[ExI] keith's article at the oll drum

Jeff Davis jrd1415 at gmail.com
Wed Jun 17 23:56:11 UTC 2009

On Wed, Jun 17, 2009 at 2:09 PM, hkhenson<hkhenson at rogers.com> wrote:
> At 05:00 AM 6/16/2009, spike wrote:
>>  I have been thinking of Jeff's
>> inflatable tower notion...

With respect Spike,... Thanks for the attribution, but the term tower
is far more applicable to that version of the "inflatable structure"
presented in


which began this thread.  I did not attempt to redirect the thread
back to my version because I prefer a more freewheeling discussion
that goes where it goes.

My notion is more ramp than tower.  A half-cone lying on its side,
west to east,  with the "base" of the cone capped by a
half-hemisphere.  The "foot of the ramp" is the pointy end of the
half-cone.  Located mid-Pacific, north of the equator at the
southernmost edge of the zone of the trade winds.   This location
chosen so that a scoop-like opening, say 10km high by two hundred
wide, at the larger (eastern) end can scoop up those trade winds and
inflate the lower, air-inflated compartments.  I've recently added the
idea of a compartmentalized interior, for a variety of potentially
virtuous reasons.

Bottom line on all of this: I'm not wedded to a single detail.
Whatever works is fine with me.  My criteria for the overall size and
precise shape of the structure is simple:  sufficient height at the
end of the launch tube so that the impact of the launch vehicle with
the atmosphere is not a deal breaker.

> Spike, I hardly discussed the power sat design.  If we go with thermal, then
> the underlying structure could be brought up in rolls and run through a beam
> spinner.
> I owe you big time for the work you did on the Neptune first stage, which I
> scaled down to 1/20th then added the laser propulsion
> So if you want to work on an inflatable structure, will help.
> Questions we need to consider, probably off this list include
> Scale height for hydrogen, hydrogen/nitrogen mixes.

Yes, probably.  "Probably", because I may not understand what you
mean.  I keep thinking about the problem of pressure differences
inside and outside the structure, particularly at the higher
altitudes.  At lower altitudes a fractional overpressure is all that
is needed to support the structure.  So everything can be quite light.
 At the top, however, where there is little external pressure, so the
overpressure may have to be larger, and the structure beefier and thus
heavier.  This is harder for me to conceptualize qualitatively, with
any confidence.

> Mass we want to be able to support at the top.


> Taper shape

> Neutral buoyancy where the part in the lower atmosphere would float and the
> top would be under compression.

An interesting consideration.  One which I've only just begun to mull over.

> Airfoil shaping
> Location  ( do we try to put it on a high mountain?  or out to sea?)
>  related weather effect.

All excellent, discriminating issues.  I've often been annoyed by
folks who look at an idea that someone has worked on for some time,
and within seconds declare "Naaah, it'll never work."  Until now, I've
never encountered someone who looked at a somewhat complex idea, and
fairly quickly and astutely identified key issues.  Years ago Keith,
you annoyed me with the former, now you impress me with the latter.

Also, I want to mention that I read Keith's piece at the oil drum, and
what I noticed there was how Keith kept his cool.  My impression is
that the site is the work of Peak Oil true believers.  You know,
"We're all doomed!!!  The apocalypse is coming!  The oil is all
gone,...well...SOON!!!!!!"  And they are so in love with their
melodramatic narrative that pragmatic solutions are not well received.
 Keith's solar power satellite solution to the energy bottleneck, is
too pragmatic, too unhysterical for them.  Their responses in the
discussion following the article were snide, combative, and
dismissive.  They didn't want to hear it.  But Keith kept his cool.
You're a better man than I am on that score, Keith.

Best, Jeff Davis

 "Everything's hard till you know how to do it."
                         Ray Charles

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