Access to High-Earth Orbit Is About to Get Much Cheapter

I agree that the concept is too premature to consider it a viable mechanism today. The current space craft programs are not in much danger of being obsolete. However, 37 mph is pretty slow and their is nothing about that number that suggests it is a speed limit which can't be violated (i.e., start out slow, but continue to accelerate as you climb).

Still, even 25 days to geostationary orbit is fine for just about any payload that doesn't have humans (or on-demand military projects).

Additionally, why would you need to ride all the way up? Seems to me that you could get off early and let the vehicle fall (trading altitude for velocity) and use that velocity to reach a stable lower orbit. I am not sure about the orbital mechanics on that one.

I don't know, I've always been very adamantly against this idea. For instance most plans call for the tether to be attached to a geostationary asteroid, but a tether requires an awful lot of precision (even if you have a slack mechanism that could dynamically tighten or loosen it). High winds, radiation, highly reactive molecules in the ionosphere. It just strikes me as extremely unrealistic.

Not to mention I'm not entirely clear on why a space elevator is so much more economical than a spacecraft.

It's just hard for me to accept that the cable wouldn't degrade in the ionosphere. Also, I don't see how the tether wouldn't snap if the distance between Earth and this Geosync terminus varied. The distance would be subject to gravitational perturbations (from the moon at least) not to mention all kinds natural phenomena such as lighting strikes and wind.

You're telling me a 100 mph gust of wind wouldn't snap the cable like a twig? I'm just not buying it. The space elevator just doesn't seem realistic to me.

Also, I'm not reading an entire book on the subject, but if you have a link that has a few pages that you think does a good job of explaning why I'm wrong, I'll definitely read that. I may not believe the space elevator concept is realistic, but I certainly do believe that there are times when I am wrong and I don't know in advance when they are .

Roger, the wikipedia article does a decent job on the subject. As is usual in these sorts of things the devil is in the details, but a lot of very smart people are looking at this and there do not appear to be any major show stoppers at this point. The big one was the cable, which appears to be solvable now.

A 100 MPH hurricane would not do anything because the crossectional area of the cable is so amazingly small that the wind resistance is for all practical purposes nil.

If my calculations are correct, the stuff is at a minimum 50 times stronger than EIPS wire rope (it may concievably be as high as 150 times stronger depending on the quality of the fiber being produced.) for a given crossectional area and 5-1/2 times lighter.

Ok, I've read the article (I skipped some the the early history part from the 1890s and 1960s (actually I skimmed it)). Here is where I'm at. I don't strongly disagree that the concept could work. I don't even disagree. Lets say I mildly disagree. The reason I want to make that clear is because on other threads on other subjects I might strongly disagree with a position and I don't want anyone reading this thinking that this is one of those cases.

Everything seems reasonable on paper. Get a cable material (carbon nanotubes) that is light and strong enough to endure it's own weight along with the stresses and strains associated with lifting payloads, surviving winds, etc.,etc. Attach it to an object in a geosync orbit. Build a climber with some sort of powering system (this seems to be a major hurtle as well, but certainly something that can be accomplished). It's just there is so much that can go wrong it makes me squeamish.

However. Clearly if it could be accomplished it would essentially be the equivalent of a space dock for any planet or moon that we set one of these things up on. It certainly would make constructing space stations much easier, not to mention that spaceships would never have to reenter the Earths atmosphere.

And even if it does prove to be impossible because of all the little details that are being airbrushed over here, the creation of such a strong lightweight cable alone has a multitude of uses.

Agreed. There are a lot of things that can go wrong, and there are still things that might turn out to be showstoppers that haven't reared their ugly heads yet. Also agreed that the material in it's own right is a major accomplishment and has multitudes of earthbound uses all by itself. everything from a cutting tool to long distance power lines to super-armor for people and vehicles and umpteen-jillion things in between.

But consider this for a moment: The safety factor for many rocket structures are often only 1.1 to 1.2. They would not be able to fly, or carry much in the way of payload if they were built with safety factors of 2 or more in many cases. So anything that has a safety factor in excess of that is an improvement over rockets. That is one reason why commercial manned rockets are still rarities and passengers must sign waivers before they are allowed to go flying. And in rockets, there are thousands of things that can go wrong too, and if they do, you are most likely dead. This is why flying in space is still very much an experimental endeavor and NOT routine. Many people do not grasp that.

I would also add that the book is a decently entertaining novel in it's own right and is worth buying just for the entertainment value, the educational bit is gravy.

In a hurricane, the problem will not be the high wind speeds, but the debris carried by those winds. Will these fibers be able to withstand repeated collisions from the side? Those collisions will send vibrations up the cable. How will those vibrations affect it?

The way I see it, the best place to anchor such a cable would be in the middle of an ocean (less debris, unless placed in an area not traversed by hurricanes), or a desert. In the ocean, the base of the cable will then be surrounded by an electrolytic solution (sea water), which could complicate the electrical situation. In the desert, the base is then surrounded by an abrasive material.

Just wondering if these factors have been considered...

"Safer if there is a mechanical problem". True as regards getting (temporarily) stuck, but if the cable breaks above you (cut by high-speed projectiles - possibly space debris?), or you fall off below about halfway you will enter the atmosphere at a velocity similar to the orbital one.

Even if the long-term low-energy launching system proves unworkable, there would still be significant advantage in being able to have geo-stationary drone satellites at heights well below the standard orbit. I suspect that this would be the preliminary objective - and you wouldn't need the tether to survive atmospheric conditions.

since the crossectional area is so small, orbital debris impact should be very unlikely. the target is practically microscopic, but that said, yes it COULD happen. So let us look at what would happen if it did shall we? There are two possible scenarios:

Scenario 1:) Break occurs BELOW the car in transit.

The car, having the same orbital velocity as a geosynchonus satellite would want to enter a higher orbit, and would swing on the tether upwards and ahead of the geosync terminus and would slingshot up and out away from the earth. If the car came off of the tether at that point it would enter an elliptical orbit with it's apogee of around 22.5K miles and perigee at whatever altitude the car was at before the tether broke. Therefore, the occupants would be in a semi-stable orbit that could allow a rescue attempt, assuming the car had adequate consumables to keep the occupants alive until rescue arrived. If the car stayed on the cable, it and the counterweight would spin like a bolo with the CG of the assembly remaining at the geosync point, again, in a semi-stable orbit which could allow a rescue attempt. The whipping cable below the car would be a hazard to any rescue attempt, so a means of shearing the cable below the car would need to be attached. Since the car is not on a simple ballistic trajectory in this scenario, matching velocities and docking with the car would be extremely difficult for the rescuers. Of the two alternate scenarios, the car releasing itself from the cable would be easier one to effect a rescue because the car would be on a simple ballistic orbital trajectory and easier to match velocities with.

Scenario 2:) break above the car.

In this scenario, the car again would have a velocity in excess of the orbital velocity at the altitude it is at. So it would want to race ahead of the cable and move to a higher orbit. if it remained on the cable it would swing down into the atmosphere and reenter. If it released itself from the cable it would enter an elliptical orbit much the same way it would in scenario #1.

In both scenarios above, the default abort procedure is to enter an elliptical orbit and await rescue. If the car had a small maneuvering thruster array and a heat shield/parachute, the orbit could be slowly lowered and circularized to allow a controlled reentry of the capsule, thereby negating the need for a rescue launch attempt.

The impact cross-section of a dart and a dart-board is not the area of the tip of the dart, but that of the dart-board. Similarly, the very narrow cable will have a substantial cross-section with space-debris. [Indeed, taking all three dimensions into account, the impact cross-section of two zero-width straight lines (of lengths L1, L2) is of the order of L1.L2/4]. So the extended length implies a very much larger total impact cross-section with other space debris than would (for example) the Earth station.

You are also mistaken about what would happen if there was a break above the car (scenario2). The orbital velocity of an inertial satellite is proportional to 1/sqrt(R), where R is its distance from the centre of the Earth. I.e., the lower the orbit, the higher the speed needs to be. For the tethered car, the angular velocity is constant - once per day - so the speed reduces linearly as the height reduces*. Admittedly, at a quarter of the geostationary height-height, the velocity is still 1/8th of the required orbital velocity, and (without checking) I doubt the elliptical orbit cause would earthly collisions - but there would still be a substantial region near the bottom of the cable that would bring it hurtling into the atmosphere (so we'd need the same type of precautions as for an inertially-orbiting satellite - except that in the worst case the velocity would actually be greater).

*I'm assuming that the car would release itself from the ground tether

ah, you are right, my math was wrong about the orbital velocity. but again if a heat shield/parachute and thruster array were on the car, even if the car was in the atmosphere, or just above it, a safe return should be possible shouldn't it?

One must also remember that rockets have relatively wide "black zones" in which a safe abort is not possible either. In fact the Apollo and Constellation and Soyuz abort windows are wider than the abort window for the Shuttle due to the use of an escape tower attached to the capsule to pull it away from a disintegrating booster.

Yes, understood. In many respects it's safer for the car than going up by rocket.

However, the systems in use for slowing present satellites rely on the fact that they enter the atmosphere at a shallow angle*, whereas a satellite falling from the cable would usually enter quite steeply. I therefore believe that a car that falls into the atmosphere would need to be treated as a write-off for about 90% of cases.

The other issue is that, given the large effective collision cross-section of the cable and the absence of damping in space, the stored (tensile) energy in the cable might be a huge issue (for other satellites). (I'm assuming here that the ground end would also be released if the cable was observed to be broken)

*So the kinetic energy can be lost relatively gradually

I will add that in some proposals, the car does not lower itself back down the cable but in fact releases itself from the cable and re-enters, not unlike the abort scenarios we are discussing.

For the reasons I already described, release-and-fall from the cable would require new entry technologies unless you restrict the release to near-vertically-parachutable height. I assume that the reason for such release is to minimise the hazard of cables coming down through the lower atmosphere - but the cost would be that you have to fly (balloon?) your car up to the cable in the first instance - so you may as well use the same system to bring it down, as this minimises the equipment you have to place on the car. (I'm afraid I tend not to believe that every proposed scenario has been decently thought through)

Just run multiple cables.

If you run 3 or more cables, a single or even double failure would not be catastrophic.

That only moves the problem. I'm not saying it's insoluble, but I certainly don't know the solution (though it might appear through detailed analysis).
What's my issue? Suppose one of the super-tensioned tensioned cables is hit by some debris and breaks. That's one hell of a lot of stored energy - and some of it might just go to severing any other cable that is within reach. (Probably not too bad a problem if we knew just where and in which cable the break was going to occur, but...)

Why not just expand on the multi-cable approach and make it more of a tube by using short laterals to join the main cables in a spider web like assembly. This would just short sections vulnerable.

Personel cars could use the inner part of the tube while larger cargo vessels use the outside.

I think the main problem is that the spiders need somehow to support the tension in the unbroken section of the broken cable while it is being de-tensioned, which means they couldn't be all that light. But it has the makings of step towards a solution.

Good Answer. Use the mutiple cross sections to reinforce the cable and lessen the chances of total catastrophic failure.

Dragon

I think not, but I could be wrong. Remember, the mass of each cable is very, very small, so it will not carry much momentum.

A break would send a wave through the cable, but the cable mass is tiny per unit length.

Good Answer. Low mass equals low inertia. Therefor the harmonics and recoil will also be very short lived.

Dragon

Low mass just means that the cable will move faster - and the only losses will be cable elastic losses (remarkably small in these materials - it would take hundreds-of-thousands of extensions and whippings to lose the energy) and that due to any collisions. The whole thing will be like a fast-moving giant cheese-wire. In any case, as any ballistics man will tell you, it's the impulse energy transfer that's important.

But this persuaded me to look at the numbers in detail (mistakes probable). I hadn't done this before - and the result says that if the cable hits you, in 1-ms you would have to stop a mass of about 350gm (you have to stop the attached cable - all travelling at 8km/sec ....
According to reports, the strongest known material is monocrystalline graphene, whose ultimate strength is about 10¹² N/m². So a cable capable of supporting a tonne (no safety margin) would need an area of about 10^-8 m² (just over 1-mm diameter) and therefore a mass of at least 22mg/m. Now, the extension of the cable at maximum tension would be about 13%, which means that (regardless of the length), the tip of a tethered cable will accelerate to a velocity of 8-km/sec. Now it may be light per length, but that is cheesewire travelling at 8 times the muzzle velocity of a high-velocity rifle - and you don't just have to stop the bit that hits you, but (best case direction of cable movement for you) in 1-ms you would need to stop the 8-km on either side of the bit that hits you first - or a mass of 350gm. That's a lot of momentum. Give the cable safety margin, and the momentum increases.
By the way, the force needed to support the cable itself looks to be about 140kg weight (=radius of Earth times linear density)

if you were to release and fall from the cable, Coriolis forces should pull you away from the cable.

Only if you were on the correct side of it.

Which comment were you replying to? Surely not #22?

All I asked was the reason that makes it sensible to drop the car from the base of the cable, given that you already have to provide full transport facilities to get it up there in the first instance. (Dropping a moon-mined payload would be a different scenario, of course)

But if there was a cable break, you could not guarantee that the car is near the base - so you now have the potential problem of a steep high-velocity entry - a problem that SFIK has yet to be solved other than with massive rocketry that is almost capable of placing the car in orbit in the first instance.

I was responding to #22.

You've read about this right?

http://www.space.com/businesstechnology/technology/space_diving_010608-1.html

Completely irrelevant to any discussion in which I would wish to participate. Of course someone will want to jump off whatever it may be - but I was scarcely considering designing an elevator for that purpose.

That was not my point of mentioning it. The point was that someone with nothing more than a space suit and a parachute was able to reenter safely from 20 miles up without needing a heat shield or a retro rocket. I would presume that an elevator car, properly designed, could do likewise.

There may well be a certain range of altitudes where neither rentry nor orbital rescue is possible without loading the car down with a heavy booster that would reduce the payload capacity to nil. I do not know what that range is or even if it exists but I will concede it may exist. there may well be a "sweet spot" in the thrust vs payload curve where you can install a relatively small OMS system to shrink or eliminate any black zones without sacrificing too much payload capacity. I simply do not know. At this point we still are speculating about the UTS of the fiber which to my knowledge has not been published yet. Granted it is informed speculation, but it is still speculation.

As far as moon or asteroid ore goes, I personally don't have a problem with casting a rough ingot into a gumdrop shape, strapping a guidance package and an OMS to it and aiming it for reentry into White Sands or Tonopah or Edwards or even Jackass Flats sans a parachute. Just dig the thing out of the hole when it hits, hose it off, and take it to a rolling mill and be done with it. an elevator system to get ore down is a waste of effort. the elevator is to get stuff and people up and people back down again. the refining and smelting would be better if it were done on orbit anyway. After all, you have all that wonderful vacuum to deoxidize the ore with. people pay good money to vacuum induction or vacuum arc melt high quality alloys here on earth.

Indeed they could (jump off safely at 20 miles) - but the issue is with falling from heights between about 500 miles and the altitude where the perigee of the orbit merely grazes the upper atmosphere.

The reason for using the elevator for moon-ore is that the other way to slow the ore's awesome orbit to the point that it can enter the atmosphere is with rocket fuel - and this you would either have to be manufactured on the moon, or transported up from the Earth. The weight of the required fuel would be many times greater than the weight of the ore - meaning that the elevator would be the only economic method for most materials.

According to the article, the Cambridge prototype facility is turning out fiber at a rate of a gram a day. That doesn't sound like much until you realize that is 18 miles of fiber!

That means a single strand of the fiber 22,000 miles long will only weigh about 1222 grams. I am guessing that it has a UTS on the low end of the nanotube range of around 65-70 GPa, but it might be as high as 150 GPa.

Not being a native speaker so to speak with metric units I translated these numbers to imperial units just now. and I have only one thing to say when I saw the results.

Mein Gott im Himmel!

One need not have 22,000 miles of fiber, all the way to geostationary orbit. An alternative launch device involves a self-supporting loop of cable long enough to get above most of the atmosphere. It is held aloft by centripetal force, like a spinning lariat, and the payload has to attach to the cable (not trivial considering the speed of the rope, escape velocity), ride it up, and let go into orbit.

There does not seem to be enough thinking outside our present experiences in these replies. Instead of a cable pulling the elevator up, why not a variation of a Gauss cannon. Produce an electric field inside coils aligned with the shaft of your tower and vary it sufficiently that the occupants of a vehicle experience less than 3 g's. You can accelerate your vehicles with no cable and the bulk of your power plant on the ground. The same coils/field would decelerate returning vehicles. Coils can do the same thing at the geostationary terminus to decelerate vehicles arriving and accelerate them to fall back to Earth.

Then, you are saying that you don't think a standard pulley and block will work?

This Cable is like a continuous lightening rod. I think electrostatic discharges will burn it up in no time! It would have to handle not only the usual electrical storms but also the massive E/M Storms from Solar Flares.

Still, it is fun to think about, so I don't mean to spoil the party.

That electricity should be able to be used as a source of power for a great many things.

Are the nano tubes conductive?

What is the resistance per unit of length?

I think the real issue is when you take a conductor 22,000 miles long and pass it threw how many(?) lines of magnetic force per second 24 hrs per day. You will not have to power your space elevator it is the power source.

My friends thought me mad when the shuttle put out its tether and I was hoping the tether burned up before the shuttle became too charged. Not a well thought out experiment.

The real trick will be getting a cable that can carry the power into position. Otherwise the discharge will make our biggest lightning bolts a spark.

Brad

Nice thought - the problem is that we need two tethers moving at different velocities across the field to get a potential difference around a circuit. But, being equatorial, the tethers can only move perpendicular to the dominant field in the same direction and at the same average speed.

I could be wrong, but I think that the only power it will give long term will be in the way it responds to changes in field strength with time; but it might be a method of damping random relative movements of closed circuits of tethers...

Well thought out. Good Answer. Like trying to attach ground wire to a live High Tension Tower cable.

Dragon

Presumably a single tether would have no problems from magnetic fields? I've no idea firm idea of the level of charge build up from passing pre-charged atmospheres, but it sounds scary - I suspect the electrical conductivity in the lower 10-km would need to be equivalent to a several sq.cm copper rod.

I don't know how large of a charge would needed to be dealt with, but I would venture a bet that an expert in the Earths magnetic field could figure it out.

I do know that there was more tether on the reel/winch than the shuttle got into space. Nor do I know what the angle the tether crossed the magnetic field at.

Another area of concern would be the stratosphere and up. Red sprites, sprite halos, blue jets, and elves could be attracted to the path of lesser resistance. Being a little understood phenomenon the issues are to be learned by experience with little knowledge at the start.

I have a gut feeling that the elevator cable itself could produce more power than our largest dams.

But harnessing a dirty 24 hour long AC wave on that scale my be a trick in its own right.

Brad

I was trying to solve one problem at a time - to get a viable tether in the first instance.

With an isolated (or single tether), I really can't see an issue with magnetic fields.

My concern (if the tether is tied below the atmosphere) is lightning strikes - I imagine that the tether passing through the cloud would allow for much higher charges than are commonly experienced. If I've got this right, 20-sq.cm aluminium for a height of 5 miles would increase the load on the cable by about 35-tonne. (As yet I don't envisage providing significant current-handling capability over the full height to the geostationary orbit)

I really can't see an issue with magnetic fields

The problem is the potential is still there circuit or not. When a conductor passes through a magnetic field the electrons are moved. In a circuit these electrons flow relieving the voltage pressure but at the same time the resistance can create heat causing a failure in the conductor. In a single conductor the electrons move but are left with no place to flow until the pressure/voltage is great enough to jump the open. In a strait conductor the electrons amass at one end and the holes at the other.

The force normally is small but a wire 22,000 miles long and at what speed will the end of the conductor be passing through the field and what are the flux densities along the conductor?

Another variable that may be useful or an issue is Peltier–Seebeck effect. (I know Physicist? knows this) The cable itself will not be effected but any conductor attached to it will. How much is another issue.

Hopefully the flux densities are low out where the cable moves the fastest but I don't have that data to figure it out.

Brad

I don't see that the field-induced voltage can be an issue with a linear wire - the surrounding insulator is subject to the same magnetic field variations and therefore the same potential gradient.

The charging current might need more thought (=sums). In spite of the rather small capacitance, sweep rates of up to maybe 3 km/sec across a non-uniform magnetic field might indeed generate significant currents in the graphene-like cable.

I've seen (so far abortive) discussions of generation using Seebeck junctions for generation using hot springs, gulf streams, etc, and this would be little different. Maybe eventually using superconductors(??), but in all cases we'd need huge changes in current-handling capability for the infrastructure cost vs power out to become remotely favourable. (We'd still need the usual care to avoid eelectrochemical effects, of course).

...eelectrochemical..., anything like an electric eel? couldn't resist. Noticed the spell checker said it was correct and learned something new Thanks again.

The nanotubes/SWNTs are fairly inert chemically but any different conductors passing a current can have an anode cathode effect.

One other thought, it would be the ultra...ultra long wave antenna. Now where do you put a 22,000 mile receiver antenna?

Brad

Good forward thinking and Good Answer.

Dragon

Mostly good, but I don't see how it gives that much help in returning mined material from the asteroids to Earth, as the energy change would be about 10 times greater than is needed to escape the Earth. (Even to use an Earthly sling to for going out to the asteroids would need a sling that was longer than the distance to the moon - which could cause some logistical problems in avoiding collisions)

Based on what I've read, any ideas for putting mass in orbit around either the earth, moon, or both, call for a mass lift from either body. I am thinking that mass from the asteroid belt will be more accessible because the gravitational acceleration from it is much lower, and therefore, more easily overcome. Once an object is put in motion, then it will stay in motion until it gets near us, then we would have to remove its motion in order to be able to use it.

On second thought, we would have to build a processing station in the asteroid belt itself, so earth/moon orbit doesn't become full of process-leftover-slag, and to make the transshipment of materials more effective and efficient.

The only explanation I've read (from ancient clay tablets that shouldn't have even known about it) calls it the 'hammered bracelet', and says it used to be part of our planet, the remains of which is now the pacific ocean. That means that there will be a lot of water, but there could also be material from up to 3000 miles below the surface of our planet. That could be interesting.

Are you saying that the energy to move a pound of mass from asteroid belt orbit to earth orbit is 10 times more than the energy to launch it from earth or moon? Please clarify.

Chris

"Are you saying that the energy to move a pound of mass from asteroid belt orbit to earth orbit is 10 times more than the energy to launch it from earth or moon? Please clarify."

Yes, that is what I meant, but it's actually only just over 4 times*. The cause is the Sun's gravitational field. The problem is that you have to change both velocity and potential energy to change orbits - and although the body is actually reducing it's orbital energy I know of no no practical way to change the velocity of an inertial body that does not require the input of energy.

*I hadn't done the sums, which need to take into account the pre-existing orbital velocities and that the asteroid belt is anly 2.4 times as far out as the Earth.

Okay I get you.. we only get to bring back the diamonds.. I wonder what will be there? What do you think?

Actually one of the Apollo asteroids could be used but finding the right one could be a job in its own. Not all are so elliptic but a solid iron or stone one would be needed to work with because we don't know enough about the rubble/conglomerate ones.

Then comes the issue of timing. Shooting a bullet with a bullet, with a cable attached to it. One kink snapped strait and you have a brake. Too much tension and you don't fly high enough. Too little and you snarl. And the first time has to work.

Getting asteroids back to earth is easy if you have lots of time but to half your time here you have to square the force.

Brad

While I like the idea, has anyone calculated the velocity relative to it's surroundings, of the cable at various altitudes?

At intermediate altitudes, the cable will be whistling along and perhaps aerodynamic heating, say around the ionosphere, would a problem.

If this was so, a small amount of water conducted up the tube and evaporated in the right areas would be one solution, assuming a material isn't found which would handle this directly without cooling.

Of course, drag from the elevator would mean that measures would be needed to periodically speed up the satellite at the top to prevent the orbit decaying.

The nanotube may also allow use as a waveguide to transport microwave frequency power from orbit to earth. Some of this power could be used to power the lifting of loads into orbit.

As I recall Arthur Clarke's novel, a future development was to interconnect many space elevators at orbital level to provide extra strength for the entire assembly. Even with nanotubes, the amount of material involved would be enormous, but technically, would it be an advantage? (Of course if this was carried to the extreme, nimble aircraft would be needed to avoid space elevators!)

I believe technical problems could be overcome. Whether it would be economically feasible is another question.

I think you have been mislead. The idea is to tether a satellite somewhere outside the geostationary orbit. It's gravitational orbital period is greater than a day, but it is constrained by tension in the tether so it actually orbits once per day; if it lags behind, the tether will drag it back into synchrony. The real concern there would be that disturbances might build up to cause a significant oscillation, but that would be a slow effect that could (for example) be (actively) damped by moving the base of the tether within a very modest area.

Then you are apparently concerned about the possibility of heating by the jet stream whistling past. Well, the ambient temperature is a long way below freezing, and the maximum speed is only about 400 kph per hour. That is not enough to raise the temperature by as much as 100 ^OC even if all the kinetic energy in the stream were to be converted to heat. The theoretical possibility of heating by energetic molecules in the ionosphere would be overcome by radiation from the (black) tether (as the density of the gas is low, so too would be the rate of heat flow).

I'm not certain about connection at orbital level. Given the large captured area, induction from the variable magnetic field of the Earth would need to be taken into account, and I can't really see how coupling over long distances would be advantageous - to my mind this would be a rare instance where AC has proposed unnecessary (and probably counter-productive) features - but I suspect this was conscious as he understood that most people would not envisage a functioning non-connected arrangement [unfortunately, I can't confirm this, as I never got to talk to him]

However, although these particular secondary issues are readily solved, the primary ones are still a very long way from such resolution.

You are quite right.

Actually, I was thinking of the speed that the wire is forced to travel to cover the distance in 24 hours at the intermediate altitudes.

When I finally dusted off my basic physics and calculated it myself, it proved to be no problem. Because it is not in orbit, the velocity turns out to be quite low relative to the atmosphere.

I was just pondering this issue, and have come up with an alternative related idea to the space elevator, based on this material. I'm not sure if this has ever been mentioned before in any Sci-Fi story or other article ... but the thing is, given a sufficiently strong 'cable', a sky hook approach can be used to pull material off the earth...

It would be a rather long and strong skyhook, connected to the Moon!

To start the scenario, the long cable must be taken into orbit by conventional means. One end of it is landed on the moon, and anchored to a mountain, such that the restraint will at least equal the breaking strength of the cable, plus the added acceleration or weight of the expected load size. Obviously, the cable needs to have a strength far in excess of its own weight, as accelerated by Earth's gravity + moon's gravity + load

The other end has a complex vehicle attached to it, which is also the 'Hook'. (think something like an existing shuttle) The length of the cable will have to be slightly larger than the distance from the earth to the moon to allow for the volute curving of the cable under tension through the atmosphere, and other variables.

In the space between the earth and moon will be a heavy duty winch system which controls the length of the entire cable. (with rocket positioners) (or a pair, at different LaGrange points) One other very important fact is that the moon always keeps the same side towards the earth (exactly.. it a miraculous anomaly) , which will prevent the moon from winching up the cable over time.

As the moon sweeps by in its orbit about the earth, rocket/jet power controls the behaviour of the hook.(whether or not it is allowed to be affected sufficiently by the Earth's gravity) Once the earth can attract the hook, it can descend from orbit. (it is not moving at orbital speed, but slightly greater than moon angular speed.) This will allow sufficient time to gently touch down, hook, and hoist off again with the rated load, (partly fuel for the rockets/jets for next time.)

It may take a bit of time, but the moon will pull the mass towards orbit, much like if your fishing boat powers up and leaves while your line and sinker are still in the water. the lure and sinker will rise to the surface (of the atmosphere in this case), plus add the velocity of the departing body (boat or moon)... so.. I'm not an orbital physicist, but I think that if the moon orbits the earth every 28 days, at a radius of 400,000 miles, then it is covering 12,560,000 miles in 28 days. There are 672 hours in 28 days. Therefore, the moon is travelling at approximately 18,690,476 mph which is um... fast enough.

Once the mass is boosted to orbital speed, the cable system is detached,(before it reaches full velocity) The Hook must accelerate more, and pass the timing point where the process can begin again, even just by decelerating and following conventional de-orbit methods.

Add some fuel for boost and control, and I think this system could work? (based on the right mix of technologies) What do you think? Would the acceleration by the moon be too great for any vehicle?

If the cable can be made to support all the 'empty weight' acceleration on it, plus a significant enough payload, then maybe it can pay off the investment?

Am I way off the mark? This all sounds like the physics of flyfishing to me.

Chris

PS.. a side benefit is that you could also use Clarke's pinch-roller tractor to take material/water to the moon.

I am reminded of undersea telegraph and telephone cables. It is amazing to me the fact that they were laid, and transmitted telegraph and telephone signals.

Russell

Hello chrisq,

The issue I see with the swinging sky hook is the unit will need to pivot around the moon. The Moon does not spin in relation to the Earth. A track around the lunar equator could be done but would be cost prohibitive. The speed of the cable base could be matched to a location on the Earths equator. More cables could be matched to different locations on the Earth's equator.

If you matched the rotation counter to the Earth the cable would appears to drop out of the sky and lift back up.

You will have to adjust the cable length for all the dynamics of the Moon Earth orbit.

The track system could be the loops for your Lunar power system, at least two tracks.

Also the sling effect of the added velocity of the moon to an orbit released from the cable on the dark-side of the Moon will put the mass into a very efficient start.

A small asteroid was considered for a system for accelerating masses using two arms but I don't recall any lunar system based sky hook system.

Brad

Here is a quick sketch of my plan.(nts) I don't see why a track around the moon would be requred as the moon always keeps the same face towards the earth. (more specifically, its rate of rotation synchs with its orbit) I do see that it is in an elliptical orbit, but that is what the winch system in the middle is for.. to keep the length of cable correct for the position. It will of course take a lot of looking into the science and math.. but that is what CR4 is for

The track was to match the rotation speed of the earth to the speed of the cable. And then sling it into high solar orbit.

Surface speed a the equator is 1041 miles per hour. The Moon, if I remember right, travels at 1/28th of that or reduces the cable speed by about 37 miles per hour.

So at just over 1000 miles per hour that is one big cheese cutter. Not that it is not possible, just not as easy as it seems.

I suppose you could put a jet powered hook to guide it to the lift pad. The winch system will be out in micro gravity so any non accounted for torque will cause mischief. Also the spools on the winch will need to be of a large diameter to reduce flex stress on the cable. ( besides reeling in hundreds of miles of cable)

Brad

Here is a similar proposal, for Mars/Phobos.

Chris

The earth rotates, once a day. I'm stll confused about why the cable doesn't wind up around the earth, shortening by about 25,000 miles per day. Having the end stay opposite the moon requires that it go in excess of 1000 mph through the atmosphere, and most of its path will be over/through ocean. Given the density of water, you can't make it go 1000 mph through the water, and building a bridge across the Pacific seems a bit ambitious.

Did you consider the rotation of the Earth - that the ground will be moving at about 1004-mph relative to the bottom of the cable (and vice-versa)?

PS. Apologies Brad - I see you got there first. (I didn't see your comment initially as it was in answer to a later posting).

Hi Physicist,

Yes, I thought of it, and will keep thinking of it. My answer to this is that if you have something like the shuttle, it will have to de-orbit, and use atmospheric friction to lose velocity. As it has to lose ~17000 mph in order to land, what little difference will the rotation of the earth make? here is a link that shows the rotation/orbit of the earth/moon, which are co-directional.

This is the effect that will allow this plan to work. What it needs is enough slack in the cable to land, load, and prepare to launch again (power assisted to reduce shock load). This slack is accomplished by boosting ahead after dropping its payload in orbit, at orbital velocity. It must boost ahead just enought to create the slack in the cable, allowing for de-orbit time, etc.

This is why I compared it to flyfishing.. first a pull from the the planet, then an acceleration to orbital speed, then then a boost, then a landing. but I don't know how to calculate it? can you help?

Chris

My concern is that if we had brought the moon-cable into the atmosphere we would have about 5 miles of cable running inside the atmosphere, and at supersonic velocity. That's one heck of a supersonic boom, and a lateral force on the cable of many tonnes. (I see that the Mars version does not enter the atmosphere; there's no track on the ground).

As regards escaping Earth's orbit, the energy gains would at first sight be considerable. You need 1000-mph to match the bottom of the cable. Once you are at the neutral point between Earth and Moon you only need another 1000-mph to escape the Earth's gravity.
But when I say "at first sight", that is precisely what I mean – the energy needed to escape Earth gravity is only the beginning – if you want to do anything useful you presumably have to go somewhere. Mars is easiest, and under most favourable conditions you need just (?!) 10-miles/second equivalent to get there. That is a great deal larger than the additional 1.6-miles/second required to escape geostationary orbit, so I don't think it justifies the additional complexity (and cable length) needed for the moon.

But the other point that is missing is that Arthur Clarke's skyhook satellites would not be in geostationary orbit. In order to provide enough tension in the cable to lift the loads, they would have to be outside the normal geostationary orbit, probably by at least 30%. They would be geostationary only because of the constraint of the tether. That extra distance means that the skyhook satellites are already travelling faster than the Earth's escape velocity – so the moon-hook actually has no advantage – other than for direct access to the moon itself, of course.

Okay thank you.

I'll keep thinking about it..

Chris

This is why I proposed the track around the Moons equator. The tip need only move the 1004 miles per hour in the direction of the Earths rotation.

The optimum release from the hook will not be in Earths orbit except in the opposite direction. Higher orbits like Mars should be easy. And a launch from the Moon would need an additional 6,000 feet per second to get out of the lunar gravity well.

Only a little energy would be needed to go from geosynchronous orbit to the lunar hook.

The big issue is the making of a track for the moving anchors that goes all the way around the lunar equator. It would need to handle mostly negative Gs over all types of smoothed terrain. The cable systems cost would be small compared to the cost of a super highway and heavy rail system around the Moon.

Personally IMHO I think the capital of the Earth will eventually be the Moon. That is if we don't manage to put ourselves back into the Dark Ages.

Brad

<<... then it is covering 12,560,000 miles in 28 days. There are 672 hours in 28 days. Therefore, the moon is travelling at approximately 18,690,476 mph which is um... fast enough.>>

I think you need to check your decimal points. 18.6 thousand mph is more reasonable. That's less than escape velocity from Earth, of course.

Still more than an order over the top. The moon averages 384,400 kilometers away - so 1.5 million miles in 27.3 days. The actual velocity of the moon is only 2288 miles per hour.

There is a little demonstration of a proposed Space Elevator on my website in the one of four links.

Far as I know the invention is dependent on carbon nanotubes to make a ribbon or cable strong and light enough for the job.

Further the place to put such a thing is in the equator, and there is supposedly a perfect place about 50 miles off of the Ecuadorian coast for both physical, and political reasons.

There are some places on Earth, where there really is hardly any wind.

Space Elevators are built from up to down, instead of up, so any building of the Space Elevator would depend on current Rocketry Skills to loft and lower carbon nano tube enabled systems over equatorial regions.

It is good to remember that early satellites were very crude, and simply let go photographic film out of them, that was captured by aircraft flying around with V scoop wire capture thingies stuck on their noses.

It could well be that it would be possible to drop a cable partway into the upper reaches of the atmosphere and dirigible dock to it, as good enough. I do doubt that hard point to hard point from the Earth to the Moon using one tether is the best way to go.

As far as any religious beliefs, or justifications, or claims about aliens, and pyramids, my attitude is that if if your spiritual life inspires you more than it inhibits you, good.

- at least I feel this way in relation to Chrisg288.

P.S. I forgot to mention the film canisters were on long parachute lines that the aircraft snagged. I also neglected to list my site http://transcendia.org where there is a link to a Space Elevator Proposal Video.