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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 |
#2
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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 |
#3
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Harmon Everett 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. A hotel mogul Robert Bigelow wants to launch inflatable hotels into orbit. (http://www.bigelowaerospace.com) This does not mean that the idea of inflatable hotels is obvious. Inflatable objects are made of rubber or plastic, which are sensitive to temperature extremes and leak air. They are more suitable as emergency shelters than long term habitats. Metals and alloys are better suited for the harsh space environment than rubber or plastics. A fairly large cylindrical habitat can be made from telescoping tubes. Probably the best design for small habitats is a rotating torus made of flat or almost flat tiles: http://www.islandone.org/LEOBiblio/SPBI1GH9.JPG As soon as the internal volume becomes even the slightest bit pressurized, the astronauts... This is a mundane job best suited for telerobots like Dextre or Robonaut. Astronauts are better suited for tasks that are too difficult for the telerobots, for example taking apart and repairing a digital camera. 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... 100 meter plastic sphere would be too thick and therefore too expensive. Epoxy produces toxic fumes. 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... It is not so brittle, but it would be good idea to wrap the plastic structure in a metal foil to protect it from temperature extremes. |
#4
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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 |
#5
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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 |
#7
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#8
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wrote: wrote: 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. Note that to get the pressure high enough for a pressure suit to be unnecessary (c3-4psi), you're going to need hundreds of tons of any gas except hydrogen or helium. What volume are you considering? 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. Does anybody know what the specs for such a pressure suit, that would deal comfortably with, oh, 1/100 of an atmosphere would be? In the discussion yesterday, I realized that once the main shells were in place, a much smaller internal tent could be inflated inside the inner shell to house - oh, let's say a hemisphere dome 20 meters in diameter. So the workers that were installing the walls and floors of the rooms in the interior of the inner shell wouldn't have to wear any protective gear whatsoever. 4,188 cubic meters of air at Denver air pressure, oh, half stp, or so, 671 grams/cubic meter times 4,188 cubic meters=2,810 kilograms or so. Plus probably another ton or two of water for humidity. Even full atmospheric pressure for that volume would only be 8,400 kilograms. I don't see a problem with having to heft even a couple dozen tons of gases up to the station in the first year. Its going to take several years to develop the entire sphere, but having it there makes everything else easier. And after 5 or ten years, there will be hundreds of tons of gases, and hundreds of tons of equipment, and hundreds of tons of water and hundreds of tons of soil and plastic and people. That's what an active space station is going to need to be. Its not how much its going to cost to get it up there that's important, it's how much income it can generate to pay for the costs. When Billy Durant started General Motors, he knew the expenses he was generating were a substantial portion of the gross national product, but between 1910 and 1920, the economy of the United States more than quadrupled, and people kept buying the cars and paying his costs. Once the inner and outer shells are up and minimally hardened, we can start charging visitors for weekly - working - vacations. How many people would pay to spend a week in space, even if for part of that week they were building some of the walls of the station itself? An inflatable that is augmented with fabric and epoxy As Andrew noted, epoxy may not be ideal. However, I'll interpret the description liberally as "some plastic binder to hold the fabric in place." Right. Harmon Let's light this candle - Alan Shepard |
#9
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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 |
#10
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Andrew Nowicki wrote:
[...] This is a mundane job best suited for telerobots like Dextre or Robonaut. Astronauts are better suited for tasks that are too difficult for the telerobots, for example taking apart and repairing a digital camera. From what I read of the NASA Robonaut tests, it appears that they are presently not a heck of a lot farther along than handing spanner A from tool tray B to the astronaut, who then tightens nut C on widget D. /dps -- Using Opera's revolutionary e-mail client: http://www.opera.com/m2/ |
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