h a l f b a k e r yContrary to popular belief
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Metal pressure vessels are often built in sections - usually barrels - using machines that take sheets of metal, run it through a device that simultaneously curls and trims the sheet into a section ready for joining to subsequent sheets.
'Metal Pressure Vessel' is a workable description of a space
station. Space station modules are currently limited in size to accomodate the launch vehicle's payload dimension limits. We could break out of this limitation by simply putting an assembly jig in orbit.
A roll of metal just three meters long and 4 meters in diameter would contain slightly more than 37 cubic meters of metal. If rolled to just one millimeter thick, this would equate to 37,000 square meters of metal sheet. By comparison, a single barrel section of the Space Shuttle's External Tank (8.6m diameter x 6m height) is only 162 square meters. In other words, a single roll of metal could yield enough sheet to build about 230 such barrel sections if desired.
37,000 square meters of metal, one millimeter thick, would build a pressure vessel close to 45 meters in diameter and 225 meters long. This is immense by current standards and well beyond the launch capacity of any vehicle known or contemplated.
Actually, two jigs would do nicely: one for the barrel sections and one for end-caps which would be spherical or elliptical in shape. Interior structurals ccould also be made from flat sheet metal and so would be done by the same jig used to make tha barrel sections.
Of course, this same approach is useful for very large propellant tanks and othe pressure vessels. . .
Particularly important is the ability to mass produce these space stations.
By now you know where this is leading to...
Low_20budget_20spacecraft
[normzone, Jun 17 2008]
Lunar Resources
http://www.asi.org/...uminum-sources.html
"Aluminum composes 10% of the atoms and 13% of the mass of lunar highland regolith, being the third most abundant element." [Klaatu, Jun 17 2008]
[link]
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It's a good idea, though not all that original. The problems I see are getting that roll of metal into space and then the automated welding robot that can also x-ray check the welds. But the toughest parts are the doors. I think Bigelow Aerospace has it right with the inflatable structure. Assemble it all on Earth out of materials that are stronger than metal and then just inflate it in place. |
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I'm all for tossing raw materials into orbit, but I prefer a giant soccer ball as the "starter" station until we get the engineering know-how for a wheel (or a moonbase which cycles station-personnel back and forth) |
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Thanks for the feedback! Just curious: why no vote, bun or bone? |
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me ? oh, I think 37 m3 of aluminum is probably a bit much for the Shuttle to carry up in one load from Earth and if you want to "mass produce space stations" you haven't stated why (stations around other planets or lagrange points, etc?) |
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/37,000 square meters of metal, one millimeter thick, would build a pressure vessel close to 45 meters in diameter and 225 meters long/ |
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Such a vessel would rupture at just 9kPa. Given that you need to withstand 100kPa, you'll need at least 11mm walls. Multiply this by the appropriate safety factor. |
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Yeah, I think mass is the factor in your idea. |
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The advantage of small modules is compartmentalization. Damage in one module is confined to that module. |
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Furthermore, is there demand or need for a large, open compartment? If you floated to the center, you could be stuck there quite a while. |
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Also, your "jigs" are going to be of a size that fits in the shuttle's bay and that probably limits the size of the sheet metal they can handle. |
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You probably want to tweak the e-mail address in your profile to make it a little harder for 'bots to harvest. |
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Shuttle? Who said anything about the Shuttle? I compared the area provided by a roll of metal to that of a barrel section of the Shuttle's External Tank as a comparison of what a relatively small-volume roll could do. . . I said nothing about the shuttle being the delivery vehicle for this idea. More likely the Ares V or some equally heavy lifter. My apologies for the confusion. |
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Mass producing space stations is more an economics issue as it pre-supposes demand follows supply - if you build it, someone will want to buy it. I agree it is MUCH wiser to build more modest-sized structures, but I would start at the maximum diameter feasible for the largest launch vehicle you can find. That would be something like ten or twelve meters for the Ares V. This would be the smallest dimension for a space-built structure. |
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The assembly jig only has to be launched once, so the issue is to provide only the metal for the subsequent modules. |
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//you probably want to tweak the e-mail address. . .// |
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I think I have heard of "'bots" before but have no recollection of what they are/do. How does one 'tweak' an e-mail address? |
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"How does one 'tweak' an e-mail address?"
Some spammers use software to look for legible e-mail addresses in web pages, then send spam to those e-mail addresses. By tweaking, I mean modify your e-mail address so it won't work if someone copied/pasted it, but is decipherable by a human who might have a legitimate reason to e-mail you.
E.g. not
me@here.com, but
ME /at/ HERE /dot/ COM
or somesuch. |
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I used to work in a plant that forms sheet metal, so I can say this idea isn't good. Metal rolls are heavy as hell, metal-forming machinery is even heavier. You are talking about a de-coiler, a punch, a press and a brake, at least, and power supplies and operators for each. Then you'll need welders. And scrap disposal. |
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37 cubic meters of aluminum is going to weigh 101,750 kilograms, by the way. That seems a bit much for any rocket to boost, but I don't know payloads capacities. |
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It'd be a lot better to send up pre-fab units nested together, or some such. You could stack hexagons into a round rocket body, with a bit of insulation for padding, and assemble a soccer ball out of them. That'd overload even the heaviest of lifters, and be a lot easier to assemble. |
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Or make the whole thing inflatable. As has been proposed. |
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Oh, I didn't bone or bun because I don't think it is a bad idea or really a good idea, but wanted to see if you'd come back with more info to tip the scales. I'm still not seeing the advantage of metal over fabric in a situation where compression isn't required. |
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Single-ply fabrics are usually much lighter than an equivalent thickness of any metal. The inflatable systems developed by Bigelow and Transhab are multilayered affairs mandated by safety and envionmental conditions. SOMETIMES multi-ply inflatable systems can weigh as much per unit area as a lightweight metal. |
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The mass I quoted was an extreme to illustrate the point that 'a little can go a long way'. I seriously doubt that we will ever need to build, from Earth, hundreds of space stations for any purpose. If there were a need for so many, we would likely use lunar resources instead. |
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About payloads: the Ares V being built now for the lunar missions is described as having a LEO payload capacity of 130,000 kilograms. IF they can launch it a the same cost as Shuttle - and I'm very dubious about this - the cost per kilogram would be something close to $4,000.00 US. |
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Final point: I have also worked in metal shops and noted that much of the mass of the fabricating equipment was required for strength. Newer composite materials are available with strength equal to or better than thick metal masses. It only remains for tool designers to work out how to design equipment for the tasks outlined. I'm very confident that, with a 130,000 kg payload capacity available, orbiting a working jig system able to meet the scale outlined is possible. Of course it would make more sense to just work composites instead of metals. . . |
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As a side point here: it would be a very good idea for NASA and anyone elese interested in the Ares V to find/develop uses for this vehicle NOT related to manned flights to the Moon or Mars. I have a hunch these objectives are not going to be around much longer. |
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//SOMETIMES multi-ply inflatable systems can weigh as much per unit area as a lightweight metal.//
Wouldn't your metal fabrications come under the same safety regs requiring more layers and more weight? Also isn't the "ripstop" nature of a fabric an important feature in a situation where puncture is possible. The question being that in the event of a meteor shower or micrometeoroid event, which construction will experience less damage? I'm a little worried that a pressurized metal enclosure will catastrophically fail where a more fibrous construction will localize the failure. |
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//lunar resources instead// I agree or asteroids. |
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//much of the mass of the fabricating equipment was required for strength// Close, but the better answer is stiffness. Stronger, lighter machines could certainly be made, but stiffer ones are tough. Also, and this is especially the case for this app, thermal tolerance would be huge. I'd hate to design the welder whose support arm is exposed to direct sunlight on one side and complete darkness on the other, and know they may switch at any moment. I guess it could be solved with insulation, but it is still tricky. The nice thing is you shouldn't need a shielding gas. Also I don't know how molten metal is effected by vacuum. Will it evaporate or gasify? Probably not, but I don’t know. |
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//I have a hunch these objectives are not going to be around much longer.// Do you think we will succeed or give up? I assume since due to your name, that you think we will succeed. I hope we succeed, but long term, I see planets as good material sources and the future is in space based ships. Mars and the Moon still seems like a one way trip. Even with good return ships, long durations in 1/3 or 1/6 gravity would seem to me to prevent you from coming home by making you a weakling. I guess you could have artificial gravity stations on the ground, but spaceships just make the solution easier, though I guess they make other dangers greater. |
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I'm saying the current NASA program for returning to the Moon and pressing on to Mars is doomed on a number of levels. NASA no longer enjoys the reputation for solving problems that matter to anyone. Instead, NASA insists on keeping costs for space access so high that - today - the lunar transportation architecture (Ares V/Orion/LSAM) would have to be regarded as a scam. What NASA NEEDS to do is reduce the cost of access to space to terms that enable common access. It refuses to do this - just look at their handling of the COTS issue. You do not get away with things like that forever and we are about to have a change of administration - and none of the candidates are wedded to this project. |
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As for the current subject, I think you have a better handle on the technology involved than I do. For me, I trend toward small-scale systems being made available to a much wider user base. This is directly opposite NASA's approach. |
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On a more general note, I learned of the Halfbakery while researching for an article I was writing about the planet Mercury. So far as I know, no one is having as lively and thought-provoking an exchange about colonizing Mercury as took place last year over 'Mercury 2.0'. I was particularly struck by the writer who called him- (her-?)self 'MercuryNotMars'. That suggests I'm not the only one who recognizes Mercury's industrial potential. I don't mind being insane, as long as I have company. Alas, MercuryNotMars did not leave an e-mail address so I've not been able to follow up. |
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Zero gravity causes calcium to essentially leach out of bones. Any gravity level would resolve that problem. As for muscular strength, that is a function of whether muscles are used (stressed) enough. Astronaute on other planets might just ghave to put more hours at work, but that is not as bad as it sounds because of the lighter gravity load. |
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O.K. I think I got it all. Thanks for the feedback. |
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I would imagine that there might be some chance of inflating a mould (mold:US) with two layers, then pumping it full of some epoxy resin to form a solid shell. |
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If I recall correctly, epoxy resins would be space-stable (against hard vacuum, that is) but I'm not so sure they stand up to intense UV. I'm looking into these for another item I'm working on. . .more later. |
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Probably only the outer layer needs to be UV resistant. |
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//Particularly important is the ability to mass produce these space stations.//
Why? |
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ECON 101: Is better to make 100 stations with a set of infrastructure than it is only 1 station. The 100 stations would each only be 1/100th the cost to the consumer. Likely results in more buyers. No guarantees, of course. . . |
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