Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: briligg on 02/04/2011 19:39:34
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I was reading the recent thread about space elevators, and i wondered, as i often have since i learned about space fountains, why that idea doesn't get discussed more. The barriers to its construction seem a lot lower.
http://en.wikipedia.org/wiki/Space_fountain (http://en.wikipedia.org/wiki/Space_fountain)
And then there is the idea of launch loops.
http://en.wikipedia.org/wiki/Launch_loop (http://en.wikipedia.org/wiki/Launch_loop)
I don't care what wacky super-expensive futuristic device gets me into orbit, i just want to get there. There is so much to do!
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What do you want to do in space?
I do not know about the whole space elevator idea. I think "Think" that if it is achievable at all, you would have to construct it from outer space, not from the ground.
Best idea I can think of would be attaching a super strong cable to a capsuel http://en.wikipedia.org/wiki/Reentry_module then dropping back to earth but I think it would probably snap.
Or burn up. I suppose you could coat it in fire retardent material, and try to protect the cable from problems before re-entry.
But it would be a very long cable. Then you would have to ankcor it and have some kind of space station to remain in the same orbit consistently.
Cant see it but never say never.
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We already have a means to get to space - rockets; and they are getting cheaper.
http://en.wikipedia.org/wiki/Virgin_galactic
These space planes can get small masses orbital as well as do the tourist run up to 100km and back.
It also seems likely that a valuable contribution will come from resources already in space, rather than struggling to get resources out of the earth's gravity well.
http://en.wikipedia.org/wiki/Asteroid_mining
I have to agree with Wybit though, what do you want to do when you get there? We have a beautiful planet - I also tend to watch too much sci-fi
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@ Wiybit - This is a different concept, no cable is required. You shoot a stream of iron pellets through a tube containing a vacuum. Everything is accomplished by electromagnetic forces. The space fountain tower has a magnetic deflector at the top and bottom. At the top, the magnets used to redirect the pellets back down the tower have an upward force naturally exerted on them through their magnetic interaction with the pellets. At the bottom, the pellets are again subjected to magnetic forces to redirect them upwards again, and to accelerate them to the proper speed. By using magnetic energy harvesting devices on the sides of the tower on the upward route, and coil guns on the downward route, forces are transferred that are sufficient to support the weight of the tower. By magnetically transferring forces around, the system can be made very efficient, losing little energy, so not a huge amount of power would need to be pumped into it.
The idea has been fleshed out and the numbers have been crunched as much as they have been with space elevators. Theoretically it is absolutely doable, but unlike with a space elevator, currently available materials would be adequate to do the job.
Launch loops are a fairly similar idea, also depending on the use of electromagnetic forces.
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@JMLCarter
Doing awesome things in space requires developing it enough for a space economy to take hold. Rockets aren't enough, the payloads they can carry are too small. Not only would a space fountain be able to lift payloads into space pretty much continuously, 24/7/365, the cost of that would be a teeny weeny fraction of what it costs to lift rocket payloads, once you paid for the construction of the tower itself. Since you don't just have a launching device, you have an actual tower, you have several options to make money on it besides charging to launch payloads. You could put solar collectors on it to generate electricity, or put a hotel at the top, for instance.
About there being so much to do, i wasn't speaking personally. Manufacturing, mining, energy, all of these fields have huge futures in space.
Although, yeah, i do want to get there...
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I'm not sure the economics are the best. These pellets have to overcome gravity as they are fired p to space type altitudes, and that takes power. Power which could be used directly to get them into space instead of support a structure.
It's more likely to be efficient if we can do this kind of thing without a structure at all, see
http://en.wikipedia.org/wiki/Laser_propulsion
I also think any life in space is going to be hard. At the moment it is like being stuck for months in a submarine in free fall with regular radiation leaks (solar wind). No doubt it will become easier, though.
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@ Wiybit - This is a different concept, no cable is required. You shoot a stream of iron pellets through a tube containing a vacuum. Everything is accomplished by electromagnetic forces. The space fountain tower has a magnetic deflector at the top and bottom. At the top, the magnets used to redirect the pellets back down the tower have an upward force naturally exerted on them through their magnetic interaction with the pellets. At the bottom, the pellets are again subjected to magnetic forces to redirect them upwards again, and to accelerate them to the proper speed. By using magnetic energy harvesting devices on the sides of the tower on the upward route, and coil guns on the downward route, forces are transferred that are sufficient to support the weight of the tower. By magnetically transferring forces around, the system can be made very efficient, losing little energy, so not a huge amount of power would need to be pumped into it.
The idea has been fleshed out and the numbers have been crunched as much as they have been with space elevators. Theoretically it is absolutely doable, but unlike with a space elevator, currently available materials would be adequate to do the job.
Launch loops are a fairly similar idea, also depending on the use of electromagnetic forces.
I think my long Cable idea would be cheaper.
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I'm not sure the economics are better. These pellets have to overcome gravity as they are fired p to space type altitudes, and that takes power. Power which could be used directly to get them into space instead of support a structure.
If i understand correctly - this is all based on the Wikipedia article - in theory the system only needs energy put into it to counterbalance inefficiencies in the system. By harvesting energy and redeploying it with electromagnetic devices, basically you can collect the force of the pellets as they fall, and use it to shoot them back upwards again. The big energy input occurs when the device is started up, when all the pellets are accelerated to the proper velocity the first time. After that, it is all a question of replenishing energy lost due to inefficiencies in the equipment used.
Laser propulsion would probably be a great thing to deploy at the top of the tower, to send space vehicles on their way from there.
I also think any life in space is going to be hard. At the moment it is like being stuck for months in a submarine in free fall with regular radiation leaks (solar wind). No doubt it will become easier, though.
There would be a couple of nice things about a space fountain in this respect. For one, gravity is normal. Two, you can come and go whenever you want. Earth is just a 200km elevator ride away.
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I think my long Cable idea would be cheaper.
No space elevator concept i know of is currently possible, so estimating cost is hard - but i get the impression a space fountain would be cheaper, because no new cable material is required, and you can build from the ground up instead of launching everything you use into space first. Most of the materials used would be cheap, standard construction stuff.
I don't know how your tether scheme works, but it does sound like the cable would probably snap.
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If the top of the fountain is not close to geosynchronous orbit, your satellite will need a rocket to give it orbital speed after it detaches from the top of the fountain, so you don't gain that much by putting it there.
To hold the top up, the pellets would have to be moving extremely fast as they go around the top. The force needed to reverse their direction (f = dp/dt) would need to be greater than the weight of the tube plus the climber plus anything else at the top (the wiki illustration shows some sort of magnet). So the tube would need to be almost perfectly frictionless.
Though perhaps not being as tall as a space elevator, the tube would still have to support its own weight up to where the pellets begin accelerating around the top. The closer it is to geosynchronous orbit the closer it is to a space elevator, requiring a material of the same strength to weight ratio.
How are the pellets supposed to be turned around at the bottom? Their speed near the bottom would be nearly equal to the speed at the top plus what they gain by falling back to Earth. My wild guess is that they would be moving faster than Earth's escape velocity of 11 km/s. The exact speed would depend on the ratio of pellet mass to the mass of the tube, climber and whatever else is at the top.
The basic concept of a space fountain smells a lot like a McGyverism to me. To prove it is possible, they would have to build several small scale versions, work out formulas for scaling up each parameter, and anticipate problems that would arise as the scale reaches into space.
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I think my long Cable idea would be cheaper.
No space elevator concept i know of is currently possible, so estimating cost is hard - but i get the impression a space fountain would be cheaper, because no new cable material is required, and you can build from the ground up instead of launching everything you use into space first. Most of the materials used would be cheap, standard construction stuff.
I don't know how your tether scheme works, but it does sound like the cable would probably snap.
Building it from the ground out into space I do not think will ever work, understanding all the tensions involved.
That's why I suggested dropping a cable from space. Then designing a system to climb it, it's cheaper and simpler, have a station in orbit using a cable also reduces problems involved with staying in a geostationary orbit, the cable can be tightened and loosened as needs be.
The fountain idea is basically a building out into space, I do not think the tensions involved would allow it, not forgeting all of the months and years of construction, for something that might not even work, let alone stand.
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That's why I suggested dropping a cable from space. Then designing a system to climb it, it's cheaper and simpler, have a station in orbit using a cable also reduces problems involved with staying in a geostationary orbit, the cable can be tightened and loosened as needs be.
I think you would need to assemble the whole space elevator in geosynchronous orbit; it's way too massive for a single rocket launch. Then you could feed the cable out in both directions (up and down) simultaneously while keeping the center of gravity at geosynchronous height. (Note: I think center of gravity is not the same as center of mass in this case.) As the top and bottom get farther from geosynchronous height, gravity and centrifugal force would pull the ends increasingly harder away from the middle. There would also be some Coreolis effect tending to twist the whole thing away from vertical. You would need to resist the cable as you feed it out slowly; otherwise, it would hit the atmosphere so fast it would burn up or snap in two. It might take months to reel it out.
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That's why I suggested dropping a cable from space. Then designing a system to climb it, it's cheaper and simpler, have a station in orbit using a cable also reduces problems involved with staying in a geostationary orbit, the cable can be tightened and loosened as needs be.
I think you would need to assemble the whole space elevator in geosynchronous orbit; it's way too massive for a single rocket launch. Then you could feed the cable out in both directions (up and down) simultaneously while keeping the center of gravity at geosynchronous height. (Note: I think center of gravity is not the same as center of mass in this case.) As the top and bottom get farther from geosynchronous height, gravity and centrifugal force would pull the ends increasingly harder away from the middle. There would also be some Coreolis effect tending to twist the whole thing away from vertical. You would need to resist the cable as you feed it out slowly; otherwise, it would hit the atmosphere so fast it would burn up or snap in two. It might take months to reel it out.
Not sure it was just a suggestion, what about a reentry device that released amounts of cable as it dropped back to earth, say the device fell at 100metres a secound as it fell, every minute it released 6.3KM of cable. That should protect the cable from some of the issues of tencions and heats from reentry, the reentry device would be quite big tho. but a cable can be coiled and so use less space.
other than the anckor for the cable(which we construct on earth), the whole thing would be built on earth but then sent up and prepared in space.
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If the top of the fountain is not close to geosynchronous orbit, your satellite will need a rocket to give it orbital speed after it detaches from the top of the fountain, so you don't gain that much by putting it there.
Ah, yes - after some thought about that, i suppose the idea is to accelerate a ship up the side of the tower to get it up to a good speed, and then use rockets to adjust its path. That is the idea with launch loops. One of the places i read about this - i can't remember which - pointed out that space fountains are useful mostly for non-orbital destinations - the moon, Trojan points, stuff like that. I guess that was the reason. By combining it with space tethers it could perhaps be made more useful for earth orbits.
To hold the top up, the pellets would have to be moving extremely fast as they go around the top. The force needed to reverse their direction (f = dp/dt) would need to be greater than the weight of the tube plus the climber plus anything else at the top (the wiki illustration shows some sort of magnet). So the tube would need to be almost perfectly frictionless.
The concept employs a tube containing a vacuum. Because the path of the pellets is magnetically controlled, they never touch the sides of the tube.
Though perhaps not being as tall as a space elevator, the tube would still have to support its own weight up to where the pellets begin accelerating around the top. The closer it is to geosynchronous orbit the closer it is to a space elevator, requiring a material of the same strength to weight ratio.
The structure is supported by the upward thrust transferred to it by the electromagnetic interaction of the electromagnetic drag devices harvesting kinetic energy from the pellets on the upwards path, and coil guns accelerating the pellets on the downwards path. These devices would be spaced along the entire length of the tower, meaning only manageable sections would need to support their own weight.
How are the pellets supposed to be turned around at the bottom?
Same way as they are turned at the top - magnetically. The whole scheme is entirely based on electromagnetism. The principles of electromagnetism are what need to be examined to say what the difficulties of the project would be. My understanding is the top and bottom would be something like particle accelerators, which also move things this way.
The basic concept of a space fountain smells a lot like a McGyverism to me. To prove it is possible, they would have to build several small scale versions,
It does sound pretty outlandish, but the credentials of the people who proposed the idea are pretty impressive. The main author of the concept is Robert Forward, an aerospace engineer who held 18 patents and was a consultant for NASA and the US Air Force. Additional authors are Roderick Hyde and Lowell Wood of the Lawrence Livermore National Laboratory, who are involved in researching laser-initiated fusion. Other authors are based at Stanford and MIT.
I found one reference to Roderick Hyde having built a very small prototype, but it wasn't based on the technology the real thing would be, due to the difficulty of building such a thing at any scale without a significant budget and staff.
Building it from the ground out into space I do not think will ever work, understanding all the tensions involved.
What tensions?
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If the top of the fountain is not close to geosynchronous orbit, your satellite will need
The basic concept of a space fountain smells a lot like a McGyverism to me. To prove it is possible, they would have to build several small scale versions,
It does sound pretty outlandish, but the credentials of the people who proposed the idea are pretty impressive.
Yes they are, but it is still all theory, the theory might be sound but it's still theory.
Building it from the ground out into space I do not think will ever work, understanding all the tensions involved.
What tensions?
The higher you go the more problems will be involved, building tencions. Even my idea for a cable I'm not sure could function, even if you managed to drop it and ankcor it, wether and other things, are going to be a problem.
Do you think the Fountain could with-stand a hurracain? or tornado? or an earth quake?
A cable you could un-ankcor as needs be, but still there would be huge amounts of pull upon it from gravity.
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Do you think the Fountain could with-stand a hurracain? or tornado? or an earth quake?
I'm going to beg off a little bit here by saying i asked about this because i'd like to know more about it - everything i know right now is from summaries on three or four different websites. But that said - a space fountain is an active structure concept, meaning it is held up not so much by its structural, material strength, but by it's energy. Just as a person remains standing because of the energy exerted by their muscles, otherwise we would fall. Typically, because active structures can adapt, they are more stable than other buildings. But that is only true if the structure can adjust for changes in the forces applied to it in a timely fashion. That is mostly a software issue though, not a hardware issue. You already have all kinds of machines of one kind or another running, redistributing and redirecting the forces at work on the tower - now you just need to program them to adjust properly when informed of changes in the forces affecting the tower.
It is important to keep in mind the weight of the tower rests only in part on its foundation - only in relatively small part, i believe. The transfer of magnetic forces is levitating every section of the tower with a coil gun or a drag device (there doesn't seem to be an explanation for exactly what a drag device is, but it must involve electricity generation through magnetic braking) and there is also upward force at the loop at the top. In fact, if you increase the power being put into the system, the upwards force increases.
The main vulnerability of the tower is the chance that the power source might get cut off. For this reason it needs several independent power sources, and the job of lifting should be distributed among at least three pellet streams. But if the power were to be shut off, it would be hours before the tower began to wobble because of the momentum the pellets would have. Don't ask me to explain that, it's just what the specs say.
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Do you think the Fountain could with-stand a hurracain? or tornado? or an earth quake?
I'm going to beg off a little bit here by saying i asked about this because i'd like to know more about it - everything i know right now is from summaries on three or four different websites. But that said - a space fountain is an active structure concept, meaning it is held up not so much by its structural, material strength, but by it's energy.
Im not sure that is the case it's an air tight tubes for the lower section, and it appears they are quiet long, I appears they reach atleast into the stratosphere.
Just as a person remains standing because of the energy exerted by their muscles, otherwise we would fall.
That implies with a power failure it would fall over.
Typically, because active structures can adapt, they are more stable than other buildings. But that is only true if the structure can adjust for changes in the forces applied to it in a timely fashion. That is mostly a software issue though, not a hardware issue. You already have all kinds of machines of one kind or another running, redistributing and redirecting the forces at work on the tower - now you just need to program them to adjust properly when informed of changes in the forces affecting the tower.
It is important to keep in mind the weight of the tower rests only in part on its foundation - only in relatively small part, i believe. The transfer of magnetic forces is levitating every section of the tower with a coil gun or a drag device (there doesn't seem to be an explanation for exactly what a drag device is,
Well the drag is the air drag on the pellets, I think the air tight tubes are basically there to reduce that.
but it must involve electricity generation through magnetic braking) and there is also upward force at the loop at the top. In fact, if you increase the power being put into the system, the upwards force increases.
The main vulnerability of the tower is the chance that the power source might get cut off. For this reason it needs several independent power sources, and the job of lifting should be distributed among at least three pellet streams.
Using pellets also seems a bit unstable to me.
But if the power were to be shut off, it would be hours before the tower began to wobble because of the momentum the pellets would have. Don't ask me to explain that, it's just what the specs say.
That implies that the pellets will keep going round without power for a time but considering that it is also stated that
it is an active structure, and so requires constant power input to make up energy losses and remain erect.
That isnt clear.
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@Wiybit - the best thing for you to do to understand the details would be to read the wikipedia article. Your criticisms here don't take into consideration the information i have already offered, which is all based on what i have been able to read online. None of these ideas are mine. They are the calculations done by high-level research scientists at several of America's best institutions. In all i've read about it, nobody debates whether the basic idea of space fountains is sound. It would work. The questions are about the engineering involved in actually building one, what the difficulties would be.
What the design says about how the weight is supported is very clear, and i have already explained it several times. The whole tower is lifted by the upward thrust created by the magnetic interaction of the many electromagnetic devices all over the tower with the pellet stream. If you have doubts about details like the drag devices, read the wikipedia article. I mentioned i don't know exactly what they are because, unlike coil guns and the loop of magnets at the top and bottom of the tower, they are not the same or very similar to existing devices, as far as i know. However, they are definitely electromagnetic. The tubes contain a vacuum, there is no air drag.
Explaining why the tower wouldn't even start to fail for hours after a total loss of power is something someone with a thorough understanding of the electromagnetic principles involved would have to do. The calculations have been done, and that is what they say.
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You are enchanted with your space elevator concept, but there is no reason to discard space fountains out of hand. I don't know enough about the physics involved to comment on your idea that using a re-entry vehicle would make it easier to deploy a cable. I have read about space elevators as much as i have about space fountains (or launch loops), and the designs all involved playing out the cable slowly, starting from geosynchronous orbit, that's all i know.
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You are enchanted with your space elevator concept, but there is no reason to discard space fountains out of hand. I don't know enough about the physics involved to comment on your idea that using a re-entry vehicle would make it easier to deploy a cable. I have read about space elevators as much as i have about space fountains (or launch loops), and the designs all involved playing out the cable slowly, starting from geosynchronous orbit, that's all i know.
No I'm not so enchanted by space elevators, but the fountain is just another idea for a space elevator ultimately.
The idea I suggested for a cable, it's just that, an idea. The people that thought up the fountain certainly have a better grasp on the psyics than I do.
looking at the power issues you could use a satalite in space to provide the energy for it. AS you said yourself it would need multiple energy sourses just incase one failed. Although if you used a satalite to provide it with energy that might have implications on the design for the fountain as you would have to connect it to the fountain somehow.
Again like you, a good grasp on the psyics I do not have.
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If the top of the fountain is not close to geosynchronous orbit, your satellite will need a rocket to give it orbital speed after it detaches from the top of the fountain, so you don't gain that much by putting it there.
Yes, but the launch loop variety gives the vehicle enough lateral speed to reach escape velocity without any rockets.
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looking at the power issues you could use a satalite in space to provide the energy for it. AS you said yourself it would need multiple energy sourses just incase one failed. Although if you used a satalite to provide it with energy that might have implications on the design for the fountain as you would have to connect it to the fountain somehow.
I have toyed with that thought. Maybe if the fountain was within the Arctic Circle, and was built to 200km, which seems to be a popular figure, it would have a constant view of the sun. Maybe, with new-fangled thin film solar cells, a pretty large area of solar collectors could be attached to the tower itself, providing some power. Probably not enough to maintain the tower, but maybe enough for a short-term emergency reserve. If satellites that collect solar energy were then placed in an orbit that would pass over the tower frequently, maybe they could beam their collected energy to a collector on the tower while in range, several times a day.
An interesting thing to note here is that under 'near-term applications', the wikipedia article mentions that it could be useful for energy storage, somewhat similar to flywheels.
http://en.wikipedia.org/wiki/Space_fountain#Near-term_applications (http://en.wikipedia.org/wiki/Space_fountain#Near-term_applications)
So i guess that means that the energy in the system can fluctuate. I need to find where i read that this could be made possible by making the tower partially telescoping - if it can extend some percentage at the joints between sections, everywhere there is a coil gun / drag device setup, the tower could rise in response to increased in the power supplied to it, and sink when the power is reduced again. If those expanding sections are above the atmosphere, you don't need to be concerned about maintaining the vacuum in the tubes where the pellets travel, so that wouldn't be an issue.
Or, you could put the fountain near the equator, and put a satellite above it in geosynchronous orbit, that would beam it solar energy constantly by laser. Schemes for solar satellites for energy always beam the energy to earth, usually as microwaves, because the beam has to make it through the atmosphere and not damage anything stuck in its path. But beaming to the top of a space fountain wouldn't have to consider stuff like that. Instead, the issue would be making a collector large and sturdy enough to absorb the energy in the laser beam, instead of melting.
At any rate, these are things you could only do once the fountain is built. While erecting it, you would need to supply it with energy from a plant on the ground. That is when the big energy input is needed, during the phase when the pellet stream is initially being powered up. The power would be slowly increased over time, but a huge amount is needed.
This is maybe one reason why space fountains aren't discussed more often. Probably, you would need to build several nuclear reactors dedicated purely to powering the fountain. For safety reasons, should there ever be a total failure and the fountain crash to earth, you would also need an empty space for it to fall into. There aren't an awful lot of places where people would be comfortable with nuclear reactors nearby, much less ones connected to a space fountain. Northern Canada sounds like a good option to me. If the idea of putting it in permanent view of the sun makes sense, there are a number of big, empty islands in Canada's Arctic Ocean that would make great sites.
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If the top of the fountain is not close to geosynchronous orbit, your satellite will need a rocket to give it orbital speed after it detaches from the top of the fountain, so you don't gain that much by putting it there.
Yes, but the launch loop variety gives the vehicle enough lateral speed to reach escape velocity without any rockets.
I have read that a launch loop may be an easier project in the short term, although it would require even more space. Also, most proposals do have rockets providing the final bit of acceleration to put the ships in orbit. That way, the orbit can be adjusted to make it stable. Also, there is an issue of how the rods in the loop heat up in response to the resistance created by the ships launched, and i guess rockets reduce that somewhat.
http://en.wikipedia.org/wiki/Launch_loop (http://en.wikipedia.org/wiki/Launch_loop)
But would rocket assistance for a fountain launch need to be a lot more, to get into earth orbits? Would a launch loop or a fountain be better for destinations beyond earth?
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The technology to do this more or less exists, but the costings on this are currently running at about $20k/m.
It sounds a lot, but it's not much more than the cost of a motorway or railway to go the same distance.
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Just to expand on that a bit - from Wikipedia:
Lofstrom estimates that an initial loop costing roughly $10 billion with a one-year payback could launch 40,000 metric tons per year, and cut launch costs to $300/kg, or for $30 billion, with a larger power generation capacity, the loop would be capable of launching 6 million metric tons per year, and given a five-year payback period, the costs for accessing space with a launch loop could be as low as $3/kg.
I wonder if the $10 billion version could be upgraded to the $30 billion version by enlarging its power station.
One advantage space fountains have is that small-scale versions have possible commercial applications, allowing the technology to be developed at a lower risk to the investors. Also from Wikipedia:
A very small-scale fountain tower could be used for constructing tall antenna masts rapidly, perhaps for news events and military operations. A larger and more permanent fountain tower could be ten or twenty kilometers tall, allowing one facility to provide radio and television broadcasts to enormous areas such as the steppes of Asia. Fountain towers might also prove to be an economical alternative to communication satellites for point-to-point television and FM radio communication between the various islands of some of the smaller nations in the Pacific Ocean. An elevator and observation platform could also be added as a tourist attraction.
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Yes, I believe it can be upgraded like that.
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My question now is about the the different launch trajectories of each system. Launch loops are a horizontal launch, space fountains are a vertical launch. If a vehicle is accelerated up the height of the fountain and flung outward into space, how much energy does it take to then turn it into a stable earth orbit? Could you have rockets kick in at its apogee to give it the orbital speed it needs?
The thing is, space fountains appeal to me more because they are more efficient. The energy lost due to waste heat is huge in the case of launch loops.
btw, this thread now shows up in position 16 in google if you search for 'space fountains'. sheesh.
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Going above about 80kms makes the structure susceptible to meteorites and space junk. You need a long structure anyway, because otherwise the accelerations need to become too high to be survivable; you end up with a spam launcher (people get spammed).
Note also that launch loops are not inherently more inefficient than space fountains; in fact it's pretty much the other way around, the higher the vertical aspect of the structure, the more the structure weighs; these types of structures hang down from the top, and the tensile members have to be tapered; as the height increases you need more and more taper, and for any given capacity, the weight of the tension members increases.
That means that you get more waste heat from the small fraction of stabilisation power to handle the magnetic instabilities associated with Earnshaw's theorem to carry these extra loads.
And in any case you need lots of sideways speed to reach stable orbit.
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Note also that launch loops are not inherently more inefficient than space fountains; in fact it's pretty much the other way around, the higher the vertical aspect of the structure, the more the structure weighs; these types of structures hang down from the top, and the tensile members have to be tapered; as the height increases you need more and more taper, and for any given capacity, the weight of the tension members increases.
That means that you get more waste heat from the small fraction of stabilisation power to handle the magnetic instabilities associated with Earnshaw's theorem to carry these extra loads.
Huh, that's new information, and quite over my head, i'm afraid. I waded through the Wikipedia article on Earnshaw's theorem, but i don't have the math. One question though - are you considering that all the weight is supported at the top? Because a large portion is supported by the coil guns and drag devices on the sides.
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Btw - here is a great site on launch loops, way better than anything i've found for space fountains.
http://launchloop.com/LaunchLoop
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And now, Saudi Arabia is about to spend the $30 billion necessary for the really good launch loop - on one really huge skyscraper a mile high.
http://gizmodo.com/#!5790505/saudi-arabia-to-be-permanent-member-of-mile+high-club (http://gizmodo.com/#!5790505/saudi-arabia-to-be-permanent-member-of-mile+high-club)
sigh...
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These types of dynamic structures are not very good at heavy lifting, but they could look down on those more traditional structures from above easily enough.