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## Comment Re: But (Score 1)130

Science works by peer-review. There's ample peer-review on the topic. If the word "nutter" has any meaning, it's "people who refuse to accept peer-reviewed science."

And obsessing over past interactions with people and following them around (including mentioning them in places where they're not even involved in the conversation) is otherwise known as cyberstalking

## Comment Re:How does space elevator save energy? (Score 1)130

Talking about "energy costs" shows rank amateurism when talking about space flight. Virtually the entire cost is the flight hardware and ground support infrastructure. Energy costs aren't even rounding error on those.

Wow, it's almost as if my original post didn't read:

. 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.

## Comment Re:How does space elevator save energy? (Score 1)130

And you plan to propose a rotating cable that somehow maintains its original taper as it rotates how, exactly? As soon as you start rotating it, the thick part will begin moving downward and the thin part upwards. At the bottom of its rotation it's precisely the inverse of what you need.

## Comment Re:How does space elevator save energy? (Score 1)130

What do you mean "you were using"? Gravitational potential energy at Earth at sea level is 9,81 * ChangeInAltitude * mass. 35,5 m/s * 9,81 * 20000 = 7MJ/s = 7MW. If you "were using" 2,4MW then you were only climbing at 12,2m/s meaning your entire trip takes 41 days - over a month. Which means that your elevator has laughably worthless throughput. And 20k kg climber requires a massive elevator massing millions of tonnes *with* unobtanium. So you're proposing to launch millions of tonnes of unobtanium to GEO in order to send a fraction of 20tonnes up once every 41 days? Good luck with that.

You could expect 60% efficiency

That's exceedingly optimistic even for monochromatic light (which I see we're back to discussing). Have you ever priced the sort of Spectrolab cells you're proposing here? And anyway the highest monochromatic conversion rate ever recorded - lab scale - was 53%.

Remember that PV efficiency goes up as the light gets brighter

Only when you can keep the cells cooled to the same ambient temperature (and it's only a relatively small gain). How exactly do you propose to ditch megawatts of waste heat up there? Heat is a killer to solar cell efficiency. And several megawatts shining on a relatively small area is otherwise known as "vaporizing it".

No comments about the 0,1%-ish efficiency of the sorts of lasers that actually have the coherency and power to beam over such distances, I see. Even over the distances of your "in-orbit" lasers, of which apparently you want there to be hundreds of thousands if you want to ensure that there's one close to the tower at all altitudes at all points in time. Hundreds of thousands of multi-megawatt lasers each consuming a gigawatt or so of power. In order to launch a fraction of 20 tonnes to GEO once every 41 days. Great strategy.

Economically the construction cost will be huge, but once you have one you can build more relatively cheaply because it costs very little to get mass into orbit.

There is nothing "cheap" about what you're proposing. Your capital costs are nonsensically high, and you have to pay interest on capital costs if you want to live in the real world, and interest accrues interest. You will never, ever reach an economically valid argument for it. And for what gain? If you're turning \$0,08/kWh industrial-rate grid electricity into climbing power at 0,05% efficiency then you're paying \$160/kg to get to orbit, several times the price to orbit of what's possible with a rocket if it can be made reusable with minimal turnaround costs between flights (as mentioned earlier, the Shuttle's propellant cost to orbit was only \$80/kg, most of that in the SRBs, which aren't the cheapest of propellants). And of course it's not even close to a Lofstrom loop, which can be made without unobtanium and deliver payloads at an energy cost to orbit of about \$1,60/kg, with present tech.

Speed isn't a huge problem if your cable can support multiple climbers.

So you want to make your cable even bigger, heavier, and more expensive. How many times more expensive do you want to make it? 5 times? 10 times? 100 times? Why not just say that your cable is going to be the mass of the moon's worth of unobtanium while you're at it?

And again, we're only talking about the most basic of problems with space elevators here, let alone actually getting into the countless engineering problems, some of which have no known solutions, and none of which you really have a mass safety margin to properly address. The resonance issues are some of my favorite ones: from the climbers, from the atmosphere, from the sun and from the moon. You have a giant cable which has basically zero ability to damp itself, and no mass leeway to install any sort of damping system of the sort of magnitude needed to counter oscillations. On top of the fact that even made of unobtanium it's an ultrathin structure that can barely support itself and has to be able to withstand hypersonic impacts of microscopic debris and long-term exposure to the Van Allen belts at the time time, while in the atmosphere it's going to face wind loading (they call it a ribbon for a reason, and ribbons *blow*), potentially many times higher than that of climbers, potential icing, certain wetting, lighting (which even if the cable itself isn't conductive, the water on it will make for an easier ground path than the air), upper atmospheric (sprite) lightning as well, oxidation (no mass margin for protective coatings), and on and on down the line.

The space elevator concept needs to be consigned to the dustbin. It was a neat thought experiment for a while until the real-world hit. And now we have actually potentially workable structures (the actively suspended ones) that supercede it in every measure, so there's no point to it.

## Comment Re:How does space elevator save energy? (Score 1)130

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)130

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)130

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)130

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)203

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)203

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)203

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)130

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)130

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.

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)203

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"

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