Hi,

For some reason, in the last few days I have been thinking about designs for
spherical and cylindrical rotating habitats following what I call "Frazer's
Guidelines" (*) for lighting: instead of having huge transparent areas for
letting sunlight in, they make use of relatively small transparent "holes"
where concentrated sunlight gets into the habitat and is used for lighting.
At first, as usual, I thought about mirrors inside the colony to disperse
the incoming sunlight in a useful way. But after a while I thought: wouldn't
simply making the sunlight hit an opaque and purely white surface be a
simpler and cheaper alternative to a mirror system?

To illustrate my reasoning, I'll use the case of a spheric colony with a
transparent cap 60 degrees in diameter centered at one of the poles.
Concentrated sunlight enters throught that "window" and has to illuminate
the whole interior of the sphere.

First I thought about using a spherical convex mirror either protuding from
the opposite cap or hanging in the space between the two poles to do the
job. Then, I thought that it would be simpler to just coat the opposite cap
with reflexive material, transforming it into a concave mirror: the sunlight
would be concentrated into a focus and then spread to all the internal
surface of the colony. However, that could overheat and even ionize the air
at the focus, and so I considered it a not-so-elegant approach...

Finally, I saw that if the task is to disperse the light along the internal
spherical surface, then simply painting the opposite cap with pristine white
would do the job without the unpleasant effect of an overheated focus.
Sunlight would hit the white cap and then suffer diffuse reflection: an
effect analogous to a spot light hitting a white wall and providing indirect
illumination.

For those who think that a colony should be as eartlike as possible, of
course that does not sound good, but then neither does the "Frazer's
Guidelines", so that's outside discussion here. My major concerns are more
practical, and I would much apreciate any references or answers to them:

- Are there white surfaces with albedo comparable to that of mirrors? In
other words, would the vast majority of sunlight be reflected or would a
significant fraction of it be absorbed by the white cap?

- For some reason, does vegetal life prefers "hard", "direct" sunlight
instead of a soft indirect glow?

Thanks in advance,

Lucio Coelho

* I say "Frazer's Guidelines" because John Frazer was the first one that I
saw mentioning them, in the Space Settlers list...

"Dr. Omni" wrote:
>
> - For some reason, does vegetal life prefers "hard", "direct" sunlight
> instead of a soft indirect glow?
>

Depends on the plant. Some like diffuse light, others require direct
sunlight.
I think most food crops prefer direct sunlight.

--
Al Globus
aglobus@..., (650) 604-4404
http://www.nas.nasa.gov/~globus/home.html

The dinosaurs weren't spacefaring. We are. I don't think that's an
accident.
Maybe we are life's taxi to the stars. Let's start with space tourism,
and
graduate to orbital colonies.

To answer your first question. A white surface actually absorbs about
50% of the light that hits it. I'm sure special paints could be
created to lower that down to 20%.

The first real problem is keeping the white surface white. Dust and
dirt will fall on it lowering the albedo of the surface.

Paint fades in direct sunlight. Again special paint could be used, but
the maintenance needed maybe much higher then cleaning windows.

Now I had read a novel about a simialr concept. It was a group of
comet cowboys (there term) that was mining a comet from the inside out
and had created "windows" out of the translucent ice.

To answer your second, I don't know but I suspect that it is very
dependant on the type of plants.

Bill

--- In space

settlers@y..., "Dr. Omni" wrote:
> Hi,
>
> For some reason, in the last few days I have been thinking about
designs for
> spherical and cylindrical rotating habitats following what I call
"Frazer's
> Guidelines" (*) for lighting: instead of having huge transparent
areas for
> letting sunlight in, they make use of relatively small transparent
"holes"
> where concentrated sunlight gets into the habitat and is used for
lighting.
> At first, as usual, I thought about mirrors inside the colony to
disperse
> the incoming sunlight in a useful way. But after a while I thought:
wouldn't
> simply making the sunlight hit an opaque and purely white surface be
a
> simpler and cheaper alternative to a mirror system?
>
> To illustrate my reasoning, I'll use the case of a spheric colony
with a
> transparent cap 60 degrees in diameter centered at one of the poles.
> Concentrated sunlight enters throught that "window" and has to
illuminate
> the whole interior of the sphere.
>
> First I thought about using a spherical convex mirror either
protuding from
> the opposite cap or hanging in the space between the two poles to do
the
> job. Then, I thought that it would be simpler to just coat the
opposite cap
> with reflexive material, transforming it into a concave mirror: the
sunlight
> would be concentrated into a focus and then spread to all the
internal
> surface of the colony. However, that could overheat and even ionize
the air
> at the focus, and so I considered it a not-so-elegant approach...
>
> Finally, I saw that if the task is to disperse the light along the
internal
> spherical surface, then simply painting the opposite cap with
pristine white
> would do the job without the unpleasant effect of an overheated
focus.
> Sunlight would hit the white cap and then suffer diffuse reflection:
an
> effect analogous to a spot light hitting a white wall and providing
indirect
> illumination.
>
> For those who think that a colony should be as eartlike as possible,
of
> course that does not sound good, but then neither does the "Frazer's
> Guidelines", so that's outside discussion here. My major concerns
are more
> practical, and I would much apreciate any references or answers to
them:
>
> - Are there white surfaces with albedo comparable to that of
mirrors? In
> other words, would the vast majority of sunlight be reflected or
would a
> significant fraction of it be absorbed by the white cap?
>
> - For some reason, does vegetal life prefers "hard", "direct"
sunlight
> instead of a soft indirect glow?
>
> Thanks in advance,
>
> Lucio Coelho
>
> * I say "Frazer's Guidelines" because John Frazer was the first one
that I

This is not exactly on topic, but could you not have seperate modules
for growing food. Plants are not as exacting about living conditions
as humans are, and small cylinders with a small spin (0.1 g) with
growing conditions tailored to the plant being grown could increase
yeilds and make pest control fairly easy. Also ten or twenty such
small greenhouses floating seperately means that crop failures or
accidents would not destroy the entire food source.

Bill

--- In spacesettlers@y..., Al Globus wrote:
>
> "Dr. Omni" wrote:
> >
> > - For some reason, does vegetal life prefers "hard", "direct"
sunlight
> > instead of a soft indirect glow?
> >
> Depends on the plant. Some like diffuse light, others require
direct
> sunlight.
> I think most food crops prefer direct sunlight.
>
> --
> Al Globus
> aglobus@m..., (650) 604-4404
> http://www.nas.nasa.gov/~globus/home.html
>
> The dinosaurs weren't spacefaring. We are. I don't think that's an
> accident.
> Maybe we are life's taxi to the stars. Let's start with space
tourism,

Jus another thought about diffuse lighting. If you change the design
to a cone or a paraboloid (half of a football shape) with the base as
a large window, the requirement for diffuse lighting is minimized. The
place will look like the side of a mountain at dawn or dusk all the
time (which may become a pain after a while).

Just a thought.

Bill

--- In spacesettlers@y..., "Dr. Omni" wrote:
> Hi,
>
> For some reason, in the last few days I have been thinking about
designs for
> spherical and cylindrical rotating habitats following what I call
"Frazer's
> Guidelines" (*) for lighting: instead of having huge transparent
areas for
> letting sunlight in, they make use of relatively small transparent
"holes"
> where concentrated sunlight gets into the habitat and is used for
lighting.
> At first, as usual, I thought about mirrors inside the colony to
disperse
> the incoming sunlight in a useful way. But after a while I thought:
wouldn't
> simply making the sunlight hit an opaque and purely white surface be
a
> simpler and cheaper alternative to a mirror system?
>
> To illustrate my reasoning, I'll use the case of a spheric colony
with a
> transparent cap 60 degrees in diameter centered at one of the poles.
> Concentrated sunlight enters throught that "window" and has to
illuminate
> the whole interior of the sphere.
>
> First I thought about using a spherical convex mirror either
protuding from
> the opposite cap or hanging in the space between the two poles to do
the
> job. Then, I thought that it would be simpler to just coat the
opposite cap
> with reflexive material, transforming it into a concave mirror: the
sunlight
> would be concentrated into a focus and then spread to all the
internal
> surface of the colony. However, that could overheat and even ionize
the air
> at the focus, and so I considered it a not-so-elegant approach...
>
> Finally, I saw that if the task is to disperse the light along the
internal
> spherical surface, then simply painting the opposite cap with
pristine white
> would do the job without the unpleasant effect of an overheated
focus.
> Sunlight would hit the white cap and then suffer diffuse reflection:
an
> effect analogous to a spot light hitting a white wall and providing
indirect
> illumination.
>
> For those who think that a colony should be as eartlike as possible,
of
> course that does not sound good, but then neither does the "Frazer's
> Guidelines", so that's outside discussion here. My major concerns
are more
> practical, and I would much apreciate any references or answers to
them:
>
> - Are there white surfaces with albedo comparable to that of
mirrors? In
> other words, would the vast majority of sunlight be reflected or
would a
> significant fraction of it be absorbed by the white cap?
>
> - For some reason, does vegetal life prefers "hard", "direct"
sunlight
> instead of a soft indirect glow?
>
> Thanks in advance,
>
> Lucio Coelho
>
> * I say "Frazer's Guidelines" because John Frazer was the first one
that I

From: "Bill"
To:
Sent: Friday, June 01, 2001 2:36 PM
Subject: [spacesettlers] Re: Mirrors versus diffuse reflection

>
> Jus another thought about diffuse lighting. If you change the design
> to a cone or a paraboloid (half of a football shape) with the base as
> a large window, the requirement for diffuse lighting is minimized. The
> place will look like the side of a mountain at dawn or dusk all the
> time (which may become a pain after a while).
>

I remember that once upon a time I thought about something like that, but I
discarded the idea for two reasons:

- A cone or a paraboloid are not "pressure friendly" shapes such as
cylinders and tori, so the structural requirements for the habitat would be
more complex and (probably) expensive.

- As you said, living in a perpetual sunset could be a pain in the ass after
some (very small, I think) time. In particular, for the case of large
habitats, it would be specially anoying for someone to drive a car with the
sun hitting one or both of your eyes at any given time...

[snikt]
> Bill
[snikt]

Lucio

Dr. Omni wrote:
> I have been thinking about designs for spherical and cylindrical
rotating habitats following what I call "Frazer's
Guidelines" ...because John Frazer was the first one that I saw
mentioning them, in the Space Settlers list...

First on this list, maybe. I cribbed most of it from Andrew
Nowicki's "greenhouse" model habitat, and A.C. Clarke's "Rama"
spacecraft. I did roughly develop most of the rest of it (with some
help from members of the LUF email lists): the "light ducts"
admitting light through the floor of the hab to the opposite side of
the interior, glass block mirrors/deflectors/difusers, etc.
Note that such "light ducts" may also work through very great
thicknesses of floor space, such as under-levels of decks for
machinery or habitation under the inner open volume.
Nowicki has most of the good work on focussed sunlight entry in
print, and Clarke definately originated the "light emmiter" slit or
spot on the opposite landscape floor (albeit using rather "soft" S.F.
artificial energy & light).

> At first, as usual, I thought about mirrors inside the colony to
disperse the incoming sunlight in a useful way. But after a while I
thought: wouldn't simply making the sunlight hit an opaque and purely
white surface be a simpler and cheaper alternative to a mirror system?

How about a polished, but pebbled-textured aluminum surface?
(pebbled texture, to diffuse the light, but polished for efficient
reflection)
Overall, this sounds a little like the "hatbox" design, or
the "sunflower". Redirect the sunlight to the land surface, after
it's already been reflected into the hab volume.

I take it the polished reflecting surface is an end cap? Remember
that dust won't settle onto it: It's vertical with referrence to
local gravity, and the gravity is nil.

With referrence to the light ducts, why not just have a small "Rama"
type hole or spot in the landscape, which shines light onto a broad
area of landscape overhead?
We don't know about the intensity of sunlight needed to be piped in
through a duct, and we don't know about the intensity of convergent
beams of light in the center of the hab.

Any of these design options are high maintenance (but so are the
huge, fragile, rotating exterior mirrors of O'Neill's designs).
The "Island One" Bernal sphere comes closest to any of these ideas:
small window area, with most mirror being non-rotating.

How about efficient solar->electric conversion and efficient LED based
artificial lighting? If you can nearly match optical energy efficiency
artificial lighting makes everything *a lot* easier.

John Frazer wrote:
>
> Dr. Omni wrote:
> > I have been thinking about designs for spherical and cylindrical
> rotating habitats following what I call "Frazer's
> Guidelines" ...because John Frazer was the first one that I saw
> mentioning them, in the Space Settlers list...
>
> First on this list, maybe. I cribbed most of it from Andrew
> Nowicki's "greenhouse" model habitat, and A.C. Clarke's "Rama"
> spacecraft. I did roughly develop most of the rest of it (with some
> help from members of the LUF email lists): the "light ducts"
> admitting light through the floor of the hab to the opposite side of
> the interior, glass block mirrors/deflectors/difusers, etc.
> Note that such "light ducts" may also work through very great
> thicknesses of floor space, such as under-levels of decks for
> machinery or habitation under the inner open volume.
> Nowicki has most of the good work on focussed sunlight entry in
> print, and Clarke definately originated the "light emmiter" slit or
> spot on the opposite landscape floor (albeit using rather "soft" S.F.
> artificial energy & light).
>
> > At first, as usual, I thought about mirrors inside the colony to
> disperse the incoming sunlight in a useful way. But after a while I
> thought: wouldn't simply making the sunlight hit an opaque and purely
> white surface be a simpler and cheaper alternative to a mirror system?
>
> How about a polished, but pebbled-textured aluminum surface?
> (pebbled texture, to diffuse the light, but polished for efficient
> reflection)
> Overall, this sounds a little like the "hatbox" design, or
> the "sunflower". Redirect the sunlight to the land surface, after
> it's already been reflected into the hab volume.
>
> I take it the polished reflecting surface is an end cap? Remember
> that dust won't settle onto it: It's vertical with referrence to
> local gravity, and the gravity is nil.
>
> With referrence to the light ducts, why not just have a small "Rama"
> type hole or spot in the landscape, which shines light onto a broad
> area of landscape overhead?
> We don't know about the intensity of sunlight needed to be piped in
> through a duct, and we don't know about the intensity of convergent
> beams of light in the center of the hab.
>
> Any of these design options are high maintenance (but so are the
> huge, fragile, rotating exterior mirrors of O'Neill's designs).
> The "Island One" Bernal sphere comes closest to any of these ideas:
> small window area, with most mirror being non-rotating.
>

--
Al Globus
aglobus@..., (650) 604-4404
http://www.nas.nasa.gov/~globus/home.html

The dinosaurs weren't spacefaring. We are. I don't think that's an
accident.
Maybe we are life's taxi to the stars. Let's start with space tourism,
and
graduate to orbital colonies.

Al Globus wrote
> How about efficient solar->electric conversion and efficient LED
based artificial lighting? If you can nearly match optical energy
efficiency artificial lighting makes everything *a lot* easier.

True. I doubt the efficiency of conversion. In between receiving
sunlight & shining light into the habitat, there's a lot of waste
heat (but we are aready assuming a lot of heat rejection capability
for the colony). It depends on the economies of the moment.
By the way, does this stand as another refutal of Zubrin's numbers?
He wrote the obviously wrong statement that you can't use natural
sunlight in space habitats, and then said that the engineering of
such amounts of artificial lights would present as big an engineering
problem as using sunlight. Crops need a lot of light. (But agronomy
might go on elsewhere? What about the amount of lights to flood the
interior to allow natural trees & such throughout the hab?)

I tend to agree with the added difficulty of artificial lighting,
but see no reason not to transmit sunlight into the interior via
intense, small sources which might be mistaken for artificial light
sources.
There might also be a psychological benefit to using real sunlight
-albeit filtered beyond recognition from its nature as it hits the
first mirror. Indeed, filtered to be different from Earth normal: No
UV, little IR. Otherwise, like a normal, warm beam from the Sun,
shining into any room in the volume via light pipes or mirror blocks
in tunnels through the hull.

It might have been this list or one from the LUF, but somebody
submitted a design for a vacation home/dome on the Moon or an
asteroid.
Concrete dome over a 20 meter crater, and seal the underside and
tunnels & rooms.
Admit light from the surface via picture windows in rooms: Sunlight
is sent from mirror arrays which allow sunlight throughout the
"days" and seasons, to a vertical slit down to the depth of the room.
A 45 degree mirror turns it to shine into a room via a wall sized
window. ("outdoor" lighting, in the open bowl perhaps through mirror
'chevrons' built into the thickness of the dome).
The mirror shape & angle would need to vary, if you needed to avoid
a vertical slit as wide as the window is tall, and image integrity
would need to be ensured as a consequence.
The wall of the room is a window out onto the surface.

It may be possible to do much the same with fiberoptics. Resolve
each fiber as a pixel? This leads up to reproducing the whole effect
via electro-optics & wall sized display screens (which could also
include communications screens and displays for PCs or whatever.
Virtual "Windows".)
Again, questions of efficiency, budget, and psychological benefits of
knowing that you're in real warm sunlight, instead of in front of a
high powered display screen flooding the room with frequencies &
intensities like filtered sunlight. You couldn't walk up to the
'picture window' screen and see the outside with absolutely no
pixelation -certainly not as economical as mirrors. (Or am I
underestimating advancements in electronics?)

I have reservations about transmitting a window image via light
pipes.
A beam of sunlight diffusing from the end of a pipe is much simpler.
This allows fiber or glass pipe or glass blocks to admit general
interior lighting into a hab, but it may not be economical for an
image window.