Please create an account to participate in the Slashdot moderation system


Forgot your password?
Slashdot Deals: Cyber Monday Sale! Courses ranging from coding to project management - all eLearning deals 25% off with coupon code "CYBERMONDAY25". ×

Comment Re: The treaty says no such thing. (Score 1) 176

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 1) 35

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 1) 35

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:Punishing people who get degrees we need the mo (Score 1) 172

Unfortunately, the current social sciences at U.S. Universities is more likely to turn out a 26 year-old government social worker who thinks all parents are idiots who need her detailed supervision and spends her free time in "safe spaces" demonstrating for vague left-wing causes in the hopes of finding an enlightened boyfriend who'll stay longer than one night.

If instead, it were to actually "teach people critical thinking, how to argue and write persuasively." and produce "well-rounded individuals who can go on to be successful in a number of fields.", then the ISA market will value that future success and ability to repay in the future appropriately.

Comment Re:Trees and powerlines? (Score 1) 162

Not counting your airport problem, it's quite possible that properties like yours will simply be on the "Sorry, we can't deliver to your address by this mechanism" list. That's going to be true of millions and millions of residences. Probably MOST residences. This will be more useful for exurbs, and for deliveries to places like corporate office parks, hospitals, or other spots that might need rush deliveries and have more reliably plausible LZs. Logistics are likely to be case by case.

Comment Re:Americans...why ? (Score 1) 162

Because drones flying over your house are an invasion of privacy

Actually no, no they're not. You might have an argument if the machine is being operated literally feet above your house, or below your treetops. But traversing the airspace above your house isn't any more invasion of your property than is driving by it with a car. Do you feel that your privacy is being invaded when a traffic reporting Cessna flies over? No? Why not? Be specific.

Comment Re:Americans...why ? (Score 1) 162

Why do Americans want to shoot anything/everything ?

No, the question is why does everyone else feel the need to keep that meme alive? Is it to make themselves feel better about having given away their own ability to defend themselves? There are plenty of places around the world where people go and spend an hour on the trap and skeet ranges. It's like bowling or golf. Why do all of the Germans, Swedes, French, Italians, Japanese, British, Russian, Brazilian, Spanish, Chinese, Australian, Latvian, and everyone else who do that want to shoot everything? Or is that maybe not really a reasonable characterization, as it turns out?

Comment Re:The law is ridiculous anyway (Score 1) 176

We can't really discuss the subject with you when you keep asking irrelevant, leading questions. Suppose the previous poster was a hard-core "manifest destiny" type who actually does agree that colonialism is an unalloyed great thing. Or not. It's completely irrelevant to their point about the natives being unable to maintain possession of land they used to occupy.

Comment Re:the main legit use i can see (Score 1) 162

Really? How do you use an airport in a no-fly zone?

Don't be an idiot. You know perfectly well what the GP is referring to. The FAA says no UAS activity within 5 miles of an airport. To the extent that one can make advance arrangements - including special permission, a filed flight plan, etc - per flight, you might be able to get away with that. That completely rules out on-demand delivery services like those being discussed. In every practical sense, that makes the five miles surrounding airports UAS delivery NFZ's. The entire DC metro area and many other spots are also completely, permanently off limits.

Comment Re:The treaty says no such thing. (Score 1) 176

I'm not saying it won't happen eventually, but it won't be profitable until we're measuring cost per pound to orbit in pennies rather than thousands of dollars.

In other words, it won't be profitable until the mass for that machinery and propellant comes from somewhere much cheaper than Earth, say the asteroid you're mining.

Comment Re:Restaining growth (Score 1) 176

"Economic growth" can't be sustained forever. A new social model will have to replace that idea. So sorry.

So what when there are at the least, centuries of growth left? After all, not everyone currently enjoys a developed world lifestyle. That's one avenue for growth. Not every society is fully industrialized. That's another avenue. We don't live indefinitely; we don't have massive space civilizations; we don't have post-scarcity conditions; we don't fully understand the universe; we don't have a host of things which we can put into our grasp eventually.

There's plenty of room for growth and it makes no sense to talk about imaginary "new social models" which are irrelevant to a world in growth for the practical future.

Comment Re:Sigh... (Score 2) 176

A private entitey gaining ownership over what is currently public could be looked on as theft from the public.

There are surprisingly few things owned in space by the public or anyone else. If some crazy dude with a bunch of robots can keep the rest of humanity from doing anything with the Moon other than look at it, then he effectively owns it even if no one else agrees.

Comment Re:Absence of Evidence is not Evidence of Absence (Score 1) 186

It's also a matter of intent. Intentionally, being a dick is macroaggression. Accidentally being a dick is a microaggression. But this leads to an important secondary matter, that of interpretation. After all, if I'm trying to be a dick, then by my own viewpoint I am macroaggressing. If I'm not trying, then how does anyone know I'm microaggressing? The answer is that someone observes my behavior and decides it is a microaggression.

That leads to the second observation, that microagression is a matter of perception and subjectivity, often by people with chips on their thin-skinned shoulders. It can be an obvious insult, like assuming someone is a drooling idiot because they're a certain ethnicity. But it can also be something pretentious like someone deciding that the word, "niggardly" is an insult against African Americans even though the word doesn't have racist origins (unlike say, "indian summer"). The attitude is particularly pernicious when the person who perceives the insult is acting as an unauthorized proxy acting on the behalf of an apathetic or completely absent group.

All I can say is that I didn't care before microaggression became a thing and the situation hasn't changed now that I've been made aware of this dire threat to humanity. I think it has to do with the fundamental observation that people can choose not to be insulted by non-insults. Thus, anyone who has a serious problem with microaggressions needs to look in a mirror to see who is responsible for fixing that.

"Don't worry about people stealing your ideas. If your ideas are any good, you'll have to ram them down people's throats." -- Howard Aiken