Space Elevator Even Theoretically Possible?

[rogerinnh]

I'm wondering, is the space elevator idea even theoretically possible? I know that lots of people have proposed carbon nanotubes. But are there actually atomic attraction forces capable of providing the kind of tensile strength needed for a space elevator? Surely there are physical relationships between atomic forces, atomic/molecular weight, and the forces inherent in a 32 thousand mile (or is it 64 thousand mile) cable or structure. Is it actually theoretically possible to build such a thing?

 

[fatal291]

ive always asked if this can be done or not because there is so much junk in orbit now. Wouldnt the dust or other man made stuff pose a threat of crashing or just collecting where it should not be? I know the iss is in space also, but the ISS is much closer to earth and would not be as long i distance as a space elevator would be

 

[space_coops]

The idea has been around for a while. I remember reading about it in 3001: The Final Odyssey by Arthur C Clarke. <br /><br />

 

[qso1]

It is theoretically possible and some of the details can be found at the link I posted below:<br /><br />http://en.wikipedia.org/wiki/Space_elevator<br /><br />Whether theory can be transformed into fact on both technical and economic grounds remains to be seen. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[thebigcat]

I have some problems with "Theoretically". I recall a story a friend told me, allegorical, of a teen-aged boy who went to his father because he was having some problems in school, particularly in a class where they were discussing "Theoretically" and "In Reality", the finer points there-of. <br /><br />The father told his son that he figured he could help out with that. First, he told him, he should go ask his mother if she would have sex with a complete stranger for half a million dollars. The son, puzzled, complied and the response from his mother, which he relayed to his father was "Hell yes". The father then directed his son to put the question to his twin sister (fraternal, obviously) and the answer was the same as their mother had given.<br /><br />The father upon hearing the sister's remark told his son "Now here's the difference. 'Theoretically' we are worth a million dollars. 'In Reality' we are living with a couple of whores."<br /><br /><img src="/images/icons/wink.gif" /><br /><br />The theory of this whole idea is so shakey, there are so many potential flaws, that the reality would be impossibility.<br /><br />One thing the Wiki article mentions, and I find laughable, is that it lists the "projected cost" of lifting a payload to LEO. It is impossible for a space cable to lift an object to LEO. You can lift an object to 120 miles, but it wouldn't be in LEO. It would be stationary at an altitude of 120 miles while objects in LEO whiz by at 30,000 MPH. And yet, the space tether enterpreneurs advertize lifting payloads to LEO as one of the projected capacities of the system. WHAT??? <div class="Discussion_UserSignature"> </div>

 

[qso1]

The reason I use theoretical is that "Anything is possible" which is similar to saying "Its theoretically possible". The only way theory can be converted into fact is to fund it...test it...see if testing warrants further funding and if so, develop it. If we decide that something cannot possibly work and do nothing...we have fufilled our own prophecy.<br /><br />After all, even the Father in your father/son story (Hilarious BTW, I'm still LMAO) didn't put theory to an actual test. Lately, there have been an awful lot of theoretical concepts biting the dust and it makes you wonder if were ever going to get beyond the crude chemical rocket/subsonic commercial jet/internal combustion engine surface vehicle age. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[adrenalynn]

<font color="yellow">It would be stationary at an altitude of 120 miles while objects in LEO whiz by at 30,000 MPH.</font><br /><br />Takes a whole heck of a lot less thrust (and accompanying fuel/weight) to accelerate an object @ 120mi AGL to orbital velocity than it does to escape earth's pull and THEN accelerate to orbital velocity... <div class="Discussion_UserSignature"> <p>.</p><p><font size="3">bipartisan</font>  (<span style="color:blue" class="pointer"><span class="pron"><font face="Lucida Sans Unicode" size="2">bī-pär'tĭ-zən, -sən</font></span></span>) [Adj.]  Maintaining the ability to blame republications when your stimulus plan proves to be a devastating failure.</p><p><strong><font color="#ff0000"><font color="#ff0000">IMPE</font><font color="#c0c0c0">ACH</font> <font color="#0000ff"><font color="#c0c0c0">O</font>BAMA</font>!</font></strong></p> </div>

 

[yevaud]

True. A Space Elevator would must need have it's upper terminus at Geosynchronous orbit. It will not work otherwise. Mismatched orbital/surface rotational velocities would tear it apart the moment it was constructed.<br /><br />Just FYI. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[arkady]

<font color="yellow">The theory of this whole idea is so shakey, there are so many potential flaws, that the reality would be impossibility.</font><br /><br />Essentially I would agree, but Id be much more comfortable with terms like highly unlikely or improbable within the foreseeable future. <br /><br />And btw, as Yevaud pointed out, perhaps you should try familiarize yourself a bit more with the concept before you bury it. 120 miles isnt even close. You want ~200 times that, in the order of 22000 miles of cable, which would provide an orbital velocity of ~3 km/s. Thats the real hurdle. Cost and construction of the mother of all cables.<br /><br />(how to actually climb this cable is another aspect obviously) <div class="Discussion_UserSignature"> "<font color="#0000ff"><em>The choice is the Universe, or nothing</em> ... </font>" - H.G Wells </div>

 

[yevaud]

Not certain I would wish to be on the surface, with 120 miles of Carbon nanofibre falling on me. Messy and probably lethal. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[arkady]

Not a good time to try the one foot on each hemisphere thingy. <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> "<font color="#0000ff"><em>The choice is the Universe, or nothing</em> ... </font>" - H.G Wells </div>

 

[michaelmozina]

<blockquote><font class="small">In reply to:</font><hr /><p>Not certain I would wish to be on the surface, with 120 miles of Carbon nanofibre falling on me. Messy and probably lethal.<p><hr /></p></p></blockquote><br /><br />Messy? LOL! I think even a 120 miles of feathers would probably be lethal. <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. - Kristian Birkeland </div>

 

[vandivx]

"A Space Elevator would must need have it's upper terminus at Geosynchronous orbit. It will not work otherwise. Mismatched orbital/surface rotational velocities would tear it apart the moment it was constructed."<br />---<br /><br />actually I don't know where the upper terminus should be, I imagine it should be somewhat higher than that, thing is below the Geosynchronous orbit you have to move faster than Earth's surface to stay up and above this orbit you have to move slower than the surface in order not to rise to higher orbit... <br /><br />if the cable below G orbit is to move slower than it should (if it were to support its own weight) it will present a net weight to upper stages of the elevator and if we ended at G orbit then the weight pull of lower stages would pull the terminus down and the whole edifice would come crashing on our heads<br /><br />ergo we have to place the terminus somewhat higher than the Geosynchronous orbit - in that case the terminus would orbit faster (it would be effectively Geosynchronous at altitude higher than Geosynchronous orbital level) and thus it would be able to carry the weight of the lower stages of cable which would be below the Geosynchronous orbit altitude and therefore present net weight on the terminus<br /><br />so what I am saying is that the terminus would have to be higher than the Geosynchronous orbit and how much higher would depend on how light or how heavy we could manufacture the cable plus it would depend on the loads we would expect to transport up with some extra lift (which translates to more total height of terminus) to spare to keep the cable properly tensioned and provide safety margin<br /><br />for those who didn't or can't follow what I am saying they can understand the problem in these terms: Geosynchronous orbit for satelites is situated at a given height above Earth's surface and the determinant of that height is the gravitational force at that altitude which is such that the satelite stays unmoving above E <div class="Discussion_UserSignature"> </div>

 

[heyscottie]

To simplify vanDivX's post, the requirement is that the center of mass of the system be at geosynchronous orbit.<br /><br />For another idea I find particulary appealing, look up the Space Fountain. It has a number of advantages (and a number of disadvantages, too) over the Space Elevator.

 

[danhezee]

I used to like the idea of a space elevator but i went to the 2006 xprize cup and saw the damn ribbon shaking violently coz of the wind. also, i would like to point on the ground the wind was very calm, if we had breeze that day i dont remember it. the elevator wont work on a planet or moon with an atmosphere because of varying wind speeds at different altitudes. i am more optimistic that the technology might be applicable on the moon, though. <div class="Discussion_UserSignature"> </div>

 

[tom_hobbes]

I often wondered about wind when reading Arthur C Clarke and Charles Sheffield (<i>Fountains Of Paradise</i> and <i>Web Between Worlds</i>). <div class="Discussion_UserSignature"> <p><font size="2" color="#339966"> I wish I could remember<br /> But my selective memory<br /> Won't let me</font><font size="2" color="#99cc00"> </font><font size="3" color="#339966"><font size="2">- </font></font><font size="1" color="#339966">Mark Oliver Everett</font></p><p> </p> </div>

 

[yevaud]

<i>the pull of the cable is quite another matter because that is equivalent to increased gravitational pull and for the satelite (terminus) to stay Geosynchronous it has to be situated higher up above satelite Geosynchronus orbital altitude</i><br /><br />That is true. The best orbital "fit" for the upper terminus of a "Beanstalk" is just slightly beyond Geosynchronous orbit - no doubt accommodating this fact. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[arkady]

Yes. I suppose it would be more accurate to say that a space elevator would need to have it's center of mass at Geosynchronous orbit. (which as you say indeed involves an even longer cable, or some kind of counterweight)<br /><br />On first thought Id say your suggestion provides more complications than it provides solutions, but interesting nonetheless. Certainly, if Im not mistaken, even though the last 15km might seem insignificant, considering the overall cable length, it would save quite abit of cable reaching beyond geostationary orbit. Also it might help limit the impact of a number of other problematics associated with wind, lightning, ice, collision, perhaps oxygenic corrosion to some extent, dunno. However, such a system would add significantly to the cost and effort of shipping up stuff. The holy grail of the project. If we go to such lengths as to actually build one, youd expect it would make putting stuff into orbit somewhat of a trivial matter, and not involve operation of big aircraft. <br /><br />edit: slow typer, bleh<br /><br /> <div class="Discussion_UserSignature"> "<font color="#0000ff"><em>The choice is the Universe, or nothing</em> ... </font>" - H.G Wells </div>

 

[vandivx]

with lower end of cable attached to the ground I am not sure how much length that would add beyond the satelite geostationary point but there would have to be some although probably not significantly changing things, I just shoot from waist and really have gone into it for those who have only basic understanding of gravitation because that's good excercise (like it would be good quiz for phys101 students if they would fall for upper station at geosynchronous satelite orbit)<br /><br />vanDivX <div class="Discussion_UserSignature"> </div>

 

[vandivx]

I only got the idea for few minutes and then wrote it down and it also strikes me as problematic (if not downright crackpot idea perhaps) to start from some 15km high up but then again it may turn up to be the viable solution in the end never mind that it would raise the cost of using it but then again ground attached elevator might be simply not feasible at all in practice or be way too expensive if doable at all and spacelift seems to be the logical way of the future unless some exotic propulsion is found (like that which those ET flying saucers have) that would get around blasting rockets with their high acceleration and everything around that which is expensive and dangerous at best of times and likely always will be, on the other hand the lift once you have it built would be fairly safe with no worry about heat through air friction and all that space shuttles for example have to go through<br /><br />vanDivX <div class="Discussion_UserSignature"> </div>

 

[comga]

"perhaps we should consider having lower terminus above clouds"<br /><br />This has already been proposed. I believe that one person presenting this as an option is named Garret Campbell from Colorado.<br /><br />Of course, you couldn't reach the "base" by airplane unless it was moving at some speed that you could match with the airplane. That would impose drag on the "line" so both have to stand still. That probably means access through a balloon or dirigible. Now the higher they situate the base to avoid storms, the lower the capacity of any craft that brings people or hardware to the "base".<br /><br />An interesting concept, but no panacea.

 

[billslugg]

Great idea having the base station above the clouds. Avoids the whole issue of airplanes hitting it, keeps it away from terrorists, obviates need for thrusters, keeps it out of the rain, lightning, wind. Now - if you cannot figure out a way to get your payloads up to the terminus and back down again - you have no business building it! <div class="Discussion_UserSignature"> <p> </p><p> </p> </div>

 

[comga]

It is a simple matter to solve numerically for the minimum mass of such a structure given the force on the ground and the used strength (ultimate strength divided by a safety factor) of the cable. It can also be, and has been, solved in closed form. That is, you can derive either a table of numbers or an equation for the mass. <br /><br />In its most mass efficient form, the tower has a long tail that extends way beyond geosynchronous. Look at it this way. The cable starts thin at the bottom and grows fatter as it climbs and the force increases.<br /><br />At geosynch, there is a huge force that needs to be applied. One can imagine a mass just beyond geosynch, but the force per unit mass is minuscule, so you need an enormous mass. <br /><br />If you double the distance above geosynch, you roughly double the pull per unit mass, so you just about cut the required mass in half. In addition, the mass of the cable between geosynch and the end mass helps pull the tower up a little bit, so that the force required is less. Go farther out, there is more "supra-geosynch" cable mass pulling harder, and the mass decreases some more. Eventually, the most mass efficient system has a huge tail and almost no balance mass.<br /><br />There are obvious compromises. Since the system will have the most tension at geosynch, and the cable is sized for that tension, the cable could be extended without getting thinner. At some point, there would be almost enough mass in just the cable to balance the system.<br /><br />This is a good point for a "far-point station". There would be some "artificial gravity" pointing AWAY from the center of the Earth. Items let go from here would fly to higher orbits. At some point, this "higher orbit" would go to the moon, or beyond, out or in to the orbits other planets. Not having looked at the numbers in a few decades, (yes, decades) I don't recall just how fast would be "reasonable".<br />

 

[vogon13]

Have the bottom of the tether at the altitude SS1 reaches.<br /><br />You avoid the most expensive and dangerous part of the tether to build, and SS1 is dead cheapest access to bottom of tether at 60 miles altitude.<br /><br />Toot sweet.<br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[billslugg]

Vogon13<br />Put the access point in geosynchronous orbit versus geostationary orbit. Put it an inclined orbit. Every day its ground track would meander from the equator to some point north to some point south and back. When you shot your payload up there, it would negate the need to bring it to a stop or to snag it somehow. You could arrange for the speeds to be matched. <div class="Discussion_UserSignature"> <p> </p><p> </p> </div>