Space elevator ? How can it work?

[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.

 

[wolfkeeper]

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.

Potentially. And that's true of cars and aeroplanes, rockets.

Basically anything with enough energy to get you around fast can sometimes release it very quickly and kill you.

There are design details that can minimise the chances of a loop failing. It's probably a lot less likely to fail than a rocket, if you overbuild a rocket it doesn't make orbit. With launch loops it should be possible for it to be built very conservatively. It's held together with magnets and magnets can have a very good strength/weight ratios, so you have performance in hand that you can spend beefing things up.

 

[dr dodge]

rockets, cars, and airplanes are not 1200 miles long so the area of effect is greatly decreased
what kind of linear velocity does the cable have?
when you suddenly attach the projectile, how do you keep that velocity up inless the thing has a massive amount of inertia, or lots of power on reserve?

dr

 

[wolfkeeper]

The launch loop cable's rotor moves at 14km/s (i.e. well above escape velocity!)

When you launch stuff you need to feed in power equal to the energy needed for the vehicle, allowing for losses. This is a few hundred megawatts of power.

 

[Phrak]

wolfkeeper, ShotmanMaslo; thanks guys.

And I finally found the original paper by Keith Lofstrom, that explains the idea very well.

http://launchloop.com/LaunchLoop?action=AttachFile&do=get&target=launchloop.pdf"

"Imagine a stream of water from a hose pointed at an angle into the sky. Neglecting effects of air friction, the stream forms a continuous parabolic arc, the ballistic trajectory of the individual particles in the stream. ... If a flat plate is brought up against the stream at a slight angle downward, the stream is deflected downward, putting an upward force on the plate. In this way, the moving stream may be used to support a stationary weight."

 

[SpaceShaft]

See the proposed space elevator by Prof. quine of the York university in Canada.

http://www.ctv.ca/servlet/ArticleNews/story/CTVNews/20090724/space_elevator_090725/20090725?hub=SciTech

and

http://alumni-matters.blog.yorku.ca...ith-space-elevator-reaching-20km-above-earth/

I know that Astronuc is reluctant having me write about these topics, however I feel this type of information should be mentioned in this forum since it is directly related to the discussion being held.