idea for a coin-shaped space habitat.

Here's a little idea that's been in my head for a while. I wonder if
I'm the first to come up with it (unlikely) or if it already has a
name, or is just completely unworkable. I thought I'd run it past this
group to see if it's original, and if it's possible. If it turns out to
be not only an original idea, but a good one, I'd like like to stake a
claim to it and get it named after me =-)

I got to thinking about space habitats, and possible designs for them.
I came up with a structure somewhere between a Stanford Torus (
http://en.wikipedia.org/wiki/Stanford_torus ) and an O'Neill cylinder (
http://en.wikipedia.org/wiki/O%27Neill_cylinder ) that seems, in some
ways, a little simpler than either.

The problem I have with these two designs is that they both rely on
huge arrays of moving mirrors to direct sunlight into the habitat.
While this is might not be the biggest technical obstacle to such a
structure, they will require rather a lot of maintainence. I have an
idea to eliminate the need for them. Here's what I propose:

Imagine a hollow coin shape. Basically, so far, it's a very narrow
O'Neill cylinder. This gets very difficult to explain without diagrams,
so I'm going to start labelling stuff. We'll stick with the 'coin'
analogy and label the two circular surface 'heads' and 'tails'. I'm
going to say that heads and tails are each x metres in diameter. The
'ring' shaped surface that connects heads and tails, well let's just
call it 'the ring', shall we? The ring has a circumference of pi*x. It
has a width of y metres. (To put it another way, heads and tails are y
metres apart.) You can play with different values if you like, but I
think an upper limit for y would be about 20% of x. I've not idea what
real values for x and y would be feasible, and it doesn't really matter
as far as I'm concerned, but in my mind they're in the kilometres/ tens
of kilometres range.

Because the whole structure is hollow, heads, tails and the ring all
have both outer and inner surfaces. With me so far? Good.

Align your coin so that heads and tails are in the same line as the
direction of sunlight. In other words, if you imagine the direction of
sunlight as a line drawn on a table, and then you were to roll a coin
along that line toward the sun, you'd have the correct alignment. Spin
your coin-habitat about an axis through the centres of heads and tails.
One rotation per 24 hours would be ideal, because this is going to be
the length of your day, but whatever you can manage is fine. This means
that the outside surface of the ring gets all the sunlight, the heads
and tails surfaces get very little sunlight (if any) and the inside
surface of the ring gets the pseudo-gravity.

Right, you've got the basic shape. First up, make heads and tails
opaque to harmful cosmic radiation, with thick layers of whatever
material you think is best. I'm thinking, lots and lots of rock,
because there seems to be a fair bit of that kicking about in space. At
the centre of heads and tails you can have your docking facilities,
your zero-gravity fun-rooms, and lifts/ ladders down the inside of the
circular surfaces towards the living space on the inside surface of the
ring.

Now, get inside your coin (having first filled it with a breathable
atmosphere, of course), and stand on the inner surface of the ring.
walk up to the "wall" that is the inner surface of heads. Now walk at a
right-angle away from heads, so you are moving directly toward tails.
When you have walked exactly y/3 metres, stop. Get a permanent marker,
and start drawing a line on the floor. Maintaining a distance of y/3
metres from heads, do an entire circuit of the ring, until your line
joins back up with itself. Depending on the value of x, you may need
several markers. Now walk another y/3 metres away from heads, and do
the same thing once more. You've just divided the inner surface of your
ring into three equal, narrower rings. To avoid confusion, we'll call
these the strips.

In the outer two of these three strips, start dumping loads of heavy
material. Again, rock would be good, because not only is this your
radiation shielding, it's the 'land' that you will be living on. Try to
keep roughly within the lines you drew, but it doesn't have to be too
precise- minor irregularities will add charm. Pile it up high, and
eventually you see that you have two strips of well-protected land
running around the inner surface of the ring, and a deep valley
seperating them.

Now we're ready for the final and the (I hope) clever bit. Simply fill
your valley with water. As I understand it, a certain depth of water is
great for keeping out bad radiation, but lets in good radiation (ie
sunlight) just fine. The valley floor (ie, the central strip) needs to
be transparent, so that if you were swimming in your new pool, you'd be
able to look down and see the sun below you. If you were to stay in the
water for several hours, you'd notice that as the coin rotates, the sun
moves from beneath you, along the strip of water, until eventually it
is shining directly overhead, peeking between the two strips of land on
the far side of the ring. A big boat on the far side might eclipse the
sun altogether. People on the land near you will see the sun overhead
as well, so this is midday. If you now hang around in the water for
another half-rotation, the sun will be directly below you again,
warming the soles of your now-wrinkly feet. However if you climb out of
the water at this time, you will see that it's actually quite dark. The
water would be lit beautifully from below, but the land where you are
won't be getting any light at all, because the rock below your feet
blocks it all out. This is midnight. Look straight up and all you'll
see are sunbathers on the 'midday' side of the ring above your head,
and starlight shining through the water.

So there it is. (pi*x*y*2)/3 metres squared of living space, a huge
reservoir of water for drinking, swimming in etc, well proteceted from
harmful radiation but with a very natural day/night cycle and no giant
motorised mirrors required. What's more, the movement of water created
by the coin's roations combined with irregularities in the coastline
ought to make great surfing conditions. All you need is a lot of rock,
a lot of water and a very big box of permanent markers. Oh, and you
might want some machinery to sweep the bottom of the pool from time to
time- I don't think algae will be a problem, what with all the solar
radiation, but junk and dirt collecting down there will reduce the
amount of light that gets into the habitat.

Now, who's going to be the first to tell me it doesn't work?

wrote in message
oups.com...
Here's a little idea that's been in my head for a while. I wonder if
I'm the first to come up with it (unlikely) or if it already has a
name, or is just completely unworkable. I thought I'd run it past this
group to see if it's original, and if it's possible. If it turns out to
be not only an original idea, but a good one, I'd like like to stake a
claim to it and get it named after me =-)
snip
Align your coin so that heads and tails are in the same line as the
direction of sunlight. In other words, if you imagine the direction of
sunlight as a line drawn on a table, and then you were to roll a coin
along that line toward the sun, you'd have the correct alignment. Spin
your coin-habitat about an axis through the centres of heads and tails.
One rotation per 24 hours would be ideal, because this is going to be
the length of your day, but whatever you can manage is fine. This means
that the outside surface of the ring gets all the sunlight, the heads
and tails surfaces get very little sunlight (if any) and the inside
surface of the ring gets the pseudo-gravity.

Right, you've got the basic shape. First up, make heads and tails
opaque to harmful cosmic radiation, with thick layers of whatever
material you think is best. I'm thinking, lots and lots of rock,
because there seems to be a fair bit of that kicking about in space. At
the centre of heads and tails you can have your docking facilities,
your zero-gravity fun-rooms, and lifts/ ladders down the inside of the
circular surfaces towards the living space on the inside surface of the
ring.
snip
Now we're ready for the final and the (I hope) clever bit. Simply fill
your valley with water. As I understand it, a certain depth of water is
great for keeping out bad radiation, but lets in good radiation (ie
sunlight) just fine. The valley floor (ie, the central strip) needs to
be transparent, so that if you were swimming in your new pool, you'd be
able to look down and see the sun below you. If you were to stay in the
water for several hours, you'd notice that as the coin rotates, the sun
moves from beneath you, along the strip of water, until eventually it
is shining directly overhead, peeking between the two strips of land on
the far side of the ring. A big boat on the far side might eclipse the
sun altogether. People on the land near you will see the sun overhead
as well, so this is midday. If you now hang around in the water for
another half-rotation, the sun will be directly below you again,
warming the soles of your now-wrinkly feet. However if you climb out of
the water at this time, you will see that it's actually quite dark. The
water would be lit beautifully from below, but the land where you are
won't be getting any light at all, because the rock below your feet
blocks it all out. This is midnight. Look straight up and all you'll
see are sunbathers on the 'midday' side of the ring above your head,
and starlight shining through the water.
snip
Now, who's going to be the first to tell me it doesn't work?

It seems sound in principle. There are several restrictions that go with it,
though.

If it spins perpendicular to the plane of its orbit, the sun will only be
visible through the floor-window twice a year, so you'll probably want to
have it spinning flat in the plane of its orbit, or else paired with a
second one spinning in the opposite direction to give zero net angular
momentum, such that the pair can be rotated to keep the floor-windows always
facing the sn as they orbit.

You can't make the water too deep, or it'll filter out too much visible
light. If you get thinking really big, you also have to worry about the
weight of the water and the land, but for O'Neill cylinder sized objects the
internal air pressure actually produces more strain on the hull than the
weight of the ground.

In order to have twenty-four hour day and 1g of apparent gravity, you need
to make it Really Big. You've already got hull strength issues before you
start building quite that big, and you'll probably have a harder time
finding transparent high tensile strength building materials than you will
finding opaque ones, which will further restrict the size of the habitat.
Thus, you need to make do with either a shorter day or significantly less
than 1g of apparent gravity.

-l.
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