Talk:Island Three

Could?

Could a single O'Neill Cylinder function on its own? —Preceding unsigned comment added by 76.184.133.222 (talk) 02:18, 9 April 2010 (UTC)

• Yes but considerable thuster energy and ejection mass are needed to aim the cylinder toward the sun, due to the million plus tons of mass in the cylinder. On third thought, the twin cylinder idea likely is not good engineering, as the first ten may not work and it will be very difficult to repair when it malfunctions. We needed the trusters to get the rotation up to speed, they can make the adjustments in the atitude, and they can dampen any wobble and vibration that arises. Lots of independent thrusters means good redundency and indivial thrusters are easier to repair. Worse the twin cylinder system will slow the rotation each time it changes the attitude. We should not suppose it is a free energy devise. The many moving mirrors may also be unreliable. Two spheres rotating each other, with a kilometer of tether, may prove most reliable, most versitile and least costly, per habitat dweller, partly because a sphere is stronger than other shapes. Admittedly docking at either sphere is chalanging. Thousands of individuasl window panes may also be bad for reliability and low air leakage. The thick walls required even if they are made of diamond may be show stopper as the stress with rapid temperature change can be enourmous. Neil66.177.105.109 (talk) 07:30, 26 September 2010 (UTC).

Can't it just fly on nuclear energy so that it needn't constantly aim to the sun? 84.192.205.136 (talk) 18:16, 5 May 2012 (UTC)

A bit on the heavy side

Given the stated dimensions of 32km length and 4km radius, the hull of one of the cylinders would have a surface area of 900km². Very conservatively assuming that a 1 m² section of a cylinder has a mass of 1 tonne, and disregarding the mass of the contained air, a single cylinder would have a mass upwards of 900 million tonnes. This represents the LEO lifting capacity of 45 million Ariane V launchers. The biggest spacecraft ever seriously proposed, the H-Bomb-propelled "Super Orion", would require 112 round-trips to lift that much material. Assuming a space elevator could reduce the cost of lifting material to GEO to $10/kg, lifting one cylinder's worth would cost $9 trillion.--174.118.10.147 (talk) 09:12, 21 February 2011 (UTC)

I'm unaware of anyone proposing to build a hab from terrestrial resources. (Unless you count opponents of the space program...) TREKphiler ^{any time you're ready, Uhura} 12:39, 21 February 2011 (UTC)

Centripetal vs. Centrifugal

Shouldn't the sentence "They rotate so as to provide artificial gravity via centrifugal force on their inner surfaces," instead list "centripetal force"? On its article page, centrifugal force is listed as "represent[ing] the effects of inertia that arise in connection with rotation and which are experienced as an outward force away from the center of rotation." In other words, centrifugal is the motion after an object in centripetal motion is released- the motion tangential to the point of release along the circular path of motion. 68.10.137.78 (talk) 02:05, 27 May 2011 (UTC)

the air within the cylinder and the shell of the cylinder provide adequate shielding against cosmic rays.[

Would it be enough to protect against a super flare, like the one that occurred in 1859?108.23.147.17 (talk) —Preceding undated comment added 06:57, 30 September 2011 (UTC).

Criticism section

Not only the numbers sounded really exotic, since 24kg of steel per square metre means a mere 3 mm total thickest since a cubic metre of steel is 7800 kg and 24/7800 of a metre is about 3mm. It is essentially comparing apple with oranges. It is also using the most inefficient design (island 1) as a compare.(which does not even have even distribution of gravity.) Having a chain of small balls also pose a very inconvenient traveling infrastructure, and the essential materials needed to build an equivalent living area of an island 3 is likely to be much more with added material for connection, travel, radiation shielding and safety issues. If you need the most flat surface area from such a ball, you get a 314 square metre from each(no one wants to live on a curved 10 metre diameter surface.). The Island 3 gives you a total of 804 square kilometre area, and 402 minus the "rivers", which is 402000000 square metre, and one would need 1280649.2 balls(10m diameter) to have the same comparison. If each ball really only need 24 kg of steel per square metre (which I assume to be related to surface area, and surface area of a 10m ball is about 1257 square metre), each will weight about 30 tons(rounded down), so the complete structure, with same living area(but much less radiation shielding and safety net since you are holding 314 square metre of objects with 3mm walls) will weight about 1280650 X 30 (you can't have 0.2 of a ball in the chained structure), 38419500 metric tons. (if the island 3 had a 10 metre thick hull, it would weight something like 62712000000 metric tons though) This is without and structural weight to sustain the chain, and you need structural weight between each ball to sustain about 300kN+double of its own weight of force for a static loading, safety factor of 1, that is another few cubic metres of steel per ball(needed for both sides), and now you really need to thicken the walls of the balls since the 3mm thickness cannot sustain the force between each ball. Since the claim is so exotic, you need an extremely reliable source to support it. (see WP:OR, WP:RS and WP:undue as well) I was just about to ask for a source with a citation tag, but the 3mm thickness really worries me and seemed unrealistic, so I am hiding the whole section before anyone can give a reliable source. Also, think carefully why could someone build a 10 metre thick hull structure with a 3mm thick hull. —Preceding signed comment added by MythSearcher^talk 15:18, 11 December 2011 (UTC) P.S. a 3mm hull would also have a really great loss of air and water. The more you think about it, the more you feel like that section was written by someone with minimal knowledge of craft/building design, or I must have made an error up there. —Preceding signed comment added by MythSearcher^talk 15:30, 11 December 2011 (UTC)

I'm glad for the review. O'Neil's crucial error is to assume that common materials will become arbitrarily inexpensive. This false. There will be an active market in materials, so the most efficient use of materials will win most designs. In a dimensional analysis of the stresses on the structures for Island 1, 2 or 3, self-support is dwarfed by the hoop-stresses to contain the air. So, in that design, using the same structure for both is very sensible, but uses very large amounts of material to handle the hoop-stresses. The fact that the material is enough shield the cosmic rays is gravy. I calculated something like 80cm for the shell of Island 3. At $450/tonne, the current world cost for steel, the cost per hectare in Island 3 is something like a million dollars (forgot the exact amount, sorry). A smaller cross-sectional area, say a 10m ball, has much smaller hoop stresses because it has a much smaller cross-sectional area. This is not a new idea: The NASA study co-chaired by O'Neil mentions it. The assumption in this case is that an optimized internal truss supports the internal floors, and the hull just contains the pressure, which in O'Neil's proposal is 40% of normal. The upper part of the hull should be supported by air pressure, and the lower part by external tensile members soldered to the hull, and formed into pad-eyes for cables. Inexpensive strong materials are likely to be used to save both structural and transportation mass, so assume Eglin Steel, not mild steel. Since the strongest steels are heat-treated, the hull will be assembled by crimping and soldering the crimps, probably nickel soldering. Now, this same basic design is the normal design for pressurized liquid-fueled rockets' tanks, except they use weaker stainless steel, rather than Eglin steel, so I think it probably works fine, and holds pressure in just fine, as well. Corrosion control is a live issue, but unlike a rocket tank, the outside is always in vacuum (i.e. no problem). The likely solution to the inside is to keep the living quarters, including interior walls, inside a plastic baggie, and keep CO2 or some other non-corrosive gas next to the hull. Hydrogen can't be used because it's corrosive and flammable. CO2 is cheaper than nitrogen in space because it can be had from rock. Nitrates are rarer than carbonates. Radiation shielding should be dual-use storage containers or mining waste. It can be cheaply supported in fractional-G structures rotating more slowly outside the pressure hulls. This is much less expensive than keeping it at one G as in the Islands. This was always the plan in the NASA design, and it makes even more sense if you have to buy the materials. Ray Van De Walker 01:28, 12 December 2011 (UTC)

So this is completely your own research, and thus not suitable for wikipedia per WP:OR. You assumption ignored the loss of air and water due to the gravity and pressure difference, in fact, you don't want the structure to be supported by the air pressure inside it, you'll want to have a pressure vessel to contain the pressure inside in order to minimize loss. And the calculated weight per square metre is a thickness of 3mm in your design, not 80 cm, which is about 27 times heavier. Also, your designed basically handled only the air pressure, with no gravity added into the account. BTW, the price of steel will become inexpensive is assumed to be true since materials will be gathered in space, you can move the whole mine(like a small metal asteroid) to where you want to build the colony, or simple use a mass driver, powered by solar energy, to launch material from the moon, instead of building transportation vehicles to transport stuff hundreds or maybe thousands of times. If you are talking about using new building materials, like carbon nanotubes, than it helps both O'Neil's design and you design. Also, you ignored the heating cycle in space. The surface that faces the sun can heat up to a few hundred K, but the side away from it can be only a few K. You need some design to distribute the heat to prevent it from wearing the hull. A 3mm hull will hardly have any internal mechanism to do so(like fluid cycling through the system), or you will end up having more structure to support the pressure of the fluid(usually water or air). Also, radiation shielding, in today's technology, you can only use thicker and denser material to have a good shielding(thus the great steel hull for the damaged nuclear plants, thick concrete walls and lead for storage of nuclear waste etc.) so you cannot have a light alternative if you want people to live in space for an extended period. And your design simply reduce the gravity to minimize structural weight, which is simply not the design intend of Island 3, for it is aimed to have an environment as similar to Earth as possible, to have Earth's gravity at almost 1g, most likely to prevent muscle reduction and calcium loss in bones. If you say it was always the plan in the NASA design, and you say it is the criticism of Island 3, please provide a link or name of the article. If it is mainly calculated and designed by you, then it is not suitable in wikipedia, and you really don't have to reply about the calculation anymore, since this is not a discussion board(per WP:NOT), and we really shouldn't discuss details that will not be placed in the articles. —Preceding signed comment added by MythSearcher^talk 07:32, 12 December 2011 (UTC)

"radiation shielding, in today's technology, you can only use thicker and denser material to have a good shielding(thus the great steel hull for the damaged nuclear plants, thick concrete walls and lead for storage of nuclear waste etc.) so you cannot have a light alternative if you want people to live in space for an extended period." Why do you conclude this must be structural steel? None of the proposals I've seen suggest it is. In fact, O'Neill & Pournelle both expressly say they'd use asteroidal rock, essentially mining slag, or regolith, instead. TREKphiler ^{any time you're ready, Uhura} 14:39, 12 December 2011 (UTC)

I did not conclude it as structure steel, but essential weight. which 24 kg per square metre is not going to be enough. You can have other stuff to shield the radiation, but it essentially requires weight. —Preceding signed comment added by MythSearcher^talk 14:49, 12 December 2011 (UTC)

I won't disagree with that. You do leave me the impression it was structure you meant, tho. TREKphiler ^{any time you're ready, Uhura} 14:55, 12 December 2011 (UTC)

An "in pop culture" example

An O'Neill Tube can be seen in level 4 of the SNES game Super Earth Defense Force. For example, skip to about halfway through this video: http://www.youtube.com/watch?v=dJCt1F2dEzM

I wasn't sure whether it was kosher to post a screenshot of the game as fair use, or if it would even be considered a good addition to the article, so I'm just mentioning it here instead. --24.22.37.178 (talk) 04:56, 7 May 2012 (UTC)

The Citadel in Mass Effect is an example of an O'Neill Cylinder. This section may be possible. Blumin (talk) 00:26, 5 June 2012 (UTC)

For it to be notable, examples should be mentioned by third party sources, not just an appearance. —Preceding signed comment added by MythSearcher^talk 05:30, 5 June 2012 (UTC)