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I'm not so sure about that actually. If it's moving downwards at 5 km/s, the cable will make it through all of the "sensible air" in about 6-10 seconds. Carbon doesn't vaporize until about 4000 K and isn't very flammable. Also consider that there will probably be several coatings to the cable. While its theoretical diameter is that small it would maybe be more like... 10 cm or so around (if I had to guess). I'd expect it to make its way to the ground.
-Josh
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I'm not so sure about that actually. If it's moving downwards at 5 km/s, the cable will make it through all of the "sensible air" in about 6-10 seconds. Carbon doesn't vaporize until about 4000 K and isn't very flammable. Also consider that there will probably be several coatings to the cable. While its theoretical diameter is that small it would maybe be more like... 10 cm or so around (if I had to guess). I'd expect it to make its way to the ground.
Ever see a meteor shower? probably most of the meteors that make spectacular fireballs are no wider that 10 cm, and they don't survive the 10 second through the atmosphere to make an impact with the ground, and probably if they take 10 seconds, the temperature of reentry will be hotter that 4000 degrees, and if something I left, its not going to make much of an impact, probably the heat of impact would vaporize it, if not the fiery reentry into the atmosphere.
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I'm not so sure about that actually. If it's moving downwards at 5 km/s, the cable will make it through all of the "sensible air" in about 6-10 seconds. Carbon doesn't vaporize until about 4000 K and isn't very flammable. Also consider that there will probably be several coatings to the cable. While its theoretical diameter is that small it would maybe be more like... 10 cm or so around (if I had to guess). I'd expect it to make its way to the ground.
What was burned through most of the 19th century during the Industrial Revolution? Wasn't that coal? Coal is a form of carbon, we burned to heat our homes, to smelt steel, and to run our steam engines, it doesn't seem likely we'd do this if carbon wasn't very flammable.
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You try burning diamonds, in a standard atmosphere, then.
Graphite is what you make heat shields out of...
You wouldn't expect a steel plate to survive an atomic bomb, but...
"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony
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You try burning diamonds, in a standard atmosphere, then.
Graphite is what you make heat shields out of...
You wouldn't expect a steel plate to survive an atomic bomb, but...
This.
The extreme strength of such a material will also likely come with an increase in survivable temperature.
It will certainly come with an increase in resistance to breakup under atmospheric forces.
By the way, the typical size for a meteor seen in a meteor shower is under a gram. Think maybe a millimeter in diameter, and loosely held together.
-Josh
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The rule of thumb I learned for meteors is pea size (quarter inch)-and-up makes it to the ground, if a solid rock. Basically, rocks moving at meteor speeds will ablate away 1/8 inch on radius during atmospheric entry. This ablation is independent of whether there is actually any oxidation at all. It's a heat transfer/fluid shear force/phase change thing.
It's smaller stuff that "burns up" completely, which is most of the stuff out there. Many are not solid, and break up. Big ones breaking up violently are the bolides. The term "burn up" is extremely imprecise and misleading.
It's actually rather similar for entry of things moving only at orbital speed.
As for "combustibility" (as in coal in the argument a few posts above), that definition is subjective in the extreme.
Coal burns at very slow rates (lb/hr in several-second residence times) in an already-established fire, in large chunks. Coal can be burned at much faster rates (near a lb/sec at 1 sec residence times) in power plant furnaces if it is pulverized, and if the flame is piloted-off with oil or gas.
Very fine (colloidal-scale) carbon soot can be burned at even higher rates (a few lb/sec at residence times of few millisec) in ramjet engines, if there is a gaseous-fuel pilot flame to provide ignition, and if there is not too much soot.
So, time scale and size scale play critical roles in combustion, as does the overall (global) chemical kinetic rate description, along with mixing (however that might be be measured). None of those things is specified by the word "combustible". Kinetic rates for solids burning in air or oxygen are 10's to 100's or maybe 1000's of times slower than kinetic rates for gaseous fuels, typically.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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The other thing that may happen, is the cable slows down to terminal velocity and doesn't make a crater, it is basically a ribbon falling from the sky.
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Very, very unlikely. As in, epsilon probability. Do you realise how fast this thing is moving?
"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony
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1) Space elevator
Research and Development costs: $450 billion
Construction costs: $50 billion
Operating profit: $1 billion per year
Lifetime: 25 yearsTotal costs: $500 billion
Total Profits: $25 billion
Net return on investment: -$475 billion
Annualized return on investment: -16.2%2) Much Cheaper Chemical Rocket Technology (e.g. reusability, or SSTO, or whatever)
Research and Development costs: $4.9 billion
Up-front Construction costs: $0.1 billion
Net increase in annual profit: $0.5 billion
Useful lifetime for this technology: 15 yearsTotal Costs: $5 billion
Total (incremental) Profits: $7.5 billion
Net return on investment: $2.5 billion
Annualized return on investment: +5.5%It is my claim that these numbers are representative of the costs associated with each of these two options. It's all about the money here. Realistically, because the space elevator would need to charge more money to make up the costs associated with building it, it wouldn't be able to create a reduction in the cost of sending payload to orbit.
I would like to note that your numbers are pure invention. You have sited no source and make multiple assumption such as the life span of the ribbon (I will stop calling it a cable because no one thinks that will be the design). I think you have drastically over estimated the cost of the elevator and underestimated rocket development.
The current projected development cost for the NASA SLS is around $40B.
http://en.wikipedia.org/wiki/Space_Laun … gram_costs
The space elevator has been estimated to cost a similar amount is estimated for development AND construction of the SE. The numbers are from a 2003 proposal but it allotted almost $5B to launch and boster to take the initial payload to Geo. By the end of this year the Falcon Heavy will have flown and will be able to deliver the entire in as little as one launch for the cost of $85M. This would be a reduction of $4B in the estimated costs. so even if other costs are higher it is likely to cost less than the SLS as this proposal includes an assumption of a 100% cost overrun.
http://www.mill-creek-systems.com/HighL … ter11.html
http://www.spacex.com/about/capabilities
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I think Robinson may have dramatized that a bit, since the cable will not actually be all that big. Even at just* 65 GPa, an elevator which could support 100 tonnes under Earth's gravity would have a cross-section of about 1.5e-5 m^2, or put another way it would be a string with a diameter of 5 mm. He described it as being something closer to 10 m.
Having said that, the small theoretical size does beg the question of how exactly one is supposed to affix large masses to such a small tether.
*Given the discussion we're having here, 65 GPa is indeed a low failure strength in context
Though I did enjoy the Mars series one thing to remember here is that Kim Stanley Robinson is not an engineer. He proposed a clever but unworkable design for an ES in the series. The actual design of the ribbon (not a cable) will likely be more like about a meter wide and less than a millimeter thick. The question of what would happen if the ribbon failed depends a lot on where the cable failed and what was done.
For example if the cable were to fail at or near GEO and nothing was done it would begin to fall to Earth. This would be caused by the fact that a majority of the mass of the elevator is traveling much faster than the earth is spinning and as the tension from the anchor pulls it closer to Earth it would begin to accelerate relative to the Earth's surface. It will only a few hundred miles before it reaches supersonic speeds at which point the ribbon will likely disintegrate. At that point the average velocity of the ribbon above ground will be much greater than needed to maintain an orbit and it will drag the part of the ribbon above the point of disintegration up into space. This would be a worse case scenario. As the elevator anchor is proposed to be several hundred miles out in the pacific it is very possible the major danger would be to aircraft in the direct path of the ribbon for about 1,000 miles. As this would take hours to happen a simple solution to this is to release the anchor and let the ribbon be pulled into orbit.
For the most part an SE would be designed for cargo as it would take up to a week to get to GEO on it. Climber could be designed with quick release systems and small attitude adjustment thrusters to allow cargos to move to safe orbits for retrieval later.
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Regarding your first post that I was making those numbers up I offer the following pre-sponse:
I'm arguing that it doesn't make economic sense now and it's not going to for quite a while. The reason people like the space elevator is that they see it as a way to bring down costs. But if it costs a trillion dollars (This number is an example to illustrate my point, not an estimate) to do the basic research before you can get to the point where you spend $50 billion to build it (It's not just launch costs!) then you're probably not going to get a return on your investment. The following is an example of what I mean:
Let's take the following possibilities [Again, these are examples that I'm using to illustrate my point]:
[...]
It is my claim that these numbers are representative of the costs associated with each of these two options.
I think it's excessively clear what those numbers were for, seeing as I said it four times.
I think that the development of metamaterials stronger than anything we've ever seen before is going to be expensive. I think it'll be very expensive, because it necessitates developing substantial nanotechnological capabilities and experience. I think that the amount of profit that can be gotten from a space elevator is small even if the magnitude of the annual payload is huge.
The example of SLS is a terrible one because the cutting edge of rocket development doesn't work that way anymore. SpaceX developed Falcon 9 for about $300 million. If you lump in the cost of F1, that's about $400 million. Including Falcon Heavy and reusability, call it $500 million. That's a very different number from $40 billion. Comparable cost reductions (Better reusability, upper stage reusability, longer and longer lifetimes, better operations) are not $40 billion operations, they're on the same scale or smaller.
Meanwhile the space elevator is something that's never been done before, nothing even close. $10 Billion (Inflation adjusted) was the Panama Canal, which was incredible for its scale but not necessarily for its technology. I contend that it is every bit as big a project as the Panama Canal (Perhaps bigger), and that in order to get to the point of its construction you're going to have to spend a lot of money to develop hugely new technologies.
For an example of this, Apollo, which more or less did something completely new, cost about $175 Billion (Inflation adjusted).
Regarding your second post: I don't think KSR had an accurate depiction of the fall for just that reason. But this stuff is going to be very tough stuff. It will come to the ground, and it's long enough to wrap around the Earth. The equator cuts through Indonesia, the fourth most populous country on Earth. Densely populated parts of India, Sri Lanka, and Southeast Asia are within ten degrees of the equator, as well as most of the Philippines, some of Brazil and the equatorial regions of Africa (Like the DRC and Kenya).
A material with a tensile strength of 500 GPa (or even 50 GPa) seems unlikely to be one that will break up very easily under a force like atmospheric buffeting. The strong bonds that it necessitates between atoms (Here's an approximation: Assume a Carbon density of 2,000 kg/m^3; That means about 1.6e8 mol/m^3, or about 1e32 atoms per cubic meter. If you assume each atom inhabits a little cube, you'll get 2.2e-11 m between them. Again assuming this rectangular distribution, you have about 2.2e21 bonds per square meter. 500 GPa=5e11 Pa/m2. This implies that the force between Carbon atoms is 2.3e-10 N. Assuming that the force between Carbon atoms is ultimately a result of Coloumb attraction (e.g. obeys the inverse square law) each bond will need to have an energy of about 4.8e-21 J/bond, or about 0.03 electronvolts per bond. The C-C bond, in reality, has an energy of about 3 eV. That would mean that the strengths involved are just 2 orders of magnitude (Plus or minus an order of magnitude, let's say) short of the ultimate potential of chemical bonding (which is to say, normal matter) itself. It's possible, of course. I have no doubt of that. But it won't be easy because we're currently not close.
Now here's an idea: What could we do if we had a solid material capable of withstanding temperatures of 7000 K? I don't see why it's necessarily impossible. Metamaterials like this could probably handle it. We could get serious about doming significant parts of the Sun for power generation. We could operate nuclear fission reactors at much higher temperatures. Rocket engines would get easier, all turbines more efficient, scramjets closer... You name it, it could be progress. That's something new to go for.
-Josh
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By the way, no estimate of the cost of a space elevator is reliable. Fundamentally, any cable is based on materials that don't exist. It will be built with techniques that don't exist now with tools that haven't even been thought of yet. That kind of thing is impossible to give a price on.
-Josh
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Unconventional ways to LEO: what about that light gas gun launch of gee-hardened stuff? Last time I saw anybody talk about it, they were talking under $100/lb to LEO.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Unconventional ways to LEO: what about that light gas gun launch of gee-hardened stuff? Last time I saw anybody talk about it, they were talking under $100/lb to LEO.
GW
Interesting idea, especially for basic raw materials that can be processed into something useful in orbit. The sonic boom problem could be reduced by building the gun on a floating platform and launching from the Western Pacific. Maybe a plasma gun of some sort? A hydrogen propellant charge heated using microwaves or an electric field? The whole thing could be mounted onto an old oil tanker and powered by a battery of gas turbines.
A slightly less ambitious concept could use the gas gun as a booster for an SSTO. The propulsive efficiency of the engines is extremely poor at low velocity associated with takeoff and the engines are less efficient at sea level pressure. If the gas gun could provide the vehicle with an initial boost of say 200m/s, it would certainly reduce the mass ratio needed to reach orbit.
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IIRC the biggest problem with that was the atmospheric drag, right? Plus the problem of Orbit circularization, since it probably wouldn't be possible for any kind of rocket engine to survive a launch like that.
-Josh
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I'm thinking a solid rocket to near-circularize, plus a small hydrazine thruster to "fine-tune" the circularization. Both technologies can be adapted to very high gee. I personally have worked on solids for 5000 gee+.
The launcher is a tube floating semi-submerged in the mid-Pacific. You "fuel" it with hydrogen and oxygen gases.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Regarding your first post that I was making those numbers up I offer the following pre-sponse:
I think it's excessively clear what those numbers were for, seeing as I said it four times.
I think that the development of metamaterials stronger than anything we've ever seen before is going to be expensive. I think it'll be very expensive, because it necessitates developing substantial nanotechnological capabilities and experience. I think that the amount of profit that can be gotten from a space elevator is small even if the magnitude of the annual payload is huge.
What your saying is you are coming up with the number on the fly and you have no real source.
Regarding your second post: I don't think KSR had an accurate depiction of the fall for just that reason. But this stuff is going to be very tough stuff. It will come to the ground, and it's long enough to wrap around the Earth. The equator cuts through Indonesia, the fourth most populous country on Earth. Densely populated parts of India, Sri Lanka, and Southeast Asia are within ten degrees of the equator, as well as most of the Philippines, some of Brazil and the equatorial regions of Africa (Like the DRC and Kenya).
Your opinion is that the concept dreamt up by a fiction writer with a Master in english is a better technical authority than Dr. Bradley Edwards a former NASA engineer.
For someone who claims to find the idea interesting you seem to have surprisingly little real knowledge of it. You sound more like someone who hates the idea and is inventing reason why it would not work.
One of the main reasons for the extremely limited progress in the past 40 years in space is because of an attitude that it is just not worth the effort. You mentioned the Panama Canal, one of the reasons this took so long to be realized is just that, too few thought it was worth the effort. I think Clarke was right, the SE will happen once the fools stop laughing.
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What your[sic] saying is you are coming up with the number on the fly and you have no real source.
What I'm saying is that developing the technology to the point where we'll actually be able to build a space elevator is going to be expensive, and my numbers were meant to show how that can easily sink the viability of a space elevator project. I used numbers because I thought they would convey this more clearly than words, I guess I was wrong in saying that. It doesn't matter that I made the numbers up because they're a way of explaining my claim. They are not themselves the claim. They could be off by an order of magnitude or more and my point would still be made, because the point is fundamentally valid: Space elevator technology is not present-day technology.
Your opinion is that the concept dreamt up by a fiction writer with a Master in english is a better technical authority than Dr. Bradley Edwards a former NASA engineer.
What are you talking about? I'm not treating KSR as a technological authority on anything. Again:
I think Robinson may have dramatized that a bit
If you're citing that book, as it appears you are (?) then good. But I still think it's a concern. I don't see it addressed in that book. in a quick skim. It's definitely a concern worth considering, but given that we don't know what the tether is to be made of it's almost impossible to answer.
For someone who claims to find the idea interesting you seem to have surprisingly little real knowledge of it. You sound more like someone who hates the idea and is inventing reason why it would not work.
One of the main reasons for the extremely limited progress in the past 40 years in space is because of an attitude that it is just not worth the effort. You mentioned the Panama Canal, one of the reasons this took so long to be realized is just that, too few thought it was worth the effort. I think Clarke was right, the SE will happen once the fools stop laughing.
I consider myself to be a realist. Often this is interpreted with pessimism. My focus is on details and technology and things that have been proven because I like to get into the nitty-gritty. If the details aren't there, I'm skeptical.
So: I think that tethers of all kinds for use in space are awesome. I think that arbitrarily low prices are awesome. I think that in the long run a space-elevator like system is how we're going to get there. But I don't think that the space elevator is something we're ready to do. If that makes me a fool or an ignoramus in your eyes then so be it.
-Josh
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JCO wrote:What your[sic] saying is you are coming up with the number on the fly and you have no real source.
What I'm saying is that developing the technology to the point where we'll actually be able to build a space elevator is going to be expensive, and my numbers were meant to show how that can easily sink the viability of a space elevator project. I used numbers because I thought they would convey this more clearly than words, I guess I was wrong in saying that. It doesn't matter that I made the numbers up because they're a way of explaining my claim. They are not themselves the claim. They could be off by an order of magnitude or more and my point would still be made, because the point is fundamentally valid: Space elevator technology is not present-day technology.
Your statement was presented as a cost benefit analysis. When I presented sources that suggested that your estimates were way off base and pointed out that you had provided no reference you followed up with a statement that you stood by your numbers. The only thing your number make clear is your lack of knowledge about the subject and your unwillingness to look at expert opinion.
JCO wrote:Your opinion is that the concept dreamt up by a fiction writer with a Master in english is a better technical authority than Dr. Bradley Edwards a former NASA engineer.
What are you talking about? I'm not treating KSR as a technological authority on anything. Again:
I wrote:I think Robinson may have dramatized that a bit
If you're citing that book, as it appears you are (?) then good. But I still think it's a concern. I don't see it addressed in that book. in a quick skim. It's definitely a concern worth considering, but given that we don't know what the tether is to be made of it's almost impossible to answer.
I was actually responding to a later quote of yours.
Regarding your second post: I don't think KSR had an accurate depiction of the fall for just that reason. But this stuff is going to be very tough stuff. It will come to the ground, and it's long enough to wrap around the Earth. The equator cuts through Indonesia, the fourth most populous country on Earth. Densely populated parts of India, Sri Lanka, and Southeast Asia are within ten degrees of the equator, as well as most of the Philippines, some of Brazil and the equatorial regions of Africa (Like the DRC and Kenya).
What I was citing was actually this source from a recognized expert in the field http://www.mill-creek-systems.com/HighL … tml#impact
Depending on the location of the break, the epoxy used, the dynamics of the fall, etc. the cable will re-enter the Earth's atmosphere at a velocity sufficient to heat the cable above several hundred degrees Celsius (figure 10.9.1). If the cable is designed properly, the epoxy in the cable composite will disintegrate at this temperature. This means the cable above a certain point will re-enter Earth's atmosphere in small segments or carbon nanotube / epoxy dust. About 3000 kg of 2 square millimeter crosssection cable (20 ton capacity) may fall to Earth intact and east of the anchor. Detailed simulations will be required to determine the possible sizes of segments that will survive and the health risks associated with carbon nanotube and epoxy dust. In terms of the mass of dust and debris that will be deposited, we can compare what will happen to what naturally happens now. Each year 10,000 tons of dust accrete onto Earth from space, the additional 750 tons of the first cable will increase that year's infall by 7.5%. A larger 1000-ton capacity cable would have a mass of 30,000 tons or roughly equivalent to 3 years of normal global dust accretion. Further investigations are required to determine the environmental impact of depositing this much dust along the Earth's equator.
Which includes a chart that makes it clear your concerns of even reaching Indonesia are completely groundless.
JCO wrote:For someone who claims to find the idea interesting you seem to have surprisingly little real knowledge of it. You sound more like someone who hates the idea and is inventing reason why it would not work.
One of the main reasons for the extremely limited progress in the past 40 years in space is because of an attitude that it is just not worth the effort. You mentioned the Panama Canal, one of the reasons this took so long to be realized is just that, too few thought it was worth the effort. I think Clarke was right, the SE will happen once the fools stop laughing.
I consider myself to be a realist. Often this is interpreted with pessimism. My focus is on details and technology and things that have been proven because I like to get into the nitty-gritty. If the details aren't there, I'm skeptical.
So: I think that tethers of all kinds for use in space are awesome. I think that arbitrarily low prices are awesome. I think that in the long run a space-elevator like system is how we're going to get there. But I don't think that the space elevator is something we're ready to do. If that makes me a fool or an ignoramus in your eyes then so be it.
My problem with your objections is that I have been providing specific details and you have not. You have based your opinion seems to be based on a 20 year old fiction an personal assumptions of the potential cost. You have failed to understand the difference between engineering specification for a specific use (standard building elevator cable) and scientific measurements of material properties (tensile strength).
I myself am a skeptic but I recognize the potential of ideas and their actual limitations. Some years ago I attended a talk by Dr. Edwards about the SE. At the time I expressed my doubt that it would ever be used to transport people as it would mean being cooped up for an entire week. I got the answer that they would be willing to do just that. Technology is not currently the real obstacle for the SE it is the gulf between the people who have no money who risk anything to get to space and the people with money who will use the Panama canal once someone else pays to build it.
Last edited by JCO (2015-02-07 22:20:17)
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Here's an unconventional way to LEO: Initial launch with a water gun.
The basic idea is that the speed of sound in water is much faster than the speed of sound in air, at roughly 1500 m/s (vs 340 m/s for air and 1240 for H2).
I would put this into motion by having a giant tank of water with a piston at one end (or alternatively maybe just an inflatable balloon, perhaps inflated by vaporizing dry ice using heat exchange with seawater). The top of the tank would be a converging nozzle that accelerates the water to its speed of sound. A rocket would get caught up in this flow and come out moving at 1500 m/s, which will have the effect of substantially reducing the required delta-V of the rocket.
-Josh
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Ok, see we are engaging in lateral thinking:
Could you build a 100 KM tower using inflatable spheres under pressure, placed in layers on top of each other, like a grocer's display of apples. Not being an engineer I am now quite sure how the force of the mass is distributed...I am assuming at each layer the downward force is countered by the pressurised gas in the sphere and that there isn't a cumulative mass being distributed down to lower layers (maybe some of the mass is, but not all of it?). To enhance this effect up to about 30 kms they could be lighter than air. Each sphere to be about 50 metres in diameter, so we are talking about 2000 layers. The sides would gradually taper in pyramid fashion but with steeper gradients. Start with a base of say 50 x 50 kms in a desert and work your way up. The spheres would be physically attached. The "space elevator" could be a pressurised corridor weaving its way through the spheres.
Top climbers can climb a steep mountain ascent of 1800 metres in two hours. With grip and hand holds people might be able to climb the 100 Kms in say 40 hours - maybe 64 hours with sleep.
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The forces would work more-or-less as they would if you'd stacked a bunch of very light marbles on top of each other. If you use a gas like hydrogen or helium to make the spheres lighter than air, you might be able to get the whole thing to float!
Earlier in this thread, there was discussion of an object called a "Rotovator", which I'd never heard of before. It seems like the basic idea is to have a tower with long arms that spin so fast that the tips are in orbit.
It seems like a crazy idea, so let's do some calculations!
The minimum length of the arms is determined by the required tip speed and the maximum total acceleration. Let's say 7.5 km/s and 5 gs (50 m/s^2).
a=v^2/r
r=1125 km.
This seems pretty reasonable to me, so next we need to look at the tensile requirements. As a back-of-the-envelope estimate, I'm going to assume the rotovator is not tapered at all. Another equation for centripetal acceleration is:
a=w^2*r
Where w is the angular velocity. w=v/r. In this case, w=.00667. I want to try to compute the tensile strength requirement at the centerpoint, so I need to integrate as follows:
S=int(d*a)dr from 0 to r
Where S is the required strength, d is the density, and a is the centripetal acceleration. Using the equation above:
S=int(d*w^2*r)dr from 0 to r
Because d and w^2 are constants,
S=d*w^2*r^2/2+c
Where c is a constant (0 in this case, because there is no pre-load at the tip). Assuming a density of 1,000 kg/m^3, S is in the range of 28 GPa, so still way above what we can reasonably do.
Substituting into the above equation, it actually gets even worse:
S=d*v^2/2
So that the required strength is only affected by material density and tip velocity. Looks like this one is a no-go.
-Josh
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louis,
That idea was proposed a couple of years ago - http://www.cbc.ca/news/technology/space … -1.3194738 I don't know what's happening with it.
"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony
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Well don't let arguments referring to Hindenburg put you off. The Hindenburg disaster was down to doping its surface with nitro cellulose. Basically this is gun-cotton explosive. The nitro groups in the molecule provide its own oxidiser. Hydrogen is flammable, but not that bad!
Still helium would be better apart from a slight reduction in lift and the expense.
Building a tower on top of Olympus Mons might be attractive.
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Interesting idea here from nearly 40 years ago: An Earth-launch mass driver.
http://www.nss.org/settlement/L5news/19 … driver.htm
The mass driver would accelerate 12' diameter 'telegraph pole' projectiles to Earth escape velocity from a surface launch. Atmospheric drag would have resulted in 3% mass abrasion and 20% energy loss. The mass driver itself would be vertical and some 7.8km long.
The idea never came to anything, presumably because of the high capital cost of the launcher and power supply and its inflexibility - the 1000g acceleration limits it to dumb payloads launched on escape trajectories.
Still, a high volume low cost option like this could still be useful provided the payloads could somehow be intercepted in high orbit and used as feedstock for space manufacturing. Back in 1980, the energy and amortisation cost were reckoned to be $20-40/lb - about $40-80/kg. One would need a large power plant to power such a device. A 1GW powerplant would limit launch rate to once every 90 seconds. Since the launch rate is limited by power supply, ideally one would want half a dozen PWRs powering this thing. That would bring amortisation costs down to a few dollars per kg (1980$, presumably).
Last edited by Antius (2017-12-07 06:24:58)
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