Space elevator ? How can it work?

[Gfellow]

"Space Elevator" has been in my Google Alert for quite some years now, and I have noticed a tenfold increase in the chatter on the subject. It would appear that the concept is rapidly becoming part of the collective consciousness.
It is notable that the Japanese are looking to spend 8 billion on such a project, and while that might seem an insignificant fraction of the final cost, it makes for interesting seed money.

Whether building a space elevator is feasible can be an arguable subject, but IMHO there is little doubt that someone will try. The rewards are just too big to ignore. I won't go into the mass/lift ratio advantage here, but considering the relatively small resource outlay, the political stature and military advantage that a space elevator will afford, will ultimately be too tempting for any number of powerful nations.

As a real-estate speculator, my focus of interest is where it might be located. For logistical, physical and political reasons, my bet is the island nation state of http://pantheoanimist.blogspot.com/2008/02/ideal-space-elevator-location.html" . The island is on the equator, minimum security issues, harbor installations, commercial runway, tarmacked road rings the island.

The only other places available on, or near the equator are either politically insecure, or have no infrastructure.

 

[FredGarvin]

...but considering the relatively small resource outlay, the political stature and military advantage that a space elevator will afford, will ultimately be too tempting for any number of powerful nations.

I'm not sure of what you mean by that. There is nothing involved with this fantasy that would be small. The amount of resources required will be huge, especially in the manufacturing sector.

You do bring up an interesting point about the military. Not so much in its use, but in how anyone could ever hope to defend a space elevator if someone really wanted to put one out of commission.

 

[DaveC426913]

You do bring up an interesting point about the military. Not so much in its use, but in how anyone could ever hope to defend a space elevator if someone really wanted to put one out of commission.

Yes, this is definitely something that cannot be ignored. I think it will limit anyone nation from attempting it. The space elevator is too much of a game-changer.

 

[DaveC426913]

By the way, I REALLY think we should make a concerted effort to popularize the nickname: It's a MAGIC BEANSTALK, or BEANSTALK for short. The name fits it perfectly.

Come on everybody, we can make a change if only we truly BELIEVE!

 

[FredGarvin]

Magic Beanstalk...I like it.

 

[Gfellow]

I'm not sure of what you mean by that. There is nothing involved with this fantasy that would be small. The amount of resources required will be huge, especially in the manufacturing sector.

Greetings FredGarvin - Perhaps comparable to the Panama Canal in terms or resource and effort? Was it worth it?

You do bring up an interesting point about the military. Not so much in its use, but in how anyone could ever hope to defend a space elevator if someone really wanted to put one out of commission.

Several famous quotes of different personages come to mind. The slightly misquoted General Nathan Bedford Forrest's "git thar fustest with the mostest," comes to mind, or perhaps "command the high ground" of which there are too many authors to count.

From a combative point of view, the nation-state with the space elevator would definitely hold a strategic advantage over an opponent. The loss of the bridge out of the gravity well would be regrettable, but assuming you have ferried up a considerable quantity of resources, it would be of little consequence once you have obtained the sustained ability to look down upon and strike your enemy during a crisis.
From a tactical point of view the gravity-bound opponent might think twice about initializing hostilities.

 

[DaveC426913]

From a combative point of view, the nation-state with the space elevator would definitely hold a strategic advantage over an opponent. The loss of the bridge out of the gravity well would be regrettable, but assuming you have ferried up a considerable quantity of resources, it would be of little consequence once you have obtained the sustained ability to look down upon and strike your enemy during a crisis.
From a tactical point of view the gravity-bound opponent might think twice about initializing hostilities.

OK, well that's an escalation even above what we are talking about. If there is the slightest hint (or even if there isn't) that the elevator will be used for strategic purposes, the whole world will rise up against them before it ever gets off the ground.

 

[Gfellow]

MAGIC BEANSTALK

Nice! Another possible suggestion? "http://pantheoanimist.blogspot.com/2008/04/space-elevator-and-old-testament.html" " This name has a messianic flavor and would galvanize the religious conservatives to your side:
"...He came to the place and stayed there that night, because the sun
had set. Taking one of the stones of the place, he put it under his
head and lay down in that place to sleep. And he dreamed that there
was a ladder set up on the earth, and the top of it reached to heaven;
and behold, the angels of God were ascending and descending on it! And
behold, the LORD stood above it [or "beside him"] and said, "I am the
LORD, the God of Abraham your father and the God of Isaac; the land on
which you lie I will give to you and to your descendants; and your
descendants shall be like the dust of the earth, and you shall spread
abroad to the west and to the east and to the north and to the south;
and by you and your descendants shall all the families of the earth
bless themselves..."
(I realize we are getting a little off-topic here, but I am sure the admins don't mind a bit of humor.)

 

[Gfellow]

If there is the slightest hint (or even if there isn't) that the elevator will be used for strategic purposes, the whole world will rise up against them before it ever gets off the ground.

Do you believe the US would have placed a man on the moon if the USSR was not on the agenda? Major resource hungry efforts by nation-states have a combative proponent. They may never mention it, but it is still there.
Ideally, the space elevator ought to be an international effort - perhaps it might happen that way. However, if that does not occur, the advantage afforded to an individual nation-state would eventually be too great a temptation.

 

[FredGarvin]

Greetings FredGarvin - Perhaps comparable to the Panama Canal in terms or resource and effort? Was it worth it?

Greetings to you as well.
Like I have mentioned before, the Panama Canal is not even close in the terms of what is required. The pieces and abilities to build the canal were already in place and understood. There just needed to be a huge man power commitment (and money). With the bean stalk we are talking about using materials that have not been invented yet, and building techniques that do not exist. Once we figure that out we have to figure out how to do it on a massive scale. Then you bring in all of the other issues also mentioned like satellites, etc...Honestly, I can not think of anything on this planet that is a good comparison to what needs to be done. Perhaps the Great Wall of China...

 

[Gfellow]

...huge man power commitment (and money). With the bean stalk we are talking about using materials that have not been invented yet, and building techniques that do not exist.

I put it to you that we have emerged into a new paradigm. The adept control of manpower and resources was the great triumph of the past two centuries, a tool we now take for granted. The flower of our epoch is the additional thrust of efficient research towards a given end.
When Kennedy told the world the US was going to put a man on the moon in a decade, the NASA science staff were gobsmacked. Although it is what they wanted, they had not really taken the time to sweat the details. However, it turned out to be a confirmation that this paradigm was upon us.

The REAL issue comes down to, 'is it worth it?'.

As a rule, nation-state military systems tend to be conservative and usually remain complacent unless there is an imminent and obvious threat. Seen in this light, the space elevator can be dealt with in three ways:
1. A space elevator race could ensue between nation-states.
2. An agreement might be forged to share costs and build an international space elevator, the advantage being that no individual nation-state gains an overall advantage.
3. Agreeing amongst themselves not to build it at all, which would suggest a conspiratorial component historically uncharacteristic of such entities.

 

[mugaliens]

OK, we make the cable, how are we supposed to get it to the earth.

You build the geosynchronous location, along with the counterweight, then slowly lower the cable while simultaneously extending the counterweight further out. Once the cable is anchored on Earth, you can extent the counterweight further in order to apply tension along the length of the cable.

 

[DaveC426913]

You build the geosynchronous location, along with the counterweight, then slowly lower the cable while simultaneously extending the counterweight further out. Once the cable is anchored on Earth, you can extent the counterweight further in order to apply tension along the length of the cable.

You stopped reading halfway through his sentence. He explains why he thinks getting it to Earth might be problematic.

 

[Phrak]

There are about 400 satellites in geosynchronous orbit. At present, launch costs run from $4K to $40K per kilogram dependent upon dependability of launch. Taking $10K/kilogram cost as a near-future cost for rocket launches, how much will the cost equivalent of a space elevator be to amortize 4000 satellites to break even with rocket lauch profits? (Hint: you need to know the average mass of a satellite.)

 

[Phrak]

The folks I work for make boxes that cost the customers x dollars apiece. At the premium launch dependability demanded, the customer pays 0.2x to get it to orbit. For this particular component, launch cost is only 1/5 of payload cost. I don't see any significant economic advantage for a marginal price break to develop this technology.

 

[mugaliens]

Agreed, Phrak - Not in the case of your customer and their product, no.

Before anyone, private or government, begins to work in ernest on the space elevator, there will have to be demonstrable economic benefit over current Earth to LEO launch platforms.

It's not necessarily a pipe dream, but it's both a long way off, and may never be economically viable.

One principle tenet of management is to ensure technology is developed in support of business goals, principles, and practices, and never becomes a driver of those business rules. This holds as true for the space program as it does for Company X looking to upgrade aging computer systems. Define the need, then find the best solution.

Occasionally, it'll be something as exotic as the space elevator! Given the fact my alma mater's entire computing storage across all university and student-owned storage passed the 1 TB hurdle in 1986, I agree that a 1 TB external hard sitting on my desk is ridiculous! Yet I have two of them. Go figure.

But I didn't buy them because they existed. I bought them because I do daily incremental, and weekly full backups of my computer's 120 GB hard drive, of which about 80 GB is full of user data. I swap out the TB drives weekly, storing them off-site, as I've literally decades of data on them.

I bought them because my needs were such that I needed two 1 TB drives, not because 1 TB drives were "cool," or that I had money to blow. They're simply a safe and effective tool to ensure my computing requires would continue relatively unabated in the event of theft or fire.

Given that my off-site storage is only a mile away, however, I think I'm pretty susceptible to nuclear holocaust...

...but I'm hoping and praying against all hope that will never be the case! LoL!

Back to the space elevator concept: Noteworthy concept! Proponents must learn that technology doesn't drive adoption. Econonomics drive adoption. If it's cheaper in the long run, and only well-proven to be so, it will be adopted. Otherwise, it will remain a "gee whiz" technology, neat, but not economically useful.

 

[dr dodge]

an elevator space race...could you imagine
the satelites would have to be swerving around like a race at sears point.
the Earth would look like a daisy from space.

can a geosat have an eliptical orbit, or will they always be a (somewhat) perfect circle?
what linear distance is the actual wobble of the earth?
we'd need to handle that slack, and keep a constant even tension

dr

 

[mgb_phys]

Proponents must learn that technology doesn't drive adoption. Econonomics drive adoption.

But sometimes technology drives economics.
Just like your Tb harddrives and fast internet connection chnages the economics of selling movies container ships change the economics of where you build stuff.

If you can put somethign into orbit for the same price as airmail it's likely to have some unforseen economic effects beyond what we currently use space for.

 

[mugaliens]

But sometimes technology drives economics.
Just like your Tb harddrives and fast internet connection chnages the economics of selling movies container ships change the economics of where you build stuff.

Oh, I agree! I wouldn't be working from home without it! However, technology is an enabler, not a driver. As an enabler, it's certainly changed the variables in the economnic equation of whether to work from home or sit in a corporate office.

If you can put something into orbit for the same price as airmail it's likely to have some unforseen economic effects beyond what we currently use space for.

Absolutely. Currently, space elevators are not technologically feasible. If/when they become technologically feasible, they may or may not ever become economically feasible.

Given unlimited funds we might accomplish all sorts of technical feats! However, our funds are limited, so we follow (more or less) the most economical approach.

As for our use of space, communication satellites were once considered the heat, but advances in fiber optics (the ocean floors are littered with them) have resulted in fiber carrying nearly all global communication traffic. NASA would love to sell you space, but aside from exploring, there's exceedingly little space offers at economically more favorable rates than we can achieve here on Earth. As for manned exploration, those unmanned Martian rovers are still kicking!

 

[Phrak]

Otherwise, it will remain a "gee whiz" technology, neat, but not economically useful.

It's pretty 'gee whiz' to me, otherwise I wouldn't be posting to see if someone can show me wrong.

But I still want to see the equations for things like required tensile strength and things like that (this is, after all a physics forum) so I don't have to derive them.

(And what would the unloaded diameter of the cable be as a function of height such that each element of the cable is under the same tension, anyway?)

 

[mgb_phys]

but aside from exploring, there's exceedingly little space offers at economically more favorable rates than we can achieve here on Earth.

If transport was cheap enough there a bunch of alloys and materials that would be easier to make in zero G, access to infinite vacuum and cold might also be handy industrially.

It's going to have to get a lot cheaper than the Shuttle though !

 

[Gfellow]

there will have to be demonstrable economic benefit...
Proponents must learn that technology doesn't drive adoption. Econonomics drive adoption. If it's cheaper in the long run, and only well-proven to be so, it will be adopted. Otherwise, it will remain a "gee whiz" technology, neat, but not economically useful.

Finding an immediate economic reason would be nice and I'm sure that there are SE proponents who might expand on that, but as unpopular as my comment might be, the foremost priority is tactical. If it is not an international effort, some nation state - US, China, Japan, will make the move. Whoever does it will insist it is economic in nature, but the fact is that the owner of the SE gets to decide what goes up.

 

[LURCH]

This is an area of lively study. The cable is heap big flexible and can be maneuvered. Simulations have been done that show the cable can be moved out of the way of any satellites. (Don't assume that it is as simplistic as I describe. There's a lot more to it.)

I do believe it is possible, and even probable, that the materials to build a space elevator will soon be developed. However, the simple construction of an inanimate tether would be a gargantuan engineering challenge. The idea that we could ever build one that spends its entire operational life performing a combination of dodge ball and hula dance is beyond the limits of mike credulity.

At this point putting a space elevator on Mars is the equivilent to putting a Starbucks there. When it does become possible it will probably be ancient technology.

The beanstalk on Mars would have the same problem I'm concerned about with an Earth based system, but on steroids: the satellite it would have to dodge is Phobos!

 

[DaveC426913]

The idea that we could ever build one that spends its entire operational life performing a combination of dodge ball and hula dance is beyond the limits of mike credulity.

Based on what? Your intuition?

How many satellites is the cable actually likely to encounter?

Consider that, with all the satellites we currently have in orbit, we almost never have collisions. We almost never worry about the ISS colliding with anything.

Granted, the cable is a line instead of a point, which multiplies the odds. But what do you get when my multiply "very-nearly zero" by even a largish value? You get "something a little more than zero".

Your intuition is not a reliable yardstick in this case.

 

[mugaliens]

If transport was cheap enough...

Aye, there's the rub.

It's going to have to get a lot cheaper than the Shuttle though !

Unfortunately, it will require several hundred heavy lifts simply to construct it! That doesn't seem to daunt http://www.liftport.com/" , however. Their FAQs page addresses most of the concerns raised here.

 

[LURCH]

Based on what? Your intuition?

Based on the rarity of any extremely complex system operating perfectly 100% of the time.

How many satellites is the cable actually likely to encounter?

A few thousand (nearly every satellite that isn't in geosynchronous orbit), and each one repeating over and over, ad nausium.

Consider that, with all the satellites we currently have in orbit, we almost never have collisions. We almost never worry about the ISS colliding with anything.

Granted, the cable is a line instead of a point, which multiplies the odds. But what do you get when my multiply "very-nearly zero" by even a largish value? You get "something a little more than zero".

It's not the geometry of the cable that makes the biggest difference, but the fact that it is stationary. Every satellite that is below geosynch (and not in some orbital period that is a factor of 24hr) must eventually pass through the space occupied by the cable. That's somewhere around 3,000 to 5,000 satellites (at a rough guess), each one repeating the encounter thousands of times. That's millions of encounters that must be avoided, and a single failure would spell disaster.

Your intuition is not a reliable yardstick in this case.

No-one's intuition, whether based on pecimism or wishfull thinking, is a reliable yardstick in this case.

 

[ShotmanMaslo]

All space elevator concepts don't require currently unfeasible high tensile strenght materials. The Launch Loop substitutes tensile strenght with kinetic energy of moving belt, so no new materials need to be developed.

I think the best alternative would be either the launch loop, electromagnetic mass drivers, or heavy lifters (150 tons or more). Of course I am not talking about satellite lifts, current rockets are enough for them, but things like space stations, tourism, moon colony, asteroid mining.. cannot be feasibly acomplished with current rocket technology.

 

[FredGarvin]

The Launch Loop topic has really injected a dose of reality to this thread

 

[DaveC426913]

Every satellite that is below geosynch (and not in some orbital period that is a factor of 24hr) must eventually pass through the space occupied by the cable.

That's not true.

 

[Phrak]

Um. How about every satellite or orbital debree that is below geosynchronous orbit, whose period is irrational with respect to a sidereal day, will eventually thread the space occupied by the cable?

Of course it could take good a while to sweep out enough area, and other collisions, solar wind, and perturbations have been ignored in the argument.

What's the diameter of the cable?

 

[DaveC426913]

What's the diameter of the cable?

A couple of metres.


[ EDIT: No idea. ]

 

[wolfkeeper]

The Launch Loop topic has really injected a dose of reality to this thread

Space elevators currently are impossible to build; the carbon nanotube *cable* doesn't exist to do this right now; not even 6 inches of it. The strongest engineering materials available can't build the space elevator.

So far as anyone has been able to show, launch loops are actually possible right now, and fairly economic as well.

Basically, space elevators are a very elegant idea; but elegance isn't enough.

With space elevators if you get past the materials problem, there's the space radiation problem lurking- space elevators are only good for cargo because the van Allen belts are like experiencing continuous dental x-rays for several days; you wouldn't *quite* get radiation sickness unless the elevator car broke down, but it's far, far above permitted limits. The materials or techniques to shield humans better don't exist either (until you get to very, very big and very, very expensive space elevators), existing materials would be too heavy.

Launch loops have the same problem to some degree; the radiation is annoyingly high; but launch loops payloads traverse the belts *very* fast and the radiation limits aren't exceeded.

 

[ShotmanMaslo]

Space elevators currently are impossible to build; the carbon nanotube *cable* doesn't exist to do this right now; not even 6 inches of it. The strongest engineering materials available can't build the space elevator.

So far as anyone has been able to show, launch loops are actually possible right now, and fairly economic as well.

Basically, space elevators are a very elegant idea; but elegance isn't enough.

With space elevators if you get past the materials problem, there's the space radiation problem lurking- space elevators are only good for cargo because the van Allen belts are like experiencing continuous dental x-rays for several days; you wouldn't *quite* get radiation sickness unless the elevator car broke down, but it's far, far above permitted limits. The materials or techniques to shield humans better don't exist either (until you get to very, very big and very, very expensive space elevators), existing materials would be too heavy.

Launch loops have the same problem to some degree; the radiation is annoyingly high; but launch loops payloads traverse the belts *very* fast and the radiation limits aren't exceeded.

I agree, Launch Loops are more possible now because they don't require sci-fi materials. Engineering problems can be overcomed, but if you don't have material with enough tensile strenght, cable approach is just a no go...

Why would you want to go through van Allen belts? LEO is almost completely under them. And Launch Loop will certainly not be higher than 80 km..

 

[wolfkeeper]

I agree, Launch Loops are more possible now because they don't require sci-fi materials.
Why would you want to go through van Allen belts?

You don't particularly, but you don't have *that* much choice.

LEO is almost completely under them.

Yes, there's no way to get directly to LEO from a space elevator of course, you have to go to GEO first. Well, you can, you can go up an elevator with a rocket ~1000km and then go from there, single stage. It's quite a small rocket actually, because of the height and lack of atmosphere.

And Launch Loop will certainly not be higher than 80 km..

Yup. But Lofstrom's launch loops are sized to throw to escape velocity. You can use them to reach LEO as well, but you really want to go to escape because that allows you to reach the moon, Mars etc. LLs also don't like being off the equator that much due to coriolis effects, but it's probably not a show-stopper to put them elsewhere, it just costs a bit more.

 

[dr dodge]

I just researched the launch loop.
again, all I can say is...
how is that any more do-able than the elevator?

1200 miles long and hanging 50 miles in the air

rockets and aerospace investment is still way more cost effective

dr

 

[wolfkeeper]

Launch loops scale much better than rockets.

If you want to build a bigger rocket, you pretty much need a clean sheet of paper; rockets scale badly, you have to redesign *everything*.

If you want a bigger launch loop, you just build more cable; the same design of cable.

And launch loops are not currently impossible (so far as anyone knows, space elevators ARE currently impossible).

Magnetic bearings have no known upper speed limit, so launch loops have a much higher rotor velocity than rockets' exhaust- a launch loop is fully reusable and single stage to escape velocity; rockets are 3 stages to escape, and expendable.

 

[ShotmanMaslo]

rockets and aerospace investment is still way more cost effective

dr

For launching satelittes, yes. But for space colonisation and tourism, it is not enough. I don't think it will ever achieve few dollars per kg launch cost like space elevator (launch loop) approaches. Even with huge 200+ t rockets, it may be far more expensive.

 

[wolfkeeper]

For launching satelittes, yes. But for space colonisation and tourism, it is not enough. I don't think it will ever achieve few dollars per kg launch cost like space elevator approaches. Even with huge 200+ t rockets, it may be far more expensive.

Don't believe the hype; space elevators won't realistically reach those numbers for a long, long time, if ever.

Most of the costs are infrastructure. The space elevator is only cheap at really *enormous* launch rates, after operating at maximum capacity for years. Launch loops can handle higher launch rates, are probably cheaper to make in the first place and the energy cost is pretty similar (a bit higher, the space elevator steals energy from the Earth's rotation as it launches).

Incidentally, unlike space elevators, launch loops can be made subscale; they can be used as a first stage for rockets. Rockets get a *lot* more efficient if you give them initial altitude and lots of speed; when they take off from the ground they're horribly inefficient until they reach about Mach 3 or so.

That also makes launch loops advantageous; because you can start small.

 

[ShotmanMaslo]

Don't believe the hype; space elevators won't realistically reach those numbers for a long, long time, if ever.

Most of the costs are infrastructure. The space elevator is only cheap at really *enormous* launch rates, after operating at maximum capacity for years. Launch loops can handle higher launch rates, are probably cheaper to make in the first place and the energy cost is pretty similar (a bit higher, the space elevator steals energy from the Earth's rotation as it launches).

Incidentally, unlike space elevators, launch loops can be made subscale; they can be used as a first stage for rockets. Rockets get a *lot* more efficient if you give them initial altitude and lots of speed; when they take off from the ground they're horribly inefficient until they reach about Mach 3 or so.

That also makes launch loops advantageous; because you can start small.

By "space elevator" I meant launch loop too, which is a type of space elevator (I had misquoted dr dodge, edited now..). Yes, they are the best and only realistic choice now, compared to other designs. :)

 

[wolfkeeper]

By "space elevator" I meant launch loop too, which is a type of space elevator (I had misquoted dr dodge, edited now..). Yes, they are the best and only realistic choice now, compared to other designs. :)

Hopefully.

Still, nobody has even built a launch loop a few feet across yet, never mind thousands of miles.

 

[Phrak]

So far as anyone has been able to show, launch loops are actually possible right now, and fairly economic as well.

Let me get this right about a Launch Loop.

If I have a section of steel 2 inches wide and 0.3 inches thick, as stated, moving at some xxx meters per second, according to the original published paper, this steel will tend to pull upward due to centrfugal force. (And yes, I know it's a Newtonian pseudoforce. Let's not get into that, please.)

So, if I take a gyroscope made of a steel band 2 inches by 0.3 inches and spin it up to the same velocity, xxx, it will lift off the Earth, right?

 

[wolfkeeper]

Let me get this right about a Launch Loop.

If I have a section of steel 2 inches wide and 0.3 inches thick, as stated, moving at some xxx meters per second, according to the original published paper, this steel will tend to pull upward due to centrfugal force. (And yes, I know it's a Newtonian pseudoforce. Let's not get into that, please.)

Nope. In this case it's the reactive centrifugal force- it's a REAL force. It's NOT a pseudoforce. It's pushed up by the curvature of the cable forcing the rotor downward more than it would naturally fall under gravity, and that pushes the sheath upwards.

So, if I take a gyroscope made of a steel band 2 inches by 0.3 inches and spin it up to the same velocity, xxx, it will lift off the Earth, right?

If you mean a small gyroscope, no it won't. The curvature of the cable has to be substantially vertical and the force holding the gyro together must be external, not a solid disk, and the external stuff doing that has to be free to move.

 

[ShotmanMaslo]

Let me get this right about a Launch Loop.

If I have a section of steel 2 inches wide and 0.3 inches thick, as stated, moving at some xxx meters per second, according to the original published paper, this steel will tend to pull upward due to centrfugal force. (And yes, I know it's a Newtonian pseudoforce. Let's not get into that, please.)

So, if I take a gyroscope made of a steel band 2 inches by 0.3 inches and spin it up to the same velocity, xxx, it will lift off the Earth, right?

Imagine the cable as a stream of particles - because only its own tensile strenght is insufficient to hold it together against the gravity in the scale of Launch Loop, it actually is a "stream of particles", holding against gravity by its kinetic energy, not tensile strenght.

 

[dr dodge]

don't you still end up with a cable that's 1300 miles long, only supported on the ends?
then same said cable only can support itself when under velocity of rotation?
and this same cable has added mass of an outer cover?
now do you build it? you don't just get out a cherry picker and hoist a crew of men 50 miles in the air? small army of blimps?
I just don't get this one.

Why not take a surplus B52 and launch rockets off of them?

dr

 

[wolfkeeper]

don't you still end up with a cable that's 1300 miles long, only supported on the ends?
then same said cable only can support itself when under velocity of rotation?
and this same cable has added mass of an outer cover?
now do you build it? you don't just get out a cherry picker and hoist a crew of men 50 miles in the air? small army of blimps?
I just don't get this one.

You start in the middle with a small loop and move outwards, growing it as you go.

Why not take a surplus B52 and launch rockets off of them?

dr

B52s don't go fast enough or high enough to make the rockets significantly smaller.

With a launch loop, you don't need rockets at all- it can throw to escape velocity.

 

[dr dodge]

You start in the middle with a small loop and move outwards, growing it as you go..

so, you are saying that we would need to fly in the air at about 26,000 ft, loop the cable between 2 points, start its rotation, then slowly increase the distance to 1200 miles. then attach it to the 50 mile tall sign posts. If the cable stops, breaks, or needs to be repaired, we repeat this process. Then, install the track/sleath/assembly.
how do you start with a long cable, get it up to speed, then put the outer covering assemblies without stopping the cable?
I am seriously not getting this is any more able to be built than the elevator, or for that matter the transporter beam.
but maybe I just don't understand completely, that I will admit

dr

 

[wolfkeeper]

so, you are saying that we would need to fly in the air at about 26,000 ft

No, you do it on the ground, you lay the cable straight along the ground, stationary, and then you go to the mid-point and put deflection sections either side, and put some supports under it so it forms an arc. Just a small one a few tens of feet long or whatever.

Then run the rotor up to speed, and you can remove the supports.

Then you move the deflection sections progressively outwards.

It's a bit fiddly because the deflection sections have to be vacuum tight and the deflection sections have to grow bigger as you move them apart because they're supporting more cable.

 

[dr dodge]

but during this whole thing, you can not stop the rotation, and must have the whole loop of cable already attached, then add more mass to the assembly while maintaining constant critical velocity.

correct?

dr

 

[DaveC426913]

I always thought these things were a bomb just waiting to go off. There is so much stored energy, and it's so delicately balanced that, if anything goes wrong, the whole thing explodes.

 

[wolfkeeper]

Well, it's tied down to the ground, so it can go significantly faster than the minimum speed. If you go slower than the minimum speed then it falls down.

And you certainly can't stop it; there's enormous kinetic energy there, even if you stopped putting energy in, it would stay up for perhaps weeks or months, depending on details of the design.