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forming composit space station skin in situ
In order to produce the most effective orbiting facility with the least
amount of materials and the least effort, it seems obvious that it should be an inflatable sphere. As soon as the internal volume becomes even the slightest bit pressurized, the astronauts can begin dispensing with the bulk of many of the layers of the space suit. This will allow them to work more efficiently for longer periods of time. Working inside a huge single sphere is difficult - scaffolding is nearly impossible to construct for such a situation. The solution will be to use the same technique Brunelleschi used for the dome at the cathedral of Santa Maria del Fiore - use two closely spaced shells, one inside the other. Once the volume is enclosed and the workmen are inside a moderately pressurized space, the ensuing work can proceed at practically breakneck speed, unencumbered by a bulky space suit. I'm considering a sphere 100 meters across, with an internal shell 3 meters inside that. The inner and outer shells will eventually be augmented with many layers of fabric and epoxy, but initially are essentially just aluminized mylar and very fragile. I know plastic at exremely low temperatures is extremely brittle. Because this is in the vacuum of space, will this aluminized mylar shatter at the slightest touch, or will astronauts inside the shell be able to spread strips of fabric and epoxy on it to augment and reinforce it without too much trouble? Harmon Let's light this candle. - Alan Shepard |
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"harmoneverett" wrote:
In order to produce the most effective orbiting facility with the least amount of materials and the least effort, it seems obvious that it should be an inflatable sphere. You might enjoy reading Tim Tyler's work on double geodesic domes, which might be a bit more practical as a way to approach the same goal with smaller bites taken per chew: http://hex.alife.co.uk/domes/ HTH xanthian. -- Posted via Mailgate.ORG Server - http://www.Mailgate.ORG |
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Very interesting site! I don't think it is applicable, however, as his
domes deal with *compressive* forces, and a space sphere would be dealing entirely with *tension* forces. I'm also trying to minimize the amount of work anyone would have to do while wearing a space suit, and enclose as much volume as possible as quickly as possible. The more volume that can be enclosed, the more you can rent to more clients, and the sooner you can ditch the space suit, the easier and faster it will be to construct the facility. Once the major outer shell is in place, with a tiny bit of atmosphere - even if it is nitrogen and carbon dioxide, the bulk of a space suit can be largely reduced. Smaller internal rooms can be fully developed, hardened, pressurized, equipped and used or leased out at that point, without having to fully develop the entire structure. So once the outer skin is in place, everything else is easier, cheaper, and can be bringing in income almost immediately. An inflatable that is augmented with fabric and epoxy is also much easier to pack into a launch vehicle, and erect once in orbit - no wasted space between components, and relatively few steps to getting the structure erected once there. Harmon Kent Paul Dolan wrote: "harmoneverett" wrote: In order to produce the most effective orbiting facility with the least amount of materials and the least effort, it seems obvious that it should be an inflatable sphere. You might enjoy reading Tim Tyler's work on double geodesic domes, which might be a bit more practical as a way to approach the same goal with smaller bites taken per chew: http://hex.alife.co.uk/domes/ HTH xanthian. -- Posted via Mailgate.ORG Server - http://www.Mailgate.ORG |
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In article .com,
wrote: ...you're going to need hundreds of tons of [gas]... What volume are you considering? For any big unobstructed volume at any breathable pressure, gas mass is going to be serious. Air at 1atm weighs about 1.25kg/m^3 -- rather more than people think. And I didn't say a pressure suit would be unnecessary, I think the *space* suit would be unnecessary. In between the shells, the workers would probably need something like a flight suit pressure suit, but not the full bulk of the space suit. Unfortunately, the big problem of working in spacesuits is the stiffness resulting from suit pressurization. Getting rid of the outer thermal/micrometeorite protection would help only a little. I'm not sure what you mean by "flight suit pressure suit", but note that the suits worn (for example) for shuttle ascent are *emergency* suits, which get their lighter weight and greater *unpressurized* flexibility partly by accepting that they will be uncomfortable and very difficult to work in when pressurized. Does anybody know what the specs for such a pressure suit, that would deal comfortably with, oh, 1/100 of an atmosphere would be? It would have to be essentially a full spacesuit. ...4,188 cubic meters of air at Denver air pressure, oh, half stp, or so... Uh, no, sorry, Denver pressure is much higher than that. Even if we make it Quito instead -- nearly twice as high as Denver -- air pressure and density are still about 75% of sea level. (And if you're doing physical work at that pressure, you'll want higher than normal oxygen content, as anyone who has been to Quito will tell you...) -- "Think outside the box -- the box isn't our friend." | Henry Spencer -- George Herbert | |
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wrote: it seems obvious that it should be an inflatable sphere. Have you looked into NASA's Transhab? A quick overview of Transhab: http://www.astronautix.com/craft/traodule.htm This link details its materials selections and structu http://faculty.erau.edu/ericksol/pro.../transhab.html Maker of the Transhab test article: http://www.ilcdover.com/products/aer...e/habitats.htm I'm considering a sphere 100 meters across, with an internal shell 3 meters inside that. The inner and outer shells will eventually be augmented with many layers of fabric and epoxy, but initially are essentially just aluminized mylar and very fragile. You can probably start more robustly than that. If you don't mind developing a big rocket (like Boeing's 7-core Delta IV concept), then you can launch a sizable, robust sphere immediately. A 100m sphere pressurized to 4.9psi with oxygen and a dash of nitrogen would generate 61300psi of stress in a 2mm (1/12") shell. That's well within the strength capability of a plastic like Kevlar (or the more modern Zylon). The shell would be about 80-90 metric tons, depending on the particular shell material selected. Then, of course, you'd want to look into insulation, debris shields, additional shells, etc. Scaling up from the 8.2m Transhab cylinder to a 100m sphere suggests about 500-600 metric tons of internal material would be needed. Interestingly, the resulting shell (all ~700 tons) is just about as heavy as the air inside. A 100m sphere of air at sea level pressure (80/20 nitrogen/oxygen) is 673 metric tons at 25C, if I did my math correctly. Actually, that's a thought...the 4.9psi (1/3-bar) initial oxygen atmosphere I suggested would be 250 metric tons. This level of bulk material delivery would really encourage the development of a big launcher. I know plastic at exremely low temperatures is extremely brittle. Only if you use the wrong plastic. Some plastics behave very well at cryogenic temperatures. See the Transhab development notes I linked in above. Kevlar and polyethylene remain fairly tough and ductile at cryogenic temperatures. Mike Miller, Materials Engineer |
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wrote: wrote: it seems obvious that it should be an inflatable sphere. Have you looked into NASA's Transhab? Yes, It seemed too much trouble for too little additional volume. More of a way to put a bigger tin can into space. If you realize you can augment the outer shells after they are inflated, and add the equipment as you go along, you can really get a lot of controllable volume from an inflatable quickly with low cost. I'm considering a sphere 100 meters across, You can probably start more robustly than that. If you don't mind developing a big rocket (like Boeing's 7-core Delta IV concept), then you can launch a sizable, robust sphere immediately. Not interested in developing new launchers. I want it up there NOW. If not last week. Its going to take a couple years to develop an internal ecosystem anyway,.. Moving lots of equipment in, shipping up lots of water. I can send up a crew bunkhouse module, and inflatable skins - almost off the shelf stuff, within a couple of months of getting the financing. A 100m sphere pressurized to 4.9psi with oxygen and a dash of nitrogen would generate 61300psi of stress in a 2mm (1/12") shell. That's well within the strength capability of a plastic like Kevlar (or the more modern Zylon). The shell would be about 80-90 metric tons, depending on the particular shell material selected. Tempting. Very tempting. But too heavy for right now. I have been reading good things about aluminized Kapton. Get it up and inflated, harden it with some epoxy and then start sending up regular small supply shipments of pvc beads to make structural pipes and fabric and epoxy to reinforce the shells. Then, of course, you'd want to look into insulation, debris shields, additional shells, etc. Scaling up from the 8.2m Transhab cylinder to a 100m sphere suggests about 500-600 metric tons of internal material would be needed. Eventually yes, Not right away. There will need to be weekly shipments of all sorts of materials and equipment. In inexpensive 5, ten and twenty ton launches. Once the outer shells are in place, individual smaller rooms can be (and would have to be ) developed on an as needed basis. But since they would be INSIDE the shell, they can very easily be put up by astronauts wearing essentially air tanks and flight suits. The whole shell wouldn't have to be pressurized for a couple of years, but the individual rooms could be pressurized and used immediately. The rooms wouldn't have to be developed until a client was willing to pay for using them. Eventually, plumbing, trash, wiring, sewage treatment, storage, and all sorts of stuff will be placed between the two shells. But that can wait for long term development. Once the shell is up and only slightly pressurized, the facility is open for business. Interestingly, the resulting shell (all ~700 tons) is just about as heavy as the air inside. A 100m sphere of air at sea level pressure (80/20 nitrogen/oxygen) is 673 metric tons at 25C, if I did my math correctly. Sounds about right. But you wouldn't have to go sea level. You could easily opt for oh, Denver, for half that. Eventually. The thing is, it wouldn't have to be anywhere near that for the first several years. And as people worked in it wearing air tanks, the exhaust would just be vented to the inside of the shell and gradually build up, too. You need to have the shell there, so that people can be working "inside", and so there is a little pressure above absolute vacuum, but it doesn't take much to make it possible to work with just a flight suit, rather than the whole space suit. What? 1/100 of an atmosphere? And it doesn't have to be oxygen. initially. And the astronauts won't primarily be working inside the inner shell - the vacant 400,000 some cubic meters; mostly they'd be working between the two shells, which they could pressurize for a lot less. When utility workers have to work down a manhole in subzero weather, they often set up a tent over it. If the astronauts have to work inside the inner shell, they could easily set up a much smaller temporary inflatable dome and work happily inside that - at pressure, and with air and temperature control. OOh, that's a new thought. Actually, that's a thought...the 4.9psi (1/3-bar) initial oxygen atmosphere I suggested would be 250 metric tons. This level of bulk material delivery would really encourage the development of a big launcher. Once the initial shells are up, a big launcher won't be necessary, because most of the rest of the deliveries can be in practically arbitrary amounts. Water, air, plastic beads to feed into the on site pvc pipe extruder. soil. seeds. fabric. epoxy. The limitation is that the first couple of inner and outer shells really need to be in one piece. I think I can get them down to about 25 thousand kilograms. I know plastic at exremely low temperatures is extremely brittle. Only if you use the wrong plastic. Some plastics behave very well at cryogenic temperatures. See the Transhab development notes I linked in above. Kevlar and polyethylene remain fairly tough and ductile at cryogenic temperatures. Ooops, my mistake. Obviously NOT a materials engineer. And I have been reading very nice things about kapton. Mike Miller, Materials Engineer Thanks Mike! Brunelleschi used the inner and outer shell concept to build his famous dome. It made the work much easier than trying to do a single shell with lots of scaffolding. If we consider having these thin plastic shells floating in orbit, with about 3 meters between them, the astronauts will still need some way to get around, and station themselves within the cavity. There will still need to be some sort of scaffolding. I'm considering sending up a pvc pipe extruder and setting it up as one of the first rooms inside the shell. Then, run 3/4 inch "great circle" lengths of pipe around the structure, between the inner and outer shells. Run one from pole to pole, to establish a meridian so to speak, and then run another at 90° from that, and then another positioned to attach to the other two at the equator. It seems to me that then, the best way to organize the placement of further great circles, is to divide the lengths of pipe between intersections in half, and attach new great circles at the half way points. Continue that process until you have intersections oh, about every 10 meters or so. After the 3rd set of great circles, you have intersections about every 20 meters, and can probably settle down to a slower pace. Harmon |
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wrote: wrote: Have you looked into NASA's Transhab? Yes, It seemed too much trouble for too little additional volume. I was recommending looking into Transhab not because it gave you the space structure you wanted, but because it answered your material questions and would give you working mass estimates. I've used Transhab's shell mass to scale up to assorted hypothetical inflated stations. Not interested in developing new launchers. I want it up there NOW. Well, alrighty then. I can work with that estimate. But there are some problems with insisting on First problem: Shell strength and mass. 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). If you cut the first shell down to a bare minimum with little margin of safety for restraining just 3psi, it's still going to need to be 0.5mm thick and made out of an ultra-strong fiber like Zylon. At a minimum, the shell will be 24 tons (assuming a fully dense Zylon shell; more likely it'd be about 36-40 tons). That shell will be inadequate for a 14.7psi atmosphere. Aluminized Kapton does not have anywhere near the yield strength to handle 3psi at 0.5mm thickness. With a 30000psi yield strength (at room temperature), a Kapton sphere would need to be 3.5-4mm thick, which would result in a 160-ton shell (just to handle 3psi). Second problem: air mass. The 3psi oxygen atmosphere will be about 250 tons. That's a lot of tonnage to lift with current launchers. Which brings up problem three... Third problem: existing rocket payload capacity. If you want existing, in-production launchers to get the job done, you're going to need 11-12 uprated Delta IV heavy launches (22 metric tons to LEO) or 11 shuttle launches just to get to the stage where you have a bare minimum, air-filled sphere. However, you'll probably want a couple more launchers to deliver some climate control equipment (to keep all that air from overheating), power systems, etc. So you're up to about 13 launches before the workers get to climb out of their space suits during construction. Note that the Delta IV heavy, as currently flown, is not really up to snuff for launching the initial, bare minimum shell. Alternately, if you don't want to wait on internal construction activities for 11 big launches to fill the sphere with air, then you can deliver the sphere shell (1 launch) and support equipment, probably including that bunkhouse you mentioned (2 more launches) and get to work after 3 launches. But then the astronauts will be spending all their construction time in suits, at least until 11 more launches have delivered enough oxygen to give the sphere minimal pressure. Fourth problem: existing launch capacity This goal... "There will need to be weekly shipments of all sorts of materials and equipment. In inexpensive 5, ten and twenty ton launches." ...requires greater commerical rocket production than is (I think) currently available. Boeing would LOVE to expand its factories to help you launch 20-ton payloads every week. The idea of firing off 12-13 Delta IV Heavies (33 total common core boosters! wee! profits!) just to get the station started would make Boeing very happy. And you'll eventually need 30 such launches just to bring the sphere up to 14.7psi, not to mention another 30 launches to get the shell up to full strength, plus an unknown number of launches to fill the station with that water, machinery, etc... Yes, you could be looking at 100 launches of some rocket in the class of the Delta IV heavy (or a lot more launches of smaller rockets). If you want that to happen on a weekly basis, using existing rockets, the rocket maker(s) you contract will need to expand their factories. Which leads me back to my prior suggestion of taking the time to modify the rockets. You're already going to have to pay for changes in the rocket industry, so why not simplify the construction process with bigger launchers? The bare minimum shell you want is probably going to be 36-40 tons even with super strong materials. Just sticking with the Delta IV example so I don't have to google up alternatives, you can get about 30-35 tons to LEO with the Delta IV heavy if you strap some solid boosters to it. Boeing hasn't flown that yet, but it looks like an easy stretch. Boeing also claims its Delta IV common core booster can be scaled up to Saturn V payloads. It'll take modifications to the launch pad and some engineering work, but its mostly just strapping 7 common core boosters together. It recently flew 3 of them strapped together. With such an (almost off-the-shelf) rocket, you could launch a full-strength shell in one leap. You could give a minimum working atmosphere in the shell in 2 launches, not 11-12. Alternately, if you're really insistent on launching weekly, perhaps you should take the time to develop a reusable launcher like the VentureStar. It'll probably save you headaches in the long run. Summary of problems: Getting the station built in exactly the manner you want is somewhere on the edge of possible/impossible with existing rockets. You need a shell launched in one piece that's probably going to be 35-40 tons. Your bare minimum air pressurization ("Once the shell is up and only slightly pressurized, the facility is open for business") is going to need 250 tons of oxygen. You want flight rates that are beyond the immediate abilities of rocketmakers, but could be achieved with a little development. I recommend you relax some of your requirements - particularly for existing rockets - and pay for the development of a higher capacity rocket. It'll make everything else much more possible. Mike Miller, Materials Engineer |
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" wrote:
I recommend you relax some of your requirements - particularly for existing rockets - and pay for the development of a higher capacity rocket. It'll make everything else much more possible. An alternative that has lots of obvious arguments going for it, like redundancy for safety reasons, more reasonable single-launch lift requirements, and a stageable startup, would be to replace the "one big sphere" concept with a "bunch of grapes" design. Yes, the eventual surface area, mass, and so forth would be greater [but not that much greater when the partitioning for the unit sphere design is counted in], but the project could be practical and feasible with current technology, instead of straining at every seam. Also, the "bunch of grapes" has room to grow if the project succeeds, again in chewable sized bites. xanhian. -- Posted via Mailgate.ORG Server - http://www.Mailgate.ORG |
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