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Offline thebrain13

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« Reply #50 on: 19/12/2007 16:43:41 »
you wouldnt have to travel up it at 100km/hr the whole time. You can dock at a different speed than you travel up. The pulleys at the bottom loading area would move very slow compared to the pulleys at the top of the elevator. I dont see any reason why you couldnt get it to move 1000km/hr.

I'd also like to see what the military could do about stopping space debris.
 

Offline ukmicky

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« Reply #51 on: 19/12/2007 19:22:05 »
How big would the coils of wire need to be to generate power in space and transfer it to the earth using cordless electromagnetic induction systems .  The same type of system used to charge tooth brushes and very soon mobile phones ,powertools etc.
« Last Edit: 19/12/2007 19:24:22 by ukmicky »
 

lyner

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« Reply #52 on: 19/12/2007 19:38:56 »
Quote
How big would the coils of wire need to be to generate power in space. . . . . .
You can't use the same method for power transfer at such a distance. The toothbrush charging system is, essentially, a transformer. The system used for charging toothbrushes is a particularly inefficient form of transformer because you need a complete path of iron core to contain all the magnetic flux for good efficiency.  (Useful - but inefficient).

I still reckon that linear motors would be a much better propulsion system - virtually no limit on top speed!
 

Offline ukmicky

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« Reply #53 on: 19/12/2007 20:25:24 »
The tooth brush system maybe but they will soon be bringing out a new and much more efficient system with one central unit attached to the fusebox of your house and car with a range that allows you to charge all rechargeable apparatus in your home. You will no longer need to plug things in. As soon as you enter your house they will start charging provided they have a small electronic component installed. I heard about the new system on the beeb the  other day ,I dont know exactly how it all works but they gave a demo using a working system.
« Last Edit: 19/12/2007 20:33:19 by ukmicky »
 

Offline Pumblechook

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« Reply #54 on: 19/12/2007 21:09:04 »
It is rubbush that.  As another poster has pointed out...any such system will be inefficient and in an age where we are supposed to conserving energy it makes no sense.   
 

lyner

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« Reply #55 on: 19/12/2007 21:29:43 »
Yes that has to be either rubbish or you heard wrong. If you don't have a good magnetic circuit, you lose most of your energy. You either need a good magnetic contact or a good electrical contact for any significant amount of power transfer. End of.
 

Offline Pumblechook

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« Reply #56 on: 19/12/2007 21:59:59 »
There is a company who make a charging pad where the item (modified or made compatible in the first place) to be charged is just plonked on it but I have been unable to get an efficiency figure which I would think is not very good.

I would have though that a 'docking station' where spring loaded contacts are used is just as convenient and does not require a pick up coil in the item and will be lossless.

« Last Edit: 19/12/2007 22:03:32 by Pumblechook »
 

lyner

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« Reply #57 on: 19/12/2007 22:19:08 »
It's probably easier to get a good electrical contact - involving very little pressure - than it is to get a good low reluctance contact in a magnetic circuit. It may be less of a problem if you use a high frequency for your induction loop system but it sounds a bit of a gimmick rather than anything worth having..
« Last Edit: 19/12/2007 22:27:13 by sophiecentaur »
 

Offline ukmicky

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« Reply #58 on: 19/12/2007 22:27:00 »
yeah your right the misus said it was a station that you had to place the item on and have an adapter fitted to the device.
She even rememebered its name. Splashpower
« Last Edit: 19/12/2007 22:29:48 by ukmicky »
 

Offline Pumblechook

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« Reply #59 on: 19/12/2007 22:30:49 »
They dress it up as if it was new technology that they have invented..  Really dates back to Faraday's age.


http://www.splashpower.com/




« Last Edit: 19/12/2007 22:38:21 by Pumblechook »
 

Offline Pumblechook

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« Reply #60 on: 19/12/2007 22:43:02 »
"Up to a centimeter away from the SplashPad the energy transfer drops very slowly." The inductive coupling operates at a frequency of, "a few kilohertz," Halfpenny said.

This is crazy..  The conversion AC-DC-RF...coupling...RF-DC will lose power along the chain.  The overall efficiency will be poor.


Better to go AC - DC in one simple efficient step.
 

another_someone

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« Reply #61 on: 20/12/2007 05:13:06 »
Centrifugal / centripetal; back to O level again.
We were hit (literally) if we used the word 'centrifugal' when at School. Yes, of course, when a string is whirling round with a conker on the end, there is tension and a force inwards and outwards. BUT the 'centrifugal' force is only there because the centripetal force is constraining the conker to move in a circle and providing a radial acceleration.  When you are in orbit, there is only one force acting on you. That force is gravity and it is inwards - keeping you accelerating in a circle.  - it is a centripetal force. If you switch off gravity or cut the conker string, there is no motion outwards; in both cases, the motion is tangential (Newton I).


For a stationary object (i.e. one that feels no force), the forces acting upon it must be balanced.  For a satellite in orbit, it feels no force, and therefore the forces acting upon it must be balanced.

You could take the relativistic approach, and suggest there is no force acting upon the satellite at all, because gravity is not a force but a distortion of space, and so the satellite is merely in freefall.  Alternatively, you could say there is a balance between centrifugal and centripetal forces.  It makes no sense to me to say that gravity is the only force acting upon it, since those within the satellite cannot detect an imbalance in forces.

As for cutting the conker string, ofcourse there is a motion outwards.  Ofcourse it is also true that the conker keeps going in a straight line.  You are looking at the same thing from at once a polar coordinate system and a rectilinear coordinate system - and each statement is true with reference to their own coordinate system.

From the point of view of someone who is above the Earth, and does not want to get further away from the Earth, then the polar coordinate system may be a more natural way for him to look at his predicament than a rectilinear coordinate system.

If you cut the tether just below the space station, it will fall towards the Earth because of the weight of the (mainly lower) parts.

I doubt it will be that simple.

It is true that the tether will start to fall to Earth, but as its fall accelerates, it will start to burn up in the atmosphere (when that happens will depend on many factors, and it will certainly not happen in the initial stages of the fall), and when the lower portions of it have burnt off, depending on how much tether is left, it may continue to fall (and burn up as it hits the atmosphere), or may fly off into space (most likely its momentum by then would be sufficient to continue sending the remainder of the tether Earthwards).

It is very unlikely to fall straight down, if for no other reason than the stiffness of the tether will make this unlikely, as would any winds it encounters.  Once it starts to topple in one direction or the other, it will probably continue further in that direction - but I agree that it wont as such wrap itself around the Earth.

Long or short cables: Having a cable loop, as in a conventional lift, is very attractive. It balances out the vehicle weights. You would only need to pay for the payload lift. One long cable would certainly be very hard to control; I could imagine all  sorts of problems with longitudinal standing waves being set up which would produce extra stresses.

I am sure there must be ways of applying damping to the cable loop to make that less likely.

A series of short loops sounds much better; transferring between loops would not be a major problem but you migh need to synchronise transfers from one cable to another so that each loop was balanced.

That would add considerable weight to the whole mechanism, add vibration at the transfer points, and each of the transfer points will inevitably involve energy loss.  The increased complexity will also lead to far higher risk of failure.

There is an alternative to cables and that would be to use electric motors with regenerative braking; all the descending cars would be generating power towards the lifting motors.

That was my original notion of what this was about, before the idea of the cable loop was explained; but that now means you need massive conductors to take the current (even for fairly low currents, because of the length of the system, you need to keep resistance to an absolute minimum - you may even want to look at superconductors).

You also have to think about how the electrical energy is converted to mechanical energy.  You could have a linear induction motor built with coils build into the tether, but that now adds more weight to the tether.  Alternatively, you transfer the power to the cars, and have motor drives in the cars, but now you need a way to transfer that energy across (a 36,000Km live rail system?).

This would make it much easier to stabilise the loading of the tether because you could control the speed / acceleration of each car, actively damping out longitudinal waves.

Could you not damp longitudinal waves simply by building discontinuities in the materials used to construct the tether, and let those longitudinal waves be dissipated as heat at the discontinuities (it would require that the tether then be efficient at carrying away that heat, since there will be no atmosphere for most of the distance into which you can dump the heat generated).  Ofcourse, those same discontinuities will also represent potential weakpoints in the structure, and these have to be accounted for in the load distribution management of the design.

Safety:  A major factor, of course. If you are thinking in terms of collision with debris then you could deal with a 'direct hit' on the cable by a large object by having a number of cables, spread out. They could be linked, at intervals, by horizontal ties. If one cable is severed then the others could take up the tension and the structure would survive. A major repair job, not a rebuild, and much less risk of any loss of life.

How large an object are we talking about?

If we are to protect ourselves against an object that is 100m wide, we need a cable separation that is significantly wider that 100m, we need to make sure that there are sufficient numbers of cable to be able to survive the loss of one cable (i.e. 2 cables will not be sufficient, since the loss of one cable would represent an instantaneous increase of 100% load on the other cable, plus the shock).  Also, one has to look not only at the loss of one cable, but the loss of all cables in any given line that an object may travel along through the cables.

Since the idea is that the load of the cars is spread across all of the cables, if one takes the simplest example (I am not sure if the simplest example is sufficient in terms of load sharing) of 9 cables distributed as if in a 3 x 3 matrix, but with the middle cable removed, and each cable being 110m from its neighbour (thus allowing a 100m object to hit 3 cables in a row, and the remaining 6 cable distributing the weight between them), that would require the car to be at least 220m x 220m in size.  If you are looking to survive a hit by a largest object, or a hit by multiple objects in a cluster, then the size has to increase accordingly.  It is possible that you could improve survivability a bit better by not distributing the cables in a regular grid, and so reduce the number of cables in a direct line with each other.  On the other hand, you may also want to think about ricochets.


The space station crew would be quite safe, even if a single tether were used. They would remain in orbit but would need a bit of rocket power to adjust their position.

It depends on where they are.

If you are talking about a 36,000Km orbit, then I agree, the risks are slight.  If you are talking about a 100,000Km orbit, then in fact they are on a hyperbolic trajectory, and if the tether is cut, they will quickly go out of orbit unless massive amounts of rocket power (needed to shift a massive object) were used to decelerate them and/or reduce their orbital height by a massive amount.

Also, the loss of a shuttle, as tragic as it is, cost the lives of 7 people, and the loss of a single vehicle.  A major failure of a large integrated system of this nature could lose a lot more than that (it is as much about distributing risk as eliminating it).

The elevator would be less hazardous than the present shuttle system - that's brown trousers every time it lands!

The present system is totally inadequate, but then it is also something that is only launched a few times a years, with massive checks and rechecks (which, as has been seen, if not done, will lead to disasters) every time it goes up.  On the other hand, the system we are proposing will have to run continuously, without the ability to spend several months with the system grounded for checks; so the level of innate reliability must be orders of magnitude better because our ability to cope with problems during operation is less.

If a car became detached or the cable was broken there could be a serious problem when near the Earth but, for the majority of the journey, it would end up in some an of obit (elliptical) and would have a chance of being rescued.

Depends where?

Again, if we limit ourselves to a geostationary orbit, then all orbits below that are indeed elliptical, but if we extend ourselves above that (and given the angular speed we will be travelling at in order to remain geostationary) then we will be on a hyperbolic trajectory, and will not be going into any kind of orbit.

As you say, close to Earth (not only within the atmosphere), even if you end up in an elliptical orbit, if that orbit impinges upon the upper atmosphere then you will rapidly lose angular velocity and will fall to Earth (actually, more likely, burn up in the upper atmosphere).

The falling bit of tether would present a bit of a hazard, I admit, but it would 'fall' to Earth in a region near its base - Newton I rules, again. It would not wrap itself around the Earth.

Why?

Why is the tether any different to a car - all matter, no matter what its mass, at a given altitude and given velocity, in the absence of atmosphere, will follow the same path.

It is true that the tether may cover a range of altitudes, rather than a (almost) single level of altitude that the car would occupy, so that would mean that different parts of the tether would be pulled into different orbits, causing to to rotate - but each section of the tether will be effected by exactly the same forces as any of the cars would be.

Also, what happens if the tether snaps with the cars attached?   In this case you cannot say that what happens to the cars is different from what happens to the tether, because they are still locked together.
« Last Edit: 20/12/2007 05:40:05 by another_someone »
 

lyner

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« Reply #62 on: 20/12/2007 12:06:10 »
1. When you cut the string there is no FORCE outwards. If there were a force, the conker would accelerate away. It doesn't; it moves away, of course, but at its original tangential speed. There is no point introducing Einsteinian ideas to a simple bit of classical Newtonian mechanics. Einstein, himself wouldn't have because he understood both the old and the new. What 'outwards' force is there when in orbit? Nobody detects one when on a satellite - everything 'floats' or falls towards the Earth.  The satellite (and contents) is ACCELERATING towards Earth, constantly. If it were 'stationary' it would fall (accelerate) right towards the centre of Earth. It is not in equilibrium; forces are not balanced so Newton 1 doesn't apply. This scenario is precisely the one which Newton was thinking about when he came up with his laws of motion and gravitation. Oh yes, and the 'reaction force', which has to be there (Newton 3) is pulling the Earth towards the Satellite and the acceleration is g (Newton 2). Get your basics right or your conclusions can be wrong.

2. A series of short loops would allow different speeds - fastest when the car is outside the atmosphere and slowing down as it gets to its destination. Clutches / springs would allow for the speed changes. The result of a breakage or a fault would be much worse  for one long cable rather than many short ones.

3. You mention resistive losses for an electricity supply. What sort of friction forces do you think would operate on a 7000km cable loop with the necessary guides and pulleys? Electrical power distribution tends to be less lossy than mechanical forms and it doesn't wear out. The motors for the cars would not need a lot of power - a few kW would produce a small,  constant, acceleration which would soon have a car traveling at  very high speed. You wouldn't need railway traction powers for this job. At a few 100kV, the current could be less than a  hundred A - a trivial resistance problem for aluminium cabling.  How many surface transports use cable rather than electric traction? (Situation is different, I admit,)

4. The probability of meeting a 100m object is small and the collision cross section of the tether is vastly less than that of the Earth - which would pose a  major problem! Why do you need 200m wide cars? Small cars would go up each line. And about multiple cables being hit. Objects of 10m (still much bigger than we see very often)  would be very unlikely to hit more than two lines if they are arranged in a large enough  circle.  It would be mostly space between the cables (think spider's web). As we don't know the actual statistical size and speed distribution of debris, we can't come to any real conclusions but 'large' objects do not land on Earth often. Some data might be useful.

5. As you say, the shuttle system is very unsafe. You want the tether system to be totally safe. It is an unfair comparison. The equivalent scenario to the whole tether being destroyed might be the same as that of a major crash of a fuel transporter rocket falling on a major city.  Both are unthinkable but impossible to rule out completely. Enough redundancy, built into the tether structure, could reduce the probability of  major catastrophic failure to near zero - just as with rocket system design. The tether would obviously be sited in mid Pacific /  Atlantic so damage to the population would be low - a fuel tanker could, in principle, come down anywhere. I think the risks would need serious analysis rather than gut reaction.

6. For a broken tether, the space station would, by design, be very near the geostationary position, assuming it is more massive than the tether, (the whole basis of the system design)  so there can be no doubt that it would remain near there, with or without the tether. In any case,  control ballast which was further out or inside could be jettisoned in case of a disaster and things would happen very slowly to the flying portion of the structure; plenty of time to take action. The cars on that section would be relatively safe, also.
The lower part of the tether is very different from a car, once detached, in that it would be pulled down by the weight of the bottom portion - very quickly; at something like 10m/s^2 . The car, once detached, would be in an elliptical orbit, as stated before, and this orbit would only involve hitting the  Earth for cars nearer the Earth.  For most of the journey, the cars would be further away than this and their orbits would make them recoverable if they were detached. Most cars would be unmanned so they could would not matter.
Launching from an 'extended' section of tether, beyond the geosynchronous distance, doe not automatically put you into an escape condition. You would just be in a bigger ellipse, unless the tether was very much extended. That would not be part of my idea . Detached cars near the Earth would not have the same trouble as spacecraft re-entering; they would start off with no effective KE and their  PE would gradually transfer to KE. This could be dissipated with a system of parachutes rather than needing the dreaded heat resistant tiles.
The falling tether would, of course have a lot of GPE  (the top bits, at least) and this would end up as 'disaster energy' once it hit the ground. It wouldn't be hard to relate this to asteroid impact, actually; perhaps someone would like to do this for us? A nice after-Christmas Dinner activity. But,certainly, the smaller the tether, the less of a disaster.

George, this makes a change from usual. I am nearly always the one pouring cold water on your ideas. This time it's the other way round.
I'm up for buying a few shares in this one, perhaps.
 

another_someone

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« Reply #63 on: 21/12/2007 11:40:38 »
2. A series of short loops would allow different speeds - fastest when the car is outside the atmosphere and slowing down as it gets to its destination. Clutches / springs would allow for the speed changes. The result of a breakage or a fault would be much worse  for one long cable rather than many short ones.

3. You mention resistive losses for an electricity supply. What sort of friction forces do you think would operate on a 7000km cable loop with the necessary guides and pulleys? Electrical power distribution tends to be less lossy than mechanical forms and it doesn't wear out. The motors for the cars would not need a lot of power - a few kW would produce a small,  constant, acceleration which would soon have a car traveling at  very high speed. You wouldn't need railway traction powers for this job. At a few 100kV, the current could be less than a  hundred A - a trivial resistance problem for aluminium cabling.  How many surface transports use cable rather than electric traction? (Situation is different, I admit,)

Do you need guides and pulleys?

You need guides and pulleys on Earth because of all the environmental forces (e.g. winds) that would effect the car, but they do not exist in space, so if the cable is just pulling the car upwards, what is going to deflect its path?  Why the guides?

You need pulleys at the end points, and maybe need pulleys or guides in the first 100Km, within the atmosphere but do you really need them beyond that?

Bear in mind that if you do need guides and pulleys along the way, these are going to wear out, and you will have an impossible maintenance job constantly replacing them (assume a life expectancy of 10 years constant use, and 1 guide per 100m, so you will need 360,000 guides, and an average of 36,000 guides replaced per year, which is 100 guides per day replaced and this for each cable).

I am not saying that 100A is a lot, but pass 100A down 36,000Km of aluminium (you could power it from both ends, and so bring it down to 18,000Km), it had better be very thick aluminium if you are not going to lose a fair amount of voltage on that trip.  Then you also have to worry about what you do with the heat associated with that resistance you have no atmosphere to dissipate that heat, so you have to conduct the heat away, the full 18,000Km distance.

On the other hand, if you do use superconductors, the lack of atmosphere to carry heat becomes an asset rather than a problem.  Nonetheless, it will be a lot more weight than the light weight nanotube structures people were talking about.

4. The probability of meeting a 100m object is small and the collision cross section of the tether is vastly less than that of the Earth - which would pose a  major problem! Why do you need 200m wide cars? Small cars would go up each line. And about multiple cables being hit. Objects of 10m (still much bigger than we see very often)  would be very unlikely to hit more than two lines if they are arranged in a large enough  circle.  It would be mostly space between the cables (think spider's web). As we don't know the actual statistical size and speed distribution of debris, we can't come to any real conclusions but 'large' objects do not land on Earth often. Some data might be useful.

The largest meteor to land in recent years (1920) was about 3m across when it hit Earth, but a lot of that ablated before reaching the ground but I agree, probably I have about a factor of 10 overestimate 10m objects might be sufficient.

Yes, arranging them is a circle is fine, but a circle is a hypothetical shape, and in reality you would be arranging them in a polygon.  But, if you are going to have 9 cables, are they really going to be more compact arranged in a 9 sided polygon than arranged as a 3x3 matrix (slightly offset to minimise alignment)?

The reason why one would wish to have a single car linked across all the cables, rather than one car per cable, is because if you did have a single cable strike, if you had one car per cable, you would be guaranteeing setting that car adrift, whereas spanning the cars across the cables would allow the car to survive the cable strike.

5. As you say, the shuttle system is very unsafe. You want the tether system to be totally safe. It is an unfair comparison. The equivalent scenario to the whole tether being destroyed might be the same as that of a major crash of a fuel transporter rocket falling on a major city.  Both are unthinkable but impossible to rule out completely. Enough redundancy, built into the tether structure, could reduce the probability of  major catastrophic failure to near zero - just as with rocket system design. The tether would obviously be sited in mid Pacific /  Atlantic so damage to the population would be low - a fuel tanker could, in principle, come down anywhere. I think the risks would need serious analysis rather than gut reaction.

Given the takeoff path of the shuttle, over the sea, the tank cannot fall onto land (which is exactly what happened when the challenger suffered a catastrophic failure on launch).

But my concern about the tether system, where is seriously differs from the shuttle, is the duty cycle.  The shuttle spends most of its life in maintenance, and very little of its life actually in service (this is expensive, but increases safety significantly and despite this, disasters happen).  The system we are talking about, once constructed, will not be taken down, and will be almost 100% duty cycle, and what little maintenance it will have will be in situ rather than in a workshop.

6. For a broken tether, the space station would, by design, be very near the geostationary position, assuming it is more massive than the tether, (the whole basis of the system design)  so there can be no doubt that it would remain near there, with or without the tether. In any case,  control ballast which was further out or inside could be jettisoned in case of a disaster and things would happen very slowly to the flying portion of the structure; plenty of time to take action.

The problem was trying to address two different concepts thebran13's concept of a terminal satellite at 100,000Km, and the more conventional concept of a terminal satellite at around 36,000Km.

With a terminal satellite just inside geostationary orbit, and a dummy mass about 100Km above it, so the the initial break would allow the terminal satellite to be pulled up to geostationary orbit by the dummy mass, before releasing the dummy mass and parking in geostationary orbit.

The cars on that section would be relatively safe, also.
The lower part of the tether is very different from a car, once detached, in that it would be pulled down by the weight of the bottom portion - very quickly; at something like 10m/s^2 . The car, once detached, would be in an elliptical orbit, as stated before, and this orbit would only involve hitting the  Earth for cars nearer the Earth.  For most of the journey, the cars would be further away than this and their orbits would make them recoverable if they were detached. Most cars would be unmanned so they could would not matter.

I think you are missing a key point.

While you are right to be concerned about the differential gravitational effects, but remember that the different portions of the system are travelling at very different velocities (same angular velocity, but very different linear velocities).  Thus, the lower portions of the system (this could be true even of portions a mere 1,000Km below the terminal satellite) will have a backward drag on the upper portions, both pulling it down, and reducing its angular velocity, and also causing a rotation of the system.


Launching from an 'extended' section of tether, beyond the geosynchronous distance, doe not automatically put you into an escape condition. You would just be in a bigger ellipse, unless the tether was very much extended.

Not my understanding.

It is not where you are that matters, it is where you are and what your angular velocity is.

Yes, being outside geostationary orbit, if your angular velocity was less than geostationary, could then put you in either a circular or elliptical orbit.  The trouble is that you are beyond geostationary orbit, but still carry the angular momentum for the geostationary orbit, so you are carrying too much angular momentum to retain either a circular or elliptical orbit, so you will be taking a hyperbolic trajectory.


That would not be part of my idea . Detached cars near the Earth would not have the same trouble as spacecraft re-entering; they would start off with no effective KE and their  PE would gradually transfer to KE. This could be dissipated with a system of parachutes rather than needing the dreaded heat resistant tiles.

Sorry, I don't understand this.

Ofcourse they have KE.  You may be saying they have no KE in the vertical direction, but they certainly have KE in the horizontal direction, and this has to be accounted for in your calculations.

I assumed you had taken account of that KE when you spoke of them going into an elliptical orbit (because their KE is too small to take them into a circular orbit).


The falling tether would, of course have a lot of GPE  (the top bits, at least) and this would end up as 'disaster energy' once it hit the ground. It wouldn't be hard to relate this to asteroid impact, actually; perhaps someone would like to do this for us?

But the tether would still have angular momentum, just as the cars would.

George, this makes a change from usual. I am nearly always the one pouring cold water on your ideas. This time it's the other way round.

Is that not the whole point and idea is only worth while after you throw every problem you can think of at it, and it still survives.

I'm up for buying a few shares in this one, perhaps.

Not unless you really want to lose the money.

Even if the idea works, there are very few major infrastructure projects, even if they have proved a long term success, that have actually made money for the original speculators (just look at the channel tunnel it would be a great success, if only it did not have to repay the the cost of construction).
 

lyner

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« Reply #64 on: 22/12/2007 00:54:35 »
A number of issues - thank you.

Quotes take up too much room - I assume you are across this so you will remember what has been said.

1. I really wouldn't fancy a 70,000km loop of wire, flailing around with nothing to guide it. AS I, actually don't fancy the idea of doing it mechanically, in any case, then I don't want to go into too much detail regarding lots of small loops. I can see many advantages - not least , when some replacement sections are needed.
2. Electrical Power vs Mechanical: As soon as you get above the atmosphere, there is plenty of sunlight to provide electrical power at stations all the way up, so you may not even need long supply cables. The effective night is not that long, at distances of 10km+ and you could suspend operations, if necessary- maintenance time, perhaps. Once above 100km, or so, the cars could even be solar self-powered - present satellite  panels provide several kW  and that could be sufficient, as I have already said - low acceleration would be no embarrassment.
3. I don't understand the idea behind the very long tether system of thebrain - it wouldn't be in a naturally geostationary orbit so what would it do? I suspect it would just trail behind the geostationary main station - or even be attracted to it. It's not part of my system and needs some clarification.
4. I obviously meant that the cables would be arranged around a circle - what else could I have meant? Such an arrangement would have all the  advantages of a spider's web (redundancy). Have one car in the middle, if  you like but that would pull the lines together if there were much  driving force. Un-tensioned cross links would provide the same safety function and cars could pass each other safely as they would be separated by tens of metres on separate cables.
5. You are right about the tanker crash scenario as long as launch methods are kept the same. Will it always be the case that orbital height is reached within a few hundred km?
6. In the event of  the tether being actually severed, the 'drag, to which you refer, would have been there all the time. There would now be less and the outer portion would go outwards rather than inwards.
7.
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The trouble is that you are beyond geostationary orbit, but still carry the angular momentum for the geostationary orbit, so you are carrying too much angular momentum to retain either a circular or elliptical orbit, so you will be taking a hyperbolic trajectory.
No; forgetting the tether, if you are going a bit faster (which is all that would happen)  your orbit would take you a bit farther out by the time you were 90o further around on the orbit - an ellipse.  It's not angular momentum but KE that counts for orbits; KE + PE is a constant. Adding KE (i.e. going a bit faster) at the low point gives extra PE (height) at the high point. You need a lot of KE to make your escape.
8. When you are low down on the tether - near LEO position- your KE is much less than the KE of an normally orbiting object - that's what I mean by negligible effective KE. Instead of an orbit time of 90minutes it is 24 hours - that implies a tiny fraction of the normal KE (about 1/120 ) This is very relevant to the amount of energy which the vehicle would have to shed.
9. I am still tempted with it as an investment!
« Last Edit: 22/12/2007 00:56:42 by sophiecentaur »
 

Offline thebrain13

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Space Station Economical Resupplies
« Reply #65 on: 22/12/2007 06:47:48 »
the point of the longer tether, is it would allow you to ramp up the upwards force for an object that was moving up it, if it was shorter it would spend too much time where gravity is the stronger force. if you designed a pulley system, the higher the tether the more energy you could liberate, that would allow you to pull objects up faster, and harder, and give it a jump start to wherever you wanted to go.

just because the tether is outside of geostationary orbit, doesnt mean that it wouldnt rotate around the earth, it would still stick straight up. The geostationary satelite is not the guiding force. what determines if it stands or not is the overall force upwards verses downwards. (as long as friction is somewhat negligilbe)

Also the large mass or counterweight would be located at 36000 km up, not at the end of the longer cable. That would generate too much strain on the cable. However when you initialy built the structure the counterweight has to be outside of geostationary orbit, since most of the mass of the tether is located where gravity is the prominent force. In that scenario (a shorter tether) the purpose of the counterweight is to hold the cable up.
 

lyner

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« Reply #66 on: 22/12/2007 10:35:26 »
Quote
just because the tether is outside of geostationary orbit, doesnt mean that it wouldnt rotate around the earth, it would still stick straight up. The geostationary satelite is not the guiding force. what determines if it stands or not is the overall force upwards verses downwards. (as long as friction is somewhat negligilbe)
You will, of course, have some calculations to back this up. It certainly isn't what conventional ideas  of the energy and forces involved in orbits under and inverse square law would predict.  Are you proposing a rigid tether, 70,000km long? If not, how can you prove that your system will work with a flexible line? Unless the velocity of the 'remote' end is high enough for circular motion (which it isn't), the mass will follow an elliptical orbit.

What does 'ramp up the upwards force' mean?  Please use terms that actually mean something  in the classical mechanics / dynamics sense.
I sense that you are drawing a parallel with throwing a stone out of the end of a pipe - or, possibly, the Aboriginal 'Woomera' principle. This is no good without a rigid system.
 
« Last Edit: 24/12/2007 10:31:42 by sophiecentaur »
 

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« Reply #66 on: 22/12/2007 10:35:26 »

 

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