From: The Butterfly (salsbury_at_bootstrap.sculptors.com)
Date: 02/25/98
Date: Wed, 25 Feb 1998 10:25:50 -0800 Message-Id: <199802251825.KAA08984@bootstrap.sculptors.com> From: The Butterfly <salsbury_at_bootstrap.sculptors.com> Subject: Re: Helios: zero mass balloon
-C. McCoy writes:
- > Problem with this is creating a vacume chamber strong enough to maintain
- > its area without collapse. You would need something like a submarine,
- > but larger, and lighter.
-
-and if you succeed, you don't get that huge of a win.
Well, it depends. If you use geodesic architecture, you get
EXTREMELY strong structures, with very light, mass-producible parts. And
the larger you build a geodesic, the stronger it gets.
- > Some of the new carbon compounds (C60) might be strong enough, but the
- > as far as I know, c60 is RARE. They make it one at a time. Until mass
- > production is figured out, It would be too expensive.
-
-in other words: it is not possible to make the materials at this time.
Not true. C60 *used* to be really expensive, about 8-10 years ago,
when they were still just learning about it. Nowadays, they churn it
out. It's quite easy to do, and they're making all sorts of novel nanoscale
structures out of it. (C70, C90, etc.). Working this stuff into macro-scale
materials is still the trick, but there are some neat papers coming out on
the use of things like Fullerine Nanotubes worked into carbon fiber
composites that have absolutely astonishing strength-to-weight ratios. (On
the order of 10 to 100 time stronger than steel, according to one
projection I saw.)
->> Kevin Christopher Lampo wrote:
->>>
->>> I, as I am working on a small hot air balloon, had a thought about lift.
->>> archimedies law says that the lift is calculated by the eq.
->>> l=(densityout-densityin)*gravity*Volumeofobject. now if the inside density
->>> could go, for hypathetical thinking, zero. then we would get max lift. so
->>> I ask you, is there a way to make a rigid body with a highly non-porous
->>> material and create a near vacume? Say on the ground a big suction unit
->>> pulled out the gas initialy to near weightlessness. then using thrust
->>> vectors, the craft could achieve lift, and forward thrust... think it
->>> over.
->>>
They've discussed this on the GEODESIC list in the past. I think
the consensus was you'd need lightweight wire and mylar, and probably
something at least a meter or two in diameter before it'd lift its own
weight. It's been a long time since I've seen the calculations, though, so
I'm not sure.
Another fun one is the idea of floating cities in the sky. You can
do this with megascale geodesics...structures more than .5 or 1 mile in
diameter.
I'm also beginning to research nanoscale materials with the hope of
creating lighter-than-air materials that are stronger than
diamond. However, I'm still working out the math on these. They may end up
just slightly more than air (like aerogels, which have gotten down to .0003
density of air) but be much stronger. (Aerogels break very easily.)
Here's part of a letter I sent to someone in a private conversation
about the megastructure principle. The math needs to be re-done, but it
explains the basic idea... We were discussing nanotech engineering, so
there are several mentions of that in here, too, but it's not needed for
this type of project.
(Snip snip)
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--BTW, have you run the numbers yet on the floating buildings to make sure
--vacuum gives you enough lift for the bulk strength you'll need in the
--structure for reasonable designs? I haven't thought much about
--nano-macroarchitecture -- floating cities would be cool if the numbers will
--work. I'm also (as always) concerned about power requirements and related
--issues for a structure this large, since nanorobots in bulk quantities tend
--to be huge heat generators.
- Well, putting nanotech aside for a minute, there are a few tricks
-in megascale architecture that we can employ to achieve the same
-things. Nanotech materials would lend tremendous strength, (orders of
-magnitude better than conventional materials, from what I can figure), but
-they aren't required to utilize the basic principles.
- I haven't yet ran the numbers for people-scaled structures, such as
-air-cars and air-buses, so I'm not sure exactly how much hull-volume you'd
-need to displace the weight of passengers, but we've done airships like the
-zeppelins with bulk materials like magnesium struts, rubber sheeting, and
-gas bladders filled with helium or hydrogen. All of those weights can be
-reduced, and a geodesic, ultra-strong, lightweight framework holding open a
-vacuum bubble of just about any size is going to have some floatation,
-although working load lift wouldn't come until you got to a larger
-size. (For reference, a 16' weather balloon filled with helium will lift
-something in the range of 130-140 lbs, filling it with hydrogen, while much
-more explosive, would provide a lift factor of aproximately 4x as much.)
- Still not really going into nanotech, here are some numbers from
-Bucky Fuller's research and proposals for building "Cloud 9" airborne
-floating cities, spherically shaped, and several miles across... Bucky
-talked about how the surface area of a sphere increases as a function of
-the 2nd power, while volume increases as a function of the 3rd. So every
-time you double the diameter of the sphere, you square the surface (i.e. -
-the materials it's built out of) and cube the space enclosed by the
-surface.
- His numbers, which I'm recalling from memory, went something like
-this (These numbers for the weight of Aluminum in the trusswork are
-illustrative, but from memory, I can dig up the reference, if you'd like):
-Also, it's late and I don't want to figure out all the partial-pressures
-for air to determine it's actual molecular weight, (wasn't able to find a
-handy figure in my chem books, either...) so I'm going to make a wild guess
-and use nice round numbers. It will still demonstrate the principle.
-
-For a sphere:
-Surface area = 4pi(r^2)
-Volume = 4/3pi(r^3)
-
-Diameter of Surface Area Approx Weight Volume/Weight of Air
-Sphere of Al to build enclosed by sphere
- sphere
-100' 31,415.9'^2 3.5 tons 523,589.8'^3 / 1 ton
-200' 125,663.7'^2 14 tons 4,188,790.2'^3/ 8 tons
-400' 502,654.8'^2 56 tons 33.5M'^3 / 64 tons
-800' 2.0M'^2 224 tons 268M'^3 / 512 tons
-
- I think my air-weight estimates are off, because I remember it
-being close to .5 miles in diameter before the equilibrium point was
-reached, but as you can see, volume quickly outstrips the amount of
-material required to surround it, and when you get to these large scales, a
-temperature fluctuation as small as 1 degree Fahrenheit will cause such a
-massive gas expansion and displacement that the overall combined mass of
-containing sphere and contained atmosphere has a lower overall density that
-the surrounding air, and the structure floats. No power necessary, other
-than sunlight to provide heat for gas expansion. If nanobots want to kick
-off extra heat, that would probably just help things stay afloat. :-)
-
- Coming back to the nanoscale, I could see nanotech providing
-super-strong and super-light materials, perhaps even employing the same
-principle on smaller scale with enforced vacuum to create people-scale
-components with little to no weight, and building these into a larger
-structure, but the nanotech itself wouldn't be a requirement for building
-floating megastructures. We could do that today.
------------------------------------------------------------------------------
(Snip snip)
-- Pat ___________________Think For Yourself____________________ Patrick G. Salsbury - http://www.sculptors.com/~salsbury/ --------------------------------------------------------- "I only touch base with reality on an as-needed basis!" -- Royal Floyd Mengot (Klaus)