As with many of my generation, the dream of cosmic exploration by the commomn-man is quickly being usurped by the likely reality that perhaps our grandkids or great-grandkids will have that chance. That said, I am hopeful that perhaps this will lead to private venture a la Ansari to egg our governements on to partner with private industry to actually move us beyond our 30-year-old boundaries.
The main barrier to the common man exploring space, and even to things like a Moon or Mars mission, is that getting into space is very expensive. This is due to physical laws (delta-v required is much higher than any chemical rocket's exhaust velocity), so it isn't likely to change any time soon.
Better materials for rockets will drop the costs by a factor of 10 within my lifetime, at minimum. Other technologies like laser launchers or space elevators have the potential to drastically reduce launch costs, but it remains to be seen whether or not they actually _will_.
If costs drop to the point where lifting a minivan-sized spacecraft to orbit costs no more than a year or three's salary, we'll see the common man in space (and doing with duct tape and baling wire what costs the government billions and industry tens or hundreds of millions, at the cost of much greater risk to the common men doing it).
Elements of the experiment have been attempted previously -- Do we remember that mockery of BioSphere 2? (no, not the appauling Paulie Shore movie, "Bio-Dome") This site does a nice job of outlining the requirements of a viable biosphere or otherwise self-contained environment.
The point is that this _isn't_ a self-sufficient environment, and what I was trying to show in my post was that it doesn't _have_ to be. They're bringing enough supplies to easily last them for the alotted time with no recycling at all. Brute-force recycling using proven technologies can extend that time by a factor of 5 or more (though it's only practical to do so when the mass of your recycler and its power plant are less than the mass of the extra supplies you'd otherwise have to bring).
So, we don't need the kind of closed-loop biosphere that Biosphere 2 and other experiments have tried to produce, and the Russians aren't testing one (instead, they're testing a disposables/consumables scenario more or less in line with a Mars trip).
If I'm doing my math right (no guarantee there), 12 Tons of payload (assuming the need to protect the raw material and the need to divide the raw material into reasonable payload weight (per Arian 5 current specifications) (not including the habitat and its associated sundries) in current terms equates to, about $300M. That's just launch cost, and says nothing about development, storage, maintenance, docking, or any of those other fun things, bringinng the ticket (less development costs) close to $13B (figure another $30-50B for development costs). The other item of concern is the processing of waste.. If they're BRINGING their food, and not growing it, there's the associated packaging that goes hand-in-hand. Last I checked, that plastic baggie burried in my back yard with my dearly-departed hampster from 3rd grade is still intact.
Your own numbers show that the cost of lugging the supplies is a very small part of the mission cost. Designing and building any kind of one-off man-rated spacecraft is horrifically expensive, especially if it's a government job.
As the cycle isn't closed-loop, reclaiming wastes (like packaging) isn't an issue. Even with the air and water recycling schemes I illustrated, it wouldn't be an issue, because dry waste is still disposable.
A system that tried to recycle dry waste would either have to do it biologically and use waxed paper or otherwise biodegradable packaging, or else would use a more complicated brute force and ignorance chemical recycler that reduced everything to oxides and hydrides (giving you metal oxides from metals, and water and methane and either elemental nitrogen or ammonia from CHON-type hydrocarbons). These simple chemicals would be further processed into useful forms (methane can be turned into methanol, which can re-enter the food chain and be turned into something edible, for example).
Both biological and non-biological solid waste recyclers are complicated enough, energy-intensive enough, and heavy enough that I don't think they're worthwhile to put into a spacecraft. You can carry enough extra supplies to last years or decades instead, so they'd only be used for missions that were to _last_ decades without easy resupply windows.
Food, other consumables, oxygen, water, yes, these are valid simulations. I'd also like to see what the options are for running a hydroponics lab to oxygenate the air and cleanse sewer waste, though not to eat necessarily since this would involve a fair amount of work.
I'd thought about the air and water recycling problem when running a different thought experiment (was planning what amounted to a single-person spacecraft with a 1-2 week nominal mission duration capacity).
It turns out that if you're only going out for a couple of weeks, or if you have a significant mass budget, recycling isn't important at all. The mass of food consumed is surprisingly low, and we have plenty of experience keeping it light and compact (think "MRE"s; the military has a vested interest in food that keeps and is easy to transport). Oxygen consumed will at most be enough to burn that food - the part of that food that's not already oxidized (water-based). Water consumption is relatively low - a couple of litres per day for a comfortable allocation. So you have a few pounds of supplies used per day, and can easily store a year or more's supplies without the supplies outweighing the rest of your expedition's equipment.
For recycling, air and water are the most important. Water because you go through a significant amount of it, but it's still fairly easy to recycle, and air because you go through a _lot_ of it (2-3 times the dry weight of your food). Both of these turn out to be easy to do if you have _power_. Brute force chemical processes and (for water) techniques like distillation come to the rescue. While 100% recycling of water is hard to do, even 80-90% would have a huge impact on your supply mass, and air recycling is very nearly perfect.
A biologically based recycler has the advantage of being able to turn solid waste into food, but that's about its only advantage. System efficiency vs. energy in (light) is actually pretty poor, and it takes a lot of space and a lot of mass, even if you use something like algae that's near the bottom of the food chain and has low infrastructure requirements.
Biological recyclers are useful when you can afford a large facility mass, and when you have a lot of people to feed. These are true on a large space station (think "colony") or planetary base (again think "colony"), but not for most spacecraft.
Still very interesting to think through the options for.
Yes, magnetic confinement is very lossy and low-density. Except in the case of antimatter, its probably not worth the trouble. Though a prior poster had an interesting idea about magnetic confinement in space - kinda like an M2P2 (mini-magnetospheric plasma propulsion
If it was a reply in this thread, that prior poster was me:).
Thinking about it, the best approach is probably to build a bent dipole (for preferential emission on one side), store both reagents in the same field, and vary the field strength to control reaction rate (which goes up with density, which is proportional to the square of the field strength). This lets you go from "takes a century to burn all the fuel" to "takes a week to burn all the fuel" with a factor of 100 field strength change. When you're at high field strengths, the plasma's dense enough that charged reaction products have time to thermalize with the rest of the plasma, giving you a way to tap the energy (assuming it doesn't just fly away in photons).
The catch is that you have a lower limit to field strength imposed by the ambient solar wind plasma. Too low, and the solar wind deforms your field and ruins containment (though as you point out, for MMPP that can be a benefit).
As for being useful - you can get very close to fusion numbers for magnetic confinement, and with a cold plasma, you can store your material at far, far higher density. If fusion drives are worth it, why wouldn't this be?
As for my choice of numbers - with a bit of work, one can come up with fuels that are as high in energy density if not higher.
Any higher than about 20 eV ionization energy for the ions, and you can't keep the fuel stable in a pressurized helium crystal. This places a limit on what you can use as a fuel without having to resort to magnetic confinement schemes.
I'm not trying to belittle your choice of numbers - I'm just trying to extend them:).
A good rocket fuel does not care how much energy is released, it more cares about increasing in volumne as quickly as possible.
A good rocket fuel cares only about exhaust velocity. This is a function of the number of moles of exhaust product, and their kinetic energy (temperature).
All of the fuels described above have spectacularly good Isp despite having few moles of reaction product, because energy per mole of product is huge, and the molecular weight of the products is very low compared to most things (H2O has an atomic weight of around 18, while H2 has an atomic weight of 2 - meaning at the same temperature you get about 3x the exhaust velocity (and Isp) from expanding molecular hydrogen than expanding steam).
In summary, energies this high help a _lot_, number of moles notwithstanding.
Metastable Helium: He* -> He 480 MJ/kg As much fun as you can have without going nuclear...
Isomeric transition is a nuclear process.
This isn't a nuclear isomer - it's an electronic isomer. Helium normally has both electrons in the 1s orbital with opposite spins. He* has one in 1s and one in 2s, with the same spin, so there's no one-photon decay path. This state is therefore much more stable than most excited states (half life of around 2.3 hours if undisturbed).
Keeping He* contained is another matter. If it can interact with other matter - even itself, if in a disordered gas - that hastens the decay process by allowing other decay modes that involve exchange of angular momentum with other atoms. There was an interesting study about binding it as molecular helium with He + He*, and attempting to keep spins stabilized by applying a strong external field, but funding was cancelled for that (review board didn't think it had enough chance of working to continue studying it past the review time).
And is it the radio frequency that would cause the problem? The power output? The heat? The volume level?...The solvents used in the plastic of the handset?
Assuming that the problem is RF related is premature (though that is, of course, one of the options, if the study is corroborated). I'm still waiting for the studies about power lines and cancer to look for soil contaminants. Transformer coolants used to be extremely nasty (and now are only _moderately_ nasty).
It occurs to me that if you're prepared to use magnetic confinement to store reagent ions, you can get an Isp as high as you like by using electrons and fully- (or just deeply-) ionized heavy atoms.
Hydrogen's ionization potential of 13.6 eV gives 1.3 GJ/kg on recombination. Helium's ioniztion potentials of 24.5 and 54.4 eV give 1.9 GJ/kg. Fully-ionized carbon gives 8.3 GJ/kg.
While magnetic confinement only allows low storage densities, with enough energy, this stops mattering. The only catch is that you have to have to be able to do something useful with the resulting photons (i.e. use them to heat an exhaust plasma, or in the worst case power an electric drive, though conversion efficiencies bite you there, as these photons are mostly soft x-rays).
For very heavy elements, with inner-shell electrons orbiting fast enough to be relativistic, you can get energy to mass ratios almost as good as fusion (one to two orders of magnitude worse).
Of course, ionized hydrogen has the virtue of being stable as crystal defects in frozen helium, unlike more aggressively ionized elements (though storing it like that gives a hefty Isp penalty).
I was actually thinking about the unburned D in the outer stellar envelope. I'm not sure how much there would be, though - I can't find measurements of the Sun's deuterium abundance in the outer region of the star. The reason I was saying so is that with hydrogen burning, the star actually stops burning hydrogen far before it runs out of hydrogen in the star - it's just that the outer shell hydrogen has no chance to reach the core so long as the star burns at all.
This is only true for stars about the size of the sun. Stars that are red dwarf sized have deep convective layers throughout, mixing the star's material pretty thoroughly. It's only heavier stars that have non-convective cores (and stars much heavier than the sun have cores dominated by convection and outer layers that are dominated by radiative heat dissipation; I was very surprised to learn that - it stems from the CNO reaction rate going up as a ludicrous power of temperature).
The original star would have been segregated. The outer layers would have been stripped off by the companion star. While some mixing between what used to be mantle and what used to be outer core would have occurred when "outer core" was reassigned as "mantle", over time the net effect of the companion's stripping of material would be to remove most of the material that was originally non-core, leaving an object the mass of a red dwarf that contained mostly material that was from the original star's core (rich in metals, depleted in primordial deuterium and lithium). As the star's mass dropped to the point where it became a red dwarf, it would lose internal structure due to deep convection, burning any deuterium left from previous hydrogen-fusing phases.
I hope that this clarifies why I don't think any of the original star's primordial deuterium would be left in this object. (Non-primordial deuterium has already been addressed.)
I doubt the outer atmosphere would bear much resemblance to the "old" inner core of the star: the core would contain the heaviest elements, and the outer atmosphere would be primarily hydrogen. It would depend a lot on the exact mass loss mechanism and the density profile of the dying star, actually! The sun's 'burning region' is quite large - fusion is occurring in almost 1/3 the radius of the Sun. For a dying star that was losing mass very slowly, the core would shrink slowly over time, and in the end, the outer region of the star would be quite different than the interior (because it was the star's 'core' long ago). But if was losing mass quickly, then the star would be more uniform.
I'd be more concerned with convective mixing polluting old-core material with convectively down-swept material from the old mantle. I wouldn't expect fusion in the shrinking star to substantially taint composition, as fusion rate drops so quickly with decreasing stellar mass (projected lifetime goes from billions of years as a yellow dwarf to hundreds of billions or longer for a red dwarf). That, combined with convective mixing, suggests that we should have an object with reasonably uniform composition, that more or less reflects the composition of the original core.
Gravitational fractioning after fusion stops is another matter. You've indicated that you believe this would occur relatively quickly; I'm not so sure (you'd have convection from residual heat for a long time, and there's a lot of really dense material that you'd need to segregate to get significant fractioning). However, you almost certainly know more about those mechanisms than I do.
As I said before, though, it's an amazingly interesting object. I think 'brown dwarf of a new spectral class' is actually appropriate for a name, though.
Now, what do we call it when it's below the mass threshold for hypothetical deuterium burning?;)
Storing hydrogen ions is a *huge* problem as you can well imagine. Some thoughts include magnetic confinement (probably more trouble than its worth)
For space applications, you could use a large wire loop to make a big and _light_ dipole magnet, and store the ionized hydrogen in the extended side lobes (much as particles are trapped in Earth's van Allen belts). Density is low, but it's mass of the craft that matters, not size. You can only use it slowly, but that isn't a big disadvantage either (it's only launch that requires high thrust; high-Isp, low thrust drives are perfectly acceptable once you're in space).
You could use two dipoles like this that were of opposite polarity and tethered axially, to store both types of ion. Reel in the tethers, and there's enough leakage between the gas toruses for reaction to occur. As long as you can set things up so that there's a favoured direction for production (different sized magnets?), the resulting energetic neutral hydrogen makes a very nice rocket plume.
Alternatively, you could use three coils and do a solenoid with two field bulges separated by a pinch, but that's worse for long-term containment.
I'm kind of wondering where the energy goes when you react two ions in vacuum, though. I think you'd either get it dumped as light (not very useful for a space drive), or you'd get H2+ and one of the electrons kicked off at high speed to shed energy (which means the reaction product is charged, and so affected by your containment field). Can anyone who's actually studied monatomic H+/H- reactions clarify this for me?
In summary, I think the problem is solvable in a way that's useful for a space drive.
It doesn't matter what you burn in there, any combustion temperatures over a thousand degrees C or so has sufficient energy to drive the NOx chemical reaction. Petrol, Diesel, Hydrogen... all of those fuels indirectly produce NOx.
"Hydrogen" usually refers to fuel cells, which combine hydrogen and oxygen in a low-temperature electrochemical reaction rather than a high-temperature combustion reaction.
Hydrogen fuel cell cars have plenty of problems, but NOx emissions isn't one of them.
Sure an electric furnace would be 100% efficient in my house, but the power plant that makes that electricity is at most 60% efficient. Already a large gap to overcome.
This was pointed out in my original post, and in my responses to the first three replies, who also seemed to have missed that part.
Actually tailings are really really nasty; there are lots of problems with water contamination.
Quantities will still be far less than the wastes (and other environmental disruption) caused by coal mining and oil drilling and shipping of both substances. I agree that with any form of mining, you have a negative environmental impact; it's just that I rarely see people appreciating exactly how much less material is needed.
I'm also amused by listing sodium chloride as a contaminant. While it will cause problems with the local environment, calling it "salt" would put things like its relative toxicity in perspective.
Not if you consider the small percentage of the heat energy at the power plant being converted to electricity.
Apparently I should have put the sentences about production of electricity causing it to cost more per delivered joule in bold caps, because you're the third person who seems to have missed it.
Not quite. Uranium is still a limited resource; the idea of "electricity too cheap to meter" is (like a lot of pro-fission thinking) is a product of Gernsbackian imagination.
The idea of "electricity too cheap to meter" is a fantasy because you still need a bigarsed steam-powered generator no matter what the heat source, not because of fuel concerns. The quantity of fuel used is so vastly lower than the amount of coal and oil burned in fossil fuel plants that the cost of mining really isn't that much, even given the relative scarcity of the element itself.
It won't run out any time soon either if you reprocess spent fuel and also breed fissile materials from thorium, but both of those have materials-handling and security problems (not unsolvable, but enough that the US doesn't use them).
Electric heat, no; very inefficient. Ground source heat-pumps, yes.
Electric heating is as efficient as gas heating; in both cases, you're turning virtually all of the available energy into heat. A heat pump is more efficient than either because it draws heat from the surrounding area (at such a relatively small temperature difference, it costs less to do this than to just dump heat into the house). The reason we use gas heating instead of electric is that electrical energy is more expensive to produce, joule for joule, than the equivalent amount of natural gas. This is a production issue, as opposed to a point-of-use issue.
In short, while I agree with your positions, I disagree with the reasons:).
Granted, in 6 or 12 months, you can get the upgrades necessary to play Doom3 for just a couple hundred dollars,... But unless by "waiting for games" you mean "waiting 5 years for games," you're not going to beat the console upgrade cycle.
Notice how both of these points are strikingly similar to what I wrote in my original post...:)
Please point me to where I can get one of those setups for $149, or $100 used.
Hell, for the price of just the FX6800 I can get *3* X-Boxes and games and plug them in around the house for network head-2-head play!
The difference is that I already have a PC. The marginal cost between an office-use PC and a PC that can play games from six months ago is $200-$300. The marginal cost between an office-use PC and a PC that can play games from three years ago is $0.
If, like me, you're one of those people who doesn't mind waiting for games, PC games have little to no added cost.
Also, it is constructive (you are trying to get 10 points) than destructive (you are trying to make everyone else bankrupt).
For Settlers of Catan, the distinction is kind of blurry. While you do have to play in a way that builds up your resource base, a large part of the game is figuring out how to best screw over the other players (placing a settlement so as to prohibit several other settlement placements, figuring out where to best place the robber, figuring out how to deny "longest road" and "largest army" to others for long enough to win, and so forth).
So while there's no direct violence against the other players, there's plenty of indirect pressure being applied. Such is the nature of competitive games.
Not too much difference. it was a hypothesis that would have failed and was revised later as more information was gathered. There are plenty of failed hyothesis' around by notable scientists to discuss.
The idea would be to test the hypothesis before sending a human up there. The modern space program did this (many incremental milestones before humans or even animals were sent into space).
It's a stupid self diagnosis test... not AI... overhyped buzzword... It simply runs a simulation and tests its results against the actual ones, and generates a report... that's not AI...
It's an expert system, which is indeed AI. You're probably thinking of "strong AI", which is AI that can function as powerfully and flexibly as a human [and if that definition is vague, it's because nobody's nailed down something more solid that everyone agrees on].
Expert system AIs have been around for a long time in a wide variety of fields. They are designed to handle a narrow range of tasks (like fault diagnosis, medical diagnosis, or playing chess) better or more quickly than a human could.
I'm working on a hybrid vehicle, and finding a way to make good use of the regenerative braking power is a real challenge. Lead acids can only take a charge so fast, usually less than 0.1 of the power available during braking, unless you completely oversize the battery banks.
I want something with a very low charge impedance that can basically lock the shaft of the motor/generator, if need be.. completely eliminating friction brakes.
You can probably do that with a superconducting inductor reinforced with glass fiber (or carbon composites, or yadda yadda). Just not at the point where it's close to economically viable yet.
You'd also always need a mechanical brake as a backup, as even in a very strong field, eddy currents only apply so much drag to a conductor. Don't use the regenerator as your parking brake:).
Nanotubes could have a major commercial future if they are harder then TiN, non reactive to iron, but softer then diamond.
I strongly suspect that nanotube coatings on iron won't work, unless you have a coating of some barrier material (in which case, diamond coating would also work). Any form of carbon would be likely to react to form iron carbides when heated.
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As with many of my generation, the dream of cosmic exploration by the commomn-man is quickly being usurped by the likely reality that perhaps our grandkids or great-grandkids will have that chance. That said, I am hopeful that perhaps this will lead to private venture a la Ansari to egg our governements on to partner with private industry to actually move us beyond our 30-year-old boundaries.
The main barrier to the common man exploring space, and even to things like a Moon or Mars mission, is that getting into space is very expensive. This is due to physical laws (delta-v required is much higher than any chemical rocket's exhaust velocity), so it isn't likely to change any time soon.
Better materials for rockets will drop the costs by a factor of 10 within my lifetime, at minimum. Other technologies like laser launchers or space elevators have the potential to drastically reduce launch costs, but it remains to be seen whether or not they actually _will_.
If costs drop to the point where lifting a minivan-sized spacecraft to orbit costs no more than a year or three's salary, we'll see the common man in space (and doing with duct tape and baling wire what costs the government billions and industry tens or hundreds of millions, at the cost of much greater risk to the common men doing it).
Elements of the experiment have been attempted previously -- Do we remember that mockery of BioSphere 2? (no, not the appauling Paulie Shore movie, "Bio-Dome") This site does a nice job of outlining the requirements of a viable biosphere or otherwise self-contained environment.
The point is that this _isn't_ a self-sufficient environment, and what I was trying to show in my post was that it doesn't _have_ to be. They're bringing enough supplies to easily last them for the alotted time with no recycling at all. Brute-force recycling using proven technologies can extend that time by a factor of 5 or more (though it's only practical to do so when the mass of your recycler and its power plant are less than the mass of the extra supplies you'd otherwise have to bring).
So, we don't need the kind of closed-loop biosphere that Biosphere 2 and other experiments have tried to produce, and the Russians aren't testing one (instead, they're testing a disposables/consumables scenario more or less in line with a Mars trip).
If I'm doing my math right (no guarantee there), 12 Tons of payload (assuming the need to protect the raw material and the need to divide the raw material into reasonable payload weight (per Arian 5 current specifications) (not including the habitat and its associated sundries) in current terms equates to, about $300M. That's just launch cost, and says nothing about development, storage, maintenance, docking, or any of those other fun things, bringinng the ticket (less development costs) close to $13B (figure another $30-50B for development costs). The other item of concern is the processing of waste.. If they're BRINGING their food, and not growing it, there's the associated packaging that goes hand-in-hand. Last I checked, that plastic baggie burried in my back yard with my dearly-departed hampster from 3rd grade is still intact.
Your own numbers show that the cost of lugging the supplies is a very small part of the mission cost. Designing and building any kind of one-off man-rated spacecraft is horrifically expensive, especially if it's a government job.
As the cycle isn't closed-loop, reclaiming wastes (like packaging) isn't an issue. Even with the air and water recycling schemes I illustrated, it wouldn't be an issue, because dry waste is still disposable.
A system that tried to recycle dry waste would either have to do it biologically and use waxed paper or otherwise biodegradable packaging, or else would use a more complicated brute force and ignorance chemical recycler that reduced everything to oxides and hydrides (giving you metal oxides from metals, and water and methane and either elemental nitrogen or ammonia from CHON-type hydrocarbons). These simple chemicals would be further processed into useful forms (methane can be turned into methanol, which can re-enter the food chain and be turned into something edible, for example).
Both biological and non-biological solid waste recyclers are complicated enough, energy-intensive enough, and heavy enough that I don't think they're worthwhile to put into a spacecraft. You can carry enough extra supplies to last years or decades instead, so they'd only be used for missions that were to _last_ decades without easy resupply windows.
Food, other consumables, oxygen, water, yes, these are valid simulations. I'd also like to see what the options are for running a hydroponics lab to oxygenate the air and cleanse sewer waste, though not to eat necessarily since this would involve a fair amount of work.
I'd thought about the air and water recycling problem when running a different thought experiment (was planning what amounted to a single-person spacecraft with a 1-2 week nominal mission duration capacity).
It turns out that if you're only going out for a couple of weeks, or if you have a significant mass budget, recycling isn't important at all. The mass of food consumed is surprisingly low, and we have plenty of experience keeping it light and compact (think "MRE"s; the military has a vested interest in food that keeps and is easy to transport). Oxygen consumed will at most be enough to burn that food - the part of that food that's not already oxidized (water-based). Water consumption is relatively low - a couple of litres per day for a comfortable allocation. So you have a few pounds of supplies used per day, and can easily store a year or more's supplies without the supplies outweighing the rest of your expedition's equipment.
For recycling, air and water are the most important. Water because you go through a significant amount of it, but it's still fairly easy to recycle, and air because you go through a _lot_ of it (2-3 times the dry weight of your food). Both of these turn out to be easy to do if you have _power_. Brute force chemical processes and (for water) techniques like distillation come to the rescue. While 100% recycling of water is hard to do, even 80-90% would have a huge impact on your supply mass, and air recycling is very nearly perfect.
A biologically based recycler has the advantage of being able to turn solid waste into food, but that's about its only advantage. System efficiency vs. energy in (light) is actually pretty poor, and it takes a lot of space and a lot of mass, even if you use something like algae that's near the bottom of the food chain and has low infrastructure requirements.
Biological recyclers are useful when you can afford a large facility mass, and when you have a lot of people to feed. These are true on a large space station (think "colony") or planetary base (again think "colony"), but not for most spacecraft.
Still very interesting to think through the options for.
Yes, magnetic confinement is very lossy and low-density. Except in the case of antimatter, its probably not worth the trouble. Though a prior poster had an interesting idea about magnetic confinement in space - kinda like an M2P2 (mini-magnetospheric plasma propulsion
:).
:).
If it was a reply in this thread, that prior poster was me
Thinking about it, the best approach is probably to build a bent dipole (for preferential emission on one side), store both reagents in the same field, and vary the field strength to control reaction rate (which goes up with density, which is proportional to the square of the field strength). This lets you go from "takes a century to burn all the fuel" to "takes a week to burn all the fuel" with a factor of 100 field strength change. When you're at high field strengths, the plasma's dense enough that charged reaction products have time to thermalize with the rest of the plasma, giving you a way to tap the energy (assuming it doesn't just fly away in photons).
The catch is that you have a lower limit to field strength imposed by the ambient solar wind plasma. Too low, and the solar wind deforms your field and ruins containment (though as you point out, for MMPP that can be a benefit).
As for being useful - you can get very close to fusion numbers for magnetic confinement, and with a cold plasma, you can store your material at far, far higher density. If fusion drives are worth it, why wouldn't this be?
As for my choice of numbers - with a bit of work, one can come up with fuels that are as high in energy density if not higher.
Any higher than about 20 eV ionization energy for the ions, and you can't keep the fuel stable in a pressurized helium crystal. This places a limit on what you can use as a fuel without having to resort to magnetic confinement schemes.
I'm not trying to belittle your choice of numbers - I'm just trying to extend them
A good rocket fuel does not care how much energy is released, it more cares about increasing in volumne as quickly as possible.
A good rocket fuel cares only about exhaust velocity. This is a function of the number of moles of exhaust product, and their kinetic energy (temperature).
All of the fuels described above have spectacularly good Isp despite having few moles of reaction product, because energy per mole of product is huge, and the molecular weight of the products is very low compared to most things (H2O has an atomic weight of around 18, while H2 has an atomic weight of 2 - meaning at the same temperature you get about 3x the exhaust velocity (and Isp) from expanding molecular hydrogen than expanding steam).
In summary, energies this high help a _lot_, number of moles notwithstanding.
Metastable Helium: He* -> He 480 MJ/kg
As much fun as you can have without going nuclear...
Isomeric transition is a nuclear process.
This isn't a nuclear isomer - it's an electronic isomer. Helium normally has both electrons in the 1s orbital with opposite spins. He* has one in 1s and one in 2s, with the same spin, so there's no one-photon decay path. This state is therefore much more stable than most excited states (half life of around 2.3 hours if undisturbed).
Keeping He* contained is another matter. If it can interact with other matter - even itself, if in a disordered gas - that hastens the decay process by allowing other decay modes that involve exchange of angular momentum with other atoms. There was an interesting study about binding it as molecular helium with He + He*, and attempting to keep spins stabilized by applying a strong external field, but funding was cancelled for that (review board didn't think it had enough chance of working to continue studying it past the review time).
And is it the radio frequency that would cause the problem? The power output? The heat? The volume level? ...The solvents used in the plastic of the handset?
Assuming that the problem is RF related is premature (though that is, of course, one of the options, if the study is corroborated). I'm still waiting for the studies about power lines and cancer to look for soil contaminants. Transformer coolants used to be extremely nasty (and now are only _moderately_ nasty).
Other, even higher energy (non-nuclear) fuels include:
Metallic Hydrogen: 2 H(s) -> H2(g) 138 MJ/kg
Free-Radical Hydrogen: H + H -> H2 104 MJ/kg
Metastable Helium: He* -> He 480 MJ/kg
Ionic Hydrogen: H(+) + H(-) -> H2 835 MJ/kg
It occurs to me that if you're prepared to use magnetic confinement to store reagent ions, you can get an Isp as high as you like by using electrons and fully- (or just deeply-) ionized heavy atoms.
Hydrogen's ionization potential of 13.6 eV gives 1.3 GJ/kg on recombination.
Helium's ioniztion potentials of 24.5 and 54.4 eV give 1.9 GJ/kg.
Fully-ionized carbon gives 8.3 GJ/kg.
While magnetic confinement only allows low storage densities, with enough energy, this stops mattering. The only catch is that you have to have to be able to do something useful with the resulting photons (i.e. use them to heat an exhaust plasma, or in the worst case power an electric drive, though conversion efficiencies bite you there, as these photons are mostly soft x-rays).
For very heavy elements, with inner-shell electrons orbiting fast enough to be relativistic, you can get energy to mass ratios almost as good as fusion (one to two orders of magnitude worse).
Of course, ionized hydrogen has the virtue of being stable as crystal defects in frozen helium, unlike more aggressively ionized elements (though storing it like that gives a hefty Isp penalty).
I was actually thinking about the unburned D in the outer stellar envelope. I'm not sure how much there would be, though - I can't find measurements of the Sun's deuterium abundance in the outer region of the star. The reason I was saying so is that with hydrogen burning, the star actually stops burning hydrogen far before it runs out of hydrogen in the star - it's just that the outer shell hydrogen has no chance to reach the core so long as the star burns at all.
;)
This is only true for stars about the size of the sun. Stars that are red dwarf sized have deep convective layers throughout, mixing the star's material pretty thoroughly. It's only heavier stars that have non-convective cores (and stars much heavier than the sun have cores dominated by convection and outer layers that are dominated by radiative heat dissipation; I was very surprised to learn that - it stems from the CNO reaction rate going up as a ludicrous power of temperature).
The original star would have been segregated. The outer layers would have been stripped off by the companion star. While some mixing between what used to be mantle and what used to be outer core would have occurred when "outer core" was reassigned as "mantle", over time the net effect of the companion's stripping of material would be to remove most of the material that was originally non-core, leaving an object the mass of a red dwarf that contained mostly material that was from the original star's core (rich in metals, depleted in primordial deuterium and lithium). As the star's mass dropped to the point where it became a red dwarf, it would lose internal structure due to deep convection, burning any deuterium left from previous hydrogen-fusing phases.
I hope that this clarifies why I don't think any of the original star's primordial deuterium would be left in this object. (Non-primordial deuterium has already been addressed.)
I doubt the outer atmosphere would bear much resemblance to the "old" inner core of the star: the core would contain the heaviest elements, and the outer atmosphere would be primarily hydrogen. It would depend a lot on the exact mass loss mechanism and the density profile of the dying star, actually! The sun's 'burning region' is quite large - fusion is occurring in almost 1/3 the radius of the Sun. For a dying star that was losing mass very slowly, the core would shrink slowly over time, and in the end, the outer region of the star would be quite different than the interior (because it was the star's 'core' long ago). But if was losing mass quickly, then the star would be more uniform.
I'd be more concerned with convective mixing polluting old-core material with convectively down-swept material from the old mantle. I wouldn't expect fusion in the shrinking star to substantially taint composition, as fusion rate drops so quickly with decreasing stellar mass (projected lifetime goes from billions of years as a yellow dwarf to hundreds of billions or longer for a red dwarf). That, combined with convective mixing, suggests that we should have an object with reasonably uniform composition, that more or less reflects the composition of the original core.
Gravitational fractioning after fusion stops is another matter. You've indicated that you believe this would occur relatively quickly; I'm not so sure (you'd have convection from residual heat for a long time, and there's a lot of really dense material that you'd need to segregate to get significant fractioning). However, you almost certainly know more about those mechanisms than I do.
As I said before, though, it's an amazingly interesting object. I think 'brown dwarf of a new spectral class' is actually appropriate for a name, though.
Now, what do we call it when it's below the mass threshold for hypothetical deuterium burning?
Storing hydrogen ions is a *huge* problem as you can well imagine. Some thoughts include magnetic confinement (probably more trouble than its worth)
For space applications, you could use a large wire loop to make a big and _light_ dipole magnet, and store the ionized hydrogen in the extended side lobes (much as particles are trapped in Earth's van Allen belts). Density is low, but it's mass of the craft that matters, not size. You can only use it slowly, but that isn't a big disadvantage either (it's only launch that requires high thrust; high-Isp, low thrust drives are perfectly acceptable once you're in space).
You could use two dipoles like this that were of opposite polarity and tethered axially, to store both types of ion. Reel in the tethers, and there's enough leakage between the gas toruses for reaction to occur. As long as you can set things up so that there's a favoured direction for production (different sized magnets?), the resulting energetic neutral hydrogen makes a very nice rocket plume.
Alternatively, you could use three coils and do a solenoid with two field bulges separated by a pinch, but that's worse for long-term containment.
I'm kind of wondering where the energy goes when you react two ions in vacuum, though. I think you'd either get it dumped as light (not very useful for a space drive), or you'd get H2+ and one of the electrons kicked off at high speed to shed energy (which means the reaction product is charged, and so affected by your containment field). Can anyone who's actually studied monatomic H+/H- reactions clarify this for me?
In summary, I think the problem is solvable in a way that's useful for a space drive.
It doesn't matter what you burn in there, any combustion temperatures over a thousand degrees C or so has sufficient energy to drive the NOx chemical reaction. Petrol, Diesel, Hydrogen... all of those fuels indirectly produce NOx.
"Hydrogen" usually refers to fuel cells, which combine hydrogen and oxygen in a low-temperature electrochemical reaction rather than a high-temperature combustion reaction.
Hydrogen fuel cell cars have plenty of problems, but NOx emissions isn't one of them.
Sure an electric furnace would be 100% efficient in my house, but the power plant that makes that electricity is at most 60% efficient. Already a large gap to overcome.
This was pointed out in my original post, and in my responses to the first three replies, who also seemed to have missed that part.
But producing electricity is not 100% efficient, so elettricity heating is a lot less efficient than gas heating !
This was pointed out in my original post, and in my response to the first three replies, who also seemed to have missed that part.
Actually tailings are really really nasty; there are lots of problems with water contamination.
Quantities will still be far less than the wastes (and other environmental disruption) caused by coal mining and oil drilling and shipping of both substances. I agree that with any form of mining, you have a negative environmental impact; it's just that I rarely see people appreciating exactly how much less material is needed.
I'm also amused by listing sodium chloride as a contaminant. While it will cause problems with the local environment, calling it "salt" would put things like its relative toxicity in perspective.
Not if you consider the small percentage of the heat energy at the power plant being converted to electricity.
Apparently I should have put the sentences about production of electricity causing it to cost more per delivered joule in bold caps, because you're the third person who seems to have missed it.
And in your opinion, the later is equal efficiency to the first?
What part of "joule for joule, electrical energy is more expensive to produce" wasn't clear enough in my original post? You even quoted this.
You've just spent 20 lines agreeing with me.
Electric heating is not efficient if you examine the problem from a systems perspective.
This was clearly spelled out in my original post. Where are you disagreeing with me?
Not quite. Uranium is still a limited resource; the idea of "electricity too cheap to meter" is (like a lot of pro-fission thinking) is a product of Gernsbackian imagination.
:).
The idea of "electricity too cheap to meter" is a fantasy because you still need a bigarsed steam-powered generator no matter what the heat source, not because of fuel concerns. The quantity of fuel used is so vastly lower than the amount of coal and oil burned in fossil fuel plants that the cost of mining really isn't that much, even given the relative scarcity of the element itself.
It won't run out any time soon either if you reprocess spent fuel and also breed fissile materials from thorium, but both of those have materials-handling and security problems (not unsolvable, but enough that the US doesn't use them).
Electric heat, no; very inefficient. Ground source heat-pumps, yes.
Electric heating is as efficient as gas heating; in both cases, you're turning virtually all of the available energy into heat. A heat pump is more efficient than either because it draws heat from the surrounding area (at such a relatively small temperature difference, it costs less to do this than to just dump heat into the house). The reason we use gas heating instead of electric is that electrical energy is more expensive to produce, joule for joule, than the equivalent amount of natural gas. This is a production issue, as opposed to a point-of-use issue.
In short, while I agree with your positions, I disagree with the reasons
Granted, in 6 or 12 months, you can get the upgrades necessary to play Doom3 for just a couple hundred dollars, ...
:)
But unless by "waiting for games" you mean "waiting 5 years for games," you're not going to beat the console upgrade cycle.
Notice how both of these points are strikingly similar to what I wrote in my original post...
Please point me to where I can get one of those setups for $149, or $100 used.
:).
Hell, for the price of just the FX6800 I can get *3* X-Boxes and games and plug them in around the house for network head-2-head play!
The difference is that I already have a PC. The marginal cost between an office-use PC and a PC that can play games from six months ago is $200-$300. The marginal cost between an office-use PC and a PC that can play games from three years ago is $0.
If, like me, you're one of those people who doesn't mind waiting for games, PC games have little to no added cost.
Of course, I like console gaming too
Also, it is constructive (you are trying to get 10 points) than destructive (you are trying to make everyone else bankrupt).
For Settlers of Catan, the distinction is kind of blurry. While you do have to play in a way that builds up your resource base, a large part of the game is figuring out how to best screw over the other players (placing a settlement so as to prohibit several other settlement placements, figuring out where to best place the robber, figuring out how to deny "longest road" and "largest army" to others for long enough to win, and so forth).
So while there's no direct violence against the other players, there's plenty of indirect pressure being applied. Such is the nature of competitive games.
There's also Sea3D, and a number of other open source implementations.
Not too much difference. it was a hypothesis that would have failed and was revised later as more information was gathered. There are plenty of failed hyothesis' around by notable scientists to discuss.
The idea would be to test the hypothesis before sending a human up there. The modern space program did this (many incremental milestones before humans or even animals were sent into space).
It's a stupid self diagnosis test... not AI... overhyped buzzword... It simply runs a simulation and tests its results against the actual ones, and generates a report... that's not AI...
It's an expert system, which is indeed AI. You're probably thinking of "strong AI", which is AI that can function as powerfully and flexibly as a human [and if that definition is vague, it's because nobody's nailed down something more solid that everyone agrees on].
Expert system AIs have been around for a long time in a wide variety of fields. They are designed to handle a narrow range of tasks (like fault diagnosis, medical diagnosis, or playing chess) better or more quickly than a human could.
I'm working on a hybrid vehicle, and finding a way to make good use of the regenerative braking power is a real challenge. Lead acids can only take a charge so fast, usually less than 0.1 of the power available during braking, unless you completely oversize the battery banks.
:).
I want something with a very low charge impedance that can basically lock the shaft of the motor/generator, if need be.. completely eliminating friction brakes.
You can probably do that with a superconducting inductor reinforced with glass fiber (or carbon composites, or yadda yadda). Just not at the point where it's close to economically viable yet.
You'd also always need a mechanical brake as a backup, as even in a very strong field, eddy currents only apply so much drag to a conductor. Don't use the regenerator as your parking brake
Nanotubes could have a major commercial future if they are harder then TiN, non reactive to iron, but softer then diamond.
I strongly suspect that nanotube coatings on iron won't work, unless you have a coating of some barrier material (in which case, diamond coating would also work). Any form of carbon would be likely to react to form iron carbides when heated.