-up method is also prone to creating resin-rich areas. You might be limited to a fraction of the fiber strength - like 50,000psi instead of 500,000psi. Isn't that what we want anyway? Why would we want to cripple the strength of the material? True. But meanwhile, you have enough internal controlled volume to lease to paying customers. Correct. And in the years it takes you to slowly hand-assemble your giant sphere, those customers might as well be operating in a normal space station, since the enclosing sphere isn't doing much for their modules. In fact, they could go to the competitor who doesn't increase rates to pay for a big, non-profitable sphere. If you want that sphere to do something useful, you'll want to build it quickly to the point it can house occupants without separate, vacuum-rated modules. This painstaking patchwork method does not seem good for business. Why weave it on site? Does it not compress or bend well? I would think making it on earth and unfolding it in space would be easier. If you have a rocket that can put a 650-ton shell into orbit, sure, make it on Earth. If you don't, some on-orbit assembly of individual full-strength segments will probably be necessary. Of those methods, the hand lay-up method you like is one of the slower and less safe methods. So the argument against working in space suits is that they break and kill people? There's multiple arguments against them, including their clumsiness. Is the same argument valid against the stacking multiple tin cans with space walks concept in developing the ISS? Spacesuits are much less of a problem for the ISS. The spacewalks required for the ISS's construction take much less time than assembling 31416 square meters of multi-layered composite in zero-G. It's about 1900 man-hours for the ISS, while it might be over 3000 man-hours per layer of the sphere with hand lay-up. If you are working in a space suit inside a volume with 1/2 psi, with the space suit pressurized to 3 psi, and the space suit develops a leak, are you more likely to get a slow leak, which you can get back to the fully pressurized area and patch, or explosive decompression? Astronauts exploding in a vacuum is a Hollywood invention, and the difference between 0.5psi and 0psi isn't significant to the leak rate. Again: this all gets much easier if you're willing to use somewhat enhanced launchers. You'll strangle the project if you insist on countless hundreds of little launches and tedious hand-assembly of the sphere. It won't take Boeing much to strap some SRBs onto its Delta IV heavy and give you a 40-ton payload. With that, you can launch entire 0.5mm shells into orbit in a single bound. If you go larger, up to a 100- or 120-ton launcher, you can put the full pressure shell into orbit in a single launch. Then its just a matter of spraying on foam insulation, inside and out, and laying down some non-structural liners and insulation. Mike Miller, Materials Engineer |
#30
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In sci.space.tech Kent Paul Dolan wrote:
"harmoneverett" wrote: wrote: You want an environment with enough pressure that construction workers can promptly ditch their space suits, or at least reduce them. That's going to require ~3psi of air pressure (pure oxygen). why pure oxygen? The eventual goal is to be able to breathe in it, but for the moment, an air tank doesn't weigh anything. Because if you're going to be sending gases up to achieve ~3 psi of blood oxygen tension, the minimum IIUC to sustain human life for extended periods, you are money ahead to send oxygen, which is breathable, I'd argue slightly about the 3PSI, you can go a fair bit lower if your goal is "won't die in 5 minutes without exertion". At the lung wall at 37C is 47 torr (780 torr = 1 atmosphere = 14.7 PSI) of water vapour. This can't be reduced, and is a hard limit (barring hypothermia). About 15 torr of CO2, at normal metabolic rates. People (nutters) have climbed everest without supplemental oxygen. At the top, you're looking at 276 torr, of which about 1/5 is O2. So, at the lung wall, we have 276-62 torr = 214 torr of atmosphere, or 43 torr of oxygen. So, for pure O2, 43+62 = 125 torr or 2.35 PSI will get you the same oxygen saturation as on the top of everest. About 1.2PSI or so is the pressure at which you're about as well off as you are holding your breath in normal atmosphere. Below this, you get rapid de-oxygenation of the blood as it passes through the lungs. snip I think you're missing the point that if you put 3 psi of oxygen _inside_ the human body, you have to put 3 psi _outside_ the human body as well, or the person just explodes. Err, no. If you try to hold your breath, your lungs rupture. If you don't, you'r fine until you die from lack of oxygen (about a minute until you need more than CPR). |
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