Novel Space Habitats
Logan Kearsley
habitat. After a few sketches and some serious consultation between myself,
my TI, and _The Universe, 5th Edition_, I come up with a double planet
consisting of two egg-shaped lobes sharing a single atmosphere. And then I
find out that Robert Forward beat me too it.
So, back to the desk I go, and I think I might finally have something
original this time. 'Tis similar in concept to Niven's Integral Trees, but
much bigger, which I have for the moment dubbed Tide World.
Two large flat plates of habitable landscape face each other, and are
connected by cables at the corners and/or center. The whole structure orbits
around a high-gravity body, and gravity is generated on each plate by the
tidal force across the structure.
If the object which Tide World is orbiting is not its light source (and
assuming that it is orbiting its primary in a different plane from that in
which the primary is orbiting the light source, unless the light source also
happens to be orbiting the primary), day and night cycles will be created as
each end swings to face the light source, like the Integral Trees. If the
Tide World orbits its own light source, however, a bit of extra engineering
is in order if one wants day/night cycles.
The sunward side would be in constant darkness, and the outward side would
be in constant light, save for the bit on the middle that falls in the
sunward side's shadow. If we make the structure wobble up and down as it
orbits, the shadow will travel back and forth across the lightside,
simulating day/night cycles. Mirrors could be used to light the sunward
darkside.
In order to maximize the strength of each living surface, they could be
formed into shallow (relative to their width, anyway) dishes with cross
sections that are catenary arcs. Additionally, in _really_, _really_ big
ones, the slope would keep the edges high enough above the middle of each
dish to hold the atmosphere in, eliminating, or at least reducing, the need
for heavy walls like a Ringworld.
One particularly interesting property of Tide Worlds is that they can be
used to construct Ringworlds. Typically, a Niven-esque Ringworld would be
uninhabitable until it is completely finished. Until then, there is no
gravity to hold in the atmosphere, and a nearly-finished Ringworld must be
spun up, which requires obscenely large amounts of energy. Now imagine that
the flat surfaces of a Tide World are not just isolated chunks, but sections
of a ring. Rather than being bowls, each section would be a trough with a
cross-section perpendicular to its length that is a catenary arc, and flat
walls at the ends. To increase the strength of the final structure and allow
it to be partitioned into sections containing different environments, the
sections could be either triangles or parallelograms with a cross-bar. A
Ringworld could be constructed by tacking together a long string of Tide
Worlds, until the collection is large enough to circle the entire star (or
whatever other body you happen to be using). Unlike a normal Ringworld, the
Tide World version can be built in stages, so if a shortage of energy or
resources or political support or some other catastrophe necessitates the
abandonment of the project half-way through, the bits that are already done
can still be inhabited. Additionally, the material used in the construction
of the rings does not need to be quite so ludicrously strong as scrith, as
much of the stress will now be born by the cables connecting them together;
this is sort of cheating, though as it's really just shifting the stress
somewhere else rather than eliminating it, and it is now the cables which
have to be ludicrously strong.
The smallest Tide World that could be constructed around the Sun and have
Earth-normal gravity (~9.8 meters per second squared) would be 33700
kilometers long and orbit at a distance of approximately 770000 kilometers
(assuming that it would behave like a point mass, which it doesn't, as
significantly lengthy objects orbit slightly faster than point-masses at the
same altitude due to the fact that gravity obeys and inverse-square rather
than a linear equation, and thus the increased gravitational attraction at
the inward extremity is not exactly balanced by the decreased attraction at
the outward extremity, so it would orbit with its center of mass slightly
farther out, but this works well enough as an approximation). This is,
however, only 75000 kilometers above the Sun's surface, so things would get
a bit hot. The size of the Tide World necessary to maintain the same gravity
increases as its orbital radius increases, and of course it can never have
gravity higher than the gravity of its primary.
-l.
------------------------------------
My inbox is a sacred shrine, none shall enter that are not worthy.
Erik Max Francis
> Two large flat plates of habitable landscape face each other, and are
> connected by cables at the corners and/or center. The whole structure
> orbits
> around a high-gravity body, and gravity is generated on each plate by
> the
> tidal force across the structure.
What torque keeps the structure oriented consistently so that the force
due to gravity from the primary is normal to the plates?
--
__ Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
/ \ San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
\__/ Well I have been puppetized / Oh how I have compromised
-- Lamya
Logan Kearsley
> > connected by cables at the corners and/or center. The whole structure
> > orbits
> > around a high-gravity body, and gravity is generated on each plate by
> > the
> > tidal force across the structure.
>
> What torque keeps the structure oriented consistently so that the force
> due to gravity from the primary is normal to the plates?
The same tide that generates gravity on the plates. The inner plate feels a
net force towards the primary, while the outer plate feels a net force away
from the primary. Therefore, the inner plate will try to fall as close to
the primary as possible, while the outer plate will try to fall as far away
from the primary as possible, and the whole structure will therefore tend to
remain parallel to a ray from the primary, like a very long, thin,
tidelocked moon. I believe that several real-world satellites have used / do
use tidal stabilization.
Additionally, gyroscopic effects from the Tide World's rotation would tend
to keep it in the same plane.
mechdan
"Logan Kearsley" <chrono...@verizon.net> wrote in message
news:Abo7d.1406$Xk1.1039@trnddc02...
> The smallest Tide World that could be constructed around the Sun and have
> Earth-normal gravity (~9.8 meters per second squared) would be 33700
> kilometers long and orbit at a distance of approximately 770000 kilometers
33700 kilometers is a few orders of magnitude too long for a
tether with known materials to support its own weight, but
let's not let this detail spoil the fun just yet...
>This is, however, only 75000 kilometers above the Sun's surface, so things
>would get a bit hot.
Hmm...maybe you inhabit the lower side, which is heavily insulated
with...umm...something. You get sunlight reflected off of the upper
side, or perhaps just the light reflected off the tether.
Isaac Kuo
mechdan
"Erik Max Francis" <m...@alcyone.com> wrote in message
news:415E1156...@alcyone.com...
>Logan Kearsley wrote:
>>Two large flat plates of habitable landscape face each other, and are
>>connected by cables at the corners and/or center. The whole structure
>>orbits around a high-gravity body, and gravity is generated on each plate
by
>>the tidal force across the structure.
>What torque keeps the structure oriented consistently so that the force
>due to gravity from the primary is normal to the plates?
From Logan's descriptions and numbers, it's obviously tidal locking
forces which keep it oriented properly. The length of tether between
the plates seems to be overwhelmingly greater than the size of the
plates themselves.
Isaac Kuo
Logan Kearsley
have
> > Earth-normal gravity (~9.8 meters per second squared) would be 33700
> > kilometers long and orbit at a distance of approximately 770000
kilometers
>
> 33700 kilometers is a few orders of magnitude too long for a
> tether with known materials to support its own weight, but
> let's not let this detail spoil the fun just yet...
Yup. I suspect that Tide Worlds would probably not be a good idea for
colonies around sun-like stars. Not if you want to have more than a few
milligees, anyway. Red dwarfs, brown dwarfs, even just really big gas giants
seem to be good building spots, though, especially if one isn't a Tellurian
Chauvinist and can put up with less than 1g. And, of course, as Niven tells
us, a neutron star would be ideal.
> >This is, however, only 75000 kilometers above the Sun's surface, so
things
> >would get a bit hot.
>
> Hmm...maybe you inhabit the lower side, which is heavily insulated
> with...umm...something. You get sunlight reflected off of the upper
> side, or perhaps just the light reflected off the tether.
Something tells me that whatever that something is would be quickly melted
away or snapped off by the strain of being repeatedly buffeted by large
masses of superheated gas.
The best analogy I can come up with for this thing (like "a suspension
bridge without ends" for a Ringworld) is a world built on a swing seat,
suspended above the ground not by a crossbar, but by another upside-down
swing seat. And hey, swing seats (the floppy kind, anyway) even have the
right catenary arc shape!
Erik Max Francis
> The same tide that generates gravity on the plates. The inner plate
> feels a
> net force towards the primary, while the outer plate feels a net force
> away
> from the primary. Therefore, the inner plate will try to fall as close
> to
> the primary as possible, while the outer plate will try to fall as far
> away
> from the primary as possible, and the whole structure will therefore
> tend to
> remain parallel to a ray from the primary, like a very long, thin,
> tidelocked moon. I believe that several real-world satellites have
> used / do
> use tidal stabilization.
I think you're going to need to run some numbers, I doubt that you're
going to maintain enough torque without having huge tidal forces that
are far from pleasant.
Furthermore, tides on a non-uniform object tend to stabilize when the
orientation of the object ends up with the longest axis pointing through
the direction of gravity. That is, your double plane trick, even if you
had sufficient gravitational force to apply enough tidal torque to keep
the object oriented properly, is going to be a position of unstable
equilibrium. Any perturbation will cause the structure to ultimately
end up in an end-over-end situation, with the normal of the planes
perpendicular to the gravity. How do you keep it oriented?
I think you're quite a bit away from demonstrating the idea can work.
--
__ Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
/ \ San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
\__/ Eppur, si muove! [But still it moves!]
-- Galileo Galilei
Hop David
Erik Max Francis wrote:
> I think you're going to need to run some numbers, I doubt that you're
> going to maintain enough torque without having huge tidal forces that
> are far from pleasant.
>
> Furthermore, tides on a non-uniform object tend to stabilize when the
> orientation of the object ends up with the longest axis pointing through
> the direction of gravity. That is, your double plane trick, even if you
> had sufficient gravitational force to apply enough tidal torque to keep
> the object oriented properly, is going to be a position of unstable
> equilibrium.
Near the center of the tether centrifugal force cancels gravity and no
acceleration is felt.
Further out, w remains constant so w^2 * r is greater. But gravity is
weaker: mu/r^2. The outer part is pulled outwards.
By the same argument, the bottom is pulled sunwards.
An article on tethers in the August 2004 Scientific American noted this
effect.
> Any perturbation will cause the structure to ultimately
> end up in an end-over-end situation, with the normal of the planes
> perpendicular to the gravity. How do you keep it oriented?
So we can expect minor perturbations of gas giant moons to release them
from their tide locked status.
--
Hop David
http://clowder.net/hop/index.html
Hop David
Logan Kearsley wrote:
(snip good post to save bandwidth)
This is a really neat idea. Of course your tethers would be made of
unobtainium. But if yarns using stuff like scrith can fly, this should
do O.K.
It's off the newstands now, but you could probably find the August 2004
edition of Scientific American at your library. They have an article on
tidelocked tethers. The accelerations you talk about are discussed.
They also talk about electricly conductive tethers passing through the
central body's magnetic field.
You suggest a series of tide worlds making a Niven Ring. I've played
with something kind of similar. But much smaller and the center of the
tether is center of rotation rather than tidelocked tethers moving about
the sun's center
Start with bolos: Two small habs linked by a tether spinning about the
tether's center (Zubrin describes something similar in his plans for
Mars missions). Bolos could be linked to build rings (like a Stanford
Torus). Rings could be stacked to build cylinders (like an O'Neil colony).
The bolo to torus is Dave Boll's idea, I believe.
http://www.daveboll.com/
At 1 gee gravity, radiation shielding mass may put too much stress on
the tethers, but perhaps 1/6 gravity is sufficient to maintain health.
In this way a cylinder could be built in increments with some Return On
Investment enjoyed at each increment.