Space elevator ? How can it work?

[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

 

[DaveC426913]

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

Sure. Am I on your team now?

No, the onus is on you to show that you've thought this through.


Everything else you posted simply restates your original claim, without addressing the problem that the bouyancy effect on your tower is limited to a small fraction of its height.

 

[DaveC426913]

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.

I read this as:

We have a solution for which a problem does not yet exist.

 

[russ_watters]

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.

I understand you used km, but it doesn't have any impact on the calculations I did this morning, so it doesn't have any impact on the issues.

In any case, I'm still not sure that you understand that a 100 km (or even 100 mi) high tower doesn't have a whole lot of value. More to the point, it doesn't satisfy the goal of a "space elevator", which is to lift a payload into orbit. It isn't' clear to me that you understand that just lifting a payload to 100 km doesn't mean that that payload is in orbit. Could you explain what you think the value of a 100 km tower is? What happens to the payload when it gets to the top of the tower?

 

[DaveC426913]

What happens to the payload when it gets to the top of the tower?

This is what I've been asking. Several times now. Strangely, answers are not forthcoming.

 

[dr dodge]

what happens at the top?
Momentum will carry it past its bouyancy point, then it will fall back down the hole, only to float back up with less velocity, and eventually come to a stop floating around in the air.
I feel we are wandering further and further from (reasonable) realities
and ya'll called some of my ideas "crackpot"

dr

 

[DaveC426913]

what happens at the top?
Momentum will carry it past its bouyancy point,

There is no momentum at that point. The rise is slow and, since there's vacuum, it's all dead-weight.

 

[Gfellow]

I agree with SpaceShaft. A very interesting thread.

 

[SpaceShaft]

russ_watters you state that:

"it doesn't satisfy the goal of a "space elevator", which is to lift a payload into orbit."

are you implying that a CNT tether based space elevator will put things in orbit?

if yes can you explain how? since I don't believe that will be the case.

 

[russ_watters]

russ_watters you state that:

"it doesn't satisfy the goal of a "space elevator", which is to lift a payload into orbit."

are you implying that a CNT tether based space elevator will put things in orbit?

if yes can you explain how? since I don't believe that will be the case.

The goal of a space elevator (whatever it is made of) is to lift objects to about 22,000 miles, where just by being there puts them in geostationary orbit.

Could you explain what you think the purpose of a space elevator is? By now, I'm pretty certain you have no idea, since after repeated requests, you have yet to explain what your ideas goal is/what it does.

The opening paragraph of your website says:

At this website we want to introduce a new method for reaching orbital space. From the employment of this method, a resulting structure can be deployed, which can be definitely cataloged as a Space Elevator.

This implies you think that "reaching orbital space" (presumably, you mean the height of a low-earth-orbit satellite: 110+ miles) accomplishes something useful. Tell me what you think it accomplishes!

One of your drawings appears to show a space shuttle docked with it...

 

[SpaceShaft]

I have discussed this matter with other participants at the conferences. Bringing up stuff up to the counterweight at GEO means only to pile stuff at that altitude. The CNT tether, just like the SpaceShaft only brings things to a certain altitude from where they have to be launched.

Only Rockets are capable of fulfilling both requirements. That is; bringing a payload up to an operational altitude and giving the object enough velocity to make of it a satellite capable of counteracting gravity.

I will like to point out that in the event that deployment of a CNT tether to GEO Is unfeasible the only “plan B” out there is the SpaceShaft. It may not be as sexy as the popular system but it will work.

To your question: Basically it accomplishes the same thing.

 

[russ_watters]

That's what I thought: You don't get it and you aren't listening. Here it is for the last time:

Bring an object up to 100 miles and it falls back to earth, accomplishing nothing (well - unless the goal is to dig a big hole).
Bring an object up to 22,000 miles and it is in orbit, which is very useful.

The idea that things "pile up" at the top of a space elevator is very silly, since it only takes very small thrusters to move objects around the globe once in orbit at the top of a space elevator. That's nothing compared to the massive rockets required just to achieve orbit after leaving the top of your tower.

Here is the wiki on space elevators, and you really should read it: http://en.wikipedia.org/wiki/Space_elevator

You've made other conceptual errors that you should want to correct ("Bringing up stuff up to the counterweight at GEO" is also wrong - read the wiki and learn for yourself what is wrong about it)and it willl help as a starting point for learning about space elevators. You need to start from scratch because what you think know now is worse than knowing nothing: what you think you know now is basically all wrong.

This thread has become all crackpot nonsense and is therefore locked.