Author Topic: The Space Elevator Thread  (Read 18560 times)

Offline tnphysics

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The Space Elevator Thread
« on: 10/08/2007 11:45 pm »
This thread is for any discussion about space elevators.

They would provide CATS IMO.

Offline A_M_Swallow

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Re: The Space Elevator Thread
« Reply #1 on: 10/09/2007 01:29 am »
We could build a Space Elevator on the Moon with current materials such as Kevlar and M5.
http://en.wikipedia.org/wiki/Lunar_space_elevator
Lifting many tons of carbon will be very expensive.  A stronger version of glass fiber (silicon) that can be manufactured from regolith would be nice.

Mars's moons get in the way of building a space elevator on Mars.  However attaching a long tether to Deimos would be nearly as good.  A say 5 mile flight to the surface could be used.  Alternatively the tether could be winched up and down.  Rotovators have also be suggested.

The Earth Space Elevator needs a very strong material inventing.  Carbon nanotubes have sufficient theoretical strength but materials currently on sale are an order of magnitude too weak.  The coming power beaming challenge may reveal a stronger material.

Offline coach

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RE: The Space Elevator Thread
« Reply #2 on: 10/09/2007 03:00 pm »
http://physorg.com/news110727530.html

Here's some brand new stuff regarding nanotubes and the matrix material they would be bonded into.  The major hurdle in building the SE is that the material doesn't yet exist.  The good news is that carbon nanotubes are theoretically strong enough so we have a path to follow.  


Coach

Offline tnphysics

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Re: The Space Elevator Thread
« Reply #3 on: 10/14/2007 11:52 pm »
That's good.

Now, what is the optimum trajectory for an elevator extended beyond GEO being used for lunar missions?

Offline PurduesUSAFguy

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Re: The Space Elevator Thread
« Reply #4 on: 10/15/2007 02:36 am »
This is the kind of high-risk, high pay-off technology that NASA should be pursuing through an arm dedicated to such advanced research, like there own version of DARPA, maybe they could call it the NASA Institute for Advanced Concepts, or NIAC for short.


...oh wait...

Offline tnphysics

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Re: The Space Elevator Thread
« Reply #5 on: 10/18/2007 12:44 am »
Good idea.

Offline BarryKirk

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Re: The Space Elevator Thread
« Reply #6 on: 10/18/2007 12:53 pm »
Well, I like the idea of a Space Elevator... but.  As a first step, a rotovator would be far easier to build and could make a huge dent in the CATS problem.

With a proper rotovator, true re-usable cheap SSTO would become a possibility.  Once we've got rotovators operational and the bugs worked out, then and only then should we be looking to see if the next step, a true space elevator is viable.

Offline khallow

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Re: The Space Elevator Thread
« Reply #7 on: 10/19/2007 06:46 pm »
Barry, I don't see a rotovator working from Earth's surface due to a combination of air resistance losses (both in winding up to speed and operating at speed) and just the physical space that the rotovator would operate in. If you were speaking of using this on the Moon, then that would be a different story.
Karl Hallowell

Offline chazmataz

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Re: The Space Elevator Thread
« Reply #8 on: 10/23/2007 08:23 am »
Quote
khallow - 19/10/2007  7:46 PM

Barry, I don't see a rotovator working from Earth's surface due to a combination of air resistance losses (both in winding up to speed and operating at speed) and just the physical space that the rotovator would operate in. If you were speaking of using this on the Moon, then that would be a different story.

Nobody is suggesting that a rotovator that lifts payloads all the way from the Earth's surface to LEO would be practical with current technology.

What I believe Barry was suggesting is a rotovator which captures and lifts fast-moving payloads from the high stratosphere, at least 50 miles up, and gives them a boost of between two and four km/sec to place them in LEO.  See tethers.com for more details.  It is much technologically easier than a space elevator, and could be built with current materials.

Offline BarryKirk

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Re: The Space Elevator Thread
« Reply #9 on: 10/23/2007 01:10 pm »
I was referring to a rotovator in LEO.  It would reduce the delta v required for a rocket to acheive to reach LEO.  Small reductions in required delta v to acheive orbit make for massive increases in payload mass fraction.

And if the delta V is decreased enough ( read that large and capable rotovator in LEO ), SSTO re-usable becomes economical.  The rotovator can also reduce the heat shield requirements on the trip down as well as using downmass to help reboost.

The rotovator can be re-boosted by any number of methods including EM against the earth's magnetic field or high ISP electric rockets.

The whole point is that a rotovator could substantially reduce cost to acheive LEO and would be cheaper and technically easier to build than a full blown elevator.

Offline colbourne

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Re: The Space Elevator Thread
« Reply #10 on: 11/22/2007 05:41 am »
Once we have rotorvators working successfully, and I believe they will be made to work, there will be almost no area in which a true SE will offer any real advantage.
Space elevators are going to be slow, limited to low mass loads and due to their extreme size very costly to build.

The problem that both the SE and rotovator will suffer from is that they will both interfere with existing satallite orbits and some kind of active avoidance will have to be allowed for .
It should be possible to build a series of rotorvators that will pass loads from one to another to launch loads towards other planets and support colonies.


If we do decide to go ahead with a sunshield to prevent global warming , some kind of cheap access to space could be very useful, and the rotorvator would provide this.

Offline Michael Z Freeman

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Re: The Space Elevator Thread
« Reply #11 on: 01/08/2011 01:19 pm »
I had not considered the Rotovator up till now ...

Quote
Therefore another trick to achieve lower stresses is that rather than picking up a cargo from the ground at zero velocity, a rotovator could pick up a moving vehicle and sling it into orbit. For example, a rotovator could pick up a Mach-12 aircraft from the upper atmosphere of the Earth and move it into orbit without using rockets, and could likewise catch such a vehicle and lower it into atmospheric flight. It is easier for a rocket to achieve the lower tip speed, so "Single Stage To Tether" has been proposed. One such is called the Hypersonic Airplane Space Tether Orbital Launch (HASTOL).[9] Either air breathing or rocket to tether could save a great deal of fuel per flight, and would permit for both a simpler vehicle and more cargo.

http://en.wikipedia.org/wiki/Tether_propulsion#HASTOL_.E2.80.94_Earth_launch_assist_rotovator

That does look like a good intermediary technology in the context of CATS. Current projections based on progress of material and power beaming competitions cite a possible 2035 date for the Elevator.

Quote
Space elevators are going to be slow, limited to low mass loads and due to their extreme size very costly to build.

That's not what I'm seeing cited by the current SE experts who are in practical development of the SE ( see links here). A dollar value is cited that is much less than comparable construction values for ISS or rockets. I'll dig out the exact refs and citations but here's one ...

Quote
Rocket-based space launch systems are inherently limited by the physics of rocket propulsion. More than 90% of the rocket's weight is propellant, and the rest is split between the weight of the fuel tank and the payload. It is very difficult (if not impossible) to make such a vehicle safe or low cost. A target cost of $1000 per kg is proving to be impossible to reach. In comparison, airliners charge us about $1 per pound, and train transportation is in cents per pound

Quote
The Space Elevator is the most promising Space Transportation system on the drawing boards today, combining scalability, low cost, qualify of ride, and safety to deliver truly commercial-grade space access - practically comparable to a train ride to space.

Quote
The climbers travel at speeds comparable to a fast train, and carry no fuel on board ...

The International Space Elevator Consortium

A "fast train" is no where near a fast rocket but with the other advatages I'm not sure how much of a problem that would be.

Of course the SE still has to prove itself but what I am seeing now is projections and statements beginning to be based on R&D and engineering sense.
« Last Edit: 01/08/2011 01:23 pm by DJ Barney »
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Offline TyMoore

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Re: The Space Elevator Thread
« Reply #12 on: 01/08/2011 02:58 pm »
Build an orbital "Sky Bridge" all the way around the planet, despin the structure until it matches speed with the ground, and then lower guide cables to the ground, followed by construction of towers.

Should take only a 1000 years of concerted effort or so. Then access to space would be cheap and routine. Maybe.

:)

Offline aquanaut99

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Re: The Space Elevator Thread
« Reply #13 on: 01/08/2011 04:31 pm »
A space elevator will never work.

Even if some wonder material were discovered that could actually take the stress (instead of snapping under its own weight), that cable would not survive long. After all, it has to go through LEO, and will inevitably be struck by space debris.

Offline scienceguy

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Re: The Space Elevator Thread
« Reply #14 on: 01/08/2011 04:57 pm »
A space elevator will never work.

Even if some wonder material were discovered that could actually take the stress (instead of snapping under its own weight), that cable would not survive long. After all, it has to go through LEO, and will inevitably be struck by space debris.


What if you just made a shield or shields for the tether in LEO? (Please see diagram)
e^(pi*i) = -1

Offline Michael Z Freeman

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Re: The Space Elevator Thread
« Reply #15 on: 01/08/2011 04:59 pm »
It's possible to predict debris pass (as is currently done with the ISS) and move the tether appropriately.
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Offline colbourne

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Re: The Space Elevator Thread
« Reply #16 on: 01/09/2011 03:50 am »
Build an orbital "Sky Bridge" all the way around the planet, despin the structure until it matches speed with the ground, and then lower guide cables to the ground, followed by construction of towers.
Should take only a 1000 years of concerted effort or so. Then access to space would be cheap and routine. Maybe.


All this would achieve is getting you up to the altitude of LEO. If you are not moving at orbital velocity , you really have achieved very little.



Offline colbourne

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Re: The Space Elevator Thread
« Reply #17 on: 01/09/2011 03:51 am »
A space elevator will never work.

Even if some wonder material were discovered that could actually take the stress (instead of snapping under its own weight), that cable would not survive long. After all, it has to go through LEO, and will inevitably be struck by space debris.


What if you just made a shield or shields for the tether in LEO? (Please see diagram)

Having a shield on the tether will add so much mass to the tether which has to be supported  from the top that it is very likely impossible to build .

Offline colbourne

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Re: The Space Elevator Thread
« Reply #18 on: 01/09/2011 04:00 am »

Quote
Space elevators are going to be slow, limited to low mass loads and due to their extreme size very costly to build.

That's not what I'm seeing cited by the current SE experts who are in practical development of the SE ( see links here). A dollar value is cited that is much less than comparable construction values for ISS or rockets. I'll dig out the exact refs and citations but here's one ...


To work a space elevator has to reach at least GEO at 35,786 km (22,236 mi).
Any train journey this long is going to take a very long time. At 200mph it would take 5 days.
For a marginal SE only one shuttle can travel at a time and the mass of the cable is going to be so massive if tapering is required (almost definately) that it will take many Saturn V launches to get it up in the first place.
 Compared to the rotating tether which will only take 1 hour approximately.

Offline Michael Z Freeman

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Re: The Space Elevator Thread
« Reply #19 on: 01/09/2011 10:44 am »
5 days to lift ? How often is there a rocket launch ? 5 days is good at the potentially vastly reduced cost. The materials are a problem ...

Quote
Thus, is the space elevator out of order? Our opinion is: at present, yes; but never say never. However, our proposed flaw-tolerant concept could be key for a terrestrial space elevator design far in the future. Moreover, a lunar space elevator, because of the lower gravity, could perhaps be realized with existing materials and an opportune flaw-tolerant structural design. Tethered space systems, pioneered by Grossi and Colombo in 1972, are more intriguing in the new era of nanomaterials.

1. N. M Pugno, “Space elevator: out of order?,” Nano Today 2, no. 6 (2007): 44–47.

But engineers thrive on solving these problems and the results of development helps other areas (tether?) even if an SE is never built. I think it will be in the longterm (~2035).
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