Just Like 1 - below?
Frank
in "The High Frontier." A worker 1/10th of the radius of the cylinder
from the axis drops a rivet.
Look out below? Not quite.
Look out? Yes.
Below? No.
It's easy to see what happens in a Newtonian reference frame. The
rivet starts out moving at 1/10th the speed at which the surface
rotates. It keeps on at that speed and that direction until it
collides with the surface .995 radii later. It's velocity when it hits
the surface has a vertical component of .0995 the speed of surface
rotation radially and .01 that speed eastward (All my rotating bodies
rotate eastward, just like Earth does.) Meanwhile, the cylinder
rotates 9.95 / 2 pi (about 1.58) times.
The picture in the rotating reference frame of somebody standing on
the inner surface is a bit more complex. The straight line of the
unaccelerated reference frame becomes a spiral which curls westward
more and more obliquely. It curls around the axis 1.58 times. Its
radial velocity when it hits is still .0995 the speed of rotation. Its
velocity westward is 99% of the eastward speed of the surface of the
cylinder. That is to say that you experience something not dropping
down but traveling mostly along the surface. (About ten feet westward
for every foot it drops near the end of its journey.)
Writers of stories set in rotating space stations tend to say
"centripetal acceleration [or centrifugal force] takes the place of
gravity" and then write as if gravity were in effect. After all, they
live with gravity pressing them against the floor; they know how that
operates. And, if you stand quite still, you can't tell the difference
as long as the station is large enough so that it doesn't make you
dizzy.
But motion where the floor's pressure against your feet is due to
centripetal acceleration is always slightly different from motion on
Earth. How different depends on the velocity of the motion and the
size -- and, therefore, rotation -- of the station. In the rotating
frame of reference:
1) You are slightly heavier going east than you are going west.
2) An increase in height means an addition of eastward velocity. A
decrease in height leads to an addition of westward velocity.
Number (2) could mess up sports in space. I wrote a story --
rejected, as were all my stories which got all the way to the
submission phase -- in which the "Coriolis force" had persuaded kids
in the station that head shots in soccer were beyond their skill
level. If soccer head shots are a problem -- and I'm not sure they
would be in real life; the deviation isn't that much -- imagine the
problems involved in basketball.
One place that you can see important Coriolis effects on Earth is in
the weather. "The High Frontier" postulated weather in their
cylinders. (I'm less certain. Earth weather depends on a great deal of
heat being radiated into space from the upper regions of the
atmosphere. Why should that occur in an enclosed cylinder?) If they
are right, the weather would be strange and, perhaps, violent. Falling
rain would experience air resistance, something I ignored with my
rivet. But the air resistance which would slow the westward movement
of the rain would generate a westward movement of the air. Likewise,
rising air would move east.
In the soccer story, I had a "Coriolis Fountain." This started with
a stream of water moving up and slightly east. It turned as it rose,
moved west at the top, and finally fell into a basin directly under
the tube which began it. The shape of the stream of water was a loop.
Such a fountain could be built on a rotating space station.
Mike Williams
There was a considerable discussion about this in the B5 newsgroups
after the baseball practice episode of Babylon 5. A baseball hit to one
side would appear to swing downwards much more rapidly than you'd
expect, and one hit to the other side would hang in the air much longer.
Possibly giving a significant advantage to either a left or right handed
batsman depending on whether the pitcher is throwing from the North or
South. I assume that the pitch would be aligned with the axis to
minimise such effects.
I imagine that for the first few hours or so fielders with Earth
reflexes would perform absolutely abysmally, but after that they'd
adjust to the new physics and be able to perform as well as they do on
Earth.
I imagine that all sports facilities like football fields and basketball
courts would be aligned along the axis, so as not favour one end over
the other.
--
Mike Williams
Gentleman of Leisure
Dorothy J Heydt
It does depend heavily on what you're used to. Take the
sequence in Heinlein's _The Rolling Stones_ where Roger is
trying to persuade his sons to go to university on Earth and
do some of the things he did as a kid: play baseball, ride
horseback, swim in the ocean.
"Take baseball," Castor continued. "It's not practical. How
can you figure a one-g trajectory and place your hand at the
point of contact in the free-flight time between bases?
We're not miracle men."
"I played it."
"But you grew up in a one-g field; you've got a distorted
notion of physics. Anyhow, why would we want to learn to
play baseball? When we come back, we wouldn't be able to
play it here. Why, you might crack your helmet."
--
Dorothy J. Heydt
Vallejo, California
djheydt at hotmail dot com
Should you wish to email me, you'd better use the hotmail edress.
Kithrup is getting too damn much spam, even with the sysop's filters.
Frank
> In article <qVcY7wMGlizKF...@econym.demon.co.uk>,
Of course, he got some things wrong. In "Moon iaHM," he had money
backed by steel on the moon retain its worth earthside more than money
which would be need to ship the steel if you ever acquired the steel.
Brian Davis
> Writers of stories set in rotating space stations tend to say
> "centripetal acceleration [or centrifugal force] takes the place of
> gravity" and then write as if gravity were in effect.
Quibble; not *good* hard-SF authors.
> Number (2) could mess up sports in space. I wrote a story --
> rejected, as were all my stories which got all the way to the
> submission phase -- in which the "Coriolis force" had persuaded kids
> in the station that head shots in soccer were beyond their skill
> level.
I really doubt that, actually. Adults, maybe, kids, never. Try playing
catch on a merry-go-round sometime; you get the hang of it within a
few minutes or so, even though it "feels terribly wrong" at first.
Humans are very good at re-learning things.
There was a story I remember where a competitive sport way to "bounce
around the station" on very large trampolines placed in the middle of
a cylindrical sea. It was fairly nicely done, although I don't
remember the name of the story (anyone?), or working out the details.
> Earth weather depends on a great deal of heat being radiated
> into space from the upper regions of the atmosphere. Why
> should that occur in an enclosed cylinder?
First, I'm not sure that it does; the atmosphere gets colder as you go
up due to adiabatic compression, not radiative equilibrium. Weather on
Earth is largely due to horizontal difference in air masses (humidity,
temperature, altitude, etc.). Second, you can bet the cylindrical
atmosphere will have the same heating and cooling issues - if it's
gaining energy (and ground, illuminated by sunlight, certainly is),
it's loosing it from somewhere. The where might be a bigger question.
> In the soccer story, I had a "Coriolis Fountain."
My personal favorite was always the polar cap waterfall on Rama. The
first time I read the description, the mental image (as well as the
wonderful way the characters reactions were discussed) made me
immediately want to work out the math. There's another great bit about
throwing an object from the hub to the ground, and how to do it to hit
the target. Great, because it's both obvious (or should be), and
unexpected.
Actually, somewhere in the rasfs archives should be some more on this.
I remember working out the variation of pressure with respect to
"altitude" in a Rama-like environment a long time ago, and I thought I
posted it.
--
Brian Davis
Steve Hix
<d136b0ba-0c52-46c7...@z24g2000yqb.googlegroups.com>,
Brian Davis <brd...@iusb.edu> wrote:
> > Earth weather depends on a great deal of heat being�radiated
> > into space from the upper regions of the atmosphere. Why
> > should that occur in an enclosed cylinder?
>
> First, I'm not sure that it does; the atmosphere gets colder as you go
> up due to adiabatic compression, not radiative equilibrium.
That's only true for a little while.
There's a typically cooling trend (adiabatic lapse rate) as you ascend,
ignoring thermal inversions, through the troposphere. (If you live in
L.A., you can't ignore the thermal inversion, which traps smog over the
whole area.)
Once you hit the tropopause at about 12 km, the temperature doesn't
change much up through the stratosphere until you reach the mesosphere
at about 50 to 80 km, where the temperature drops from about -60�C to
about -100�C, which is about as cold as the atmosphere generally gets.
Above 80km you're in the thermosphere, where the temperatures can rise
up to as much as 2000�C, mostly from ionization effects.
Brian Davis
> In article
> <d136b0ba-0c52-46c7-8d3f-89865bd29...@z24g2000yqb.googlegroups.com>,
> Brian Davis <brda...@iusb.edu> wrote:
>
> > > Earth weather depends on a great deal of heat being radiated
> > > into space from the upper regions of the atmosphere. Why
> > > should that occur in an enclosed cylinder?
>
> > First, I'm not sure that it does; the atmosphere gets colder as you go
> > up due to adiabatic compression, not radiative equilibrium.
>
> That's only true for a little while.
Of course. But note the context of the original poster. If what I'm
worried about is weather, adiabatic cooling and spatial variability
gets you a very long way, including thunderstorms, frontal systems,
etc.
If I'm worried about understanding weather, radiative cooling of the
air and heating due to ionization effects really can be largely
neglected. That was my point.
--
Brian Davis
Luke Campbell
> If I'm worried about understanding weather, radiative cooling of the
Can it? My understanding is that the air is heated from below (by
sunlight warming the ground, which conducts its heat to the air), and
cooled from above (by thermal radiation from water vapor and carbon
dioxide). This leads to air near the ground being more buoyant than
the air above it, resulting in turbulent mixing.
If the air is heated from above, or cooled from below (as would be the
case for a space habitat, I would think), I would expect you to
approach thermal equilibrium, with an isothermal volume of gas.
Is there a flaw in my reasoning?
Luke
Brian Davis
> My understanding is that the air is heated from below (by
> sunlight warming the ground, which conducts its heat to
> the air), and cooled from above (by thermal radiation from
> water vapor and carbon dioxide).
If there was significant external cooling, of any type, the
temperature in the upper troposphere would be lower than otherwise
expected. It's not. Instead, the temperature gradient in the
troposphere follows an adiabatic gradient.
> This leads to air near the ground being more buoyant than
> the air above it, resulting in turbulent mixing.
...which restores an adiabatic gradient.
> If the air is heated from above, or cooled from below (as would
> be the case for a space habitat, I would think), I would expect
> you to approach thermal equilibrium, with an isothermal volume
> of gas.
>
> Is there a flaw in my reasoning?
If the pressure changes, and energy is not gained or lost (the change
is adiabatic), then the temperature changes. Basic gas laws.
For a cylindrical habitat, much of the heating, pretty much any way
you cut it, will be on the "ground". If the air absorbed significant
amounts of radiation, it wouldn't be transparent. The ground has no
such problem. There's the question of where the light is coming from
(got a tube of multi-thousand-degree plasma along the axis? Yes, that
will supply some heat), but as long as their is a pressure change with
elevation, there is a temperature change. The *stability* is a
different issue (there a reason an atmosphere follows an adiabatic
law).
--
Brian Davis
Luke Campbell
> If there was significant external cooling, of any type, the
> temperature in the upper troposphere would be lower than otherwise
> expected. It's not. Instead, the temperature gradient in the
> troposphere follows an adiabatic gradient.
Since the air is fairly opaque to much of the thermal infrared, and
infrared radiation is the only way to dump heat back into space, it
would seem that a significant amount of the heat loss occurs at the
level where the atmosphere goes from being optically thick to
optically thin (which is, of course wavelength dependent, so you would
get heat loss from the air to space from a range of altitudes). Since
much of the infrared absorption is due to water vapor, and as I
understand it most of the water vapor is confined to the troposphere,
I would naively expect a significant amount of heat loss from the
water vapor at the top of the troposphere.
> > This leads to air near the ground being more buoyant than
> > the air above it, resulting in turbulent mixing.
>
> ...which restores an adiabatic gradient.
Yes. Exactly my reasoning. If it is being cooled from above, you get
mixing that preserves the adiabatic gradient. If this is so, then
increased cooling from above simply leads to more violent weather, but
the temperature gradient remains approximately the same.
> > If the air is heated from above, or cooled from below (as would
> > be the case for a space habitat, I would think), I would expect
> > you to approach thermal equilibrium, with an isothermal volume
> > of gas.
>
> > Is there a flaw in my reasoning?
>
> If the pressure changes, and energy is not gained or lost (the change
> is adiabatic), then the temperature changes. Basic gas laws.
>
> For a cylindrical habitat, much of the heating, pretty much any way
> you cut it, will be on the "ground". If the air absorbed significant
> amounts of radiation, it wouldn't be transparent. The ground has no
> such problem. There's the question of where the light is coming from
> (got a tube of multi-thousand-degree plasma along the axis? Yes, that
> will supply some heat), but as long as their is a pressure change with
> elevation, there is a temperature change. The *stability* is a
> different issue (there a reason an atmosphere follows an adiabatic
> law).
I am not so much concerned with where the heating is occurring (since
I fully expect the heating to occur at the ground), as where the
cooling is occurring. If the heat must be lost through the ground (as
you would expect if the heat loss is through radiation from the sides
of the habitat, or if life support runs air conditioning through the
inhabited portions and dumps the heat through radiator panels) then
you will not have buoyant forces mixing the air. When mixing is not
occurring, heat flow happens through diffusion rather than
convection. You now are no longer within the adiabatic approximation,
as heat is being transferred between volumes of air. This leads to
thermal equilibrium and an isothermal gas volume. [Although it may be
that the inhabitants do not want stagnant air in their habitat,
leading them to devise methods to artificially mix the air (such as
with mechanical blowers) which would again lead to an adiabatic
gradient.]
Although - if you have uneven heating and cooling on the surface, you
would again get mixing, as the hot land areas will lead to rising
plumes of air that is warmer than average while cold land areas lead
to cold air flowing radially outward, sucking more air down. Thinking
about it, for any reasonable human habitation this will probably
dominate over heat diffusion, restoring mixing of the air. The
exception being for very large volume habitats and nearly uniform land
use patterns, where small scale mixing homogenizes the atmosphere at
low levels leading to stagnant upper levels.
Luke
Greg Goss
>For a cylindrical habitat, much of the heating, pretty much any way
>you cut it, will be on the "ground". If the air absorbed significant
>amounts of radiation, it wouldn't be transparent. The ground has no
>such problem. There's the question of where the light is coming from
>(got a tube of multi-thousand-degree plasma along the axis? Yes, that
>will supply some heat), but as long as their is a pressure change with
>elevation, there is a temperature change. The *stability* is a
>different issue (there a reason an atmosphere follows an adiabatic
>law).
I think that the standard ONeil design had a cylinder end-on to the
sun, with six wedges alternating of pseudo-glass and land. Three
angled mirrors would send sunlight through the glass to the opposite
land strip. The mirrors would rotate the sunlight off in another
direction (industrial use?) for night in the colony.
--
apart from one noisy guy up in Canada, no-one wants
a three-cylinder tissue box on bicycle tires.
Wayne Throop
: I think that the standard ONeil design had a cylinder end-on to the sun,
Anybody know how it *stays* end-on to the sun?
What mechanism supplies the torque to make it happen?
Wayne Throop thr...@sheol.org http://sheol.org/throopw
Greg Goss
>: Greg Goss <go...@gossg.org>
>: I think that the standard ONeil design had a cylinder end-on to the sun,
>
>Anybody know how it *stays* end-on to the sun?
>What mechanism supplies the torque to make it happen?
If you have two cylinders end to end, rotating in opposite directions,
does their angular momentum cancel? At that point, can tide hold them
pointing towards the sun?
And the whole system can cancel but are the forces at the join
intolerable?
Wayne Throop
: If you have two cylinders end to end, rotating in opposite directions,
: does their angular momentum cancel? At that point, can tide hold them
: pointing towards the sun?
No. Because the tides at L5 don't point at the sun.
Frank
>
> - Show quoted text -
A great deal of the incident sunlight is reflected by clouds. Another
large bit is absorbed at ground level. A third, but the smallest,
amount is absorbed in the atmosphere. (Sorry, I've read these figures,
but I don't have them with me.
Some of the surface-absorbed heat is radiated back into space. (Some
of that is absorbed in the atmosphere -- see the many discussions of
global warming and the greenhouse effect.) A great deal of the heat on
the surface evaporates water; this water vapor condenses i nhe
atmosphere and half that heat radiates out into space.
The whole idea of adiabatic temperatures depends on mixing, which
depends on hot air rising, which also moves heat from the surface
higher.
Yhr ccylinders I was considering were O'neil cylinders, described
later in the thread.
Frank
> : Greg Goss <go...@gossg.org>
> : If you have two cylinders end to end, rotating in opposite directions,
> : does their angular momentum cancel? At that point, can tide hold them
> : pointing towards the sun?
>
> No. Because the tides at L5 don't point at the sun.
>
The O'neil-adopted idea was:
1) Two cylinders would be tethered together at their ends -- long
cables -- and rotate in opposite directions. The tethers would cause
precession in opposite directions. That would cause the system to
rotate once a year, always with one end pointed at the sun.
2) The cylinders would be illuminated by mirrors lsupported by (super-
strong, the book doesn't make that calculation) cables they would be
let down for dawn and drawn up for dusk.
Brian Davis
a heated surface. That surface will warm the lowest layer of air,
which is now buoyant, and rises, mixing heat upwards. But as it rises
it expands (lower pressure), so it cools. It will continue rising as
long as it is warmer than the surround air... which in an isothermal
atmosphere won't be long. The result is air near the bottom is warmed
until it reaches an adiabatic gradient, and that process continues
until the entire atmosphere reaches an adiabatic gradient. That's
fairly simple thermodynamics - and does not need to invoke any cooling
at all (in fact, in this model you would get an adiabatic gradient
even as the mean temperature gets warmer and warmer as there is no
heat sink in this model). Any time you put in a heat source or sink,
you'll get adjustments via convection... until an adiabatic gradient
is reestablished.
There's a reason planets, from Mars (essentially little to no
greenhouse effect) to Venus (essentially little or no heat flux at the
base) all have an adiabatic gradient. So will the temperature radially
along an Rama-style habitat.
On Oct 9, 5:50 pm, Luke Campbell <lwc...@gmail.com> wrote:
> If it is being cooled from above, you get mixing that preserves the
> adiabatic gradient. If this is so, then increased cooling from above
> simply leads to more violent weather, but the temperature gradient
> remains approximately the same.
The temperature gradient remains the same, on that we agree. I'm not
convinced that "weather" is due to the global heat transport through
the atmosphere - it's largely due to local effect. These local effects
can still occur in cylindrical habitats.
For instance, consider a classic O'Neil cylinder. Heat input to the
atmosphere comes from the three sun-warmed sectors. Heat loss has to
come from either the window sectors, or the polar caps (it can't come,
without active pumping, from the land sectors; they must radiate at
least half their acquired energy inward, and realistically potentially
more due to things like latent heat and convection). Heat can't be
lost from the "top" of the atmosphere either in this case (without,
again, active pumping: to "top" here being the axis).
So you have a situation with warm air rising over three land sectors,
and as it rises moving spinward (Coriolis force), generating a
circular air current around the central axis. But if air is rising
over those land sectors, the pressure there is lower than average, and
air moves from the window sectors over the land sectors; and that air
would be sourced mainly from the window sector to spinward (airflow
would be anti-spinward). The result would be three circulation cells,
with air rising over the heated land, moving spinward, to cool and
drop over the windows sector, only to drift back anti-spinward back
over the land.
That's exactly the sort of circulation you get along shorelines, for
instance (local convection depending on difference in surface
temperature), and it will happen due to pressure and temperature
difference, not just loosing heat at the top of the atmosphere; even
without that, the air flow will produce pressure difference. You'll
get this in a cylinder too.
On top of that, any moisture in the air will potentially condense out
during the ascent over the land sector, producing clouds (if you want
them; you're going to have to regulate weather in this thing somehow).
Those clouds will dissipate in the subsidence over the window sectors
(adiabatic warming as the pressure increases as the airmass descends).
A potentially... interesting... question is then how clouds might
alter this scheme, being great reflectors of short-wave light
(scattering light from reaching the land sector across the way, but
preferentially on spinward edge of it) and great absorbers of IR
(leading to them warming and dissipating, but the geometry of the IR
source is complex, as it's coming from three land sectors and
potentially other clouds). Of course latent heating effects will
release heat as the warm moist air ascends, keeping it warmer than a
dry adiabatic gradient and punching convection through to higher
levels, potentially changing the size of the convection cells (or at
least where the cloud cover goes) and therefore wind speeds aloft.
And we've not brought in turbulent mixing if different airmasses yet,
which is certainly going to play a role in such a small environment
where Coriolis effects will be strong and wind shears can get rough
with radial air motions.
Cool. Interesting. And ugly to work out in detail.
And of course, one of the major constraints on this is where exactly
you are gaining and loosing heat. I originally worked this out for
Rama, where I assumed heat loss was more significant through the polar
endcaps. That induces another circulation in the system (global air
circulation is upward over the cylidrical sea, moves poleward along
the axis, cooling and descending along the endcap surfaces).
> When mixing is not occurring, heat flow happens through diffusion
> rather than convection.
Say you have an isothermal atmosphere. Put in a little bit of heat
*anywhere*. You'll get convection if there's a pressure gradient. And
that convection will start establishing an adiabatic gradient.
> Thinking about it, for any reasonable human habitation this will probably
> dominate over heat diffusion, restoring mixing of the air.
Yes.
> The exception being for very large volume habitats and nearly uniform
> land use patterns, where small scale mixing homogenizes the
> atmosphere at low levels leading to stagnant upper levels.
I don't think you can get that uniform a land use profile. We get
noticeable convection by small lakes and cities here on Earth. Unless
you paint the inside flat grey and don't have anybody move, you'll
have convection somewhere... and once you set up convection, even on a
small scale, you've just changed the heat balance across the surface.
--
Brian Davis
Frank
[snip]
> --
> Brian Davis
I think your insistence that heat can't be radiated from the land
sectors assumes more than I can allow you.
On Earth, the land radiates off all the heat that reaches it (some to
the atmosphere, some to space). Yet it radiates in only one
direction.
What is true is that the O'Neill cylinders get much more radiation
(thanks to the mirrors) than they can lose by black-body radiation at
a livable temperature. So there has to be heat poumping.
Brian Davis
> On Oct 10, 11:19 am, Brian Davis <brda...@iusb.edu> wrote:
>
>> Heat input to the atmosphere comes from the three sun-warmed
>> sectors. Heat loss has to come from either the window sectors, or
>> the polar caps (it can't come, without active pumping, from the
>> land sectors; they must radiate at least half their acquired energy
>> inward...
>
> I think your insistence that heat can't be radiated from the land
> sectors assumes more than I can allow you.
Well, you can choose to allow me anything you wish - I'm not sure that
alters physical principles. At least that was my position with a bunch
of people over LCROSS and knocking the moon out of orbit ;).
Notice I never insisted the land sectors "can't radiate" - I implied
that heat *loss* has to come from somewhere else. For the land sectors
to absorb heat from the air (cooling the atmosphere), they would have
to be colder than the air - something that can't happen at least
during daylight hours.
Consider a square meter of land sector. During the day, it's going to
be acquiring something like 400 W/m^2, warming it up. It's going to
eventually reach some equilibrium temperature where it radiates 200 W/
m^2 both up (into the cylinder atmosphere) and "down" (out into
space). In order for the air to have a net transfer of thermal energy
*into* the land sector, it's going to have to be warmer than it.
Right?
Now, how does the air get to a higher temperature than the land
sector, since the major input of energy here is radiation on the land
surface?
> What is true is that the O'Neill cylinders get much more radiation
> (thanks to the mirrors) than they can lose by black-body radiation at
> a livable temperature. So there has to be heat pumping.
Really? The amount of heat input is proportional to the amount of land
surface exposed to sunlight (reflected or otherwise), while the heat
loss is due to black body radiation from *all* surfaces. If you want
to make the system balance at a livable temperature, you adjust the
area of the land sectors relative to the size of the cylinder, or
alternatively change the intensity of sunlight reflected to the land
sectors (there's no need for 1370 W/m^2... in fact, that's probably
too much, given the lack of a dense atmosphere).
The Earth absorbs over an area pi R^2, while it radiates over 4 pi
R^2... so it has a radiating surface effectively four times as large
as the collecting surface. A cylinder that's half land sectors has a
radiating surface that is twice as large as the collecting surface, so
you might like to reduce the surface insolation by another factor of
two, but that should be enough to bring it in the ballpark.
--
Brian Davis
Frank
2) Probably the Moon is a better comparison than the Earth. But the
area figures are the same. (The temperature is not.)
1) Okay, the "ground" loses heat to the air -- some by radiation, some
by evaporation -- the air absorbs the heat when the vapor condenses.
Then, what happens to the heat? If it accumulates, the air finally
gets hotter than the "ground." Before that happens, the vapor stops
condensing.
Frank
That's me.
> The O'neil-adopted idea was:
> 2) The cylinders would be illuminated by mirrors lsupported by (super-
> strong, (the book doesn't make that calculation) cables they would be
> let down for dawn and drawn up for dusk.
At the time I remembered having done the calculations, but not the
numbers.
I did them again. The the cables still look superstrong. Please pardon
moving from English to metric and back again. It's the figures I have.
O'Neil's "Island 3" is 4 miles in diameter and 20 miles long. For the
mirror to cover all the "land" area with light, it must be at 45
degrees. So the suspending cable at the end must be 20 miles long,
that's 32 KM. At a radius of 2 miles, the acceleration is 1 g. Thus,
at the radius of 22 miles -- cylinder radius plus suspended cable to
support the mirror -- the acceleration must be 11 g.
If you have a 1 cm^2 steel rod going from the surface to the mirror,
it would have 3.2*10^7 cm^3 volume, At density 8, that's 2.56 *10^8
grams.
The average acceleration is 6 g, That's 5.88*10^3 cm/sec/sec The
force on the top of the rod is 1.6*10^12 dynes. That's 1.6*10^7
newtons. or 3.4*10^6 pounds.Since 1 in^2 = 6.5cm^2, a 1 in^2 rod would
exert a force of 2.2*10^7 lb.
The highest tensile strength I can find in a quick look up was
pearlite at 1.4*10^5 lb/in^2.
That means that the chain or cable wouldn't support 1% of its own
weight if it were of even thickness throughout.
Of course, it could be tapered, but this looks like dramatic tapering
to me.
And what would be the design and support of the mirror.The
illustrations have it supported on the corners -- 2 miles wide at 11
gravities.
Brian Davis
> Probably the Moon is a better comparison than the Earth. But the
> area figures are the same. (The temperature is not.)
The area figures are the same for all the planets. My point was that
aspect is simply geometry. What the actual equilibrium temperature is
is often determined by the the emmisivity, and that different for the
Moon, the Earth, or a habitat... but even if you *don't* want to leave
those as a free parameter, you can still set the equilibrium
temperature, without active pumping, by changing the geometry (in this
case, changing the size of the land vs. window sectors, for instance).
> Okay, the "ground" loses heat to the air...
By radiation, latent heating effects (evaporation and later
condensation), and direct thermal conduction and convection - that
last is very significant.
> ...the air absorbs the heat when the vapor condenses.
> Then, what happens to the heat? If it accumulates, the air finally
> gets hotter than the "ground." Before that happens, the vapor stops
> condensing.
If the air became warm enough that condensation was no longer
efficient*, then conduction and convection would still play a role, as
would radiation, until the air got *as hot* as the ground: not hotter.
If the air ever got hotter than the ground, heat would obviously flow
the other way.
As to "what happens to the heat", it ends up doing things like warming
the window sectors, for instance - these are going to be colder
(probably much colder) than the land sectors. Why? Because the land
sectors absorb SW radiation almost by definition (they are opaque),
while the window sectors do not (being transparent).
So you end up with warm land, and cool windows. The system as a whole
warms up until it reaches equilibrium: the amount of energy absorbed
by the inside of the land sectors is the same as the amount of energy
radiated out by the window sectors and the "backside" of the land
sectors. Again, changing the relative proportion of land to window, or
changing the flux on the land sectors by using bigger or smaller
mirrors, is enough to solve the problem.
As to the original issue of adiabatic gradients radially within the
cylinder... as long as you have a heat sink, you'll have convection,
and as long as you have convection, you should end up with an
adiabatic gradient.
*Note that condensation is still going to be a factor until ground
temperatures would end up very unlivable, as the cylinder is cooler in
the center than at the inner surface, due, once again, to adiabatic
cooling as the pressure drops.
--
Brian Davis
Frank
Mr. Davis has convinced me that there would be (convection and, hence)
weather in an O'Neill cylinder.
I wrote a longer comment but don't seem to have it to post.
I still maintain the Earth weather is driven -- in large extent -- by
the radiation out into space of heat from the upper atmosphere.Why is
the air that falls cool? Were it entirely adiabatic, it would warm by
the time it got to ground level.
Frank
This is the post I just said I couldn't find. Well, I found it.
I'll stick to my statement that a good deal of the weather on Earth
depends on radiation from the upper atmosphere. For one thing, we all
agree that the ground transfers a good deal of energy to the air near
it, which then rises. If that air does not, when high up, radiate that
energy into space, where does it go?
OTOH, Brian Davis has been quite persuasive in demonstrating that
something of the same effect would happen in an O'Neill cylinder.
Since I'm interested in O'Neill cylinders mostly as counterexamples,
I'm not going to work this through. It's also not my best field of
science.
I'll leave it to those more interested and more competent. I will,
however, leave them with these tidbits of complexity:
1) If it rains on the ground, it will rain on the windows. What do you
do with that water? That question would be easier to answer were "The
High Frontier" a blueprint for O'Neill's plans rather than a sales
brochure.
2) "Sunlight" is an involuntary pun.
Sunlight1 is what you get in your backyard on a clear day.
Sunlight2 is what the sun puts out.
Sunlight2 contains a good deal of noxious stuff (mostly UV) that is
filtered out by the upper atmosphere. Island 3 would need to filter
that out. If the mirrors can't be designed so that they don't reflect
it and if the windows can't have a coating which does reflect it, then
the windows must absorb it. That's energy, which means that they will
radiate as much energy in IR.
3) If the caps were frictionless, then the air would have the same
LINEAR velocity at any altitude. Half way to the axis, the air would
have the twice the speed of rotation as the surface.
Since the caps won't be frictionless, you're going to have interesting
wind effects near the caps.
Brian Davis
> I'll stick to my statement that a good deal of the weather on
> Earth depends on radiation from the upper atmosphere. For
> one thing, we all agree that the ground transfers a good deal
> of energy to the air near it, which then rises. If that air does
> not, when high up, radiate that energy into space, where does
> it go?
On Earth? Near the equator it moves north at altitude - not down. It
finally moves down when it has traveled a good ways north, partly
because it has radiated its heat, and partly because the air below is
moving south... because of the pressure difference that has occurred
due to rising air near the equator.
To put it shorter, Hadley cells (direct thermal cells) are driven by
ground temperature difference. On all planets. On a rapidly rotating
planet these are deflected east & west (Earth has two thermally direct
cells with an indirect cell between them; Jupiter has bunches) because
it's a sphere. I'm still not sure exactly what they would do in a
cylindrical habitat.
> OTOH, Brian Davis has been quite persuasive in demonstrating that
> something of the same effect would happen in an O'Neill cylinder.
Thanks, but *I* really wouldn't trust me or my powers of persuasion.
Work the physics, that's all I'm suggesting (and trying to do).
> If it rains on the ground, it will rain on the windows.
Sort of. You're likely to get rain if you have air being cooled -
that's going to occur as wamr air convects upward (generally over
land), not when air sinks downward (as it descends, it compresses,
warming along an adiabat... there's a reason it doesn't rain at the
center of high-pressure systems). You might get some rain over the
windows depending on the deflection and mixing, so it's a
consideration. Making the windows slightly peaked in the center could
be enough... or, you could just let them collect the water and act as
shallow "seas". That not only takes care of some of the water issues,
but...
> Sunlight2 contains a good deal of noxious stuff (mostly UV) that
> is filtered out by the upper atmosphere. Island 3 would need to
> filter that out. If the mirrors can't be designed so that they don't
> reflect it and if the windows can't have a coating which does reflect
> it, then the windows must absorb it. That's energy, which means
> that they will radiate as much energy in IR.
First, making mirrors that are better in one wavelength than another
is old-hat. The question is if you can do them reliably on this scale.
Tuned mirrors then are one possible solution (and while you're at it,
don't bother putting them at 45°... as discussed, you can get by with
a lot less sunlight than that, and angling the panel as a whole to a
shallower angle helps a lot... you can make vanes on the panel angled
differently so as to bounce sunlight, they types you want, into the
hab).
Second, the fact that a trivial column density of O3 in the upper
atmosphere takes out the nasty UV tells you it's not hard to do. And
while that does absorb energy, it's also not a huge chunk of the total
energy delivered (take a look at the Sun's Black Body curve, and the
O3 absorption bands).
Third, go back to the "water on the windows" thing again. A very thin
layer of water can serve as an additional barrier for UV (just like it
did for early sea life on a largely anoxic Earth). This may be a
problem with a partial solution already in place. Keep in mind too
that the atmosphere within the cylinder will also be helping (it
doesn't thin out nearly as fast as on Earth; I'm not sure if you could
arrange for an "ozone axis", but it's a possibility perhaps).
> 3) If the caps were frictionless, then the air would have the
> same LINEAR velocity at any altitude.
You might want to think about that some more. Coriolis forces don't
act that way, and in a co-rotating frame the linear velocities by
definition aren't all the same (think about what that would mean at
the axis).
> you're going to have interesting wind effects near the caps.
That's true, but not for the reasons you state.
--
Brian Davis
Greg Goss
>1) If it rains on the ground, it will rain on the windows. What do you
>do with that water? That question would be easier to answer were "The
>High Frontier" a blueprint for O'Neill's plans rather than a sales
>brochure.
Hump the glass up a little. (Or, really, bow it outwards a little bit
less than a segment of a circle.) Water falls onto the glass; runs to
the edge of the glass, where it's gathered into storage tanks.
Erik Max Francis
> Frank <fpfran...@gmail.com> wrote:
>
>> 1) If it rains on the ground, it will rain on the windows. What do you
>> do with that water? That question would be easier to answer were "The
>> High Frontier" a blueprint for O'Neill's plans rather than a sales
>> brochure.
>
> Hump the glass up a little. (Or, really, bow it outwards a little bit
> less than a segment of a circle.) Water falls onto the glass; runs to
> the edge of the glass, where it's gathered into storage tanks.
Please don't hump my glass. Thank you.
--
Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 18 N 121 57 W && AIM/Y!M/Skype erikmaxfrancis
It dives and it jumps / And it ripples like the deepest ocean
-- Sade
Mike Dworetsky
news:e9119f12-2063-4a5b...@g23g2000vbr.googlegroups.com...
MD: Yeah, but...steel on the moon could get a "free" one-way ride to Earth
as a catapult container. The catapult system needed ferrous metal in order
to "grab" it magnetically and fling the container into a path for safe
descent to Earth with cargo. And the catapult was powered by solar panels,
as I recall (possibly imperfectly). So lunar steel was a perfectly
reasonable commodity for trade and barter.
There was also a lunar currency backed by gold, which was actually hauled up
to Luna from Earth and stored in the vaults of the bank for that purpose.
(Hong Kong in Luna Bank, ISTR). Was it bought with the proceeds from the
steel?
--
Mike Dworetsky
(Remove pants sp*mbl*ck to reply)