Mars is kind of short of nitrogen

"Marvin" wrote in message
...
"Mike Combs" wrote in
:

Most of what you say makes sense, however:
What about an orbital habitat built next door to a Carbonaceous
Chondritic NEO?
Pick. Earth orbit, or by the NEO asteroid. The two *cannot* be the same
place.

In my view, certainly the first habitat will be built in HEO (due to the
"closeness to available markets" point I was making). Maybe the first dozen
or more. But past a point, when trade with Earth becomes a smaller portion
of the total trade, I'd anticipate many new habitats would get built
adjacent to NEOs, due to the more economical access to raw materials. In a
similiar vein, taking the long view, I'd anticipate most habitats will get
built in the Asteroid Belt: the most convenient source of raw materials.

Unless you plan to move asteroids in the near future, in which case
i gotta laugh.

It all depends on how one defines "near future", I suppose. There were NASA
studies done suggesting NEO asteroids (or at least sizeable amounts of raw
material from them) could be brought back via mass-driver tug. It involved
gravity assist maneuvers around Venus and the moon.

Inside the first half of this century, I'd consider the Earth having a tiny
second moon at L-4 or L-5 to be a distinct possibility.

Given the concern about the consequences of a major asteroid strike, we
might better develop technologies for moving asteroids around, even if not
for this purpose.

H2 for making water for humans, fine. H2 for facilitating chemical
production methods, sure.
H2 for bulk rocket fuel? No ways.
Any scheme that uses lunar sourced H2, that removes the H2 from the moon
in bulk, will strangle itself rapidly. Even under best estimates Lunar H2
will be very very scarce.

We might have several decades worth of lunar water available. At the end of
that period, we'd probably have material coming in from NEOs. The
admittedly-limited resources of lunar water might at least enable us to
"prime the pump".

--


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"

"G EddieA95" wrote in message
...
shedding heat in vacuum is valid, but
is Mars significantly better? What is the convection current rate when
the
atmosphere is only 1% as dense as what industry is used to here on Earth?

High winds are common on Mars, and are useful for convecting away heat.

Yes, but those winds are fast but thin. I'm arguing entirely from
intuition, here (I had to switch my major away from physics because I
couldn't handle the math), but I'm suspecting that a 100 mph wind on Mars
might only carry away as much heat as a 1 mph wind on Earth.

You
also have the very cold ground as a heat dump.

My understanding is that dust is a pretty good insulator. Seems that would
severely limit the ground's potential as a heat dump.

--


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"

"Bill Bogen" wrote in message
m...

If true, swell, but this is still a pretty elaborate system. Since
we'd have landscaping inside the habitat anyway, I'd just let that act
as the shielding and let it all rotate. The load a couple of meters
of dirt would add is comparable to the loading from the atmosphere so
the structure would be beefier but more simple than mixing massive
rotating and non-rotating structures in close proximity.

I think that might have been the conclusions of the MIT study which produced
the habitat design I posted the URL to the picture of. The caption
mentioned "integral shielding".

--


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"

"Mike Combs" wrote in message ...
"Bill Bogen" wrote in message
m...

If true, swell, but this is still a pretty elaborate system. Since
we'd have landscaping inside the habitat anyway, I'd just let that act
as the shielding and let it all rotate. The load a couple of meters
of dirt would add is comparable to the loading from the atmosphere so
the structure would be beefier but more simple than mixing massive
rotating and non-rotating structures in close proximity.

I think that might have been the conclusions of the MIT study which produced
the habitat design I posted the URL to the picture of. The caption
mentioned "integral shielding".

Given the level of criticality, I would want to rely on a proper
shield. Perhaps we need to rate terrorism as a higher risk than
meteorite impact.

The sort of shell I outlined (5cm steel, 50m vacuum, 4m cheap slag,
50m vacuum, 5cm steel) could save the colony from a small external
nuclear bomb.

Also, the shield is dirt cheap, because it's mostly dirt.

Thanks for the calculations. You should assume:

1. The whole colony is shrouded by the solar array, so receives no
sunlight on the exterior.
2. The IR component of the light is filtered out - that possibly
halves the amount of light energy.
3. To complicate, temperature will vary by night and day - dynamic
modelling will be very complex.
4. The shield is as good as a thermos, as it's multi layer with vacuum
between the layers. However, you could put large radiators through it.

"John Savard" wrote in message
...

I did not include details of heat, or even of distributing the
sunlight to the habitat surface, in my design, because I was
addressing one specific claim that I had seen made - that secondary
radiation debunks the O'Neill colony notion.

I think I mentioned to you before that the person who made this claim to you
was mistaken. He was one of those kinds who condescendingly supposes that a
thinker on the level of Gerard O'Neill (not to mention entire teams of NASA
scientists) might absent-mindedly forget all about a commonly-known aspect
of the space environment.

It doesn't. A design is
possible that allows adequate shielding against that.

The designs which were published back in the 1970's provide adequate
shielding. 12 feet of solid rock is overkill; 6 feet of slag is sufficient
to mop up both primaries and their secondaries.

--


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"

John Savard wrote:

Space habitats are possible.

Are they economic? I think thorium breeders, not solar power
satellites, are going to be the stopgap until fusion, so I make no
claims in that department.

I think its not a question of "will they be economic" but "when will
they be economic". If you have fusion, a lot of teh present problems
with a sizable habitat in space or on Moon go away, especially for
the bootstrapping phases - you can simply beam them power.


John Savard
http://home.ecn.ab.ca/~jsavard/index.html

--
Sander

+++ Out of cheese error +++

(Bill Bogen) writes:

(John Schilling) wrote in message ...

With the habitat completely surrounded by a (non-rotating?)
bottle-shaped shield, how do you propose to cool the habitat?

Blackbody radiation from the habitat shell to the shield, and from
the shield to deep space, ought to suffice. Well, very dark grey
bodies in practice, just so long as you don't try to duplicate the
thermos-bottle trick of using mirror-polished silver bodies.

[...]

You mirror the outer surface of the shield in silver, yes, but over
that put a layer of fused quartz - optically transparent (so incident
sunlight passes through to reflect from the silver underlayer), but
very close to an IR blackbody. You paint the inner surface of the
shield and the outer surface of the habitat shell flat black. And
you give the inner shield and outer habitat surfaces interlaced
radiator fins with a 10:1 aspect ratio.

Pretty scary, what with the habitat fins zipping by 'above' the
stationary shield fins at 100 m/sec (227 miles/hr). Fun to service!

Given the scale of the proposed colonies, you can have several meters
of seperation everywhere if you want it. At that point, it's no
scarier that riding a TGV or other high-speed train on a dual-track
line.

Illuminate the inner surface with sunlight corresponding to the
long-term average for Earth at 45 degrees latitude, or 305 Watts
per square meter. Assume that none of this radiates or reflects
back out the window, the colony is a perfect greenhouse. Also
assume that we want the colony to be maintained at nominal room
temperature, 298 K.

One square meter of habitat shell then recieves 305 Watts of interior
illumination. It radiates 7855 Watts from the ten square meters of
associated double-sided radiator fin on the outer surface,......

This may reveal more of my thermodynamical ignorance but how could the
radiator fins have a power density of 785.5 W/m^2 while the inside
surface of the habitat has a power density of 305 W/m^2?

7855 Watts from ten square meters of *Double-Sided* radiator fin, equals
392.75 Watts per square meter of surface area. A 298 K blackbody will
radiate 450 W/m^2, the discrepancy being that black paint, isn't.

Strictly speaking, the inner surface has a heat balance of 305 W/m^2 of
sunlight in, 392.75 W/m^2 of IR radiated across to the far side of the
habitat interior, and 392.75 W/m^2 recieved *from* said far side. Or
some lesser value if we don't paint the interior black, but the point
is that we're assuming a perfect greenhouse so IR emission and absorbition
across the colony interior is balanced and it's only the solar term that
gives a net energy flow.


--
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