"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?
They were 'launched' according a schedule. They need to arrive on schedule.
Only a complete idiot or a politician would make that part of the
requirement. They all go up at the same speed. They arrive at the station at
the same regular intervals that they departed the anchor stations, unless
they happen to be launching themselves from the cable, in which case some
acceleration might be allowed in the last part of the trip, but then you're
probably talking about a much bigger cargo that need the elevator's full
capacity anyway so there would have been no other cars on the cable.

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. 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.

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.

If your economy need to double the capacity you send up another cable with
the next car and string it out to another anchor station and another
geosynchonous station. That is another fundamental difference between the
modern elevator cable concept and its predeccessors. The modern elevator
cable is automatically seen as the staging area for the construction of its
own replacements, not the end product.

And what is on any one individual cable at any one time?

The Highlift systems cables will be lifting something like 20 tons
travelling in three or five cars (or presumably eventually dropping) their
maximum size. Each cargo is travelling three days apart. Earth absorbs a
couple of twenty ton objects a day, especially if said twenty ton object has
the necessary safety equipment aboard to make its descent controlled or
safe.

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.

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. Because guaranteed the
moment a terrorists faction uses an ICBM, them, their loved ones, their
country of origin, and the country of origin of the ICBM are going to wacked
with an extremely big stick (the kind with big cans of EXTREMELY BRIGHT
INSTANT SUNSHINE). The elevator anchor is isolated and easily guarded from
rogue air attack. Cargos going up the cable will be vigoriously inspected
and checked. And even if something does go wrong then:

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.

A monofilament to space is a neat idea, but by itself it's nothing
but cute engineering tricks. Making it useful takes a lot more

The carbon nanotube is not a monofilament. That would be cool though. One
molecule of carbon 36000 kilometers long, nice.

It is not 'just' a 'cute engineering trick'. It is a fundamental adjustment
in our thinking on how to build elevators, and how to manage them.

investment that shows up in mass and exposure.

And that, as much as anything, is Robinson's point.

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.


Diane

Regards
Frank