Space elevator ? How can it work?

[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.

 

[DaveC426913]

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.

Hm. Those articles are not nearly so informative as I'd have liked.

The first one is simply a pop news article flogging the concept and application of space elevators to the layreader; there's no details at all.

The second isn't about space elevators at all; it's about some sort of high altitude tower.

 

[SpaceShaft]

look at these other site, the math of the claims are to be posted in a near future

http://spaceshaft.org

 

[russ_watters]

You posted that link before and quite frankly, it is just awful. The most basic problem with it is that it is far too short to be useful. Beyond that, though, I'm not sure how you would propose to build a 6x6x6m cube with the structural integrity required to lift a 100km tower!

 

[DaveC426913]

You posted that link before and quite frankly, it is just awful. The most basic problem with it is that it is far too short to be useful. Beyond that, though, I'm not sure how you would propose to build a 6x6x6m cube with the structural integrity required to lift a 100km tower!

I have read as much as I can manage. Perhaps you could help me out.

What exactly is the force/mechanism by which the cargo is lifted? I'm thinking the bouyancy of vacuum but I'm not sure how he's tapping it.


[ EDIT ]
Oh I see. He never actually says so but clearly the "hypercubes" are evacuated. This gives them a bouyancy of (1.2kg/m³ * 6³m³) = 260kg (at sea level).

So he's allowing 160kg for structural integrity, and 100kg for cargo (at sea level. At 200km of course, they will have zero bouyancy, so will weigh 260kg).

Which means he's going to build an 'H'-shaped container of 216m³ that will withstand ( 240"x240"x6 x 14.7psi ) = 2,540 tons of pressure using a mere 160kg of materials.

 

[russ_watters]

...unless they are filled with helium, which takes care of the vacuum issue but not the issue of supporting the tower. One convenient assumption made in the calcs is that the atmosphere is a constant density - sea level density. But for this problem, if you are going to assume a constant density, it would be much more accurate to assume zero density!

 

[DaveC426913]

...unless they are filled with helium, which takes care of the vacuum issue but not the issue of supporting the tower.

Hm. OK. That muxh helium only weighs 36kg.

One convenient assumption made in the calcs is that the atmosphere is a constant density - sea level density.

That would be a disastrous assumption...

 

[SpaceShaft]

wow! you guys are getting close to the solution.

 

[SpaceShaft]

but not quite yet :)

 

[SpaceShaft]

russ, the descriptions placed on the website (spaceshaft.org) are very simplified, although the altitude of 100 km is mentioned it is only to illustrate the uptrhusting mechanism and power of the system. I can assure you that there are several ways to increase the upthrusting force. One of the unmentioned characteristics of the system is that it is telescopic, therefore an internal shaft with 100 m in diameter will be surrounded by a number of other concentric shafts that will never reach space. For sure the core shaft can easily go beyond 100 km, but at this time is not really meant to be that way. A hint all proposed technologies are based on maritime technologies, I am not an aerospace guy, I just started on this, soon I will put some figures to chew on.

 

[russ_watters]

How much further than 100km, exactly do you thnk it can go?

 

[DaveC426913]

Yeah, SpaceShaft, above a few dozen km your bouyancy effect drops to near zero, so everything above that is dead-weight, and you're still only a fraction of the way to operating altitude.

Question: what happens to the cargo at-altitude? It has 0 orbital velocity, which is about 25,000mph shy of orbital velocity.

 

[SpaceShaft]

DaveC426913, write down your estimates, I will look at them.

But consider the following. We are speaking of a buoyant system and, as with any balloon, the first thing to do is to select the altitude at which we want it to operate or reach, from there the system is then designed.

For example with a zero pressure balloon; 1) Get the mass of material for the shell, the gas, and payload. 2) Estimate the required spherical diameter be expanded for buoyancy. Note that many agencies (NASA, ESA …) have balloons with payloads of 100kg, 200kg, ... and are well documented on the internet.

By the almost same mechanism super-pressurized balloons are designed, this is also well documented. (super-pressure balloon have shells that are already expanded to its full at launch time).

make a stack of such balloons. Assuming that the top one will be buoyant to that x-altitude chosen, all the ones below add to the upthrust power. This is a observable fact, we agree on that I am sure.

Like with any spar buoy one portion of it will "float" out of the fluid from which is buoyant the other part will be below the waterline. of course you need to take into consideration if you want to either ballast the system or use anchoring to keep it upright.

Now consider again those science balloons, historically there are several that have reached +50km, with a payload of +/- 250kg, and instead of having the volume extend their geometries as a sphere, let us force the geometry into the shape of a disk of 1m in thickness. And stack them all for 50000 meters… , you do the math. And with this example I am not considering that the air density at ground level is far superior to that at 50km.

Also, even if we needed more upthrust, the easy option to do this of increasing the volume of the vessel, or if really necessary we really needed not thousands of tons but … of tons, we should not be just limited to the atmospheric pressures but the system could be deployed from underwater. Such a underwater technique will increase the upthrust efficiency x 1000, since sea water is about 1000 times denser than air.

I can understand the anxiety my claims can generate and how much people want to know more on how I am proposing to do this, but I can't give away all the answers, since I have some patent applications for the underlying tech.. The reason I am making the claims public is because there are other groups coming up with similar claims and generating the public belief that they may have been the first to bring up the idea, as is the case of the hyperlinked movies I provided.

NB do not expect me to respond to further postings until the week end since I will not be available. Best regards

 

[russ_watters]

It's not anxiety, it is incredulity since you haven't even done the most basic math required to validate your idea and you don't seem to understand that a 100 mile tower doesn't allow your payload to achieve orbit!

 

[russ_watters]

Yeah, SpaceShaft, above a few dozen km your bouyancy effect drops to near zero, so everything above that is dead-weight, and you're still only a fraction of the way to operating altitude.

Question: what happens to the cargo at-altitude? It has 0 orbital velocity, which is about 25,000mph shy of orbital velocity.

Well...at 100 miles altitude, if the tower is located at the equator it will have a speed of 1063 mph and need a speed of 17,500 mph (orbital speed is less than escape velocity), but yeah, you nailed the problem. The vast majority of the energy required is to gain the speed, not the altitude.

I'm loath to do other peoples' math for them, but in the interest of putting to bed this rediculous claim, there is an easy way to calculate the maximum height of a buoyancy-lifted tower. Air pressure at sea level is 101,325 N/sq meter. That means the total weight of the 1 sq meter column of air and thus the total buyant force is 101,325 N. So you just divide that by the unit mass of your tower. Ie, in terms of mass, 101,325/9.8= 10339 kg. If Dave did the math right in finding the 6x6x6m cube has a mass of 160 kg (not including if it is filled with anything to make it rigid or a payload), that's 0.7 kg/cu meter. So dividing, the tower has a maximum height of 10339/0.7=13,958 m or just under 14 km.

Even easier, SpaceShaft, you should try calculating the maximum height of a steel or titanium cable (your guy wires) before it snaps under its own weight...

 

[SpaceShaft]

Hey Russ, thank for figures, please note this is just a quick reply, therefore my apologies for its qualitative nature.

Just a couple of points. Within the description we speak of kilometers and not of miles, although 100 miles is an altitude that can be reached, and is an altitude at which human made artifacts do operate it is not the (+/-) official boundary of space.
Second one of the proposed uses of a SpaceShaft is for the deployment of the CNT tether, the SpaceShaft on its own does not need a cable to operate.

Let me point out that the proposed tower with the name SpaceShaft is an extreme application example of what will become, hopefully, a more down to Earth tool for other uses, such as in enveloping buildings for maintenance, etc..

What we are ultimately proposing is the infrastructure for others to develop other applications, we do not aim to provide a full package of solutions, just to find other partners.

Again my excuses for not dedicating more time, right now, to respond