Re: beanstalks (was Re: Metallic hydrogen ...)

From: George William Herbert (gherbert_at_gw.retro.com)
Date: 06/07/04 

Date: 7 Jun 2004 15:45:53 -0700

Uncle Al <UncleAl0@hate.spam.net> wrote:
>>[...]
>Listen up, git,

This is uncalled for. Please treat this subject with
appropriate professionalism.

> 1) Effectively *all* graphene systems (e.g., nanotubes, carbon
>fiber, char) are electrical conductors. The very, very few that are
>dielectics trivially dope (oxidation, radiation, mechanical damage to
>molecular structure) to being electrical conductors.

Real elevator will have segment boundaries, which can be
made to be insulating, even if the fibers are conductive.

Dr Edwards has quantitatively analyzed the overall charge
and current flow issue and believes it to not be a problem,
with realistic current flows into the fiber and down the
fiber with its real resistance. And any segment where charging
is felt to be a major issue can be isolated with nonconductive
fibers.

If you don't like his analysis, please read it and respond
in detail as to why he's wrong.

> 2) Diamond fibers don't exist. If they did, their brittleness and
>perfect cleavage planes would damn them.

Aren't required.

> 3) Dielectric organics will crumble in solar UV, radiation fields,
>ozone... Any insulation blows you way the Hell over your mass/distance
>limits. Kevlar, Spectra, and carbon fiber sails have remarkably short
>lives in sunlight and mechanical operating conditions.

You mean boat sails? Those are subjected to intense vibrations,
and the sails which use those materials are racing sails built
to the edge of the material performance envelope. And Carbon Fiber
is inherently brittle, so flexing it a lot like sails do is a
bad idea anyways. And in boats, subject to salt and salt water
as well as sunlight.

It's not comparable. The elevator fibers will be in tension,
not cycling too deeply. Much more benign chemical environment
except the bottom tip of the elevator.

I'm a boats guy and have a naval architecture degree.
There's no comparison, in my opinion.

We can easily do demos for elevator near-ground performance
just by building 500 meter towers and hanging sample tether
ends off them, in the breeze and with sample loads and climbers.

Not trivially cheap, but not more than a few million bucks including
the tethers, once we have the fibers identified and produced in
testbed quantities.

> 4) We already have the limits of high tensile strength small
>diameter fibers being used. The vertical suspension of an Eotvos
>balance rotor is a meter or two of the smallest diameter fiber
>possible. Loading is typically 80+% of breakage. Fiber cost/meter is
>irrelevant. They use 6-micron diameter tungsten filament.

Tethers and space elevators use the figure of merit not of
raw strength, but strength/density. Not comparable.

>NOBODY has answered the question about what makes the beanstalk
>elevator go up and down.

Everybody has answered it. You are chosing to disbelieve
the solutions which have been put forwards. Which have been
hashed out and designed in fair detail, by highly competent
physicists and engineers in government, academia, and construction
industries, despite your lack of faith in their concepts.

It's perfectly fine for you to argue that they're all wrong.
But claiming that nobody has answered the question is
disingenuous or ill educated.

If you'd like to specifically argue against the proposed designs,
feel free to look them up and post or publish rebuttals.
Strong professional criticism of technical advances is
justified and better for everyone.

> Wires conducting electricity are out, as is
>*any* modality the adds mass/length to the entire length of the
>beanstalk. A rocket is silly. Start by asking "How many kilowatts
>will you need?" Let's say 100 horsepower (5/6 of a 2004 1.6 liter
>Mini Cooper) will get the elevator and its contents adequately arisen
>(or do you want to move one kilogram at a time?). 100 hp is 75
>kilowatts. NOTHING can power the elevator. (How long would a Mini
>Cooper take to drive around the Earth? Would you want your ***
>permanently planted in it as it did it?)
>
>A funicular system is beneath derision for obvious reasons. A laser
>light to electricity scheme is ludicrous. A 100 hp mechanical
>gripper? HA HA HA.

Why do you find mechanical grippers to be laughable?
There are alread track based elevators that do the same
thing gripping on to more solid rails.

Why do you find laser light to electricity schemes to be ludicrous?
They are being proposed across a wide variety of space
applications, including supplying eclipse power to GEO comsats,
and even powering Lunar bases through the Lunar night cycle.
Photovoltaic cells are cheap and well understood. Lasers are not
cheap but well understood. Efficiency of transmission can be upwards
of 40% and of reception the same, given a narrow laser frequency
to tune the photovoltaic cells for.

1 ton (1000 kg) ascending 100 m/s (about 4 days to GEO) is going
to require about 1,000 KW worth of power. Assuming grip and
motor inefficiencies, figure 1,500. No more than 5 MW of power
received at the photovoltaic cell array, and no more than around
15 MW of power input at the bottom. 11 cents per kWh, $110 per
MWh, $1,650 or so per hour to run for 4 days or $165,000 in juice
off the grid for the total lift. 15 MW of laser with sufficient
aperture to keep Rayleigh range at GEO is not cheap, but it's within
existing CW laser capabilities. Laser power is just a dollar function,
and it's down to a few dollars a watt.

>Are ya feelin' lucky, punk? Ask what happens given a fiber at 80-90%
>of breakage tension and then notched.

The margins proposed are greater than 10-20%. Most everyone is using
safety factors around 2.

Think civil engineering not physics experiment. We *know* that.
Margins and redundancy proposed are comparable to the standards
used in civil engineering projects.

>A thick Pyrex tube is trivially
>split by stressing a hair scratch. Cheap glass cutters are cemented
>tungsten carbide scribes. Better ones are a diamond. The absolute
>best glass cutter I have ever seen in action was a plate of raw
>furnace boron carbide the size of a postage stamp from East Germany.
>The post-doc touched the Pyrex tube with the lightest caress of one
>black sharp edge... and the tube parted under its own weight without
>so much as a whisper.
>
>Your 22,300 mile-long beanstalk will be brought down (and up) by a
>scratch. How much LEO orbital debris do you think there is? Answer:
>Humongous numbers of particles. SNAP!

That's why all the long tether and elevator proposals use multiple
strand cables with separation between the strands. See Hoytether
and related concepts. This was known decades ago and engineering
solutions well demonstrated a decade ago.

Redundancy is understood and required.

Repair and maintenance are factored in to deployment and ongoing
operations costs and design.

>BTW, all superstrong materials are brittle. Kevlar and Spectra, for
>all their extraordinary tensile strength, are trivially broken by the
>simple expedient of tying an overhand knot and pulling. SNAP! 1/16"
>wire tungsten chain mail (hydrogen furnace shields) can be crushed in
>your fist. Diamond spalls [1,1,1] triangular platelets with a light
>tap, hence diamond cutting with a little mallet and a blade.

We won't be tying any of this in knots.

>Before you go spending a few $trillion of my tax money,

Ten billion, if current estimates are correct.

>plan something
>that will hold together long enough to be built -

Orbital debris modeling is part of the current proposals.
Repair and ribbon replacement and upgrade is planned to
be an ongoing process. The operational and cost impacts
have been modeled and included. It is not a showstopper.
It is a significant cost fraction, but of a very low overall
operational cost per kilogram delivered.

>and then be useful
>for doing something revenue-generating afterwards. We already have
>one International Space Station Freedom FUBAR Space Hole One Alpha.
>It is a technological atrocity and a money-sucking wound that does
>NOTHING.

A space elevator would not be nothing; it would allow us to
launch moderately sized payloads to GEO for total costs on the
order of $200/lb. That would pay for itself launching GEO
comsats in short order. At those delivery prices, comsats
could be made of orbitally-integrated parts and much much
larger and cheaper; the price of bandwidth delivery to the
ground would plummet. Space tourism at costs of roughly
$50-100k/person rather than $10-20 million would be available.
Manned missions to the Moon and Mars would depart from an
energetically very favorable position, assembled out of
components lifted up the elevator to the GEO station.

A GEO elevator is difficult and expensive. It is not
that expensive compared to NASA's annual budget ($16 billion)
or the total space industry worldwide ($50-70 billion).
The difficulties are primarily in materials, which are
coming along nicely and should be available in another
few years at this rate of progress.

I'm a rockets guy and I have my skepticism about various
other space access methods. But, I do not have any
serious doubt that a Space Elevator can be built if the
materials technology continues to improve as physics
and historical trends indicate it can, and the market
demand is large enough that the initial capital cost
will be paid off.

There is no guarantee that the materials problem will
continue to improve, but the physics of the materials
has been solved, it's now purely a question of being
able to manufacture them in sufficient quantity and
quality to actually build something with them.

Enlightened skepticism and analysis of failure modes
and risks are always welcome, but irrational fear and
kneejerk responses without studying the problem in
depth and looking at the body of literature are
not useful and do not reflect well on you.

-george william herbert
gherbert@retro.com

Quantcast