Space Elevator

[nexium]

A short (low performance) rotovator should be built in LEO, to test some of the technology for the Edwards type elevator. The math I have seen indicates that neither flying vertical ribbons nor rotavators will reduce cost to space by more than a few percent. Inital costs to develop the vehical that makes the attachment will be very high, unless the military already is developing hypersonic craft secretly. Neil

 

[barrykirk]

Why finish the job and send the final segment from LEO to the surface?<br /><br />The only thing I can think of is to provide a means of transferring the earths's rotational momentum to the tether/elevator.<br /><br />The last 200 miles may run into engineering difficulties such as the presence of substances in the atmosphere that could degrade that portion of the elevator in the atmoshpere.<br /><br />If the elevator were to use ion engines or push off the earth's magnetic field to reboost. Then the final 200 miles may not be necessary. Especially, if the cost of suborbital rockets drops.

 

[barrykirk]

Yes, <br /><br />It would be good to build a low performance rotovator or vertical tether just as a proof of concept.<br /><br />Your probably right that a low performance version wouldn't increase payload mass fraction by much, but the higher the performance of the tether, the less capability is needed by the vehicle attaching to it.<br /><br />This makes for an interesting choice of where to compromise for a limited functionality proof of concept.

 

[nexium]

I'm not sure of the meaning of the last paragraph of mlorrey's last post. A GEO sychronous ribbon must stradle GEO altitude with more mass beyond GEO altitude than below GEO altitude. If nonsychonous near GEO, the ribbon will have near misses of all the GEO satellites.<br />We likely can build a faster than sychronous flying vertical ribbon between LEO and GEO altitude up to about 33,000 kilometers long, with something stronger than kevar. With CNT (near optimistic strength projections) we could rotate = tumble the ribbon end over end making it into a rotovator. Neither would threaten existing satellites. If we then bring the 33,000 kilometer ribbon to low altitude, the LEO satellites are threatened, but we can have ribbon air speed as low as a few hundred kilometers per hour through out Earth's atmosphere. With skillful use of the transients and superb timing we can snatch a pay load off the surface of Earth with a speed of 1 kilometer per hour very briefly. The timing is increasing critical with a ribbon less than 33,000 kilometers long, upper atmospheric speeds are supersonic, and the payload and tip of the ribbon are subject to increasing g forces.<br />We can then stop the rotation returning to a flying vertical ribbon; add lots of mass beyond GEO altitude to slow the ribbon to GEO sychronous speed, so the bottom end can be attached at the Earth's surface, so it seems to me. Neil

 

[mlorrey]

What I was commenting was a response to Stevehw's complaint that an elevator was impossible because it would be hit by every LEO satellite. As a GEO elevator is built from GEO downward and outward, the last section that gets elevator built across it is the gap from LEO to Earth. By that time, all LEO satellites would be obsolete, too costly to replace in orbit with new models, because once you have a tether to LEO from GEO, the cost to put a satellite in GEO isn't much more than the cost to launch it in a suborbital trip to the LEO end of the elevator. A suborbital trip to the low end of the elevator would be many times cheaper than a trip to LEO. For this reason, LEO satellites will not be able to compete in the market against GEO satellites, a curious flip in the market that few people understand. <br /><br />By the time the LEO to Earth gap is built across, all LEO satellites will reenter or be collected, replaced by GEO satellites.

 

[larper]

You can do GPS from GEO? News to me. Somehow, I doubt it.<br /><br />LEO has lots of uses. It is not just a matter of cost. Tell the NRO to give up their GEO sats, for one. See what they say. <div class="Discussion_UserSignature"> <p><strong><font color="#ff0000">Vote </font><font color="#3366ff">Libertarian</font></strong></p> </div>

 

[mlorrey]

"You can do GPS from GEO? News to me. Somehow, I doubt it. <br /><br />LEO has lots of uses. It is not just a matter of cost. Tell the NRO to give up their GEO sats, for one. See what they say. "<br /><br />You need to study up on the history of satellite navigation systems.<br /><br />In fact, a GPS system could function from GEO. Since there is no need for a GPS unit to communicate to the satellite, all it needs is to receive timing signals from enough satellites. From GEO this only requires that the signal come from a 2-3 times more powerful transmitter, and because a GEO sat can be seen from more of the earth's surface, a GEO GPS constellation requires fewer satellites to provide global coverage. You could get global coverage with as little as 9, more powerful, GPS satellites in GEO. There are currently 24 GPS sats in 55 degree inclined orbit, plus a few spares, and they already orbit at 10,000 miles altitude, nearly half way to GEO. So GPS satellites are not LEO satellites, ergo your arguments are meaningless in this context.

 

[larper]

What I mean is, I would think you need satelites at inclinations other than 0 to get GPS to work best. I may be wrong. Anyway, still doesn't discount the other uses of LEO. Like I said, ask the NRO. <div class="Discussion_UserSignature"> <p><strong><font color="#ff0000">Vote </font><font color="#3366ff">Libertarian</font></strong></p> </div>

 

[mlorrey]

No, while you'd need satellites above 0 degrees inclination only to cover very high latitudes, there is also no reason why you cannot have a GEO satellite in an inclined orbit. GEO is not only being at the equator. Being at the equator is a GSO for Geosynchronous Stationary Orbit.<br /><br />What I was envisioning was to have three sets of three GPS satellites, with each set spaced 120 degrees from each other, and the three sats of each set would be in 120 degree phase staggered 30-40 degree inclined GEO orbits, essentially they'd be orbiting around a point above the equator. With this sort of constellation, even someone at the poles would be able to see at least three satellites in the sky at all times.

 

[nexium]

Can we orbit the next generation of GPS satelites at 70,000 miles and increase the transmitter power by 49 times? That would, I think, allow navagation as high as the top of the Space Elevators we may be building soon. Neil

 

[mlorrey]

What is the point of navigating that way? If you are on the elevator, all you need to know is how far up you are, which can be done by a timing signal from the surface.

 

[larper]

I think what he meant was that you would use GPS for all GEO and inward 3 dimensional navigation and target location. Might come in handy if traffic density got high enough. Oh, what a wonderful problem that would be! <div class="Discussion_UserSignature"> <p><strong><font color="#ff0000">Vote </font><font color="#3366ff">Libertarian</font></strong></p> </div>

 

[mlorrey]

Ah, well, with enough power, you just put 6 transponders on each GPS satellite so they can radiate their signal in all directions. Ought to be able to navigate anywhere from Earth to translunar space with sats spaced up to 50,000 miles from each other.

 

[nexium]

Also slow transients move the ribbon in all dirctions including twisting and the ground lasers need to hit the photovoltaic panels on the moving climbers to provide power. Plus or minus one meter is barely close enough. Neil

 

[nexium]

I'm thinking of yet another variation on the space elevator. Four separate ribbons attached to four anchor ships. The ribbons form a square and the and the climber attaches, sort of, to all 4 ribbons. Before launch we increase the anchor tension on one or more of the ribbons by reeling in some of the ribbon quickly. The climber grips the ribbon with the most tension (or second most) if that much additional tension is not safe for that ribbon. The ribbon tension lifts the climber to some height, perhaps 20 kilometers. The climber is now high enough that it can receive laser energy from one or more directions. Now it can climb partly on it's own power any of the ribbons moving upward unless this puts excessive strain on a ribbon. Ribbons moving downward due to transients and/or reeling in by the anchor ship will not be clamped, so they can slip though the rollars with minimum friction. More than 200 kilometers per hour will sometimes be achievable, thus shortening the trip to GEO altitude, and increasing thoughput.<br />If one or more of the ribbons are damaged, the rollars for that ribbon can be revesed, so as to reduce tension at the weak point, thus preventing severing of the damaged ribbon before repair can be made. This will slow, or even reverse the ascent of the climber, but it is important not to break a ribbon, if it can be avoided by any means. Computers can monitor the entire length of the ribbions and the transients being generated by up to five or ten climbers at various altitudes. This is possible as it takes hours for tension transients to travel the many thousands of miles of ribbon length. Multiple anchor ships are needed as they need to manuver to prevent the 4 ribbons tangling with each other. Please comment, refute and/or embellish.

 

[kg]

<p>I am kind of bewildered by this space elevator thing.&nbsp; Putting aside the materials problem (carbon nanotube fibers and whatnot) can such a thing work?&nbsp; I read that as an object is lifted up the elevator Earth's gravity affects it less and less&nbsp;so it takes very little energy to raise it all the way up to geosynchronous orbit.&nbsp; The article I read didn't mention anything about accelerating the object to&nbsp;orbital speed, only lifting&nbsp;it straight up.&nbsp; </p><p>So, would an object climbing this elevator be tugged in a westward direction as it goes from the 1000 mph at the equator to the several thousand mph it takes to orbit the earth?&nbsp; What keeps the elevator itself from pulled out of orbit as&nbsp;this object&nbsp;climbs up?&nbsp;&nbsp;</p><p>&nbsp;And, when a rocket climbs up to a geosynchronous orbit which takes more work: climbing up to altitude or accelerating it up to orbital speed?</p><p>&nbsp;</p>

 

[UncertainH]

<p>< The article I read didn't mention anything about accelerating the object to&nbsp;orbital speed, only lifting&nbsp;it straight up.&nbsp;></p><p>Since it goes up to the geosynchronous position it is already at orbital&nbsp;speed by definition.</p><p>As far as I remember the actual shaft ( or tether ) has to extend twice as far beyond synchronous orbit even though the cargo would always get off at the geosynchronous height. As far as the forces acting on the tether goes. I'm sure they are enormous hence the need for the carbon nano tubes<br /></p>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>< The article I read didn't mention anything about accelerating the object to&nbsp;orbital speed, only lifting&nbsp;it straight up.&nbsp;>Since it goes up to the geosynchronous position it is already at orbital&nbsp;speed by definition.As far as I remember the actual shaft ( or tether ) has to extend twice as far beyond synchronous orbit even though the cargo would always get off at the geosynchronous height. As far as the forces acting on the tether goes. I'm sure they are enormous hence the need for the carbon nano tubes <br />Posted by UncertainH</DIV></p><p>If you lift the object straight up, on a shaft that is stiff, it gains the orbital speed from the rotation of the earth.&nbsp; At the height of a geosynchronous orbit, it will automatically be traveling at the appropriate speed for such an orbit.&nbsp; The far end of the shaft would also be traveling at a geosynchronous speed, which is much faster than the speed required for an orbit at that higher altitude.&nbsp; That provides a great deal of force on the shaft from centrifugal force, presumable helping to keep it straight and in tension.</p><p>The engineering problems associated with a such a structure are daunting, carbon nanotubes or no.&nbsp; What you would need would be carbon tubes of enormous length, replacements for&nbsp;the carbon fiber in current composites, and even then the matrix would have to also be extremely strong and well bonded to the fibers to allow transfer of load through shear.&nbsp; Then you need to deal with the details of construction of a practical structure, with attachments, mechanisms, and a means of supplying the energy needed to raise the load.&nbsp;&nbsp;It would need to&nbsp;accomodate weather, air flow, etc.&nbsp; It would need to be able to take large bending loads as the load goes up and accelerates in a direction perpendicular to the shaft.&nbsp; Maintenance would be a consideration. &nbsp; I strongly doubt that such a structure will ever be built.&nbsp; </p><p><br /><br />&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[kg]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;&nbsp; If you lift the object straight up, on a shaft that is stiff, it gains the orbital speed from the rotation of the earth...&nbsp; The far end of the shaft would also be traveling at a geosynchronous speed, which is much faster than the speed required for an orbit at that higher altitude...&nbsp; It would need to be able to take large bending loads as the load goes up and accelerates in a direction perpendicular to the shaft.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <br />Posted by DrRocket</DIV><br /><br />Here is an article from Space.com about the elevator. http://www.space.com/businesstechnology/technology/space_elevator_020327-1.html</p><p>I'm just wondering if there is a flaw in the basic concept of the thing.&nbsp; Everything&nbsp;I've read so far talks about using a ribbon (not a stiff shaft) attached to a counter weight.&nbsp; Does the object being lifted gain orbital speed from the earth AND the counterweight?&nbsp; If so won't the counterweight loose this tug of war and&nbsp;drop in&nbsp;altitude?&nbsp; Would the force perpendicular to the ribbon be greater than the force&nbsp;needed to raise the object?</p>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Here is an article from Space.com about the elevator. http://www.space.com/businesstechnology/technology/space_elevator_020327-1.htmlI'm just wondering if there is a flaw in the basic concept of the thing.&nbsp; Everything&nbsp;I've read so far talks about using a ribbon (not a stiff shaft) attached to a counter weight.&nbsp; Does the object being lifted gain orbital speed from the earth AND the counterweight?&nbsp; If so won't the counterweight loose this tug of war and&nbsp;drop in&nbsp;altitude?&nbsp; Would the force perpendicular to the ribbon be greater than the force&nbsp;needed to raise the object? <br />Posted by kg</DIV></p><p>The basic idea is, as I understand it, rather like swinging a weight on the end of a long rope.&nbsp; It works better with a stiff rope or a stick.&nbsp; The object gains speed from the motion of the rope and farther out it goes the faster it goes, so long as the rope runs roughly radially outward from the center of revolution.</p><p>This concept works a lot better in science fiction than as a real engineering concept.&nbsp; It has a lot of problems.&nbsp; It has been around for quite a while.&nbsp; I don't know any serious engineers who don't giggle up their sleeve when it is discussed.&nbsp; The last time I heard the giggling was this morning.</p> <div class="Discussion_UserSignature"> </div>

 

[kg]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp; It has a lot of problems.&nbsp; It has been around for quite a while.&nbsp; I don't know any serious engineers who don't giggle up their sleeve when it is discussed.&nbsp; The last time I heard the giggling was this morning. <br />Posted by DrRocket</DIV><br /><br />So how much freight lifted into space would it take to replace global warming fears with global rotation slowing fears?&nbsp; I actually thing I could benefit from a longer day...</p><p>I seem to remember NASA playing around with long tethers stretching from the cargo bay&nbsp;of the space shuttle.&nbsp; Didn't it have disastrous results like power surges as the tether passed through magnetic fields or something?&nbsp; Is that one of the problems...along with space junk crashing into the thing?&nbsp; Is NASA really&nbsp;persueing this?&nbsp; The&nbsp;space elevator blog makes it all sound like&nbsp;it's&nbsp;prity much certain thing.</p><p>Hey!&nbsp; They are even looking for help on their website from any qualified interested persons!&nbsp;&nbsp;http://www.spaceelevator.com/Developer_Wiki&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</p>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>So how much freight lifted into space would it take to replace global warming fears with global rotation slowing fears?&nbsp; I actually thing I could benefit from a longer day...I seem to remember NASA playing around with long tethers stretching from the cargo bay&nbsp;of the space shuttle.&nbsp; Didn't it have disastrous results like power surges as the tether passed through magnetic fields or something?&nbsp; Is that one of the problems...along with space junk crashing into the thing?&nbsp; Is NASA really&nbsp;persueing this?&nbsp; The&nbsp;space elevator blog makes it all sound like&nbsp;it's&nbsp;prity much certain thing.Hey!&nbsp; They are even looking for help on their website from any qualified interested persons!&nbsp;&nbsp;http://www.spaceelevator.com/Developer_Wiki <br />Posted by kg</DIV></p><p>I have a vague recollection of some kind of tether experiment conducted from the shuttle.&nbsp; I think it was an Italian experiment.&nbsp; I seem to recall that it failed.&nbsp; I think I know a guy who was called in afterward to look at the project for NASA, but I don't remember any details or how that came out.</p><p>That web site looks like a typical wacko construction.&nbsp; I think it is rather far from a done deal.</p><p>I don't think NASA is pursuing the elevator.&nbsp; I certainly hope not.&nbsp; But stranger things have happened.<br /></p> <div class="Discussion_UserSignature"> </div>

 

[centsworth_II]

<p><font color="#333399"><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I don't think NASA is pursuing the elevator. <br /> Posted by DrRocket</DIV></font></p><p>NASA is sponsoring the Power Beaming (Climber) Competition which encourages development of technology that would be needed for a space elevator.&nbsp; </p><p><font color="#800000">"The Power Beaming challenge will continue to influence public perception of the Space Elevator project by demonstrating progressively more accurate (and more impressive!) prototypes of the Space Elevator system.... The total NASA provided prize purse is $2,000,000, highlighting its commitment to the development of power beaming technologies."</font></p> <div class="Discussion_UserSignature"> </div>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>NASA is sponsoring the Power Beaming (Climber) Competition which encourages development of technology that would be needed for a space elevator.&nbsp; "The Power Beaming challenge will continue to influence public perception of the Space Elevator project by demonstrating progressively more accurate (and more impressive!) prototypes of the Space Elevator system.... The total NASA provided prize purse is $2,000,000, highlighting its commitment to the development of power beaming technologies." <br />Posted by centsworth_II</DIV></p><p>Your tax dollars at work.<br /></p> <div class="Discussion_UserSignature"> </div>

 

[centsworth_II]

<p><font color="#333399"><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Your tax dollars at work. <br /> Posted by DrRocket</DIV></font><br />I think two million dollars is a small price to pay to keep motivated human minds at work on technological problems that may not give immediate commercial results but which may well lead to useful technologies in the future.&nbsp; Laying the groundwork.&nbsp; Heck, two million dollars is just the purse for a typical weekend of pro golf!&nbsp; And any new inventions that result will not be limited to use in a space elevator.&nbsp;&nbsp; </p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>