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#11
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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 |
#12
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Kent Paul Dolan wrote: 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. That's a reasonable point. By halving the diameter of the sphere to 50m, you quarter the mass of shell that needs to be launched at once. The mass of air drops 1/8th that of a 100m sphere, too. In fact, with a 50m sphere, you would be able to launch a shell of the same weight as the 100m sphere but able to handle 4x the internal pressure. That's a 40-ton payload that gives you the immediate capability to handle 1 atmosphere of pressure. Further, if you're playing around with Saturn V-grade launchers, the required air mass for 1 atmosphere of pressure (80ish tons) can be delivered in one payload rather. A single off-the-shelf Delta IV Heavy can deliver a breathable, 3-4psi oxygen atmosphere for a 50m sphere. but the project could be practical and feasible with current technology, instead of straining at every seam. Yep. And at 30-33m spheres (100ft across), you can much more easily use existing launchers. The shell of a 33m, 1atm sphere would be about 20 tons. wrote: Does anybody know what the specs for such a pressure suit, that would deal comfortably with, oh, 1/100 of an atmosphere would be? Yes. It would be something like a normal spacesuit, minus the thermal and debris protection. The bulk of the suit would still be present because the bulk (if not the weight) of a spacesuit is the pressure-resistant shell and the constant-volume joints that allow the astronaut to move despite being stuck in a rigidly-inflated, human-shaped balloon. A simple flight suit would not be adequate. The 1/100th atmosphere environment you're proposing is not much different than a vacuum, though I think it'll complicate cooling by making normal sublimative cooling difficult. 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. That's a fairly reasonable approach. However, you still have some logistical concerns to deal with, because the initial shell will still be fairly heavy (c40 tons). That runs into launch problems. If you're willing to use a tent approach but not bend on developing/modifying rockets for heavier payload capacity, perhaps you should extend the tent approach to its logical end: Assemble sections of the main sphere in a smaller "workshack." As I noted above, a 30m sphere with a normal environment would be within the capability of existing rockets to launch (in perhaps 2 launches). Over the next 30-35 launches, you could assemble enough material in the "workshack" to build the complete, 1atm 100m sphere (with debris shields and insulation). Workers in the workshack could (somehow) stitch, glue, and bond this supersized, multi-walled balloon together and then kick it out an airlock. Another 11 launches later, you'd have a minimum breathable atmosphere in the main sphere, then about 30 launches later, you'd have a full atmosphere in the main sphere. Mike Miller, Materials Engineer |
#13
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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. D Schneider wrote: 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. This is a highly politicized issue because jobs are at stake. Dextre or Robonaut makers claim that these telerobots can do anything. Astronauts and Shuttle makers claim that they are totally useless unless the astronauts are nearby to help them. Louis J. Lanzerotti, chair of the Hubble report, changed his mind after President George W. Bush nominated him to serve on the National Science Board (NSB), the 24-member governing body of the National Science Foundation (NSF) in September of 2004. The nomination looks to me like a bribe to persuade Lanzerotti to scuttle the foreign-made Dextre. |
#14
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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 | |
#16
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In article .com,
wrote: By halving the diameter of the sphere to 50m, you quarter the mass of shell that needs to be launched at once. The mass of air drops 1/8th that of a 100m sphere, too. Shell mass drops to 1/8 too, actually. 1/4 of the surface area, plus it only needs to be half as thick to hold the same pressure. -- "Think outside the box -- the box isn't our friend." | Henry Spencer -- George Herbert | |
#17
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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?). I gather that the abbrev. is a little imprecise. http://www.nasatech.com/Briefs/Sept03/KSC12092.HTML says The present thermal-insulation systems are layer composites based partly on the older class of thermal-insulation systems denoted generally as "multilayer insulation" (MLI). A typical MLI structure includes an evacuated jacket, within which many layers of radiation shields are stacked or wrapped close together. Low-thermal-conductivity spacers are typically placed between the reflection layers to keep them from touching. MLI can work very well when a high vacuum level (10-4 torr) is maintained and utmost care is taken during installation, but its thermal performance deteriorates sharply as the pressure in the evacuated space rises into the "soft vacuum" range [pressures 0.1 torr (13 Pa)]. In addition, the thermal performance of MLI is extremely sensitive to mechanical compression and edge effects and can easily decrease from one to two orders of magnitude from its ideal value even when the MLI is kept under high vacuum condition. -- Tim McDaniel; Reply-To: |
#18
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On Fri, 4 Feb 2005, in sci.space.tech,
" said: Kent Paul Dolan wrote: 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. That's a reasonable point. By halving the diameter of the sphere to 50m, you quarter the mass of shell that needs to be launched at once. Even more than that. The larger the sphere, the stronger the skin has to be to contain the same pressure. In general, wall thickness goes up linearly with diameter, if pressure is the overriding factor determining wall thickness. In other words, for a given pressure and material strength, wall thickness/diameter is a design constant, and shell mass goes up with the diameter cubed, not squared. Halving the diameter probably wouldn't reduce the mass by a factor of eight, because there are other drivers to the wall thickness than just pressure containment, but if pressure containment is not irrelevant to the design, then it will be a factor of more than four. -- Del Cotter Thanks to the recent increase in UBE, I will soon be ignoring email sent to . Please send your email to del2 instead. |
#19
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wrote: wrote: wrote: 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. multi layered sandwich and insulation and such. Ok. Point taken. 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). 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. 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. Sure, reinforced with some sort of ultra strong fiber and adhesive matrix. What about Zylon degrading in UV light? 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.(Sent up in much smaller, easier and less expensive shipments) Of course the main shell wouldn't be able to be fully pressurized for years, but with it up, you could easily set up smaller interior rooms that COULD be fully pressurized. And which you could lease out for income while you worked on augmenting the entire shell. 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. Yes. I was SO disappointed when informed that the current launchers only can carry 20 tons or so. Even if the workers have to use full space suits for a while, working INSIDE, they don't have to worry about falling, or dropping things, or drifting away, so I think it would still be much easier. 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). What about a multilayer sandwich - aluminized Kapton outer shell to help shield from UV,(oh, 2 mil thick. Check me on this, wouldn't that be 1.46 grams for 200 square centimeters? Then, with Zylon fabric inner shell bonded to it? Perhaps with another layer of Kapton inside it? The separate layers could even be launched separately and inflated inside each other before the bonding agent sets up, not necessarily with anything near 3 psi, just enough to push them together under tension. 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... We don't need to start out with anything near 3 psi, or 1 psi or 1/2 psi. The outside of the space station is vacuum. The inflatable will inflate with practically nothing. What was the inside pressure of ECHO I? 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. We don't need to start with an air filled sphere. We just need the sphere. Once we have the sphere up - everything else is easier. 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. 3 launches is what I've been figuring lately. 4 when I consider an inner shell. At $250 million per. 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. NO! you inflate a much smaller tent inside the sphere, and fully pressurize that to do most of the construction in, a couple of rooms at a time. In your shirt sleeves. The main sphere NEVER gets fully pressurized for years. You just don't worry about it until some contractor is willing to pay to do it. Meanwhile, the folks pasting the extra layers on the inside of the exterior shell will probably have to wear almost a full space suit,(per Henry) and the folks constructing interior walls and rooms will be inside a much smaller (oh, 20 meter diameter) inflated tent, working in their shirt sleeves. 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. And I'd LOVE to pay them to do so! 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... Eventually. Sure.. It could take years. What a boring thought. :-) Meanwhile, we'll be developing an internal ecosystem, plumbing, going from one or two paying guests per week to 10 or 20, and from one lessee, paying to use one 10 meter by 10 meter by 10 meter cube to 25 paying contractors, and giving the passenger space flight industry time to develop. But meanwhile, THEY would have a destination to take customers too - and would be able to charge the $5 million dollars per round trip flight that they will have to, in order to make a profit. Good development all the way around. 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? I think simple is what I can do now. More complicated is something that will take maybe a couple years to develop the concept. I think I can do this now. Once the launch market starts heating up (I really think I can use two launches per week -- Yes, I'll pay what you are wanting to charge...) Somebody out there will develop bigger capacity. I don't have to worry about that. And when we start turning a profit, we can think about bigger projects. Once this is up and operating, outfitting a Mars expedition will be much simpler. And we will once again need 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. No it won't! It will only take a couple of tons of air to make a couple of rooms fully operational and able to be leased out. A big skyscraper doesn't wait to start leasing and opening stores and rooms until all the floors are finished - as soon as a couple of floors are finished, they move in paying clients and open for business. You want flight rates that are beyond the immediate abilities of rocketmakers, but could be achieved with a little development. If I start paying for regular launches, the launch market will develop on its own. This is good, Mike. You want to go into business? Harmon |
#20
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Henry Spencer said:
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...) Gee, Henry, pop my bubble... |
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