Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!caen!ox.com!fmsrl7!wreck
From: wreck@fmsrl7.UUCP (Ron Carter)
Newsgroups: sci.space
Subject: Re: Beanstalk analysis reprise
Summary: It's time for Walter to start paying tuition.
Message-ID: <43882@fmsrl7.UUCP>
Date: 17 Jun 91 17:39:16 GMT
References: <43279@fmsrl7.UUCP> <FeJc41w164w@w-dnes.guild.org>
Reply-To: wreck@fmsrl7.UUCP (Ron Carter)
Organization: Ford Motor Company, Scientific Research Labs, Dearborn, MI
Lines: 145
In article <FeJc41w164w@w-dnes.guild.org>, w-dnes.guild.org!waltdnes
(Walter Dnes) of "Ye Greate Calkulatinge Machine Hoaxe" writes:
>wreck@fmsrl7.UUCP (Ron Carter) writes:
> TV transmitters and microwave relay towers aren't *DESIGNED*
>to "do work on the air" (pun not intended). Yet occasional
>failures/collapses do happen.
Because loads on the structure exceed its strength. However,
you've not shown a single calculation to test the proposition
that this is likely in the case of a beanstalk.
Why not? Is expressing your ignorance your best tactic?
> 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.
Wonderful. The smaller the net force on the beanstalk, the
smaller the net offset it will assume from vertical. The
worst-case situation is all winds in the same direction.
>>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.
Of course, you didn't bother to consider the possibility of
thermostatic control. Nor did you calculate the power required
to keep ice thickness to less than some arbitrary value. Graphite
is very refractory; it gets stronger with increasing temperature.
Again, the argument from ignorance: "If I don't know that
it won't be a problem without doing any work to see if it
might not be, it is." Very poor technique.
> 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.
Don't tell me about pilot's nightmares. I've lived a few.
>A falling
>beanstalk can wrap around most of the equator and cause damage in
>lots of countries.
Not unless it breaks far, far above the surface. The portion of
the beanstalk above the break remains in orbit; only the portion
below will fall anywhere. If the portion below is large enough,
breaking it further will allow the upper parts of that to remain
in orbit as well.
The terminal velocity of a cable of density 1.7 must be
considered. If the cable is only an inch or two in diameter
and the lengths are not long enough to whip the ends up to
high speed ("range-safety" equipment is indicated!), terminal
velocity will not be high, and damage will be small.
> 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 ?
Why didn't you calculate this yourself? Are you incapable?
How do you know it is an issue at all?
>Does the whole beanstalk need to be made thicker ? How much ?
Why didn't you calculate this yourself? Are you incapable?
How do you know it is an issue at all?
>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.
Of course, you never considered systems not in use on aircraft.
Alternatives include piezoelectric flexors to deform the beanstalk's
cross-section and flake ice off, flash heaters to evaporate ice into
steam and blow overlying ice off, and other devices not compatible
with bent sheet metal structures. Use some imagination!
> In summary, wind and ice loading is an important real world
>problem that no amount of hand-waving will make go away.
Again, how do you know it is an issue at all? Have you calculated
the loadings and found them excessive, or are you just hand-waving?
> 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.
How much cable do you need? If you don't know, how do you know
it is an issue?
> The thread title says "Beanstalk reprise".
Beanstalks are a class of tether. Weren't you here for the lecture?
> More to the point is... 40,000 km worth of the stuff put
>together as one piece.
Ever consider that it might NOT be one piece? That it might have
joints and connectors? That individual strands might be testable
and replacable while in use, like a suspension bridge? Where's
your imagination?
> Beanstalks aren't possible given today's technology. I
>agree with you... again !!
Agreed. However, they are possible given MATERIALS known
today. This is a crucial distinction; we know what to shoot
for, and even many of the physical processes required.
As for ice loading and wind loading, I'm not going to lecture
for free to address your misconceptions any longer. If you
want to continue responding to my data with hand-waving, you
can pay for the priviledge. Ergo, I offer you this deal.
I bet that I can do the following:
1.) Refute the contention that ice loading on a beanstalk
of design chosen by me (within reason) presents any
structural difficulties, given the use of known de-icing
technology, and
2.) Refute the contention that wind loading at a wind speed
of 250 KPH could bring a beanstalk of design chosen by
me (within reason) down, given ice loads limited by
de-icing equipment a la 1.) above.
I assume that you will bet that I cannot refute these contentions.
I offer the sum of $100 American on each of these two assertions.
We must agree on a judge. This has advantages for you: you get
the lecture, and YOU get paid if it is wrong. You only have to
lay out money if you are truly getting educated. What a deal!
So, are you ready to put your money where your mouth is?