# How could the manufacturing of an 8km diameter and 32km length cylinder in zero gravity work? **URL:** \ **Category:** Factual Questions\ **Created:** [May 11, 2018, 12:19pm UTC](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986 "2018-05-11T12:19:58Z")\ **Posts on this page:** 19\ **Page:** 3
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [May 13, 2018, 10:41pm UTC](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986/41 "2018-05-13T22:41:03Z")
> [@Stranger\_On\_A\_Train](#): > > … any method can produce steel pipe either by rolling and seam welding or drown-over-mandrel (DOM) manufacture, and again, you cannot extrude thick wall pipe like Play-Doh. > > Stranger I have seen pressure vessels for the nuclear and urea industries with comparable thickness made by explosion cladding / welding of two shells. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [May 14, 2018, 12:22am UTC](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986/42 "2018-05-14T00:22:18Z")
> [@k9bfriender](#): > > Does adding radial spokes help at all, or would that just make the problem worse? Pressure acts uniformly against the interior of a pressure vessel, so localized reinforcement does not really help. In order to strengthen the vessel without adding thickness, “radial spokes” would have to extend along the length of the cylinder and the span betweem them would have to be arched in order to distribute the load, which wouldn’t make for a very usable interior volume. Again, the way to deal with this is not to just make a ridiculously thick-walled steel cylinder but to reinforce the pressure vessel with a much higher strength reinforcement again to a composite overwrap pressure vessel (COPV). Aramid and carbon fiber have tensile strengths that are an order of magnitude greater than standard construction steel. No one has ever made a COPV, or indeed, any pressure vessel that is 8 000 meters in diameter so there are certainly a lot of unknowns about how you would actually construct such a thing but it is at least plausible from structural point of view. > [@Whack-a-Mole](#): > > A [couple astronauts](https://en.wikipedia.org/wiki/List_of_spaceflight_records#Ten_longest_human_space_flights) have spent more than a year in space. Spending a few months at a time in orbit is fairly common these days. > > Astronauts spend a few hours a day doing exercises meant to ward off the deleterious effects of long times in zero gravity. It helps but I think some loss of bone mass and some other issues still occur. I am well aware that astronauts stationed at the ISS spend months in _freefall_ conditions; however, we have essentially no experience with human or even mammalian physiology between freefall and 1 g for extended durations; in fact, the only experience we have is from the Apollo lunar missions, and the J-class missions lasted about three days which does not give sufficient time to assess the long duration effects of fractional gravity environment. However, based upon some of the human physiological responses in freefall conditions, many space physiologists believe that gravity below a certain threshold is likely to result in physical degradation. Exercise using resistance to simulate the load of gravity has demonstrated some modest benefits in retarding decalcification and limiting muscle loss but astronauts on the ISS still suffer from significant bone density loss and muscle mass reduction, as well as more nuanced effects on the brain and nervous system, immune system response, disorientation and proprioception issues, and other effects going right down to the level of cellular metabolism. It isn’t certain how much of the effects are due to freefall versus the high energy cosmic radiation environment but the default assumption at this point is that a permanent space habitation environment would need to reproduce terrestrial conditions including simulated gravity (to a necessary threshold) and radiation protection. Stranger ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [May 14, 2018, 2:02am UTC](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986/43 "2018-05-14T02:02:59Z")
> [@Stranger On A Train](#): > > Again, the way to deal with this is not to just make a ridiculously thick-walled steel cylinder but to reinforce the pressure vessel with a much higher strength reinforcement again to a composite overwrap pressure vessel (COPV). That maybe one way to do it but COPVs are known for stress rupture so lifing maybe iffy. Also, in place of making one thick metal pressure vessel, there could be multiple shells with compartments in between. The space between the shells could be differentially pressurized like 10 shells with a differential in pressure of 1.5 psi in each Shell. The shells can be few meters apart too - so maintenance could be done on them. Of course, you’ll need a active pressure control system to balance the pressure in each Shell. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [May 14, 2018, 3:20am UTC](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986/44 "2018-05-14T03:20:47Z")
> [@am77494](#): > > That maybe one way to do it but COPVs are known for stress rupture so lifing maybe iffy. I cannot parse your statement but any pressure vessel can “stress rupture”. COPVs have some particular failure modes owing to their construction, and paricularly failures in processing the liner (insufficient autofrettage). In any case, an 8 km shell would not be constructed the way one makes a 500 liter COPV, and steel would probably not be the ideal liner material for any number of reasons, but the point remains that it would be easier to make a pressure vessel of that size using a much higher tensile strength material rather than trying to somehow weld or extrude a tube of steel with a thickness of feet. > [@am77494](#): > > Also, in place of making one thick metal pressure vessel, there could be multiple shells with compartments in between. The space between the shells could be differentially pressurized like 10 shells with a differential in pressure of 1.5 psi in each Shell. The shells can be few meters apart too - so maintenance could be done on them. Of course, you’ll need a active pressure control system to balance the pressure in each Shell. Nesting shells like Russian dolls doesn’t do anything to reduce the total thickness required. There is no trickery around having to resist the same total load regardless of how it is spread out. Stranger ---
**Author:** ![Lucubratory](https://avatars.discourse-cdn.com/v4/letter/l/fbc32d/32.png) [@Lucubratory](https://boards.straightdope.com/u/Lucubratory)\ **Post date:** [May 14, 2018, 8:21am UTC](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986/45 "2018-05-14T08:21:54Z")
Most of the points I would have raised are covered, except cooling down and being too brittle because of cold: cooling down would still take a very long time on consumer timescales, but such a structure would need heat transfer and radiation systems anyway. Even just using flat panel radiators perpendicular to the surface would dramatically decrease cooling time. As well, when you calculated the 300 year figure, was that for a solid asteroid 8km in diameter, or a hollow cylinder, 8km in diameter, with a wall a meter or two thick? With respect to the steel being brittle at low temperatures, in space around Earth orbit someone else noted temperatures aren’t that low, as long as you have your own solar orbit. For people to live in it, it will need a lot of radiators and other heat management equipment to not kill everyone inside from too much heat, and could shade itself with solar panels quite easily. Brittle temperatures probably won’t be an issue without a significant failure of some kind. Stranger, it’s interesting that you mention COPVs, because one of the other materials I mentioned was basalt fibre. Apparently, it’s made by extruding basalt, and has a higher tensile strength than steel. Do you think that could work? What could an effective liner be? The reason I ask is that ideally, the materials used would be common in asteroids (like carbon and iron), and resistant to the stresses the habitats are likely to encounter (ultra ultra hard vacuum, UV light and micrometeoroids if unshielded). ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [May 14, 2018, 12:05pm UTC](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986/46 "2018-05-14T12:05:12Z")
> [@eschereal](#): > > And what happens to a spinning gas in a cylinder? Will it naturally rarify along the axis and concentrate at the wall? In other words, we assume a gas volume of around 1.6 trillion cubic meters, but how thin will it be in the center (and would it make sense to have a 2km radius displacement cylinder in the center to reduce the gas requirement)? For a spinning body, centripetal acceleration scales linearly with radius measured from the axis of rotation. I tweaked my atmosphere spreadsheet to account for this and determined that if you have a 4000-meter radius cylinder spinning such that you have 1 g (and 14.7 psi of atmospheric pressure) at the surface, then at the axis of rotation, the atmospheric pressure is 11.52 psi. This is comparable to an elevation of just 2000 meters above sea level on earth. ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [May 14, 2018, 1:34pm UTC](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986/47 "2018-05-14T13:34:04Z")
> [@Machine\_Elf](#): > > For a spinning body, centripetal acceleration scales linearly with radius measured from the axis of rotation. I tweaked my atmosphere spreadsheet to account for this and determined that if you have a 4000-meter radius cylinder spinning such that you have 1 g (and 14.7 psi of atmospheric pressure) at the surface, then at the axis of rotation, the atmospheric pressure is 11.52 psi. This is comparable to an elevation of just 2000 meters above sea level on earth. That’s a great calculation. Did you consider adiabatic or isothermal conditions for the atmosphere? What will happen to water evaporating from the periphery and reaching the axis : will it rain like on earth ? ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [May 14, 2018, 2:03pm UTC](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986/48 "2018-05-14T14:03:01Z")
> [@am77494](#): > > That’s a great calculation. Did you consider adiabatic or isothermal conditions for the atmosphere? What will happen to water evaporating from the periphery and reaching the axis : will it rain like on earth ? Kept it simple. Constant temperature throughout. No circulation, which would develop an adiabatic lapse rate - although such a lapse rate would be less than on earth, due to reduced gravity at higher elevations. By the time you get to the axis of rotation, the lapse rate must be zero. ISTM weather would be less severe than on earth for several reasons: -the reduced lapse rate (as compared to earth) -the cylindrical geometry (compared to the [relatively] planar geometry of the earth’s surface) means that higher clouds can’t be very massive. -the absolute upper altitude limit (4000m) limits how big storms can get. Don’t count on seeing any anvil-headed cumulonimbus clouds. -Coriolis effects may result in tangential winds as air moves vertically, but there won’t be a natural tendency for axial circulation. Artificial drivers would be required for that to happen (e.g. by adding or removing heat at the ends of the cylinder), and we could adjust that to influence circulation and any resultant weather. ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [May 14, 2018, 2:08pm UTC](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986/49 "2018-05-14T14:08:17Z")
> [@Machine\_Elf](#): > > For a spinning body, centripetal acceleration scales linearly with radius measured from the axis of rotation. I tweaked my atmosphere spreadsheet to account for this and determined that if you have a 4000-meter radius cylinder spinning such that you have 1 g (and 14.7 psi of atmospheric pressure) at the surface, then at the axis of rotation, the atmospheric pressure is 11.52 psi. This is comparable to an elevation of just 2000 meters above sea level on earth. Thanks for doing this calculation. ---
**Author:** ![Jasmine](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jasmine/32/2964_2.png) [@Jasmine](https://boards.straightdope.com/u/Jasmine)\ **Post date:** [May 14, 2018, 2:22pm UTC](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986/50 "2018-05-14T14:22:37Z")
Even if such a monumental endeavor were possible, the cost of getting all the necessary machinery and personnel into orbit, building the space stations necessary for housing and feeding said personnel, getting the material to make the pipeline into space, and then actually creating the pipeline would be stupendous. I’m sure it would easily soar past the trillion dollar mark. Also, in a project of that unimaginable size and complexity, the number of things that could go wrong boggle the mind. ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [May 14, 2018, 3:56pm UTC](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986/51 "2018-05-14T15:56:59Z")
> [@rat\_avatar](#): > > Ignoring the much smaller tidal forces this would not work, Objects in orbit are following the geodesic through space time and are not being subject to _acceleration._ For all intensive purposes an orbiting object is traveling in the equivalent of a straight line. This would not be the same for a singular object around the star, while it would work for a ring of particles. > > When not ignoring the smaller tidal forces and the impacts of frame dragging you would have to deal with a tendency of it to break apart due to factors like rotational splitting or just the speed of causality. > > Consider the amount of time it would take for a rotational force on one portion of the ring to reach the other side, which cannot be FTL as an example. > > Space is elastic, and particles in it will exchange energy with it. No, the hula-hoop isn’t getting gravity by rotating around the sun, you’re right that just leaves you at zero-G unless you’re spinning faster than orbital speed which means you need scrith to hold it together. It gets gravity by being a rotating cylinder, just like a 2001-style torus or an O’Neil-style cylinder. Except the torus is longer than it is wide. Much much longer. Much much much longer. I was just imagining the OP’s rotating cylinder, but longer and longer, and then stretching it around the Sun, just for fun. And the best part is that it doesn’t matter if the hula-hoop breaks or anything, since as you say the hula-hoop itself is at zero-G with respect to the sun. Of course all this is nonsensical. Gigantic 1-G shirtsleeve megastructure environments in space don’t make sense. If you have the technology to build one, you’ve got enough magic to not need to build one. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [May 14, 2018, 4:12pm UTC](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986/52 "2018-05-14T16:12:32Z")
Just as an aside, isn’t there a stability issue with spinning a cylinder on its long axis? I thought I’d read something to the effect that a spinning cylinder will tend to begin tumbling end over end instead ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [May 14, 2018, 4:15pm UTC](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986/53 "2018-05-14T16:15:44Z")
> [@Lemur866](#): > > Of course all this is nonsensical. Gigantic 1-G shirtsleeve megastructure environments in space don’t make sense. If you have the technology to build one, you’ve got enough magic to not need to build one. In general, megascale structures for space habitation make little sense. It is far easier to make smaller structures to produce terrestrial habitats, and they are far easier to protect against hazards and present a lower risk. But realistically, the route to permanent space habitation is to modify the human form such that it does not require so much protection against the space environment. This is well beyond the state of the art in medical science but is still far more plausible than building giant Ringworld like structures requiring material strengths exceeding anything known in nature. > [@Mangetout](#): > > Just as an aside, isn’t there a stability issue with spinning a cylinder on its long axis? I thought I’d read something to the effect that a spinning cylinder will tend to begin tumbling end over end instead Objects will tend to rotate around both their long and short axes, so it is important to stabilize such an object so it does not nutate and start rocking in cross-axis rotation. The use of tidal forces combined with some kind of damping system is the easiest way to prevent this from happening. Stranger ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [May 14, 2018, 4:26pm UTC](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986/54 "2018-05-14T16:26:54Z")
> [@Stranger\_On\_A\_Train](#): > > Objects will tend to rotate around both their long and short axes, so it is important to stabilize such an object so it does not nutate and start rocking in cross-axis rotation. The use of tidal forces combined with some kind of damping system is the easiest way to prevent this from happening. I thought it would be stable on its long axis. See [tennis racket theorem,](https://en.wikipedia.org/wiki/Tennis_racket_theorem) which I think may be applicable here. ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [May 14, 2018, 4:42pm UTC](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986/55 "2018-05-14T16:42:01Z")
> [@Mangetout](#): > > Just as an aside, isn’t there a stability issue with spinning a cylinder on its long axis? I thought I’d read something to the effect that a spinning cylinder will tend to begin tumbling end over end instead I think so. (as I recall) tumbling end over end is has the smallest rotational kinetic energy for a given angular momentum, so any dissipation of rotational kinetic energy (and there’s always dissipation) will result in tumbling end over end (see what happened with Explorer [Explorer 1 - Wikipedia](https://en.wikipedia.org/wiki/Explorer_1#Results)). The tennis racket theorem doesn’t apply in this case because two of the moments of inertia are equal (the TRT requires distinct moments for each axis). ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [May 14, 2018, 5:01pm UTC](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986/56 "2018-05-14T17:01:07Z")
> [@Lemur866](#): > > No, the hula-hoop isn’t getting gravity by rotating around the sun, you’re right that just leaves you at zero-G unless you’re spinning faster than orbital speed which means you need scrith to hold it together. It gets gravity by being a rotating cylinder, just like a 2001-style torus or an O’Neil-style cylinder. Except the torus is longer than it is wide. Much much longer. Much much much longer. I was just imagining the OP’s rotating cylinder, but longer and longer, and then stretching it around the Sun, just for fun. And the best part is that it doesn’t matter if the hula-hoop breaks or anything, since as you say the hula-hoop itself is at zero-G with respect to the sun. > > Of course all this is nonsensical. Gigantic 1-G shirtsleeve megastructure environments in space don’t make sense. If you have the technology to build one, you’ve got enough magic to not need to build one. The problem is that the location wouldn’t be stable, or be zero-G as those effects are a result of a body following the geodesic through spacetime. An object orbits another object because that geodesic happens to follow a path that results in an orbit, and the observed zero-G or micro-gravity is a result of it not being subjected to meaningful changes in that path along the geodesic. This is where the Newtonian model breaks down, due to the FTL action of gravity under that model. The Lense–Thirring effect may be small but would be very important in this case, as the gravitational field would be impacted by both the rotation of the ring and the sun. While an extreme example, this orbital path around a spinning black hole is a good example of what I am talking about. > **[Kerr metric](https://en.wikipedia.org/wiki/Kerr_metric#/media/File:Generic_geodesic_orbit_around_a_Kerr_black_hole.png)** > > The Kerr metric or Kerr geometry describes the geometry of empty spacetime around a rotating uncharged axially symmetric black hole with a quasispherical event horizon. The Kerr metric is an exact solution of the Einstein field equations of general relativity; these equations are highly non-linear, which makes exact solutions very difficult to find. > The Kerr metric is a generalization to a rotating body of the Schwarzschild metric, discovered by Karl Schwarzschild in 1915, which described the ge... I fully agree that other limits like those of chemical or electrical bonds will pose an issue way before these effects. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [May 14, 2018, 7:19pm UTC](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986/57 "2018-05-14T19:19:03Z")
Is the spin rate about 2rpm to get a full G? That seems pretty fast. The other thing is, how many humans in it? Because humans move around in rather Brownian ways, so the body of the thing has to be massive enough to mitigate those changes. I mean, if you have a concert and everyone all gather together for it, a thing that small could be affected by hundreds of people all in the same spot. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [May 14, 2018, 7:44pm UTC](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986/58 "2018-05-14T19:44:42Z")
> [@eschereal](#): > > Is the spin rate about 2rpm to get a full G? That seems pretty fast. I came up with 0.47 RPM. w[sup]2[/sup]\*R = 9.81 w[sup]2[/sup] = 0.0024525 w = 0.049523 rad/s w = 0.0078818 rev/s w = 0.47 RPM ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 14, 2018, 8:45pm UTC](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986/59 "2018-05-14T20:45:37Z")
If you want axial air circulation, it’d be simple enough to accomplish. Put your ponds at one end, for instance: If you have any sort of heating-cooling cycle, the ponds will change temperature slower, so there will be axial temperature gradients, so there will be axial convection. [Previous page](https://boards.straightdope.com/t/how-could-the-manufacturing-of-an-8km-diameter-and-32km-length-cylinder-in-zero-gravity-work/813986.md?page=2)