The pipeline is elevated on columns. That's be one heck of a fire to reach it up there. In a really terrible fire (ignoring that most columns aren't over anything of significance that could burn) you might spall some of the concrete after a couple hours, but that would be bloody amazing if they could get to that point without noticing anything.
a,b) 0.02 PSI is extremely mild by vacuum standards. By contrast, ultra-high vacuum is defined as less than 0.0000000000145 PSI. 0.02 PSI is not a difficult pumping challenge by any stretch. And after the initial pumping, the only vacuuming requirements are 1) airlocks at the end stations, and 2) overcoming the rate of leaks. The pump sizing and power consumption needed is well less than with equivalent-sized oil or water pipelines.
c) And too bad inch-thick steel is such a fragile, flexible material, utterly vulnerable to M80s! Oh wait....
You do realize that the buckling force of a cylindrical shell is actually far easier to work out (with safety margins) than the physics calculations for the structural stability of the capsules, right? Or for that matter, cars, airplanes... throw in buildings while we're at it.
d) The plan is not to "find all the little leaks". The little leaks are the only reason that any continued pumping is required at all. Only major leaks need to be found. The pipeline is to be made by the same technology as makes our water and oil pipelines today (automated orbital welding), plus an additional finishing step on the inside.
There are a number of serious issues that the Hyperloop teams need to show that they need to overcome. You didn't hit on a single one of them.
What road do you live near where the surface is packed full of rubber tire marks? Must be pretty miserable to live there, with people burning tires all the time.
A solar panel is in fact an EXACT OPPOSITE of a greenhouse - the greenhouse relies on IR alone,
Hahahaha.... oh geez...:)
Let's back all the way back to third grade and cover the topic of "photosynthesis". You see, plants need light from the sun to grow! Now class, take one of those seeds you sprouted and put it on your windowsill, and put the other in the closet... we'll bring them back to compare in two weeks. Don't forget to water!
The amount of light transmission is probably the biggest factor in greenhouse design. Here in Iceland people have to use glass (most common) or hard plastic (less common) because of the wind, thin plastic hoop houses don't survive here. Most commonly used is single pane glass. Yes, you read that right. Here in a country with "ice" in the name, it's still considered worthwhile to let the heat pour out of your greenhouse in order to get a few extra percent sunlight. Now, we have hot water for heating which reduces (but doesn't eliminate) heating costs, but still, it drives home the point: to growers, light equals growth.
Greenhouses most definitely do not rely on "IR alone".
If you're curious as to why fogged surfaces are often seen as desirable in greenhouses - it's because of shading. Fogging only causes the greenhouse to lose a couple to several percent of the light (depending on the type of plastic or glass), but it means that all of the light is no longer coming from the same angle. This helps get light to leaves that would otherwise be shaded by other leaves.
Ironically, contrarily to what you wrote, glass-covered solar panels do care about IR transmission. They don't generate power from IR, but their efficiency is correlated to their temperature, and the temperature is correlated with the radiative equilibrium of their environment.
Like how hold concrete becomes slippery? Yep, just like with concrete, you need to resurface. But one expects them to use anti-scratch coatings, which would significantly reduce the rate of wear. The aggregate in typical concrete can be up to Mohs 7, but the cement is only Mohs 2-5. Raw unprotected glass is Mohs 5-6,5, but scratch resistant coatings can raise it to over 7 to avoid being scratched by quartz sand.
1) Traction glass. You can see through it just fine. And you don't need to be able to see through it (light rays taking parallel paths), you just need light - refraction and all - to largely get through. And not even all of it, it's fine to lose a good chunk of it compared to rooftop installs - see ""They'd be better on roofs" in my reply above.
How well can you see through your typical modern greenhouse? You don't need to have "perfect visual transparency" to let lots of light past a surface. In fact, your surface texturing can actually increase your potentential generation (see my comment about the potential of fresnel lensing above).
2) Most rooftops are also not angled correctly either. And unlike roads, most rooftops are not designed to bear the extra weight of panels. And again, see the "They'd be better on roofs" reply.
3) See the comments about damage and loadbearing in the same post.
4) Tanks rip all roads to pieces. But your not-so-subtle jab at the French who basically were responsible for you being an independent country (rather than a bunch of rabble-rousers quickly captured and hung by the British) is well noted.
5) Fields A) mean building dedicated projects, rather than hitting two birds with one stone (getting a road and a solar farm out of the same build process); and B) using up greenspace that most people would rather keep or use for other purposes.
Or see my reply above, where I cover a lot of the criticisms (I'll gladly go into more). There is nothing at all exotic about traction glass (aka "anti-slip glass").
It's one of the "solar freaking roadways" peoples' concepts that makes me sigh out loud, even though I actually think that the concept of solar paving warrants further research. Having roads have "give" and generating power from that is like making cars constantly have to drive uphill. You're just stealing energy from the cars. Very inefficiently.
Meh, there's a solar bike path in the Netherlands and they don't seem to have excessive problems with dirt. Because rain exists. They got significantly higher generation than they were expecting - only about 1/3rd less than what you'd expect from rooftop mounted panels.
I too have criticisms of the "Solar Freaking Roadways", but let's start with common criticisms that aren't well grounded:
1) They'll scratch up: first off scratches can reduce light transmission but solar panels don't require good "optical quality", only transmission; the light is free to scatter on its way in. It's the same thing that applies to greenhouses - you may have noticed that many greenhouses use "fogged" plastic that you can't see through, yet still lets the vast majority of the light in (in that case, the scattering is actually seen as advantageous). Beyond that, in the case of roadways, I'd think it a given that they'd coat them with a an anti-scratch coat (aka harder than Mohs 7 / quartz sand, the hardest common natural material))
2) Traction: Traction glass exists - it's just surface texturing. They use it for semi-transparent flooring, it's nothing special.
3) "Glass would break and then shred tires": It's easy to make glass bear purely compressive loads (solid objects on both sides of it) without fracture - that's what it's best at. It's shear and tensile loads that glass is bad at, but these aren't applicable when it's flat on a hard surface. And lamination, like in windshields, prevents dangerous shards from coming off in the event of a fracture. This is not an actual limitation.
3) Shadowing: Go to Google Maps satellite view and look up random roads. The overwhelming majority of road surface is completely unshadowed at any point in time. Even in-city roads are overwhelmingly unshadowed. Shadows are practically irrelevant in the countryside except in wooded areas.
4) Costs: The costs of the materials for a road are a minority of the costs of the project, and continue to be a minority of the cost of the project under any realistic pricing for large-scale production of paving panels. A key driver for affordability, however, would be scale: this means large scale production (so road panels are similarly priced to rooftop panels plus the extra glass costs) and continuous paving systems. Anything smaller scale would have elevated costs.
5) "They'd be better on roofs": the main problem with roof installations is there is no way to do mass-scale continuous install (the sort of possibility that paving gives). Each roof has to be handled on its own, with its own engineering issues, with its own project overhead, its own inverters, etc. The key issue to cost reduction these days is getting rid of the overhead; panel production costs themselves have gotten quite low and keep going down. Furthermore, with a road you get "two birds with one stone" - a driving surface and a power generation surface built at the same time in the same space, sharing the same project overhead. It's fine to sacrifice some panel efficiency to glass, shadows, dirt, etc if it reduces your overhead costs.
All of this is not to say that I think they're inherently some sort of great idea that we should dump billions of USD into right this moment I simply think that they do deserve more development and testing, and I have issues with some of the criticisms that have been levied. On the other hand, I do have some issues with the "solar freakin' roadways" people. Number one on my list is the snow-melting concept. It takes five minutes to run the numbers on that and find that it takes way more energy than could ever be considered reasonable. You could melt thin layers of frost off the surface, but nothing of any relevant mass.
If one wants to pursue an anti-snow approach, my personal alternative is having an air bl
The summary is wrong. There is no surprise about how much water ice Pluto has, it's always been expected that it's predominantly water ice.
The actual article linked says that the maps show more water ice than was previously known, not than previously thought. It's hard to see through the surface frosts to see the water ice. Mountains are impossible on Pluto without water ice (or other high compressive strength material - aka, not N2, CH4, CO, etc). The instant mountains were seen, we knew that the crust was mostly water ice. And even before then, we knew that - regardless of what its crust was made of - that Pluto is in large part water ice, due to its density (1,86g/cm3).
We've known that water is one of the most common components of the universe, and the most dominant compound of the outer solar system, for over a century.
The summary is lousy. It's not "much less water ice than thought", it's much less "than was previously known". It had been hard to detect the water ice through the frosts previously.
It's always been expected that a large portion of Pluto's mass is water ice. Also, it was well known before NH arrived that any surface topography of significance would have to be from water ice, as the other ices are just too "soft" to hold up strong contours.
As for water ice being buried, why would you expect that? Water ice is lighter than nitrogen and carbon monoxide ices. It basically "floats" on them. There seems to be a sort of N2/CO/CH4 "mantle" which is exposed to the surface (and convecting) at Sputnik (the point nearest Charon). Elsewhere, however, a water ice crust floats atop it, seemingly progressively thicker the further one gets from Sputnik/Charon.
I find it interesting - perhaps coincidental, perhaps not - that Pluto is like our moon, with a crust thinner and more geologically active on the side of which it's tidally locked to its partner, and thicker/less active on the opposite side. If we can figure out Pluto's dynamics better, it might help us understand our own moon better.
Pluto is a beautifully, fascinatingly weird place. There's some good evidence that entire water-ice floating mountains have washed ashore and collected on the shores of Sputnik - perhaps water ice from the deep depths. Certainly there are shorelines that have this appearance today, and we can see smaller water-ice chunks floating and stuck between the roiling convection cells. If one pictures rolling back the clock, Pluto started out very hot (alternatively with multiple periods of heat, such as during the formation and/or capture of Charon). The first things to condense out would have been rocks, such as silicates, with a water ice ocean and a nitrogen/methane/CO atmosphere. Then the water ice would have frozen. Then the gases would have frozen atop it. But then you have a situation where you have an extensive heavier layer over an even more extensive, lighter layer. So there may be potential for cycling. But it's hard to say, because different crystal forms in different temperature and pressure conditions have different densities.
Charon also has a look of large chunks of water ice drifting around. But while Pluto has its active mantle exposed to space, Charon seems frozen in time. You can see structures that look like massive islands (or even continents) that have broken off from each other, drifted, then became frozen into place. And there's some crazy-massive rifting, as if some layers changed dramatically in size relative to others as they froze (Pluto too has rifting, but Charon's rifts are even more spectacular)
I have, in fact, looked at ISP tables, but I was going off memory. Apparently I remember it being a lot more efficient than it is - I think I was remembering sea-level efficiencies rather than vacuum.
Huh? Sea level and vacuum performances are directly proportional, within only a small variation between propellants. Do you even understand why there's a difference between sea level and vacuum performance?
7% is not an insubstantial amount, particularly when Falcon's figures for "all non-propellant, non-payload mass" are down to 3-5%.
It is a small difference compared to a 21 percent difference in ISP.
The tank skin mass difference due to the density is a more relevant issue. But even still, as a general rule, hydrogen-based upper stages perform well better than RP-1 on a mass basis, which is why most companies and space programs use them. The main reason SpaceX doesn't is economic - they're going for mass production of nearly-identical stages with just small variations (engine nozzle shapes, tank lengths, etc).
I wasn't expecting to pull it out of the atmosphere. Many of the theories for where the methane is coming from imply the existence of stores of methane somewhere on Mars. If, for example, it were trapped in underground deposits, we could tap into it relatively easily.
No we could not do something that would be difficult on Earth "relatively easily" on Mars. We're not going to be sending freaking natural gas drilling rigs to Mars (Mars being a highly natural gas poor planet), nor are we even going to have the sort of detailed geological survey data we'd need to be able to do that for many decades. We consider it challenging to build a bloody shelter on Mars, and you want to set up a petrochemical industry?
Things have to be kept simple to make them plausible and affordable. Production systems have to be small, light, exceedingly reliable and not subject to be thrown off by unexpected local variations, with the whole process well-quantified from a Martian perspective. Drilling for resources on Mars fails on every last one of those.
My impression when they wrote "clean" was "clean from an environmental perspective".:)
Thrust is strongly correlated with density (as how fast you can burn a fuel depends on how fast your turbopumps can pump it into the chambers), so one can get a good sense of how good a fuel will be from a thrust perspective by its density. Which is why hydrogen makes for lousy first stages;) Still, methane's reduced density definitely loses out over RP1. But I'm sure the thrust level will be fine.
You're correct about the "super-cooling" (they refer to it as densification, to avoid being mistaken for the phenomenon "supercooling"), which gives more thrust and lets them store more propellant - at a cost of additional complexity (mainly on the ground). I imagine they're probably not going to want to have to deal with that sort of complexity on Mars... but who knows?
You mention slush... slush and gel propellants provide an additional interest possibility, which is the ability to incorporate metal dusts into the burn. Aluminum offers a huge improvement to hydrocarbons and small improvement to LOX/LH in terms of ISP; it also provides a density boost. Lithium provides an even bigger boost to all cases, although obviously it poses additional handling difficulties. The most efficient chemical rocket engine ever tested dispensed with that altogether and burned molten lithium with hydrogen and fluorine (triprop... the hydrogen is there as a working gas, it doesn't contribute to the reaction). Got 542 sec ISP;) According to CEA sims it's still a killer mix even if you use LOX instead of LF2... although it still depends on how much one is willing to hazard working with lithium. But that's all sort of a side point... if they use gel or slush propellants, particularly with hydrocarbons, they can really benefit by incorporating aluminum powder, which is quite safe and offers excellent density. Aluminum also tends to even out the burn and reduce vibration.
CH4 has a specific impulse much closer to LH2 than RP1
False. But don't just take my word for it, take CEA2's. Parameters: all chamber pressures set to identical 204.08, pi/pe set to give a constant 100:1 expansion ratio, mdot=2223.8 (same as the SSME). All fuels burned with LOX at a stoichiometric ratio. All chemicals at their boiling point except the RP1, which is set to 300K. RP1 simulated by dodecane.
ISP: H2: 436,9 CH4: 365,6 C12H26: 360,6
Seriously, have you never looked at an ISP table before?
The mass of insulation needed it pretty severe, particularly when you account for its low density.
Nope. As is typical, it made up about 7% of the shuttle ET's mass. Nowhere near comparable to such an ISP difference.
CH4 boils at a much, much more reasonable 110K, making it just barely thermally compatible with LOX at 90K
Nope, CH4 freezes solid at 90,7K (versus LOX boiling at 90,2K). And it becomes way too viscous as it approaches its freezing point. That doesn't mean that they can't share a common bulkhead, but it does complicate it for long-term storage (aka, Mars missions)
That's one reason most interplanetary probes use hydrazine for maneuvering once past Earth orbit
That and because it's hypergolic and requires only trivial, lightweight engines - which isn't applicable to CH4.
Also, natural methane has been detected on Mars. If we can determine the source...
This is pure fantasy. Mars's atmospheric concentration is 10ppb - in an atmosphere that's only 0,7% the pressure of Earth's to begin with. Earth's is 1700 ppb at two orders of magnitude higher pressure, and the concept of condensing methane out of the atmosphere at "rich spots" is ridiculous even here - where we have extremely detailed global surface-level data on where "rich spots" are. Lastly, as much as I'd love a detailed surface-level whole-planet geological resource survey of Mars, that's just not going to happen anytime remotely soon - if in our lifetimes at all.
Realistic missions involve using as little speculative technology or speculative data-finds as possible. Even the concept of producing hydrogen from water on Mars is looked at with hesitation (O2 from CO2 is trusted more; the feedstock is much more pure and predictable - the Mars 2020 rover will be testing that one out, hopefully it will go well). Even for O2 we still need to demonstrate a reliable, deliverable system for local storage (as well as industrial-scale production rather than tiny lab-scale production).
First off, I love your expectation that the instant a purchase takes place, everything is supposed to change, as if making and implementing plans and policy changes takes five seconds to complete.
Secondly, whether you like it or not, lots of people here have interest in SpaceX - both positive and negative. Which you can see by how many people comment on every one of these threads. So if you don't like it, tough. Go read a thread on some other topic.
Meh. CH4, H2 and RP1 are all clean, cheap fuels - the levels of pollution and fuel costs are practically non-issues here. ISP, thrust and density are what matter. Methane simply lies on the curve between RP-1 and H2 in terms of thrust, density and ISP (significantly closer to RP-1 than H2). H2 is easier to produce on Mars than methane, which is in turn easier to produce than RP-1 - in this regard, methane is closer to H2 than RP-1 (the mass fractions of current hydrocarbon synthesis from CO2 and H2 tend to produce more methane than heavier hydrocarbons, although the ratios depend on the catalyst, and new catalysts could change this, and you could always do subsequent steps to combine light hydrocarbons)
Methane probably is a good balance for Mars if you want local propellant production. And really, since Mars round trips are so far down the rocket equation chain, you pretty much have to either use extremely high ISP fuels, or go with local propellant production. SpaceX has chosen the latter.
What sort of filament were you using, out of curiosity? Were you using ABS? It's a lot more durable than, say, polyamide. Also, if they wanted, they could (unlike legos) add internal structural supports.
Also, my impresson was indeed that they wanted to print legos not to save money, but to make parts that don't exist elsewhere.
My presumption is that they're not trying to save money, that they're wanting to make parts that you can't get elsewhere (such as connectors to various types of real-world objects)
Hmm, just checked Shapeways, looks like their "frosted ultra-detail plastic" has a 0,1mm resolution. Sounds like the best option so far (if you don't mind it not being from ABS)
I suppose you could take the totally opposite route and choose Shapeways or iMaterialize's rubber/elastic type materials, to deliberately add extra flex into your connector at a cost of lower resolution.
For some reason I doubt that you need that sort of precision. I mean, five microns? The details inside the 8086 processor were 1,5 to 3 microns. Why would you ever need that kind of resolution for a plastic piece?
Lego interconnectors are 4,8mm across. 0,005mm would mean accurate to 0,1%. Looking at iMaterialize's printing options, one could use ABS like legos and get 0,3mm resolution, or high detail (UV cured) resin and get as low as 0,2mm resolution (but no colour options). Polyamide would also offer 0,3mm resolution and more colour options than ABS. Most other plastics are around 0,5mm resolution. The best resolution above (0,2mm) would yield an error of 4,2% on the connector. ABS and polyamide would be 6,3%. Given how much plastic flexes with such thin wall thicknesses I'd think that you could get a good fit like that.
Another option would be, if you had to err, err on the side of too tight of a fit, and if they don't fit together, sand it down.
Hmm, looking over it again, there is one option that offers 0,1mm resolution. But it's stainless steel, and unlike plastics, you're not going to get much flex in that;)
Indeed, that's what I was recommending. Take it off the front page, but that doesn't mean that the comments need to be deleted. It just means that new people coming to the site aren't going to be bothered with a dupe.
Slashdot Mirror
The pipeline is elevated on columns. That's be one heck of a fire to reach it up there. In a really terrible fire (ignoring that most columns aren't over anything of significance that could burn) you might spall some of the concrete after a couple hours, but that would be bloody amazing if they could get to that point without noticing anything.
a,b) 0.02 PSI is extremely mild by vacuum standards. By contrast, ultra-high vacuum is defined as less than 0.0000000000145 PSI. 0.02 PSI is not a difficult pumping challenge by any stretch. And after the initial pumping, the only vacuuming requirements are 1) airlocks at the end stations, and 2) overcoming the rate of leaks. The pump sizing and power consumption needed is well less than with equivalent-sized oil or water pipelines.
c) And too bad inch-thick steel is such a fragile, flexible material, utterly vulnerable to M80s! Oh wait....
You do realize that the buckling force of a cylindrical shell is actually far easier to work out (with safety margins) than the physics calculations for the structural stability of the capsules, right? Or for that matter, cars, airplanes... throw in buildings while we're at it.
d) The plan is not to "find all the little leaks". The little leaks are the only reason that any continued pumping is required at all. Only major leaks need to be found. The pipeline is to be made by the same technology as makes our water and oil pipelines today (automated orbital welding), plus an additional finishing step on the inside.
There are a number of serious issues that the Hyperloop teams need to show that they need to overcome. You didn't hit on a single one of them.
Unfortunately, as we know, there's absolutely no ways known to man to texture glass that could be fitted onto a truck.
What road do you live near where the surface is packed full of rubber tire marks? Must be pretty miserable to live there, with people burning tires all the time.
Hahahaha.... oh geez... :)
Let's back all the way back to third grade and cover the topic of "photosynthesis". You see, plants need light from the sun to grow! Now class, take one of those seeds you sprouted and put it on your windowsill, and put the other in the closet... we'll bring them back to compare in two weeks. Don't forget to water!
The amount of light transmission is probably the biggest factor in greenhouse design. Here in Iceland people have to use glass (most common) or hard plastic (less common) because of the wind, thin plastic hoop houses don't survive here. Most commonly used is single pane glass. Yes, you read that right. Here in a country with "ice" in the name, it's still considered worthwhile to let the heat pour out of your greenhouse in order to get a few extra percent sunlight. Now, we have hot water for heating which reduces (but doesn't eliminate) heating costs, but still, it drives home the point: to growers, light equals growth.
Greenhouses most definitely do not rely on "IR alone".
If you're curious as to why fogged surfaces are often seen as desirable in greenhouses - it's because of shading. Fogging only causes the greenhouse to lose a couple to several percent of the light (depending on the type of plastic or glass), but it means that all of the light is no longer coming from the same angle. This helps get light to leaves that would otherwise be shaded by other leaves.
Ironically, contrarily to what you wrote, glass-covered solar panels do care about IR transmission. They don't generate power from IR, but their efficiency is correlated to their temperature, and the temperature is correlated with the radiative equilibrium of their environment.
Like how hold concrete becomes slippery? Yep, just like with concrete, you need to resurface. But one expects them to use anti-scratch coatings, which would significantly reduce the rate of wear. The aggregate in typical concrete can be up to Mohs 7, but the cement is only Mohs 2-5. Raw unprotected glass is Mohs 5-6,5, but scratch resistant coatings can raise it to over 7 to avoid being scratched by quartz sand.
1) Traction glass. You can see through it just fine. And you don't need to be able to see through it (light rays taking parallel paths), you just need light - refraction and all - to largely get through. And not even all of it, it's fine to lose a good chunk of it compared to rooftop installs - see ""They'd be better on roofs" in my reply above.
How well can you see through your typical modern greenhouse? You don't need to have "perfect visual transparency" to let lots of light past a surface. In fact, your surface texturing can actually increase your potentential generation (see my comment about the potential of fresnel lensing above).
2) Most rooftops are also not angled correctly either. And unlike roads, most rooftops are not designed to bear the extra weight of panels. And again, see the "They'd be better on roofs" reply.
3) See the comments about damage and loadbearing in the same post.
4) Tanks rip all roads to pieces. But your not-so-subtle jab at the French who basically were responsible for you being an independent country (rather than a bunch of rabble-rousers quickly captured and hung by the British) is well noted.
5) Fields A) mean building dedicated projects, rather than hitting two birds with one stone (getting a road and a solar farm out of the same build process); and B) using up greenspace that most people would rather keep or use for other purposes.
Or see my reply above, where I cover a lot of the criticisms (I'll gladly go into more). There is nothing at all exotic about traction glass (aka "anti-slip glass").
Even in heavy traffic, the overwhelming majority of the road is exposed. And yes, that's the 405, in a high traffic area.
I assume that's a joke.
It's one of the "solar freaking roadways" peoples' concepts that makes me sigh out loud, even though I actually think that the concept of solar paving warrants further research. Having roads have "give" and generating power from that is like making cars constantly have to drive uphill. You're just stealing energy from the cars. Very inefficiently.
Meh, there's a solar bike path in the Netherlands and they don't seem to have excessive problems with dirt. Because rain exists. They got significantly higher generation than they were expecting - only about 1/3rd less than what you'd expect from rooftop mounted panels.
I too have criticisms of the "Solar Freaking Roadways", but let's start with common criticisms that aren't well grounded:
1) They'll scratch up: first off scratches can reduce light transmission but solar panels don't require good "optical quality", only transmission; the light is free to scatter on its way in. It's the same thing that applies to greenhouses - you may have noticed that many greenhouses use "fogged" plastic that you can't see through, yet still lets the vast majority of the light in (in that case, the scattering is actually seen as advantageous). Beyond that, in the case of roadways, I'd think it a given that they'd coat them with a an anti-scratch coat (aka harder than Mohs 7 / quartz sand, the hardest common natural material))
2) Traction: Traction glass exists - it's just surface texturing. They use it for semi-transparent flooring, it's nothing special.
3) "Glass would break and then shred tires": It's easy to make glass bear purely compressive loads (solid objects on both sides of it) without fracture - that's what it's best at. It's shear and tensile loads that glass is bad at, but these aren't applicable when it's flat on a hard surface. And lamination, like in windshields, prevents dangerous shards from coming off in the event of a fracture. This is not an actual limitation.
3) Shadowing: Go to Google Maps satellite view and look up random roads. The overwhelming majority of road surface is completely unshadowed at any point in time. Even in-city roads are overwhelmingly unshadowed. Shadows are practically irrelevant in the countryside except in wooded areas.
4) Costs: The costs of the materials for a road are a minority of the costs of the project, and continue to be a minority of the cost of the project under any realistic pricing for large-scale production of paving panels. A key driver for affordability, however, would be scale: this means large scale production (so road panels are similarly priced to rooftop panels plus the extra glass costs) and continuous paving systems. Anything smaller scale would have elevated costs.
5) "They'd be better on roofs": the main problem with roof installations is there is no way to do mass-scale continuous install (the sort of possibility that paving gives). Each roof has to be handled on its own, with its own engineering issues, with its own project overhead, its own inverters, etc. The key issue to cost reduction these days is getting rid of the overhead; panel production costs themselves have gotten quite low and keep going down. Furthermore, with a road you get "two birds with one stone" - a driving surface and a power generation surface built at the same time in the same space, sharing the same project overhead. It's fine to sacrifice some panel efficiency to glass, shadows, dirt, etc if it reduces your overhead costs.
All of this is not to say that I think they're inherently some sort of great idea that we should dump billions of USD into right this moment I simply think that they do deserve more development and testing, and I have issues with some of the criticisms that have been levied. On the other hand, I do have some issues with the "solar freakin' roadways" people. Number one on my list is the snow-melting concept. It takes five minutes to run the numbers on that and find that it takes way more energy than could ever be considered reasonable. You could melt thin layers of frost off the surface, but nothing of any relevant mass.
If one wants to pursue an anti-snow approach, my personal alternative is having an air bl
The summary is wrong. There is no surprise about how much water ice Pluto has, it's always been expected that it's predominantly water ice.
The actual article linked says that the maps show more water ice than was previously known, not than previously thought. It's hard to see through the surface frosts to see the water ice. Mountains are impossible on Pluto without water ice (or other high compressive strength material - aka, not N2, CH4, CO, etc). The instant mountains were seen, we knew that the crust was mostly water ice. And even before then, we knew that - regardless of what its crust was made of - that Pluto is in large part water ice, due to its density (1,86g/cm3).
We've known that water is one of the most common components of the universe, and the most dominant compound of the outer solar system, for over a century.
The summary is lousy. It's not "much less water ice than thought", it's much less "than was previously known". It had been hard to detect the water ice through the frosts previously.
It's always been expected that a large portion of Pluto's mass is water ice. Also, it was well known before NH arrived that any surface topography of significance would have to be from water ice, as the other ices are just too "soft" to hold up strong contours.
As for water ice being buried, why would you expect that? Water ice is lighter than nitrogen and carbon monoxide ices. It basically "floats" on them. There seems to be a sort of N2/CO/CH4 "mantle" which is exposed to the surface (and convecting) at Sputnik (the point nearest Charon). Elsewhere, however, a water ice crust floats atop it, seemingly progressively thicker the further one gets from Sputnik/Charon.
I find it interesting - perhaps coincidental, perhaps not - that Pluto is like our moon, with a crust thinner and more geologically active on the side of which it's tidally locked to its partner, and thicker/less active on the opposite side. If we can figure out Pluto's dynamics better, it might help us understand our own moon better.
Pluto is a beautifully, fascinatingly weird place. There's some good evidence that entire water-ice floating mountains have washed ashore and collected on the shores of Sputnik - perhaps water ice from the deep depths. Certainly there are shorelines that have this appearance today, and we can see smaller water-ice chunks floating and stuck between the roiling convection cells. If one pictures rolling back the clock, Pluto started out very hot (alternatively with multiple periods of heat, such as during the formation and/or capture of Charon). The first things to condense out would have been rocks, such as silicates, with a water ice ocean and a nitrogen/methane/CO atmosphere. Then the water ice would have frozen. Then the gases would have frozen atop it. But then you have a situation where you have an extensive heavier layer over an even more extensive, lighter layer. So there may be potential for cycling. But it's hard to say, because different crystal forms in different temperature and pressure conditions have different densities.
Charon also has a look of large chunks of water ice drifting around. But while Pluto has its active mantle exposed to space, Charon seems frozen in time. You can see structures that look like massive islands (or even continents) that have broken off from each other, drifted, then became frozen into place. And there's some crazy-massive rifting, as if some layers changed dramatically in size relative to others as they froze (Pluto too has rifting, but Charon's rifts are even more spectacular)
Huh? Sea level and vacuum performances are directly proportional, within only a small variation between propellants. Do you even understand why there's a difference between sea level and vacuum performance?
It is a small difference compared to a 21 percent difference in ISP.
The tank skin mass difference due to the density is a more relevant issue. But even still, as a general rule, hydrogen-based upper stages perform well better than RP-1 on a mass basis, which is why most companies and space programs use them. The main reason SpaceX doesn't is economic - they're going for mass production of nearly-identical stages with just small variations (engine nozzle shapes, tank lengths, etc).
No we could not do something that would be difficult on Earth "relatively easily" on Mars. We're not going to be sending freaking natural gas drilling rigs to Mars (Mars being a highly natural gas poor planet), nor are we even going to have the sort of detailed geological survey data we'd need to be able to do that for many decades. We consider it challenging to build a bloody shelter on Mars, and you want to set up a petrochemical industry?
Things have to be kept simple to make them plausible and affordable. Production systems have to be small, light, exceedingly reliable and not subject to be thrown off by unexpected local variations, with the whole process well-quantified from a Martian perspective. Drilling for resources on Mars fails on every last one of those.
My impression when they wrote "clean" was "clean from an environmental perspective". :)
Thrust is strongly correlated with density (as how fast you can burn a fuel depends on how fast your turbopumps can pump it into the chambers), so one can get a good sense of how good a fuel will be from a thrust perspective by its density. Which is why hydrogen makes for lousy first stages ;) Still, methane's reduced density definitely loses out over RP1. But I'm sure the thrust level will be fine.
You're correct about the "super-cooling" (they refer to it as densification, to avoid being mistaken for the phenomenon "supercooling"), which gives more thrust and lets them store more propellant - at a cost of additional complexity (mainly on the ground). I imagine they're probably not going to want to have to deal with that sort of complexity on Mars... but who knows?
You mention slush... slush and gel propellants provide an additional interest possibility, which is the ability to incorporate metal dusts into the burn. Aluminum offers a huge improvement to hydrocarbons and small improvement to LOX/LH in terms of ISP; it also provides a density boost. Lithium provides an even bigger boost to all cases, although obviously it poses additional handling difficulties. The most efficient chemical rocket engine ever tested dispensed with that altogether and burned molten lithium with hydrogen and fluorine (triprop... the hydrogen is there as a working gas, it doesn't contribute to the reaction). Got 542 sec ISP ;) According to CEA sims it's still a killer mix even if you use LOX instead of LF2... although it still depends on how much one is willing to hazard working with lithium. But that's all sort of a side point... if they use gel or slush propellants, particularly with hydrocarbons, they can really benefit by incorporating aluminum powder, which is quite safe and offers excellent density. Aluminum also tends to even out the burn and reduce vibration.
False. But don't just take my word for it, take CEA2's. Parameters: all chamber pressures set to identical 204.08, pi/pe set to give a constant 100:1 expansion ratio, mdot=2223.8 (same as the SSME). All fuels burned with LOX at a stoichiometric ratio. All chemicals at their boiling point except the RP1, which is set to 300K. RP1 simulated by dodecane.
ISP:
H2: 436,9
CH4: 365,6
C12H26: 360,6
Seriously, have you never looked at an ISP table before?
Nope. As is typical, it made up about 7% of the shuttle ET's mass. Nowhere near comparable to such an ISP difference.
Nope, CH4 freezes solid at 90,7K (versus LOX boiling at 90,2K). And it becomes way too viscous as it approaches its freezing point. That doesn't mean that they can't share a common bulkhead, but it does complicate it for long-term storage (aka, Mars missions)
That and because it's hypergolic and requires only trivial, lightweight engines - which isn't applicable to CH4.
This is pure fantasy. Mars's atmospheric concentration is 10ppb - in an atmosphere that's only 0,7% the pressure of Earth's to begin with. Earth's is 1700 ppb at two orders of magnitude higher pressure, and the concept of condensing methane out of the atmosphere at "rich spots" is ridiculous even here - where we have extremely detailed global surface-level data on where "rich spots" are. Lastly, as much as I'd love a detailed surface-level whole-planet geological resource survey of Mars, that's just not going to happen anytime remotely soon - if in our lifetimes at all.
Realistic missions involve using as little speculative technology or speculative data-finds as possible. Even the concept of producing hydrogen from water on Mars is looked at with hesitation (O2 from CO2 is trusted more; the feedstock is much more pure and predictable - the Mars 2020 rover will be testing that one out, hopefully it will go well). Even for O2 we still need to demonstrate a reliable, deliverable system for local storage (as well as industrial-scale production rather than tiny lab-scale production).
First off, I love your expectation that the instant a purchase takes place, everything is supposed to change, as if making and implementing plans and policy changes takes five seconds to complete.
Secondly, whether you like it or not, lots of people here have interest in SpaceX - both positive and negative. Which you can see by how many people comment on every one of these threads. So if you don't like it, tough. Go read a thread on some other topic.
Meh. CH4, H2 and RP1 are all clean, cheap fuels - the levels of pollution and fuel costs are practically non-issues here. ISP, thrust and density are what matter. Methane simply lies on the curve between RP-1 and H2 in terms of thrust, density and ISP (significantly closer to RP-1 than H2). H2 is easier to produce on Mars than methane, which is in turn easier to produce than RP-1 - in this regard, methane is closer to H2 than RP-1 (the mass fractions of current hydrocarbon synthesis from CO2 and H2 tend to produce more methane than heavier hydrocarbons, although the ratios depend on the catalyst, and new catalysts could change this, and you could always do subsequent steps to combine light hydrocarbons)
Methane probably is a good balance for Mars if you want local propellant production. And really, since Mars round trips are so far down the rocket equation chain, you pretty much have to either use extremely high ISP fuels, or go with local propellant production. SpaceX has chosen the latter.
So for the CEO of a rocket company, making a rocket is "outside his sphere"? Interesting.
What sort of filament were you using, out of curiosity? Were you using ABS? It's a lot more durable than, say, polyamide. Also, if they wanted, they could (unlike legos) add internal structural supports.
Also, my impresson was indeed that they wanted to print legos not to save money, but to make parts that don't exist elsewhere.
My presumption is that they're not trying to save money, that they're wanting to make parts that you can't get elsewhere (such as connectors to various types of real-world objects)
Hmm, just checked Shapeways, looks like their "frosted ultra-detail plastic" has a 0,1mm resolution. Sounds like the best option so far (if you don't mind it not being from ABS)
I suppose you could take the totally opposite route and choose Shapeways or iMaterialize's rubber/elastic type materials, to deliberately add extra flex into your connector at a cost of lower resolution.
For some reason I doubt that you need that sort of precision. I mean, five microns? The details inside the 8086 processor were 1,5 to 3 microns. Why would you ever need that kind of resolution for a plastic piece?
Lego interconnectors are 4,8mm across. 0,005mm would mean accurate to 0,1%. Looking at iMaterialize's printing options, one could use ABS like legos and get 0,3mm resolution, or high detail (UV cured) resin and get as low as 0,2mm resolution (but no colour options). Polyamide would also offer 0,3mm resolution and more colour options than ABS. Most other plastics are around 0,5mm resolution. The best resolution above (0,2mm) would yield an error of 4,2% on the connector. ABS and polyamide would be 6,3%. Given how much plastic flexes with such thin wall thicknesses I'd think that you could get a good fit like that.
Another option would be, if you had to err, err on the side of too tight of a fit, and if they don't fit together, sand it down.
Hmm, looking over it again, there is one option that offers 0,1mm resolution. But it's stainless steel, and unlike plastics, you're not going to get much flex in that ;)
Indeed, that's what I was recommending. Take it off the front page, but that doesn't mean that the comments need to be deleted. It just means that new people coming to the site aren't going to be bothered with a dupe.
Like the "mu" character that disappeared from the article about 3d printers today, leaving to lots of confusion in the comments?