Another Space Elevator Concept

[Buffy]

The first group to create such a device should be able to get their investment back VERY quickly, as the only competition is VERY costly. They could undercut them by 30%, make a MASSIVE margin, and recoup investment in short order.

Remember to go back to your spreadsheets, take your absolute worst case cost and multiply by 4 to account for underestimated construction schedules and by another factor of 4 for Rummy's "unknown unknowns". Now recompute. Oh and don't forget to add additional huge amounts for the construction R&D, and the two failures that will occur because somebody forgot something. :hihi:

 

Murphy was right,

Buffy

[Kayra]

Remember to go back to your spreadsheets, take your absolute worst case cost and multiply by 4 to account for underestimated construction schedules and by another factor of 4 for Rummy's "unknown unknowns". Now recompute. Oh and don't forget to add additional huge amounts for the construction R&D, and the two failures that will occur because somebody forgot something. :hihi:

 

Murphy was right,

Buffy

 

 

Ouch. that is a lot of "Factors" :eek2: I understand the necessity of such when dealing with the "first of".

 

If I had any concept of the projects estimated costs I could try to make a business case. Unfortunately, I don't.

 

Would this help the case at all? If I were an owner of such a magical device, and actually got it running. (those overruns were murder), I would try to circumvent my future competition by helping them. (eventually)

 

Offer to loft a cable for them.. 3 conditions apply. They can not aid anyone else in lofting one, you are granted license to any improvements they may come up with, and you get a reasonable amount of royalties. Repeat for all competitors with sufficient funds until demand can meet market requirements.

 

Even if (after the first couple years of operation) you never lifted anything other then other tethers, and used the entire capacity for power transmission, you should be able to recoup your costs in a reasonable time frame.. no?

[Buffy]

Would this help the case at all? ...I would try to circumvent my future competition by helping them....Offer to loft a cable for them.. 3 conditions apply....Even if (after the first couple years of operation) you never lifted anything other then other tethers, and used the entire capacity for power transmission, you should be able to recoup your costs in a reasonable time frame.. no?

That's a completely rational business plan *structurally*, but the devil is always in the details... The question is, how long can you keep your invested capital tied up in this for the amount of time that it will take to build up demand by your competitors, and can you *really* be sure you can get them to agree to pay royalties that match your investment. Donno. I'd be sure to patent something in the process, or else someone with bigger funds and a longer time scale will duplicate your plan and simply be able to price you out of business.

 

Even with a patent of course, you run into the 17 year curse, where your competitors invest in building up their solutions and suppressing demand until your patent runs out...

 

Projections beyond 5 years are always pure conjecture....

 

Grounded, :hihi:

Buffy

[TheFaithfulStone]

Hey, it sounds pretty similar to the space fountain.

 

http://en.wikipedia.org/wiki/Space_fountain

 

Space fountains are cool because they can be anywhere, not just at the equator, they don't have to go all they up to GEO, and they don't require unobtainium cables. (It's debatable whether SWNT have the necessary tensile strength. I bet they do - but not yet.)

 

Also, the idea of the Loop is suggested on Wikipedia, but there's no reference to whose idea it is. It requires a tensile strength on the cable of 62.5 GPA. BUT - the thinner cable you suggest requires a tensile strength of 130 GPA. Most SWNT top out around 30-50 with a maximum theoretical limit of around 120.

 

Cool idea though.

 

Accelerating at two G's would let you reach escape velocity 3,000km up. But how would you climb a space fountain?

 

TFS

 

BTW, that's my quote! I'm flattered.

[Kayra]

You know.. it never ceases to amaze me how often I open my mouth before doing sufficient research :hihi:

 

Wiki Touched on almost everything I stated here.

 

Even the idea I was toying with of having multiple segment loops was noted. Using larger tether only where required.

 

I still believe this would be the best way to go. All of the points I made in the first few posts are still salient. 3 especially of note are

1) Continious ability to monitor and repair the cable at ground level

2) Powering the system efficienctly from ground or space

3) Redundancy. If one side of the tether breaks, simply clamp the cable at both ends. rewind the tether until the base station is holding one end. Capture the other end.. and repair.

[Jay-qu]

Errr... I may have gotten the words reversed, too. I'll have to look them up. :hihi:

 

I think that you may have! With the human spinning with buckets analogy, the buckets have a net force radially inwards, the bucket feels like its pulled out because it has a reaction force to your hand holding it and likewise the water on the inside of the bucket 'feels' like its pushing out but its just the reaction force to the bottom of the bucket.

 

With this conveyer belt idea, what is holding the cables ie stopping them from falling down - I suppose the satellite, there is no way the satellite could counter such a large force, unless it had some constat means of propulsion on board..

[Kayra]

What is holding it up should be the centri**** force from the counterweight at 62,000 miles distance from the earth.

 

The counterweight is actually the bucket in your anology.

[Jay-qu]

That wont work, the reason things end up in orbit is because they are spinning around the planet - there is no outward force, only an inwards.. Trying to haul something up would result in pulling it back down to earth IMO

[Kayra]

Hmm.

 

I have far to little knowledge of the math involved in orbital mechanics to argue difinitively that it will or will not work. I have a tendancy to visualize things things. hile this often serves me well, it just as often gets me in trouble. Especially when trying to understand most aspects of quantum mechanics.

 

This is how I visualize the orbit of an object. Please feel free to correct my misunderstandings.

 

When an object is in a stable orbit around a planet, that means that its velocity is exactly enough to counter the force of gravity. since its velocity is at a right angle to the force of gravity, it is in a state of constantly falling into the planet, and constantly moving away. Hence, no gravity.

 

If you slow the object down, it will decend to a lower orbit until it is again stable. The opposite occurs if you add velocity to it.

 

If you were to increase the velocity, but prevent the object from moving to a higher orbit, it would pull against what was preventing it from moving.

 

The counterweight is such an object, and the tether is the what is preventing it. The farther out the counterweight is, the greater it's velocity is, and the stronger it will pull in order to stabilize it's orbit.

 

Ugh. It is 2:30 in the morning and I need to sleep. I hope my ramblings made sense. (they always do to me :steering: )

[TheBigDog]

At the bottom end of the cable, you only need to support the elevator.

10 Km up, the cable needs to support the elevator AND 10 Km of cable, which may equal the weight of the elevator. At some point, you need to double the "thickness" of the cable to support the weight of all the cable below.

 

100 Km up, the cable needs to support the elevator AND 10 Km of 1-strand cable AND 10 Km of 2-strand cable AND 10 Km of 3-strand cable AND 10 Km of 4-strand cable AND 10 Km of 5-strand cable AND...etc.

You lost me here Pyro. The cable is being stretched, not compressed. So the tension should be equal over the whole length.

 

But wait... because it is vertical the top is not only under tension, but also supporting the weight of everything below it. Now I think I get it.

 

I am personally doutful that it can be engineered. The stability issues during the process of erecting the thing would be daunting. Assuming that you had all the materials, how would something like this get built?

 

Bill

[Kayra]

I am personally doutful that it can be engineered. The stability issues during the process of erecting the thing would be daunting. Assuming that you had all the materials, how would something like this get built?

 

Bill

 

Which stability issues? There are likely to be many, and I suspect each can be mitigated or eliminated through proper design and engineering.

 

I described one method on the first page (in VERY simplified form), and I am certain there are others.

 

To put in perspective what the material we require for the tether is capable of:

 

A typical sewing thread thickness Carbon Nano Tube (CNT) is capable of supporting a medium sized vehicle. A 5 KM stretch of the starting cable would weigh something in the order of 1 Kg.

 

Someone with some math skills might want to jump in at this point and extrapolate on these base values :steering:

[Kayra]

Here is a question for the physics folk.

 

The system would likely have a reduced cargo capacity due to the fact that the cable needs a consistent diameter for it's entire length.

 

Since it is powered from the ground, space, or both, would it be likely to meet or exceed the capacity of the other designs simply due to its ability to loft cargo at a much higher velocity?

 

One method of reducing startup strain (loading a cargo pod onto the system)on the cable would be by using a capstan type system similar to that used on a reel to reel tape, it would be possible to keep the entire cable moving at high speed, while stopping a small part of it. While stopped, the cargo pod could be attached, and then accelerated up to the cable's speed.

 

In space, the cargo pod could release itself before it reaches the platform, with enough momentum to ensure it reaches stable orbit. Going down, it would use the cable as a guide as it fell. Acceleration from gravity would allow it to catch up to the cable velocity, at which point it could clamp back down.

 

I am not certain how to handle the tricky part of undocking an empty cargo pod. Any suggestions there?

[Jay-qu]

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..

[CraigD]

All this space elevator stuff got me to figuring, the result of which was this simple ([M]UMPS) program

S D=1440,S=2.76e9 ;density (in kg/m^3) and tensile strength (in N/m^2) of kevlar
S R=.05 ;initial radius (in m) of cable
S (M,W)=0,H0=6378,H1=42200,WF=0
F H=H0:1 S CA=R*R*$zpi,A=398600000/H/H-(H/189089),MI=CA*1000*D,F=A*MI,W=W+F,M=M+MI S:W/CA>S H=H-1,W=W-F,M=M-MI,CA=0,R=R*1.01 I CA W $J(H-H0,8),$J(H1-H,8),$J(R,16,2),$J(M,32,0)," (",$L(M1),")",! Q:H'<H1(M>6e24)

What this does is simulate raising a cable from the ground (H=6378 km) to geostationary orbit (42200 km), increasing its radius ® from an given initial value as needed to avoid exceeding its tensile strength (S). If the mass of the cable exceeds the mass of the earth (M>6e24 kg), it gives up.

 

In the real world, of course, you couldn’t build a space elevator like this – the usual approach proposes dropping equal weights of cable up, above geostat, and down, toward the ground. The end result is the same, though, so this program gives a decent approximation of half the mass of cable needed.

 

I think this provides some answers to some of the last couple of day’s questions. My calculations are badly in need of an independent (not me) check and corroboration, however, so anyone so inclined, please jump in!

 

Here’s output for a space elevator made out of high-strength steel, Kevlar, semi-theoretical giant carbon molecule tubes (“carbon nanotubes”, or “buckytubes”), and 2 fictional materials needed to get a constant-thickness cable to work: “2*Buckytube”, the same density but twice as strong as a buckytube, an “light buckytube”, the same strength as buckytube but half the density. All start with a cable capable of supporting 25 tons. I’ve just included output for interesting heights – ground level (0 km), GEO (35822), and half way (17911)

  Height            Cable Radius                            Mass
D: 7840  S: 1500000000  Steel
      0   35822          0.0016                              65 (2)
   1132   34690   96609376.8335       6154320793811586380000000 (25)
                                   W=43550661170960867800000000 (72%)
D: 1440  S: 2760000000  Kevlar
      0   35822          0.0012                               7 (1)
  17911   17911         94.5240                 106627525649432 (15)
  35822       0        258.2265                3530743734692777 (16)
                                              W=572688616807228 (2%)
D: 1440  S: 2760000000  Kevlar
      0   35822          0.0012                               7 (1)
  17911   17911         94.5240                 106627525649432 (15)
  35822       0        258.2265                3530743734692777 (16)
                                              W=572688616807228 (2%)
D: 2600  S: 65000000000  Buckytube
      0   35822        0.000247                               1 (1)
  17911   17911        0.000368                           13895 (5)
  35822       0        0.000399                           36209 (5)
                                                        W=32244 (9%)
D: 2600  S: 162500000000  2.5*buckytube
      0   35822        0.000156                               0 (1)
  17911   17911        0.000156                            3582 (4)
  35822       0        0.000156                            7165 (4)
                                                         W=9690 (14%)
D: 1300  S: 65000000000  Light buckytube
      0   35822    0.0002474135                               0 (1)
  17911   17911    0.0002474135                            4478 (4)
  35822       0    0.0002474135                            8956 (4)
                                                        W=12113 (14%)

I didn’t expect steel to be feasible, and it isn’t, requiring more than the mass of the Earth before it reached 1200 km. Ordinary Kevlar worked, but requires a mass greater than 35 million aircraft carriers!

 

Buckytubes seem to be the first really feasible material. A single-strand to GEO, with a counterbalancing strand above GEO, masses just a bit more than 2 Apollo spacecraft, within current launch capabilities.

 

:steering: Note, though, that the Buckytube-based system requires a variable cable thickness, making a “pulley” type space elevator like kayra proposes unworkable. My numeric fiddlings show 2 ways to achieve a material strong enough to have a constant cable thickness:

1) increase the strength of a buckytube by about a factor of 2.5 (a “2.5*buckytube”)

2) decrease the density of a buckytube by about a factor of 2 (a “light buckytube”).

 

Note also that all of these potentially feasible space-elevators have much thinner cables than we’re accustom to seeing in ordinary engineering: around .0005 meters, or about half the thickness of a typical human hair. Due to their unusual, molecular structure, buckytubes are likely to be much “poofier” than ordinary engineering material, but even if they’re 99% empty space, they’d still be less than .01 meter thick, less than the thickness of ordinary cotton clothesline!

 

:gift: All this leads me back to the conclusion that space elevators are a daunting engineering challenge, requiring that the strongest material currently being researched – buckytube – can be made several times stronger than expected. Actual experiments, such as 1992 and 1996’s joint US-Italian shuttle experiments show that there can be unexpected and catastrophic problems with space tethers, while

1992’s Small Expendable-Tether Deployer System (SEDS) experiment showed that a thin (.008 meter) tether can be expected to last about 4 days until destroyed by a micro-meteorite collision.

 

:hyper: If these challenges can be overcome, though, Earth’s gravity well could be made hardly a barrier:

• The energy cost of lifting payloads into space with such a system is fantastically low – ignoring friction, about 50 MJ/kg (based on a variation of the program above). At US residential electric power costs, this comes to about $0.30/Kg, for a one-person ticket to geostationary orbit cost of about $60. Of course, the investment capitol and maintenance cost of such a system would likely be many times its energy cost, but still, it’s likely to remain fantastically inexpensive.
  
• The total mass of a space elevator cable is likely to be fairly small – around 10,000 kg, so operations are likely to involvre using multiple cables and dropping them on-demand to the surface.
  
• Maintaining the system in orbit would, I expect, be a trivial challenge. Due to the small cable weight, a modest counter-weight system could be used to offset any lifted or dropped payloads while no more than doubling the energy cost of the lift.
  

[CraigD]

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)

 

One can see that, for any Ma and Da, and Mb, the equation can be solved for Db.

 

Since the mass of the cable connecting Ma and Mb to the satellite are not negligible, this calculation is actually harder than this, but still solvable.

[alxian]

lets just all read friday by heinlein and say that a tri axial fountain could lift a payload of several humans at a time.

 

where "elevator" is taken quite literally. maybe it could be good for launching micro satelite too.. it'll need all the business it can get to remain operational.

 

but not something like a space ship or large amount of freight.

 

i like this idea but its only practical for something like a lunar transfer station, where people working shift on the moon would constantly be going to and from earth, also tourism would keep it running.

 

what i don't get is why they don't feed it power from solar powered satelites. it couldn't be that power hungry that a few satelites attached by tethers couldn't porvide enough power, possibly in surplus enough for the fountain to supply that power to the local power grid.

 

just for the purposes of pushing matter into low earth orbit this would be a collosal waste of time.

[Kayra]

:steering: Note, though, that the Buckytube-based system requires a variable cable thickness, making a “pulley” type space elevator like kayra proposes unworkable. My numeric fiddlings show 2 ways to achieve a material strong enough to have a constant cable thickness:

1) increase the strength of a buckytube by about a factor of 2.5 (a “2.5*buckytube”)

2) decrease the density of a buckytube by about a factor of 2 (a “light buckytube”).

 

 

I had suspected that might be the case.

Since it is unlikely that the density of new materials will decrease while maintaining the tensile strength, that leaves 2 alternatives for my concept.

1) That a stronger material be found. (still a possibility)

2) That a method for using different thickness materials at different altitudes be found.

 

Would a system like this fit the bill for #2?

 

Instead of a constantly increasing cable thickness, have the thickness increase in stages. At each cable thickness change junction, have 2 sets of pullies connected to each other. One connected to the lower tether, and one connected to the higher tether. This would allow for a series of connected loops to be used.

 

Main issues with this concept:

1) More complex (greater opportunity for failure)

2) Difficulty transfering cargo from one tether segment to another (an engineering issue)

3) Not able to monitor entire tether from ground

4) Not able to repair entire tether from ground.

5) Construction MUCH more daunting

 

CraigD, would a staged system still exceed current estimates of Buckytube tensile strength?