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A Moon base is too far; an asteroid ship better alternative:)



 
 
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  #22  
Old March 16th 05, 04:54 PM
Joe Strout
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In article ,
"Gene P." wrote:

I'd consider being isolated from your power supply 50% of the time (for two
weeks at a time) to be a greater problem in need of a solution than the
modest requirements for orbital station-keeping.


I've got 2 different answers to this non-issue:

1. The Lunar Power Grid + electric furnace. Who cares if the electricity
comes from solar panels on the other side of the moon or from a great big
nuclear pile a couple of miles away...


Running power lines all the way around the Moon is itself a daunting
engineering challenge (though admittedly, one probably on the same order
as a mass launcher and large-scale orbital manufactury). A reasonable
solution, but not such a trivial one as to make lunar night a non-issue.

A nuclear power plant is also a reasonable solution, but again, it
doesn't offer the same flexibility or convenience as continuous sunlight.

2. Space furnace mirrors can point down at the lunar surface just as
easy as at an orbital processing facility...


Can they? From where? There are no selenosynchronous orbits.

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  #23  
Old March 16th 05, 05:05 PM
El Pollo Borracho
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"Gene P." wrote in message
...

2. Space furnace mirrors can point down at the lunar surface just as
easy as at an orbital processing facility...



Wrong. Think about it.


  #24  
Old March 16th 05, 07:34 PM
David Summers
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Then why don't we use such things on Earth? Nuclear power is WAY
cheaper in Mexico (or even Nevada compared to New York)!

The fact is, transmitting power via cables over long distances is
expensive. The grid uses nearby sources, not far away ones. Losses on
long distance power cables become very large very fast.

-David

  #25  
Old March 17th 05, 02:38 AM
D Schneider
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David Summers wrote:

[...]
The fact is, transmitting power via cables over long distances is
expensive. The grid uses nearby sources, not far away ones. Losses on
long distance power cables become very large very fast.


Well, depends on the long distance, I suppose. There's a intertie running
down eastern Oregon; probably from Bonneville on the Columbia river, and
probably to somewhere around Red Bluffs or Sacramento, so in excess of 300
miles doesn't seem strange. Also, 250 miles from Hoover Dam to LA.

Losses would go down with superconductor cabling, which is still
expensive, and the support equipment may still be prohibitively heavy.
But it looks like it might be practical and available within about the
same time as return to the moon.

/dps

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  #27  
Old March 17th 05, 08:09 PM
Mike Combs
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"Gene P." wrote in message
...

I've got 2 different answers to this non-issue:


NASA didn't consider this a non-issue when they made the only detailed
studies of space industrialization using ET resources they ever did in their
history. In case you thought I was arguing from my imagination, or from
what happens to strike me as reasonable, I'm arguing from the NASA Summer
Studies on space settlement.

1. The Lunar Power Grid + electric furnace. Who cares if the electricity
comes from solar panels on the other side of the moon or from a great big
nuclear pile a couple of miles away...


A power grid spanning the entire globe of the moon would be a pretty
formidable industrial accomplishment. I can't see it happening in any
near-term future.

It would be a shame if we went to all the expense of developing nuclear
power on the moon just because we couldn't overcome our planetary chauvinism
long enough to develop solar power outside the shadows of planets. Nukes
are fairly high-tech, large mylar mirrors are pretty low-tech. I know which
is going to have the bigger power bill. With the space mirror, the heat
generated is used directly without any conversions and consequent efficiency
losses.

2. Space furnace mirrors can point down at the lunar surface just as
easy as at an orbital processing facility...


No, actually, that's where you're wrong. The optical physics of it are such
that at several miles distance one would be forced to use mirror many times
bigger than otherwise (and also be forced to illuminate a much wider area
that what's desired). In discussing a High Frontier type solar furnace,
we're discussing mirrors perhaps one or two times the area of a football
field. To do what you propose would require mirrors the size of states or
small nations.

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Regards,
Mike Combs
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Member of the National Non-sequitur Society. We may not make
much sense, but we do like pizza.


  #28  
Old March 17th 05, 08:15 PM
Mike Combs
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"Joe Strout" wrote in message
...

Running power lines all the way around the Moon is itself a daunting
engineering challenge (though admittedly, one probably on the same order
as a mass launcher and large-scale orbital manufactury).


I'm not even sure it would compare favorably with those items. I'm a little
bit vague on the mass budget for the orbital manufacturing facility O'Neill
proposed, but as for the mass launcher, I remember him commenting that the
components for the mass-driver itself would fit into a single Space Shuttle
cargo bay, although the components for the power supply would be several
times that.

2. Space furnace mirrors can point down at the lunar surface just as
easy as at an orbital processing facility...


Can they? From where? There are no selenosynchronous orbits.


Yet another complication. And the L-1 and L-2 points are so far away that I
think we'd be discussing mirrors bigger than continents.

--


Regards,
Mike Combs
----------------------------------------------------------------------
Member of the National Non-sequitur Society. We may not make
much sense, but we do like pizza.


  #29  
Old March 17th 05, 08:21 PM
Mike Combs
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"Fred J. McCall" wrote in message
...
wrote:

:I believe the lighter the molecule in the exhaust, the more efficient
:the engine? If so, it might be better to make pellets of silicon (MW=
:14) as we process the asteroid, charge them, and accelerate them using
:an electrostatic engine. Oxygen has a molecular weight of 16, would be
:rather corrosive in a high-temp exhaust, and is more useful than
:silicon for other purposes.

But do you really want to be spraying what are essentially high speed
bullets around where they can eventually hit other spacecraft? Better
something that isn't solid for your 'exhaust'.


Yes, but space is already criss-crossed with high-speed micrometeoroids. So
the only sensible question that needs answering is are we making a
significant contribution to an already-existing problem. At many levels of
scale, the answer is probably "no".

That said, I remember that in the "High Frontier" plan, it was proposed that
mass-drivers start out using pelletized Space Shuttle ET's for their
reaction mass, but at a fairly early point switch over to locally-produced
oxygen, which would vaporize on release. So the impression that I get is
that it's not an issue to be disregarded, but it's not a big issue.

--


Regards,
Mike Combs
----------------------------------------------------------------------
Member of the National Non-sequitur Society. We may not make
much sense, but we do like pizza.


  #30  
Old March 18th 05, 04:34 AM
Cameron Dorrough
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"Paul F. Dietz" wrote in message
news
Mike Combs wrote:

A power grid spanning the entire globe of the moon would be a pretty
formidable industrial accomplishment. I can't see it happening in any
near-term future.


I suspect a power grid on the moon is considerably more difficult than
one on earth, even ignoring the difference in labor cost. A high voltage
conductor in dense air is insulated by that air, but in vacuum you'll be
constantly generating high energy ions and electrons in the surrounding

plasma,
and possibly causing runaway discharge due to their collision with

surfaces
and secondary ion production.


That's assuming that you'd run the cables suspended above the surface
somehow...

If you were serious, you'd probably direct bury them - AIUI, moon dust is a
great insulator.

Cameron:-)



 




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