ISP is most commonly given in units of "seconds", although the way they're measured is a bit misleading as the values are divided by Earth's gravity. Also note that the SP should really be subscript (it's "Impulse (SPecific)"), but there's no way to write that on Slashdot. ISP has nothing to do with burn times.:)
Burn times? I haven't discussed burn times. ISP is independent of burn times.
Yes, ISP is specific impulse. Okay, let's back up. The thing all rockets are trying to achieve is delta-V - change in velocity, generally in meters per second. Low-Earth orbit (really, the minimum anyone cares about, excepting the rather small sounding rocket market) requires 300-400km altitude and 7800 meters per second (the latter representing far more energy requirements). You also have two other main sources of losses: aerodynamic losses (only at the very start of the launch, but it's very significant during that timeperiod) and so-called "gravity losses", aka making up for what your rocket falls after it's launched and before it's reached orbital velocity. Depending on aero and gravity losses, a rocket will typically require more than 10k m/s delta-V total.
The more energetic your combustion process and the more efficient your engine, the faster the average velocity of your exhaust. The exhaust passes through the throat at mach 1 (it's not capable of moving faster than the local sonic velocity through the throat), then in the expansion region converts its thermal energy to kinetic energy, increasing its velocity to several thousand meters per second. But note that this is still far way less than the velocity that you have to have to achieve to reach orbit. Hence you're subject to the tyrrany of the Tsiolkovsky Rocket Equation, which mandates exponential growth in terms of the size of your rocket to achieve linear growth in delta-V. The exponent is dependent on that ISP, which is based on how fast your exhaust moving, which is in turn based on how energetic your propellant mix is and how efficient your engines are.
Note of course that ISP is far more critical for upper stages. Because each increase in mass of the topmost stage dramatically increases the mass of each stage under it, it's important to keem them light. For lower stages, by contrast, thrust is key. A rocket just leaving Earth is subject to full gravity losses. If it only has just enough thrust to just barely lift off, it'll be wasting most of its energy just making up for the distance that it falls. The biggest factor in determining thrust is the volumetric, not mass, density - meaning that their density is key (density also reduces your tankage mass by making your tanks smaller). So for example hydrogen-based propellant mixtures are often high ISP, but since liquid hydrogen has a density around that of thick foam insulation, it's hard to get significant thrust out of it, and thus it's not often used for lower stages. But it's very commonly used for upper stages, where gravity losses are low to nonexistent. That comes with the caveat that sometimes the need for the engine to be lightweight outweighs the need for high ISP, and so for such cases one may still choose low ISP thrusters. The classic example would be the MMU (Manned Maneuvering Unit, aka, "astronaut jetpack"); it uses cold gas nitrogen thrusters, which are literally just a pressurized nitrogen tank hooked up to a nozzle. (There also exists a variant that some satellites use, aka where power is abundant but mass isn't, called a resistojet - it's basically a cold gas thruster but has a resistive heating element on the line to the nozzle, to get rocketlike ISP with something not much heavier or more complex than a cold gas thruster)
So anyway, that's the basics. And as for metalized propellants, they're already used in solid rockets. It was a huge breakthrough for them, adding aluminum - it's basically what made solid ICBMs possible (the Soviets, coming to the realization of the benefits much later than the US, fell well behind and were stuck using liquid-fueled ICBMs much longer); it both increased density (aluminum is much more dense than most propellants) and ISP, by a significant margin. It even makes the burn better - faster, more even ignition, and the molten aluminum droplets damp resonant vibrations, leading to more steady combustion. While aluminum offers many bene
I think the point of that statement is that the virilization pathway requires additional action, an additional trigger, while female is "default" in the absence of said trigger.
There've been lots of studies finding "psychological differences between the sexes". But when you look into them the statistical correlations are usually terribly weak, barely above statistical significance. And you have to question how much you can trust them anyway. Remember that metastudy that showed that half of all psychological studies can't be reproduced? I downloaded their study data. Every topic related to gender differences was in the "couldn't be reproduced" category. Now, of course that's a tiny fraction of all research that they attempted to reproduce. There surely are psychological differences, even ones that aren't pure upbringing/society related. But its important not to overplay the amount or degree of them.
That's part of the problem. Generally when one takes a complex system and focuses in a narrow-minded approach toward optimizing just one aspect they end up blowing it on other aspects. For example, an equally well reasoned but precisely opposite argument to OTRAG is Big Dumb Booster concept, where rather than trying to mass-produce many small rockets, you make singular giant rockets because when you compare the economies of giant rockets to those of small rockets, the giant rockets usually win.
OTRAG has some good concepts, but again I think they went too far. Not only are they pushing their propellant costs way up - which to be fair, is by design, accepting the fact that propellant is only a very small fraction of total costs - but they're also pushing up every last part of the handling costs, which unfortunately is not so small of a fraction of the total costs. And they're incurring a lot of size-related costs - load capacity of the pad and tower, environmental impacts on the surrounding area, etc - without gaining the typical size-related economies of scale, as OTRAG's extreme size only yields proportionally small payloads. It has almost no potential to optimize costs further, as they're willfully making propellant a significant fraction of total costs and the design basically throws away any potential for economic reuse. And with numerous heavy steel stages and the first stages having to separate at low altitude due to the low performance, it's basically a bomber;) And with all of those stages clustered together they're really putting themselves at risk for cascading failures - stage separations are one of the riskiest parts of rocketry as-is, and cluster elements can interact in unexpected ways even when you only have a few of them.
So no, I'm not a big OTRAG fan, I think the design goes too far. I think SpaceX hit the right balancing point in this regard - enough of a degree of mass production to keep production streamlined (dozens of tanks and hundreds of engines per year), but not so much that you have to have huge numbers of stages and crazy-low performance (aka crazy-huge mass). They did this sort of balancing act in a lot of regards. For example, in rocketry there's often been a conflict between structural tanks (which can bear all of the loads during launch) and balloon tanks (which rely on internal pressure not to collapse). Balloon tanks have much better performance (meaning that they save you a lot of mass and thrust requirement - aka money), but they're a pain when it comes to handling because you have to keep them pressurized at all times after construction, even during transport, and if you have to do repairs, it's expensive. SpaceX uses a sort of semi-balloon tank design - their tanks are strong enough unpressurized to hold themselves up, but not to bear the forces of launch - they require internal pressure for that. So you can transport and handle them without hassle, but they still get excellent payload fractions - to the point that that if they were to launch their first stages without upper stages or payloads on them, they'd nearly be SSTOs. And the design is of course aided by their use of aluminum-lithium alloy - which normally is expensive to work in a reliable manner (it doesn't take well to being melted), but the friction stir seam welding system they use is really near ideally suited for it.
Just like in life, rocketry is about balance. OTRAG is more Kerbal-ish;)
See this. Oregon's prediction is about average, so the RCP8,5 would be about 2-4 feet tall (a normal-sized person sitting, kneeling, or somesuch), with some other indicator for the RCP2,6 at about half that. And yes, the pedestal in that location would be larger than in a location like NYC.
RCP8,5 is 0,53-0,98m by 2100... which is only about 84 years from now. With the rise at 2100 predicted at around 0,9-1,8cm/yr over the 2100-2116 period (minus the current 0,32-0,36mm/yr) the total would be something like 0,62m-1,21m (2' to 4') - basically, a typical person sitting, kneeling, or similar. The amount of rise however does vary to some degree based on location, and some isolated areas (like Baffin Bay) are even expected to get a drop (about 5% of the worlds' oceans). The northeastern US and northeastern Canada are projected to get a particularly large rise, so a statue there could be in a more upright position or built to a larger scale - the waters off of New York are projected to rise a median value of 0,3 meters in just the 2081-2100 period alone. New York's 2100 RCP8,5 range is about 0,5 to 1,2m - adjusting to 2116 would put it at 0,6-1,5m (on top of the pedestal of course, which would be about 1,3 meters tall).
RCP8,5 is of course the "business as usual" line... which has been the best bet thusfar. The "if we make huge efforts" RCP2,6 prediction is about half of the RCP8,5 predictions. There could be some other object on each statue to denote the RCP2,6 line.
Huh? It says right in the summary: "Moody's family eventually moved to Springdale to live with him and work for Tyson and other poultry companies based in Arkansas". Is "working for Tyson" slang for "running from climate change" that I've never heard of?
Too bad I'm not a sculptor, I'd love to launch a climate change-related kickstarter which both sides could get behind. I'd offer to - if I could raise the expenses - make life-sized bronze statues of the world's most prominent climate-change deniers and install them on popular beaches around the world where permission could be gotten. Each statue would be on a pedestal on which is engraved one of their more prominent quotes denying climate change. The proportions of the statues would be such that at low tide the base of the pedestal is at sea height, while at high tide the top of the pedestal is at sea height, and the total height of the person matches up to the projected sea level rise over the next century.
Hence, if those denying climate change are right, a century forth they're left with a statue on their beach mocking all of the Chicken Littles. If those arguing that it's real are correct, they get to gloat as they watch the statue sink a bit further beneath the waves every year for the rest of their lives and a cautionary dive site for future generations.
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.
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)
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.
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 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".
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.
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...";)
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
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.
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.
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
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.
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.
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.
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.
Slashdot Mirror
ISP is most commonly given in units of "seconds", although the way they're measured is a bit misleading as the values are divided by Earth's gravity. Also note that the SP should really be subscript (it's "Impulse (SPecific)"), but there's no way to write that on Slashdot. ISP has nothing to do with burn times. :)
Burn times? I haven't discussed burn times. ISP is independent of burn times.
Yes, ISP is specific impulse. Okay, let's back up. The thing all rockets are trying to achieve is delta-V - change in velocity, generally in meters per second. Low-Earth orbit (really, the minimum anyone cares about, excepting the rather small sounding rocket market) requires 300-400km altitude and 7800 meters per second (the latter representing far more energy requirements). You also have two other main sources of losses: aerodynamic losses (only at the very start of the launch, but it's very significant during that timeperiod) and so-called "gravity losses", aka making up for what your rocket falls after it's launched and before it's reached orbital velocity. Depending on aero and gravity losses, a rocket will typically require more than 10k m/s delta-V total.
The more energetic your combustion process and the more efficient your engine, the faster the average velocity of your exhaust. The exhaust passes through the throat at mach 1 (it's not capable of moving faster than the local sonic velocity through the throat), then in the expansion region converts its thermal energy to kinetic energy, increasing its velocity to several thousand meters per second. But note that this is still far way less than the velocity that you have to have to achieve to reach orbit. Hence you're subject to the tyrrany of the Tsiolkovsky Rocket Equation, which mandates exponential growth in terms of the size of your rocket to achieve linear growth in delta-V. The exponent is dependent on that ISP, which is based on how fast your exhaust moving, which is in turn based on how energetic your propellant mix is and how efficient your engines are.
Note of course that ISP is far more critical for upper stages. Because each increase in mass of the topmost stage dramatically increases the mass of each stage under it, it's important to keem them light. For lower stages, by contrast, thrust is key. A rocket just leaving Earth is subject to full gravity losses. If it only has just enough thrust to just barely lift off, it'll be wasting most of its energy just making up for the distance that it falls. The biggest factor in determining thrust is the volumetric, not mass, density - meaning that their density is key (density also reduces your tankage mass by making your tanks smaller). So for example hydrogen-based propellant mixtures are often high ISP, but since liquid hydrogen has a density around that of thick foam insulation, it's hard to get significant thrust out of it, and thus it's not often used for lower stages. But it's very commonly used for upper stages, where gravity losses are low to nonexistent. That comes with the caveat that sometimes the need for the engine to be lightweight outweighs the need for high ISP, and so for such cases one may still choose low ISP thrusters. The classic example would be the MMU (Manned Maneuvering Unit, aka, "astronaut jetpack"); it uses cold gas nitrogen thrusters, which are literally just a pressurized nitrogen tank hooked up to a nozzle. (There also exists a variant that some satellites use, aka where power is abundant but mass isn't, called a resistojet - it's basically a cold gas thruster but has a resistive heating element on the line to the nozzle, to get rocketlike ISP with something not much heavier or more complex than a cold gas thruster)
So anyway, that's the basics. And as for metalized propellants, they're already used in solid rockets. It was a huge breakthrough for them, adding aluminum - it's basically what made solid ICBMs possible (the Soviets, coming to the realization of the benefits much later than the US, fell well behind and were stuck using liquid-fueled ICBMs much longer); it both increased density (aluminum is much more dense than most propellants) and ISP, by a significant margin. It even makes the burn better - faster, more even ignition, and the molten aluminum droplets damp resonant vibrations, leading to more steady combustion. While aluminum offers many bene
I think the point of that statement is that the virilization pathway requires additional action, an additional trigger, while female is "default" in the absence of said trigger.
There've been lots of studies finding "psychological differences between the sexes". But when you look into them the statistical correlations are usually terribly weak, barely above statistical significance. And you have to question how much you can trust them anyway. Remember that metastudy that showed that half of all psychological studies can't be reproduced? I downloaded their study data. Every topic related to gender differences was in the "couldn't be reproduced" category. Now, of course that's a tiny fraction of all research that they attempted to reproduce. There surely are psychological differences, even ones that aren't pure upbringing/society related. But its important not to overplay the amount or degree of them.
That's part of the problem. Generally when one takes a complex system and focuses in a narrow-minded approach toward optimizing just one aspect they end up blowing it on other aspects. For example, an equally well reasoned but precisely opposite argument to OTRAG is Big Dumb Booster concept, where rather than trying to mass-produce many small rockets, you make singular giant rockets because when you compare the economies of giant rockets to those of small rockets, the giant rockets usually win.
OTRAG has some good concepts, but again I think they went too far. Not only are they pushing their propellant costs way up - which to be fair, is by design, accepting the fact that propellant is only a very small fraction of total costs - but they're also pushing up every last part of the handling costs, which unfortunately is not so small of a fraction of the total costs. And they're incurring a lot of size-related costs - load capacity of the pad and tower, environmental impacts on the surrounding area, etc - without gaining the typical size-related economies of scale, as OTRAG's extreme size only yields proportionally small payloads. It has almost no potential to optimize costs further, as they're willfully making propellant a significant fraction of total costs and the design basically throws away any potential for economic reuse. And with numerous heavy steel stages and the first stages having to separate at low altitude due to the low performance, it's basically a bomber ;) And with all of those stages clustered together they're really putting themselves at risk for cascading failures - stage separations are one of the riskiest parts of rocketry as-is, and cluster elements can interact in unexpected ways even when you only have a few of them.
So no, I'm not a big OTRAG fan, I think the design goes too far. I think SpaceX hit the right balancing point in this regard - enough of a degree of mass production to keep production streamlined (dozens of tanks and hundreds of engines per year), but not so much that you have to have huge numbers of stages and crazy-low performance (aka crazy-huge mass). They did this sort of balancing act in a lot of regards. For example, in rocketry there's often been a conflict between structural tanks (which can bear all of the loads during launch) and balloon tanks (which rely on internal pressure not to collapse). Balloon tanks have much better performance (meaning that they save you a lot of mass and thrust requirement - aka money), but they're a pain when it comes to handling because you have to keep them pressurized at all times after construction, even during transport, and if you have to do repairs, it's expensive. SpaceX uses a sort of semi-balloon tank design - their tanks are strong enough unpressurized to hold themselves up, but not to bear the forces of launch - they require internal pressure for that. So you can transport and handle them without hassle, but they still get excellent payload fractions - to the point that that if they were to launch their first stages without upper stages or payloads on them, they'd nearly be SSTOs. And the design is of course aided by their use of aluminum-lithium alloy - which normally is expensive to work in a reliable manner (it doesn't take well to being melted), but the friction stir seam welding system they use is really near ideally suited for it.
Just like in life, rocketry is about balance. OTRAG is more Kerbal-ish ;)
See this. Oregon's prediction is about average, so the RCP8,5 would be about 2-4 feet tall (a normal-sized person sitting, kneeling, or somesuch), with some other indicator for the RCP2,6 at about half that. And yes, the pedestal in that location would be larger than in a location like NYC.
RCP8,5 is 0,53-0,98m by 2100... which is only about 84 years from now. With the rise at 2100 predicted at around 0,9-1,8cm/yr over the 2100-2116 period (minus the current 0,32-0,36mm/yr) the total would be something like 0,62m-1,21m (2' to 4') - basically, a typical person sitting, kneeling, or similar. The amount of rise however does vary to some degree based on location, and some isolated areas (like Baffin Bay) are even expected to get a drop (about 5% of the worlds' oceans). The northeastern US and northeastern Canada are projected to get a particularly large rise, so a statue there could be in a more upright position or built to a larger scale - the waters off of New York are projected to rise a median value of 0,3 meters in just the 2081-2100 period alone. New York's 2100 RCP8,5 range is about 0,5 to 1,2m - adjusting to 2116 would put it at 0,6-1,5m (on top of the pedestal of course, which would be about 1,3 meters tall).
RCP8,5 is of course the "business as usual" line... which has been the best bet thusfar. The "if we make huge efforts" RCP2,6 prediction is about half of the RCP8,5 predictions. There could be some other object on each statue to denote the RCP2,6 line.
Huh? It says right in the summary: "Moody's family eventually moved to Springdale to live with him and work for Tyson and other poultry companies based in Arkansas". Is "working for Tyson" slang for "running from climate change" that I've never heard of?
Too bad I'm not a sculptor, I'd love to launch a climate change-related kickstarter which both sides could get behind. I'd offer to - if I could raise the expenses - make life-sized bronze statues of the world's most prominent climate-change deniers and install them on popular beaches around the world where permission could be gotten. Each statue would be on a pedestal on which is engraved one of their more prominent quotes denying climate change. The proportions of the statues would be such that at low tide the base of the pedestal is at sea height, while at high tide the top of the pedestal is at sea height, and the total height of the person matches up to the projected sea level rise over the next century.
Hence, if those denying climate change are right, a century forth they're left with a statue on their beach mocking all of the Chicken Littles. If those arguing that it's real are correct, they get to gloat as they watch the statue sink a bit further beneath the waves every year for the rest of their lives and a cautionary dive site for future generations.
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.
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)
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.
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.
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".
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.
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..." ;)
Yeay! Because you know that $7-8/kg for lithium carbonate was really breaking the bank.
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
Wow, it's almost as if my original post didn't read:
The "rank amateurism" here is in your reading comprehension.
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.
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.
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%.
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.
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.
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
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.
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.
Calculate the mass of your cable. It doesn't work.
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.
No, I mean $18k. From your link:
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.