Another Space Elevator Concept

[Kayra]

I don’t think this can be made to work

 

used to counter the weight of the tether.

:naughty: <Pries his foot out of his mouth>

Actually, I meant that the angular momentum would be used to help create a stable pully (structurally help support it), not that it would magically make the system defy gravity :umno:. The intent was that a giant diamond structure would not have to be built. Sorry for the confusion.. I make so much more sense when I just keep my mouth shut :hyper:

 

Fortunately, I don’t think exotic schemes like this are necessary.This statement assumes a dense, many-walled buckytube with a density over twice that of water. Buckytubes are, however, just rolled-up sheets of single atom-thick graphite. In the extreme, a buckytube can be single walled, so that, compressed laterally as by a pulley, would be effectively 2 single atom-thick sheets of graphite. Doing the math, a 40000 kg, 35922 km single-walled buckytube, flattened out, averages about 700 meters wide! The pressure on a 700-meter wide pulley would be very slight – less than ordinary car tire pressure!

 

So, I think that pulley pressures can be managed by carefully choosing the number of buckytube walls.

 

Sorry craig, you lost me there. Could you expand on that? If I understand what your saying, we could (assuming we have the manufacturing capabilities) construct a tether of any width desired?

[CraigD]

Fortunately, I don’t think exotic schemes like this are necessary.This statement assumes a dense, many-walled buckytube with a density over twice that of water. Buckytubes are, however, just rolled-up sheets of single atom-thick graphite. In the extreme, a buckytube can be single walled, so that, compressed laterally as by a pulley, would be effectively 2 single atom-thick sheets of graphite. Doing the math, a 40000 kg, 35922 km single-walled buckytube, flattened out, averages about 700 meters wide! The pressure on a 700-meter wide pulley would be very slight – less than ordinary car tire pressure!

 

So, I think that pulley pressures can be managed by carefully choosing the number of buckytube walls.

Sorry craig, you lost me there. Could you expand on that? If I understand what your saying, we could (assuming we have the manufacturing capabilities) construct a tether of any width desired?

Correct.

 

The 36209 kg buckytube I calculated is actually a sheet of graphite about 2.3*10^17 high, 8.6*10^12 atoms wide and 1 atom thick (35922 km by 1321 m by 1.54*10^-10 m) . Its manufacturing can cut it into multiple segments roll it up into nested tubes, and join it edge-to-edge in many ways, resulting in a combined width of the flattened cable(s) of anywhere from half its total 1321 meter width to a near microscopic 0.0006 meters. Somewhere between these 2 extremes should be an optimal solution, not so thin that it results in physically irresistible pressure on the pulleys, nor so wide that the pulleys are so excessively massive.

 

A critical enabling technology for this scheme is the engineering of machinery that can form carbon into nearly perfect sheets/tubes of hexagonal crystals (graphite). There appears to be serious commercial interest in this technology, an immediate goal being large architectural structures like the Tokyo Bay “city within a pyramid”.

 

I recently saw this link’s companion Discovery Channel “Extreme Engineering” TV episode. It featured interviews with apparently serious professional architects concerning buckytube fabrication. Although ideas abound, everyone interviewed expressed the opinion that such technology would require decades to develop, with project like the “city in a pyramid” unlikely to begin until late in the 21st century.

[Kayra]

<blink blink>

 

The possibilities for the tether structures you describe are.. mind boggling. I can see all sorts of problems I had envisioned can be resolved by that fact alone.

 

It sounds like any remaining issues would be strictly engineering related, and not basic limitations of physics.

 

Kudos to CraigD for putting so much thought into this.

 

With different sized pulleys, the entire center of the tether could also be set to run at a much higher speed.

 

If the transit time could be brought down to 1 day, then the lower capacity would likely be inconsequential.

 

I realize it is much more complex then a single tether, but I think the advantages completely outweigh the disadvantages.

 

What other major issues would need to be resolved in a system like this?

[InfiniteNow]

Kudos to CraigD for putting so much thought into this.

I'm gonna go all "dittohead" for a moment and second the above. Indeed... CraigD's da man.

[Jay-qu]

So how is it that you attach something to a cable so microscopically thin?

[Kayra]

So how is it that you attach something to a cable so microscopically thin?

 

That was one of the reasons I was so happy to hear that making this tether a ribbon was no problem.

 

If the cargo pods are attached to the side of a ribbon, using a series of offset wheels, sufficient surface contact should be possible. (Think serpentine) This arrangment would also allow the cargo pod to run at any speed up to and including the speed of the tether, simply by applying braking to those wheels.

 

As an added bonus, at each pulley site, a pickup rail on the side of the pulley could allow the pod to go around the pulley and re-attach itself to the ribbon, without even having to stop. (think railroad switch) No stopping, or even slowing down required. no robotic arms moving pods around... simple inertia and solid design. I can visualize the solution, but am having problems describing it.

[Pyrotex]

...nearly perfect sheets/tubes of hexagonal crystals (graphite)....

Be aware that even though graphite and Buckytubes have hexagonal arrangements of carbon atoms, they are considered two unique and distinct forms of Carbon. Currently, four "macro" forms of Carbon are known: amorphous, diamond, graphite, and fullerenes. The fullerenes are the only form that is "closed"--that is, the carbon atoms combine in discrete "molecules" where all carbon bonds are attached entirely within the molecule.

[Kayra]

Would a 2 meter diameter tube pressed flat be considered a fullerene, with all the strength and chemical stability that comes with it?

 

I never thought of it before, but each loop might be considered a single molecule, unless the structure is woven from many smaller tubes of course.

[Kayra]

http://www.sciencedaily.com/releases/2006/04/060414012311.htm

 

From this article, I can see that Graphene will likely be producing a lot of scientific interest in the near future. As graphene is most likely to be the material that meets CraigD's specifications (in my opinion) for a space elevator, perhaps some of the newly discovered electrical properties will act to accelerate research in this area.

 

It also seems more likely that they will be able to find a way to make contiguous ribbons of this material, without needing weighty fillers, plastics, or epoxies to make a cohesive fabric.

[wolfkeeper]

OK, just for the record, I and others have already been down these roads you're on, and have worked out some things:

 

a) a single loop running from the ground to beyond GEO and back down to the ground is considered possible if CNT stronger than IRC ~65 GPA can be made (Blaise Gassend worked on this a bit). But if you do that, the payload takes quite a hit because the cable is more stressed at GEO than at the ground and you can't carry as much without snapping it. OTOH on the upside you can supply mechanical power to drive the whole system, rather than use laser beaming, and that may mean you can go faster.

 

:) multiple loops hanging off each other might also work, however the pulleys in between are a lot heavier- the pulleys vary in size from heavy- at orbit, and lighter nearer the ground... it's probably awkward to build something like that- it's difficult to move the heavier pulleys from the ground to GEO.

 

c) lighter, and possibly better- if you have a tapered cable hanging down from orbit and have lightweight loops spinning around, hanging off that, for the payload, then you still lose about 50% of the payload, but you get the mechanical power idea in there again. It's probably easier than :doh: because you can potentially deploy the tapered cable first in relatively conventional ways, and then walk the loops/pulleys up the cable from the ground- there's at least one way known way to do that.

[Eclipse Now]

Would it be strong enough to take "large" components of a spaceship up one and a time and then assemble a Mars-ship up their? What about something like an ONeil colony?

 

How LONG would the trip take? In Kim Stanley Robinson's books on terraforming Mars, the elevators took 4 or 5 days on earth because it just had to be soooo long!

 

So would an elevator be able to have a number of lifts/craft on it, passing one another in some manner?

 

And what speed would a Mars-Craft be able to achieve just be 'letting go' of the elevator when it was swinging into the right direction?

 

Cheers.

[CraigD]

Would it [a space elevator] be strong enough to take "large" components of a spaceship up one and a time and then assemble a Mars-ship up their? What about something like an ONeil colony?

In every design with which I’ve played, the total mass of the elevator was orders of magnitude larger than the largest planned spaceships, so there’s no practical reason the non-detachable parts of the spacecraft couldn’t be assembled on the ground and lifted intact via the elevator.

 

Note that while it makes sense for a space elevator to use standard size “cars” designed to hold passengers and freight containers smaller than a Mars ship, there’s no prohibition on creating custom cars that would allow large cargo, such as a Mars ship, to be lifted unenclosed.

How LONG would the trip take? In Kim Stanley Robinson's books on terraforming Mars, the elevators took 4 or 5 days on earth because it just had to be soooo long!

A week’s not an unreasonable estimate, and requires about a 200 km/hr average speed similar to present-day fast trains. If the moving belts (in this design) or the car moving over fixed cables (in may other designs) could be engineered to safely move much faster, however, the trip could take much less time.

So would an elevator be able to have a number of lifts/craft on it, passing one another in some manner?

That’s a more detailed design question than can be answered in much detail at the present-day stage of design discussions, but this thread’s moving belt design involves there be at least 2 cars passing one another, one up-going, the other down-going.

And what speed would a Mars-Craft be able to achieve just be 'letting go' of the elevator when it was swinging into the right direction?

Recall that you can make a space elevator with a long section above geostationary orbit – in fact, this is a good idea, to keep the its total mass low. As the speed of a point on as a space elevator is proportional to the distance from the center of the earth, while the orbital speed of that point is proportional to the square root , if you make the above-GEO section long enough, you can release objects from its end with any excess speed you wish

 

I did the math a few years ago. As I recall, for a practical length, Earth escape speed is achievable, but solar is not. I don’t recall if a Mars transfer orbit is practically achievable – I’ll see if I can find my old notes, and check.

[Eclipse Now]

Either way, it's still a lot of velocity 'for free'. Add a bit of kick from some ion thruster / space sails / good old chemical rockets, and we've got some action.

[modest]

I stick with what I said earlier: hanging anything from a satellite is going to just pull the satellite out of orbit.. I just cant get my head around having all the weight suspended from a satellite and it not having any effect on its motion..

The usual solution to the “pulling out of orbit” problem is to “hang” a mass above (in a higher orbit) the satellite at the same time you hang a mass below it.

 

The net force on a satellite is

F = Fcentripetal –Fgravity

For a satellite in GEO (orbital radius about 42200 km), with a mass Ma hanging Da above and a mass Mb hangin Db below is

(1/189089646)Ma(42200+Da) –(398600)Mb(42200-Db)

 

Yes, but there should also be a net tangent force on the cable. Each time you take a mass up it has to accelerate from the equatorial surface speed to the speed of the tethered satellite—a net tangent acceleration. Essentially, pushing the cable westward all the way up.

 

Lowering the empty car puts a force in the opposite direction, but the force would be less because the mass is less (the car is empty assuming we are launching things off the tether). The net result, as I figure it, would be a net force on the satellite in a direction opposite its rotational velocity.

 

I think after each trip the satellite would move westward no longer being directly above its base and by extension be a little closer to the ground. Eventually the tangent velocity of the satellite would slow to a geosynchronous velocity and would have a geosynchronous height, and I guess even before that happened the weight of the cable would pull it down completely.

 

I really don't know anything about space elevators so I certainly could be wildly off about this.

 

~modest

[JMJones0424]

As long as we're building space elevators and flitting around space-

 

If there is a problem with the mass of the empty car returning to earth being less than the loaded car leaving Earth, then why not fill the car coming back to earth with an equivalent mass of space stuff

 

It doesn't even have to be valuable, but as long as you are doing it, it might as well be. Helium 3 laden regolith from the moon would be an obvious choice, but anything would do. Granted, finding mass in space is not easy, but at the very least could we not much more easily accelerate mass out of the moon's gravity well and use that to help bring mass up out of Earth's.

 

Now living and mining the moon becomes a means for the ends of constructing a space elevator in order to live and mine the moon. When we construct lines of communication (and transportation) on Earth in order to link locales, it generally has the effect of increasing communication between those locales.

[Eclipse Now]

Wow, reading through this thread again from the beginning... the conversations about moving belt's on the elevator just blew my mind. I just can't conceive of a belt that long that strong that can actually bend around a gear/pivot of some sort.

 

Much of the sci-fi I've read have the 'lift' powered by laser for the first part of the trip, and then other things take over.

 

I'm imagining the elevator itself takes over powering the craft. Solar cells on the elevator's closest 100km could feed into the nearest craft. Remember we're talking about something maybe longer than 32 to 38 thousand km's... (or was that miles?)

 

If we're discussing a sci-fi like future that has materials strong enough to build a space elevator, why not coat the elevator in cheap spray on nano-solar that delivers electricity into the 'grooves', which the 'lifts' then feed of?

 

Or else just make the elevator stronger, the lift bigger, and whack a maintenance-free Hyperion nuclear reactor battery onto the beast and run it for 5 years before taking the battery off to send back to the factory!

 

Once sited safely in its underground containment vessel, an HPM is monitored but does not require a battery of operational personnel. It just quietly delivers safe, reliable power – 70 MW thermal or 25 MW electric via steam turbine – for a period of seven to 10 years.

 

A good bit bigger than the typical consumer battery, HPMs are, however, just a fraction of the size of conventional nuclear power plants. The Hyperion Power Module is 1.5 meters across and 2.5 meters in height. It’s the size, along with the transportability and ease of operation, that make the self-contained HPM such a desirable choice for providing consistent, reliable, affordable power in remote locations.

 

(And if we're talking real sci-fi, there's always Polywell!)

 

 

Heck, if we actually crack Polywell, will we even need the space elevator? Polywell reactors are supposed to be small enough to fit onto a sub (the US Navy is working on them). Surely we could work em over a bit and stick em on a shuttle, and piggyback the shuttle up on a Polywell super-jumbo and then Polywell the Shuttle off the plane, super-man style? (Not sure what the Polywell would use for thrust but it is an amazing source of power IF we ever crack it!)

[CraigD]

And what speed would a Mars-Craft be able to achieve just be 'letting go' of the elevator when it was swinging into the right direction?

I did the math a few years ago. As I recall, for a practical length, Earth escape speed is achievable, but solar is not. I don’t recall if a Mars transfer orbit is practically achievable – I’ll see if I can find my old notes, and check.

I found my old notes, which went along with this 5/10/09 “Colonizing the Solar System thread post.

 

For a space elevator to provide a “free trip to Mars” transfer orbit insertion, it extend about 93225299 m from the Earth’s center, about 86847162 above ground level. At this radius, its speed would be about 2924+2929=5853 m/s, earth escape velocity at that height plus Mars transfer orbit deltaV. Geostationary orbit, the elevator’s center of mass, is about 35786033 AGL, so this means about 59% of the elevator would be above GEO.

 

You’d have significant centrifugal pseudogravity at this distance above GEO, about .45 gees, so the "drop" when you were released would be an appreciable one.

Either way, it's still a lot of velocity 'for free'. Add a bit of kick from some ion thruster / space sails / good old chemical rockets, and we've got some action.

Since the space elevator would most likely (but not absolutely necessarily) in Earth equatorial orbit, depending on the date of the launch, you’d likely need some small amount of deltaV to correct the Mar ship’s course, so you’d need some rockets, sails, etc. Unless you waited for a least-energy launch date, you’d need to plot something more complicated and higher-energy than a simple transfer orbit to Mars, so that you exactly intercept Mars, so the elevator would need to be a bit longer than 86847 km AGL, and the release point chosen for the specific trip parameters. This is because a Mars trip has to shed a lot of speed when it intercepts Mars – for a simple transfer orbit, about 2636 m/s – and the most efficient way to do this is with aerobraking in Mars’s atmosphere. Edited December 17, 2014 by CraigD
Fixed broken link