Question: space elevator
CG
I'm writing it into a short story. Is it possible to
create a space elevator with current or possible
near future tech?
I was thinking that nano-carbon tubing might do it
and I know they are already doing that--saw an article
on it. But with the Earth spinning, would the elevator
spin with it like a satellite or would you need to somehow keep pushing it
to keep it in geosynchronized orbit?
And I mean an elevator to a space station, not the moon. I can't even get
my head wrapped around that one.
Thanks,
--
CG
cgan...@myuw.net
**Goals are just DREAMS with DEADLINES!
**Live your life with passion and risk!
website: http://home.myuw.net/cganders
humor blog: Musings and Meanings on NonSensical Events and Canada
http://ahablogolicious.blogspot.com/
Vendikarr
current tech.
http://www.sciencenews.org/articles/20021005/bob9.asp
PV
> I'm writing it into a short story. Is it possible to
> create a space elevator with current or possible
> near future tech?
I'm going to use some buzzwords here - they'll be useful for doing more
googling.
Ribbons made of carbon nanotubes still can't QUITE be made yet, but all
indications are, once they can become longer than 18 inches, that they will
have the strength needed for such a project, with some clever engineering
hacks. Some say we're 15 years away from being able to make the cable, some
as short as 5 years.
>on it. But with the Earth spinning, would the elevator
>spin with it like a satellite or would you need to somehow keep pushing it
> to keep it in geosynchronized orbit?
An object in geosyncronous orbit is stationary in respect to the rotating
earth. So, what you have is an 'anchor' object up in space, and a tether
going to the ground directly under it (and possibly lots of other places
nearby). The cable is essentially supporting only its OWN weight, plus the
weight of anything climbing on it, plus a bit more (the anchor is placed a
bit further than geosync, which means it pulls a bit on the tether) to
maintain tension.
>And I mean an elevator to a space station, not the moon. I can't even get
>my head wrapped around that one.
There's really no way to make a space elevator to the moon, since the moon
moves relative to the surface of the earth. There ARE points of stability
(libration points), so a totally far-out idea would be to string cable
between these points and have a trolley system between the earth and moon.
Making a space elevator on the moon itself would be a lot simpler - you
would need a much shorter cable, you don't have to deal with the stress
from wind, and the cable doesn't have to be as strong. *
--
* PV something like badgers--something like lizards--and something
like corkscrews.
CG
--
"Vendikarr" <vend...@aol.com> wrote in message
news:1151509497.0...@x69g2000cwx.googlegroups.com...
CG
build a space elevator that runs up from the moon, rather than
the earth itself.
--
CG
cgan...@myuw.net
**Goals are just Dreams with Deadlines! ...Keith Ferrazzi, et. al.
website: http://home.myuw.net/cganders
humor blog: http://ahablogolicious.blogspot.com/
"PV" <pv+u...@pobox.com> wrote in message
news:12a5chd...@news.supernews.com...
William George Ferguson
>
> I'm writing it into a short story. Is it possible to
> create a space elevator with current or possible
> near future tech?
>
> I was thinking that nano-carbon tubing might do it
>and I know they are already doing that--saw an article
>on it. But with the Earth spinning, would the elevator
>spin with it like a satellite or would you need to somehow keep pushing it
> to keep it in geosynchronized orbit?
Something stays in geosynchronous orbit because it keeps fall to Earth and
missing at exactly the speed to make it orbit the Earth every 24 hours (and
mumblety-mumble minutes and seconds). Once there, it will stay there, more
or less.
The space elevator concept is to have a cable (actually a group of cables)
that goes from the Earth to an orbital structure in geosynchronous orbit.
The exact details and orbital height varies with different projects. With
the development of carbon nanotubes, the concept is generally conceded to
have moved at least partially out of the vaporware stage (the cable was the
one piece of unobtanium, the rest is just engineering with today's tech).
There are at least two private corporations in the U.S. actively working on
building a space elevator. At least three other programs (Chinese,
Japanese, and European Space Agency) are known to exist, although they
generally don't talk about how far along they are. The Liftport Group (one
of the U.S. corporations formed to build a space elevator) lists its
current target date for for first payload going up the cable as 2018.
They've tested models of the elevator cars, using tethered balloons, In
open air tests in inclement weather, they've had a lifter climb 290 feet up
the tether.
>And I mean an elevator to a space station, not the moon. I can't even get
>my head wrapped around that one.
The proposed moon elevator would be the same sort of thing as the Earth
space elevator, except going from the moon into space (not from the Earth
to the moon). Instead of using a selenosynchronous orbit (which would be
tricky to make stable, because of that huge chunk of real estate the moon
orbits), the moon elevator would use an Earth-Moon gravitational balance
point, Lagrange Point 1, as the location of the upper end of the cable.
With both an earth elevator/skyhook and a moon elevator/skyhook, it would
be fairly easy to transfer between them by slingshotting from one skyhook
to the other.
Now if you had this parrot named Lil, you might think about a true
Earth-Moon elevator, sort of a 'star bridge'.
--
... and my sister is a vampire slayer, her best friend is a witch who
went bonkers and tried to destroy the world, um, I actually used to be
a little ball of energy until about two years ago when some monks
changed the past and made me Buffy's sister and for some reason, a big
klepto. My best friends are Leticia Jones, who moved to San Diego
because this town is evil, and a floppy eared demon named Clem.
(Dawn's fantasy of her intro speech in "Lessons", from the shooting script)
Wayne Throop
: But with the Earth spinning, would the elevator spin with it like a
: satellite or would you need to somehow keep pushing it to keep it in
: geosynchronized orbit?
The way to think of it is to note that a space elevator of this simple
type is not just *like* a satellite, it *is* a satellite. Just a long
skinny one; so long that the bottom end touches the ground. Note that as
you conceptually stretch a satellite to make it reach the earth, you also
have to stretch it *above* geosynchronous orbit, so its center of mass
stays at the right distance from earth. So just pull on both ends of
this stretchy satellite until it fits. And since it's a geosynchronous
satellite, it actually can be simply touching the earth's surface,
since it's, well, geosynchronous.
Now, since the bottom is dipping into the atmosphere, winds and such
could be pushing on it. But not to the extent of braking it for reentry,
and further, you can anchor the bottom end and move a counterweight up a
bit so the center of mass is a bit above geosync, to keep it in tension.
Well, more tension than tides are already putting on it. Indeed, for
it to be able to lift things to orbit, you'd want to do it that way.
So. The answer is yes and no. No, to a first approximation, you don't
need to "keep pushing it"; it's just a normal satellite, but very long.
But yes, in order to lift cargo, it's probably best to ensure that
"centrifugal force" is pushing (or pulling, whatever) upwards on it.
So you have to bolt it to the ground. With very VERY big bolts.
: I'm writing it into a short story. Is it possible to create a space
: elevator with current or possible near future tech?
I don't think so. Depends on what practical strides you think might
occur in macroscopic cable strengths in the near future, but there are
many many orders of magnitude of improvements to make before a simple
space elevator concept would work. I mean, what's the longest
suspension bridge ever built? Yeesh, we haven't even done the Gibraltar
Bridge yet. Now scale that up by a few hundred (or more like thousand)
times. I don't think it'll happen in the next couple-three decades.
IIRC, the engineer that built the space elevator in "Fountains of Paradise"
had previously built the Gibraltar Bridge.
Wayne Throop thr...@sheol.org http://sheol.org/throopw
PV
>thanks!! very useful...sounds like it would be better to first
>build a space elevator that runs up from the moon, rather than
>the earth itself.
There are some good reasons for doing that, including it being a safer
place to test in. On the other hand, since there's no air and weak
gravity, getting things off the moon is already a lot easier than off
the earth, even without a space elevator. *
lal_truckee
>
> Now if you had this parrot named Lil, you might think about a true
> Earth-Moon elevator, sort of a 'star bridge'.
Doesn't it turn out that Lil had Wu? Not the other way round?
Per the original poster's query about rotation (caused by
misunderstanding geostationary) the Star Bridges are attached to polar
caps that counter rotate while floating on a film of mercury IIRC, to
keep the Bridges from winding up like yarn. But that's really a
different situation.
Anyone have a diamond for Lil?
Joer...@yahoo.de
CG wrote:
> I'm writing it into a short story. Is it possible to
> create a space elevator with current or possible
> near future tech?
Do I understand the concept correctly when I assume that a space
elevator has to be based at the equator since any GEO has to be above
the equator?
(AFAIK, this was the biggest thing Clarke changed when making Sri Lanka
into Taprobane, since SL isn´t at the equator.)
So, where along the equator would a good place for the base of an SE
be?
Is it better to pick an already elevated place like the Andes near
Quito or the mountains of Sumatra or Borneo - or is the difference in
cable length negligible?
Jörg
CG
of orbit into dense atmosphere then the whole geosync satellite assumption
becomes problematic. And I was concerned about the mass moving up and
down the elevator, changing its 'weight' as it moves...
and wondering whether the mechanism moving the elevator
should be based on the satellite or on the earth...or both..
in order to handle the changing gravitational effects on the mass...
and whether rotating the elevator as it gradually moves up
from earth gravity to no gravity would work
as a way of giving the occupants a sense of artificial gravity instead of
weightlessness.
I'm trying to be accurate and foresee as many problems and possible
solutions
as I can...but it just gets more and more complicated...maybe I should just
pull
a SG1 and call it magic (aka alien crystals power it)
and forgive my ignorance, but I haven't read or heard of "Fountains of
Paradise",
who wrote it so I can get a copy and update my ignorance to something less
so.
--
**Goals are just Dreams with Deadlines! ...Keith Ferrazzi, et. al.
website: http://home.myuw.net/cganders
humor blog: http://ahablogolicious.blogspot.com/
"Wayne Throop" <thr...@sheol.org> wrote in message
news:11515...@sheol.org...
Marilee J. Layman
dropped.
On Wed, 28 Jun 2006 08:28:32 -0700, "CG" <cgan...@u.washington.edu>
wrote:
>
--
Marilee J. Layman
http://mjlayman.livejournal.com/
Sea Wasp
> I'm writing it into a short story. Is it possible to
> create a space elevator with current or possible
> near future tech?
>
Yep. I've had to research it for the sequel to Boundary.
Look up the guys at "Liftport".
--
Sea Wasp
/^\
;;;
Live Journal: http://www.livejournal.com/users/seawasp/
Matthew B. Tepper
letters to be typed in news:e7v26o$pn9$1...@gnus01.u.washington.edu:
> and forgive my ignorance, but I haven't read or heard of "Fountains of
> Paradise", who wrote it so I can get a copy and update my ignorance to
> something less so.
Arthur C. Clarke (now Sir Arthur).
--
Matthew B. Tepper: WWW, science fiction, classical music, ducks!
My personal home page -- http://home.earthlink.net/~oy/index.html
My main music page --- http://home.earthlink.net/~oy/berlioz.html
To write to me, do for my address what Androcles did for the lion
Take THAT, Daniel Lin, Mark Sadek, James Lin & Christopher Chung!
Michael Bowker
> thank you! and yes, I was assuming that if something extends down out
> of orbit into dense atmosphere then the whole geosync satellite assumption
> becomes problematic. And I was concerned about the mass moving up and
> down the elevator, changing its 'weight' as it moves...
>
> and wondering whether the mechanism moving the elevator
> should be based on the satellite or on the earth...or both..
> in order to handle the changing gravitational effects on the mass...
>
> and whether rotating the elevator as it gradually moves up
> from earth gravity to no gravity would work
> as a way of giving the occupants a sense of artificial gravity instead of
> weightlessness.
>
> I'm trying to be accurate and foresee as many problems and possible
> solutions
> as I can...but it just gets more and more complicated...maybe I should just
> pull
> a SG1 and call it magic (aka alien crystals power it)
>
> and forgive my ignorance, but I haven't read or heard of "Fountains of
> Paradise",
> who wrote it so I can get a copy and update my ignorance to something less
> so.
>
Arthur C. Clark
http://en.wikipedia.org/wiki/Fountains_of_Paradise
The Fountains of Paradise - Wikipedia, the free encyclopedia
The thing about Space elevators that most people ignore or don't know is
that it would be a Dynamo (ie a conductor rotating through a magnetic
field). Thus you would have to get rid of the generated electricity or
be subject to massive static problems.
Keith F. Lynch
> Do I understand the concept correctly when I assume that a space
> elevator has to be based at the equator since any GEO has to be
> above the equator?
It should at least be close to the equator. It could be a little off,
and ascend at an angle.
> Is it better to pick an already elevated place like the Andes near
> Quito or the mountains of Sumatra or Borneo - or is the difference
> in cable length negligible?
High altitude might be a good idea just to get above most of the
weather and a fair percentage of the atmosphere.
--
Keith F. Lynch - http://keithlynch.net/
Please see http://keithlynch.net/email.html before emailing me.
David Friedman
Joer...@yahoo.de wrote:
> CG wrote:
> > I'm writing it into a short story. Is it possible to
> > create a space elevator with current or possible
> > near future tech?
>
>
> Do I understand the concept correctly when I assume that a space
> elevator has to be based at the equator since any GEO has to be above
> the equator?
The standard version does. There are a variety of more complicated
versions in which the bottom end doesn't touch the ground, and I'm not
sure that all of them have to be equatorial.
There is quite an ingenious one, equatorial but in lower than
geosynchronous orbit, where the ladder is like two opposite spokes of a
rolling wheel. When one end reaches its lower point, it is moving
backwards relative to the center of mass of the ladder just as fast as
the center of mass is moving forwards relative to the earth, so standing
still relative to the earth--just like the bottom of the tire of a
moving automobile.
--
http://www.daviddfriedman.com/ http://daviddfriedman.blogspot.com/
Author of _Harald_, a fantasy without magic.
Published by Baen, in bookstores now
CG
that one. I'll check the local library.
--
CG
cgan...@myuw.net
**Goals are just Dreams with Deadlines! ...Keith Ferrazzi, et. al.
website: http://home.myuw.net/cganders
humor blog: http://ahablogolicious.blogspot.com/
"Matthew B. Tepper" <oy兀earthlink.net> wrote in message
news:Xns97F0B459945...@207.217.125.201...
Matthew B. Tepper
following letters to be typed in news:12a694o...@corp.supernews.com:
> Arthur C. Clark
+mc^2
walt...@mindspring.com
assembly . . .
Walt BJ
Wayne Throop
: I keep wondering about atmospheric drag on the space elevator's cable
: assembly . . .
Why should there be any?
( Wind loads could technically be drag, but aren't
usually thought of that way, are they? )
Joe Bednorz
[rec.arts.sf.science added]
>I keep wondering about atmospheric drag on the space elevator's cable
>assembly . . .
>Walt BJ
None. The magic is that the space elevator does not move relative to
the planet. It's anchored at the base, after all. In one sense, it's
just a very tall building.
In another sense, it's a cable "hanging" off of a space station in
geosynchronous orbit. Geosynchronous means the orbit lasts exactly one
day, so the station would seem to 'hang' over a given point on the
earth's equator. Note that geosynchronous orbits can only work if the
orbit is entirely in the earth's equatorial plane.
Geosynchronous orbits are also restricted to a height of 22,000 miles
above the earth's surface. Any higher and they would take longer than
24 hours to circle the earth. Any lower and they would take less than
24 hours.
So the location of the base of the space elevator must be on the
equator. It also must be at least 22,000 miles high. For fun, get a
globe to see what countries could have a space elevator.
See this link for NASA's take on geosynchronous orbits:
<http://liftoff.msfc.nasa.gov/academy/rocket_sci/satellites/geo-high.html>
It's a nice bit of magic that A. C. Clarke apparently mentioned first
in 'Islands in the Sky'.
--
Alice in Wonderland Interactive Adventure: <http://www.ruthannzaroff.com/wonderland/>
Baen Free Online SciFi Library: <http://www.baen.com/library/>
SciFi.com classic & original works: <http://www.scifi.com/scifiction/archive.html>
All the best, Joe Bednorz
David Friedman
Joe Bednorz <inv...@invalid.invalid> wrote:
> It's a nice bit of magic that A. C. Clarke apparently mentioned first
> in 'Islands in the Sky'.
Clarke isn't even close to the first person to mention the idea. It
seems to have been first proposed by Yuri Artsutanov, a Leningrad
engineer, in 1960, and has been independently invented multiple times
since.
Wayne Throop
:: <http://liftoff.msfc.nasa.gov/academy/rocket_sci/satellites/geo-high.html>
:: It's a nice bit of magic that A. C. Clarke apparently mentioned
:: first in 'Islands in the Sky'.
: David Friedman <dd...@daviddfriedman.nopsam.com>
: Clarke isn't even close to the first person to mention the idea. It
: seems to have been first proposed by Yuri Artsutanov, a Leningrad
: engineer, in 1960, and has been independently invented multiple times
: since.
Well, since Clarke copyrighted Islands in the Sky in 1952,
that's some meaning of "first proposed" with which I have previously
been unaquainted.
Note that the "nice bit of magic" refered to above is geosync orbit.
Not orbital towers or space elevators.
Paul Colquhoun
| In article <1151530245.7...@i40g2000cwc.googlegroups.com>,
| Joer...@yahoo.de wrote:
|
|> CG wrote:
|> > I'm writing it into a short story. Is it possible to
|> > create a space elevator with current or possible
|> > near future tech?
|>
|>
|> Do I understand the concept correctly when I assume that a space
|> elevator has to be based at the equator since any GEO has to be above
|> the equator?
|
| The standard version does. There are a variety of more complicated
| versions in which the bottom end doesn't touch the ground, and I'm not
| sure that all of them have to be equatorial.
|
| There is quite an ingenious one, equatorial but in lower than
| geosynchronous orbit, where the ladder is like two opposite spokes of a
| rolling wheel. When one end reaches its lower point, it is moving
| backwards relative to the center of mass of the ladder just as fast as
| the center of mass is moving forwards relative to the earth, so standing
| still relative to the earth--just like the bottom of the tire of a
| moving automobile.
This variant is quite often called a "skyhook"
http://en.wikipedia.org/wiki/Skyhook_%28structure%29
--
Reverend Paul Colquhoun, ULC. http://andor.dropbear.id.au/~paulcol
Asking for technical help in newsgroups? Read this first:
http://catb.org/~esr/faqs/smart-questions.html#intro
David Friedman
wrote:
Then I misread your post. I thought you were talking about space
elevators.
I don't know who first proposed geosynchronous orbit, or when.
But Google does--and it apparently wasn't Clarke:
"The concept of the geostationary orbit has been around since the early
part of the twentieth century. Apparently, the concept was originated by
Russian theorist Konstantin Tsiolkovsky‹who wrote numerous science and
science-fiction articles on space travel at the turn of the century. In
the 1920s, Hermann Oberth and Herman Potocnik‹perhaps better known by
his pseudonym, Herman Noordung‹wrote about space stations which
maintained a unique vantage over the earth.1 Each author described an
orbit at an altitude of 35,900 kilometers whose period exactly matched
the earth's rotational period, making it appear to hover over a fixed
point on the earth's equator.
However, the person most widely given credit for the concept of using
this orbit for communications is Arthur C. Clarke. In an article he
published in Wireless World in October 1945 titled "Extra-Terrestrial
Relays: Can Rocket Stations Give World-wide Radio Coverage?" Clarke "
Ken from Chicago
Why not an artificial ring, ala HALO the videogame series, but big enough to
ring the Earth in orbit? Skylines could go into Earth orbit and to the space
ring then a MOVING skyline could go from the Moon to the space ring. A space
cab ride up the line from Earth to the space ring in Earth orbit then travel
along the ring to catch the moving skyline going to the moon and travel to
the moon--and vice versa.
-- Ken from Chicago
Leif Magnar Kj|nn|y
>
> [rec.arts.sf.science added]
>
>>I keep wondering about atmospheric drag on the space elevator's cable
>>assembly . . .
>>Walt BJ
>
> None. The magic is that the space elevator does not move relative to
>the planet. It's anchored at the base, after all. In one sense, it's
>just a very tall building.
Although its weight is not resting on the ground and it's not held up
by compressive strength. It's under tension, hanging down from orbit.
> In another sense, it's a cable "hanging" off of a space station in
>geosynchronous orbit. Geosynchronous means the orbit lasts exactly one
>day, so the station would seem to 'hang' over a given point on the
>earth's equator. Note that geosynchronous orbits can only work if the
>orbit is entirely in the earth's equatorial plane.
Strictly speaking, a geosynchronous orbit is any orbit with a period
equal to the Earth's rotation, so that the orbiter will pass
over the same spots on the surface on the same time each day. The
special case where the orbit is also circular and equatorial is called
a geostationary orbit, and that is what's needed for this setup.
The cable needs to either continue quite far outside of geostationary
orbit, or else be attached to a counterweight. In order for the whole
thing to stay up, its center of gravity must be in geostationary orbit
(or just a tad outside of it), and on this scale we cannot approximate
the Earth's gravity field as constant (so its center of gravity and
center of mass are not approximately in the same place).
--
Leif Kjønnøy, cunctator maximus. http://www.pvv.org/~leifmk
Mark L. Fergerson
> On 28 Jun 2006 20:14:34 -0700, walt...@mindspring.com wrote:
>
> [rec.arts.sf.science added]
>>I keep wondering about atmospheric drag on the space elevator's cable
>>assembly . . .
> None. The magic is that the space elevator does not move relative to
> the planet. It's anchored at the base, after all. In one sense, it's
> just a very tall building.
Aaand the entire volume of air surrounding the cable is stationary
WRT the cable? And very tall buildings never have frinst windows sucked
right out of them by winds?
> ...the location of the base of the space elevator must be on the
> equator. It also must be at least 22,000 miles high. For fun, get a
> globe to see what countries could have a space elevator.
For extra fun, see how many of those places frequently have violently
non-stationary air masses (hurricanes, typhoons, etc.) pass over them.
Mark L. Fergerson
Joe Ellis
"Mark L. Fergerson" <mferg...@cox.net> wrote:
> Joe Bednorz wrote:
> > On 28 Jun 2006 20:14:34 -0700, walt...@mindspring.com wrote:
> >
> > [rec.arts.sf.science added]
>
> >>I keep wondering about atmospheric drag on the space elevator's cable
> >>assembly . . .
>
> > None. The magic is that the space elevator does not move relative to
> > the planet. It's anchored at the base, after all. In one sense, it's
> > just a very tall building.
>
> Aaand the entire volume of air surrounding the cable is stationary
> WRT the cable? And very tall buildings never have frinst windows sucked
> right out of them by winds?
Simple engineering problems. Wind makes tall buildings sway, but I don't
recall many modern ones being blown over. And windows don't seem to get
sucked out of the space shuttle at Mach 25.
> > ...the location of the base of the space elevator must be on the
> > equator. It also must be at least 22,000 miles high. For fun, get a
> > globe to see what countries could have a space elevator.
>
> For extra fun, see how many of those places frequently have violently
> non-stationary air masses (hurricanes, typhoons, etc.) pass over them.
This is why equatorial Africa is usually proposed as the site.
But then, imagine the security problems. One of the stories involving a
"beanstalk" had a terrorist bomb going off in a car part way up the
elevator... and tens of thousands of miles of cable falling to earth.
Ouch.
Even if only the lower 100 miles or so survived re-entry.
Ouch.
--
Evaluating all GUIs by the example of Windows is like evaluating all cars
by the example of Yugos.
Paul Harman
news:synthfilker-2237...@newsclstr02.news.prodigy.com...
> But then, imagine the security problems. One of the stories involving a
> "beanstalk" had a terrorist bomb going off in a car part way up the
> elevator... and tens of thousands of miles of cable falling to earth.
ObSF: Kim Stanley Robinson's "Mars" series of novels.
Paul
Michael Ash
>
> But then, imagine the security problems. One of the stories involving a
> "beanstalk" had a terrorist bomb going off in a car part way up the
> elevator... and tens of thousands of miles of cable falling to earth.
>
> Ouch.
>
> Even if only the lower 100 miles or so survived re-entry.
>
> Ouch.
A space elevator will resemble ribbon more than cable. Imagine thousands
of miles of ribbon falling to earth from space and surviving reentry.
Scared? You shouldn't be. It will flutter gently to the ground and harm
nothing. The biggest worry will be people cutting themselves on the edges,
or possibly getting poisoned from it. A KSR-esque planetwide catastrophe
doesn't bear much resemblance to what it seems like a real space elevator
will be, at least at first.
--
Michael Ash
Rogue Amoeba Software
PV
>thank you! and yes, I was assuming that if something extends down out
>of orbit into dense atmosphere then the whole geosync satellite assumption
>becomes problematic.
Since the elevator is stationary with respect to the weather as much as it
is with the ground, it's not a problem. There was some worry that a space
elevator would become a giant lightning rod, but that's not a problem with
the materials being discussed.
>and I was concerned with the mass moving up and down the elevator,
>changing its 'weight' as it moves...
Earth's gravity becomes less and less of a factor as you climb. The only
way a passenger's apparent weight would change otherwise would be if the
car was under constant accelleration. What they're actually talking about
right now is having the car reach about 120mph, and then cruise at a
constant speed up the cable for a week.
>and wondering whether the mechanism moving the elevator
>should be based on the satellite or on the earth...or both..
>in order to handle the changing gravitational effects on the mass...
There's lots of ways it could be done. You want weirdness, look up
'skyhook', a special case of a space elevator. What's being proposed right
now is that the payload will simply climb the cable, with power beamed up
to it from the ground by a laser.
>and whether rotating the elevator as it gradually moves up
>from earth gravity to no gravity would work as a way of giving the
>occupants a sense of artificial gravity instead of weightlessness.
I suppose you could build a spinning wheel structure that climbs with
the cable at the center, but there doesn't seem to be much point to it
- low gravity is a GOOD thing for fragile payloads. Shaking and bumping
are one of the problems of rocket propulsion. You have to build your
satellites robust enough to survive launch, and then they never will
be subjected to those stresses ever again. Also, you'd need a fairly large
wheel, or you'd have to spin very fast, to simulate significant gravity,
and even then it can cause nausea, if that's what you're trying to avoid.
>I'm trying to be accurate and foresee as many problems and possible
>solutions as I can...but it just gets more and more complicated...maybe
>I should just pull a SG1 and call it magic (aka alien crystals power it)
Your desire to do something in the hard-SF area admirable. However, you
should probably leave the nuts and bolts details to a minimum in the story
UNLESS they're important to the plot. Otherwise you end up with the
Gernsback syndrome - read one of his early stories if you don't know what I
mean.
>and forgive my ignorance, but I haven't read or heard of "Fountains of
>Paradise", who wrote it so I can get a copy and update my ignorance
>to something less so.
Arthur C. Clarke. His space elevator is not all that different than the
ideas being kicked around now. The man knows how to make predictions. *
PV
>The thing about Space elevators that most people ignore or don't know is
>that it would be a Dynamo (ie a conductor rotating through a magnetic
>field). Thus you would have to get rid of the generated electricity or
>be subject to massive static problems.
No it won't, because the cable is stationary - it's not like the tether
experiments in orbit, where the cable was whipping through earth's magnetic
field at 19,000 mph.
There are a lot of 'most people ignore' things that critics say about space
elevators that are simply not true. *
Mark L. Fergerson
> In article <0vQog.655$Mz3.461@fed1read07>,
> "Mark L. Fergerson" <mferg...@cox.net> wrote:
>>Joe Bednorz wrote:
>>
>>>On 28 Jun 2006 20:14:34 -0700, walt...@mindspring.com wrote:
>>>
>>> [rec.arts.sf.science added]
>>
>>>>I keep wondering about atmospheric drag on the space elevator's cable
>>>>assembly . . .
>>
>>> None. The magic is that the space elevator does not move relative to
>>>the planet. It's anchored at the base, after all. In one sense, it's
>>>just a very tall building.
>>
>> Aaand the entire volume of air surrounding the cable is stationary
>>WRT the cable? And very tall buildings never have frinst windows sucked
>>right out of them by winds?
> Simple engineering problems. Wind makes tall buildings sway, but I don't
> recall many modern ones being blown over. And windows don't seem to get
> sucked out of the space shuttle at Mach 25.
Current "tall buildings" don't stick all the way up into say jet
streams; lateral forces from winds (especially shear from different wind
directions at different altitudes) will bend the thing, effectively
shortening it. Anyway, "none" is just wrong.
And yes, shuttle windows were engineered not to blow out, but then
laminar flow=/=turbulent flow.
Note to beanstalk designers: make it in steerable airfoil
cross-section segments so it can "fly" in winds to minimize stresses.
And no windows. ;>)
>>> ...the location of the base of the space elevator must be on the
>>>equator. It also must be at least 22,000 miles high. For fun, get a
>>>globe to see what countries could have a space elevator.
>>
>> For extra fun, see how many of those places frequently have violently
>>non-stationary air masses (hurricanes, typhoons, etc.) pass over them.
> This is why equatorial Africa is usually proposed as the site.
Exactly; all the naive (just because they're on the equator)
candidate sites are not equal.
> But then, imagine the security problems. One of the stories involving a
> "beanstalk" had a terrorist bomb going off in a car part way up the
> elevator... and tens of thousands of miles of cable falling to earth.
>
> Ouch.
>
> Even if only the lower 100 miles or so survived re-entry.
>
> Ouch.
Michael Ash notes a fairly "soft" landing, i.e. no segments of cable
whacking out great linear craters or javelining in at Mach way-too-fast;
it'd be more like the monofilament fall in _Ringworld_. Still, even
discounting the putative large-scale economic hit from the trade up and
down the cable being disrupted, it'd be locally damn inconvenient to
have miles and miles of the stuff gently draped over one's city. Or
farm, FTM.
I still like the (completely improbable) worst-case scenario where
the whole thing soft-lands, wrapping it nearly thrice around the
equator. More, if we include the counterweight part.
Mark L. Fergerson
PV
>equator. It also must be at least 22,000 miles high. For fun, get a
>globe to see what countries could have a space elevator.
Chances are, if/when one gets built, the earth end will be in the ocean, as
far from air and sea routes as possible. It would be a giant navigation
hazard in a populated area. *
PV
>But then, imagine the security problems. One of the stories involving a
>"beanstalk" had a terrorist bomb going off in a car part way up the
>elevator... and tens of thousands of miles of cable falling to earth.
One of the mars books. And their elevator used very heavy materials. If a
carbon nanotube ribbon broke, it would flutter to the ground like paper. *
William December Starr
Joe Bednorz <inv...@invalid.invalid> said:
> So the location of the base of the space elevator must be on the
> equator. It also must be at least 22,000 miles high. For fun,
> get a globe to see what countries could have a space elevator.
The United States. Remember how the Panama Canal came into being
and who effectively owned it for the first eight decades or so of
its existence.
--
William December Starr <wds...@panix.com>
Mark Blunden
> Joe Ellis wrote:
>> This is why equatorial Africa is usually proposed as the site.
>
> Exactly; all the naive (just because they're on the equator)
> candidate sites are not equal.
>
>> But then, imagine the security problems. One of the stories
>> involving a "beanstalk" had a terrorist bomb going off in a car part
>> way up the elevator... and tens of thousands of miles of cable
>> falling to earth. Ouch.
>>
>> Even if only the lower 100 miles or so survived re-entry.
>>
>> Ouch.
>
> Michael Ash notes a fairly "soft" landing, i.e. no segments of cable
> whacking out great linear craters or javelining in at Mach
> way-too-fast; it'd be more like the monofilament fall in _Ringworld_.
> Still, even discounting the putative large-scale economic hit from
> the trade up and down the cable being disrupted, it'd be locally damn
> inconvenient to have miles and miles of the stuff gently draped over
> one's city. Or farm, FTM.
Or motorway. It may not be high-impact in absolute terms, but it's got high
tensile strength, and I'm guessing it's not going to be pleasant having your
car wrapped in it at 70 mph.
--
Mark.
Joe Ellis
That would be a neat trick... considering that it's being held in a
lower orbit than it would naturally take by the lower section. It would
be outbound in the event of failure.
Wayne Throop
:: Michael Ash notes a fairly "soft" landing, i.e. no segments of cable
:: whacking out great linear craters or javelining in at Mach way-too-fast
Sounds nice, but I'm not sure how you arrange for that to happen.
I mean... if suspension bridge designers thought it could be done, seems
likely they'd have tried it. And I don't think just going to something
as dense as carbon filaments instead of something as dense as steel is
going to help; square-cube seems to imply it'll still "flutter gently"
much the way a brick does.
Is this "fluttering gently" upon breakage really a plausible scenario?
On the other hand, I kind of liked the cable design in Gerrold's Dingilliad,
as an approach to safety against breakage.
Joe Ellis
Michael Ash <mi...@mikeash.com> wrote:
I didn't say anything about impact damage, did I?
I _was_ thinking more in terms of "shadow square wire" than "suspension
bridge cable" The tangled mess would still be a major problem.
William George Ferguson
<mferg...@cox.net> wrote:
>Joe Bednorz wrote:
>> On 28 Jun 2006 20:14:34 -0700, walt...@mindspring.com wrote:
>>
>> [rec.arts.sf.science added]
>
>>>I keep wondering about atmospheric drag on the space elevator's cable
>>>assembly . . .
>
>> None. The magic is that the space elevator does not move relative to
>> the planet. It's anchored at the base, after all. In one sense, it's
>> just a very tall building.
>
> Aaand the entire volume of air surrounding the cable is stationary
>WRT the cable?
No more (or less) than it is stationary around any structure on Earth.
>And very tall buildings never have frinst windows sucked right out of them
>by winds?
Never is, of course, a very big word, but generally, no, they don't if they
are properly constructed (and I'm fair certain there are no plans to
install windows on the cable, or even have a hollow within the cable to
create the sort of pressure differential that you are actually talking
about).
>> ...the location of the base of the space elevator must be on the
>> equator. It also must be at least 22,000 miles high. For fun, get a
>> globe to see what countries could have a space elevator.
>
> For extra fun, see how many of those places frequently have violently
>non-stationary air masses (hurricanes, typhoons, etc.) pass over them.
Not that many. Quoting from the Wikipedia wiki, "As long as the tether's
anchor remains within two degrees of the equator, it will remain in the
quiet zone between the Earth's Hadley cells, where there is relatively
little violent weather."
Basically, rain and stuff is driven by insolation, but the really strong
wind patterns are driven by coriolisis force (this is a simplification).
So the the hurricanes, typhoons, etc. (all coriolisis artifacts) 'grow in
the zones from about 3 degrees north or south of the equator to about 30
degrees north or south of the equator, and then move north or south, away
from the equatorial zone. The 5 degree zone straddling the equator is
called 'The Doldrums' for a reason. You get rain, and even thunderstorms
there, but not big wind driven storm cells.
The base doesn't actually have to be on the equator, that's just the most
efficient place for it (requiring the shortest tether). You could
theoretically run the cable between any point on the Earth up to that
geostationary orbit, but the longer the cable, the heavier the cable, and
since the mass of the cable versus its shear strength is the sticking point
of the whole exercise (everything else is engineering within today's
existing technological base), you want to keep that cable length as short
as possible.
That's the reason that Clarke put his base, in Fountains of Paradise, on
top of a mountain in Sri Lanka (name changed in the book to protect the
guilty), and Heinlein had his beanstalk in in Friday based on top of
Kilimnajaro. The savings of starting with a base several thousand feet
above sea level means that the cable would be within the parameters of the
nanotube ribbons thus far produced. With the base at sea level, they are
still a bit short of the low end of the necessary shear strength. However,
putting the base on a mountain top has its own problems, not the least of
which are political. If you use a floating base, you can put it outside
any nation's claimed territory. Also a floating base could do limited
maneauvering, to avoid the thunderstorms and such that do appear at the
equator (storm cells at the equator can be fairly intense, but can't be
widespread the way the coriolisis driven cells are).
If we do get a space elevator built by 2020, it will be because Michael
Laine really is Delos Harriman.
--
I must not fear. Fear is the mind-killer.
Fear is the little-death that brings total obliteration.
I will face my fear. I will permit it to pass over me and through me.
And when it has gone past I will turn the inner eye to see its path.
Where the fear has gone there will be nothing. Only I will remain.
(Bene Gesserit)
David Friedman
possibility of using a space elevator to mine the rotational energy of
the earth.
The satellite the elevator hangs from is at least roughly in free fall,
assuming it's considerably more massive than the elevator. So by the
time a capsule reaches the elevator, assuming it isn't accelerating or
decelerating along the elevator, centrifugal force just about balances
gravitational attraction.
Suppose you extend the elevator beyond the satellite, and let the
capsule keep going further. Centrifugal force is now stronger than
gravitational, so the capsule accelerates. Let it go at the far end, on
the way to another planet. Or slow it down by regenerative braking, and
use the energy to pull the next capsule up.
Where is the energy coming from? If you work it out, it turns out that
you are mining the rotational energy of the earth. Do it long enough and
the day gets a little longer.
One can imagine an sf story where we discover a solar system whose
planets aren't rotating--and eventually figure out why.
Bill Higgins
> Why not an artificial ring, ala HALO the videogame series, but big enough to
> ring the Earth in orbit? Skylines could go into Earth orbit and to the space
> ring then a MOVING skyline could go from the Moon to the space ring. A space
> cab ride up the line from Earth to the space ring in Earth orbit then travel
> along the ring to catch the moving skyline going to the moon and travel to
> the moon--and vice versa.
A cute picture, but the orbit of the Moon is not in the same plane as the
Earth's equator.
--
Bill Higgins | "None of [Fred Hoyle's] books read
Fermilab | as well today as they did, but the
| best of them should appeal to readers
Internet: | who enjoy hard sf with squishy centers."
hig...@fnal.gov | --Dani Zweig in rec.arts.sf.written
Clell Harmon
Covered in detail in the Mars Trilogy... Green Mars I believe, the
cable rapped around Mars 1 1/2 times
>
Clell Harmon
Well there is the theory that Heinlein just went into mascarade...
Midnighter
Weird thought, and I don't have the maths for it. But what if the cable was
stretched to two points on the planet? Lets say a high northern latitud,
and a high southern, with the midpoing being over the equator? The cable
would have to be longer, but would it have to be as strong?
Robert Sneddon
Higgins <hig...@fnal.gov> writes
>A cute picture, but the orbit of the Moon is not in the same plane as
>the Earth's equator.
This can be dealt with using large spherical ball bearing races and a
telescoping section in the connecting rod between the two bearing
housings. Alternatively we could simply regularise the Earth-Moon orbits
and use plain needle-roller bearings and a fixed link instead.
--
To reply, my gmail address is nojay1 Robert Sneddon
Michael Ash
> In article <11515916...@nfs-db1.segnet.com>,
> Michael Ash <mi...@mikeash.com> wrote:
>
>> In rec.arts.sf.science Joe Ellis <synth...@sbcglobal.net> wrote:
>> >
>> > But then, imagine the security problems. One of the stories involving a
>> > "beanstalk" had a terrorist bomb going off in a car part way up the
>> > elevator... and tens of thousands of miles of cable falling to earth.
>> >
>> > Ouch.
>> >
>> > Even if only the lower 100 miles or so survived re-entry.
>> >
>> > Ouch.
>>
>> A space elevator will resemble ribbon more than cable. Imagine thousands
>> of miles of ribbon falling to earth from space and surviving reentry.
>> Scared? You shouldn't be. It will flutter gently to the ground and harm
>> nothing. The biggest worry will be people cutting themselves on the edges,
>> or possibly getting poisoned from it. A KSR-esque planetwide catastrophe
>> doesn't bear much resemblance to what it seems like a real space elevator
>> will be, at least at first.
>
> I didn't say anything about impact damage, did I?
>
> I _was_ thinking more in terms of "shadow square wire" than "suspension
> bridge cable" The tangled mess would still be a major problem.
Would it, though?
For one, you have a relatively thin cable that's designed to take exactly
one kind of stress in exactly one direction, while remaining in exactly
one shape. Obviously the part that stays in the atmosphere is going to be
a bit more robust than this, but it's still going to be pretty fragile.
Will it really be all that inconvenient, or will it just crumple and shred
as it's run over and trampled upon?
For another, you have a material with extremely tight tolerances. (This is
pretty much by definition no matter what it's made out of, unless you want
to consider a second or third generation elevator.) These tolerances have
just been deeply violated by a ride down from space or high atmosphere.
Will it still maintain anything like its original strength after that?
I'm not saying with total certainty that it won't be dangerous but my
feeling is that it won't. Does somebody have something more than
handwaving on this subject?
David Dyer-Bennet
> But then, imagine the security problems. One of the stories involving a
> "beanstalk" had a terrorist bomb going off in a car part way up the
> elevator... and tens of thousands of miles of cable falling to earth.
> Ouch.
But not possible. Remember the orbital mechanics -- the beanstalk is
*in orbit*. The part above the break, therefore, will not fall. In
fact, it'll probably rise (most designs have it under tension). Only
the part *below* the break will fall. And the cable will presumably
taper, so the bottom 100 miles or so won't be anywhere near as thick
or heavy as the higher bits.
--
David Dyer-Bennet, <mailto:dd...@dd-b.net>, <http://www.dd-b.net/dd-b/>
RKBA: <http://www.dd-b.net/carry/>
Pics: <http://dd-b.lighthunters.net/> <http://www.dd-b.net/dd-b/SnapshotAlbum/>
Dragaera/Steven Brust: <http://dragaera.info/>
Sean O'Hara
> William George Ferguson wrote:
>
>> Now if you had this parrot named Lil, you might think about a true
>> Earth-Moon elevator, sort of a 'star bridge'.
>
> Doesn't it turn out that Lil had Wu? Not the other way round?
>
> Per the original poster's query about rotation (caused by
> misunderstanding geostationary) the Star Bridges are attached to polar
> caps that counter rotate while floating on a film of mercury IIRC, to
> keep the Bridges from winding up like yarn. But that's really a
> different situation.
>
How do you put something in geostationary orbit at the poles?
--
Sean O'Hara | http://diogenes-sinope.blogspot.com
Brigadier: Jenkins! Chap with the wings there -- five rounds rapid.
-Doctor Who
Joe Bednorz
>In article <11515...@sheol.org>, thr...@sheol.org (Wayne Throop)
>wrote:
>
>> :: See this link for NASA's take on geosynchronous orbits:
>> :: <http://liftoff.msfc.nasa.gov/academy/rocket_sci/satellites/geo-high.html>
>> :: It's a nice bit of magic that A. C. Clarke apparently mentioned
>> :: first in 'Islands in the Sky'.
>>
>> : David Friedman <dd...@daviddfriedman.nopsam.com>
>> : Clarke isn't even close to the first person to mention the idea. It
>> : seems to have been first proposed by Yuri Artsutanov, a Leningrad
>> : engineer, in 1960, and has been independently invented multiple times
>> : since.
>>
>> Well, since Clarke copyrighted Islands in the Sky in 1952,
>> that's some meaning of "first proposed" with which I have previously
>> been unaquainted.
>>
>> Note that the "nice bit of magic" refered to above is geosync orbit.
>> Not orbital towers or space elevators.
>
>Then I misread your post. I thought you were talking about space
>elevators.
A. It was my post, not Wayne's.
B. Geosynchronous orbits are part and parcel of space elevators.
While you can have a geosynchronous orbit without a space elevator, you
cannot have a space elevator without connecting-to/reaching
geosynchronous orbit. That's why space elevators must be built on the
equator. That's also why space elevators must be 22,250 miles tall.
<snip excellent reference clarifying geosynchronous orbit and ACC's
idea for communication satellites in them.>
--
Alice in Wonderland Interactive Adventure: <http://www.ruthannzaroff.com/wonderland/>
Baen Free Online SciFi Library: <http://www.baen.com/library/>
SciFi.com classic & original works: <http://www.scifi.com/scifiction/archive.html>
All the best, Joe Bednorz
Joe Bednorz
I suspect that any wind-shear forces would be minimal compared to the
strain of holding up a 22,250 mile high tower. Flexibility of the
structure would be critical just for varying orbital stresses at
different heights. Flexibility would also be a result of using cables
to "hang" off of a structure in geostationary orbit. (Thanks to Leif
Kjønnøy for explicitly pointing out the correct terminology.)
The main concern for wind would be side stress on the anchor point.
PV
>One point that hasn't, I think, come up in the discussion is the
>possibility of using a space elevator to mine the rotational energy of
>the earth.
Just by climbing the cable, that's what you're doing, and you're right, you
could easily extend the cable out past the balance point. If you let go
at the right time, you could be whipped out into space at a good speed.
>One can imagine an sf story where we discover a solar system whose
>planets aren't rotating--and eventually figure out why.
You're vastly underestimating the rotational energy of the earth. *
Joe Ellis
David Dyer-Bennet <dd...@dd-b.net> wrote:
> Joe Ellis <synth...@sbcglobal.net> writes:
>
> > But then, imagine the security problems. One of the stories involving a
> > "beanstalk" had a terrorist bomb going off in a car part way up the
> > elevator... and tens of thousands of miles of cable falling to earth.
>
> > Ouch.
>
> But not possible. Remember the orbital mechanics -- the beanstalk is
> *in orbit*. The part above the break, therefore, will not fall. In
> fact, it'll probably rise (most designs have it under tension). Only
> the part *below* the break will fall. And the cable will presumably
> taper, so the bottom 100 miles or so won't be anywhere near as thick
> or heavy as the higher bits.
Where does it say the cable must break in the first hundred miles? What
if it breaks somewhere near 20,000 miles? The satellite will squirt into
a higher orbit, and the cable will... fall.
...as I said... ouch.
William George Ferguson
wrote:
Stronger. The 'strength' of the individual cable needs to be sufficient to
support the gravitational drag on the cable at that point, hence most
designs now use a tapered ribbon cable, narrowest at the base, down here on
Earth, and widest at the center of mass in geostationary orbit. The higher
along the cable, the more mass there is below it, so the stronger it has to
be not to just part from the pull of gravity on the cable below it.
I, and others, have said that the cable is the sticking point, and why,
until the development of nanotube ribbons, the concept was basically only
science fiction, dependent on unobtanium. A ribbon cable running from
sea level to geostationary orbit (and beyond) would need to have a tensile
strength of in excess of 65 GPa (GigaPascals). Carbon steel wire has been
produced which has a tensile of strength of around 1.6 GPa. A ribbon cable
made from diamond filaments could possibly be a little over 20 GPa. That's
about as strong a tensile strength we had in macroscopic materials until
the development (still ongoing) of the carbon nanotubes. Single walled
nanotubes have been produced with a measured strength of 53 GPa, and have a
theoretical limit of around 300 GPa. To do the tether all the way to sea
level, they really need to have mass-produced ribbon at 100+ GPa, and from
elevations of 5000 feet, around 50 GPa (so they have actually produced
nantubes strong enough for a Kilimnjaro beanstalk, although not
mass-produced).
Wayne Throop
: That's the reason that Clarke put his base, in Fountains of Paradise, on
: top of a mountain in Sri Lanka (name changed in the book to protect the
: guilty), and Heinlein had his beanstalk in in Friday based on top of
: Kilimnajaro.
I doubt it very much. Google says Kilimanjaro is 3 degrees off the
equator. That loses it 6 kilometers distance from the spin axis if
I've done my sums right, and it's a tad less than 6 kilometers tall.
So... first, it doesn't seem to help distancewise. And second, let me
doubt that 6 kilometers would make that large a difference out of more
than 30,000.
Hm. I don't recall a rationale given for the location of those two.
But length of cable doesn't seem to make much sense, though altitude
might.
I could of course be wrong. Do you have numbers/calculations supporting
your rationale for putting it on a mountaintop?
John Dallman
> David Friedman <dd...@daviddfriedman.nopsam.com> writes:
> >One can imagine an sf story where we discover a solar system
> >whose planets aren't rotating--and eventually figure out why.
> You're vastly underestimating the rotational energy of the earth. *
Absolutely. I ran across a claim that Earth's rotational energy
comfortably exceed the kinetic energy of its orbit round the Sun, but
can't find the reference now. I thought it was in _War in 2080_, but the
five-minute skim didn't find it. But Earth spins /fast/.
---
John Dallman, j...@cix.co.uk, HTML mail is treated as probable spam.
William George Ferguson
wrote:
>In the Year of the Dog, the Great and Powerful lal_truckee declared:
>> William George Ferguson wrote:
>>
>>> Now if you had this parrot named Lil, you might think about a true
>>> Earth-Moon elevator, sort of a 'star bridge'.
>>
>> Doesn't it turn out that Lil had Wu? Not the other way round?
>>
>> Per the original poster's query about rotation (caused by
>> misunderstanding geostationary) the Star Bridges are attached to polar
>> caps that counter rotate while floating on a film of mercury IIRC, to
>> keep the Bridges from winding up like yarn. But that's really a
>> different situation.
>>
>
>How do you put something in geostationary orbit at the poles?
lal-truckee is conflating two things, and/or you're conflating his conjoint
discussion of them.
The original poster mentioned not being able to get his head around a
proposed 'moon elevator', I explained that the proposed 'moon elevator' was
an elevator from the Moon to space, not from Earth to the Moon, but that
Lil could probably do it (the Earth-Moon). Lal-truckee then commented on
how the termini of the tubes (the 'star bridges' of Star Bridge) were
arranged on Eron, acknowledging that it was, of course, a completely
different situation.
As to how you put something in geostationary orbit at the poles, you use a
solar sail. The satellite is basically orbiting the sun along with the
Earth, and is kept from being pulled to Earth by the sail. There are folks
working on building pole-sitting satellites right now.
Sea Wasp
> In article <0vQog.655$Mz3.461@fed1read07>,
>
>
>>Joe Bednorz wrote:
>>
>>>On 28 Jun 2006 20:14:34 -0700, walt...@mindspring.com wrote:
>>>
>>> [rec.arts.sf.science added]
>>
>>>>I keep wondering about atmospheric drag on the space elevator's cable
>>>>assembly . . .
>>>
>>> None. The magic is that the space elevator does not move relative to
>>>the planet. It's anchored at the base, after all. In one sense, it's
>>>just a very tall building.
>>
>> Aaand the entire volume of air surrounding the cable is stationary
>>WRT the cable? And very tall buildings never have frinst windows sucked
>>right out of them by winds?
>
>
> recall many modern ones being blown over. And windows don't seem to get
> sucked out of the space shuttle at Mach 25.
>
>
>>>equator. It also must be at least 22,000 miles high. For fun, get a
>>>globe to see what countries could have a space elevator.
>>
>> For extra fun, see how many of those places frequently have violently
>>non-stationary air masses (hurricanes, typhoons, etc.) pass over them.
>
>
>
> "beanstalk" had a terrorist bomb going off in a car part way up the
> elevator... and tens of thousands of miles of cable falling to earth.
>
> Ouch.
>
>
> Ouch.
>
The cable is a ribbon ranging from about 15-20 inches to a few feet
in diameter. And very, very thin. The transfer machinery would be the
only real threat.
--
Sea Wasp
/^\
;;;
Live Journal: http://www.livejournal.com/users/seawasp/
Michael Ash
>
> B. Geosynchronous orbits are part and parcel of space elevators.
> While you can have a geosynchronous orbit without a space elevator, you
> cannot have a space elevator without connecting-to/reaching
> geosynchronous orbit. That's why space elevators must be built on the
> equator.
Nothing says a space elevator needs to be built on the equator. Building
one off-equator requires more and stronger material, and places a lateral
force on the anchor, but neither problem would necessarily be
insurmountable. Certainly being on or very near the equator is a big
advantage though.
> That's also why space elevators must be 22,250 miles tall.
ITYM *over* 22,250 miles tall. Having the top be at geosynchronous orbit
would work if you had a counterweight and if your stalk material had zero
weight, which is obviously impossible. With any positive stalk mass your
top has to be above geosynch, and for any practical elevator design it
will be significantly above.
My wording makes me think of elevators made out of materials with negative
mass. Hmm.....
Wayne Throop
: William George Ferguson <wmgf...@newsguy.com>
: you use a solar sail. The satellite is basically orbiting the sun
: along with the Earth, and is kept from being pulled to Earth by the
: sail. There are folks working on building pole-sitting satellites
: right now.
Hm. Couldn't a space elevator be anchored at the pole, and be
geosynchronous? And would it not then be geostationary? (Of course,
it's not quite a satellite... it's cheating with extra forces, much the
way a solar sail would be, only different) Just an extreme case of being
offset from the equator. If necessary, move the counterweight out far
enough that tension keeps it from collapsing equatorwards. And use
a higher grade of unobtanium, of course.
Richard Kennaway
> In article <12a8e8e...@news.supernews.com>, pv+u...@pobox.com
> (PV) wrote:
> > David Friedman <dd...@daviddfriedman.nopsam.com> writes:
> > >One can imagine an sf story where we discover a solar system
> > >whose planets aren't rotating--and eventually figure out why.
> > You're vastly underestimating the rotational energy of the earth. *
> Absolutely. I ran across a claim that Earth's rotational energy
> comfortably exceed the kinetic energy of its orbit round the Sun, but
> can't find the reference now. I thought it was in _War in 2080_, but the
> five-minute skim didn't find it. But Earth spins /fast/.
Not that fast. The ratio of rotational to orbital energy is:
k r^2 T^2
---------
R^2 t^2
where r = radius of Earth, R = orbital radius, t = 1 day, T = 1 year,
and k = 2/5 (or a little less, since the Earth is denser in the middle).
Since T/t = 365 and r/R = 1/24000, the energy ratio is about 0.0001. To
spin fast enough for the two energies to be equal, one would have to
reduce t to 1/100 of a day, or just under 15 minutes. However, at that
speed the Earth would tear itself apart.
--
Richard Kennaway
David Friedman
> David Friedman <dd...@daviddfriedman.nopsam.com> writes:
> >One point that hasn't, I think, come up in the discussion is the
> >possibility of using a space elevator to mine the rotational energy of
> >the earth.
>
> Just by climbing the cable, that's what you're doing, and you're right, you
> could easily extend the cable out past the balance point. If you let go
> at the right time, you could be whipped out into space at a good speed.
>
> >One can imagine an sf story where we discover a solar system whose
> >planets aren't rotating--and eventually figure out why.
>
> You're vastly underestimating the rotational energy of the earth. *
I don't think so.
I didn't say how long it took, or how much use they were making of the
technique. Given enough time, a flow beats a stock.
David Friedman
Joe Bednorz <inv...@invalid.invalid> wrote:
> On Thu, 29 Jun 2006 01:17:59 -0700, David Friedman wrote:
>
> >In article <11515...@sheol.org>, thr...@sheol.org (Wayne Throop)
> >wrote:
> >
> >> :: See this link for NASA's take on geosynchronous orbits:
> >> :: <http://liftoff.msfc.nasa.gov/academy/rocket_sci/satellites/geo-high.htm
> >> :: l>
> >> :: It's a nice bit of magic that A. C. Clarke apparently mentioned
> >> :: first in 'Islands in the Sky'.
> >>
> >> : David Friedman <dd...@daviddfriedman.nopsam.com>
> >> : Clarke isn't even close to the first person to mention the idea. It
> >> : seems to have been first proposed by Yuri Artsutanov, a Leningrad
> >> : engineer, in 1960, and has been independently invented multiple times
> >> : since.
> >>
> >> Well, since Clarke copyrighted Islands in the Sky in 1952,
> >> that's some meaning of "first proposed" with which I have previously
> >> been unaquainted.
> >>
> >> Note that the "nice bit of magic" refered to above is geosync orbit.
> >> Not orbital towers or space elevators.
> >
> >Then I misread your post. I thought you were talking about space
> >elevators.
>
> A. It was my post, not Wayne's.
>
> B. Geosynchronous orbits are part and parcel of space elevators.
> While you can have a geosynchronous orbit without a space elevator, you
> cannot have a space elevator without connecting-to/reaching
> geosynchronous orbit. That's why space elevators must be built on the
> equator. That's also why space elevators must be 22,250 miles tall.
And, returning to the subject of priority and Clarke, Clarke was neither
the first person to propose satellites in geosynchronous orbit nor the
first person to propose a space elevator. He may have been the first
person to propose using satellites in geosynchronous orbit for a
communication system, however.
Michael Bowker
> Michael Bowker <mi...@blueneptune.com> writes:
>
>>The thing about Space elevators that most people ignore or don't know is
>>that it would be a Dynamo (ie a conductor rotating through a magnetic
>>field). Thus you would have to get rid of the generated electricity or
>>be subject to massive static problems.
>
>
> No it won't, because the cable is stationary - it's not like the tether
> experiments in orbit, where the cable was whipping through earth's magnetic
> field at 19,000 mph.
Stationary relative to the surface yes. But It's not Stationary
relative to the earths magnetic fields, right? It's moving through the
fields at geostationary velocities.
>
> There are a lot of 'most people ignore' things that critics say about space
> elevators that are simply not true. *
George W Harris
:Just by climbing the cable, that's what you're doing, and you're right, you
:could easily extend the cable out past the balance point. If you let go
:at the right time, you could be whipped out into space at a good speed.
:
You *have* to extend the cable out past the
balance point, otherwise the whole thing comes
crashing down. In fact, the best way to build a space
elevator is to start at the balance point and build out
and in simultaneously.
--
Doesn't the fact that there are *exactly* 50 states seem a little suspicious?
George W. Harris For actual email address, replace each 'u' with an 'i'
George W Harris
:Joe Ellis <synth...@sbcglobal.net> writes:
:>But then, imagine the security problems. One of the stories involving a
:>"beanstalk" had a terrorist bomb going off in a car part way up the
:>elevator... and tens of thousands of miles of cable falling to earth.
:
:One of the mars books. And their elevator used very heavy materials. If a
:carbon nanotube ribbon broke, it would flutter to the ground like paper. *
And if the space elevator were made out of a
carbon nanotube ribbon, it would break immediately.
The structure has to withstand enormous tension, and
it's not going to be flimsy. We're talking 'ribbon' in the
same way the Golden Gate Bridge is a ribbon.
--
I'm not an actor, but I play one on TV!
lal_truckee
> On Thu, 29 Jun 2006 20:33:18 -0000, pv+u...@pobox.com (PV) wrote:
>
> :Just by climbing the cable, that's what you're doing, and you're right, you
> :could easily extend the cable out past the balance point. If you let go
> :at the right time, you could be whipped out into space at a good speed.
> :
> You *have* to extend the cable out past the
> balance point, otherwise the whole thing comes
> crashing down. In fact, the best way to build a space
> elevator is to start at the balance point and build out
> and in simultaneously.
I wonder what part of the definition of "balance" eludes people these
days. Aren't there teeter-totters in the playgrounds any more?
Mike Schilling
"David Friedman" <dd...@daviddfriedman.nopsam.com> wrote in message
news:ddfr-9658B0.1...@news.isp.giganews.com...
> In article <12a8e8e...@news.supernews.com>,
> pv+u...@pobox.com (PV) wrote:
>
>> David Friedman <dd...@daviddfriedman.nopsam.com> writes:
>> >One point that hasn't, I think, come up in the discussion is the
>> >possibility of using a space elevator to mine the rotational energy of
>> >the earth.
>>
>> Just by climbing the cable, that's what you're doing, and you're right,
>> you
>> could easily extend the cable out past the balance point. If you let go
>> at the right time, you could be whipped out into space at a good speed.
>>
>> >One can imagine an sf story where we discover a solar system whose
>> >planets aren't rotating--and eventually figure out why.
>>
>> You're vastly underestimating the rotational energy of the earth. *
>
> I don't think so.
>
> I didn't say how long it took, or how much use they were making of the
> technique. Given enough time, a flow beats a stock.
I have another story idea. A planet's rotational energy has become its
inhabitants' main energy source, to the point where the slowing has begun to
affect the climate adversely. There's a conflict between those who
recognize this and want to switch to another form of energy production
(fossil fuels?) before thing sgte worse, and those who refuse to admit
there's any problem.
William George Ferguson
wrote:
>On Thu, 29 Jun 2006 15:40:12 -0000, pv+u...@pobox.com (PV) wrote:
>
>:Joe Ellis <synth...@sbcglobal.net> writes:
>:>But then, imagine the security problems. One of the stories involving a
>:>"beanstalk" had a terrorist bomb going off in a car part way up the
>:>elevator... and tens of thousands of miles of cable falling to earth.
>:
>:One of the mars books. And their elevator used very heavy materials. If a
>:carbon nanotube ribbon broke, it would flutter to the ground like paper. *
>
> And if the space elevator were made out of a
>carbon nanotube ribbon, it would break immediately.
>The structure has to withstand enormous tension, and
>it's not going to be flimsy. We're talking 'ribbon' in the
>same way the Golden Gate Bridge is a ribbon.
The ribbon will be less thick than a typical piece of paper, and will have
a tapered width, starting at the bottom onley a few millimeters wide, and
will widen exponentially until it reaches approximately a meter, at which
point it it will remain until it reaches the balance point (geostationary
orbit), then it will taper down as it extends outward. the idea is to have
it at the smallest cross-section that can bear the load at any given point
on the cable.
The widest (3 feet or so) and heaviest part of the cable will be pretty
much entirely outside the atmosphere. The cable will be under about 20
tons of tension. Keep in mind that the proposed carbon nanotube ribbon
will be about 100 times as strong as the same size steel ribbon, and about
5 times as strong as the same size diamond fiber ribbon, and will be
lighter than them. (the industry isn't there yet, right now they can only
do about 30 times as strong as steel and about 4 times as strong as
diamond).
Joe Ellis
lal_truckee <lal_t...@yahoo.com> wrote:
Most places, no.
"Some poor child might get hurt!"
Bah.
Carl Dershem
@individual.net:
> How do you put something in geostationary orbit at the poles?
Very carefully?
cd
--
The difference between immorality and immortality is "T". I like Earl
Grey.
David Dyer-Bennet
Sea Wasp
> On Thu, 29 Jun 2006 15:40:12 -0000, pv+u...@pobox.com (PV) wrote:
>
> :Joe Ellis <synth...@sbcglobal.net> writes:
> :>But then, imagine the security problems. One of the stories involving a
> :>"beanstalk" had a terrorist bomb going off in a car part way up the
> :>elevator... and tens of thousands of miles of cable falling to earth.
> :
> :One of the mars books. And their elevator used very heavy materials. If a
> :carbon nanotube ribbon broke, it would flutter to the ground like paper. *
>
> And if the space elevator were made out of a
> carbon nanotube ribbon, it would break immediately.
> The structure has to withstand enormous tension, and
> it's not going to be flimsy. We're talking 'ribbon' in the
> same way the Golden Gate Bridge is a ribbon.
You have NO concept of the strength of carbon nanotube ribbon.
We are talking ribbon in the sense of averaging a foot or two wide
and fractions of an inch thick. The ENTIRE elevator weighing less than
most ships do -- ships which measure a couple of hundred feet long, as
opposed to tens of thousands of miles.
Joe Ellis
David Dyer-Bennet <dd...@dd-b.net> wrote:
> Joe Ellis <synth...@sbcglobal.net> writes:
>
> > In article <87irmji...@gw.dd-b.net>,
> > David Dyer-Bennet <dd...@dd-b.net> wrote:
> >
> > > Joe Ellis <synth...@sbcglobal.net> writes:
> > >
> > > > But then, imagine the security problems. One of the stories involving a
> > > > "beanstalk" had a terrorist bomb going off in a car part way up the
> > > > elevator... and tens of thousands of miles of cable falling to earth.
> > >
> > > > Ouch.
> > >
> > > But not possible. Remember the orbital mechanics -- the beanstalk is
> > > *in orbit*. The part above the break, therefore, will not fall. In
> > > fact, it'll probably rise (most designs have it under tension). Only
> > > the part *below* the break will fall. And the cable will presumably
> > > taper, so the bottom 100 miles or so won't be anywhere near as thick
> > > or heavy as the higher bits.
> >
> > Where does it say the cable must break in the first hundred miles? What
> > if it breaks somewhere near 20,000 miles? The satellite will squirt into
> > a higher orbit, and the cable will... fall.
> >
> > ...as I said... ouch.
>
> Gets harder and harder to cut as you go up, though.
But not impossible.
And since the goal of terrorists would be to cause as much damage as
possible, cutting the cable as high as possible would be their goal.
El Puerco
news:synthfilker-08FC...@newsclstr02.news.prodigy.com...
> In article <ic_og.57615$Lm5....@newssvr12.news.prodigy.com>,
> lal_truckee <lal_t...@yahoo.com> wrote:
>
>> George W Harris wrote:
>> > On Thu, 29 Jun 2006 20:33:18 -0000, pv+u...@pobox.com (PV) wrote:
>> >
>> > :Just by climbing the cable, that's what you're doing, and you're
>> > right, you
>> > :could easily extend the cable out past the balance point. If you let
>> > go
>> > :at the right time, you could be whipped out into space at a good
>> > speed.
>> > :
>> > You *have* to extend the cable out past the
>> > balance point, otherwise the whole thing comes
>> > crashing down. In fact, the best way to build a space
>> > elevator is to start at the balance point and build out
>> > and in simultaneously.
>>
>> I wonder what part of the definition of "balance" eludes people these
>> days. Aren't there teeter-totters in the playgrounds any more?
>
> Most places, no.
>
> "Some poor child might get hurt!"
>
> Bah.
Seriously? The one by our house in Chicago has a really cool,
spring-assisted teeter-totter. I can almost fling my kids into orbit with
it! IMO, playgrounds have become much more fun since the advent of plastic.
That really was the industry to get into... ;-)
Clell Harmon
> PV wrote:
>> Michael Bowker <mi...@blueneptune.com> writes:
>>
>>> The thing about Space elevators that most people ignore or don't know
>>> is that it would be a Dynamo (ie a conductor rotating through a
>>> magnetic field). Thus you would have to get rid of the generated
>>> electricity or be subject to massive static problems.
>>
>>
>> No it won't, because the cable is stationary - it's not like the tether
>> experiments in orbit, where the cable was whipping through earth's
>> magnetic
>> field at 19,000 mph.
>
> Stationary relative to the surface yes. But It's not Stationary
> relative to the earths magnetic fields, right? It's moving through the
> fields at geostationary velocities.
One revolution per day?
John Schilling
>CG wrote:
>> I'm writing it into a short story. Is it possible to
>> create a space elevator with current or possible
>> near future tech?
>Do I understand the concept correctly when I assume that a space
>elevator has to be based at the equator since any GEO has to be above
>the equator?
That is certainly the most convenient way to do it, but it isn't
absolutely necessary. As a trivial counterexample, one could have
a forked elevator with two surface terminals, symmetric with respect
to the equator. One could also, with a bit of care in the balancing,
have a skewed elevator with a single, non-equatorial terminal. But
you probably do want to at least be close to the terminal.
One other consideration: the preferred method of delivering power to
the elevator cars, is through laser power beaming. For geometric
reasons, this means you probably want a second site a few hundred
to a thousand kilometers away to host the lasers.
>So, where along the equator would a good place for the base of an SE
>be?
>Is it better to pick an already elevated place like the Andes near
>Quito or the mountains of Sumatra or Borneo - or is the difference in
>cable length negligible?
The difference in cable length is almost certainly negligible compared
to the operational considerations. You're going to want someplace that
is politically stable, NIMBY-immune, and reasonably well connected to
transportation, power, and industrial infrastructure. Reasonably low
population density, though you can work around a single concentration
and you probably do want a city in the region. A suitable laser site
under the same political jurisdictio is a plus.
Mainland Equatorial Africa is probably right out, unless the project's
budget is big enough to simply buy political stability in someplace
like Somalia. Sao Tome is an outside possibility, depending on how
they handle their oil money over the next decade or two.
Quito, in Ecuador, is actually a pretty decent choice, independant of
its altitude. But again, it depends on how the local politics play
out. Brazil, probably less so - the equatorial regions are not well
developed or governed. But possibly the city of Macapa, at the Amazon
delta, would serve as a base.
Indonesia, right out for quite some time to come on political and
related economic grounds.
There are some islands here and there that might work. Most of them
are pretty remote and you'd have to build a lot of infrastructure from
scratch. But they are by definition accessible from the sea, and a
lot of them have airstrips and/or ports left over from World War II.
Makin/Butaritari in the Gilberts, for example. Not the Galapagos,
for obvious reasons.
And you don't have to put your terminus on land. An offshore platform
would do nicely, and might have some advantages to justify the cost and
complexity. One could concievably even have the lower terminal of the
beanstalk be an aerostat, though that would probably be more trouble
than it is worth.
--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
*White Elephant Research, LLC * "There is no substitute *
*schi...@spock.usc.edu * for success" *
*661-951-9107 or 661-275-6795 * -58th Rule of Acquisition *
El Puerco
news:1hh8a2lku3iki28ng...@4ax.com...
> Mainland Equatorial Africa is probably right out, unless the project's
> budget is big enough to simply buy political stability in someplace
> like Somalia. Sao Tome is an outside possibility, depending on how
> they handle their oil money over the next decade or two.
Isn't Uganda stable (enough, anyway)? Museveni may be a benevolent
strongman but I don't think the society itself is all that fractious. All
this is ignoring the Sudanese, though, and maybe they'd be enough of a
threat?
> There are some islands here and there that might work. Most of them
> are pretty remote and you'd have to build a lot of infrastructure from
> scratch.
But wouldn't the cost of building such infrastructure be insignificant
compared with the SE itself (or am I being naive)?
Michael Ash
>> > Where does it say the cable must break in the first hundred miles? What
>> > if it breaks somewhere near 20,000 miles? The satellite will squirt into
>> > a higher orbit, and the cable will... fall.
>> >
>> > ...as I said... ouch.
>>
>> Gets harder and harder to cut as you go up, though.
>
> But not impossible.
>
> And since the goal of terrorists would be to cause as much damage as
> possible, cutting the cable as high as possible would be their goal.
Possible in theory, possible for wealthy countries, and possible for big
terrorist organizations are completely different things, though.
Modern terrorist resources are minisculed compared to even small or poor
nation states. Without being able to send something into orbit, the only
way to attack stuff high up would be to place a bomb or something similar
into an elevator car. Considering the infrastructure value and the
relative costs, I'm sure every bit of cargo will be gone over with a
fine-toothed comb, so I don't think that's an option.
If the terrorists can put an ASAT weapon into orbit that can take down a
beanstalk, then they've either become so powerful that they should more
properly be called an enemy country (and a wealthy one at that), or
non-beastalk access to space has become so easy and cheap that there's no
point in building one
It's possible that non-elevator tech is similar to today when the elevator
is built, and then improves dramatically afterwards, posing an
unanticipated threat. But such a rapid advance is unprecedented and
doubtful, particularly since very little R&D effort would be put into it
given the availability of a cheap and already-built alternative.
George W Harris
<seawasp...@obvioussgeinc.com> wrote:
:George W Harris wrote:
:> On Thu, 29 Jun 2006 15:40:12 -0000, pv+u...@pobox.com (PV) wrote:
:>
:> :Joe Ellis <synth...@sbcglobal.net> writes:
:> :>But then, imagine the security problems. One of the stories involving a
:> :>"beanstalk" had a terrorist bomb going off in a car part way up the
:> :>elevator... and tens of thousands of miles of cable falling to earth.
:> :
:> :One of the mars books. And their elevator used very heavy materials. If a
:> :carbon nanotube ribbon broke, it would flutter to the ground like paper. *
:>
:> And if the space elevator were made out of a
:> carbon nanotube ribbon, it would break immediately.
:> The structure has to withstand enormous tension, and
:> it's not going to be flimsy. We're talking 'ribbon' in the
:> same way the Golden Gate Bridge is a ribbon.
:
: You have NO concept of the strength of carbon nanotube ribbon.
The theoretical strength, which may never be
approached, or the currently achieved strength, which
is insufficient for an elevator that doesn't do anything
but just sit there? Remember it has to support not only
itself, but whatever cargo will be carried on it, plus the
vehicles to hold that cargo, plus the structures to
attach the vehicles to the elevator, plus the systems to
power the vehicles, etc., etc.... Plus try getting financing
without a safety margin. All that, and the doubtfulness of
approaching the theoretical maximum strength, and I'm
betting my estimate is closer than yours...
: Sea Wasp
--
Never give a loaded gun to a woman in labor.
George W. Harris For actual email address, replace each 'u' with an 'i'.
Bernard Peek
> PV wrote:
> >Michael Bowker <mi...@blueneptune.com> writes:
> >
> > > The thing about Space elevators that most people ignore or don't
> > > know is that it would be a Dynamo (ie a conductor rotating
> > > through a magnetic field). Thus you would have to get rid of the
> > > generated electricity or be subject to massive static problems.
> >
> >
> > No it won't, because the cable is stationary - it's not like the
> > tether experiments in orbit, where the cable was whipping through
> > earth's magnetic field at 19,000 mph.
>
> Stationary relative to the surface yes. But It's not Stationary
> relative to the earths magnetic fields, right? It's moving through
> the fields at geostationary velocities.
But that's the same speed at which the fields themselves move, so
there's zero relative speed.
--
--
Bernard Peek
b...@shrdlu.com
Michael Bowker
Karl Johanson
I hate it when that happens.
Karl Johanson
Karl Johanson
news:4gipn0F...@individual.net...
> In the Year of the Dog, the Great and Powerful lal_truckee declared:
>> William George Ferguson wrote:
>>
>>> Now if you had this parrot named Lil, you might think about a true
>>> Earth-Moon elevator, sort of a 'star bridge'.
>>
>> Doesn't it turn out that Lil had Wu? Not the other way round?
>>
>> Per the original poster's query about rotation (caused by
>> misunderstanding geostationary) the Star Bridges are attached to
>> polar caps that counter rotate while floating on a film of mercury
>> IIRC, to keep the Bridges from winding up like yarn. But that's
>> really a different situation.
>>
>
> How do you put something in geostationary orbit at the poles?
You do it on a planet with a magnetic pole at its equator.
I think Robert Forward proposed a light sale 'satellite' that would sit
over the Earth's north or south pole. You use enough solar sale material
to balance out the tug of gravity. You use flaps or some such, to adjust
for variations in the solar flux. Such a device wouldn't be in orbit.
Karl Johanson
mike weber
David Friedman wrote:
> The satellite the elevator hangs from is at least roughly in free fall,
> assuming it's considerably more massive than the elevator. So by the
> time a capsule reaches the elevator, assuming it isn't accelerating or
> decelerating along the elevator, centrifugal force just about balances
> gravitational attraction.
The elevator *is* the satellite. Just vertically stretched.
> Suppose you extend the elevator beyond the satellite,
Tbe elevator *has* to extend beyond the geosynchronous point in order
to keep the center of mass in geosynch orbit.
mike weber
David Friedman wrote:
> And, returning to the subject of priority and Clarke, Clarke was neither
> the first person to propose satellites in geosynchronous orbit nor the
> first person to propose a space elevator. He may have been the first
> person to propose using satellites in geosynchronous orbit for a
> communication system, however.
>
Ummm, i don't believe that he did, actually. He proposed satellite
relays, but i don't think he proposed them in geosynch -- as i recall
it, they were at 120 degree intervals, but not geosynchronous.
But i could be confusing him with someone else.
Leif Magnar Kj|nn|y
mike weber <fairp...@gmail.com> wrote:
>
>Tbe elevator *has* to extend beyond the geosynchronous point in order
>to keep the center of mass in geosynch orbit.
The center of gravity, not the center of mass. They won't be anything
like in the same place, since you cannot approximate the Earth's gravity
field as uniform at this scale.
--
Leif Kjønnøy, cunctator maximus. http://www.pvv.org/~leifmk
Joe Ellis
Michael Ash <mi...@mikeash.com> wrote:
> In rec.arts.sf.science Joe Ellis <synth...@sbcglobal.net> wrote:
> >> > Where does it say the cable must break in the first hundred miles? What
> >> > if it breaks somewhere near 20,000 miles? The satellite will squirt into
> >> > a higher orbit, and the cable will... fall.
> >> >
> >> > ...as I said... ouch.
> >>
> >> Gets harder and harder to cut as you go up, though.
> >
> > But not impossible.
> >
> > And since the goal of terrorists would be to cause as much damage as
> > possible, cutting the cable as high as possible would be their goal.
>
> Possible in theory, possible for wealthy countries, and possible for big
> terrorist organizations are completely different things, though.
>
> Modern terrorist resources are minisculed compared to even small or poor
> nation states. Without being able to send something into orbit, the only
> way to attack stuff high up would be to place a bomb or something similar
> into an elevator car. Considering the infrastructure value and the
> relative costs, I'm sure every bit of cargo will be gone over with a
> fine-toothed comb, so I don't think that's an option.
You're assuming all security measures work all the time. I'm being more
realistic and assuming it's cheaper to bribe a few security people (or
plant your own) than it is to defeat security measures.
Much like the situation now. You have to be GOOD _all_ the time, every
time. They only have to be lucky _once_.
Sea Wasp
> On Fri, 30 Jun 2006 01:53:41 GMT, Sea Wasp
> <seawasp...@obvioussgeinc.com> wrote:
>
> :George W Harris wrote:
> :> On Thu, 29 Jun 2006 15:40:12 -0000, pv+u...@pobox.com (PV) wrote:
> :> :> :Joe Ellis <synth...@sbcglobal.net> writes:
> :> :>But then, imagine the security problems. One of the stories involving a
> :> :>"beanstalk" had a terrorist bomb going off in a car part way up the
> :> :>elevator... and tens of thousands of miles of cable falling to earth.
> :> :
> :> :One of the mars books. And their elevator used very heavy materials. If a
> :> :carbon nanotube ribbon broke, it would flutter to the ground like paper. *
> :> :> And if the space elevator were made out of a
> :> carbon nanotube ribbon, it would break immediately.
> :> The structure has to withstand enormous tension, and
> :> it's not going to be flimsy. We're talking 'ribbon' in the
> :> same way the Golden Gate Bridge is a ribbon.
> :
> : You have NO concept of the strength of carbon nanotube ribbon.
>
> The theoretical strength, which may never be
> approached, or the currently achieved strength, which
> is insufficient for an elevator that doesn't do anything
> but just sit there?
No, the actual strength.
The numbers I got are for an elevator with considerable practical
capabilities. Hundreds of tons to orbit per month.
Sure, some of the attached hardware is pretty heavy, in the
aggregate. Per unit distance, it's STILL miniscule.
El Puerco
> You're assuming all security measures work all the time. I'm being more
> realistic and assuming it's cheaper to bribe a few security people (or
> plant your own) than it is to defeat security measures.
>
> Much like the situation now. You have to be GOOD _all_ the time, every
> time. They only have to be lucky _once_.
Couldn't you look at it the other way 'round? "They" have to execute a
complex operation and "we" only have to notice one screw-up. So you only
have to be good most of the time but they have to be lucky all the time. Or
something.
PV
> And if the space elevator were made out of a
>carbon nanotube ribbon, it would break immediately.
>The structure has to withstand enormous tension, and
>it's not going to be flimsy. We're talking 'ribbon' in the
>same way the Golden Gate Bridge is a ribbon.
Incorrect, look it up. *
--
* PV something like badgers--something like lizards--and something
like corkscrews.
PV
>You're assuming all security measures work all the time. I'm being more
>realistic and assuming it's cheaper to bribe a few security people (or
>plant your own) than it is to defeat security measures.
You're not really being realistic, you've simply fallen for the "terrorists
are smarter than everyone" theory, that's been put forward so we'll all
cower in our homes and buy stuff.
>Much like the situation now. You have to be GOOD _all_ the time, every
>time. They only have to be lucky _once_.
You can be quite sure, that once there's ONE beanstalk, there will soon be
many more. *
PV
> You *have* to extend the cable out past the
>balance point, otherwise the whole thing comes
>crashing down. In fact, the best way to build a space
>elevator is to start at the balance point and build out
>and in simultaneously.
The balance point of the cable/anchor system has to be at or past
geosyncronous orbit. if you want to achieve that with just ribbon, then the
ribbon needs to be about 3 times longer if I remember right. Initially
that's what you're going to have to do, but over the time the climbers are
going to bring up more and more mass, so the system can reel in quite a
bit. Or maybe you snag an asteroid, or round up lots of space junk, and use
that as an anchor. *
Joe Ellis
pv+u...@pobox.com (PV) wrote:
> Joe Ellis <synth...@sbcglobal.net> writes:
> >You're assuming all security measures work all the time. I'm being more
> >realistic and assuming it's cheaper to bribe a few security people (or
> >plant your own) than it is to defeat security measures.
>
> You're not really being realistic, you've simply fallen for the "terrorists
> are smarter than everyone" theory, that's been put forward so we'll all
> cower in our homes and buy stuff.
Horsehockey. _YOU'RE_ falling for the myth that "all terrorists are
stupid, so we have nothing to worry about."
> >Much like the situation now. You have to be GOOD _all_ the time, every
> >time. They only have to be lucky _once_.
>
> You can be quite sure, that once there's ONE beanstalk, there will soon be
> many more. *
And that keeps one from being sabotaged how, exactly?
Rather, it multiplies targets.
I think beanstalks are a GOOD idea... but what Man can make, Man can
destroy.
Hop David
> In article <1151662887....@m73g2000cwd.googlegroups.com>,
> mike weber <fairp...@gmail.com> wrote:
>
>>Tbe elevator *has* to extend beyond the geosynchronous point in order
>>to keep the center of mass in geosynch orbit.
>
>
> The center of gravity, not the center of mass. They won't be anything
> like in the same place, since you cannot approximate the Earth's gravity
> field as uniform at this scale.
>
>
>
>
Indeed. The tug of war between gravity and centrifugal force is very
asymmetric about geostationary altitude. Centrifugal force scales with
radius and gravity scales with 1/radius^2.
I did a spreadsheet comparing gravity with centrifugal force when
angular velocity is 1 revolution per day.
It was interesting to see that the downward pull of an object 5857 km
above earth's surface beats the outward push of the same mass positioned
past the moon's orbit.
The arm of the stalk above geostationary would have to be much thicker
and/or longer than the arm below.
Radius Gravity Centrifugal Net
(km) (m/sec^2) (m/sec^2) (m/sec^2)
12235.0000 -2.6618 0.0647 -2.5970 5857 km above earth
22235.0000 -0.8059 0.1176 -0.6883
32235.0000 -0.3835 0.1705 -0.2130
42235.00 -0.2234 0.2234 0.0000 geostationary altitude
52235.0000 -0.1460 0.2762 0.1302
62235.0000 -0.1029 0.3291 0.2263
72235.0000 -0.0764 0.3820 0.3057
82235.0000 -0.0589 0.4349 0.3760
92235.0000 -0.0468 0.4878 0.4409
102235.0000 -0.0381 0.5407 0.5025
112235.0000 -0.0316 0.5936 0.5619
122235.0000 -0.0267 0.6464 0.6198
132235.0000 -0.0228 0.6993 0.6765
142235.0000 -0.0197 0.7522 0.7325
152235.0000 -0.0172 0.8051 0.7879
162235.0000 -0.0151 0.8580 0.8428
172235.0000 -0.0134 0.9109 0.8974
182235.0000 -0.0120 0.9637 0.9518
192235.0000 -0.0108 1.0166 1.0059
202235.0000 -0.0097 1.0695 1.0598
212235.0000 -0.0088 1.1224 1.1136
222235.0000 -0.0081 1.1753 1.1672
232235.0000 -0.0074 1.2282 1.2208
242235.0000 -0.0068 1.2811 1.2743
252235.0000 -0.0063 1.3339 1.3277
262235.0000 -0.0058 1.3868 1.3810
272235.0000 -0.0054 1.4397 1.4343
282235.0000 -0.0050 1.4926 1.4876
292235.0000 -0.0047 1.5455 1.5408
302235.0000 -0.0044 1.5984 1.5940
312235.0000 -0.0041 1.6513 1.6472
322235.0000 -0.0038 1.7041 1.7003
332235.0000 -0.0036 1.7570 1.7534
342235.0000 -0.0034 1.8099 1.8065
352235.0000 -0.0032 1.8628 1.8596
362235.0000 -0.0030 1.9157 1.9126
372235.0000 -0.0029 1.9686 1.9657
382235.0000 -0.0027 2.0214 2.0187
392235.0000 -0.0026 2.0743 2.0717 beyond moon's orbit
Hop
George W Harris
<seawasp...@obvioussgeinc.com> wrote:
:> The theoretical strength, which may never be
:> approached, or the currently achieved strength, which
:> is insufficient for an elevator that doesn't do anything
:> but just sit there?
:
: No, the actual strength.
The actual achieved strength of 56 GPa which
is less then the minimum necessary strength of 65 GPa?
Really?
--
They say there's air in your lungs that's been there for years.
George W Harris
:gha...@mundsprung.com writes:
:> You *have* to extend the cable out past the
:>balance point, otherwise the whole thing comes
:>crashing down. In fact, the best way to build a space
:>elevator is to start at the balance point and build out
:>and in simultaneously.
:
:The balance point of the cable/anchor system has to be at or past
:geosyncronous orbit. if you want to achieve that with just ribbon, then the
:ribbon needs to be about 3 times longer if I remember right. Initially
:that's what you're going to have to do, but over the time the climbers are
:going to bring up more and more mass, so the system can reel in quite a
:bit. Or maybe you snag an asteroid, or round up lots of space junk, and use
:that as an anchor. *
Actually, you don't have to do that initially. If you
put all the mass you'll need in GSO to start with, build
the ribbon up there and reel it down, you'll end up with a
long ribbon reaching down from the ground to a big hunka
mass just outside of GSO. That hunk can just be a chunk
of asteroid, which is a lot cheaper than carbon nanotubes.
:--
:* PV something like badgers--something like lizards--and something
: like corkscrews.
--
"The truths of mathematics describe a bright and clear universe,
exquisite and beautiful in its structure, in comparison with
which the physical world is turbid and confused."
-Eulogy for G.H.Hardy