Frosted cones and other thoughts

But 1st, -an ininteresting URL..

Nanotubes at 1/10 the cost
http://www.evworld.com/databases/shownews.cfm?pageid=news230702-01

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According to "High frontier" [ -P. 64 2nd Ed., -P. 37 3rd Ed.]

Island III was designed to be 4 Mi. in diameter and 20 Mi long. with a
'land' area of 500 sq. miles.

[He's including the windows and both of the cylinders.]
-The actual land area in each cylinder would be about 120 Sq. miles.

3 mirrors 20 miles long [actually they should be about 28.3 mi. long
to give a noonday sun along the full length] X 2 miles wide at a
45 degr. angle present an 'effective' solar capture surface of 60 Sq.
mi. [or 85 Sq. mi, if 28.3] spread over 120 Sq. mi. of land.
[equates to 0.5 [ 0.7]available solar intensity]

An end cap with a diam. of 4 mi has a capture surface of
(Pi x r square) = 12.56 Sq. Mi. [at 1.0 intensity would still be worth
only 25 [18] Sq. miles of mirror].

This would require an additional focusing disc reflector large enough
to make up the difference. [say, slightly over 10 mi. in Dia. with an
id. of somewhat more than 4 mi.]

But then you wouldn't want a cone base of much over 2 mi. else too
much interior volume is taken up; plus the effect on the weather is
imponderable at any substantial diameter.

If you are willing to increase the disk size sufficiently you may be
able to decrease the cone base diameter to something livable...

P.S.

Have you thought of making your non-rotating protective shield
large enough to enclose the mirrors at full [45 degr.]extension?

Of course for economy's sake you would want to rotate the cylinder
120 degr. at midlength so as to provide 6 mirrors only 10 [14] mi.
in length. thus allowing a non-rotating cylinder shield of about 15
[19] mi. [or so] in Diameter.

[The back half could be tapered at 45 degr. to reduce mass.]

More expensive than you had in mind, but it might be worth it in the
long run.

P.P.S.

I haven't thought this through, and considering the math, probably
never will, -but, if the mirrors were halved lengthwise, separated,
and set at an angle to each other, couldn't the windows be reduced
nearly by half in width, thus increasing both protection and land
area? [-or perhaps a concave mirror?]

-Or would this mean excessive heat where the beams cross thru the
window?

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I've been kicking around Bob Hardman's 7-30-02 figures & believe
we MUST lower our sights. Perhaps 500 meters diameter like O'Neill's
Island I (J.D.Bernal sphere) design.

Even at 500 meter diameter with 30 psi design pressure a cylindrical
vessel would need ~23" wall thickness for old aluminum alloy with
15000 psi working stress. Anyone know what allowable working
stress we can use with that new aluminum-lithium alloy?

Also noticed that going from sphere to cylinder shape DOUBLED
wall thickness (for same diameter & internal design pressure).
No wonder G.K.O'Neill mentioned staying with spherical shape for
first colonies in his video tape.

My big hope is to go with cylindrical shape/center light cone design
using the Al-Li alloy with far higher than 15000 psi working stress.
Also consider circumferential cables in tension on outside of shell
every few meters letting us half that required wall thickness.

Hallelujah - Praise Spacesettlers ! ! ! Ed S.

--- In spacesettlers, "Ed Schonert" wrote:

> Even at 500 meter diameter with 30 psi design pressure a
> cylindrical vessel would need ~23" wall thickness for old aluminum
> alloy with 15000 psi working stress. Anyone know what allowable
> working stress we can use with that new aluminum-lithium alloy?

How about glass fibers? Glass made in the vacuum (anhydrous, but I
won't swear to the spelling) are supposed to be very strong, and
lunar regolith (and perhaps many NEO's) have a lot more silicon than
they do aluminum, iron, titanium, etc.

> Also noticed that going from sphere to cylinder shape DOUBLED
> wall thickness (for same diameter & internal design pressure).
> No wonder G.K.O'Neill mentioned staying with spherical shape for
> first colonies in his video tape.

What about tori?

> My big hope is to go with cylindrical shape/center light cone
> design using the Al-Li alloy with far higher than 15000 psi
> working stress.

I'm glad to hear you talking like this. We don't need to wait for
bucky nanotubes!

> Also consider circumferential cables

Perhaps made of glass fibers?

> in tension on outside of shell every few meters letting us half
> that required wall thickness.

> Hallelujah - Praise Spacesettlers ! ! ! Ed
S.

Xenophile (who is happy to use the bucky nanotubes once they become
available)

From: xenophile2002
>> My big hope is to go with cylindrical shape/center light cone
>> design using the Al-Li alloy with far higher than 15000 psi
>> working stress.
>I'm glad to hear you talking like this. We don't need to wait for
>bucky nanotubes!

You need them to lift the initial cargo to start build in space.
Also you need them to bring stuff from earth and to send stuff to earth.

They are the first ten step of the stairs.
You can do witout, but will difficult and dangerous and not cheap.

Mirco