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Comment Re:How does space elevator save energy? (Score 1) 84

It's a lot more fundamental than that. Even with 120 GPa unobtanium they still can't support themselves over those sorts of distances - any cable has to have a large taper factor (the lower the breaking strength, the larger the taper factor is needed). Which makes moving cables impossible, because as soon as you rotate it, the taper is structured all wrong - it has to constantly be thickest at the top and thinnest at the bottom or it will break.

Comment Re:How does space elevator save energy? (Score 2) 84

Solar cells may produce - on a clear day - 200W/m^2, if they're sun-tracking and unshadowed. A climber climbing over the course of two weeks (more on that in just a second, you need to climb far faster) has to climb 35,5 meters per second. A small 1 tonne climber with 2 tonnes of cargo requires 1 megawatt of power, meaning 5000 square meters. Think you can fit 5000 square meters of sun-tracking solar cells on a climber that only weighs one tonne?

Speed is important because it defines throughput, and your cables - even if you have some mythical unobtanium 100-120 Gpa diamond filament tether - are still very massive objects with very tiny objects climbing them, meaning you need high throughput to make them economically justifiable.

I don't think most people discussing space elevators realize how tiny the margins on these things have to be even with a cable made of unobtanium. Inside the atmosphere is irrelevant. It's the tiniest fraction of your 43000 kilometer trip, you have no margin to make a special case for in-atmosphere propulsion. It's only relevant for the additional problems it causes your cable, such as wind, lightning, ice, oxidation, etc.

Space elevators really aren't a good design. They're just totally impractical even when made of unobtanium. But science fiction has locked a generation onto this concept when there are far better concepts available.

Comment Re: But (Score 1) 84

Aww, my stalker is back! Hi, stalker!

Don't you have some nutters over at the USGS to argue with? Damned USGS and their pie-in-the-sky analysis that is pretty much exactly what I wrote a couple weeks ago concerning resource availability and work/uncertainties that remain to be resolved! Given that this is what led you to start stalking me, you might want to split your time with stalking them too.

Comment Re:How does space elevator save energy? (Score 1) 84

No, I mean $18k. From your link:

by 2011, the incremental cost per flight of the Space Shuttle was estimated at $450 million,[3] or $18,000 per kilogram (approximately $8,000 per pound) to low Earth orbit (LEO).

The $60k is when you include the cost of the whole program (including the design/development phase) which no figure in my post included. If you want to compare, you need to compare equivalent situations: the incremental cost per launch. And the incremental cost per launch of the Shuttle was an estimated $18k/kg.

Comment Re: The treaty says no such thing. (Score 1) 191

No need to "wipe a small country off the map". Take any of the countless areas on Earth with low populations of ideally nomadic people and offer them a nice chunk of money if they'll be willing to, every few years with long advance warning, move out of the impact zone along with their livestock. Or simply pick an area with no people at all. Greenland would love some extra income, they're big into encouraging mining and have vast glacial landscapes which would be easy to find your impactors on (it'd have no relevant impact on the rate of melt, and meteor-hunting expeditions are often done in Antarctica because they stand out so well against the snow). Shallow seas might be a good option. Salars would be great - generally little to nothing lives there and they're naturally resurfaced annually, so the impactors wouldn't leave a scar. It all depends on how accurate you can be with your impactors.

As for the environment, when you're talking about vaporized rock ablating in the air and plumes of dust being kicked up on impact... it's really not going to be anything compared to what, say, volcanoes do, or wind erosion. Really, I'd expect less environmental impact than a normal terrestrial mine. You could probably even sell your tailings to people who want to build things out of rock from space ;)

Comment Re:The treaty says no such thing. (Score 1) 191

You don't have to pre-enrich it to those extremes. With a delta-V requirement of only dozens of meters per second, your cost to lob either single-stage concentrated ore, or even raw ore, back to Earth... hmm, let's do some calculations.

Solar panels for space usage are generally cited at 300W/kg (although with a large fixed installation one could probably do a lot better with concentrated solar or nuclear... and there's a lot of room for improvement on that 300 figure.. but let's go with it). 1kg to a NEO surface probably costs around $20k. So about $67 per watt. Let's go with a required delta-V of 50m/s. A coilgun shooting sintered ore would require 0,35 watt hours/kg at 100% efficiency... let's say 0,5 for losses. So $33 pays for 1kg return per hour. Let's say that of every kg you send to Earth 90% reaches the surface and is recovered (the rest ablating on reentry or being lost at the recovery site), so $37/kg. Let's assume that we only want to recover precious metals (even though nickel is worth about $10/kg, for example, and there's lots of other stuff worthwhile), and let's assume that the average precious metal price is $20k/kg (2/3rds the value of gold). If you only got a single hour's worth of returns out of it, you would only need to have refined your precious metal concentration of 0,5% to justify your costs to send it to Earth. From a single hour's worth of returns. If you got 20 years out of it, then your cost per kg to send to Earth (from the power perspective alone) is $0.0002/kg, and 200ppm ore at $20k/kg precious metal would pay for itself 19000x over.

This is why people complaining about the energy required to send things to Earth are not even close to having a valid complaint. It's a non-issue. Getting things to an asteroid is hard, but getting bulk material sent back is easy. It doesn't have to be concentrated. Heck, rather than the energy to send it back one should be more concerned with the energy to mine and sinter it into large shaped blocks for return, that's much more significant (probably in the ballpark of 0,1 to 5kWh per kg, depending on the methods employed - hundreds to thousands of times more than the energy cost to launch it back to Earth). And of course the capital costs to get your hardware sent there - your mining equipment, your coilgun or other launch method (heck, even a torsion catapult would work ;) ) sent there, etc and keep it operational. And the vast amounts of prep work that would need to be done to convince investors that the technology is ready. But that said, the economic potential is huge.

Note that if one felt some reason to concentrate ore (probably not economically justifiable), there's lots of relatively easy "first stage" concentration methods available that can eliminate a large chunk of the bulk.

In general, for asteroid mining, even if your capital costs are 1-2 orders of magnitude more per unit throughput, it's probably a solid economic decision. 3 orders of magnitude, maybe. 4 or more orders of magnitude, probably not. Now it's easy to be pessimistic about people's ability to make and launch lightweight, microgravity-and-vacuum tolerant mining hardware, even for a couple orders of magnitude more money. But I personally would not put so much doubt in engineers' ability to do that sort of job. It's not going to happen tomorrow. Or next year. Or next decade. But in decades after that, it's certainly possible.

Comment Re: The treaty says no such thing. (Score 1) 191

I don't get your argument. How is saying "I'm not going to take it from you" equivalent to "I hereby claim an asteroid in the name of the United States"? So do you think that the US government is required by the treaty to confiscate the material? Or if not, that some other entity is?

I don't get your line of argument. If a private entity mines an asteroid - the very using of space for the benefit of mankind repeatedly discussed as being beneficial in the OST - then what exactly do you think should happen to it? How should the government treat that material when it returns to Earth? Because everything is in the ownership of someone, whether private or governmental - the law doesn't account for things that no entity has a right or responsibility to.

And anyway: even if the government declared a right to confiscate (rather than an obligation to *not confiscate*) goods returned by private mining - in what way would the claimed right to confiscate the goods be a claim to confiscate the mine? If the US government confiscated a couple tonnes of copper would that be the same as the US government confiscating a copper mine? Of course not, one is the production facility, the other is a product.

Comment Re:How does space elevator save energy? (Score 5, Informative) 84

Your post is simply incorrect.

1) Rockets are not "quite inefficient". Their Carnot efficiency is usually 80%, net propulsive efficiency around 70% - way better than a gasoline engine (~35%) or diesel engine (40-45%). What they suffer from is totally different: the rocket equation. This mandates exponentially increasing fuel needs to reach a given delta-V, with the exponent proportional to the ISP. But fuel costs have nothing to do with how expensive today's rockets are, we're nowhere near that limit. The Space Shuttle consumed about $2m of propellant to deliver 25 tonnes to LEO, or $80/kg. Using electricity at 100% efficiency and $0,80/kWh it would cost about $0,80/kg to reach orbit. Today's launch costs are about $5k-10k/kg for large launches (the Shuttle was said to be about $18k). So you can see that the fuel costs are just the tiniest fraction, and that it's the engineering challenges of cost-effective production and reuse that are the issue.

2) The "keeping power beaming losses reasonable" is the problem the parent was describing. There is no known way to efficiently transfer power to a small object over tens of thousands of kilometers. Direct transmission isn't even close with conventional conductors, a superconducting line would be many orders of magnitude too heavy, and the cable itself would not be a superconductor, and even if it were its cross section would be way too low. Batteries don't cut it in terms of energy density. And the requirements that climbers be very light precludes nuclear except for the most unrealistically-massive of space elevators. To make RF power beaming remotely efficient over such distances requires a receiving antenna taking up dozens of square kilometers. Laser power beaming means receiving end (solar cell) losses (which even if the solar cells are tuned to a particular frequency you're unlikely to do better than maybe 30-40%) and laser losses (high power lasers are generally in the ballpark of 0,1% efficient; diode lasers can reach up to 25% or so but have far too poor beam quality and are way too weak to be practical). And of course you need a frequency that minimizes atmospheric losses at that.

Perhaps some day power transmission over those distances might become practical, but today it isn't.

This is just the very start of the problems with space elevators, of course. I know space elevators make great books, but they're not practical in the real world. Look into actively suspended structures for your "direct climb to space" needs. They're buildable with today's materials and can get greater than 50% efficiency in energy transfer.

Comment Re: But (Score 5, Informative) 84

From the perspective of a space elevator, it's not. Read this paper linked from the article. There's no talk of space elevators, that's just their way to entice the reader into listening to them.

That is to say, the space elevator mention is just clickbait.

As the paper notes, "experimentally measured tensile Young's modulus for SWNTs ranges from 320 GPa to 1.47 TPa with the breaking strengths ranging from 13 to 52 GPa". A material with the density of SWNTs is generally considered to need at least 100-120 GPa irreversible yield strength (less than breaking strength) to make a "practical" elevator (although if you read those proposals it's hard to come across with any conclusion other than that they're being way too optimistic even with those numbers). Note: 13-52 GPa for individual tubes. Ropes of multiple tubes are 1-2 orders of magnitude weaker.

So what about these diamond nanothreads?

The yield strength experienced more than 25% reduction (from ~ 75 GPa to ~ 56 GPa) for the DNT-14 when the sample length increases from ~ 13 nm to 26 nm. Afterward, it fluctuates around 56 GPa. Unlike the yield strain, the yield strength for all considered DNTs saturates to a similar value (around 56 GPa) and exhibits a relation irrelevant with the constituent units for the investigated length scope (fro ~13 - 92 nm)

  Their data is pretty consistent, with graphs showing a clear dropoff and stabilization around 56 GPa. Obviously nm-sized fibers are pretty worthless for the purposes of an elevator, there'd be way too little Van der Walls holding them together into a rope.

Now, these are just simulations. But more often than not real world seems to underperform simulations rather than overperform, so I wouldn't get too optimistic about the real-world greatly exceeding these figures. For example, early simulations of SWNTs said they'd be around 120GPa; few believe nowadays that they can even approach those figures.

But what about the density side of the equation? After all, a material can be weaker, but if it's correspondingly lighter, then that's not a problem. The density is not in the paper, but this cites the tenacity (breaking strength over mass) as 4.1e10^7 N-m/kg. While the yield strength is going to be a bit less than the breaking strength, it shouldn't be too far off - this means that the density should be somewhere less than - but not too much less than - 1,37g/cm^3. That's on the same order as SWNTs, unfortunately.

Short answer? We're still nowhere even remotely close to being even capable of making a space elevator.

Space elevators face such numerous problems anyway (really don't want to have to go into them all) that they're really not a fruitful avenue of pursuit. We'd do far better to direct such efforts to more realistic access methods, such as a Lofstrom loop or variant thereof, which requires no unobtanium and is far more efficient (space elevators lose huge amounts of energy to transmission losses, throwing away a large chunk of the advantage that they gain from bypassing the rocket equation). Active suspension via recirculating kinetic transfer, by one means or another, is something we can do today.

Comment Re: The treaty says no such thing. (Score 1) 191

National ownership and private ownership are two entirely different things. The US has no right to grant or deny access to an asteroid, under the Outer Space Treaty. But once there's property in question within the United States (having been returned to the surface), ownership of that property is a key issue that needs to be decided by law. The US has made clear that it considers that the private property of the company in question. This is in no way "national appropriation by claim of sovereignty" to the asteroid. It's just saying, "Yup, you mined it, you own it, we're not going to confiscate it or anything of the sort"

Comment Re:The treaty says no such thing. (Score 1) 191

First, the UK was trying to encroach on waters already owned; no such ownership claim exists to objects in space.

It's not that simple. In each case Iceland was pushing the boundaries of law on ownership of seas. Remember, there was a time where there was no such thing as coastal waters, and then later when there was no concept of an EEZ. In fact, Iceland was the first country to lay claim to an EEZ for fishing (Britain cried foul, but they helped pioneer the concept by laying claim to ocean-bottom mineral resources a couple years earlier in a different kind of EEZ). Now every coastal state has an EEZ, but back then it was a new concept.

For your other two points I think I may have lost the thread here. Or maybe you did. Either way, my point was that larger states can't always successfully bully smaller states by military might in today's international world. I don't see why that wouldn't apply to space as well.

Comment Re:The treaty says no such thing. (Score 2) 191

. So far as we know the bulk of that material is stuff that's easy to get here on Earth: silicates, sulfides, iron, nickel etc. Judging from meteors found here on Earth there are exotic materials like iridium, but in trace quantities.

Not at all. In a similar thread I linked to a USGS study on the prospects of space mining that showed that for an entire class of asteroids the average precious metals concentration is 28 ppm, with findings as high as 200ppm. In bulk, not concentrates, no overburden. I mean, that's insanely rich deposits. The richest gold mine on Earth is something like 40ppm - with lots of overburden. Most are 1-2 orders of magnitude less rich than that.

The problem with Earth is that most of the precious metals in the planet have sunk into the depths, with the crust mostly containing only that which has been deposited by later bombardments. But asteroids (with the possible exception of large ones like Ceres) are undifferentiated. Look at 16 Psyche, for example - it makes up 1% of the total mass of the asteroid belt and it's an estimated 90% metal. Ever seen anything like that occurring naturally on Earth? ;) Now Psyche itself wouldn't be an ideal target, it's a main belt asteroid, but still, it drives home how much these objects are not like Earth.

The platinum deposits in Canada's Sudbury Basin were delivered by a meteor

I think you're mixing things up. Sudbury is mainly mined for nickel - the platinum is recovered as a secondary product and is not the prime mining target (while not precious, nickel is a rather valuable mineral (nearly twice as valuable as copper), and Sudbury is one of the world's best deposits). And its minerals, while the result of a meteor strike, didn't come from the meteor itself. The meteor (now believed more likely to have been a comet than an asteroid) overwhelmingly converted to vapor and plasma and was blasted into the upper atmosphere and circulated around the Earth. The giant "wound" however, penetrated all the way down to the mantle, which bulged up and diffused with a giant pool of liquified rock and let to melt differentiation mineralization processes, creating areas of very rich deposits. The key issue is that overwhelmingly the minerals at Sudbury are believed to be terrestrial-sourced igneous deposit, even though the concentrations were caused by an impact.

Comment Re: The treaty says no such thing. (Score 1) 191

You know, you post as AC but it's really obvious who you are, you have the same writing style everywhere you post ;)

Anyway, here's what the treaty actually says:

Outer space, including the moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means.

Any questions?

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