[CraigD]

Originally Posted by Moontanman

First a meteorite is not a shaped charge made to penetrate as far as possible. Say a dime sized meteor hits something, it's energy is does not cause a shaped charge type of explosion. The energy of impact simply vaporises a small crater in what ever it hits. The vapor doesn't have the penetrating power it's speed would suggest.

I believe MTman is thinking too intuitively in his comparison of meteors and explosives.

Shaped charges are explosive devices designed to overcome a fundamental shortcoming of simple, un-encased explosives: that their energy spreads from them in many directions. Though it’s uncommon to consider them so, the most common shaped charge devices in most peoples’ experience are small guns. The small amount of low explosive in a typical rifle cartridge, spread on an ordinary thin wood table and lit from the distance afforded by a long match, is harmless, while the same charge driving a bullet from a gun barrel readily penetrates the table.

A projectile, such as a small or large meteor, delivers all of its energy in a single direction. It is, essentially, the effective part of a shape charge, without all the less effective parts.

Our experience living in an atmosphere is that low-density “projectiles” such as puffs of gas or “soft” ones such as streams of water are less destructive than dense, hard ones such as bullets and arrows. However, in vacuum, such differences are less significant.

A rough approximation of the penetration of a meteor can be had by comparing the vaporization energy of a hemisphere of water to the kinetic energy of the projectile. This given the required thickness of armor to stop a meteor of mass and speed as:

where is a constant
where is the specific heat of water. For a range of masses from micrometeor to boat-size, and speeds from human running to the fastest observed meteoroids, in meters is

Mass      Speed (m/s)
(kg)          10      40     100     400    1000    4000   10000   40000   72000
.001      0.0004  0.0010  0.0018  0.0045  0.0083  0.0209  0.0385  0.0970  0.1435
.004      0.0006  0.0015  0.0028  0.0071  0.0132  0.0332  0.0611  0.1540  0.2279
.01       0.0008  0.0021  0.0038  0.0097  0.0179  0.0450  0.0829  0.2090  0.3093
.04       0.0013  0.0033  0.0061  0.0154  0.0284  0.0715  0.1317  0.3318  0.4909
.1        0.0018  0.0045  0.0083  0.0209  0.0385  0.0970  0.1787  0.4503  0.6663
.4        0.0028  0.0071  0.0132  0.0332  0.0611  0.1540  0.2837  0.7148  1.0577
1         0.0038  0.0097  0.0179  0.0450  0.0829  0.2090  0.3850  0.9701  1.4355
4         0.0061  0.0154  0.0284  0.0715  0.1317  0.3318  0.6111  1.5399  2.2787
10        0.0083  0.0209  0.0385  0.0970  0.1787  0.4503  0.8294  2.0900  3.0926
40        0.0132  0.0332  0.0611  0.1540  0.2837  0.7148  1.3166  3.3177  4.9092
100       0.0179  0.0450  0.0829  0.2090  0.3850  0.9701  1.7869  4.5028  6.6629
400       0.0284  0.0715  0.1317  0.3318  0.6111  1.5399  2.8366  7.1477 10.5767
1000      0.0385  0.0970  0.1787  0.4503  0.8294  2.0900  3.8498  9.7009 14.3547
40000     0.1317  0.3318  0.6111  1.5399  2.8366  7.1477 13.1662 33.1767 49.0925
100000    0.1787  0.4503  0.8294  2.0900  3.8498  9.7009 17.8693 45.0277 66.6287

This simple model assumes a perfectly ablative shield material. In reality, armor must resist complicated effects such as spalling, while material in a space station may need to retain structural integrity when penetrated or pitted, and must resist structural failure due to cracking.

Originally Posted by Moontanman

the idea is not stop the meteor but to have it expend it's energy as heat and only destroy a small area. something like ablative armor.

At common meteor speeds, any material (with the exception of some sort of exotic, beyond-current-material-technology substance like neutronium, that could elastically “bounce” the remnants of a collided meteor with little loss of total kinetic energy), is ablative.

Originally Posted by Moontanman

Brute force isn't what will stop meteors. You use their own energy against them.

I don’t think you can use an impactor’s energy against it – even such mundane projectiles as armor piercing bullets and shells – which have maximum speeds of around 1000 m/s - are heated into a liquid and/or gas state on impact, yet are still effective penetrators.

Rather than attempting to armor a giant spacecraft, you could follow Bill’s advice about “just moving on with life [aboard a spacecraft]”, and make its skin as thin as structurally practical while providing adequate radiation shielding, accepting that an occasional meteor will cleanly penetrate it. Unless an inhabitant is unlucky enough to be in its path, or the designer or maintainer foolish enough to have a dusty, high-oxygen, explosive atmosphere, a layer of suitable dirt and glop should be able to quickly seal even a fairly large hole, making a meteor penetration a potentially loud and spectacular, but survivable, event.

I can’t do justice to the many good points raised in this thread in a single post, but want to just summarily comment on one:

Originally Posted by Moontanman

But the elements do occur there and with nuclear power huge amounts of metallic/rocky asteroids can be processed for everything in them.

Details aside, this is, IMHO, the most important observation concerning the making of space colonies. As Uncle Al describes, the many costs of lifting materials from Earth are likely prohibitive for building large spacecraft with such materials, so such construction necessarily must use what’s already floating freely in space.

I’d take it a step further, and suggest that it’ll also be necessary to use energy already freely available in space. By far, the most abundant energy source there is sunlight.

Though the details are … well … detailed, consider this “first, build a factory-making factory” scenario:

• A Earth-built spacecraft rendezvous with an asteroid..
• Using a large earth-built Fresnel lens, asteroid material is smelted into useful engineering material
• This material is fabricated into more Fresnel lenses, smelters, and fabricators.
• Repeat

Though the engineering challenges of such a scheme are great, it is not thwarted by a shortage of sunlight and asteroid material.

[Thunderbird]

What this comes down to simple economics. The amount of energy, time, and expense for such a venture would greatly out weigh any returns or benefits.

I do not see how this would be solving population problems for one thing. The amount of energy and resources to transport and keep one human in space would be in the millions annually.

You could build cites under, or on the sea cheaper.
You could mine resources from or own earth cheaper, we have no shortage of minerals.
You can distil sea water cheaper.
You could turn deserts into farmland cheaper.
You could turn technology eco friendly cheaper.
all of these alternatives combined would cost much less in resources to feed, house burgeoning populations in the far future than the cost it would take to maintain even a small city in space, not to mention the quality of life that would be enjoyed by an earthling , compared to a human living in the contained artificial environment.

I am sorry I just do not see this as a viable solution to anything. Unless it was financed in the a private sector for individuals who could afford the novelty of vacation in space. It would cost billions just to do it on a very small scale, but it could possibly expand from there. Keep in mind however the cost for a government agency provided by tax payers under the guise of the benefiting mankind's future will never be a option. It would only be a select few that would ever get to go, and would never make ethical sense for the common man to pay for it.

[UncleAl]

You are arguing flea farts in a hurricane. Matthew 7:4 "Or how can you say to your brother, 'Let me take the speck out of your eye,' and behold, the log is in your own eye."

If you need one truly huge launch/week for 600 years to orbit your whole thingie, it matters not what your thingie is. If you must commute to the asteroid belt, you won't. If you get it all hung together in place - no matter where and what it is - and it doesn't pay for its $quadrillion self, it isn't.

If you cannot solve the propulsion problem you have nothing in space. You cannot, you don't. 1960 to 1970 a handful of unrepentent Nazis - starting with a V-2, slide rules, and immigrant machinists - went to the moon big time for $135 million/pop. In 2008 NASA - with the Space Scuttle, 10240 processor Columba supercomputer, CAD/CAM/CNC machining - cannot get back to the moon with $1.5 billion launches. Do you comprehend the real world problems?

Building a skyscraper starting with its fifth floor is unrealistic. Design a 1000 tonne payload Earth to moon heavy lifter and we'll talk.

NASA HATE CRIMES, II

[Moontanman]

Originally Posted by UncleAl

You are arguing flea farts in a hurricane. Matthew 7:4 "Or how can you say to your brother, 'Let me take the speck out of your eye,' and behold, the log is in your own eye."

If you need one truly huge launch/week for 600 years to orbit your whole thingie, it matters not what your thingie is. If you must commute to the asteroid belt, you won't. If you get it all hung together in place - no matter where and what it is - and it doesn't pay for its self, it isn't.

If you cannot solve the propulsion problem you have nothing in space. You cannot, you don't. 1960 to 1970 a handful of unrepentent Nazis - starting with a V-2, slide rules, and immigrant machinists - went to the moon big time for $135 million/pop. In 2008 NASA - with the Space Scuttle, 10240 processor Columba supercomputer, CAD/CAM/CNC machining - cannot get back to the moon with $1.5 billion launches. Do you comprehend the real world problems?

Building a skyscraper starting with its fifth floor is unrealistic. Design a 1000 tonne payload Earth to moon heavy lifter and we'll talk.

NASA HATE CRIMES, II

1000 ton launch capability? No problem

http://nextbigfuture.com/2007/07/gas...n-liberty.html

Again you are assuming we would do this all at once with launches from the earth, only the barest and smallest part would come from the earth at the start. virtually all the materials and would come from space not the earth. as for paying for it's self did the first colonies to North America pay fro themselves? what if the queen of Spain had said the new world was too far away and to transport millions of people would not be practical in any sense of the word? it will be a slow process not a one shot deal.

[Moontanman]

A more complete article about nuclear light bulb rockets.

BRUCE BEHRHORST ARTICLE LIST

[Moontanman]

What this comes down to simple economics. The amount of energy, time, and expense for such a venture would greatly out weigh any returns or benefits.

Not true, simply spreading the human race out from the Earth has the priceless benefit of allowing the human race to survive a planetary disaster.

I do not see how this would be solving population problems for one thing. The amount of energy and resources to transport and keep one human in space would be in the millions annually.

Only if you assume the energy and resources had to come from the earth.

You could build cites under, or on the sea cheaper.

Who would want to live in a tin can under the sea?

You could mine resources from or own earth cheaper, we have no shortage of minerals.

While this can be debated why would you want to continue to destroy the environment to mine minerals on the Earth when the same minerals are available from space in much larger quantities and cheaper. it doesn't cost much to bring something to the Earth from space.

You can distil sea water cheaper.

What does this have to do with space colonization?

You could turn deserts into farmland cheaper.

Maybe, but there is only so much desert and turning it to farm land destroys the desert as a unique environment and desert cannot be farmed with out other environmental costs. Desert has been turned into toxic waste land many times when irrigation is used to grow crops. A bad idea almost always in the long run.

You could turn technology eco friendly cheaper.

No matter how Eco friendly technology is it still doesn't solve all the problems of pollution, mining, disaster, lack of space (too many people), war, poverty, the list goes on. Space colonies can be made as the population expands always staying ahead of the curve. If disaster strikes it cannot strike all the colonies at once but disaster can strike the whole earth at once.

all of these alternatives combined would cost much less in resources to feed, house burgeoning populations in the far future than the cost it would take to maintain even a small city in space, not to mention the quality of life that would be enjoyed by an earthling , compared to a human living in the contained artificial environment.

You still cannot get away from the idea these colonies would be somehow stifling tin cans. The inside would be like living in a glacier valley a couple miles across and several miles long. Lots of space both for people and nature. Eventually the Earth will be far more crowded than these colonies would be. as fro the cost of maintaining them, again I'll say the Earth will not support these colonies, they will support themselves from resources at hand not from resources brought from the earth. I can see thousands of colonies in the Lagrange orbits of Jupiter using the huge number of asteroids and ice chunks orbiting there. Once established these colonies can build their own copies of themselves from materials at hand and from personal at hand as well. No support from the earth will necessary in the long term.

anything. Unless it was financed in the a private sector for individuals who could afford the novelty of vacation in space. It would cost billions just to do it on a very small scale, but it could possibly expand from there. Keep in mind however the cost for a government agency provided by tax payers under the guise of the benefiting mankind's future will never be a option. It would only be a select few that would ever get to go, and would never make ethical seI am sorry I just do not see this as a viable solution to nse for the common man to pay for it.

You are still looking at this like it is some kind of short term venture financed by the Earth for all eternity. This will be the establishment of independent worlds with their own economy, governments, and reasons for living. Not a space station that has to be supplied from the earth and existing at the whims of the earth. Once the infrastructure of this space civilization is established it becomes self sustaining and separate from the earth.

[UncleAl]

Gaseous core nuclear design, the Liberty Ship

Remember the crapstorm over Cassini's Pu-238 thermoelectric generators? The world will not tolerate Florida becoming Chernoble, ditto all points downwind. Where do you do the second launch, either way?

Nuclear rocket propulsion! HA HA HA! Welcome to 1950. You got clever ways to shield it without adding mass? Nuclear airplanes, nuclear cars, nuclear tricycles! First, we kill all the engineers...

Why is better for people to die doing mundane matters as part of mundane lives than to risk dieing trying to achieve something audacious...

Everybody has something worth dying for. What have you got that is worth living for?

Chemical rockets are likely fancy balloons filled with fuel.

Uncle Al suggests you read a reference before posting it. Have you ever designed a rocket bell? They have different aspect ratios for in-atmosphere and out-of-atmosphere operation.

[Pyrotex]

MoontanMan vs. Uncle Al

The debate of the century!

Pass the popcorn! This is just fantastic!

GO AL!! GO MOOMAN!!

[Moontanman]

Originally Posted by UncleAl

Remember the crapstorm over Cassini's Pu-238 thermoelectric generators? The world will not tolerate Florida becoming Chernoble, ditto all points downwind. Where do you do the second launch, either way?

Nuclear rocket propulsion! HA HA HA! Welcome to 1950. You got clever ways to shield it without adding mass? Nuclear airplanes, nuclear cars, nuclear tricycles! First, we kill all the engineers...
Everybody has something worth dying for. What have you got that is worth living for?
Uncle Al suggests you read a reference before posting it. Have you ever designed a rocket bell? They have different aspect ratios for in-atmosphere and out-of-atmosphere operation.

UncleAL, I am very disappointed in you. You obviously didn't read the link at all. If you had you would have found the Nuclear Light Bulb rocket is not 1950's technology, it doesn't release any radioactivity in the exhaust and even in the event of total failure of the rocket it would not release but a tiny fraction of what we released with one old style weapons test. Not only that but they would only be launched from sea platforms far away from any land or cities. Read the two links I sent you throughly and then we'll talk

[Moontanman]

Make sure you visit this site and read all the pages UncleAl, 1-14. BRUCE BEHRHORST ARTICLE LIST