Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!


Forgot your password?
Slashdot Deals: Cyber Monday Sale Extended! Courses ranging from coding to project management - all eLearning deals 20% off with coupon code "CYBERMONDAY20". ×

Comment Re:Geothermal (Score 1) 198

Here in Iceland some people are against it because of the need to build roads / powerlines out into wilderness areas (and subsequent roads/pipes to each well from the central plant), and because of the wastewater ponds. And some complain about the increased H2S emissions in the area

Personally I think that's taking things way too far. Of course there need to be regulations and environmental controls, but you really don't get much more low environmental impact per MW than geo. And there's lots more pollution controls that can be put on them if so desired than we actually impose on them, it's not like clean coal where the technologies are basically economically prohibative.

Comment Re:Geothermal (Score 1) 198

150mW (milli, not mega) per m2 at most,

Which is why geothermal isn't harvested by laying a blanket across the whole planet.

150mW * 510000000000000 square meters is 67TW, four times higher than global energy consumption.

  But gee, if only there was some sort of way to harvest geothermal other than laying a blanket across the whole planet. Something like, say, if heat would collect somewhere over long periods of time. Like, throughout the entire thickness of the many-kilometers-thick crust and so on down all the way to the center of the planet. You know, that would be so awesome if there were unfathomably vast amounts of heat trapped in the rock that makes up the Earth that has accumulated over time, and if instead of laying blankets, we could just drill into it and take the heat out of the rock in the form of steam, with each area you drill lasting for decades or even longer. Wouldn't that be great?

Too bad that's not possible....

Comment Re:Geothermal (Score 1) 198

Drilling a ton of extra holes in the planet's crust and venting our core heat all into the upper atmosphere at a massively increased rate

This is where a facepalm unicode character would be handy (not even going to *touch* the "volcano capping" thing).

Earth's temperature is what it is due to an equilibrium between inputs (primarily the sun) and outputs (primarily radiation to space). Heat radiates from the air very quickly, as you may have noticed by how cold it gets on a clear winter night vs. when it's cloudy. Heat does not "stick around". In fact, the higher the temperature, the faster it radiates, and not by a small margin - the rate of radiative heat loss is proportional to the temperature in kelvins to the *fourth* power.

The planet cannot warm because you "add in excess heat", of a magnitude not even the slightest bit comparable to the sun. It warms if you change the surface radiative balance, based on how well sunlight penetrates to the surface vs. how well heat radiates away. Sunlight enters in the visible spectrum but leaves in the IR spectrum, so a change in the proportion between these two figures changes the equilibrium temperature (that is, it rises up to the point where the increased radiation rate due to the higher temperature compensates for the lesser ability for IR to penetrate the atmosphere without absorption/re-radiation. The most powerful of gases in our atmosphere at accomplishing this is water vapor; however, water vapor has a short atmospheric residence time (it's constantly entering and leaving, with an average residence of only a couple weeks), so it's nothing more than feedback and fluctation around whatever other factors are driving the system. The two most significant gases that have relevant residence times are methane and CO2; both cycle, but methane cycles over a couple decades and CO2 over a couple hundred years. It's a bit more complicated than that - for example, an individual CO2 molecule on average will be absorbed or emitted every couple years. But in terms of the ability to be absorbed in a way that doesn't correspond to a corresponding short-term release - aka, sequestration - is a much longer timeperiod on average (and it varies depending on the total to sequester).

Comment Re:Sputnik? (Score 1) 135

Half of Soviet missions to Venus failed anyway. They were just a lot more persistant about it ;) Really, the Soviet Union had a pretty terrible record for space exploration away from the confines of Earth - near universal disasters on their Mars program and not even an attempt to explore the outer solar system. But at least their persistence with Venus paid off - the US practically ignored our "evil twin". My favorite finding was the detection of iron during their descent through the clouds - they think it was volcanic ash, but even if it's just dust it's still neat to know that there's mineral condensation nuclei in the clouds.

Comment Re:Don't hold your breath (Score 1) 135

Also, it should be noted that mass production hits some obstacles when it comes to upper stages. You need a lot fewer engines, and higher ISP than you need for the lower stages (but not as much thrust requirement). You can do it with the same or similar ISP like SpaceX does (same engine, just vacuum optimized expansion nozzle), but that limits your scaling - it's fine to LEO/GEO but you're never going to get to Mars and back with a practical-sized rocket with those kinds of ISP figures. Which is why SpaceX's future plans hinge around in-situ methane production, so that they don't have to carry all of that return mass. It's a reasonable, although challenging, approach.

There are some possibilities mind you for getting more impulse out of their current designs. They're already taking some interest steps with the Falcon 9v1.2, aka "Full Thrust" - instead of having their LOX near its boiling point, they're supercooling it to just above its triple point and cooling the propellant to the maximum level of viscosity that their turbopumps can manage, so that they both increase in density, thus increasing both tank capacity and thrust. But while they're playing with increased viscosity propellants, they could take it to the next stage and go with mildly gelled propellants. The gelling isn't in and of itself a performance enhancer, but it lets you suspend aluminum (or if you don't mind the handling problems, lithium) particles in your fuel. Aluminum gives dozens of extra sec ISP, and lithium dozens more. Aluminum also increases propellant density, meaning more thrust and tank capacity (lithium unfortunately decreases it). While lithium metal is fairly expensive (a couple dozen dollars per kg), aluminum is cheap, about $1,50/kg.

Another nice thing (according at least to my CEA simulations with lithium) is that the latter significantly lowers chamber temperature, all other conditions (mass flow rate, expansion ratio, etc) being the same. Entering the conditions for the SSME, for example (77,5:1 expansion ratio, mass flow rate per square meter = 2223,8 kg/sec), CEA calculates (if SSME were lossless) 464,5 sec vac ISP (real world, after losses is 452 sec), 0,36g/cc propellant density, 3602,82K chamber temperature (real world 3573,15K) and exhaust of H2O (~76%) + H2 (~24%). CEA says that with a slightly different ratio you could add an extra 1,4sec ISP, but it's basically near maximum. With aluminum added to the ideal mix it calculates Al (43,9%)/LOX (39,1%)/LH2 (17,0%): 544,0 sec, 0,34g/cc, 3689,38K, -> H2 (~91%), Al2O3 (~9%). And with lithium, it calculates Li (30,0%)/LOX (34,6%)/LH2 (35,4%): 583,2 sec, 0,17g/cc, 2362,44K, -> H2 (~89%), Li2O (~11%). Now, these figures assume complete burning of the metals - which is often difficult to achieve in the real world with aluminum as its oxide has such a high melting point - but in general metalized propellants offer huge potential improvements to performance, with non-esoteric technology, and without posing serious pollution problems (like, say, using fluorine as an oxidizer does). So it'd be interesting to see what SpaceX could achieve if they could get their system to handle gelled propellants - the potential is huge.

(Note: these calculations are for adding metals to LOX/LH... but the same thing applies to hydrocarbon fuels, albeit to a slightly lesser degree)

Comment Re:Don't hold your breath (Score 1) 135

Indeed, and unfortunately, rocket technology is on the opposite side of the tech/price scaling curve. NASA has their own inflation rate used for budgeting long-term projects, and it trends much higher than the US national inflation rate. The reason is obvious when you think about it: back in the 1950s, many common commercial products were handmade, with domestic labour, but are now mass-produced with cheap overseas labor and advanced labor-saving technologies (depending on the type of product). But just like in the 1950s, NASA still builds things largely by hand, generally in small numbers, and with a highly skilled domestic workforce.

"We've got to get mass production" is often a mantra of the alt-space community, and really in large part what's kept Russian costs down. It's also what makes SpaceX competitive - not only are they set up to make lots of cores per year (last I heard it was something like 40), but they put 9 engines per core, and their upper stages are just short, single-engine versions of their lower stages. And the Falcon Heavy is, to the most part, three Falcon 9s stuck together.

One can of course take the concept too far (OTRAG, I'm looking in your general direction...), but mass production is indeed a key aspect.

Comment Re:Far more abundant than lithium? (Score 1) 133

Actually, it's just the other way around. The reserves of in-demand materials - especially those for which there was relatively little demand for previously - tend to grow, by orders of magnitude, over time. And the maximum production cost of lithium is essentially capped, because the oceans have an essentially inexhaustable supply, and it costs an estimated $20-35 per kilogram (last I checked, the figure may have gone down since then) to produce lithium salts from it. But nobody is going to be touching that in the foreseeable future because there are such vast reserves onshore - salars, hectorite clays, pegmatites, geothermal lithium, etc. Actually $7-ish/kg is rather expensive for lithium salts, the long-running price has been more like $4-5/kg. Which has led to a new rush of lithium exploration, as it was so underexplored previously. And companies are finding huge lithium deposits bloody everywhere. A lot in the US, actually.

It's simply not a rare element.

Comment Re:Far more abundant than lithium? (Score 1) 133

It's mainly manufacturing/capital costs. The most expensive "raw ingredient" in the batteries BTW is not lithium but cobalt. Which nobody ever mentions because it's not in the name of the batteries - you'd have people freaking out about "peak cobalt" if we had called them "cobalt cathode" batteries instead of "lithium ion".

Comment Re:It's dug out of salt lakes (Score 1) 133

Indeed, lithium mining from salars is actually one of the more benign mining processes that exists. You're out on an area that is virtually devoid of life, pumping up saltwater, letting it evaporate in ponds to concentrate it, selectively crystalizing the desired salts (such as lithium salts) out, and setting the remaining salts back on the salt flat. Every year the annual floods come and resurface the entire thing.

You know, sometimes it feels like people just want to hate any new technology.

Comment Re:Sakura Battery (Score 5, Funny) 133

My father has had various top executive roles in oil companies for the past two decades. We often crack jokes with each other about this sort of stuff. "Gee, dad, how was work - suppress any new revolutionary clean energy technologies today?" "Only two... and you know we've only managed to buy off twelve congressmen this month - total? *Sigh*, the business just isn't what it used to be..." "Oh, sorry to hear that dad... maybe you should start a new war, that always works." "Yeah, I'll bring it up at the next Illuminati meeting..." ;)

Comment Re: But (Score 1) 143

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) 143

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.

The "rank amateurism" here is in your reading comprehension.

Comment Re:How does space elevator save energy? (Score 1) 143

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.

365 Days of drinking Lo-Cal beer. = 1 Lite-year