In contrast to towers, what about this?:
"A space elevator is a proposed type of space transportation system.[1] Its
main component is a ribbon-like cable (also called a tether) anchored to the surface
and extending into space. It is designed to permit vehicle transport along the cable
from a planetary surface, such as the Earth's, directly into space or orbit, without
the use of large rockets. An Earth-based space elevator would consist of a cable
with one end attached to the surface near the equator and the other end in space
beyond geostationary orbit (35,800 km altitude). The competing forces of gravity,
which is stronger at the lower end, and the outward/upward centrifugal force, which
is stronger at the upper end, would result in the cable being held up, under
tension, and stationary over a single position on Earth. Once the tether is
deployed, climbers would repeatedly climb the tether to space by mechanical means,
releasing their cargo to orbit. Climbers would also descend the tether to
return cargo to the surface from orbit.[2] "
https://en.wikipedia.org/wiki/Space_elevator
Greg
--------------------------------------------
On Tue, 8/18/15, Chris Burgoyne <[email protected]> wrote:
Subject: Re: [geo] space elevator
To: [email protected]
Cc: "Peter Davidson" <[email protected]>, "Hugh Hunt"
<[email protected]>
Date: Tuesday, August 18, 2015, 9:57 AM
We considered
towers quite seriously as
part of the SPICE project for delivering particles to
the
stratosphere. See the full paper
Davidson P, Burgoyne C.J., Hunt H.E.M. and
Causier
M.L.T.C., Lifting
options for Stratospheric Aerosol
Geoengineering: Advantages
of Tethered Balloon System. Proc
Roy. Soc A. 370/1974
4263-4300, Sep 2012.
doi:10.1098/rsta.2011.0639.
http://www-civ.eng.cam.ac.uk/cjb/papers/p77.pdf
and a shorter version
Burgoyne C.J., Hunt H.E.M., Davidson P. and
Causier M.L.T,
Structures
for Stratospheric Particle Injection,
Paper P-0047
IASS-IABSE Symposium “Taller, Longer, Lighter”,
London Sept 2011.
http://www-civ.eng.cam.ac.uk/cjb/papers/cp94.pdf
The issue for tall towers is not strength but
stiffness. They
would buckle under their own weight unless made very
wide.
We showed in the second paper (equation 2) that the
critical
buckling length is governed by a material property
(the ratio
(E/rho.g) where E is the Young's Modulus and rho
is the density; g
is gravity) and a geometric property (the ratio of the
radius of
gyration to the length). These are multiplied by a
number that
depends on how the tower tapers to the top but that
need not
bother us here.
The important point is that you don't get much
choice about these
ratios. About the highest material ratio is given by
Carbon Fibre
Reinforced Plastic (CFRP) which has a similar
stiffness to steel
but a quarter of the density. Almost all other
engineering
materials fall within these two extremes. What you
really want to
do is to maximise Youngs Modulus and minimise
density. But it
should be noted that even the most exotic materials
only have a
stiffness that is about twice that of CFRP (because
they are
limited by the STIFFNESS (not strength) of the C-C
bond), and very
few engineering materials have a much lower density.
In addition,
the geometric ratio can't change much. The
radius of gyration of
a solid circle of radius R is R/2. For a thin
circular tube it is
R/SQRT(2) (and interestingly independent of the
thickness). No
matter how you play with the internal structure of the
tube you
are going to be somewhere within this range. We
based our SPICE
work on the assumption that the best you could do was
to use CFRP
as a thin tube, which is about as good as you can get
with any
material we currently know about.
What about the inflated tube? The problem with this,
assuming you
could design one that you could actually build, is
that it would
be subject to the same problems of self-weight
buckling. The
internal pressure is a self-equilibrating system; when
the tube
starts to buckle globally the internal volume does not
change, so
no work is done on the internal air and thus it does
not help to
resist the buckling action. The inflation might help
to resist
local buckling (dimpling of the external surface) but
that isn't
the issue.
For the SPICE project we decided that the tower should
be ruled
out on the basis of this simple analysis alone, so we
did not go
on to consider the effects of lateral wind loads (or
the Coriolis
forces you would generate on a moving lift). These
would have the
effect of moving the tower sideways so it would be as
though you
had built a non-straight tower. These initial
imperfections would
dramatically reduce the tower's capacity to resist
buckling which
would make the situation even worse.
It is possible to make quite impressive blow up towers
at
laboratory scale, because at this scale it is local
buckling that
dominates the behaviour, but not at the scale needed
for
geoengineering (or to get into space) where global
behaviour
matters.
As most readers probably know, we ended up proposing a
balloon
supporting a pipe up which "stuff"
(undefined) could be pumped.
We were initially quite surprised how expensive the
tower was and
how cheap the balloon. The difference is that the
balloon system
is completely in tension (which lightweight materials
like) rather
than in compression, which they don't. See the
concluding page of
the second paper.
Chris Burgoyne
Prof of Structural Engineering
University of Cambridge
On 18/08/2015 16:14, Andrew Lockley wrote:
Traditional space elevators are under
tension. It's
just a taut wire you go up and down (hence very
narrow, and thus
resistant to wind shear) . This is a big fat tower,
and it's
under compression . The graphics don't show any
tethers or
taper, and the sides are not obviously wind
permeable. This
means the torque at the base will be enormous.
It's just not
clear how it will actually stay up.
A
On 18 Aug 2015
16:04, "Julia Calderone"
<[email protected]>
wrote:
Hi All,
I'm a science science journalist at Tech Insider and am
writing about
the space elevator that Dr. Boucher dropped in
here
yesterday.
I am looking for some expert commentary on
the
feasibility of this tower. What distinguishes
this one
from other "space elevators"
proposed in the past? How
likely is it to work? Are the designs and
engineering
scientifically sound?
If anyone would like to chime on, please
drop me a line
— I'd greatly appreciate the
help.
Thank you very much!
My best,
Julia Calderone
On Mon,
Aug 17, 2015 at 7:20 PM,
Alan Robock <[email protected]>
wrote:
Dear Olivier,
I discussed this option in:
Robock, Alan, Allison B. Marquardt, Ben
Kravitz, and
Georgiy Stenchikov, 2009: The benefits,
risks, and
costs of stratospheric geoengineering.
Geophys.
Res. Lett., 36, L19703,
doi:10.1029/2009GL039209.
http://climate.envsci.rutgers.edu/pdf/2009GL039209.pdf
You'll see the tower in Figs. 1
and 3. See
Section 4.4 for discussion of this
option.
Figure 1. Proposed methods of
stratospheric aerosol
injection. A mountain top location would
require less
energy for lofting to stratosphere.
Drawing by Brian
West.
Alan
Alan Robock, Distinguished Professor
Editor, Reviews of Geophysics
Department of Environmental Sciences Phone: +1-848-932-5751
Rutgers University Fax: +1-732-932-8644
14 College Farm Road E-mail: [email protected]
New Brunswick, NJ 08901-8551 USA http://envsci.rutgers.edu/~robock
http://twitter.com/AlanRobock
Watch my 18 min TEDx talk at http://www.youtube.com/watch?v=qsrEk1oZ-54
On 8/17/15 1:26 PM, Olivier
Boucher wrote:
Hello,
this is relevant to SRM by
stratospheric
particles
http://www.independent.co.uk/news/science/a-canadian-company-is-planning-to-build-a-tower-thats-20km-high-and-could-making-flying-to-space-like-taking-a-passenger-jet-10459058.html
http://thothx.com/news-2/
although I don't know how
realistic and advanced
the plans are...
Regards,
Olivier
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