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space technology
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Master_Ghost_KnightContributorUser avatarPosts: 2750Joined: Sat Feb 21, 2009 11:57 pmLocation: Netherlands Gender: Male

Post Re: space technology

Netheralian wrote:
Master_Ghost_Knight wrote:Coarse as in, Ignore the effects of earths gravity, ignore the efects of the centrifugal force, ignore elasticity, ignore that the cable must be locked in position, ignore cable thikness, ignore colapse via shearing stress


That's a pretty poor calculation if you are ignoring the main loading factors. Space elevators are feasible based on the theoretical strength of Carbon Nanotubes - although there are clearly still some practical issues to resolve (manufacture of sufficient nanotube length and cost effectiveness namely). And what collapse via shear stress are you refering too? The cable is under tension and is flexible. You seem to be under some massive misaprehensions about what a space elevator is based on your earlier posts.

Why am I getting flack from ignorants for this?
The main loading factors is the cumulative column stress due to moons gravity, ignoring earths gravity isn't a farfetched aproximation (even because the claculations would lead to a virtualy higher loading factor), neither is to ignore the centrifugal force since the moon rotation is prety fucking low. Ignoring elasticity is a trivial thing to do since this sort of materials tend to break way before it stretches significatively enough to change the order of magnitude. Cable thickness is almost irelevant since the cables are relatively thin compared to the lenght (and so the divergent effect o gravity flow is almost null). The most significant factor that was excluded was the force requiered to keep the cable in place, I supressed that on purpouse so noone could say "hey nobody said that it need to be locked into place, or that must be done this way or that way". I supressed the sheering calculation becuse they are generaly lower and dn't fall to far (meaning that I am giving you the benefit for it to work). If I am the preform a rigurous calculation, it would take much more work than I am willing to put into it. I originaly taught that this couldn't be done and it would fall several orders of magnitude short compared to what would be requiered, but since everyone started to complain then I punched in some numbers and my rough calculation falled one order of magnitude shorter and so I conceded that it might be possible to do someway.
If you are willing to put your time into performing a more rigurous calculation I will not stop you. But the truth is nobody so far was even capable to preform such a thing. And my bet my ass that you can't do it either because you didn't even knew that cables could break due to sheering stress just by pulling them (only fragile materials tend to break due to normal stress, and that is where they get the definition of fragile).
"I have an irrefutable argument for the existence of...." NO, STOP! You are already wrong!
Mon Aug 16, 2010 1:17 pm
NetheralianUser avatarPosts: 357Joined: Wed Feb 25, 2009 3:13 pmLocation: Underwater world Gender: Cake

Post Re: space technology

Master_Ghost_Knight wrote:Why am I getting flack from ignorants for this?

Bold statement since you didn't ask for any credentials.

Master_Ghost_Knight wrote:
The main loading factors is the cumulative column stress due to moons gravity,

What column stress? You were discussing a space elevator. The entire cable is in tension. *

Master_Ghost_Knight wrote: neither is to ignore the centrifugal force since the moon rotation is prety fucking low.

...Except, that is not how a space elevator works - it is essentially a geostationary spacecraft with a tether to the ground (usually with a counter weight at the other end to maintain its orbital position. In the case of lunar space elevators, the lunar-synchronous point is replace with one of the Lagrangian points (L1 or L2) You seem to be missing the fundamentals here...

Master_Ghost_Knight wrote: If I am the preform a rigurous calculation, it would take much more work than I am willing to put into it.

Really - I don't care about a rigorous calc. However, you should at least understand the concept of what a space elevator is. You seemed to have jumped to some wild conclusion that is far removed from the commonly held understanding of what sort of structure this is.

Master_Ghost_Knight wrote: I originaly taught that this couldn't be done and it would fall several orders of magnitude short compared to what would be requiered, but since everyone started to complain then I punched in some numbers and my rough calculation falled one order of magnitude shorter and so I conceded that it might be possible to do someway.

Kudos for trying.

Master_Ghost_Knight wrote:But the truth is nobody so far was even capable to preform such a thing.

Because we don't need to. Perhaps you could have started your research at the websites linked by Ozymandyus.

Master_Ghost_Knight wrote:And my bet my ass that you can't do it either because you didn't even knew that cables could break due to sheering stress just by pulling them (only fragile materials tend to break due to normal stress, and that is where they get the definition of fragile).

Making an assumption about other peoples credentials just makes you look like an idiot. You might first want to realise that not everyone here is a student.


* Edit: In my haste I also forgot to mention (and its kind of a biggy) it's not a column!!!!! It's generally a ribbon.
Mon Aug 16, 2010 3:52 pm
sgrunterundtUser avatarPosts: 254Joined: Thu Dec 17, 2009 8:23 amLocation: Niels Bohr Institute, Copenhagen Gender: Tree

Post Re: space technology

Master_Ghost_Knight wrote:If you are willing to put your time into performing a more rigurous calculation I will not stop you. But the truth is nobody so far was even capable to preform such a thing.


Eh? I already did. Just for this I took the time an repeated it, since I used the back of an envelope last time so I can't find it.

So here is the correct calculation. Including a pretty picture I photoshopped up for the occasion:

Image

X1 (Center of Earth) = 0m
X2 (Center of mass for Earth-Moon system) = m/M*X5 = 4.73*10^6m
X3 (L1, point where gravity of Moon, gravity of Earth and centrifugal force cancels) = 3.26*10^8
X4 (surface of Moon) = 3.82*10^8m
X5 (center of moon) = 3.84*10^8m
w (angular frequency of rotation about X2) = 2.66*10^-6/s
M (mass of Earth) = 5.97 × 10^24 kg
m (mass of Moon) = 7.36 × 10^22 kg
G (gravitational constant) = 6.67 × 10^-11 m^3/kg/s^2

An object on the line between the two bodies centers and in rest relative to the rotating system feels a "gravitational" field of:

g = -GM/(X-X1)^2 + Gm/(X-X5)^2 + w^2*(X-X2)

Above consists of a term for the gravity from the Earth, a term for the Moon and one for the centrifugal force because the system is rotating (don't tell me it is not a force :))

Integrating this from X3 to X4 and plugging in the numbers gives 2.8*10^6m^2/s^2. As I said earlier that corresponds to about 285km under one g, you don't even need nanotubes for that
Last edited by sgrunterundt on Mon Aug 16, 2010 9:30 pm, edited 1 time in total.
Mon Aug 16, 2010 9:17 pm
Master_Ghost_KnightContributorUser avatarPosts: 2750Joined: Sat Feb 21, 2009 11:57 pmLocation: Netherlands Gender: Male

Post Re: space technology

Netheralian wrote:Bold statement since you didn't ask for any credentials.

Are you going to claim that I am wrong? In that case prove it!

Netheralian wrote:
Master_Ghost_Knight wrote:
The main loading factors is the cumulative column stress due to moons gravity,

What column stress? You were discussing a space elevator. The entire cable is in tension. * Edit: In my haste I also forgot to mention (and its kind of a biggy) it's not a column!!!!! It's generally a ribbon.

You don't even know what the hell was I talking about. Column stress in this particular case doesn't mean that the structure is a column, but rather the contribution of stress due to the integral contribution of weight over height, which is generaly independently of the width of the cable, sice t=F/A and F=A*int(R->H,pG)dz aproximatedly (where t=stress, F=force, A=section area, R=radius to surface, H=radius to total heigh, p= function of density of material, G= function of force of gravity felt over height, and int(A,b)dz is the integral of B on the domain A over z). Now here is the magic step t=A/A*int(R->H,pG)dz=int(R->H,pG) which means that width is completly neutral. Calling this "ribbon" is completly and uterly nonsense of he highest kind.
I will sugest that you shut up because you don't have the slightest clue what you are talking about.


Netheralian wrote:
Master_Ghost_Knight wrote: neither is to ignore the centrifugal force since the moon rotation is prety fucking low.

...Except, that is not how a space elevator works - it is essentially a geostationary spacecraft with a tether to the ground (usually with a counter weight at the other end to maintain its orbital position. In the case of lunar space elevators, the lunar-synchronous point is replace with one of the Lagrangian points (L1 or L2) You seem to be missing the fundamentals here...

What? Since when did I sugested that the space elevator would work via centrifugal force? Highlight that because I totaly missed it. Centrifugal force is there no matter how it works because we are working on a rotating frame of reference, if not for that there wouldn't be no orbits what so ever, there would be no L1 to L5, in fact the universe wouldn't make any fucking sense. It is there and it makes some difference, I just decided not to account it.

Netheralian wrote:
Master_Ghost_Knight wrote: If I am the preform a rigurous calculation, it would take much more work than I am willing to put into it.

Really - I don't care about a rigorous calc. However, you should at least understand the concept of what a space elevator is. You seemed to have jumped to some wild conclusion that is far removed from the commonly held understanding of what sort of structure this is.

I understand very well how it supoused to work thank you. You on the other hand decided to make an insultingly rediculous coment on something you don't have the slightest clue about. And I have to hear your bullshit when the only thing I have done was to say, "disregard what I have said because I underestimated their capabilities".


Netheralian wrote:
Master_Ghost_Knight wrote:But the truth is nobody so far was even capable to preform such a thing.

Because we don't need to. Perhaps you could have started your research at the websites linked by Ozymandyus.

What kind of answer is that? They have no enginnering plan, they have no predicted figures. And since when have we become group that just eats every shit that is spoon feed to us?

Netheralian wrote:Making an assumption about other peoples credentials just makes you look like an idiot. You might first want to realise that not everyone here is a student.

So what? I am don't hold that against anyone. What it does piss me of is some random guy who doesn't have the slightest clue of what is he talking about trying to rub ignorant statments on my face.
"I have an irrefutable argument for the existence of...." NO, STOP! You are already wrong!
Last edited by Master_Ghost_Knight on Mon Aug 16, 2010 9:54 pm, edited 2 times in total.
Mon Aug 16, 2010 9:26 pm
Master_Ghost_KnightContributorUser avatarPosts: 2750Joined: Sat Feb 21, 2009 11:57 pmLocation: Netherlands Gender: Male

Post Re: space technology

sgrunterundt wrote:Here is the correct calculation. Including a pretty picture I photoshopped up for the occasion:

Image

X1 (Center of Earth) = 0m
X2 (Center of mass for Earth-Moon system) = m/M*X5 = 4.73*10^6m
X3 (L1, point where gravity of Moon, gravity of Earth and centrifugal force cancels) = 3.26*10^8
X4 (surface of Moon) = 3.82*10^8m
X5 (center of moon) = 3.84*10^8m
w (angular frequency of rotation about X2) = 2.66*10^-6/s
M (mass of Earth) = 5.97 × 10^24 kg
m (mass of Moon) = 7.36 × 10^22 kg
G (gravitational constant) = 6.67 × 10^-11 m^3/kg/s^2

An object on the line between the two bodies centers and in rest relative to the rotating system feels a "gravitational" field of:

g = -GM/(X-X1)^2 + Gm/(X-X5)^2 + w^2*(X-X2)

Above consists of a term for the gravity from the Earth, a term for the Moon and one for the centrifugal force because the system is rotating (don't tell me it is not a force :))

Integrating this from X3 to X4 and plugging in the numbers gives 2.8*10^6m^2/s^2. As I said earlier that corresponds to about 285km under one g, you don't even need nanotubes for that


Calculation is wrong, what you did was to calculate the integral of aceleration over distance (look at your units) which makes abolutly no phisical sence what so ever. You missed the density of the tubes (or in this case the column density) that would increase the number by at least 3 orders of magnitude, and then it would be correct (if you did your calculations correctly).

And you don't see anything absurd with 285km under 1g of any material what so ever?
"I have an irrefutable argument for the existence of...." NO, STOP! You are already wrong!
Mon Aug 16, 2010 9:33 pm
sgrunterundtUser avatarPosts: 254Joined: Thu Dec 17, 2009 8:23 amLocation: Niels Bohr Institute, Copenhagen Gender: Tree

Post Re: space technology

Master_Ghost_Knight wrote:Calculation is wrong, what you did was to calculate the integral of aceleration over distance (look at your units) which makes abolutly no phisical sence what so ever. You missed the density of th tubes (or in this case the column density) that would increase the number by at least 3 orders of magnitude.


Sigh...

I am well aware of my units. I have reduced things like thickness out of the equation from the beginning since they don't matter to the final answer. Strength scales linearly with thickness and therefore weight. Feel free to multiply the whole thing with a cross sectional area and a density, you are going to divide by them again when checking for which material are capable of lifting it (which, as I said on page one, Spectra is). In other words: I calculated the necessary specific strength.

Specific strengt

But okay, we make it so that MGK can also understand it: Lets arbitrarily assume a cross section of 1m^2. Then we get a mass of rho*m^3 per meter of tether. Multiply this on the right side of the equation for acceleration and it equals a force per length, specifically how the change tension changes as we move along the tether. Integrate up and you get the maximum tension the tether has to bear assuming the minimum tension anywhere (at the surface) is zero.

Lets plug it in for Spectra fiber: 2800000m^2/s^2 * 1m^2 * 970kg/m^3 = 2.72*10^9N (okay to do like this because a constant factor does not change the integration)

This is the tension the tether has to bear at L1, admittedly a lot, but we are talking about one of the best comercially available syntetic fibers, at one square meter cross section, it is going to be strong. Lets calculate how much:

The strength of Spectra fiber is listed at 3.51Gpa. This times one m^2 gives... 3.51*10^9N, what do you know, it is strong enough! Just as I claimed from the beginning.

Now of course we would want to make it thinner, should I try again with 1mm^2? Do you think it will make a difference.

I apologize if I sound condescending, but my patience with people calling every one else ignorant while making very basic mistakes wears thin after a while.


Master_Ghost_Knight wrote:And you don't see anything absurd with 285km under 1g of any material what so ever?


Difficult yes, absurd no. It is quite a bit more than you average suspension bridge to say the least, but as I have shown it is actually within reach the demonstrated capabilities of commercial of-the-shelf fibers. Theoretically even without taper (which will be necessary in even the most optimistic case with nanotubes for the earth-space elevator). In reality you will of course want at least a factor of two safety margin, but that is easily done by tapering the tether (letting it be thinner near the surface where the tension is less).
Last edited by sgrunterundt on Mon Aug 16, 2010 10:28 pm, edited 1 time in total.
Mon Aug 16, 2010 9:58 pm
Master_Ghost_KnightContributorUser avatarPosts: 2750Joined: Sat Feb 21, 2009 11:57 pmLocation: Netherlands Gender: Male

Post Re: space technology

I'm starting to doubt about the people ability to read what I write.
I do not contest about the simplication of ignoring thickness, shit I did that.
What I contested about the figure was the total anihalation of mass on what supoused to be a calculation of "stress". I do conceed that it was my mistake to assume that you were actualy calculating stress (since that is what you generaly do on structural analysis, never a comparitive figure for specific strenght), and that you had made a novice mistake of trying to compare data (of stress) with an unrelatable measurment, my bad the calculation is then correct (for requiered specific strenght).
"I have an irrefutable argument for the existence of...." NO, STOP! You are already wrong!
Mon Aug 16, 2010 10:27 pm
NetheralianUser avatarPosts: 357Joined: Wed Feb 25, 2009 3:13 pmLocation: Underwater world Gender: Cake

Post Re: space technology

Master_Ghost_Knight wrote:Are you going to claim that I am wrong? In that case prove it!

I'm not going to start a pissing competition. Lets just look at your previous argument to demonstrate that you had no idea what a space elevator was.

1. Reply to Unwardi
Master_Ghost_Knight wrote:I don't think you comprehend the size of the structure, even without atmosphere, even with a smaler gravity the structre would still need to be several miles in heigh and I don't think there is even any kind of material capable of suporting that, we are talking millions of tones of materials that may not even exist,

Several miles high and millions of tonnes of material? Really - are you sure you know what a space elevator is?

2. Reply to Aeroeng314
Master_Ghost_Knight wrote:The L1 point is not even stable, secondly it is about 56300 Km over the surface of the moon, you can make your cable of whatever material you like, the cable will simply break just by standing there.

That's interesting, plenty of people think that this is entirely feasible and doesn't even require advanced composites - at least you seem to be heading in the right direction even if your guesstimate of the structural integrity of the cable is way off. There are resources out there if you cared to look. Here is a good starting point. http://en.wikipedia.org/wiki/Lunar_space_elevator
Sure - you backtracked on this by doing some calcs, but again, who knows what you were calculating.
I couldn't really care about the rest and neither do I need your approval to work professionally in the space engineering industry. Perhaps you could show some of your assumptions? Because at the moment it still looks like you could be calculating something totally unrelated. You expect people just to accept your word for it after you make statments like "several miles heigh [sic]" and "millions of tones"?

Master_Ghost_Knight wrote:
I understand very well how it supoused to work thank you.

Good for you - because it really doesn't look like it.

Master_Ghost_Knight wrote:What kind of answer is that? They have no enginnering plan, they have no predicted figures. And since when have we become group that just eats every shit that is spoon feed to us?

Did you try looking? Here is some resources for you. http://wiki.spaceelevator.com/Open_Wiki ... rch_Papers
There is even a document of a lunar space elevator: http://wiki.spaceelevator.com/@api/deki ... earson.pdf

Master_Ghost_Knight wrote:So what? I am don't hold that against anyone. What it does piss me of is some random guy who doesn't have the slightest clue of what is he talking about trying to rub ignorant statments on my face.

Except, you are the only one that referred to a space elevator as being "several miles in heigh [sic]" and "millions of tones".
Tue Aug 17, 2010 7:37 am
sgrunterundtUser avatarPosts: 254Joined: Thu Dec 17, 2009 8:23 amLocation: Niels Bohr Institute, Copenhagen Gender: Tree

Post Re: space technology

Master_Ghost_Knight wrote:my bad the calculation is then correct (for requiered specific strenght.


Excellent.

Now can we also establish that although the L1 point is unstable for an orbit it is not for a space elevator? The L1 is a saddle point, unstable in the direction joining the two bodies centers but stable in the others. If a slight tension is kept even down at the lunar surface and the cables center of mass will be slightly to the Earth side of the L1, then it will continually try to move towards the center line (where we want it) and towards Earth (where it is stopped be the tension anchoring it to the Moon.) It does not require a big structure fighting huge shearing stresses, just a cable doing what cables does best: resisting a tensile stress.

Master_Ghost_Knight wrote:I do conceed that it was my mistake to assume that you were actualy calculating stress (since that is what you generaly do on structural analysis, never a comparitive figure for specific strenght)


I am sorry, I am not an engineer. But breaking lengths and specific strengths are typically what is calculated when estimating feasibility of various space tethers and space elevators since it immediately tells you which materials are adequate for a specific purpose.
Tue Aug 17, 2010 8:28 am
Master_Ghost_KnightContributorUser avatarPosts: 2750Joined: Sat Feb 21, 2009 11:57 pmLocation: Netherlands Gender: Male

Post Re: space technology

Who the hell put sand in your vagina?
Netheralian wrote:1. Reply to Unwardi
Master_Ghost_Knight wrote:I don't think you comprehend the size of the structure, even without atmosphere, even with a smaler gravity the structre would still need to be several miles in heigh and I don't think there is even any kind of material capable of suporting that, we are talking millions of tones of materials that may not even exist,

Several miles high and millions of tonnes of material? Really - are you sure you know what a space elevator is?

at least 56300Km=34983miles.
About a minimal 563 tones assuming water density (which is not, it is more) and 1/100 of a square meter wide (knowing that the resistance for the tram comes from width, it is a very conservative estimate), so yeah I have exagerated on the weight by over 3 orders of magnitude, so sue me.
How the hell did you infer from that I don't have a clue on what it supoused to be is completly beyound me, special because you have put the redicule over the heigh and not the weight (which is what was absurdly hiperbolised), or do you think that the structure is neither incredebly lengthy or heavy?


Netheralian wrote:2. Reply to Aeroeng314
Master_Ghost_Knight wrote:The L1 point is not even stable, secondly it is about 56300 Km over the surface of the moon, you can make your cable of whatever material you like, the cable will simply break just by standing there.

That's interesting, plenty of people think that this is entirely feasible and doesn't even require advanced composites

Since when did I care of what other people think rather than know, specialy if what is provided isn't beyound presentations for layman and sci-fi?
It is not like I was unwilling to consider, shit I have changed my mind on the subject. I really can't see what the hell is your problem.

Netheralian wrote: - at least you seem to be heading in the right direction even if your guesstimate of the structural integrity of the cable is way off. There are resources out there if you cared to look. Here is a good starting point. http://en.wikipedia.org/wiki/Lunar_space_elevator
Sure - you backtracked on this by doing some calcs, but again, who knows what you were calculating.

I have underestimated the strenght of carbon nanotubes. I have mentioned specificly what I have calculated and I have retracted my statment. As far as I remember I didn't post any figures. What I said was, I retract my previous objections to this even though the problem isn't solved, the end. I no longer have a fish in this.
Now for some to say that it could be done from the start, claiming that my retractment of a counter claim was wrong because I have solved a simple problem (which by the way leaned at your favour) because I was not willing to put myself to the effort of literaly building the damn thing myself (and get flack for that), can only bring a word into my mind. Jackass!

Netheralian wrote:I couldn't really care about the rest and neither do I need your approval to work professionally in the space engineering industry.

Do you feel threatned by me?

Netheralian wrote:Perhaps you could show some of your assumptions?

The assumptions have been described. Go read it.
Netheralian wrote:Because at the moment it still looks like you could be calculating something totally unrelated. You expect people just to accept your word for it after you make statments like "several miles heigh [sic]" and "millions of tones"?

Since when have I made a statment and expected anyone to take my word for it? What part of "I was originaly talking out of my own ass" does it requier anyone to take my word for it? Explain it to me because I am curious.


Netheralian wrote:
Master_Ghost_Knight wrote:So what? I am don't hold that against anyone. What it does piss me of is some random guy who doesn't have the slightest clue of what is he talking about trying to rub ignorant statments on my face.

Except, you are the only one that referred to a space elevator as being "several miles in heigh [sic]" and "millions of tones".

:facepalm:
Netheralian wrote:What column stress? You were discussing a space elevator. The entire cable is in tension. ** Edit: In my haste I also forgot to mention (and its kind of a biggy) it's not a column!!!!! It's generally a ribbon

Netheralian wrote:
Master_Ghost_Knight wrote: neither is to ignore the centrifugal force since the moon rotation is prety fucking low.

...Except, that is not how a space elevator works - it is essentially a geostationary spacecraft with a tether to the ground (usually with a counter weight at the other end to maintain its orbital position. In the case of lunar space elevators, the lunar-synchronous point is replace with one of the Lagrangian points (L1 or L2) You seem to be missing the fundamentals here...

Netheralian wrote:And what collapse via shear stress are you refering too? The cable is under tension and is flexible. You seem to be under some massive misaprehensions about what a space elevator is based on your earlier posts.

Netheralian wrote:That's a pretty poor calculation if you are ignoring the main loading factors. (...) I don't care about a rigorous calc. However, you should at least understand the concept of what a space elevator is.
"I have an irrefutable argument for the existence of...." NO, STOP! You are already wrong!
Tue Aug 17, 2010 1:36 pm
Master_Ghost_KnightContributorUser avatarPosts: 2750Joined: Sat Feb 21, 2009 11:57 pmLocation: Netherlands Gender: Male

Post Re: space technology

sgrunterundt wrote:Now can we also establish that although the L1 point is unstable for an orbit it is not for a space elevator? The L1 is a saddle point, unstable in the direction joining the two bodies centers but stable in the others. If a slight tension is kept even down at the lunar surface and the cables center of mass will be slightly to the Earth side of the L1, then it will continually try to move towards the center line (where we want it) and towards Earth (where it is stopped be the tension anchoring it to the Moon.) It does not require a big structure fighting huge shearing stresses, just a cable doing what cables does best: resisting a tensile stress.

I conceed that it might be staticaly stable and dynamicaly marginaly stable (tending to stable considering dissipation on the cable flexibility), I am not sure how it will behave to the dynamics of imperfect orbits but lets assume that this doesn't present a problem (which isn't very far fetched with autocorrection mechanisms).
Edit: It is unstable unless it is straped to the ground (which isn't very hard to do).

Where are you going with this?
People seam to be under the impression that I still stand by "it can't be done stance".
Has everyone missed:
Master_Ghost_Knight wrote:Edit: Whit a coarse calculation, I guess you can technically do it with nanotubes, some other problems where aparent like how to keep the cable in it's place which will stress the cable even more, but I will entertain the concept that it is possible, go nuts...

?

sgrunterundt wrote:I am sorry, I am not an engineer. But breaking lengths and specific strengths are typically what is calculated when estimating feasibility of various space tethers and space elevators since it immediately tells you which materials are adequate for a specific purpose.

Well yes. Specific strenght is an important factor to consider, but structures are generaly build to carry loads which does not depend necessrily of the density of the material, and the aproval of project depends if the structure underload (which is generaly fixed) is sill in the elastic domain of the material. That is why I am not used to see specific strenghts as end results. But it does make sense in your cases since the only load we are considering is the self weight (which is proportional to the density) and facilitates the comparison of the behaviour of other materials trying to do the same job.
"I have an irrefutable argument for the existence of...." NO, STOP! You are already wrong!
Tue Aug 17, 2010 2:09 pm
Master_Ghost_KnightContributorUser avatarPosts: 2750Joined: Sat Feb 21, 2009 11:57 pmLocation: Netherlands Gender: Male

Post Re: space technology

pps. gravitical constant has sucessfully put League of Reason in the second place of google.com due to my post :P
Because I am an idiot and miss speled it.
"I have an irrefutable argument for the existence of...." NO, STOP! You are already wrong!
Tue Aug 17, 2010 2:19 pm
NetheralianUser avatarPosts: 357Joined: Wed Feb 25, 2009 3:13 pmLocation: Underwater world Gender: Cake

Post Re: space technology

Master_Ghost_Knight wrote:How the hell did you infer from that I don't have a clue on what it supoused to be is completly beyound me

That would be the several miles high (~4 orders of magnitude in height wrong) and millions of tonnes (another ~4 orders of magnitude wrong). That's a pretty fundamental error.
Tue Aug 17, 2010 2:27 pm
Master_Ghost_KnightContributorUser avatarPosts: 2750Joined: Sat Feb 21, 2009 11:57 pmLocation: Netherlands Gender: Male

Post Re: space technology

Netheralian wrote:
Master_Ghost_Knight wrote:How the hell did you infer from that I don't have a clue on what it supoused to be is completly beyound me

That would be the several miles high (~4 orders of magnitude in height wrong) and millions of tonnes (another ~4 orders of magnitude wrong). That's a pretty fundamental error.

What? Can you express in a number how much is several? Because I'm prety sure that is not a number but a iterjection to unspecify many. And yeah, weight 4 orders of magnitude wrong, sue me for using hiperboles.
"I have an irrefutable argument for the existence of...." NO, STOP! You are already wrong!
Tue Aug 17, 2010 2:31 pm
sgrunterundtUser avatarPosts: 254Joined: Thu Dec 17, 2009 8:23 amLocation: Niels Bohr Institute, Copenhagen Gender: Tree

Post Re: space technology

Master_Ghost_Knight wrote:Has everyone missed:
Master_Ghost_Knight wrote:Edit: Whit a coarse calculation, I guess you can technically do it with nanotubes, some other problems where aparent like how to keep the cable in it's place which will stress the cable even more, but I will entertain the concept that it is possible, go nuts...


(My bolding)

No I had not missed it. But it is a far cry from my position that it is quite feasible to do in a foreseeable future, with conventional materials.

Therefore I stated that:

sgrunterundt wrote:That must have been a very coarse calculation. Keep in mind that the gravity drops off quickly it does not stay 0.17g all the way to L1. When adding together the gravity of the moon and the earth and the centrifugal force of the rotating coordinate system and integrating it, I get a necessary specific strength of 2800 kN*m/kg (or a breaking length of 285km under one g). A commercial spectra fiber could do that. Without taper!

How do you get numbers that suggests it is only a far out theoretical possibility with nanotubes?

And of course as I already stated it is stable. The instability of L1 is in the direction along the line joining the two bodies (a little to close to one of them and you fall towards it). The other two axes are stable. That means in order to keep stability you just make the counter weight a little too heavy so that the cable is under a slight tension even at the surface. The counterweight then wants to fall towards the earth but is stopped by the cable.


You then said that you had ignored the Earths gravity, which makes a "heluva" lot of difference given that it counters the Moons excactly in L1 but also almost completely a great deal of the way.

When Netherelian points this out six months later you write things like:

Master_Ghost_Knight wrote:Why am I getting flack from ignorants for this?


rather than accepting that you made a bad approximation, and:

Master_Ghost_Knight wrote:The main loading factors is the cumulative column stress due to moons gravity, ignoring earths gravity isn't a farfetched aproximation (even because the claculations would lead to a virtualy higher loading factor)


No it clearly leads to a lower one. Finally you make a challenge for someone to make a more detailed calculation, completely missing that I had already done it six months earlier (which I claimed in a post you replied to).

Master_Ghost_Knight wrote:If you are willing to put your time into performing a more rigurous calculation I will not stop you. But the truth is nobody so far was even capable to preform such a thing.


Which one: Started the flamewar between you and Netherelian
and two: Promted me to redo the calculation, this time showing the math in the post. Partly because I felt somewhat included in the ignorants statement.

Back to:

Master_Ghost_Knight wrote:Where are you going with this?


Thats it, I suppose.
Tue Aug 17, 2010 3:00 pm
Master_Ghost_KnightContributorUser avatarPosts: 2750Joined: Sat Feb 21, 2009 11:57 pmLocation: Netherlands Gender: Male

Post Re: space technology

sgrunterundt wrote:You then said that you had ignored the Earths gravity, which makes a "heluva" lot of difference given that it counters the Moons excactly in L1 but also almost completely a great deal of the way.

You have failed to mention that "heluva" lot is less than 10% of the gravitational influence. Fuck of! you are grasping for straws after who knows what.


sgrunterundt wrote:When Netherelian points this out six months later you write things like:

Master_Ghost_Knight wrote:Why am I getting flack from ignorants for this?


rather than accepting that you made a bad approximation, and:

The aproximation was genius, I have made the calculation in 1 minute without losing any detail, reaching at a result of 2,37E6m^2/s^2 (that you can compare to your result), and you can also comfirm it in a minute. And no it is not only the gravity of earth that contributes to the L1, centrifuge does it as well, you seam to forget that the further you go from the moon the gravity due to moon gets extremely week and so the earths influence needs only to be week as well with the downside that earths influence gets weaker as it closes to th moon while the moons influences increases fast. It was not a step of faith to do that aproximation.
The hypocrisy burns.
Now do you understand why I am upset with this absurd acusations?
"I have an irrefutable argument for the existence of...." NO, STOP! You are already wrong!
Tue Aug 17, 2010 3:35 pm
sgrunterundtUser avatarPosts: 254Joined: Thu Dec 17, 2009 8:23 amLocation: Niels Bohr Institute, Copenhagen Gender: Tree

Post Re: space technology

Master_Ghost_Knight wrote:
sgrunterundt wrote:You then said that you had ignored the Earths gravity, which makes a "heluva" lot of difference given that it counters the Moons excactly in L1 but also almost completely a great deal of the way.

You have failed to mention that "heluva" lot is less than 10% of the gravitational influence. Fuck of! you are grasping for straws after who knows what.


So it is. I apologize. I just assumed that this was the cause of our different results, without actually checking how big a difference it made. Well, thats a lesson for next time. I'm sorry.

If our results were not that different, then I just don't understand why you claimed that it was the prodiguos capabilities of nanotubes that made it a remote posibility rather than saying that the low gravity of the Moon makes it a very real possibility.
Tue Aug 17, 2010 4:17 pm
Master_Ghost_KnightContributorUser avatarPosts: 2750Joined: Sat Feb 21, 2009 11:57 pmLocation: Netherlands Gender: Male

Post Re: space technology

Theonly reason I have made that comment was because I have seen this topic popout 6 times in the past few days and everytime I read the last comment I see the guy on top criticizing that. I let it slide once, twice, 3 times, but that thing gets anoying prety fast. I'm sorry, it is nothing personal, but I didn't realise that I was allways reading the same post (so yeah... :( ) now I speculate that was because the last poster was copletly undecided editing his message several times in the past few days making me believe that I was reading a different message. So we all have stuff to work out...
"I have an irrefutable argument for the existence of...." NO, STOP! You are already wrong!
Tue Aug 17, 2010 4:43 pm
cri8rPosts: 13Joined: Sat Aug 14, 2010 9:21 am Gender: Tree

Post Re: space technology

God that was rough. Look, I'm relatively new to this board, not a supergenius or a PhD, but I can tell you that trying to muck through MGK defending himself is not only boring, but positively painful. Spelling and grammar do tend to lend credibility to arguments...that is, if you can spell or put a sentence together.

Here's the bottom line: The damn elevator is plausible, but unproven. As any inventor can tell you, just 'cause it works on paper...
It will never be built, however, unless some way to reduce costs can be found. Not the best idea out there anyway. Rocketry's bunk too--not enough bang for your buck on payload. What we need is a totally new strategy.

Has anyone considered that orbital velocity is insignificant to space travel? It's only important if you actually want to ORBIT the earth. If you just want to leave the gravity well, you just have to produce enough power to beat gravity and keep it up long enough to get past the effective well. More efficiency and less power than the current methodology, and the only thing you lose is orbital capability (which you could accomplish by the Apollo slingshot method). As for the fuel problems inherent in rocketry, how about a propulsion system based on electricity? As in, capable of being supported by solar cells? Is anyone working this angle, or am I a bigger idiot than I think I am?
Sat Aug 28, 2010 7:36 am
Master_Ghost_KnightContributorUser avatarPosts: 2750Joined: Sat Feb 21, 2009 11:57 pmLocation: Netherlands Gender: Male

Post Re: space technology

cri8r wrote:As for the fuel problems inherent in rocketry, how about a propulsion system based on electricity? As in, capable of being supported by solar cells? Is anyone working this angle, or am I a bigger idiot than I think I am?

The problem is this, the conservation of momentum boggles the all thing up, inside a isolated system for a mass to move in one direction there must be another mass moving in the opposite in the accordance to the conservation of momentum, no exceptions. The away for instance a plane moves, the way by witch motion is achieved is by pushing the air around in the opposite direction of the intended motion, this requires to transport very little to no mass since the required mass that needs to be pushed is already there and all you have to do is to harness it (via an engine), there are even solar powered electrical planes that requires no other form of fuel and are able to stay in the air indefinitely (can't carry people or heavy weights though).
In space you don't really have that benefit, so that is why any free space craft with the ability to technically go anywhere as to take all its mass with it so it can literally throw it out so the craft can move, and to have the mass where it is needed it takes even more mass to put it there.
But we can do this more efficiently, the faster we throw the mass the less mass we need to throw out to achieve the same effect. A popular form of this maximization is the ionic engine which has an outstanding efficiency, but as almost everything efficient this is paid by having low power output (this is more appropriate for interplanetary orbits, not to get off the ground).

Can we do things another way?
A less intuitive example is for instance an elevator, for the elevator to move up it has to be tracted by cables which are attached to an engine on top near the roof, the engine itself exerts force on the floor of the supporting structure and that force is transmitted to the structure of the building which in turn pushes the ground, you don't see the earth moving because the earth is massive compared to tiny elevator cabin; so when you are going up on the elevator what is happening is that the elevator system is pushing the earth in the opposite direction in a strange way in order to move up. When it goes down the gravity sort of does the work for you as the gravity of the earth pulls the elevator down (the engine of the elevator ensures that it doesn't up to fast) but also the gravity of the elevator is pulling the earth back. Notice that this dance of one mass moving in one direction for the other to go the opposite is always there.
The gravitic slingshot maneuver is a form of gaining motion trough this action at a distance proportioned by gravity, so when a space probe passes near a planet to perform that maneuver what is happening is that trough the gravitic influence the probe is "stealing" some of the motion of the planet and slightly slowing it down (accelerating it in the opposite direction that the probe is intended to be accelerated).
The space elevator would sort of work on a combination of "directly" pulling a mass and this action at a distance of gravity. When the cargo would go up, the cable and the all elevator would have been pulled down (and it would have been a very visible effect, part of the reason I said that solving some of the problems was part of the story, that and the unrealistic zero stress at level zero hypothesis, not to say that it couldn't be done but I left that out since those properties can be a bit wavy depending on how you do things). For the cargo to go down it would simply need to pull back in the opposite direction until gravity starts to do its job and starts by working by this mechanism (deceleration is going to be a bitch to, another wavy variable), (this presents a bit of problem for the space elevator because cables are very good at being pulled and not so good at being pushed, but"¦) and the way the cables could go back into place is by pushing the opposite planet via gravity (if it works by this mechanism stress zero at level zero is beyond impossible. This details will severely complicate the all thing up requiring a more sophisticated and stronger structure than what some people tried to portray here. Doing the real project is extremely complicated and in no way shape or form will it behave the way they think it would. This is why I was severely reluctant to give them all those simplifying assumptions and got more keen to be upset when I gave them all that and much more and they still weren't happy).

Could it be done some other way? Probably. But one thing is certain, that mass dance will always be there no matter how it works.
"I have an irrefutable argument for the existence of...." NO, STOP! You are already wrong!
Sat Aug 28, 2010 3:46 pm
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