Mars is kind of short of nitrogen

Ian Stirling wrote in message ...
Hop David wrote:


Ian Stirling wrote:
snip "of space habitat lighting"
For the simplest case, you'r looking at something like a cylinder,
with a parabolic mirror at one end.
The cylinder is pointed at the sun, and the mirror is coaxial with it,
with a secondary mirror to bounce the light through a hole in the endcap.

http://clowder.net/hop/etc./CylMirror.jpg

This was for a colony at 3 A.U. IIRC, where the collecting mirror's
surface would need to be greater than if it were 1 A.U.

This has 3 mirrors. The third mirror within the cylinder seems omitted
from some of the schemes I've seen. But you need something to send the
imported rays to the walls of cylinder.

It's nice, but not mandatory.
Leaving it out means the light gets less uniform, and comes down
at a shallow angle.

Cant the cylinder, and you'd get pretty even average illumination as it
spun.
Having an internal mirror is a good thing though, it drastically simplifies
day/night for one thing.

you'd want to control day/ night from an external mirror, to reduce
the amount of radiation (and hence heat) entering the cylinder.

With a multi layer radiation amnd impact shield, getting rid of heat
will a big problem.

(Alex Terrell) wrote in
om:

Herm wrote in message
. ..
places to go and explore in rovers etc.. depressing living in a spam
can in space

Any worse than living in a smaller spam can on Mars, with an
inconvenient level of gravity and no easy access to zero-g, abundant
energy, Earth maerkets etc?

On Thu, 12 Feb 2004 12:26:20 -0600, "Mike Combs"
wrote:

So aside from "the ground under your feet", what else does Mars
provide that must be provided artificially in an orbital habitat?

Assuming you go for a permanent base, some manufacturing infrastructure,
etc.
Mars has a LOT to offer.
+Gravity under your feet.
+Enough atmosphere for cooling equipment. (cooling by radiation in a vacuum
is hell)
+Sufficient water and co2 to use for making convenient fuel (ch4 + o2) for
rockets. On moon you have to supply your own fuel, or work with exotic
stuff like powdered AL + O2 hybrid. In space you supply everything, period.
+Zero-g is an *easy* SSTO flight away. Even using a low power fuel.
+Not so much atmosphere as to bother a rocket taking off. Enough atmosphere
for aero brake re-entry. Slow enough orbital speed for non-exotic materials
on fully reusable heat shielding. Because of the ease of re-entry, it's
actually easier to go to orbit and land again from Mars than from the Moon.
And about 10 times easier than from earth.
+Plenty of cheap radiation shielding lying around. Just need a shovel. In
space you need to import all your shielding.

All these make sense only if you are serious about what you are doing. When
working on the scale of science-only-base, or worse even on temporary-
visit-only, its a lot easier to never leave earth's region. But by the time
you are thinking at the scale of building o-neill stations, Mars
surface+orbit is a *lot* better buy than any earth+orbit or
earth+moon+orbit scheme.

Marvin wrote in message ...
On Thu, 12 Feb 2004 12:26:20 -0600, "Mike Combs"
wrote:

So aside from "the ground under your feet", what else does Mars
provide that must be provided artificially in an orbital habitat?

Assuming you go for a permanent base, some manufacturing infrastructure,
etc.
Mars has a LOT to offer.
+Gravity under your feet.
+Enough atmosphere for cooling equipment. (cooling by radiation in a vacuum
is hell)
+Sufficient water and co2 to use for making convenient fuel (ch4 + o2) for
rockets. On moon you have to supply your own fuel, or work with exotic
stuff like powdered AL + O2 hybrid. In space you supply everything, period.
+Zero-g is an *easy* SSTO flight away. Even using a low power fuel.
+Not so much atmosphere as to bother a rocket taking off. Enough atmosphere
for aero brake re-entry. Slow enough orbital speed for non-exotic materials
on fully reusable heat shielding. Because of the ease of re-entry, it's
actually easier to go to orbit and land again from Mars than from the Moon.
And about 10 times easier than from earth.
+Plenty of cheap radiation shielding lying around. Just need a shovel. In
space you need to import all your shielding.

Great, Excellent. Now all we need to do is to move Mars into Earth
orbit so that it can it be reached in three days with continuous
launch windows. Or develop some new propulsion method that can get us
there in a few weeks.

Until we can do either of those, Mars is best left as a research lab.

All these make sense only if you are serious about what you are doing. When
working on the scale of science-only-base, or worse even on temporary-
visit-only, its a lot easier to never leave earth's region. But by the time
you are thinking at the scale of building o-neill stations, Mars
surface+orbit is a *lot* better buy than any earth+orbit or
earth+moon+orbit scheme.

Herm wrote:
places to go and explore in rovers etc.. depressing living in a spam can in
space

On Thu, 12 Feb 2004 12:26:20 -0600, "Mike Combs"
wrote:


So aside from "the ground under your feet", what else does Mars provide that
must be provided artificially in an orbital habitat?



Herm
Astropics http://home.att.net/~hermperez

If the hab is on or near an asteroid you some interesting real estate to
explore.

Also possibly lots of in-situ resources to use.

--
Hop David
http://clowder.net/hop/index.html

Alex Terrell wrote:
Ian Stirling wrote in message ...
Hop David wrote:


Ian Stirling wrote:
snip "of space habitat lighting"
For the simplest case, you'r looking at something like a cylinder,
with a parabolic mirror at one end.
The cylinder is pointed at the sun, and the mirror is coaxial with it,
with a secondary mirror to bounce the light through a hole in the endcap.

http://clowder.net/hop/etc./CylMirror.jpg

This was for a colony at 3 A.U. IIRC, where the collecting mirror's
surface would need to be greater than if it were 1 A.U.

This has 3 mirrors. The third mirror within the cylinder seems omitted
from some of the schemes I've seen. But you need something to send the
imported rays to the walls of cylinder.

It's nice, but not mandatory.
Leaving it out means the light gets less uniform, and comes down
at a shallow angle.

Cant the cylinder, and you'd get pretty even average illumination as it
spun.
Having an internal mirror is a good thing though, it drastically simplifies
day/night for one thing.

you'd want to control day/ night from an external mirror, to reduce
the amount of radiation (and hence heat) entering the cylinder.

I was assuming that you'd have day/night in different portions of
the cylinder at once, to even out heating.
If it's pointed at the sun, and the mirror shades it, and not heated
by earth, then it will tend to equilibrate at around toom temperature,
assuming that the shell is kept at the same temp as the inside.

Hop David wrote:
I wrote

So? Thats a quite unintersting figure. Plants don't use all of incoming
solar energy either. Furhermore, you are not really area or mass limited
with those solar cells as they would be attached to something gobsmacking
large - a O'Neill's anyways.



I believe 90% loss is a more practical estimate for light to electricity
to light
(economics and engineering don't always allow you to reach the limits
from laws of physics)

Considering you can do 90% now for light - light, I really doubt that or
80% is a real limit. I might believe largish practical problem around doing
better than say 75% losses - but I'm far from certain the limit is
unbreakable, even for practical purposes.


This means the photovoltaic arrays would need to be 10 times the area of
a collecting mirror.

Only if you forget to scale it for the amount of light that actually
goes on to do photosynthesis. Plants by far don't use all the light,
or use all of it effectively. You can get much higher percentage with
articial lighting.


And per square meter, it seems to me aluminized mylar would be cheaper
than photovoltaics.

Certainly. Though you need a completely separate large structure for the
mirror, while you would have solar batteries anyways.


Also expensive would be the artificial lighting. Artificial lighting is
OK for homes and offices. But providing enough light to grow crops is a
much harder task.


There are many cases where part time or even full time artificial lighting
is used down here on earth.

--
Sander

+++ Out of cheese error +++

Ian Stirling wrote in message ...
Alex Terrell wrote:
Ian Stirling wrote in message ...
Hop David wrote:


Ian Stirling wrote:
snip "of space habitat lighting"
For the simplest case, you'r looking at something like a cylinder,
with a parabolic mirror at one end.
The cylinder is pointed at the sun, and the mirror is coaxial with it,
with a secondary mirror to bounce the light through a hole in the endcap.

http://clowder.net/hop/etc./CylMirror.jpg

This was for a colony at 3 A.U. IIRC, where the collecting mirror's
surface would need to be greater than if it were 1 A.U.

This has 3 mirrors. The third mirror within the cylinder seems omitted
from some of the schemes I've seen. But you need something to send the
imported rays to the walls of cylinder.

It's nice, but not mandatory.
Leaving it out means the light gets less uniform, and comes down
at a shallow angle.

Cant the cylinder, and you'd get pretty even average illumination as it
spun.
Having an internal mirror is a good thing though, it drastically simplifies
day/night for one thing.

you'd want to control day/ night from an external mirror, to reduce
the amount of radiation (and hence heat) entering the cylinder.

I was assuming that you'd have day/night in different portions of
the cylinder at once, to even out heating.

I had the same design, but it was pointed out (in this group) that if
you have day in one part, you have day in all the cylinder - at least
as good as a heavily overcast day.

http://groups.google.co.uk/groups?hl...g.goog le.com

If it's pointed at the sun, and the mirror shades it, and not heated
by earth, then it will tend to equilibrate at around toom temperature,
assuming that the shell is kept at the same temp as the inside.

Yes it's shielded, and the outside is very cold, and the inside is
23C. But the shell is a very good insulator. For impact protection,
the shell will not be 1m of steel (which would work as you describe) -
rather it will be a multi layer perhaps 100m thick (though still about
10 tons/m2 - say 5 cm steel, 50m vacuum gap, 4m of "slag" (left overs
from processed NEOs, sulphur etc), 50m vacuum gap, 5 cm steel.)

That means that some form of active cooling will be needed. This can
be made easier by 1. Filtering out IR before it comes into the colony
- perhaps on the large primary mirror (doing so on the secondary
mirror would overheat it) and 2. pointing the light somewhere else at
night (perhaps at the neighbouring colony).

Sander Vesik wrote:
Hop David wrote:
I wrote

So? Thats a quite unintersting figure. Plants don't use all of incoming
solar energy either. Furhermore, you are not really area or mass limited
with those solar cells as they would be attached to something gobsmacking
large - a O'Neill's anyways.



I believe 90% loss is a more practical estimate for light to electricity
to light
(economics and engineering don't always allow you to reach the limits
from laws of physics)

Considering you can do 90% now for light - light, I really doubt that or
80% is a real limit. I might believe largish practical problem around doing
better than say 75% losses - but I'm far from certain the limit is
unbreakable, even for practical purposes.

I don't think that 90% is currently possible.
Solar cells are some 30%, and the most efficiant lights some 50% (white).
Or a total of 15%.

lid (John Savard) wrote in message ...
On Sat, 14 Feb 2004 15:21:03 GMT, Ian Stirling
wrote, in part:

Then again, by complicating the mirror design a bit, you can pump all the
light through a hole that's radiologically negligable.
If you'r feeling really clever, you can even bounce it round using
mirrors once it gets inside, so that no radiation gets in.

I decided to do the bouncing on the outside...

http://www.hypermaths.org/quadibloc/science/spaint.htm

With the habitat completely surrounded by a (non-rotating?)
bottle-shaped shield, how do you propose to cool the habitat? This
seems to be an issue that colony-designers consistently neglect.
Every kilowatt of sunlight brought into the colony must and will exit
again as heat; the only question is how. If we don't include
radiators and a heat distribution system, then the heat will
eventually leave through the insulating shield walls from the glowing
cherry-red habitat within it.

"Herm" wrote in message
...
places to go and explore in rovers etc..

People living in orbital habitats will (in the long term) certainly start
moving all over the solar system. The O'Neill concept opens the possibility
of exploring all parts of the solar system while taking your home with you.
Tour the Solar System and see the sights! (But still be home in time for
dinner.)

depressing living in a spam can in
space

That's a subjective, personal opinion, not an objective fact. Other people
with tastes differing from yours will view it differently.

O'Neill advocates like to discuss the importance of nearby markets, the
vital importance of having an export to balance trade, the economics of
energy generation, etc. Mars advocates usually bring up subjective points.
O'Neill advocates tend to argue from economics and physics. Mars advocates
argue from aesthetics.

--


Regards,
Mike Combs
----------------------------------------------------------------------
We should ask, critically and with appeal to the numbers, whether the
best site for a growing advancing industrial society is Earth, the
Moon, Mars, some other planet, or somewhere else entirely.
Surprisingly, the answer will be inescapable - the best site is
"somewhere else entirely."

Gerard O'Neill - "The High Frontier"