You're insulating the hydrogen at -250C (~22K); the Lox is almost irrelevant, since it has such a higher heat of vaporization and density, and therefore low boiloff. Hydrogen insulation can be and has been done both inside and outside the tank -- the Saturn V upper stages put it inside. Inside the tank, the attachment between insulation and tank material is kept warm, which makes that problem easier. However, it's hard to make a lightweight insulation that the hydrogen doesn't soak through, and hydrogen has a very high thermal conductivity, so that destroys the insulating properties. The foam doesn't have to take pressure, but it has to be sufficiently sealed that you don't get conductive flow past eg your interlocking bricks.
Insulating hydrogen tanks is a decidedly non-trivial task, especially when you want ultra light weight for a rocket. It's rather far from obvious what the best answer is.
IMHO, the solution to the problem is very simple -- don't use hydrogen! Kerosene, propane, and methane are all better alternatives. They actually have higher performance by many relevant metrics, too. Hydrogen is *so* light weight (0.07 g/cc) that the tanks get big. The lower Isp of hydrocarbon fuels is more than compensated for by the better fuel / tank mass ratio in the vast majority of applications. And that's even before you count the high cost of handling hydrogen and designing engines to work with it -- it's enough colder than LOX to make a difference, and it has myriad other handling concerns that make the development programs expensive.
And yes, I do build rockets for a living. No, I haven't ever worked with hydrogen, but there's a reason for that...
I'm told one can get a port-a-potty delivered without any confirmation; just name and address. Of course, when you want it cleaned, taken away, or even just a month later, they want money...
Is it just me, or are the more humorous / inane tags showing up less? "duh" "haha" "itsatrap" and friends. Is this because the slashdot editors changed something, or because people are using them less?
But, then again, I'm one of the.01% of people on/. who don't think that the current White House is an incarnation of Cthulhu
I'd just like to speak up to show my solidarity here. The current White House is definitely not an incarnation of Cthulhu. Cthulhu would be far more honest about his evil ways, and certainly wouldn't need to do anything as wimpy as manufacturing data.
The default decoder is BSD licensed. This pushes adoption of the format by allowing commercial use (eg, in games) without worry. It's a case where BSD is an excellent choice. The point isn't that other people can implement their own decoders under whatever license -- it's that they can use the *default* decoder under its license in any way they want to. And, as a result, they do. That licensing decision has been a *huge* benefit to the Ogg format.
The reason rockets get cheaper is because of small entrepreneurial companies with new business methodology. Companies like XCOR (who I work for), Scaled, Armadillo, Microlaunchers, Masten, etc. A cheap space elevator can't be done by the current aerospace corporations for the same reasons they can't do rockets cheaply; claiming this is the fault of the technology is false.
The technology to make them affordable is not magic, and it's not CNT -- it's just simple engineering and business practices that are geared to a competitive commercial environment, not government contracts. It's here now, it will just take a little while before it gets all the way to orbit. CNT has the potential to shift it from affordable to dirt cheap by improving the performance an order of magnitude. When you can do SSTO with reasonable payload fraction on pressure fed (rather than pump fed) engines, everything gets easier and cheaper.
I'm unconvinced that space and weight are significant limitations; also, I don't think they're unique to rockets -- space elevators have a maximum payload mass as well. I don't think bulk is a major issue -- the only truly bulky thing is stuff like habitation space and tankage. The easy answer to that is what Bigelow is doing: make it inflatable. There's nothing inherently problematic about having 95% of your liftoff mass be propellant; it just means you need to scale up if you want a single large payload. Falcon 9 will probably be large enough for the vast majority of payloads at ~10 tons to LEO. And remember that CNT materials make the payload fraction bigger.
BTW, I think it's pretty clear that all Mars Direct needs is a 100-ton class heavy lift booster (Saturn V or Shuttle stack without the Shuttle). An elevator probably makes it somewhat cheaper, just because as you go past Earth orbit the rockets start to drop precipitously in efficiency and the elevator gains efficiency.
There is no reason to believe that the cruft attached to current rockets will remain. By the time a space elevator would be operational, you won't be buying launch services from the likes of NASA and the old aerospace companies; you'll be buying them from the plethora of small startups that are currently working on suborbital flight, with orbital to come after that. These companies are pushing hard for saner, more practical range requirements, and the Mojave, New Mexico, and Oklahoma spaceports, as well as AST (the relevant arm of the FAA) are all on their side.
Also, rockets don't have a throughput problem -- high performance reusable orbital rockets will cost similar amounts or less than a space elevator in terms of capital investment per cargo rate. Need more throughput? Build more of them and launch more often. Upgrading a space elevator, on the other hand, is harder. What cargo restrictions do you see on rockets? The only ones I can think of are that it has to survive about 3 Gs, which isn't very hard. Space elevators, on the other hand, have to survive radiation and can't go to low earth orbit.
The major case I can see for space elevators is major cargo to destinations beyond Earth orbit (Mars, asteroids) where the ability to gain energy as you fall off the end is useful, and returning bulk materials from asteroid mining, where it's useful not to have to bring the asteroid in so close. But both of those are much longer term than a company like LiftPort is looking at.
I recently heard the suggestion that one should evaluate candidate's positions not on what they say they will do, or are likely to try to do, but on what they actually *could* do if elected. Examined in this light, Paul looks a lot more appealing. And I definitely want someone with more respect for the constitution.
I don't agree with all of his policies, actually. I do, however, think that he's honest and consistent, and therefore predictable. He claims his right-to-life stance is based on a states rights stance, and that the federal government should stay out of it. In this instance I disagree with him (rather strongly), but I like the general small-federal-government stance. However, I'm not terribly worried about this -- he would have very little power to actually do anything about it. He's also against the income tax, but I'm not worried he'd repeal it -- not for lack of trying, but for lack of effective power to do so. But that comes from a desire to cut the size of the federal government, which I firmly agree with and think he would have the power to do.
He's also the sort of libertarian who actually votes to keep government small, voted against the Patriot Act, is against subsidizing large corporations... plenty of things I support. I'm not in favor of him because I think he'd be perfect, but rather because I think he'd shake things up more than a little bit, and mostly in ways I'd appreciate.
And who do you want instead? Hillary? If you thought Bush was eroding civil liberties, it would be different but the same under Hillary. "Think of the children" instead of "Think of the terrorists." The end result would be different, to be sure -- a smaller erosion of freedoms, with a direct impact on many more people. The Democratic candidates are not in favor of personal liberties in the slightest (neither are most of the republicans).
Ron Paul is a libertarian, and more than slightly loony; that said, he's not the bat-shit loco of the Libertarian party. At least with him in the White House, it wouldn't be business as usual.
Tether deployment because so far attempts to uncoil long cables in outer space have only been marginally successful. Just because it's easy to describe doesn't mean it's easy to do. Not saying it's impossible, but it needs significant R&D -- ie a breakthrough.
"Not very fast" is an understatement. You need to ascend at speeds of several hundred miles per hour in order to have the elevator be interesting. Remember, you've got over 20,000 miles to go! Even if you're moving bulk cargo that doesn't care about the speed, you need to get the car and the weight off the bottom of the elevator so you can start the next one up (the weight it puts on the tether goes down as it climbs). Cable cars transfer force by clamping the cable; an elevator needs some sort of wheels. Be they metal like train wheels or rubber like car wheels, managing 20,000 miles at speeds somewhere around mach 1, straight up, is not trivial.
That requisite speed is also why breakthroughs in power transmission and motors are required. If you can't get that speed, the economics don't work, and you lose to the (vastly improved thanks to better materials) rockets.
I recently heard a very interesting point made: when considering what a presidential candidate claims, look only at the things they actually have the power to do. Does a president have the power to cut taxes, cut spending, and shrink the government? Certainly. Do they have the power to repeal income taxes wholesale? Not bloody likely. Paul may be against income taxes and for a gold standard, but neither of those is likely to happen; a generally libertarian, small-government focus, however, just might.
Ron Paul might be a bit loony, but he'd certainly be something other than business as usual on the hill. He's honest and seems to be for a more transparent government based on principles rather than lobbying.
You also need breakthroughs in tether deployment technology, power transmission, tires, electric motors, and probably some others I'm forgetting. Power transmission is almost as hard as the materials science. And the rest, while much easier than the materials science, are by no means trivial.
Even so, most space elevator advocates miss the major point: space elevator class engineering materials will enable better rockets long before they enable a space elevator. Tanks made out of elevator-grade nanotube composites would enable cheap and easy SSTO rockets.
And before people start complaining about mass ratios: it's not about fuel mass, it's about dollars. And I won't go into the math here, but rockets aren't all that inefficient when it comes to converting chemical energy into orbital energy (~10% efficiency is a reasonable expectation for a high performance SSTO); this is close enough to space elevator efficiencies that capital and operating costs dominate.
Some of us prefer to stand by our principles, even when it means making a decision that is not the easiest one, or the one that brings us the most money. You say there's nothing we can do about the fact that media companies want DRM, but there is. We can decline to implement it. Sure, one person won't make much difference. But each skilled developer who declines to work for them means they have to pay a bit more, use someone slightly less skilled. A drop in the bucket, to be sure. Far easier to throw up our hands and say 'oh well, that's what they want, they'll get someone anyway.' Sometimes doing the right thing is hard, but if enough people do, it can make a difference.
In the real world, it takes coordination to make that happen in a way that will make a difference. The GPL, and the GPLv3, is exactly that -- a set of principles to stand upon, in a coordinated fashion.
The world needs extremists. Progress rarely happens without them.
I tend to be a GPL fan. For stuff I write, it's my preferred license. However, there are a few cases where I think BSD type licenses are superior. The major one is where you're trying to create a standard. For example, Ogg Vorbis -- it is far more valuable to the community if it *does* get included in proprietary places, because promoting the *format* is a good thing. BSD promotes exactly that. There are plenty of similar examples.
Sometimes the right solution to a problem isn't a new law. I confess I'm not sure what the right solution is (it might be "ignore it," or it might not), but I don't think it's a new law...
Slashdot Mirror
You're insulating the hydrogen at -250C (~22K); the Lox is almost irrelevant, since it has such a higher heat of vaporization and density, and therefore low boiloff. Hydrogen insulation can be and has been done both inside and outside the tank -- the Saturn V upper stages put it inside. Inside the tank, the attachment between insulation and tank material is kept warm, which makes that problem easier. However, it's hard to make a lightweight insulation that the hydrogen doesn't soak through, and hydrogen has a very high thermal conductivity, so that destroys the insulating properties. The foam doesn't have to take pressure, but it has to be sufficiently sealed that you don't get conductive flow past eg your interlocking bricks.
Insulating hydrogen tanks is a decidedly non-trivial task, especially when you want ultra light weight for a rocket. It's rather far from obvious what the best answer is.
IMHO, the solution to the problem is very simple -- don't use hydrogen! Kerosene, propane, and methane are all better alternatives. They actually have higher performance by many relevant metrics, too. Hydrogen is *so* light weight (0.07 g/cc) that the tanks get big. The lower Isp of hydrocarbon fuels is more than compensated for by the better fuel / tank mass ratio in the vast majority of applications. And that's even before you count the high cost of handling hydrogen and designing engines to work with it -- it's enough colder than LOX to make a difference, and it has myriad other handling concerns that make the development programs expensive.
And yes, I do build rockets for a living. No, I haven't ever worked with hydrogen, but there's a reason for that...
Unless I'm mistaken, this isn't an appeals court, and therefore doesn't actually set precedent. Other courts can still apply the same logic though.
I'm told one can get a port-a-potty delivered without any confirmation; just name and address. Of course, when you want it cleaned, taken away, or even just a month later, they want money...
Dupe tag, anyone? Is it me or do tags like "Dupe" no longer show up?
It would have been really fun if they turned around and threatened to print names if they didn't get ad money :)
And producer, it would seem.
Is it just me, or are the more humorous / inane tags showing up less? "duh" "haha" "itsatrap" and friends. Is this because the slashdot editors changed something, or because people are using them less?
But, then again, I'm one of the .01% of people on /. who don't think that the current White House is an incarnation of Cthulhu
I'd just like to speak up to show my solidarity here. The current White House is definitely not an incarnation of Cthulhu. Cthulhu would be far more honest about his evil ways, and certainly wouldn't need to do anything as wimpy as manufacturing data.
The default decoder is BSD licensed. This pushes adoption of the format by allowing commercial use (eg, in games) without worry. It's a case where BSD is an excellent choice. The point isn't that other people can implement their own decoders under whatever license -- it's that they can use the *default* decoder under its license in any way they want to. And, as a result, they do. That licensing decision has been a *huge* benefit to the Ogg format.
The reason rockets get cheaper is because of small entrepreneurial companies with new business methodology. Companies like XCOR (who I work for), Scaled, Armadillo, Microlaunchers, Masten, etc. A cheap space elevator can't be done by the current aerospace corporations for the same reasons they can't do rockets cheaply; claiming this is the fault of the technology is false.
The technology to make them affordable is not magic, and it's not CNT -- it's just simple engineering and business practices that are geared to a competitive commercial environment, not government contracts. It's here now, it will just take a little while before it gets all the way to orbit. CNT has the potential to shift it from affordable to dirt cheap by improving the performance an order of magnitude. When you can do SSTO with reasonable payload fraction on pressure fed (rather than pump fed) engines, everything gets easier and cheaper.
I'm unconvinced that space and weight are significant limitations; also, I don't think they're unique to rockets -- space elevators have a maximum payload mass as well. I don't think bulk is a major issue -- the only truly bulky thing is stuff like habitation space and tankage. The easy answer to that is what Bigelow is doing: make it inflatable. There's nothing inherently problematic about having 95% of your liftoff mass be propellant; it just means you need to scale up if you want a single large payload. Falcon 9 will probably be large enough for the vast majority of payloads at ~10 tons to LEO. And remember that CNT materials make the payload fraction bigger.
BTW, I think it's pretty clear that all Mars Direct needs is a 100-ton class heavy lift booster (Saturn V or Shuttle stack without the Shuttle). An elevator probably makes it somewhat cheaper, just because as you go past Earth orbit the rockets start to drop precipitously in efficiency and the elevator gains efficiency.
There is no reason to believe that the cruft attached to current rockets will remain. By the time a space elevator would be operational, you won't be buying launch services from the likes of NASA and the old aerospace companies; you'll be buying them from the plethora of small startups that are currently working on suborbital flight, with orbital to come after that. These companies are pushing hard for saner, more practical range requirements, and the Mojave, New Mexico, and Oklahoma spaceports, as well as AST (the relevant arm of the FAA) are all on their side.
Also, rockets don't have a throughput problem -- high performance reusable orbital rockets will cost similar amounts or less than a space elevator in terms of capital investment per cargo rate. Need more throughput? Build more of them and launch more often. Upgrading a space elevator, on the other hand, is harder. What cargo restrictions do you see on rockets? The only ones I can think of are that it has to survive about 3 Gs, which isn't very hard. Space elevators, on the other hand, have to survive radiation and can't go to low earth orbit.
The major case I can see for space elevators is major cargo to destinations beyond Earth orbit (Mars, asteroids) where the ability to gain energy as you fall off the end is useful, and returning bulk materials from asteroid mining, where it's useful not to have to bring the asteroid in so close. But both of those are much longer term than a company like LiftPort is looking at.
No wireless. Less space than a Nomad. Lame.
I recently heard the suggestion that one should evaluate candidate's positions not on what they say they will do, or are likely to try to do, but on what they actually *could* do if elected. Examined in this light, Paul looks a lot more appealing. And I definitely want someone with more respect for the constitution.
I don't agree with all of his policies, actually. I do, however, think that he's honest and consistent, and therefore predictable. He claims his right-to-life stance is based on a states rights stance, and that the federal government should stay out of it. In this instance I disagree with him (rather strongly), but I like the general small-federal-government stance. However, I'm not terribly worried about this -- he would have very little power to actually do anything about it. He's also against the income tax, but I'm not worried he'd repeal it -- not for lack of trying, but for lack of effective power to do so. But that comes from a desire to cut the size of the federal government, which I firmly agree with and think he would have the power to do.
He's also the sort of libertarian who actually votes to keep government small, voted against the Patriot Act, is against subsidizing large corporations... plenty of things I support. I'm not in favor of him because I think he'd be perfect, but rather because I think he'd shake things up more than a little bit, and mostly in ways I'd appreciate.
And who do you want instead? Hillary? If you thought Bush was eroding civil liberties, it would be different but the same under Hillary. "Think of the children" instead of "Think of the terrorists." The end result would be different, to be sure -- a smaller erosion of freedoms, with a direct impact on many more people. The Democratic candidates are not in favor of personal liberties in the slightest (neither are most of the republicans).
Ron Paul is a libertarian, and more than slightly loony; that said, he's not the bat-shit loco of the Libertarian party. At least with him in the White House, it wouldn't be business as usual.
Tether deployment because so far attempts to uncoil long cables in outer space have only been marginally successful. Just because it's easy to describe doesn't mean it's easy to do. Not saying it's impossible, but it needs significant R&D -- ie a breakthrough.
"Not very fast" is an understatement. You need to ascend at speeds of several hundred miles per hour in order to have the elevator be interesting. Remember, you've got over 20,000 miles to go! Even if you're moving bulk cargo that doesn't care about the speed, you need to get the car and the weight off the bottom of the elevator so you can start the next one up (the weight it puts on the tether goes down as it climbs). Cable cars transfer force by clamping the cable; an elevator needs some sort of wheels. Be they metal like train wheels or rubber like car wheels, managing 20,000 miles at speeds somewhere around mach 1, straight up, is not trivial.
That requisite speed is also why breakthroughs in power transmission and motors are required. If you can't get that speed, the economics don't work, and you lose to the (vastly improved thanks to better materials) rockets.
I recently heard a very interesting point made: when considering what a presidential candidate claims, look only at the things they actually have the power to do. Does a president have the power to cut taxes, cut spending, and shrink the government? Certainly. Do they have the power to repeal income taxes wholesale? Not bloody likely. Paul may be against income taxes and for a gold standard, but neither of those is likely to happen; a generally libertarian, small-government focus, however, just might.
Ron Paul might be a bit loony, but he'd certainly be something other than business as usual on the hill. He's honest and seems to be for a more transparent government based on principles rather than lobbying.
So support Ron Paul. He may be more than a bit loony, but you'd be hard pressed to say it would be business as usual with him in the White House.
You also need breakthroughs in tether deployment technology, power transmission, tires, electric motors, and probably some others I'm forgetting. Power transmission is almost as hard as the materials science. And the rest, while much easier than the materials science, are by no means trivial.
Even so, most space elevator advocates miss the major point: space elevator class engineering materials will enable better rockets long before they enable a space elevator. Tanks made out of elevator-grade nanotube composites would enable cheap and easy SSTO rockets.
And before people start complaining about mass ratios: it's not about fuel mass, it's about dollars. And I won't go into the math here, but rockets aren't all that inefficient when it comes to converting chemical energy into orbital energy (~10% efficiency is a reasonable expectation for a high performance SSTO); this is close enough to space elevator efficiencies that capital and operating costs dominate.
Some of us prefer to stand by our principles, even when it means making a decision that is not the easiest one, or the one that brings us the most money. You say there's nothing we can do about the fact that media companies want DRM, but there is. We can decline to implement it. Sure, one person won't make much difference. But each skilled developer who declines to work for them means they have to pay a bit more, use someone slightly less skilled. A drop in the bucket, to be sure. Far easier to throw up our hands and say 'oh well, that's what they want, they'll get someone anyway.' Sometimes doing the right thing is hard, but if enough people do, it can make a difference.
In the real world, it takes coordination to make that happen in a way that will make a difference. The GPL, and the GPLv3, is exactly that -- a set of principles to stand upon, in a coordinated fashion.
The world needs extremists. Progress rarely happens without them.
I tend to be a GPL fan. For stuff I write, it's my preferred license. However, there are a few cases where I think BSD type licenses are superior. The major one is where you're trying to create a standard. For example, Ogg Vorbis -- it is far more valuable to the community if it *does* get included in proprietary places, because promoting the *format* is a good thing. BSD promotes exactly that. There are plenty of similar examples.
So... make sure they know that. Call them up and complain.
Sometimes the right solution to a problem isn't a new law. I confess I'm not sure what the right solution is (it might be "ignore it," or it might not), but I don't think it's a new law...
Actually, that's the whole point. Did you ever hear of anyone Spiderman ensnared dieing of cancer? OK then.
I imagine that's skin / nerve temperature, not air temp. At 50F air temp, your skin is a lot warmer than that.