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Question on the space elevator



 
 
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  #11  
Old April 1st 04, 02:36 PM
Poliisi
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Default Question on the space elevator

You are going to drop if from the sky?

Yes, exactly.


Its easy to say, much harder to go into specifics. There are
atleast 2 things which are left almost completely undescribed amongst
space elevator "supporters".

1. The process before we have this massive cable under tension.

2. The lifting mechanism with a little more spesific analysis than "we
use magnets ofcourse!".

From these 2 points starts the branching of REAL problems of space

elevators and how it might not be a magical way to get things cheaply to
orbit.
  #12  
Old April 2nd 04, 08:19 AM
Keith Harwood
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Default Question on the space elevator

Henry Spencer wrote:

In article ,
Richard Lamb wrote:
don't build it from the ground up; it's lowered from above (possibly one
strand at a time rather than all at once), not raised from below.


You are going to drop if from the sky?


"Lower" it from the sky, please -- it will be supported at all times, from
above.


Then there's Sheffield's solution. Build the whole thing a long way away and
put it in place in one go.
  #13  
Old April 2nd 04, 08:22 AM
Keith Harwood
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Default Question on the space elevator

Henry Spencer wrote:

In article ,
Andromeda et Julie wrote:
imagine what impact such a material would have on architecture,
bulding, bridges design .. etc ...


Not to mention rocket design. A standard mistake made by many proponents
of advanced launch schemes is to assume that they are competing against
today's rockets, not against rockets which are given the same advantages
as their scheme (billions of dollars invested, a steady flow of traffic
guaranteed, significant technical advances made, etc.).


Yup. Suppose, for example, such a material was used to make, say, pressure
vessles that mught contain such things as, say, rocket propellants.
  #14  
Old April 5th 04, 09:59 PM
E.R.
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Default Question on the space elevator

Poliisi wrote in message ...
You are going to drop if from the sky?


Yes, exactly.


Its easy to say, much harder to go into specifics. There are
atleast 2 things which are left almost completely undescribed amongst
space elevator "supporters".

1. The process before we have this massive cable under tension.

2. The lifting mechanism with a little more spesific analysis than "we
use magnets ofcourse!".


The current answer to the last question isn't magnets but .. lasers.
Free Electron lasers beam power to the climber, which converts the
energy into mechanical energy (wheels or treads). IIRC, a FEL has
been designed that can do the job.
  #15  
Old April 6th 04, 10:37 PM
Makhno
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Default Question on the space elevator

The current answer to the last question isn't magnets but .. lasers.
Free Electron lasers beam power to the climber, which converts the
energy into mechanical energy (wheels or treads). IIRC, a FEL has
been designed that can do the job.


There's a lot of traffic in this thread about powering the climber. Why
can't it simply have a diesel/gasoline engine with its own oxygen supply?
Or run electrical cables up the elevator to power an electric motor?

Why make things more complicated than they need to be?


  #16  
Old April 7th 04, 03:08 AM
Gordon D. Pusch
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Default Question on the space elevator

"Makhno" writes:

The current answer to the last question isn't magnets but .. lasers.
Free Electron lasers beam power to the climber, which converts the
energy into mechanical energy (wheels or treads). IIRC, a FEL has
been designed that can do the job.


There's a lot of traffic in this thread about powering the climber. Why
can't it simply have a diesel/gasoline engine with its own oxygen supply?
Or run electrical cables up the elevator to power an electric motor?

Why make things more complicated than they need to be?


Your proposal is not _totally_ implausible. The energy required to climb
a beanstalk is only a small fraction of the energy required to accelerate
a payload into Low Earth Orbit; the fuel and oxygen tankage required
would be large, but not prohibitively so.


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'
  #17  
Old April 7th 04, 03:38 AM
Henry Spencer
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Default Question on the space elevator

In article ,
Makhno wrote:
There's a lot of traffic in this thread about powering the climber. Why
can't it simply have a diesel/gasoline engine with its own oxygen supply?


Because the mass of fuel and oxygen is prohibitive for a climb that long.

Or run electrical cables up the elevator to power an electric motor?


Transmitting useful amounts of electrical power thousands of kilometers
*without* adding significant mass to the cable is extremely difficult.
(The current near-term elevator designs have a total cable cross-section
of about one square millimeter. They don't have enough strength margin to
tolerate any significant increase in cross-section that doesn't add
strength too.)

Why make things more complicated than they need to be?


Because they really do need to be that complicated.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |
  #18  
Old April 7th 04, 05:19 AM
David M. Palmer
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Default Question on the space elevator

In article , Makhno
wrote:

The current answer to the last question isn't magnets but .. lasers.
Free Electron lasers beam power to the climber, which converts the
energy into mechanical energy (wheels or treads). IIRC, a FEL has
been designed that can do the job.


There's a lot of traffic in this thread about powering the climber. Why
can't it simply have a diesel/gasoline engine with its own oxygen supply?
Or run electrical cables up the elevator to power an electric motor?

Why make things more complicated than they need to be?


Roughly, 1 kg of fuel and oxidizer has about 4 megajoule of energy,
which is enough to lift 1 kg 400 km at 1g.

Climbing out of the gravity well of Earth is comparable to climbing one
Earth radius (6400 km) under a constant 1 g (there's probably a factor
of 2 or 1/2 or something like that, but back-of-the-envelope).

So it would take about 16 kg of fuel+oxidizer, give or take, to send 1
kg up the elevator. But you also have to carry the fuel to lift the
fuel, and the fuel to lift the fuel to lift the fuel, and so on.
Mathematically, you would have to carry e^16= 9 million kg of fuel+ox.
(Factors of 2 or 1/2 at that point become very important.)

Anyway, beaming the power becomes economical at that point.

--
David M. Palmer (formerly @clark.net, @ematic.com)
  #19  
Old April 7th 04, 06:32 AM
Hop David
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Default Question on the space elevator



David M. Palmer wrote:
In article , Makhno
wrote:


The current answer to the last question isn't magnets but .. lasers.
Free Electron lasers beam power to the climber, which converts the
energy into mechanical energy (wheels or treads). IIRC, a FEL has
been designed that can do the job.


There's a lot of traffic in this thread about powering the climber. Why
can't it simply have a diesel/gasoline engine with its own oxygen supply?
Or run electrical cables up the elevator to power an electric motor?

Why make things more complicated than they need to be?



Roughly, 1 kg of fuel and oxidizer has about 4 megajoule of energy,
which is enough to lift 1 kg 400 km at 1g.

Climbing out of the gravity well of Earth is comparable to climbing one
Earth radius (6400 km) under a constant 1 g (there's probably a factor
of 2 or 1/2 or something like that, but back-of-the-envelope).

So it would take about 16 kg of fuel+oxidizer, give or take, to send 1
kg up the elevator. But you also have to carry the fuel to lift the
fuel, and the fuel to lift the fuel to lift the fuel, and so on.
Mathematically, you would have to carry e^16= 9 million kg of fuel+ox.
(Factors of 2 or 1/2 at that point become very important.)

Anyway, beaming the power becomes economical at that point.


I had always envisioned cars on perpetually cycling loops, like a ski
lift. Much of the movement would be done by inertia with some energy
spent to compensate for friction loss.


--
Hop David
http://clowder.net/hop/index.html

  #20  
Old April 7th 04, 12:45 PM
Keith Harwood
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Default Question on the space elevator

Gordon D. Pusch wrote:

Keith Harwood writes:


Yup. Suppose, for example, such a material was used to make, say,
pressure vessles that mught contain such things as, say, rocket
propellants.


For any reasonable strength of material, the amount of additional energy
that can be stored by pressurizing the tanks is negligible compared to the
chemical energy stored in the propellants themselves. About all you will
do by pressurizing the tanks is to allow you to eliminate the mass of the
turbopumps and drive turbines, which is likely to be marginal compared to
the additional mass of high-pressure propellant tanks. Pressure-fed
rockets _may_ be justifiable on the basis of lower cost or higher
reliability, but are =VERY= unlikely to provide significantly better
performance than pump-fed rockets.


I was thinking that the unobtainium that had sufficient tensile strength
with low mass to build a beanstalk could also be used to make pressure
vessels that are very much lighter than those from presently existing
materials and, indeed, would be lighter than existing unpressurised tanks.
My consideration was the mass savings from no pumps and from the tankage
itself. It hadn't occurred to me to even consider the energy stored in the
pressurisation.

My point was simply that the material that made the beanstalk feasible
compared to conventional rocketry would help make rocketry more competitive
against a beanstalk.

(PS, sorry about the deplorable typing my previous post.)
 




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