See, I think that a more important list of which books were banned would be a list of which public institutions did the banning. If there are provincial, backwards-minded, insular communities out there banning books, I'm more interested in knowing where they are than what they're banning.
"We remain concerned about any devices or software that permit listeners to transform a broadcast into a music library," RIAA spokesman Jonathan Lamy said.
You mean like taping songs off the radio? You fucking whore.
Only in the sense that most high explosives are nitrogen compounds. Most WWII bombs did not, in fact, use nitroglycerin, or explosives based upon nitroglycerin. Go look it up, I'll wait.
Torpex is RDX, TNT, and powdered aluminum. Tetrytol is Tetryl and TNT. Picratol is picric acid and TNT. Pentolite is PETN and TNT. Octol is HMX and TNT. Minol is TNT, ammonium nitrate, and aluminum. Amitol is TNT and ammonion nitrate. Comp A is RDX and a plasticizer. Comb B is TNT, RDX, and wax. Baronol is TNT, barium nitrate, and aluminum powder. The PTX family is RDX, tetryl or PETN, and TNT.
Those are the major explosives used during WWII. Not a single one has nitoglycerin in it.
As for Nitrocellulose only exploding when confined. What do you think a bomb casing is, if not confinement?
There is a tremendous difference between an explosive and a high explosive. Even black powder will explode when confined, but black powder never, ever detonates. You can make a pipe bomb out of match heads, but nobody who knows anything would describe matches as a high explosive. High explosives detonate, meaning that the reaction front propagates through the material supersonically. Low-order explosives don't do that, they simply deflagrate, burn rapidly. Nobody in their right mind would use a low-order explosive like nitrocellulose in a bomb, not when anything more suitable was available.
I repeat: neither nitroglycerin nor nitrocellulose were routinely used as bomb fill in WWII. I won't rule out some Yugoslavian partisan group maybe mixing up some guncotton and using it in makeshift mortars, but that's about all it would have been used for.
TNT is most definitely not nitroglycerin. Where the hell do you people come up with this stuff?
TNT is trinitrotoluene, otherwise known as C6H2(NO2)3CH3, or 2,4,6-trinitromethylbenzene.
Nitroglycerine is otherwise known as C3H5N3O9, or 1,2,3-Tris-nitrooxy-propane.
Nitroglycerine is prepared by nitrating glycerine. TNT is prepared by nitrating toluene. They are two very different molecules, with very different properties.
I fucking love when people repeat as truth completely inaccurate information, without even the merest thought they might be spouting bullshit. I swear, some days I'm not sure whether I'm reading Slashdot or Fark.
Since HE is more potent than TNT, it's rated potential is higher than its weight.
TNT is high explosive.
ANFO's barely a high explosive, and to get it to really detonate at all, as opposed to simply burn rapidly, you need to confine it properly and set it off properly, and for ideal results you set it off with a bit of TNT.
A given weight of TNT will certainly produce better results than a given weight of ANFO.
Naw. Because the range at which you're seeing a given pressure level is much shorter. As he said, it was to simulate a nuke from a blast perspective. So to study a given level of blast pressure, you could either standoff a given distance from a 5kt blast of HE, or standoff a larger distance from an 8kt nuke.
All sorts of fun stuff has been done to simulate various aspects of nuclear weapons. Operation Sailor Hat was another blast sim, using 500 tons of TNT. When I was blowing stuff up for the Navy, I saw films of this test, from high-speed cameras mounted on a nearby destroyer, and you could see the steel torpedo tubes just ripple like a sheet in the wind when the shockwave hit.
One guy I know worked for a military contractor at one point, trying to simulate the flash effect of a bomb. They came up with a biiig double-barreled cannon. One barrel fired, at supersonic velocities, a big blast of liquid oxygen. The other fire, at supersonic velocities, a big blast of powdered aluminum. I haven't found films of that, but, wow.
What happens when explosives are stored improperly (and I can't imagine anything more improper) is the material separates. This leaves the inert material and nitroglycerine. Thats about as unstable as it gets. Nitro is bad news.
That's, of course, only the case for explosives which use nitroglycerine.
As this is WWII ordnance, we're probably not looking at any of those. Could be straight TNT, which is extremely stable, but various alkali compounds of the sort found in seawater can react with it to form a variety of compounds that are unstable to heat and impact. Could be Composition B, which is a mixture of TNT and RDX, so the same thing applies, or Comp A, which is straight RDX and a plasticizer, not so stable as Comp B. Ammonium picrate was used as a bursting charge, and is incredibly stable to shock and friction, but, again, seawater. Could also be Torpex, another popular one, and another RDX/TNT mixture. Problem with all of these is primarily the seawater environment reacting with the TNT to produce unstable products.
Nitrocellulose wasn't used in any of the common WWII high-explosives, nor was nitroglycerin; most high explosives of the day were varying mixtures of TNT, RDX, and sometimes PETN or Tetryl. Nitrocellulose isn't a high explosive at all; it doesn't detonate, it deflagrates, and the propagation of the chemical reaction through the material is below the speed of sound. What it was for, up until and probably throughout WWII, was a propellant, a replacement for gunpowder. It only explodes at all when confined; flash paper is basically straight nitrocellulose, and you can light that stuff off while holding it in your hand.
Is it possible to build a craft that can use wing lift all the way up to LEO?
Maybe.
In a real gas, aerodynamic lift is always accompanied by aerodynamic drag, and the ratio of the two is not dependent upon density or pressure or altitude. Until the point at which you actually achieve orbit, if you are relying upon aerodynamic lift to keep you in the sky, there's a certain amount of drag you have to overcome just to keep accelerating, and you can't make that problem go away by playing with the altitude.
The absolute best hypersonic lifting body designs anyone's been able to come up with, even theoretically on paper, have lift:drag ratios on the order of 10:1, so you need a thrust:weight ratio of at least.1:1 to keep accelerating.
After all, if you're on the dark side, the entire mass of the earth should be shielding you (ever so slightly) from the gravitational pull of the sun.
No it shouldn't. The dark side of the moon is frequently illuminated by sunlight; it's only "dark" in the sense that it's the side that faces away from the earth, so we can't see it from here. It doesn't mean that the sun never shines on it.
Fact is less than 25% of all oil is consumed to fuel our cars and power our homes.
FSVO 'fact.'
In the real world, upwards of 40% of a given barrel of oil ends up as gasoline, and maybe up to 60%. Gasoline. That's used in cars, military vehicles, and small planes. It's not used to power or heat our homes.
The other 75% goes directly to manufacturing, and thus demand will not be significantly reduced by simply adding solar.
Wrong. Plastics and other manufacturing concerns consume the minority of each barrel of crude. Now, granted, if we stop using the lighter fractions of crude to drive our cars, that doesn't mean we can magically turn the whole barrel into heavier stuff suitable for plastics feedstocks, but your numbers are way off.
We have solar panels today nearing the theoretical maximum effeciecy of the substrate used to convert it.
Yeah, and? Next step is to make them cheaper. Or more durable, which basically amounts to the same thing.
Besides, we've already got the technology to move beyond fossil fuels, it's as safe or safer than burning coal, pollutes a helluva lot less, and has enough fuel sitting around to last us practically forever: fission. The only thing lacking is the political will, and the only problem is that people are stupid.
Point 2: The article suggests 4 tuners, but how many should be recordable at one time? The HDTV TiVo unit can only record from any two tuners at a time.
Not to mention that if your source for your programming is digital cable, you still need a set-top box. For me to use two tuners on my TiVo, I'd still need two boxes from my cable company. I could see that as being reasonable, but come on, you've got TiVo, so it's not like you need to schedule your viewing to accomodate a program schedule, and anything worth watching is going to be repeated soon enough anyway. Four tuners strikes me as completely superfluous.
These solar sails are pretty useless. Here http://solarsails.jpl.nasa.gov/introduction/design -construction.html are calculations from NASA guys. It looks like this Japanese sail has acceleration of few mm/s^2
And a few millimeters per second per second is useless, why?
3 millimeters per second squared, and after a week you're moving at 1.8 kilometers per second. After a month, 7.2 kilometers per second. After 2 months, you've already exceeded Earth's escape velocity from the surface, let alone from orbit. Solar escape velocity at 1 AU is about 48 kilometers per second, so it would take you half a year to get fast enough to escape the solar system altogether. Actually, less than that, because as you're accelerate you're moving outward and so the solar escape velocity from your present position is continuously decreasing, but I'm in no mood for calculus right now.
These accelerations seem small, and hell, sure, they are small, but when you're applying even tiny accelerations constantly, over an extended period of time, that acceleration adds up to meaningful speeds. What kind of acceleration do you think the.09 Newtons from DS-1's ion engine was managing?
It would take solar sail 100 years to get to alpha centauri if it had acceleration 10 m/s^2
That's damned fast. Sustained 1g acceleration is pretty much up in indistinguishable-from-magic, though.
table 3 in the above link, there is "-" in the table for 5 m/s^2 and less , that is it will never get away from sun
No, that's ridiculous. As long as you have the thrust to move away from the sun, you'll "get away from the sun," because as I mentioned, the further out you are, the lower the solar escape velocity at your current position is. Hell, even the.3m/s sail listed in that table has a 'terminal velocity' of 671 kilometers per second, and solar escape velocity from the surface of the sun is only 618 kilometers per second.
And that's an entirely meaningful acceleration, because it's so constant. Your payload will be an enormous fraction of your total mass, instead of the tiny fraction of total mass it is with chemical rockets, so you're not wasting energy hauling around fuel..3m/s/s may not sound like much, but since it's constant, it adds up quick. Remember, v(t)=at+v(0), so that.3m/s/s gets you to rather incredible speeds pretty rapidly.
Hell, cut it by a factor of 1,000, and it's still tremendously useful. The engineering difficulty is in actually producing large sails, not in being able to put them to good use once we can build them.
It can actually be quite meaningful acceleration, depending upon what sort of payload you're talking about. Keep in mind that Deep Space One was a useful space mission, and its ion engine provided a maximum thrust of about.09 Newtons. At 1 AU from the sun, you're going to get about 100 times that force exerted on each square mile of sail.
That's quite acceptable, especially because it scales so well. This would be admirably suited for interplanetary bulk cargo transportation, ferinstance. Sure, it might take each particular sail/cargo unit a while to get moving, but you could set up a series chain of them and get a pretty darned good throughput.
Using onboard rockets to steer doesn't help you slow down. As you point out, the gravitational pull of the destination star will cause you to accelerate even more. You'll end up heading towards your destination at greater than the escape velocity for that system.
This doesn't help you stop. To do that, you flip yourself around so that the sail is pointing towards the destination, and you use the radiation pressure from that star to kill your velocity. Can't do this if you're already jettisoned it.
And, no, chemical rockets won't work to shed that much velocity. If you get get that much delta-v from chemical rockets, you'd just use chemical rockets to get on your way as well. But that's precisely why you're using a solar sail instead: chemical rockets suck in terms of specific impulse.
What I dont understand is how they intend to protect these massive sails from being shot full of holes by meteorites and space dust as it propels its way through space.
They don't need to. Any holes punched by micrometeorits will be, even in the aggregate, infinitesimal compared to the total sail area.
Also, seing as how it is powered by solar wind, what happens when the craft is between 2 or more stars which are all exerting equal force on the sails.
The article's claims aside, solar sails are an abysmal technology for interstellar travel.
For example, "The Theory of Flight" has not been conclusively proven as a "Law" yet.
What do you mean "yet?" There isn't some sort of progression whereby theories eventually become laws after there's enough supporting evidence.
In science, a theory is an attempt to explain a wide and diverse set of physical phenomena as arising from a smaller set of rules. Theories are never confirmed, never "proven," in the colloquial sense of the word, but they are "proven" in the classic sense of the word, meaning "tested." The test of a theory lies in explanation and prediction. Does it explain what we see? Does it predict things that we haven't yet seen? When we go out looking for those predictions, are they confirmed? Well, then, this is a successful theory.
A law is simply an ad hoc observation, a postulate, and doesn't necessarily even have any explanatory value. The Idea Gas Law, ferinstance, says PV=nRT. It doesn't tell you *why* "ideal" gases behave in this fashion; heck, real gases are only approximations of ideal ones, but it's still a useful postulate.
And a fact is simply a statement for which there is such overwhelming evidence that it would be perverse for one to withhold provisional assent.
There is no progression from theory -> law -> fact.
Re:Military Laser Tag Equipment Gone Berzerk!!!!.
on
Modding Laser Tag Gear?
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· Score: 3, Insightful
I call 'bullshit.' How would banging the emitters around result in a dramatic power increase? That's just silly.
so how bright is it to give the fundies access to an ingredient
Raw uranium is one of the most abundant metals on the planet. In a given square mile area, down to a depth of one foot, you'll find over 2,000 kilograms of uranium.
If our safety depends on keeping this ubiquitous element out of the hands of terrorists, they've Already Won[tm].
Given the other blatant misinformation in his post, I'm not inclined to lend him much credence. Example:
The chemists always chuckled at the physcicists at Los Alamos whenever they stuck a metal shovel into uranium. An intense fire starts.
This is nonsense. Uranium is only pyrophoric when finely divided. A chunk of it isn't any more likely to catch fire when you "strike a metal shovel into it" than the metal shovel itself is.
We use DU 'cause it's cheap, and there's lots of it laying around. It's used for ballast, for counterweights for aircraft control surfaces, and a variety of other uses. It's not radioactive to any meaningful degree, and it's not any more to be concerned about than any other toxic heavy metal, such as lead.
However, as far as I can tell, there isnt anything preventing DU material from being bred into isotopes with far more dangerous fission potential.
Sure there is.
First, you've actually got to transmute it. You can do this by exposing it to a thermal neutron flux, like you get from an operating fission reactor. The occasional U-238 atom will grab a neutron and transmute via a decay chain to Pu-239. That's how breeder reactors work.
So now you've got your big mass of U-238 with a few atoms of Pu-239 scattered throughout it. The chemical separation of the two is rather expensive, rather difficult.
Neither of these two steps are particularly hard to "figure out." They are very hard to implement.
You're grotesquely overstating the radiological hazards of U-238.
Some general information. Naturally-occurring uranium is composed of three different isotopes. It's 99.2745% U-238,.72% U-235, and.0055% U-234. Of these three isotopes, only U-235 will usefully sustain a fission chain reaction.
To use uranium in the production of nuclear power, it must be enriched. The result of the enrichment process is uranium with a U-235 percentage of from 3-5%, if you're talking about a civilian power plant, or upwards of 90%, if you're talking about a naval reactor.
What's left over from this process is the depleted uranium. It's called that because it's been depleted of the U-235. In other words, it's actually less radioactive than naturally occurring uranium, one of the most abundant elements on the planet.
So how radioactive is it? Not very. The measure of radioactivity is the Curie. 1 Ci is equal to 3.7*10^10 radioactive decays per second. In SI units, we use the Becquerel, and 1 Bq is equal to 1 radioactive decay per second, or 1 Bq = 2.703*10^-11 Ci.
Now, plain, natural uranium has an activity level of 25 Bq/kilogram. Consider for a second how amazingly low that is: in one kilogram of natural uranium, there are only 25 radioactive decays each second. That's about 4 moles of uranium, by the way, so that's roughly 2.4*10^24 atoms.
By comparison, the C-14 isotope of carbon is present to such a degree in organic matter that a random block of the stuff has an activity level of 6 pCi/g. Potassium-40 is also present in organic matter, to the tune of 11 pCi/g. Hell, take a 70 kilogram adult, and total up the naturally occurring radioisotopes in his body (the uranium, the thorium, the K-40, the radium, the C-14, the tritium, the polonium), and you'll see that a human being has an activity level of over 19,000 Bq, or 278 Bq/kg.
Human beings are over 11 times as radioactive as natural uranium, and even more radioactive than U-238.
I've never understood why they were so gung-ho about this stupid idea in the first place when most power grids already have multi-core fiber optic cable hidden inside the neutral wire.
What neutral wire? There's no neutral wire up on the poles. When you see three wires up there, that's one wire for each phase. In residential neighborhoods, you'll see a phase tapped off to feed a transformer. The output of the transformer feeds each house through two wires, each wire being a 120-volt leg, with 240 volts between them.
I haven't played around with the utility's stuff up on the poles, but I've replaced enough electrical services to note the absence of a neutral. There's no neutral in a earth-return system.
(in fact the US Navy uses them to transmit extremly low frequency/long wavelength signlas to its submerged subs!
No, it doesn't. The Navy has specific special-purpose antennas for that purpose. It does not use powerlines.
Sure, they look like power lines, due to the fact that they're metal wires strung overhead on poles, but they're not feeding AC to anyone's toaster or television, and total radiated power is a handful of watts.
Slashdot Mirror
See, I think that a more important list of which books were banned would be a list of which public institutions did the banning. If there are provincial, backwards-minded, insular communities out there banning books, I'm more interested in knowing where they are than what they're banning.
"We remain concerned about any devices or software that permit listeners to transform a broadcast into a music library," RIAA spokesman Jonathan Lamy said.
You mean like taping songs off the radio? You fucking whore.
Most WWII bombs used nitro based explosives.
Only in the sense that most high explosives are nitrogen compounds. Most WWII bombs did not, in fact, use nitroglycerin, or explosives based upon nitroglycerin. Go look it up, I'll wait.
Torpex is RDX, TNT, and powdered aluminum. Tetrytol is Tetryl and TNT. Picratol is picric acid and TNT. Pentolite is PETN and TNT. Octol is HMX and TNT. Minol is TNT, ammonium nitrate, and aluminum. Amitol is TNT and ammonion nitrate. Comp A is RDX and a plasticizer. Comb B is TNT, RDX, and wax. Baronol is TNT, barium nitrate, and aluminum powder. The PTX family is RDX, tetryl or PETN, and TNT.
Those are the major explosives used during WWII. Not a single one has nitoglycerin in it.
As for Nitrocellulose only exploding when confined. What do you think a bomb casing is, if not confinement?
There is a tremendous difference between an explosive and a high explosive. Even black powder will explode when confined, but black powder never, ever detonates. You can make a pipe bomb out of match heads, but nobody who knows anything would describe matches as a high explosive. High explosives detonate, meaning that the reaction front propagates through the material supersonically. Low-order explosives don't do that, they simply deflagrate, burn rapidly. Nobody in their right mind would use a low-order explosive like nitrocellulose in a bomb, not when anything more suitable was available.
I repeat: neither nitroglycerin nor nitrocellulose were routinely used as bomb fill in WWII. I won't rule out some Yugoslavian partisan group maybe mixing up some guncotton and using it in makeshift mortars, but that's about all it would have been used for.
TNT is most definitely not nitroglycerin. Where the hell do you people come up with this stuff?
TNT is trinitrotoluene, otherwise known as C6H2(NO2)3CH3, or 2,4,6-trinitromethylbenzene.
Nitroglycerine is otherwise known as C3H5N3O9, or 1,2,3-Tris-nitrooxy-propane.
Nitroglycerine is prepared by nitrating glycerine. TNT is prepared by nitrating toluene. They are two very different molecules, with very different properties.
I fucking love when people repeat as truth completely inaccurate information, without even the merest thought they might be spouting bullshit. I swear, some days I'm not sure whether I'm reading Slashdot or Fark.
Since HE is more potent than TNT, it's rated potential is higher than its weight.
TNT is high explosive.
ANFO's barely a high explosive, and to get it to really detonate at all, as opposed to simply burn rapidly, you need to confine it properly and set it off properly, and for ideal results you set it off with a bit of TNT.
A given weight of TNT will certainly produce better results than a given weight of ANFO.
Naw. Because the range at which you're seeing a given pressure level is much shorter. As he said, it was to simulate a nuke from a blast perspective. So to study a given level of blast pressure, you could either standoff a given distance from a 5kt blast of HE, or standoff a larger distance from an 8kt nuke.
All sorts of fun stuff has been done to simulate various aspects of nuclear weapons. Operation Sailor Hat was another blast sim, using 500 tons of TNT. When I was blowing stuff up for the Navy, I saw films of this test, from high-speed cameras mounted on a nearby destroyer, and you could see the steel torpedo tubes just ripple like a sheet in the wind when the shockwave hit.
One guy I know worked for a military contractor at one point, trying to simulate the flash effect of a bomb. They came up with a biiig double-barreled cannon. One barrel fired, at supersonic velocities, a big blast of liquid oxygen. The other fire, at supersonic velocities, a big blast of powdered aluminum. I haven't found films of that, but, wow.
What happens when explosives are stored improperly (and I can't imagine anything more improper) is the material separates. This leaves the inert material and nitroglycerine. Thats about as unstable as it gets. Nitro is bad news.
That's, of course, only the case for explosives which use nitroglycerine.
As this is WWII ordnance, we're probably not looking at any of those. Could be straight TNT, which is extremely stable, but various alkali compounds of the sort found in seawater can react with it to form a variety of compounds that are unstable to heat and impact. Could be Composition B, which is a mixture of TNT and RDX, so the same thing applies, or Comp A, which is straight RDX and a plasticizer, not so stable as Comp B. Ammonium picrate was used as a bursting charge, and is incredibly stable to shock and friction, but, again, seawater. Could also be Torpex, another popular one, and another RDX/TNT mixture. Problem with all of these is primarily the seawater environment reacting with the TNT to produce unstable products.
Nitrocellulose wasn't used in any of the common WWII high-explosives, nor was nitroglycerin; most high explosives of the day were varying mixtures of TNT, RDX, and sometimes PETN or Tetryl. Nitrocellulose isn't a high explosive at all; it doesn't detonate, it deflagrates, and the propagation of the chemical reaction through the material is below the speed of sound. What it was for, up until and probably throughout WWII, was a propellant, a replacement for gunpowder. It only explodes at all when confined; flash paper is basically straight nitrocellulose, and you can light that stuff off while holding it in your hand.
Is it possible to build a craft that can use wing lift all the way up to LEO?
.1:1 to keep accelerating.
Maybe.
In a real gas, aerodynamic lift is always accompanied by aerodynamic drag, and the ratio of the two is not dependent upon density or pressure or altitude. Until the point at which you actually achieve orbit, if you are relying upon aerodynamic lift to keep you in the sky, there's a certain amount of drag you have to overcome just to keep accelerating, and you can't make that problem go away by playing with the altitude.
The absolute best hypersonic lifting body designs anyone's been able to come up with, even theoretically on paper, have lift:drag ratios on the order of 10:1, so you need a thrust:weight ratio of at least
After all, if you're on the dark side, the entire mass of the earth should be shielding you (ever so slightly) from the gravitational pull of the sun.
No it shouldn't. The dark side of the moon is frequently illuminated by sunlight; it's only "dark" in the sense that it's the side that faces away from the earth, so we can't see it from here. It doesn't mean that the sun never shines on it.
Fact is less than 25% of all oil is consumed to fuel our cars and power our homes.
FSVO 'fact.'
In the real world, upwards of 40% of a given barrel of oil ends up as gasoline, and maybe up to 60%. Gasoline. That's used in cars, military vehicles, and small planes. It's not used to power or heat our homes.
The other 75% goes directly to manufacturing, and thus demand will not be significantly reduced by simply adding solar.
Wrong. Plastics and other manufacturing concerns consume the minority of each barrel of crude. Now, granted, if we stop using the lighter fractions of crude to drive our cars, that doesn't mean we can magically turn the whole barrel into heavier stuff suitable for plastics feedstocks, but your numbers are way off.
We have solar panels today nearing the theoretical maximum effeciecy of the substrate used to convert it.
Yeah, and? Next step is to make them cheaper. Or more durable, which basically amounts to the same thing.
Besides, we've already got the technology to move beyond fossil fuels, it's as safe or safer than burning coal, pollutes a helluva lot less, and has enough fuel sitting around to last us practically forever: fission. The only thing lacking is the political will, and the only problem is that people are stupid.
but most diesel technology is actually cleaner than gasoline.
Cleaner in what sense?
Certainly not in terms of particulates. True, there are low-particulate diesel engine systems. They're a lot more expensive.
Point 2: The article suggests 4 tuners, but how many should be recordable at one time? The HDTV TiVo unit can only record from any two tuners at a time.
Not to mention that if your source for your programming is digital cable, you still need a set-top box. For me to use two tuners on my TiVo, I'd still need two boxes from my cable company. I could see that as being reasonable, but come on, you've got TiVo, so it's not like you need to schedule your viewing to accomodate a program schedule, and anything worth watching is going to be repeated soon enough anyway. Four tuners strikes me as completely superfluous.
These solar sails are pretty useless. Here http://solarsails.jpl.nasa.gov/introduction/design -construction.html are calculations from NASA guys. It looks like this Japanese sail has acceleration of few mm/s^2
.09 Newtons from DS-1's ion engine was managing?
.3m/s sail listed in that table has a 'terminal velocity' of 671 kilometers per second, and solar escape velocity from the surface of the sun is only 618 kilometers per second.
And a few millimeters per second per second is useless, why?
3 millimeters per second squared, and after a week you're moving at 1.8 kilometers per second. After a month, 7.2 kilometers per second. After 2 months, you've already exceeded Earth's escape velocity from the surface, let alone from orbit. Solar escape velocity at 1 AU is about 48 kilometers per second, so it would take you half a year to get fast enough to escape the solar system altogether. Actually, less than that, because as you're accelerate you're moving outward and so the solar escape velocity from your present position is continuously decreasing, but I'm in no mood for calculus right now.
These accelerations seem small, and hell, sure, they are small, but when you're applying even tiny accelerations constantly, over an extended period of time, that acceleration adds up to meaningful speeds. What kind of acceleration do you think the
It would take solar sail 100 years to get to alpha centauri if it had acceleration 10 m/s^2
That's damned fast. Sustained 1g acceleration is pretty much up in indistinguishable-from-magic, though.
table 3 in the above link, there is "-" in the table for 5 m/s^2 and less , that is it will never get away from sun
No, that's ridiculous. As long as you have the thrust to move away from the sun, you'll "get away from the sun," because as I mentioned, the further out you are, the lower the solar escape velocity at your current position is. Hell, even the
we could see acceleration of up to .3m/s/s,
.3m/s/s may not sound like much, but since it's constant, it adds up quick. Remember, v(t)=at+v(0), so that .3m/s/s gets you to rather incredible speeds pretty rapidly.
And that's an entirely meaningful acceleration, because it's so constant. Your payload will be an enormous fraction of your total mass, instead of the tiny fraction of total mass it is with chemical rockets, so you're not wasting energy hauling around fuel.
Hell, cut it by a factor of 1,000, and it's still tremendously useful. The engineering difficulty is in actually producing large sails, not in being able to put them to good use once we can build them.
It can actually be quite meaningful acceleration, depending upon what sort of payload you're talking about. Keep in mind that Deep Space One was a useful space mission, and its ion engine provided a maximum thrust of about .09 Newtons. At 1 AU from the sun, you're going to get about 100 times that force exerted on each square mile of sail.
That's quite acceptable, especially because it scales so well. This would be admirably suited for interplanetary bulk cargo transportation, ferinstance. Sure, it might take each particular sail/cargo unit a while to get moving, but you could set up a series chain of them and get a pretty darned good throughput.
Using onboard rockets to steer doesn't help you slow down. As you point out, the gravitational pull of the destination star will cause you to accelerate even more. You'll end up heading towards your destination at greater than the escape velocity for that system.
This doesn't help you stop. To do that, you flip yourself around so that the sail is pointing towards the destination, and you use the radiation pressure from that star to kill your velocity. Can't do this if you're already jettisoned it.
And, no, chemical rockets won't work to shed that much velocity. If you get get that much delta-v from chemical rockets, you'd just use chemical rockets to get on your way as well. But that's precisely why you're using a solar sail instead: chemical rockets suck in terms of specific impulse.
What I dont understand is how they intend to protect these massive sails from being shot full of holes by meteorites and space dust as it propels its way through space.
They don't need to. Any holes punched by micrometeorits will be, even in the aggregate, infinitesimal compared to the total sail area.
Also, seing as how it is powered by solar wind, what happens when the craft is between 2 or more stars which are all exerting equal force on the sails.
The article's claims aside, solar sails are an abysmal technology for interstellar travel.
For example, "The Theory of Flight" has not been conclusively proven as a "Law" yet.
What do you mean "yet?" There isn't some sort of progression whereby theories eventually become laws after there's enough supporting evidence.
In science, a theory is an attempt to explain a wide and diverse set of physical phenomena as arising from a smaller set of rules. Theories are never confirmed, never "proven," in the colloquial sense of the word, but they are "proven" in the classic sense of the word, meaning "tested." The test of a theory lies in explanation and prediction. Does it explain what we see? Does it predict things that we haven't yet seen? When we go out looking for those predictions, are they confirmed? Well, then, this is a successful theory.
A law is simply an ad hoc observation, a postulate, and doesn't necessarily even have any explanatory value. The Idea Gas Law, ferinstance, says PV=nRT. It doesn't tell you *why* "ideal" gases behave in this fashion; heck, real gases are only approximations of ideal ones, but it's still a useful postulate.
And a fact is simply a statement for which there is such overwhelming evidence that it would be perverse for one to withhold provisional assent.
There is no progression from theory -> law -> fact.
I call 'bullshit.' How would banging the emitters around result in a dramatic power increase? That's just silly.
so how bright is it to give the fundies access to an ingredient
Raw uranium is one of the most abundant metals on the planet. In a given square mile area, down to a depth of one foot, you'll find over 2,000 kilograms of uranium.
If our safety depends on keeping this ubiquitous element out of the hands of terrorists, they've Already Won[tm].
Given the other blatant misinformation in his post, I'm not inclined to lend him much credence. Example:
The chemists always chuckled at the physcicists at Los Alamos whenever they stuck a metal shovel into uranium. An intense fire starts.
This is nonsense. Uranium is only pyrophoric when finely divided. A chunk of it isn't any more likely to catch fire when you "strike a metal shovel into it" than the metal shovel itself is.
We use DU 'cause it's cheap, and there's lots of it laying around. It's used for ballast, for counterweights for aircraft control surfaces, and a variety of other uses. It's not radioactive to any meaningful degree, and it's not any more to be concerned about than any other toxic heavy metal, such as lead.
However, as far as I can tell, there isnt anything preventing DU material from being bred into isotopes with far more dangerous fission potential.
Sure there is.
First, you've actually got to transmute it. You can do this by exposing it to a thermal neutron flux, like you get from an operating fission reactor. The occasional U-238 atom will grab a neutron and transmute via a decay chain to Pu-239. That's how breeder reactors work.
So now you've got your big mass of U-238 with a few atoms of Pu-239 scattered throughout it. The chemical separation of the two is rather expensive, rather difficult.
Neither of these two steps are particularly hard to "figure out." They are very hard to implement.
You're grotesquely overstating the radiological hazards of U-238.
.72% U-235, and .0055% U-234. Of these three isotopes, only U-235 will usefully sustain a fission chain reaction.
Some general information. Naturally-occurring uranium is composed of three different isotopes. It's 99.2745% U-238,
To use uranium in the production of nuclear power, it must be enriched. The result of the enrichment process is uranium with a U-235 percentage of from 3-5%, if you're talking about a civilian power plant, or upwards of 90%, if you're talking about a naval reactor.
What's left over from this process is the depleted uranium. It's called that because it's been depleted of the U-235. In other words, it's actually less radioactive than naturally occurring uranium, one of the most abundant elements on the planet.
So how radioactive is it? Not very. The measure of radioactivity is the Curie. 1 Ci is equal to 3.7*10^10 radioactive decays per second. In SI units, we use the Becquerel, and 1 Bq is equal to 1 radioactive decay per second, or 1 Bq = 2.703*10^-11 Ci.
Now, plain, natural uranium has an activity level of 25 Bq/kilogram. Consider for a second how amazingly low that is: in one kilogram of natural uranium, there are only 25 radioactive decays each second. That's about 4 moles of uranium, by the way, so that's roughly 2.4*10^24 atoms.
By comparison, the C-14 isotope of carbon is present to such a degree in organic matter that a random block of the stuff has an activity level of 6 pCi/g. Potassium-40 is also present in organic matter, to the tune of 11 pCi/g. Hell, take a 70 kilogram adult, and total up the naturally occurring radioisotopes in his body (the uranium, the thorium, the K-40, the radium, the C-14, the tritium, the polonium), and you'll see that a human being has an activity level of over 19,000 Bq, or 278 Bq/kg.
Human beings are over 11 times as radioactive as natural uranium, and even more radioactive than U-238.
So stop hysteria-mongering.
I've never understood why they were so gung-ho about this stupid idea in the first place when most power grids already have multi-core fiber optic cable hidden inside the neutral wire.
What neutral wire? There's no neutral wire up on the poles. When you see three wires up there, that's one wire for each phase. In residential neighborhoods, you'll see a phase tapped off to feed a transformer. The output of the transformer feeds each house through two wires, each wire being a 120-volt leg, with 240 volts between them.
I haven't played around with the utility's stuff up on the poles, but I've replaced enough electrical services to note the absence of a neutral. There's no neutral in a earth-return system.
(in fact the US Navy uses them to transmit extremly low frequency/long wavelength signlas to its submerged subs!
No, it doesn't. The Navy has specific special-purpose antennas for that purpose. It does not use powerlines.
Sure, they look like power lines, due to the fact that they're metal wires strung overhead on poles, but they're not feeding AC to anyone's toaster or television, and total radiated power is a handful of watts.