Space Elevator?

In article , says...

"Diane Wilson" wrote in message
k.net...

much snipped

If you go back and read Robinson's description, part of his point is
that the cable will need infrastructure along the way. Emergency

It needs the anchor station and the geo-synchonous counterweight. Each are
essentially a port no more complicated than a railway station or a port
anywhere else on the planet or a space station in LEO.

stops and supplies, sufficient structure for the cars to attach and
climb, the ability for cars to pass each other on the way up or down.

You don't need the cars to pass each other. Why would you want to do that?

One going up, one going down. Is that too hard to figure out?

None of this extra mass, stops or cars needing to pass each other is needed
to build a functioning elevator. Robinson was writing about an elevator
assembled from the perspective of the late 1980s before any of the miracle
carbon molecules had been discovered or before their real potential was
really understood. His elevator is made out of double helixed synthetic
diamond or some such balonium and is tens of meters thick in places. That is
absolutely unnecessary with a modern elevator. A modern elevator would only
a meter wide and a couple of centimeters thick.

Balonium? I'd say that your "modern elevator" is still built out of
unobtainium. Principles of building a carbon nanotube structure of
that size have not yet been demonstrated. As you yourself note,
the research isn't done yet.... and I wouldn't count the results
as a foregone conclusion, just because some people want it to
happen.

The hardware for the
elevator cars to attach to the cable are friction wheels that pinch the
cable between them. No extra mass on the cable for something that simple.

I'm curious. What power source are you using in those cars?
What does it weight? Is it self-contained, or available from
the elevator itself? What's its efficiency? What are its
waste products, and where do the waste products and heat go?

No matter how thin the whole thing is, there is still a lot of mass,

It does not add up to a lot of mass. The cable mass is estimated at being in
the region of 7.5 kilograms per kilometer. At 36000 kilometers that is about
250 tons, or about what a small marine vessel might weigh, or about four
slightly overloaded 18-wheeler trucks. It's a lot of mass compared with a
human being, but its piddly squat compared with a conventional structure.

Are you seriously suggesting 250 tons for the whole elevator? What kind
of mass do you propose lifting on it? Any significant payload could
seriously alter the center of gravity, which needs to stay in
geosynchronous orbit.

As you suggest three 20-ton cars on the way up at once (and let's
assume three more on the way down), that would significantly alter
the mass distribution of the entire structure.

and it's going to be more than 23,000 miles tall--literally enough
to wrap all the way around the Earth. And the entire length of that
cable is vulnerable to attack.

Just because you keep repeating this does not make it true.

Yes the cable is vulnerable to attack. But so is every airport on the
planet, the White house, oil refineries, school buses, churches and
traditional launch facilities. However who is going to attack the cable?
Nation states in an act of war? You'd better be prepared for some serious
retailiation because the elevator cable is going to support the bulk of the
world's launch industry.

The alternative targets you recommend are either point locations
which are much more easily defended, or they are sufficiently small
that they would not be worthwhile targets. The *whole* cable is
going to be vulnerable, and let's assume no monopoly on space-based
weapons once transport becomes cheap enough--which is the whole point
of the elevator.

You also assume that any weapon capable of wrecking an elevator
is bound to have a return address. I don't think that's a safe
assumption.

Terrorism? Well then only 20 kilometers of the cable is in their possible
engagement range, unless an ICBM vending nation has decided to commit
suicide by marketing ICBMs to terrorists cells.

Assuming current technology. Assuming weaponry technology stays
constant while the elevator is taking advantage of great leaps of
technology.

And assuming that the elevator would not be such an inviting target
as to spur weapons technology development for attacking the
elevator.

Before you respond, look at the way that Pakistan has been handing
out nuclear technology to a variety of unfriendlies. Anti-US
ideology seems to be the primary currency in this trade. If that kind
of thing happens once, it can happen again. At some point in time,
the weapons that can destroy such an elevator are *not* going to be
restricted to friendly nation-states.

Just for grins, let's also assume that not all elevators will be
controlled by friendly powers.

The modern carbon-nanotube based elevator cable will break up and fall to
earth in fashion similiar to so much black confetti. That is ignoring the
fact that the majority of the cable will not fall to Earth if it is severed
near the base. It flys off into space if the cable is severed near the base.
Robinson's cable only dropped the way it did because it's orbital station
was blown away and it has the mass of a small mountain range. A
carbon-nanotube based elevator cable will have the mass of a small ship and
the surface area of a small city. Comparing the two is like a truck load of
lead pipes and a bucket load of shredded paper up to the top of the Empire
State and tossing them off the edge. See which one gets the bigger reaction
from the poor sods on the ground.

Robinson dropped his first space elevator to the ground as a sort
of technology demonstration. The elevator was rebuilt, and subject
to other threats later in the series. Yes, one could also float
off into space, which still results in loss of the elevator, and
possibly loss of life to anyone on it at the time.

Robinson made the elevator seem like a big, and terrifiying mega-project
that would be eternally reserved for the 'next generation'. It would be
massively (impossibly) expensive and extremely dangerous for the planet
below. He made it seem that it would have the most terrible consequences if
there was ever one small accident with it. Well, maybe there would be if we
were building that sort of elevator. But talking about that sort of elevator
is like getting hysterical about buildings falls over because wooden
structures being unable to support a structure taller than X floors when
everyone uses steel construction.

We are no longer limited to the strait jacket that we had imposed us. Once
we have the materials (which we will have one day soon, with or without
active research toward elevators, there is too much money to be made in
longer carbon nanotubes for the research not to happen) the elevator will go
up. Someone will have the money and will consider the investment worth it.
The risks are small and the benefits are enormous.

Robinson's points are about unforeseen vulnerabilities and risks.

Diane

Jonathan Silverlight wrote in message ...
In message , Frank Scrooby
writes

Robinson made the elevator seem like a big, and terrifiying mega-project
that would be eternally reserved for the 'next generation'. It would be
massively (impossibly) expensive and extremely dangerous for the planet
below. He made it seem that it would have the most terrible consequences if
there was ever one small accident with it. Well, maybe there would be if we
were building that sort of elevator. But talking about that sort of elevator
is like getting hysterical about buildings falls over because wooden
structures being unable to support a structure taller than X floors when
everyone uses steel construction.

Interesting viewpoint. Clarke's elevator starts with a little
demonstration using hyperfilament (and it's worth remembering that the
possibilities for abuse of hyperfilament are blood-curdling. Do you want
the sort of retard who is currently happy spray-painting walls to start
stretching it across roads to cut cars and their drivers into slices?)
but it soon grows into a mega-project. Charles Sheffield's tower has to
be built in one piece. Could a small project start paying dividends
quickly?

It Depends - there are some people betting their money (see Liftport's
web site @ liftport.com) that a scaled project could. First you
invest money in CNT ribbon and make a small fortune providing THAT for
terrestial applications, then take that, plus your experience crafting
the CNT ribbon and spend a few billion making an elevator.

The _real_ payoff comes when your first SE makes .. more SEs. Tow
them off from the first SE and you've yourself an SE farm (hundreds of
clicks apart, granted) sending cargo up on a scheduled basis.

~er

Diane Wilson wrote in message nk.net...
In article , says...

"Diane Wilson" wrote in message
k.net...

much snipped

If you go back and read Robinson's description, part of his point is
that the cable will need infrastructure along the way. Emergency

It needs the anchor station and the geo-synchonous counterweight. Each are
essentially a port no more complicated than a railway station or a port
anywhere else on the planet or a space station in LEO.

stops and supplies, sufficient structure for the cars to attach and
climb, the ability for cars to pass each other on the way up or down.

You don't need the cars to pass each other. Why would you want to do that?

One going up, one going down. Is that too hard to figure out?

Who said there would be only _one_ space elevator? One up, one down.

Actually, for a number of reasons, an elevator going _down_ in
unlikely. You only need the elevator to go up. Coming back, you can
aerobrake and drop things where you need.


None of this extra mass, stops or cars needing to pass each other is needed
to build a functioning elevator. Robinson was writing about an elevator
assembled from the perspective of the late 1980s before any of the miracle
carbon molecules had been discovered or before their real potential was
really understood. His elevator is made out of double helixed synthetic
diamond or some such balonium and is tens of meters thick in places. That is
absolutely unnecessary with a modern elevator. A modern elevator would only
a meter wide and a couple of centimeters thick.

Balonium? I'd say that your "modern elevator" is still built out of
unobtainium. Principles of building a carbon nanotube structure of
that size have not yet been demonstrated. As you yourself note,
the research isn't done yet.... and I wouldn't count the results
as a foregone conclusion, just because some people want it to
happen.

There have been lengths of ribbon (meters long) crafted at Rice in
Houston, that have half the needed tensile strength. The research (as
you noted the other poster noted) isn't finished, but it's well on the
way.


The hardware for the
elevator cars to attach to the cable are friction wheels that pinch the
cable between them. No extra mass on the cable for something that simple.

I'm curious. What power source are you using in those cars?
What does it weight? Is it self-contained, or available from
the elevator itself? What's its efficiency? What are its
waste products, and where do the waste products and heat go?

You can google for this information, if you're really curious.

Free electron lasers can beam the power to collectors on the bottom of
the climbers. Or microwaves, but they cost more on both sides. The
FEL has actually been designed by an outfit in (I think) California.

snip
The modern carbon-nanotube based elevator cable will break up and fall to
earth in fashion similiar to so much black confetti. That is ignoring the
fact that the majority of the cable will not fall to Earth if it is severed
near the base. It flys off into space if the cable is severed near the base.
Robinson's cable only dropped the way it did because it's orbital station
was blown away and it has the mass of a small mountain range. A
carbon-nanotube based elevator cable will have the mass of a small ship and
the surface area of a small city. Comparing the two is like a truck load of
lead pipes and a bucket load of shredded paper up to the top of the Empire
State and tossing them off the edge. See which one gets the bigger reaction
from the poor sods on the ground.

Robinson dropped his first space elevator to the ground as a sort
of technology demonstration. The elevator was rebuilt, and subject
to other threats later in the series. Yes, one could also float
off into space, which still results in loss of the elevator, and
possibly loss of life to anyone on it at the time.

Repeat after me .. fiction. Good stuff, but fiction.

"E.R." wrote in message
om...

Actually, for a number of reasons, an elevator going _down_ in
unlikely. You only need the elevator to go up. Coming back, you can
aerobrake and drop things where you need.

Aerobrake from geosynch? That's a neat trick.

"Greg D. Moore \(Strider\)" wrote in message . ..
"E.R." wrote in message
om...

Actually, for a number of reasons, an elevator going _down_ in
unlikely. You only need the elevator to go up. Coming back, you can
aerobrake and drop things where you need.

Aerobrake from geosynch? That's a neat trick.

I must have been channelling KSR's 'Red Mars' and transposing the
planets - my mistake.

When you want to return from orbit (LEO, GEO or anywhere inbetween)
pop into a capsule, fire your retro-rockets and come back. If we
posit a working space elevator then we should assume it's dirt cheap
to ship things 'up' - including capsules with heavy heat shields.

~er

"Greg D. Moore \(Strider\)" wrote:

"E.R." wrote in message
om...

Actually, for a number of reasons, an elevator going _down_ in
unlikely. You only need the elevator to go up. Coming back, you can
aerobrake and drop things where you need.

Aerobrake from geosynch? That's a neat trick.

Isn't there some position above the counterweight that would result in
an orbit that grazes the atmosphere if you jump off?

"Ian Stirling" wrote in message
...
"Greg D. Moore \(Strider\)" wrote:

"E.R." wrote in message
om...

Actually, for a number of reasons, an elevator going _down_ in
unlikely. You only need the elevator to go up. Coming back, you can
aerobrake and drop things where you need.

Aerobrake from geosynch? That's a neat trick.

Isn't there some position above the counterweight that would result in
an orbit that grazes the atmosphere if you jump off?


Yes, many.

JRS: In article , seen in
news:sci.space.shuttle, Ian Stirling posted at
Wed, 14 Jan 2004 16:04:52 :-
"Greg D. Moore \(Strider\)" wrote:

"E.R." wrote in message
om...

Actually, for a number of reasons, an elevator going _down_ in
unlikely. You only need the elevator to go up. Coming back, you can
aerobrake and drop things where you need.

Aerobrake from geosynch? That's a neat trick.

Isn't there some position above the counterweight that would result in
an orbit that grazes the atmosphere if you jump off?

I think not, unless you jump very hard.

There is a position below the counterweight from where you fall into a
grazing orbit: URL:http://www.merlyn.demon.co.uk/gravity2.htm#Fall ;
about 18700 miles radius. The page has a calculator which can be used
for other planets; any consistent distance units can be used.

--
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Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
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