Orientation of spin axis

From: spacesettlers@yahoogroups.com
[mailto:spacesettlers@yahoogroups.com] On Behalf Of sraj

> This is in response to a post by Mike, where he had referred
> to his favourite mode of bringing sunlight into the space hab...
> Lost the original ref when I had to reconfigure my C Drive.

For those trying to follow this:
http://ssi.org/assets/images/Ch06p086.gif
http://ssi.org/assets/images/Ch06p088.gif

> In this configuration the sunlight is brought in by means of a concave

> parabolic reflector and dispersed inside the hab by means of a convex
> reflector. This will require the spin axis of the hab to point towards

> the sun.

That's one way of doing it. But actually, in the MIT design, the spin
axis is as you suggest below, and there's an oval-shaped planar mirror
above which reflects the sunlight down. In that respect it's the same
as the Stanford Torus.

> In which case, in order to track the sun it will be necessary to have
> a counter rotating hab to nullify the momentum vector. How then do we
> bring sunlight into the counter rotating hab?

If one wanted two cylinders, one could certainly go the same route as
Island 3. The only restriction there is that the habitats could not be
any closer together than the diameters of their parabolic mirrors. But
for that matter, Island 3 cylinders couldn't be so close that their
mirrors collided, so it's much the same.

> It is better I think to keep the spin axis of the hab perpendicular to

> the orbital plane. The parabolic reflector axis can point towards the
sun
> and the beam turned by 90 degrees with the help of a mirror. The
possibility
> of keeping the reflector and mirror assembly physically separate from
the
> hab can also be explored.

That might work, but the solution preferred by the MIT groups was a
planar, oval-shaped mirror at a 45 degree angle, with the parabolic
mirror having the same axis as the rest of the habitat. In other words,
for the light-path, the bending through 90 degrees happens before, not
after, the concentration. I think the advantage of this is that we must
maneuver the first mirror around, and a planar, oval mirror would mass
less than the parabolic mirror of nearly the same diameter.

Another issue is that the optics probably favor the primary and
secondary parabolic reflectors being as close to the habitat as
possible.

> With two parabolic reflector and mirror assemblies, beaming
> in sunlight from both the ends of the space hab, and with both
> these assemblies well offset from the axis of the hab,

I suppose two mirror assemblies at either end might make longer
cylinders possible, but then where would spacecraft dock?

Regards,

Mike Combs