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Date: Fri, 28 Jun 91 01:28:09 -0400 (EDT)
Subject: SPACE Digest V13 #729
SPACE Digest Volume 13 : Issue 729
Today's Topics:
Re: Pet Projects
The SPACE Digest is...
Re: Beanstalk analysis reprise
Re: Gold
Space Digest
ESA attempting to recover Olympus satellite
Administrivia:
Submissions to the SPACE Digest/sci.space should be mailed to
space+@andrew.cmu.edu. Other mail, esp. [un]subscription requests,
should be sent to space-request+@andrew.cmu.edu, or, if urgent, to
> I'm sorry if this is a FAQ or something, but what is Space Digest
> (everybody seems to talk about it, but its doesn't seem to enter the
> net)?
The SPACE Digest (don't ask me why SPACE is in all caps. As far as I
know, it's only for historical reasons) is a version of sci.space
that is available through email. Messages are gatewayed back to
sci.space through the adress space+@andrew.cmu.edu -- some broken
mailers interact badly with the andrew message system (AMS) and cause
messages
At the moment the Digest has over a thousand subscribers, is gatewayed
through four listservs, and is received on (as far as I know --
forwarding may cause this to be false) every continent. Digest
subscribers seem to account for about a quarter to a third of the
traffic on sci.space.
The Digest is lightly moderated (when I am able, I try to
slow completely outrageous conversations, such as advanced bickering
about Velikovsky's prediction of the face on mars) and has a
companion, the SPACE magazine, which is heavily moderated -- I tend
to place only factual articles into it, though the occasional
interesting interchange is added. The magazine is necessary because
of the absurd amount of traffic that goes through the Digest.
I took the Digest over from Ted Anderson two years ago, and will soon
be looking for a replacement, as I graduate in December.
Requests for subscription to the SPACE Digest go to
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Now, aren't you sorry you asked? :-)
--
Todd Masco | tm2b@andrew.cmu.edu | "Free speech is the right to shout
CMU Physics | tm2b@andrew.BITNet | 'theatre' in a crowded fire."
------------------------------
Date: Tue, 11 Jun 91 07:29:30 EDT
From: markhunt@zen.cac.stratus.com (Mark Hunt)
signoff space
------------------------------
Date: 10 Jun 91 22:09:26 GMT
From: cis.ohio-state.edu!zaphod.mps.ohio-state.edu!rpi!news-server.csri.toronto.edu!utgpu!utzoo!utdoe!torag!w-dnes!waltdnes@ucbvax.Berkeley.EDU (Walter Dnes )
Subject: Re: Beanstalk analysis reprise
wreck@fmsrl7.UUCP (Ron Carter) writes:
> In <Toss31w164w@w-dnes.guild.org>,
> waltdnes@w-dnes.guild.org (Walter Dnes) writes:
>
> >Your calculations seem to be based on an airless earth, i.e a
> >good vacuum. Don't forget that we have an atmosphere.
>
> Beanstalks don't do work on the air, so air drag is not a
> major consideration.
>
TV transmitters and microwave relay towers aren't *DESIGNED*
to "do work on the air" (pun not intended). Yet occasional
failures/collapses do happen.
> > 1) You've allowed for longitudinal forces. What about
> >perpendicular forces ? What happens when the beanstalk gets hit
> >by a 100 km/h (60 mph) wind ? How about a 250 km/h
>
> If the wind continues long enough, the beanstalk assumes a
> catenary curve rather than running upward in a straight line.
> Changing winds excite vibrations, which may have to be damped.
In the general case, you will *NOT* find wind blowing at the
same direction and speed from ground level to the top of the
stratosphere. Wind at 10,000 feet can be one speed and direction,
another at 20,000 feet and yet another at 30,000 feet, etc. The
change with elevation (vertical wind shear) can be quite abrupt.
And wind speed and direction at any one level changes with
passing fronts and general circulation. Expect the beanstalk to
be pummeled from all sides by winds at various speed and
directions.
> Alternative: trifurcate the beanstalk at a point high in
> the stratosphere. Attach each third to a separate anchor,
> on the points of an equilateral triangle. No matter which
> way the wind blows, it only moves tension from one part
> to another; it does not push the beanstalk as a whole.
>
This will mean 3 sections subject to structural icing as
discussed below.
>> 2) Since a geosynchronous orbit sits on the equator, you
>>won't have to worry about icing... *AT SEA LEVEL*. At higher
>>elevations in the atmosphere it will be a worry in two ways.
>>Heavy icing will strain the beanstalk by sheer weight alone.
>>Icing will also increase the cross-section that wind loading
>>works on.
>
>Any flex in the beanstalk, or vehicles moving up and down,
>will cause it to shed ice. Also, it can be heated electrically
>if icing is a difficulty.
Structural icing simply makes loading worse. It adds weight
to the whole structure, and increases the cross-section area that
the wind sees. Don't expect heating elements to keep the
beanstalk 100% ice-free 100% of the time. If it's hot enough to
do so, I'd hate to see what it does to the graphite beanstalk
itself. Heavy rime icing in cloud is a lot worse than the worst
freezing-rainstorm you have ever seen. It is one of the worst
nightmares for a pilot. On encountering it, a pilot basically has
to get out of there fast. Either dive down below the freezing
level or climb up over the cloud top. An anti-icing system will
hold off light icing indefinitely, assuming that the system isn't
fluid-based, in which case, when your de-icing fluid runs out,
your luck runs out. In the case of heavy rime icing, an anti-icing
system will give a plane a few minutes grace period to get away.
As for vibration knocking off all ice immediately... if that was
the case, then a light prop-driven plane should have absolutely
no worry whatsoever about icing ! I've been a passenger on prop
planes, and I can assure you they definitely aren't smooth. Ask
an experienced pilot what he does when he encounters heavy rime
icing. Also, if the beanstalk flexes violently enough to do this,
I'd start worrying about metal fatigue (or whatever-material-it-
is-you're-using fatigue).
You might also try talking to contractors who put up TV,
cellular, and microwave towers on mountaintops, where the cloud
base does frequently drop down to envelope the structure. Their
only available reaction is to build heavy-duty structures, which
could be very difficult for a beanstalk.
Those towers are usually built to a 30-year worst-case load.
If they fall over, communications can be disrupted until
alternate channels are found. No one gets physically hurt. The
financial bottom-line for the customer depends on where increased
reliability is exceeded by increased building costs. A falling
beanstalk can wrap around most of the equator and cause damage in
lots of countries. Aside from the diplomatic fallout, if any of
the (sub)contractors/builders of the failed beanstalk were
American (especially based in California), it would be a
guaranteed annual income for lawyers for the next decade.
Electrical heating is one anti-icing system. You'd need
power fed from the surface up to a height of 10 - 15 km. A couple
of insulated cables power to worry about. What does this do to
the weight of the whole system ? Does the whole beanstalk need to
be made thicker ? How much ? Your other alternatives are to pump
de-icing fluid several km uphill against gravity, or encase
several km of the beanstalk in a flexible airtight sleeve (in
short manageable sections) and inflate/deflate it in cycles to
dislodge icing as it accumulates. Those are the three main types
of anti-icing systems used on aircraft.
In summary, wind and ice loading is an important real world
problem that no amount of hand-waving will make go away.
>A much greater difficulty will be supporting the required
>weight of aircraft warning strobes and such. It may make
Better to establish a "yellow zone" around the beanstalk in
which stray aircraft would be warned away, and a smaller
"red zone" in which they would be shot down. If anybody strays
into the "red zone", assume that they are terrorists trying to
destroy the beanstalk. In that case, absolutely the last thing
you would want to do would be to give them a flashing strobe or
a radio beacon to home in on.
As far as weight is concerned, I would be much more worried
about the weight of several km of heating cable wrapped around
near the bottom of the beanstalk.
>more sense to use a Lofstrom loop for the portion of the
>structure which is in the atmosphere, because it can be
>self-supporting and carry (and power) lots of accessories.
>The tension-supported part could run from 80 km upward.
>(This also cuts the required amount of material for the
>rest of the tether by about 1/e; quite a savings!)
^^^^^^
The thread title says "Beanstalk reprise". I said in a post
almost two weeks ago that while tethers may be feasible, I didn't
think the same about beanstalks. If you're saying that tethers
are much more feasible than beanstalks, then I think we're about
to have a violent agreement ;^)
>I'm disappointed that you can't come up with better objections.
>Much more to the point would be "Where are you going to get 15
>million metric tons of graphite whisker?" That's a much more
More to the point is... 40,000 km worth of the stuff put
together as one piece.
>difficult question, because we don't know how to make the stuff
>in quantity yet.
Beanstalks aren't possible given today's technology. I
agree with you... again !!
> I'm assuming that this will be done, soon,
>because the market for high-strength fibers is large and
>growing, and the state of the art is progressing rapidly.
