Space Elevators/Space Wheel

[ihwip]

I have this theory that when we create a space elevator eventually we will create a station in space that rings the Earth along the equator. What is the going hypotheses on how to construct a space elevator?<br /><br />My thought would be to put a space station in geosynchronous orbit and unreel a really long nanofibre cable to the ground. Once the cable is grabbed on Earth it could be fixed to the ground in one way or another. This would be easier than trying to construct a huge tower.<br /><br />Another question: How far out from geosync orbit would a 'wheel' need to be for it to experience 1g of centrifugal force?

 

[brigandier]

A wheel (ring) structure that circled the Earth along the equator wouldn't be stable. That is, since it's no longer orbiting the Earth, there's nothing to keep it centered. A nudge would be enough to throw the ring off center, leading to an eventual collision! <br /><br />At least, this is what I've heard..<br /><br /><br />Or did I misunderstand your idea?

 

[Mee_n_Mac]

There was a discussion somewhere here on SDC about a ring not at geosynch orbit distance and using tethers from that to elevate material. I can't find it and don't recall it's name. The idea was that the tether would be shorter and therefore not have to withstand as much tension. No idea as to how to go about constructing such a device.<br /><br /> <div class="Discussion_UserSignature"> <p>-----------------------------------------------------</p><p><font color="#ff0000">Ask not what your Forum Software can do do on you,</font></p><p><font color="#ff0000">Ask it to, please for the love of all that's Holy, <strong>STOP</strong> !</font></p> </div>

 

[jgreimer]

The first problem is tensile strength versus the weight of the cable. At present there are no materials that even come close to the requirements. The second problem is the possible consequences if the cable should break.<br /><br />IHWIP: How far out from geosync orbit would a 'wheel' need to be for it to experience 1g of centrifugal force?<br /><br />I think we all understand that centrifugal force doesn't really exist, that it is really the force of inertia trying to keep an object going in a straight line while some other force tries to deviate it. That said, I'll use the term centrifugal force because it makes it easier to understand.<br /><br />The centrifugal force of all objects in orbit is precisely matched with gravity. If the centrifugal force is too weak, the object will fall closer to the earth, gaining speed in the process, until centrifugal force and gravity are matched. If an object in orbit is accelerated, it moves to a higher orbit where it actually has a lower velocity. Example: The moon is only traveling at about 2150 mph whereas most low orbit satellites are traveling at around 18000 mph.

 

[ihwip]

This is all helpful but I think if we were to construct a ring in geosync orbit it would have to be tethered by no less than 3 (and that's pushing it) space elevator threads to maintain its position. Then you would need backup cables just in case so eventually it would look more like a bike tire with multiple spokes etc. To maintain stability further future generations could go on to turn the Earth-Wheel system into a large rotating disc with the original material known as Earth as the axis and the original wheel being the tire. Since all the mass is migrating to geosync orbit (or further) the original Earth would be much smaller.<br /><br />What I am trying to work with is the process of converting a home world into a hollow cylinder that spins fast enough to produce artificial gravity equivalent to the original planet. So whatever distance is necessary to produce g will basically be the eventual radius of the cylinder itself. And yes, I am thinking this process would take at best thousands of years. <img src="/images/icons/wink.gif" /><br /><br />The first step in the whole process is creating a space elevator. I am not sure how that would be done.

 

[onesmallstep]

Read "3001: The Final Odyssey", Arthur C. Clarke lays it all out for you. <div class="Discussion_UserSignature"> </div>

 

[neilsox]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I have this theory that when we create a space elevator eventually we will create a station in space that rings the Earth along the equator. What is the going hypotheses on how to construct a space elevator? My thought would be to put a space station in geosynchronous orbit and unreel a really long nanofibre cable to the ground. Once the cable is grabbed on Earth it could be fixed to the ground in one way or another. This would be easier than trying to construct a huge tower. Another question: How far out from geosync orbit would a 'wheel' need to be for it to experience 1g of centrifugal force? <br />Posted by ihwip</DIV><br />A ring circling Earth needs a super strong material. CNT may soon be available that is barely strong enough. An enormous amount of this strong stuff would be needed to make a useful ring with an adequate safety factor. If the geo sychronous ring had a bit more radius than geosychronous altitude it would maintain positive tension on three or more space elevators anchored to Earth's surface near the Equator. This would make the system stable, but there would be 0.01g or less on the ring.</p><p>Making the ring radius something like 200,000 kilometers would produce the one g , but the tension on the the ring and/or the space elevators would be enormous, requiring material about a million times stronger than CNT is likely to be.</p><p>The only way I can think of, that might be workable is a space craft under continous power about 400 kilometers above Earth's surface traveling about 55,000 kilometers per hour = twice orbital speed. Down (one g) would be away from Earth. This would require a large amount of energy which could perhaps be sent to the space craft by laser beams from Earth and/or from SSP = space solar power.&nbsp;You can learn more about SSP at&nbsp; <u><font color="#0000ff">www.spacesolarpower.wordpress.com</font></u></p><p>You can learn more about space elevators at&nbsp; www.liftport.com&nbsp; Both have a good forum.&nbsp;Neil</p>

 

[Guanaco]

<p><font size="3">Check out the book by Bradley C. Edwards called "The Space Elevator"&nbsp; Edwards has a Ph.D in engineering, so he's no lightweight.&nbsp; The book&nbsp;summarizes three years of NASA-funded studies on the Space Elevator.&nbsp; The bottom line: technological advances in&nbsp;carbon nanotubes&nbsp;now make the space elevator feasible.</font>&nbsp;&nbsp;&nbsp;&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[neilsox]

Perhaps Dr. Brad Edwards has some inside information. Last I heard, CNT rope was as costly as gold and&nbsp;not much stronger&nbsp;than Kevar rope. I suppose if someone is making very strong cheap CNT they will announce as soon as they have enough production to fill both large and small orders.&nbsp;&nbsp; Neil