Please give some consideration to the following criteria for
refining the design of an O'Neill cylinder.

I've identified limitations with O'Neill's original design for a
cylinder. First, one cylinder won't precess around the sun, so you
need two counter rotating cylinders tethered together. Do they have
to be of equal mass? How could construction be structured so that
one habitat was habitable while work continued on the second
habitat? That's a problem. It may be that both cylinders will have
to be completed before either is habitable. How interdependent are
the two cylinders on equally matching mass, and mass distribution?

Second, the window areas are huge and their only purpose is to allow
light into the habitat. Further, the inhabitants living within a few
feet of the windows will have radiation protection under their feet
but the windows off to the side of their residence will allow
radiation in. Most of the references I've seen have presupposed that
a few kilometers of atmosphere would minimize the radiation for the
people directly across the cylinder. But how about radiation that
enters tangentially?

Thirdly, the surface area of the windows is unusable. So a third of
the habitat's surface area is unusable.

Fourthly, the windows make people nervous with respect to
catastrophic failure. They don't have the structural integrity of
the pressure vessel. They aren't monolithic - they are most likely
panels and will have sealing issues.

The exterior mirrors will have to be engineered for greater than 1
gravity rotational forces.

To address these issues I'm proposing a new design that I haven't
seen discussed anywhere else. I would appreciate helpful feedback
please. For reference you may want to look at the "Colony Design"
file I've posted in the files section.

I propose that a scheme in which there is only one cylinder that
doesn't precess with the sun. An exterior mirror framework will
follow the sun by rotating around a central axis. The mirrored
structure can work with one of two technologies 1.) reflecting
mirrors; 2.) fiber optic cables.

I foresee the mirrored structure capturing either one or multiple
images of the sun and through either of the two methods mentioned
above, transferring the image down the axis of the mirror framework.
At the base of the mirror framework, the images are concentrated and
redirected into the center of the cylinder.

The cylinder is constructed so that the outer shell is one complete
pressure vessel and all of the surface area of the outer skin is
usable. The interior living surface is two-thirds land and one-
third "light" area. The area usually designated for the windows will
be raised up, so that the people living in the habitat would see
them as hills transforming into cliffs. Good for mountaineering
enthusiasts. On top of these hills will be the new "light" area.
Underneath the "light" area is the light corridor which leads back
the the central axis entry point, and below the light tunnel is
usuable surface area.

The light that enters the cylinder area is split into three images
and directed down the three "light" corridors that bisect the
cirecumference of the habitat. In each corridor that light image is
split into, pick a number, a million different images and each of
those images is reflected into the interior of the habitat. Either,
each of the Reflectors can be computer controlled to effect angles
which simulate the sun's motion through the sky or the external
mirror can move along a second axis to simulate the effect of
O'Neill's mirrors shuttering closed.

Of course, there are many details yet to address, but I haven't yet
identified anything that is a show stopper. That's where everyone
here can help. Kind of a peer-review.

One design option is to have the mirror rotate with the habitat or
to allow the habitat to be the only structure to rotate. I would
prefer to not have the mirror rotate, but that introduces the
question of how to synchronize and stabilize the sun's image as it
enters the rotating habitat. I have some ideas on that but I'm not
completely comfortable with them yet, so I'll refrain from
discoursing on them just now. But I'd like to hear your thoughts.

For those who think this proposal is flawed I'd appreciate feedback.
If you think the problems I've identified with the original
cylindrical habitat are inaccurate please rebut the reasons I've
outlined.

I understand that this proposal is more complex that just having a
window into which sunlight will shine, but I don't buy the argument
that it'll be too expensive or complex to implement. Consider the
benefits: more usable land, only one mirror, more structural
integrity of the habitat, greater protection against window
blowouts, greater shielding across the entire surface of the outer
shell. The added complexity comes down to channeling, splitting and
synchronizing the image of the sun. Consider what is technologically
feasible with fiber optic multiplexing, I don't foresee a problem on
that front. Considering the beneficial trade-offs I don't consider
this a more expensive option either.

Well, it's been a long night. Please give feedback on this post.

> ...
> I propose that a scheme in which there is only one cylinder that
> doesn't precess with the sun. An exterior mirror framework will
> follow the sun by rotating around a central axis. The mirrored
> structure can work with one of two technologies 1.) reflecting
> mirrors; 2.) fiber optic cables.
>
As has been discussed before the problem with pipeing the light energy
down the center of the cylinder is the intensity of the beam. The center
window material requirements exceeds any known material. If the center
is kept evacuated and the windows align the axis then the reflector
material has the same sort of requirements. The nice thing about the
windows on the outside design is that it does not require unobtainium.
The goal is to keep all parameters within bounds of known materials. My
personal favorite is at
http://www.innertransit.org/common/designdoc.php?DocNumber=9
Look at the drawings for the insideout design.

Mitchell James

But I'm not proposing sending the light down the center of the the
cylinder! I've read that thread and agree with your statements. As
the light is split into multiple seperate paths after entering the
cylinder endcap its intensity will diminish. Also, we can design for
the light that's entering to come in via a number of light paths,
each of which doesn't stress existing material limits. We're just
bounded by the area of the endcap we want to devote to the light
paths entering the cylinder. This area can handle multiple light
paths.

> > ...
> > I propose that a scheme in which there is only one cylinder that
> > doesn't precess with the sun. An exterior mirror framework will
> > follow the sun by rotating around a central axis. The mirrored
> > structure can work with one of two technologies 1.) reflecting
> > mirrors; 2.) fiber optic cables.
> >
> As has been discussed before the problem with pipeing the light
energy
> down the center of the cylinder is the intensity of the beam. The
center
> window material requirements exceeds any known material. If the
center
> is kept evacuated and the windows align the axis then the reflector
> material has the same sort of requirements. The nice thing about
the
> windows on the outside design is that it does not require
unobtainium.
> The goal is to keep all parameters within bounds of known
materials. My

>
> > > ...
> > > I propose that a scheme in which there is only one
> > cylinder that
> > > doesn't precess with the sun. An exterior mirror
> > framework will
> > > follow the sun by rotating around a central axis.
> > The mirrored
> > > structure can work with one of two technologies
> > 1.) reflecting
> > > mirrors; 2.) fiber optic cables.
> > >
> > As has been discussed before the problem with
> > pipeing the light energy
> > down the center of the cylinder is the intensity of
> > the beam. The center
> > window material requirements exceeds any known
> > material. If the center
> > is kept evacuated and the windows align the axis
> > then the reflector
> > material has the same sort of requirements. The
> > nice thing about the
> > windows on the outside design is that it does not
> > require unobtainium.
> > The goal is to keep all parameters within bounds of
> > known materials. My
> > personal favorite is at
> >
> http://www.innertransit.org/common/designdoc.php?DocNumber=9
> > Look at the drawings for the insideout design.
> >
> > Mitchell James
> >
> What kind of material will be used? Composite? What
> kind of thermal protection?
>

Good question. I was just working on a light path design before getting
side tracked on other projects and had not thought about materials much
or internal tension members to flatten the toroid.

The above link is wrong. It will be correct as soon as I switch to the
new server. Just look on innertransit.org for habitat design and the
drawings list.

Mitchell James