Space elevator update

[chriscdc]

Carbon nanotubes can stretch to 280% of their original length but only at 2000+ degrees fahrenheit. Normally they can only stretch to around 115% of their original length.<br /><br />http://www.physorg.com/news9996.html<br /><br />However having extra cable that you can roll out at intervals of say 1000km could counteract that effect. You would need a way to store the energy required to pull the cable in once it begins to expand.<br /><br />Also even at the highest end of the cable you will go through temperature swings every 12 hours as the angle the cable makes with the sun effects the amount of energy it absorbs.

 

[mlorrey]

So long as the cable is under tension with a counterbalance, it should not need to be reeled in, however if it is not yet anchored on Earth, but has a LEO platform it would expand in both directions, proportionate to the ratio between the masses of the outer counterbalance and the LEO station and the thickness profile of the cable itself, as well as where the heating is occuring....<br /><br />For this reason, it would likely be smart to build it such that the LEO station reaches the lowest stable altitude at the point of greatest expansion in the cable. This will minimize atmospheric drag until its CG reaches GEO. Once it reaches GEO, the LEO station should be free to drop as low as possible, since being geostationary, it will not experience atmospheric drag at that point. This will likely be the way to touch down on the surface, due to thermal expansion, and place the cable into tension for permanent ground service.

 

[nexium]

Hi mlorrey: The letters CG mean center of gravity? If the ribbon is standing vertically in LEO = low Earth orbit, maximum tension will occur a bit below the mass center, including the LEO station/platform and any ribbon waiting to be unwound. Maximum stretch will occur just below the mass center unless the ribbon is tapered, so as to produce maximum stretch at at a different point.<br />The ribbon will not be geo stationary until there is two or three times as much mass beyond GEO altitude as there is below GEO altitude.The ribbon needs to be close to GEO speed when it drops into Earth's upper, or air friction will blow it approximately horizontal. Does your post need some editing? Neil

 

[mlorrey]

CG is Center of Gravity.<br /><br />What exactly are you talking about? The ribbon can be geostationary with equal mass above and below GEO altitude, and it can only be geostationary if it is so balanced until the ribbon is anchored on Earth. If it is anchored on a floating platform, the mass above GEO cannot exceed the mass of the ribbon below GEO plus the mass of the floating platform, else the platform will be lifted (if the ribbon can handle the weight) or the ribbon will snap. Who told you that 2-3 times the mass needs to be above GEO as below it? That is patently false.<br /><br />As for length, the length of ribbon above GEO only needs to be .225-.25 of the length below GEO to provide payloads with escape velocity. 0.225 length is needed if payloads are allowed to freely slide out along the tether, while 0.25 length is needed if it is going to be metered out on a climber like the way it came up, to a station at a counterweight at the end of the tether ribbon.

 

[nexium]

The gravity of Earth is about 290 times stronger at sea level than at altitude 100,000 kilometers, so it takes more mass beyond GEO altitude to counter ballance the mass below GEO altitude. That is because sea level is 17 times closer to the center of Earth than 106,000 kilometers from the center of Earth.<br />The gravity at sea level is about 100 times stronger than at an altitude of 54,000 kilometers which is 60,000 kilometers from the center of Earth. Neil

 

[nexium]

Are you saying that the total length of the ribbon only needs to be 36,000 +9000 = 45,000 kilometers (requires very heavy counterweight) to provide pay loads with escape velosity? Radius is 51,000 kilometers so circumfrence is 320,000 kilometers divide by 24 = 13,345 kilometers per hour is escape velosity at an altitude of 45,000 kilometers. That is a reasonable number, but much faster is desirable to get to destinations throughout the Solar system in less than a decade. My guess is the escape velosity from the solar system is several times that number. Neil

 

[rocketman5000]

mlorry, interesting deployment strategy.... but wouldn't moving the LEO station up and down the cable largely effect the cables CG? Does anyone have what the projected mass per unit length of the cable would be?

 

[mlorrey]

I concede that the counterbalance needs more mass than the bottom end station, though you are not accounting for centripetal/centrifugal forces accurately: mass closer to the earth will be following a smaller circumference circle at a speed below orbital speed for that altitude, while mass above GEO will be going faster than orbital velocity.<br /><br />GEO isn't 100,000 km, it is 35,786 km altitude, or 42,154 km from the center of the Earth. Given escape velocity requirements of .25 tether length beyond GEO, an elevator design only needs to extend to, at maximum 44732 km altitude, or 51,110 km from the center of the earth to the counterweight end.<br /><br />The sea level end is going ~1000 mph, or the same velocity as the Earth's equator, while the counterweight end has a orbital circumference of 321137 km, which it travels at 13380 km/hr or 3.71 km/sec, vs the 2.79 km/sec of orbital velocity at that altitude.<br /><br />Given the distance differences, one already needs significantly more mass in the counterweight: four times as much if the outer tether is only 1/4 the length of the inner tether and they have the same taper profile over their respective lengths. Given the greater counterbalance mass requirements, one would expect that some of the mass would be taken up by increasing the thickness of the outer tether to handle the greater mass (weight is weight, and mass is mass, and neither is the same as the other).<br /><br />However, one doesn't need all that extra length.

 

[nexium]

Hi mlorrey: A poster on www.liftport.com got close to your new numbers. It seems the 20 tons average tension increases the required mass beyond GEO slightly and the taper ratio and density of the ribbon has a small effect. I agree the centripical force has a larger effect, as the radius increases/perhaps directly proportional. I agree GEO altitude is 36% of 100,000 kilometers or 40 % of 106368 kilometers figuring GEO is 42,154 kilometers from the center of Earth.<br />The other poster got 85% of the mass above GEO for a total length of 91,000 kilometers, which is the length Dr. Edwards used in the his early writings. A length of 144,000 kilometers, requires 80% beyond Geo altitude, hardly any of which is counterweight.<br />I think you are correct that a shorter ribbon produces escape velosity, but up to double escape velosity is desirable to get to destinations quicker. I agree weight is weight and mass is mass and neither is the same as the other.<br />My confidence is increased because you independently arrived at approximately the same numbers as people who expect to profit from the Space elevator are tossing around. Neil

 

[pmn1]

What are the legal implications - if its in internatioanl waters, then what juristiction does the country owning the platform have on that spot - does an attack on it become an attack on that county, an act of piracy.<br /><br />How many floating platforms and teathers could you have in that spot if multiple countries or organisations wanted to use it - NASA, ESA, NASDA, the Russian and Chinese space agencies, commercial organisations....<br /><br />What are the legal arrangements with the existing Sea Launch? <div class="Discussion_UserSignature"> </div>

 

[rocketman5000]

I doubt that the tether would be in continuous use. A large portion of every science mission is the development and testing of the probe. For launching of supplies it would be in valuabe to lowering cost, but for science missions it would have very little impact on the overall budget, therefore I doubt that any one space program, at least initially, will need a tether/elevator all to themselves.

 

[nexium]

I'll guess a square in the ocean 100 miles on an edge can have a space elevator at each corner with little danger of tangling. 4 more about 200 kilometers farther from the center are likely practicle before we are running out of optimum locations. Before that many, we are likely to start using mountain peaks near the equator.

 

[pmn1]

<font color="yellow">I'll guess a square inthe ocean 100 miles on an edge can have a space elevator at each corner with little danger of tangling. 4 more about 200 kilometers farther from the center are likely practicle before we are running out of optimum locations. Before that many, we are likely to start using mountain peaks near the equator.</font><br /><br />Would an attack for whatever reason on a platform be an act of piracy or an attack on sovereign territory.<br /><br />Could someone legitimately tow someone elses platform out of an optimum poistion? <br /><br />I know i'm being a bit extreme here but its been brought up on an Alternate History board and I am curious about the legal aspects.<br /><br />http://alternatehistory.com/Discussion/showthread.php?t=27203 <div class="Discussion_UserSignature"> </div>

 

[mystex]

I would assume that the tether would fall under UN auspices. I know that sounds like a global government thing but at least that way the US wouldn't shoulder the burden alone. Plus if it was a UN thing wouldn't that make it less likely to be attacked?

 

[nexium]

The UN and the World court have a bad reputation, so an additional over head cost for the Space Elevators is some mercinaries to shoot the pirates, and terrorists. Dead men tell no tales. Neil

 

[mlorrey]

I would install multiple tethers in the same installation, under the same tension. So long as they are the same length/taper dimensions and under the same tension, they shouldn't tangle at all. Properly using old cables to leapfrog longer cables up would be a quick way to bootstrap from LEO cables up to GEO cables.<br /><br />Dropping tethers down all along the equator, even if you were to space them by 100 miles, would mean space for hundreds of tethers, given that most of the earths surface at the equator is water. 100 miles of space on the surface is 1000 miles of space at GEO.<br /><br />Also keep in mind: once you have one cable dropped, you can drop pairs of cables to locations north and south of the equator equally. This would allow cables to NYC, Washington DC, London, Paris, Rio, Sydney. Johannesburg, Buenos Aires, Tokyo, Peking, etc. while at the same time their twin cable touching down in some remote location on the opposite point across the equator would create instant boomtowns of rural locales...

 

[mikeemmert]

Hi, nexium;<br /><br />I don't see any analysis of the effects of coronal mass ejections. These high speed blobs of plasma sometimes carry enough enery to evaporate the Mediterranean Sea.<br /><br />I call it the "induction problem", just simply moving a conductor through a magnetic field. The thread somewhere has mentioned that the Shuttle was only able to deploy 12 miles (kilometers?) of cable before the induction problem caused enough arcing to cut the cable. I distinctly (and very painfully) remember that experiment. If I remember correctly, the tether in that case was made out of a supposedly insulating material.<br /><br />A flying or cartwheeling elevator (I used to call them tethers, the idea flew around the Space Studies Institute during the 80's) is automatically going to have the induction problem just from the Earth's regular magnetic field.<br /><br />(In a separate thread somewhere, the induction problem is a monster for solar power satellites. They also have long conductors).<br /><br />Decent size meteors and nuclear weapons also bring up the induction problem. I would say this problem is severe.<br /><br />I haven't responded to mlorrey's sigline on this particular problem. But I did have a magneto in my motorcycle, when I had one...

 

[nexium]

Hi mikeemert: I was vaugly aware of such problems, but thought the arced tether was an electrical conductor. If good insulators are also valnerable, the rotovator = bolo which cuts Earth's magnetic feild and plasma fields at up to three times LEO speed, is likely doomed. The anchored at sea ribbon cuts these feilds slowly, except near the far end, which we might loose in a bad CME that struck Earth. Have you any more details? Neil

 

[mlorrey]

Actually, the EM field, being a product of Earth's rotational differential between the mantle and core, itself rotates. A geostationary space elevator should not develop any more current than one would see from being at a high electrostatic potential conducting to a low potential.

 

[nexium]

Hi mlorrey: That seems correct to me. The space elevator ribbon will likely cut the magnetic field of Earth slowly enough that dangerous currents are not produced. Electrostatic accumulations might cause problems, especially during a worst case solar flare?<br />Evaporating the Mederterainian Ocean is likely the total energy of a bad flare only a billionth of which would be absorbed by the 100,000 kilometers of space elevator ribbon. Neil

 

[qso1]

Don't know if you know this, but mlorrey is long gone from SDC. <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>

 

[soccerguy789]

I suggest that everyone try to get ahold of Brad Edwards' book on the topic. its a tough find, but it sold me on Space elevators. What needs to be realized is that the fanytasy super-tower with maglevs running up and down is just that: a fantasy.<br /><br />Edwards outlines the construction of the first elevastor in detail. It's a ribbon with atracked climber. thats it. the base station and counterweight are a bit mroe complex, but it pretty much goes like this-<br /><br />Launch a single 20-30 ton initial ribbon to GEO on a single aries HLV and then lower it, and start running climbers to thicken it, and eventually, it gets pretty big. then the new elevator provides the perfect platform with which to build another.<br /><br />Basically, being very sure to give a lot of leway, he theorized that the first elevator could be done for $ 6 Billion, so let's assume 10. Thats still huge.<br /><br />The thing is, he mainatains that this will always be a ribbon. He states that he hopes that within a decade of the first elevator, he hopes to see a 1000 ton lift capacity elevator...and it would still be a ribbon with a tracked climber.<br /><br />It took the whole book to sell me, so i dont expect anyone to take to the idea from what I've written here, so just trust me: with such a revolutionary concept as a space elevator, read the book befroe passing judgement.

 

[docm]

Did he address the effect of coronal mass ejections or other events (sprites etc.) that could induce a charge in the ribbon or portions thereof? <div class="Discussion_UserSignature"> </div>