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  #51  
Old 11-05-2019, 10:41 PM
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I'm aware of who Belters are in SF. I was asking who they were in the real world. The answer is they don't exist and will probably never exist.
"If a senior scientist says something is impossible, they're probably wrong."
--One of AE Clarke's Laws.

The OP assumed the existence of technologies to push asteroids around and robotically mine them. I figured the existence of such technologies implies changed human societies, so why not use the Niven model? It's essentially economic: what's profitable will happen.

No, Belters don't yet exist, and neither do fusion drives. I'll not bet against either.
  #52  
Old 11-06-2019, 12:32 AM
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The question is - what would you find on the moon that is profitable, if you were to mine it? Water (and so Hydrogen and oxygen) would be of high value - once we have regular spaceflight beyond earth orbit and habitats. Metals? You'd have to find a serious motherlode of some very rare mineral to compete with Earth-based mining. Refining gold, right now, uses a lot of water (grind and pan on giant shake tables before smelting). While I don't doubt the process could be automated and run remotely, presumably the same sort of tech might work to process the deep layers of silt in many terrestrial rivers where there were gold finds in the Good Old Days - and a lot cheaper. And... the trick is finding the motherlodes on the moon. Here we map the general geological strata often from samples and seismic blasts, then drill the interesting bits to get a 3-d map then more intensively where we think there is something. The last stage is usually enhanced by a rush of small prospectors staking out claims to hope theirs pays off a jackpot. The process and much of the geology would be far different on the moon.

And Rico has the best point - the energy to get an asteroid to even lunar orbit would dwarf the cost of dropping chunks of it onto the Utah salt flats or Death Valley. I'll go even farther and say that the cost of prospecting the thousands of candidate asteroids to find the right one is even more daunting than prospecting the moon. A more logical process might be to mine the asteroid where it sits and only send the final product home, if it's all going to be automated anyway.

If I wasn't lazy and had more time, I'd calculate the amount of energy - in hydrogen-oxygen reaction presumably used as rocket fuel - to move 10 tons, say, of nickel from some earth approaching asteroid to low earth orbit; and how many tons of water that takes - and where we could get that sort of fuel (assuming solar power to separate the two gases). Instead I leave this as an exercise to the reader. I suspect that the cost of finding and providing that much reaction mass will make the material too expensive. What does a gallon of water in orbit cost?

(Which leads me to my next brainwave - solve the problem of propellant gas storage by storing it as frozen water, and electrolyze why you need with giant solar power panels as close to using it as is feasible. Less likely to have it all leak away, and no need for extremely large pressure vessels or thermos bottles.)
  #53  
Old 11-06-2019, 12:45 AM
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I'm reminded of Heinlein's The Moon Is A Harsh Mistress. Which is also the name of a very nice song Jimmy Webb wrote.
  #54  
Old 11-06-2019, 01:36 PM
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Originally Posted by Tim@T-Bonham.net View Post
I expect that the cost of the parachutes is less than the value of the metal that would be burned up without one. If so, the parachutes are a good investment.
Sigh.

DO you really, *REALLY* think that a parachute will help prevent part of the metal from burning up?
  #55  
Old 11-06-2019, 04:25 PM
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Right, the parachute can only be deployed once the big burning phase is over. Look at old Apollo films and such. Big hot ride until it slows down. Then pop the chute. Pop it earlier and the chute burns.

A chute is good for making sure the pod doesn't go too deep into the ground on impact. It also allows better visual tracking if the radio goes dead. And the chute itself might be easier to spot after landing.
  #56  
Old 11-07-2019, 12:29 AM
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Right, the parachute can only be deployed once the big burning phase is over. Look at old Apollo films and such. Big hot ride until it slows down. Then pop the chute. Pop it earlier and the chute burns.

A chute is good for making sure the pod doesn't go too deep into the ground on impact. It also allows better visual tracking if the radio goes dead. And the chute itself might be easier to spot after landing.
Yes, terminal velocity (air resistance = force of gravity) is usually unacceptably high for most dense objects like people and spacecraft, even at sea level atmospheric pressure. A parachute just raises the air resistance to a much higher level. Even so, the Soyuz, which landed on ground rather than water, still uses retro-rockets at the last minute to reduce the impact shock. One rule of thumb I recall from decades ago was that a typical parachute was usually the equivalent of a ten-foot drop; something easily survivable but risky if you did not prepare for impact.
  #57  
Old 11-07-2019, 01:39 AM
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I'm reminded of Heinlein's The Moon Is A Harsh Mistress.
Ditto. But let's not ignore MISTRESS' fantasy factor. Unless launching to Luna is REAL cheap, sending political prisoners there won't happen. An Antarctic penal colony to farm with available H2O would be much more cost-effective. Or just shoot the troublemakers. But spending lots of resources to exile and guard malcontents who grow a few tonnes of grain to catapult Earthward? Right.

IIRC Niven's Belters didn't ship asteroids to Terra. Don't expect future IRL humans to do so, either. What will be worth soft-landing from orbit to the bottom of Terra's gravity well? Not heavy stuff (except maybe captured quantum black holes). People and other lifeforms. Drugs and materials grown in zero- or micro-gravity. What else?
  #58  
Old 11-07-2019, 08:35 AM
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Part of the point of The Moon is a Harsh Mistress was that the system was horribly inefficient. Something doesn't need to be efficient or a good idea for people to do it. You just need a few important people who think it's a good idea.
  #59  
Old 11-07-2019, 09:02 AM
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...IIRC Niven's Belters didn't ship asteroids to Terra. Don't expect future IRL humans to do so, either. What will be worth soft-landing from orbit to the bottom of Terra's gravity well? Not heavy stuff (except maybe captured quantum black holes). People and other lifeforms. Drugs and materials grown in zero- or micro-gravity. What else?
Power, assuming solar power satellites ever become economical. Information, in the form of a persistent surveillance net. (Assuming a mirror factory in space, with sufficient material and energy inputs, what size mirrors can be made?) Turn them the other way, and what new discoveries in astronomy might we find? Or increasing the potential warning time for a significant Earth-impacting body. As well as having, already in orbit, means for adjusting its orbit to miss us.

One thing the Moon provides is isolation for things that might go 'BANG!' E.g., automated antimatter factories. Or experiments with anything we'd just as soon not allow anywhere near Earth's biosphere.
  #60  
Old 11-07-2019, 09:29 AM
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Well, I'm not sure what your argument is for Antarctica, either If it's that it's pristine and should be left that way, why would you extend that to the moon? The moon is a lifeless rock. There's nothing we could feasibly do to it that could be seen from Earth. There are no habitats to destroy.
Surprisingly, this statement is rather significantly wrong.

Today, we are nowhere close to be able to remotely afford to exploit the Moon for anything. Even if you take SpaceX's best projections as true, payload to the lunar surface will still be hundreds of dollars per kilogram. (say $100 a kilogram for orbiting payload for a SpaceX heavy lift rocket launch, then a 6:1 fuel : payload ratio for a lunar landing, also a translunar injection burn). Almost certainly at least $1000 a kg.

You aren't mining profitably with that if the equipment costs too much to haul it over.

So you need factories on the Moon, a really small and light factory that can "bootstrap", where it manufacturers all the rest of the industrial equipment needed.

It's gonna need to be pretty automated, astronauts don't get much done in balloon suits in a radiation field. Plus, why send astronauts, just run it remotely.

If the factory on the Moon is automated and can make more of itself...

Basically, I predict a whole lotta nothing - maybe decades worth, maybe centuries, then a tiny dot of light lands on the Moon. Then, in almost real time, you see an albedo change of a patch of the Lunar surface expanding to cover it all.

Last edited by SamuelA; 11-07-2019 at 09:30 AM.
  #61  
Old 11-07-2019, 09:58 AM
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Eh, if we really tried, we could probably put a recognizable soft drink logo on the surface of the Moon.
  #62  
Old 11-24-2019, 09:41 PM
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Missing some zeroes there. Like 3.
No, 7000 per month is correct. The post is in response to 500 ton capacity being available on current SpaceEx vehicles returning.

https://tradingeconomics.com/united-...eel-production
  #63  
Old 11-24-2019, 09:49 PM
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Edit, the point is, if certain minerals are more readily found in their pure states in space, being restricted to 50 tons at a time may not be a dealbreaker.
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The stuff we might bring back to Earth has to be very valuable. Gold, Platinum, other extremely rare elemenfs. We only produce 2500 tons per year or so worldwide. That 500 starship loads per year.
The problem is the overhead cost of mining in space. Millions of tons would be needed to cover the costs of operations to make the price of space minerals comparable to what's available on earth.
  #64  
Old 11-25-2019, 03:05 PM
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Eh, if we really tried, we could probably put a recognizable soft drink logo on the surface of the Moon.
Only a Moke is truly a Coke.

Let me rephrase - there is nothing we could do on the moon in the course of normal industrial activities that could be seen with the naked eye from Earth.

The unaided eye, in perfect conditions, can resolve objects about 200 km across at the Moon's distance. We can see smaller craters like Aristarchus because they are extremely bright, so we see them as bright points.

That's a pretty good example, actually. Aristarchus dwarfs the largest open pit mine on Earth. The Bingham Canyon copper mine is 1.5 kilometers deep and four kilometers wide. Aristarchus is 4 kilometers deep and 40 kilometers wide - ten times larger - and we can only see it as a bright point because the material it excavated is bright anorthosite.

So until we can build something on the moon ten times bigger than the biggest open mine on Earth, you won't be able to see it. Even a large city on the moon wouldn't be resolvable from Earth with the naked eye. Even high resolution images with my 8" scope can only resolve down to about half a kilometer in perfect conditions. The Hubble could resolve 80m objects, but we don't use Hubble to look at the Moon.

You could detonate an H-bomb on the Moon, and we wouldn't be able to see the crater.

Heinlein's idea of using rockets to launch reflective material to intentionally create a logo visible from Earth is not really feasible. You would have to lay material down over tens of thousands of square kilometers. Given how rough the surface of the moon is, you'd have to lay down a pretty thick layer.

Just for fun, I did some math. Let's say we used something very light and very bright, like talcum powder. Talcum powder weighs 2.76g per cubic centimeter. So let's say we lay it down a centimeter thick. So a square meter would weigh 2.76 kg.

Let's say we wanted to draw a logo on Mare Serenitatis (the left eye of the 'Man on the Moon'). Let's further suppose that the logo fills 10% of the area of the Mare. The Mare's area is roughly 350,000 square kilometers, so we would need 35,000 square kilometers of talc, 1 cm thick.

It turns out that we would need 2.76 million kg of talc for each square kilometer of fill, so to put our logo in the Sea of Serenity would require 96.6 billion kg of talc. And that would be just on the threshold of visibility. The Sea of Serenity itself is only resolvable as a tiny dark circle. Most people would never even notice the logo, it would take perfect vision and a clear night to be able to see it at all.

If all goes according to plan, the SpaceX Starship will be able to land 100 tonnes of material on the moon. So our little logo would require 966,000 Starship flights.

As I said, we are in no danger of despoiling the way the moon looks from Earth.
  #65  
Old 11-25-2019, 03:58 PM
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The problem is the overhead cost of mining in space. Millions of tons would be needed to cover the costs of operations to make the price of space minerals comparable to what's available on earth.
This is only true if all the stuff that's mined is being brought back to Earth. But what about the case where almost everything mined (water, carbon, iron, aluminum, etc.) is being used in space and a relatively small amount of stuff that can't be used up there comes out as a byproduct or for very little additional cost. It might be worthwhile to bring some of that byproduct (e.g. platinum or perhaps some rare earth elements such as neodymium) back if it can be done cheaply enough.

However, not gold. For that, you just store it in an "orbital vault" and sell pieces of paper giving ownership to a certain amount of space-gold. It wouldn't be all that different than how a lot of gold is owned right now.
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Old 11-25-2019, 04:01 PM
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A centimeter is much, much thicker than you'd need. You could probably make something visible with a layer a few microns thick.
  #67  
Old 11-25-2019, 04:24 PM
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A centimeter is much, much thicker than you'd need. You could probably make something visible with a layer a few microns thick.
I think we'll have to disagree. The lunar regolith is pretty coarse in places. But even if it were only 1/100 of a cm thick you'd still need almost 10,000 starship flights just to deliver the material.

Of course, what you'd probably do is make the the stuff on the moon out of titanium oxide, which is bright white, and titanium and oxygen are both abundant on the Moon.

But still, the point remains that it would take a herculean effort to make something on the Moon that could be seen from Earth, and that's if you specifically went out of your way to make such a thing.

Normal industrial activities at almost any scale we can currently imagine would not be visible from Earth. Roads would not be visible. Mines would not be visible. Giant solar installations would mot be visible. Huge telescopes would not be visible. The moon will look essentially unchanging from Earth regardless of whether we 'exploit' it or not.

Hell, even with billions people industrializing Earth for hundreds of years, human activity is not visible from the Moon with the unaided eye.

Last edited by Sam Stone; 11-25-2019 at 04:26 PM.
  #68  
Old 11-25-2019, 10:43 PM
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I opened this thread because I thought it was going to be about alien police that confiscated something. Sorry to barge in.
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  #69  
Old 11-26-2019, 08:30 AM
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The cheapest way to bring something from Low Earth Orbit to Earth is to use a ballistic entry. Dissipating several kilometers per second velocity with atmospheric friction costs almost nothing.

In regards to the costs of materials, we are approaching a time when we will have to choose between destroying our habitat and enjoying the fruits of technology. Copper is essential to electronics, but is becoming more and more difficult to extract, due to environmental concerns. Butte, Montana in the U.S.A, is a good example of what mining can do to a area. The proposed Bristol Bay mine in Alaska could destroy a major salmon run.
  #70  
Old 11-26-2019, 04:45 PM
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In regards to the costs of materials, we are approaching a time when we will have to choose between destroying our habitat and enjoying the fruits of technology.
Given those two options, I think I'd choose enjoying the fruits of technology. Rather cake-or-death, that one.
  #71  
Old 11-26-2019, 05:19 PM
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In regards to the costs of materials, we are approaching a time when we will have to choose between destroying our habitat and enjoying the fruits of technology. Copper is essential to electronics, but is becoming more and more difficult to extract, due to environmental concerns. Butte, Montana in the U.S.A, is a good example of what mining can do to a area. The proposed Bristol Bay mine in Alaska could destroy a major salmon run.
Even years ago, the largest copper 'mine' in America was ... the Bell System. Every truck had a recycling box in the back, where the workers threw excess lengths of copper wire, and every central office had a similar recycling container. Overall, these recycling efforts produced more copper than any mine in the country.

So that is what can be done in recycling. Similarly, aluminum is one of the most valuable materials in the recycling stream. Many programs have problems with people stealing the aluminum cans. And this recycling saves energy twice, since refining raw aluminum is very electricity-intensive.

So it is possible to have both. it will take increased recycling efforts, and more attention to the entire lifecycle of products that are used, but it seems qithin reach.
  #72  
Old 11-27-2019, 10:42 AM
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Yes - the same point came up with electric cars. Sooner or later (later, I hope) the batteries in electric cars will no longer be serviceable. But - unlike the carbon in regular cars, the cobalt, nickel, lithium etc. are still all there and ready to be recovered.

In fact, recovering metal - usually copper - from old buildings, often unsanctioned, is another large source of recycling. (The plumber who helped put in my college's student darkroom in the basement of a 1900's house was a volunteer, but happy to accept as payment the 18 inches of thick 4-inch lead drainpipe he recovered doing the job.)

But tech changes things and resources are lessening in demand. I imagine the house of the future where, thanks to LED lights and low-power electronics, only the kitchen and bathroom plugs and the major appliances need 15-amp circuits and everything else is wired with much lower power (a house full of USB-C plugs?) using one quarter the copper, for example.

(I think Heinlein had in mind the 7Up logo when he wrote that, he was pointing out to -I imagine - Coca Cola the difference in logo size and readability across the moon. The idea was to use something highly reflective rather than a full coat of paint. the moon is actually dark gray, and with the full moon we are almost in line with the sun, a bright reflective layer much like safety equipment material does not have to be anywhere near a complete coating to stand out.)
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