[LMB] Fw: Soletta design, and moons more generally.

Joel Polowin jpolowin at hotmail.com
Mon Oct 22 23:42:58 BST 2018


Forwarding Markus's message to the list, since it didn't make it
originally...

________________________________________
From: Baur <baur at chello.at>
Sent: Sunday, October 21, 2018 1:36 PM
To: Discussion of the works of Lois McMaster Bujold.; Joel Polowin
Subject: Re: [LMB] Soletta design, and moons more generally.

Am 21.10.2018 um 19:07 schrieb Joel Polowin:
> Baur <baur at chello.at> wrote:
>>> A disadvantage of distant orbits, either Lagrangian or geo-stationary, is
>>> that unless the mirrors are optically perfect, or nearly so, the reflected
>>> light disperses, falling with the square of distance. (With a perfectly
>>> flat mirror, the (nearly) parallel rays from the Komarran sun remain
>>> parallel when sent down.
>>
>> for the purpose of terraforming the optical quality of the mirror(s)
>> need only be good enough that a majority of reflected sunlight reaches
>> Komarr SOMEWHERE - the purpose is not optically perfect lighting, after
>> all ..
>>
>> for 12000 km diameter at 300000 km distance the cone angle (and thus the
>> necessary accuracy of the mirror) is 2.3 degrees .. NOT very flat ..
>
> For purposes of grasp-of-concept...
>
> To have the effect it's designed for, the soletta needs to have a
> diameter of the same order as that of Earth's moon, assuming that all
> of the light that hits the mirror reaches Komarr.

one needs also to consider the albedo - earth moon has a visual albedo
of 0.12 - this means only 12% of the sunlight arriving on the moon gets
reflected back (and gets reflected in all directions - not only towards
earth) ..

a mirror will have a visual albedo of close to 1 (reflecting close to
100% of the sunlight) - and it reflects the light in more or less into
one direction

a size of earth moon with an albeod of close to 1 and good control of
the direction the light is reflected in would make earth's moon as
bright as the sun and would refelct about as much light to the earths as
the sun does (the moon and sun having the same appearant size)

by how many percent do we need to increase the solar input on Komarr?

this will drive the area of the soletta - it will still be large but not
as large as earths moon (b ut it will still be VERY bright)

> For a communications
> lag of a couple of seconds, there needs to be a distance about the same
> as that between Earth and its moon.  The descriptions of its appearance
> in _Komarr_ didn't make it sound like it was filling the sky, which
> again argues for some distance.
>
> The mirror doesn't need to be optically perfect, but they're going to
> make it as close to perfect as possible.  The soletta is *expensive*.
> I'd expect that the mirror is composed of a large number of small
> panels, each panel being very nearly optically perfect and having a
> controller to allow micro-adjustment of its alignment.

yes - that is also how i see the design .. with the proviso that not all
the panels need to be connected into one single physical frame

servus

markus

> Joel


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