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How big would the coils of wire need to be to generate power in space. . . . . .
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).
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.
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.
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.
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.
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.
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.
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.
The elevator would be less hazardous than the present shuttle system - that's brown trousers every time it lands!
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.
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.
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?
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.
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.
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)