What happens if you heat bread in a vacuum? If you heat bread in atmosphere, it gets toasted -- the surface of the bread oxidizes, basically. In a vacuum, however, it would simply get warmer but there shouldn't be any kind of chemical reaction until it gets to -- dare I say it? -- the melting point of bread!
Unforunately, bread doesn't do anything this fun when heated:).
In vacuum or in an inert atmosphere, you'd get chemical transformations long before any melting occurred. Sugar and starches would shed water to become mostly carbon, and the other varied building blocks would turn the bread loaf into something resembling tar before it started boiling.
In vacuum, the water would diffuse into space immediately, and the other hydrocarbons would follow slowly (much lower vapour pressure, so less mass flow). You might have a brittle sponge-like mass of carbon left over.
In an inert atmosphere at normal pressures, the water will boil off as steam, but as long as you're in a closed container most of the medium-to-heavy hydrocarbons will stay put once a small amount has boiled into the air (it stops boiling when the partial pressure of hydrocabons in the air equals the vapour pressure).
Kind of neat to see what would result, though:). For an approximation, pour concentrated sulphuric acid on to the loaf. That catalyzes the extraction of water enough that it'll happen at room temperature, and it'll release enough heat to boil off the other volatiles. Doing this with sugar is a standard chemistry demo.
[NOTE: I can't emphasize too much how much respect you should have for concentrated acids. Wear protective gear, and use long tongs if possible, because concentrated sulphuric will eat through almost anything except glass and ceramics.]
However, isn't the issue storing the anti-protons for a long period of time, not so much producing them? If my memory is correct, current technology allows us to store 10^8 antiprotons for about a few days or so. Assuming we could reach 10%C we would have to be able to store anti-protons for about 40 years to reach the nearest star.
Penning traps and Paul traps should both be capable of storing antimatter for years, albeit at extremely low density (I think they did store a handful of antiprotons for a year to demonstrate this, but I don't have a citation offhand).
If you have a very large trap, this might be enough to let you store a microgram of antimatter.
An alternative would be to bind antiprotons and positrons as antihydrogen, freeze it, give the resulting pellet an electric charge, and then store that with electrostatic confinement. I *think* a scheme along these lines was proposed once, but I could very easily be wrong (heard about it many years ago). This would allow you to store as much antimatter as you could ever possibly produce.
HAHA several YEARS out? yeah right! Currently, it would cost more than the GNP of the United States to merely light a 75 watt light bulb with current Antimatter Power Techniques. (This is what I have heard, maybe this is no longer true, but I don't think anti-matter production techniques have improved that much in the last six months since I heard this).I would say it's more than just a few years out.
Doublecheck your source.
Antiprotons (the type of antimatter we care about for fuel) are produced at about 1e6:1 inefficiency in current accelerators. Assume a system-wide inefficiency of 100:1 on top of this for good measure. That gives you 1e8 watts of power for every watt that goes into your hypothetical light bulb.
That's 7.5e9 watts for your light bulb. At 5 cents per kilowatt-hour (3.6 MJ), that's about $100 per second (for 2.1e3 kW/h).
Substantially less than the GNP.
Hybrid antimatter/fusion craft (that use antimatter to trigger inertial confinement fusion) require on the order of one microgram of antimatter (actually a few hundred nanograms, but let's be lavish). At the efficiencies and costs listed above, it would cost $125 billion to produce the required amount of antimatter.
The US's GNP, by comparison, is about $6.7 trillion.
You'd still have to pay for the production facilities if you wanted to produce the antimatter quickly (it would take a century with our existing accelerators), but this would be at worst a comparable cost to the power used (the SSC was estimated at $20 billion, and it was a thousand times more powerful than needed).
In short, antimatter production for spacecraft is feasible (maybe even better than I've painted, as production rigs built specifically to produce antimatter are more efficient than standard accelerators).
We haven't even investigated this one yet! The cost for launching rockets should be near to $100/kg. It's currently at $2600/kg. If it reaches $100/kg then pretty much anyone reasonably well off can get to go to space. No amount of antimatter rockets can do this. Building large equipment in space is actually easier than building it on the ground; and energy to make antimatter is easy to collect up there.
We've already gone over this.
Launch cost for the ship itself at *current* prices is cheap compared to the cost of the antimatter, so launch cost for the ship is irrlelevant.
For the antimatter generation - which is cheaper? Carrying a billion tonnes of power plant and particle accelerator into space, or leaving it on the ground and carrying a hundred micrograms of antimatter into space?
There is no reason to generate the antimatter in space. We don't have a shortage of power on the ground, and we have power plant and accelerator designs that have already been field-tested on Earth.
Ground-to-orbit cost for building the probe is a non-issue. The only relevant issue is whether we think the research benefit from visiting a nearby star system is worth the cost of the antimatter and ship design engineering. So far, other projects have a better research benefit:cost ratio.
This is why the antimatter-triggered fusion rocket is the most promising design for an interstellar craft. It needed a few hundred micrograms, which is within our capacity to produce.
Look we haven't even worked out how to get off the planet cheaply- and interplanetary hasn't been done yet, and you're worried about interstellar?
Yes.
Largely because these are orthogonal problems. Ground to orbit needs a high-thrust drive, while in-space flight needs a high-Isp, low-thrust drive.
If we _can_ build an interstellar probe, why shouldn't we? It would teach us far more about other star systems than we're likely to learn by any other means.
That would be why I specified a functional thruster. The anti-matter generator would most likely need to be part of the unit. I doubt that generating it earth-side and carrying large quantities would be that good of an idea, but an onboard generator pumping out a small but constant stream would be ideal.
The problem with this is that you'd be better off just using whatever power source you'd be generating the antimatter with. Even with perfect efficiency, you won't get out any more power than you put in (antimatter generators use energy-to-matter conversion to make the antimatter).
The only known ways of producing antimatter are about a million-to-one inefficient. You're definitely generating it on the ground, where you have as much power as you need.
Nope. Antimatter, unless it is made of pure positrons; does create fallout. And you can't use pure positrons, or atleast its very hard because the charges repel each other; and the state of the art with positron production is tiny amounts; and storage is worse.
This is why you suggested a positron-powered aircraft?:)
Positron production is actually relatively easy, though storage does make it impractical as a fuel. Try to make antiprotons, and you'll mostly get muons, mesons, and other high-but-still-lower-energy crud. Try to make electron/positron pairs, and there's not a whole lot else that *can* form (though the vast majority of your energy will still be lost as braking radiation or through pick-a-random-mechanism).
[Positrons don't produce fallout because the gamma rays have insufficient energy to transmute anything- other antimatter is not so fortunate.]
You'll lose a large amount of the energy in meson production not just gamma rays. Gamma rays will also have a really lousy interaction cross-section, especially at the extreme energies involved. Most should just lose energy by pair production (at high energies) or Compton scattering (at low energies).
Compared to the neutron pulse from a fission or fusion explosion, it's a walk in the park.
From what I've seen the hard bit by far is getting into space at all. Once you're there, conventional fission can get us about the solar system plenty fast enough. The main limitation isn't energy- it's materials. We really need a cheap launch system!
Actually, unless you're talking about a nuclear-electric ion drive, fission drives are pretty lousy. The reason is that in a direct contact style drive like NERVA your core temperature has to be low enough not to melt your materials or let your exhaust gas etch the walls. This limits your exhaust temperature to the range that you'd get with chemical rockets. This means that your Isp isn't going to be much better than chemical rockets.
For anything inside the asteroid belt, solar power is probably better than nuclear, as it weighs less per unit power generation.
Deuterium fusion? Don't make me laugh. Containment is a total nightmare. It's been 50 years away for 50 years; except now it's only 30 years away; maybe, or maybe they're just being more optimistic because someone was going to cut their funding. And that's just getting it to fuse and stay contained; getting electricity from it- that's almost equally as hard.
Read about fusion drives before criticizing them. You don't generate electricity from them or run them steady-state. You perform inertial confinement fusion on micropellets, one pellet at a time, in a magnetic field so that your exhaust goes mostly in one direction. This is much, much easier than trying to extract power from the fusion reaction at reasonable efficiency.
Antimatter works wonderfully as a trigger because it doesn't suffer from laser-ignition's problem of reflecting off of the pellets once they become plasma.
I went to a talk on positron manufacture and its possible use on an unmanned air vehicle.
Positrons can be manufactured in your basement. But they're useless for space travel or any other propulsion because they're far too light (you can't store enough mass to do anything useful). Antiprotons are the fuel of choice, as they have a charge to mass ratio 2000 times greater. Depending on the storage scheme, you may also choose to let them bind to positrons to form antihydrogen and store that (you can suspend it at extremely low temperatures at far higher densities than you could store antiprotons in an ion trap).
Antiprotons, however, can only be made at million-to-one inefficiencies using a 10+ GeV accelerator. Doing this in space would be even more of a pain in the neck than on Earth, partly because you need a bigarsed device and partly because you need a bigger-arsed power plant (though you do get hard vacuum for free, which is a bonus).
Large quantities of antimatter is practically the definition of 'unobtainium' right now.
This is why the antimatter-triggered fusion rocket is the most promising design for an interstellar craft. It needed a few hundred micrograms, which is within our capacity to produce.
Mod this parent down, and while your asking, wonder if he knows how much antimatter has been made, and why it even matters.
We've made on the order of a hundred nanograms if I remember correctly. It matters because it correctly reflects the fact that antimatter is very expensive to make.
If we actually had cost effective space launch then antimatter research might actually be worth it.
With current production techniques, the cost of the antimatter would far dwarf the cost of bringing the rest of your ship into orbit, so cost-effectiveness of the launch vehicle doesn't matter.
Right now, it's so far out- a launch accident involving antimatter could go off like fission bomb. It only makes sense if you make it in space. I'm actually pro nuclear power- but launching significant antimatter from the earth 'scares even me, and I'm fearless'. Plutonium- I laugh at plutonium.
Actually, a launch failure in an antimatter rocket would be much safer than a conventional fission or fusion bomb. Firstly, you aren't going to have substantial amounts of the stuff (if you have a way to produce it in kilogram quantities, you have a lot more to worry about than rocket failures). Secondly, an antimatter annihilation should produce no fallout. You'd have a ferocious gamma-ray burst, and a giant fireball if you have enough antimatter (due to gamma rays heating the air nearby), but you'd have neither direct radioactive byproducts nor significant transmutation going on. Even a burst near ground level would be unlikely to produce substantial activated material.
In summary, I don't think antimatter explosions are a significant worry as long as everyone's a few kilometres away from the launch pad.
Be afraid of plutonium, though. If disposed of incorrectly or used in weapons, it's quite nasty.
What's the point of messing about with antimatter right now? The amount of antimatter that has ever been made is smaller than a pinhead.
But wouldn't it be nice to be able to *use* antimatter in a propulsion system when/if we ever _do_ figure out how to build it in quantity, instead twiddling our thumbs and spending more decades figuring out how to build the drives?
Better yet, if a practical antimatter drive scheme is found, it would suddenly become worth producing more antimatter. The reason so little has been produced is that current applications (physics research) don't need much.
Re. quantity, the most feasible drive plans I've seen call for small quantities of antimatter to be used to induce fusion in deuterium pellets. You wouldn't need tonnes of the stuff.
Fusion reactors and anti-matter drives sound cool, but do the math... assuming these drives can propel a craft at one-tenth the speed of light, which is a speed of approximately 66.9 Million Miles Per Hour, it would still take 30 years to reach the nearest star.
Even if we don't reach the nearest star (and 10 percent of C is very optimistic for any drive built in the near future), we'd be able to reach anywhere in the solar system with much, much better transit times and fuel to mass ratios than we currently can. This is what we'd need to do widespread exploration/colonization.
Assuming we _can_ get to 10% C, it would _definitely_ be worth it to send probes to nearby systems. We know we can build craft that last that long, and it's very unlikely we'd find a better drive in only 30 years.
In short, advanced drives would still be very, very useful.
It would be great if they actually managed to design a functional anti-matter thurster.
There are two designs already that I know of that would certainly work. The problem is that antimatter is a bugger to produce (well, antiprotons, at least).
I certainly have sympathy for the blind -- I'm color blind myself, and routinely get myself killed in FPS and other games where "good" things are green and "bad" things are red, but both colors have the same saturation and luminosity as bad things.
If your graphics card software gives you separate gamma-correction control over each colour component, you could tweak it so that one was much darker than the other, and stop accidentally TKing:).
All current graphics cards can do this easily (the 8-bit palette table is used as the gamma table in higher modes), but whether you can get at it is another matter.
Hopefully just dumbed down too far.
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Chicken-Feather Chips
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· Score: 5, Informative
The reason silicon is used for integrated circuit chips is because it's a semiconductor - a material that can conduct or insulate depending on the electrical conditions around it. Chicken feathers do not semiconduct.
As for electric signals travelling best through air... would you rather be standing ten feet from a power line, or reaching out with a metal fishing rod to touch it?
As far as I can tell, the discussion seems to be a garbled description of using organic fibers/composites as a dielectric (insulating) material instead of oxides or nitrides. Much research has been done over the past several years looking for "low-K dielectrics". The "K" parameter is a measure of how an insulator interacts with an electric field imposed on it. A high-K material has more capacitance when you put a voltage across it; low-k materials for bulk insulators reduce the capacitance between wires (and between wires and the substrate). This reduces wire delays.
An attractive area of research has been to put voids (bubbles or pores) into the dielectric material. Because gases tend to have low dielectric constants, introducing gas-filled voids in the dielectric will reduce the capacitance that two wires insulated by the dielectric will feel. This is what the "microbubbles" comment in the article refers to.
I guess this guy wants to grind up chicken feathers and paste them on to a wafer instead of growing an oxide. Among other things, he'll need to remove all particles larger than a few tens of nanometres for this to not introduce defects in the chip. Good luck.
As will undoubtedly be mentioned multiple times on this discussion, that's Robert Zubrin's Mars Direct plan, and the concept of making the fuel there for the return trip seems to be the only vaguely sane way to do things.
Not necessarily.
Mars's escape velocity is slightly less than half that of Earth. A rocket with a fuel-to-cargo ratio comparable to an earth-to-orbit booster should be able to land on Mars and take off again without refueling. You get an even better ratio if you can use a gliding or parachuting entry on Mars, but that's a lot more difficult with the thin atmosphere.
How about getting to Mars in the first place? Well, getting into Earth orbit doesn't affect your total craft fuel, because you'd logically either build the ship in orbit or launch it from Earth (using all of its delta-v in one shot), and the refuel it in orbit from supplies brought up by the shuttle. This isn't cheap, but it would be easier than trying to build a craft with a 20-25 km/sec delta V.
Getting from Earth orbit to Mars orbit can use any of a variety of low-thrust, high-Isp drives, thus avoiding eating into most of the fuel reserves for the trip.
So, while it would probably be cheaper to produce fuel on Mars if it's practical to do so, you could still get to Mars without horrible problems by carrying your fuel with you and refueling in Earth orbit.
No, fuel cells generate power..from, that's right, fuel! Think of them as doing a very slow burn, but it's done at the chemical level in a way which emits electrons.
a) RFTM. I do indeed mention fuel. By your argument, batteries generate power too (instead of storing it).
b) Calculate how much power a ton of solar cells generates at, say, 200 W/m^2 (for Mars orbit) and 15% efficiency over 400+ days. Now, calculate how much energy is in a ton of hydrogen/oxygen mix (I'm giving you a bonus here, as the storage tanks would be a large fraction of the weight).
Maybe NASA will develop a more efficient fuel-cell based power system because it's obviously just not sound to power everything by solar cells.
Fuel cells are a power _storage_ medium, not a power generator.
For a trip that will last more than a year, solar panels will give you a lot more energy than an equivalent weight in hydrogen and oxygen to supply fuel cells.
Of course, the ship would still have fuel cells for temporary power storage (they're lighter than batteries), but power generation for any craft inside the asteroid belt will be solar.
A Diamond core? That certainly is plausable, but how big of a bread-planet does that require?
Not that big. We can form diamonds in hydraulic presses, so the pressure's pretty low on a planetary scale.
On a slightly related note, check out this article [slashdot.org] from last month.
That article made my head hurt:). I didn't see a convincing argument for atoms being sufficiently mobile for the proposed concentration of actinides in the core. The paper linked to cited other papers... but most of those were by the same authour. This is suspicious (it suggests that nobody else thinks the authour's work was worth following up on).
Because diamond is the more compact form of carbon (hence its formation from other allotropes under pressure), and I'm assuming that carbon is more abundant than the other elements composing bread.
oxygen is heavier, and at large densities you would probably get some metalic phase which is not solid state.
Hmm. Diamond outer core?:)
come to think of it hyper-dense carbon should also be different than usual diamond, as the E part of the Gibbs free energy F=E-TS will be mostly a function of the density (r^-12 part of leonard-gibbs potential) and not of the chemical connection. (=> disordered state, pseudo-liquid)
My understanding was that diamond was stable up to surprisingly high pressure. The only thing that would be more compact than it would probably be some kind of metallic state with a spherical close-pack structure. Is a planet's core pressure enough to force diamond to convert to that kind of structure? (I don't have a phase diagram of carbon's allotropes handy.)
The biggest problem that I see with the proposed time system is that it's based on Earth's rotation period.
We're not going to colonize Mars next week, but we could conceivably do it within a hundred years. That makes this system just as ill-fitting as the current system is to timekeeping.
IMO, the best solution for those who insist on changing the timing scheme at all is to have the second as the fundamental unit of time, with order of magnitude multiples of seconds being the official SI units.
A hundred seconds is just over a minute and a half; close enough to serve the purpose of a "minute".
A thousand seconds is about 17 minutes. Long enough to serve the same purpose as the "centiday" proposed by the article.
The day would be an ugly number of minutes long, but we're used to this ugliness when converting days to years anyways, so I don't see this as a big problem. Earth's day is an artifact of Earth; it doesn't have to precisely match the timekeeping system any more than its size has to match the metric system.
All of our scientific literature is now based on seconds. Remember the whole ergs/joules thing, as just one small example? Changing the time base would be worse.
In summary, I think a system based on existing seconds would be best.
I'm not going to throw away my existing clocks any time soon, though.
The article pretty much covered why the moon won't ever hit the Earth (and what would happen if Q snapped his fingers and it did), so I won't touch that.
However, this does remind me of a very, very bizzare conversation I and several others had a couple of years back (while waiting for food at a restaurant, and pondering the rolls).
Q: What would happen if you had an entire planet made out of bread?
Getting the answer was a very amusing thought-experiment. It turns out that you'd eventually end up with a bacteria-infested planet with a large diamond core, a mantle of uncertain composition, a crust of tar with seas of complex hydrocarbons and carbohydrates, and an atmosphere of methane and water vapour.
So, I invite similarly bored slashdotters to consider similar questions involving other materials, or other interesting celestial thought-experiments.
A) most people would advocate a ladder or mass accelerator of some type, generally most would not suggest to do this with rockets..
The problem being that we're quite a ways away from building either of these.
A mass accelerator is a neat idea until you calculate the size of the accelerator you'd need. For human-survivable acceleration, it's insane (on the order of a thousand kilometres). For cargo-survivable acceleration you need a tower that's 10 km high or so. And that's presuming that you can get the energy-per-unit-distance of your accelerator high enough. That would be quite a trick to build.
You can't build a horizontal railroad and turn it up at the end - radius of curvature for feasible radial forces is tens of kilometres, so you might as well just build the original tower.
We can't launch at shallow angles because we'd be going through enough atmosphere to either vapourize our heat shield, slow down our projectile too much, or both, so we're stuck with having to build a gun that points upwards and imparting escape velocity to the cargo.
In short, I don't think that an earth-based mass driver will be buildable for quite a while.
As for the space elevator - the problem is that there's a big gap between being able to produce miracle materials in the laboratory and being able to mass-produce them in quantities useful for construction. Remember whisker fibers? They were the miracle material before nanotubes came along. We've known about them for a long time, and have been able to produce impressive laboratory samples for a long time, but you don't see spacecraft or suspension bridges built using them yet. I strongly suspect nanotubes will go the same way.
In summary, I don't think we'll have anything safer than rockets to launch with for the medium-term future.
B) if you have a small enough load -- in a remote enough area -- you would radiate a large area 'just a little'... There is radiation all around you now, everywhere, if properly concieved a rocket scheme could produce a risk equal to very mildy raise radiation...
I agree that the per-accident contamination is small if you're using small payloads, but that doesn't change the total amount of contamination that occurs. If you have a 1% catastrophic failure rate, then 1% of your radioactive waste is going to end up dusted across the landscape by the time you've finished launching it all. This is enough that you'll have difficulty convincing any government to approve irradiation of remote forest/ocean/ice-field territory to the required degree.
The mine-shaft approach doesn't involve loss of containment even in a catastrophic accident en route, and can keep waste contained for as long as you care to leave it there. I don't see the attractiveness of the rocket approach with respect to this.
Slashdot Mirror
Wear protective gear, and use long tongs if possible, because concentrated sulphuric will eat through almost anything except glass and ceramics.
And do this under a fume hood, because boiling acid vapour is Not Nice.
What happens if you heat bread in a vacuum? If you heat bread in atmosphere, it gets toasted -- the surface of the bread oxidizes, basically. In a vacuum, however, it would simply get warmer but there shouldn't be any kind of chemical reaction until it gets to -- dare I say it? -- the melting point of bread!
:).
:). For an approximation, pour concentrated sulphuric acid on to the loaf. That catalyzes the extraction of water enough that it'll happen at room temperature, and it'll release enough heat to boil off the other volatiles. Doing this with sugar is a standard chemistry demo.
Unforunately, bread doesn't do anything this fun when heated
In vacuum or in an inert atmosphere, you'd get chemical transformations long before any melting occurred. Sugar and starches would shed water to become mostly carbon, and the other varied building blocks would turn the bread loaf into something resembling tar before it started boiling.
In vacuum, the water would diffuse into space immediately, and the other hydrocarbons would follow slowly (much lower vapour pressure, so less mass flow). You might have a brittle sponge-like mass of carbon left over.
In an inert atmosphere at normal pressures, the water will boil off as steam, but as long as you're in a closed container most of the medium-to-heavy hydrocarbons will stay put once a small amount has boiled into the air (it stops boiling when the partial pressure of hydrocabons in the air equals the vapour pressure).
Kind of neat to see what would result, though
[NOTE: I can't emphasize too much how much respect you should have for concentrated acids. Wear protective gear, and use long tongs if possible, because concentrated sulphuric will eat through almost anything except glass and ceramics.]
However, isn't the issue storing the anti-protons for a long period of time, not so much producing them? If my memory is correct, current technology allows us to store 10^8 antiprotons for about a few days or so. Assuming we could reach 10%C we would have to be able to store anti-protons for about 40 years to reach the nearest star.
Penning traps and Paul traps should both be capable of storing antimatter for years, albeit at extremely low density (I think they did store a handful of antiprotons for a year to demonstrate this, but I don't have a citation offhand).
If you have a very large trap, this might be enough to let you store a microgram of antimatter.
An alternative would be to bind antiprotons and positrons as antihydrogen, freeze it, give the resulting pellet an electric charge, and then store that with electrostatic confinement. I *think* a scheme along these lines was proposed once, but I could very easily be wrong (heard about it many years ago). This would allow you to store as much antimatter as you could ever possibly produce.
HAHA several YEARS out? yeah right! Currently, it would cost more than the GNP of the United States to merely light a 75 watt light bulb with current Antimatter Power Techniques. (This is what I have heard, maybe this is no longer true, but I don't think anti-matter production techniques have improved that much in the last six months since I heard this).I would say it's more than just a few years out.
Doublecheck your source.
Antiprotons (the type of antimatter we care about for fuel) are produced at about 1e6:1 inefficiency in current accelerators. Assume a system-wide inefficiency of 100:1 on top of this for good measure. That gives you 1e8 watts of power for every watt that goes into your hypothetical light bulb.
That's 7.5e9 watts for your light bulb. At 5 cents per kilowatt-hour (3.6 MJ), that's about $100 per second (for 2.1e3 kW/h).
Substantially less than the GNP.
Hybrid antimatter/fusion craft (that use antimatter to trigger inertial confinement fusion) require on the order of one microgram of antimatter (actually a few hundred nanograms, but let's be lavish). At the efficiencies and costs listed above, it would cost $125 billion to produce the required amount of antimatter.
The US's GNP, by comparison, is about $6.7 trillion.
You'd still have to pay for the production facilities if you wanted to produce the antimatter quickly (it would take a century with our existing accelerators), but this would be at worst a comparable cost to the power used (the SSC was estimated at $20 billion, and it was a thousand times more powerful than needed).
In short, antimatter production for spacecraft is feasible (maybe even better than I've painted, as production rigs built specifically to produce antimatter are more efficient than standard accelerators).
We haven't even investigated this one yet! The cost for launching rockets should be near to $100/kg. It's currently at $2600/kg. If it reaches $100/kg then pretty much anyone reasonably well off can get to go to space. No amount of antimatter rockets can do this. Building large equipment in space is actually easier than building it on the ground; and energy to make antimatter is easy to collect up there.
We've already gone over this.
Launch cost for the ship itself at *current* prices is cheap compared to the cost of the antimatter, so launch cost for the ship is irrlelevant.
For the antimatter generation - which is cheaper? Carrying a billion tonnes of power plant and particle accelerator into space, or leaving it on the ground and carrying a hundred micrograms of antimatter into space?
There is no reason to generate the antimatter in space. We don't have a shortage of power on the ground, and we have power plant and accelerator designs that have already been field-tested on Earth.
Ground-to-orbit cost for building the probe is a non-issue. The only relevant issue is whether we think the research benefit from visiting a nearby star system is worth the cost of the antimatter and ship design engineering. So far, other projects have a better research benefit:cost ratio.
This is why the antimatter-triggered fusion rocket is the most promising design for an interstellar craft. It needed a few hundred micrograms, which is within our capacity to produce.
Look we haven't even worked out how to get off the planet cheaply- and interplanetary hasn't been done yet, and you're worried about interstellar?
Yes.
Largely because these are orthogonal problems. Ground to orbit needs a high-thrust drive, while in-space flight needs a high-Isp, low-thrust drive.
If we _can_ build an interstellar probe, why shouldn't we? It would teach us far more about other star systems than we're likely to learn by any other means.
That would be why I specified a functional thruster. The anti-matter generator would most likely need to be part of the unit. I doubt that generating it earth-side and carrying large quantities would be that good of an idea, but an onboard generator pumping out a small but constant stream would be ideal.
The problem with this is that you'd be better off just using whatever power source you'd be generating the antimatter with. Even with perfect efficiency, you won't get out any more power than you put in (antimatter generators use energy-to-matter conversion to make the antimatter).
The only known ways of producing antimatter are about a million-to-one inefficient. You're definitely generating it on the ground, where you have as much power as you need.
Nope. Antimatter, unless it is made of pure positrons; does create fallout. And you can't use pure positrons, or atleast its very hard because the charges repel each other; and the state of the art with positron production is tiny amounts; and storage is worse.
:)
This is why you suggested a positron-powered aircraft?
Positron production is actually relatively easy, though storage does make it impractical as a fuel. Try to make antiprotons, and you'll mostly get muons, mesons, and other high-but-still-lower-energy crud. Try to make electron/positron pairs, and there's not a whole lot else that *can* form (though the vast majority of your energy will still be lost as braking radiation or through pick-a-random-mechanism).
[Positrons don't produce fallout because the gamma rays have insufficient energy to transmute anything- other antimatter is not so fortunate.]
You'll lose a large amount of the energy in meson production not just gamma rays. Gamma rays will also have a really lousy interaction cross-section, especially at the extreme energies involved. Most should just lose energy by pair production (at high energies) or Compton scattering (at low energies).
Compared to the neutron pulse from a fission or fusion explosion, it's a walk in the park.
Oh well in that case... what a great idea, it's so much more expensive than the obscenely expensive launch vehicle that it must be a good idea!
It has the virtue of being *able* to carry a probe to the next star, unlike the launch vehicles it's more expensive than.
From what I've seen the hard bit by far is getting into space at all. Once you're there, conventional fission can get us about the solar system plenty fast enough. The main limitation isn't energy- it's materials. We really need a cheap launch system!
Actually, unless you're talking about a nuclear-electric ion drive, fission drives are pretty lousy. The reason is that in a direct contact style drive like NERVA your core temperature has to be low enough not to melt your materials or let your exhaust gas etch the walls. This limits your exhaust temperature to the range that you'd get with chemical rockets. This means that your Isp isn't going to be much better than chemical rockets.
For anything inside the asteroid belt, solar power is probably better than nuclear, as it weighs less per unit power generation.
Deuterium fusion? Don't make me laugh. Containment is a total nightmare. It's been 50 years away for 50 years; except now it's only 30 years away; maybe, or maybe they're just being more optimistic because someone was going to cut their funding. And that's just getting it to fuse and stay contained; getting electricity from it- that's almost equally as hard.
Read about fusion drives before criticizing them. You don't generate electricity from them or run them steady-state. You perform inertial confinement fusion on micropellets, one pellet at a time, in a magnetic field so that your exhaust goes mostly in one direction. This is much, much easier than trying to extract power from the fusion reaction at reasonable efficiency.
Antimatter works wonderfully as a trigger because it doesn't suffer from laser-ignition's problem of reflecting off of the pellets once they become plasma.
I went to a talk on positron manufacture and its possible use on an unmanned air vehicle.
Positrons can be manufactured in your basement. But they're useless for space travel or any other propulsion because they're far too light (you can't store enough mass to do anything useful). Antiprotons are the fuel of choice, as they have a charge to mass ratio 2000 times greater. Depending on the storage scheme, you may also choose to let them bind to positrons to form antihydrogen and store that (you can suspend it at extremely low temperatures at far higher densities than you could store antiprotons in an ion trap).
Antiprotons, however, can only be made at million-to-one inefficiencies using a 10+ GeV accelerator. Doing this in space would be even more of a pain in the neck than on Earth, partly because you need a bigarsed device and partly because you need a bigger-arsed power plant (though you do get hard vacuum for free, which is a bonus).
Large quantities of antimatter is practically the definition of 'unobtainium' right now.
This is why the antimatter-triggered fusion rocket is the most promising design for an interstellar craft. It needed a few hundred micrograms, which is within our capacity to produce.
Mod this parent down, and while your asking, wonder if he knows how much antimatter has been made, and why it even matters.
We've made on the order of a hundred nanograms if I remember correctly. It matters because it correctly reflects the fact that antimatter is very expensive to make.
If we actually had cost effective space launch then antimatter research might actually be worth it.
With current production techniques, the cost of the antimatter would far dwarf the cost of bringing the rest of your ship into orbit, so cost-effectiveness of the launch vehicle doesn't matter.
Right now, it's so far out- a launch accident involving antimatter could go off like fission bomb. It only makes sense if you make it in space. I'm actually pro nuclear power- but launching significant antimatter from the earth 'scares even me, and I'm fearless'. Plutonium- I laugh at plutonium.
Actually, a launch failure in an antimatter rocket would be much safer than a conventional fission or fusion bomb. Firstly, you aren't going to have substantial amounts of the stuff (if you have a way to produce it in kilogram quantities, you have a lot more to worry about than rocket failures). Secondly, an antimatter annihilation should produce no fallout. You'd have a ferocious gamma-ray burst, and a giant fireball if you have enough antimatter (due to gamma rays heating the air nearby), but you'd have neither direct radioactive byproducts nor significant transmutation going on. Even a burst near ground level would be unlikely to produce substantial activated material.
In summary, I don't think antimatter explosions are a significant worry as long as everyone's a few kilometres away from the launch pad.
Be afraid of plutonium, though. If disposed of incorrectly or used in weapons, it's quite nasty.
What's the point of messing about with antimatter right now? The amount of antimatter that has ever been made is smaller than a pinhead.
But wouldn't it be nice to be able to *use* antimatter in a propulsion system when/if we ever _do_ figure out how to build it in quantity, instead twiddling our thumbs and spending more decades figuring out how to build the drives?
Better yet, if a practical antimatter drive scheme is found, it would suddenly become worth producing more antimatter. The reason so little has been produced is that current applications (physics research) don't need much.
Re. quantity, the most feasible drive plans I've seen call for small quantities of antimatter to be used to induce fusion in deuterium pellets. You wouldn't need tonnes of the stuff.
Fusion reactors and anti-matter drives sound cool, but do the math ... assuming these drives can propel a craft at one-tenth the speed of light, which is a speed of approximately 66.9 Million Miles Per Hour, it would still take 30 years to reach the nearest star.
Even if we don't reach the nearest star (and 10 percent of C is very optimistic for any drive built in the near future), we'd be able to reach anywhere in the solar system with much, much better transit times and fuel to mass ratios than we currently can. This is what we'd need to do widespread exploration/colonization.
Assuming we _can_ get to 10% C, it would _definitely_ be worth it to send probes to nearby systems. We know we can build craft that last that long, and it's very unlikely we'd find a better drive in only 30 years.
In short, advanced drives would still be very, very useful.
It would be great if they actually managed to design a functional anti-matter thurster.
There are two designs already that I know of that would certainly work. The problem is that antimatter is a bugger to produce (well, antiprotons, at least).
I certainly have sympathy for the blind -- I'm color blind myself, and routinely get myself killed in FPS and other games where "good" things are green and "bad" things are red, but both colors have the same saturation and luminosity as bad things.
:).
If your graphics card software gives you separate gamma-correction control over each colour component, you could tweak it so that one was much darker than the other, and stop accidentally TKing
All current graphics cards can do this easily (the 8-bit palette table is used as the gamma table in higher modes), but whether you can get at it is another matter.
The reason silicon is used for integrated circuit chips is because it's a semiconductor - a material that can conduct or insulate depending on the electrical conditions around it. Chicken feathers do not semiconduct.
As for electric signals travelling best through air... would you rather be standing ten feet from a power line, or reaching out with a metal fishing rod to touch it?
As far as I can tell, the discussion seems to be a garbled description of using organic fibers/composites as a dielectric (insulating) material instead of oxides or nitrides. Much research has been done over the past several years looking for "low-K dielectrics". The "K" parameter is a measure of how an insulator interacts with an electric field imposed on it. A high-K material has more capacitance when you put a voltage across it; low-k materials for bulk insulators reduce the capacitance between wires (and between wires and the substrate). This reduces wire delays.
An attractive area of research has been to put voids (bubbles or pores) into the dielectric material. Because gases tend to have low dielectric constants, introducing gas-filled voids in the dielectric will reduce the capacitance that two wires insulated by the dielectric will feel. This is what the "microbubbles" comment in the article refers to.
I guess this guy wants to grind up chicken feathers and paste them on to a wafer instead of growing an oxide. Among other things, he'll need to remove all particles larger than a few tens of nanometres for this to not introduce defects in the chip. Good luck.
If you've already gotten coffe and made a sandwich and the slides still haven't loaded, here's something to keep you occupied in the meantime:
Google cache of a list of talks the same authour has done
Turn off images before loading this page, as they're taken from the same server that we melted down with slides requests.
As will undoubtedly be mentioned multiple times on this discussion, that's Robert Zubrin's Mars Direct plan, and the concept of making the fuel there for the return trip seems to be the only vaguely sane way to do things.
Not necessarily.
Mars's escape velocity is slightly less than half that of Earth. A rocket with a fuel-to-cargo ratio comparable to an earth-to-orbit booster should be able to land on Mars and take off again without refueling. You get an even better ratio if you can use a gliding or parachuting entry on Mars, but that's a lot more difficult with the thin atmosphere.
How about getting to Mars in the first place? Well, getting into Earth orbit doesn't affect your total craft fuel, because you'd logically either build the ship in orbit or launch it from Earth (using all of its delta-v in one shot), and the refuel it in orbit from supplies brought up by the shuttle. This isn't cheap, but it would be easier than trying to build a craft with a 20-25 km/sec delta V.
Getting from Earth orbit to Mars orbit can use any of a variety of low-thrust, high-Isp drives, thus avoiding eating into most of the fuel reserves for the trip.
So, while it would probably be cheaper to produce fuel on Mars if it's practical to do so, you could still get to Mars without horrible problems by carrying your fuel with you and refueling in Earth orbit.
No, fuel cells generate power..from, that's right, fuel! Think of them as doing a very slow burn, but it's done at the chemical level in a way which emits electrons.
a) RFTM. I do indeed mention fuel. By your argument, batteries generate power too (instead of storing it).
b) Calculate how much power a ton of solar cells generates at, say, 200 W/m^2 (for Mars orbit) and 15% efficiency over 400+ days. Now, calculate how much energy is in a ton of hydrogen/oxygen mix (I'm giving you a bonus here, as the storage tanks would be a large fraction of the weight).
See the problem with fuel cells now? Good.
Maybe NASA will develop a more efficient fuel-cell based power system because it's obviously just not sound to power everything by solar cells.
Fuel cells are a power _storage_ medium, not a power generator.
For a trip that will last more than a year, solar panels will give you a lot more energy than an equivalent weight in hydrogen and oxygen to supply fuel cells.
Of course, the ship would still have fuel cells for temporary power storage (they're lighter than batteries), but power generation for any craft inside the asteroid belt will be solar.
A Diamond core? That certainly is plausable, but how big of a bread-planet does that require?
:). I didn't see a convincing argument for atoms being sufficiently mobile for the proposed concentration of actinides in the core. The paper linked to cited other papers... but most of those were by the same authour. This is suspicious (it suggests that nobody else thinks the authour's work was worth following up on).
Not that big. We can form diamonds in hydraulic presses, so the pressure's pretty low on a planetary scale.
On a slightly related note, check out this article [slashdot.org] from last month.
That article made my head hurt
why a diamond core ?
:)
Because diamond is the more compact form of carbon (hence its formation from other allotropes under pressure), and I'm assuming that carbon is more abundant than the other elements composing bread.
oxygen is heavier, and at large densities you would probably get some metalic phase which is not solid state.
Hmm. Diamond outer core?
come to think of it hyper-dense carbon should also be different than usual diamond, as the E part of the Gibbs free energy F=E-TS will be mostly a function of the density (r^-12 part of leonard-gibbs potential) and not of the chemical connection. (=> disordered state, pseudo-liquid)
My understanding was that diamond was stable up to surprisingly high pressure. The only thing that would be more compact than it would probably be some kind of metallic state with a spherical close-pack structure. Is a planet's core pressure enough to force diamond to convert to that kind of structure? (I don't have a phase diagram of carbon's allotropes handy.)
The biggest problem that I see with the proposed time system is that it's based on Earth's rotation period.
We're not going to colonize Mars next week, but we could conceivably do it within a hundred years. That makes this system just as ill-fitting as the current system is to timekeeping.
IMO, the best solution for those who insist on changing the timing scheme at all is to have the second as the fundamental unit of time, with order of magnitude multiples of seconds being the official SI units.
A hundred seconds is just over a minute and a half; close enough to serve the purpose of a "minute".
A thousand seconds is about 17 minutes. Long enough to serve the same purpose as the "centiday" proposed by the article.
The day would be an ugly number of minutes long, but we're used to this ugliness when converting days to years anyways, so I don't see this as a big problem. Earth's day is an artifact of Earth; it doesn't have to precisely match the timekeeping system any more than its size has to match the metric system.
All of our scientific literature is now based on seconds. Remember the whole ergs/joules thing, as just one small example? Changing the time base would be worse.
In summary, I think a system based on existing seconds would be best.
I'm not going to throw away my existing clocks any time soon, though.
The article pretty much covered why the moon won't ever hit the Earth (and what would happen if Q snapped his fingers and it did), so I won't touch that.
However, this does remind me of a very, very bizzare conversation I and several others had a couple of years back (while waiting for food at a restaurant, and pondering the rolls).
Q: What would happen if you had an entire planet made out of bread?
Getting the answer was a very amusing thought-experiment. It turns out that you'd eventually end up with a bacteria-infested planet with a large diamond core, a mantle of uncertain composition, a crust of tar with seas of complex hydrocarbons and carbohydrates, and an atmosphere of methane and water vapour.
So, I invite similarly bored slashdotters to consider similar questions involving other materials, or other interesting celestial thought-experiments.
A) most people would advocate a ladder or mass accelerator of some type, generally most would not suggest to do this with rockets..
:).
The problem being that we're quite a ways away from building either of these.
A mass accelerator is a neat idea until you calculate the size of the accelerator you'd need. For human-survivable acceleration, it's insane (on the order of a thousand kilometres). For cargo-survivable acceleration you need a tower that's 10 km high or so. And that's presuming that you can get the energy-per-unit-distance of your accelerator high enough. That would be quite a trick to build.
You can't build a horizontal railroad and turn it up at the end - radius of curvature for feasible radial forces is tens of kilometres, so you might as well just build the original tower.
We can't launch at shallow angles because we'd be going through enough atmosphere to either vapourize our heat shield, slow down our projectile too much, or both, so we're stuck with having to build a gun that points upwards and imparting escape velocity to the cargo.
In short, I don't think that an earth-based mass driver will be buildable for quite a while.
As for the space elevator - the problem is that there's a big gap between being able to produce miracle materials in the laboratory and being able to mass-produce them in quantities useful for construction. Remember whisker fibers? They were the miracle material before nanotubes came along. We've known about them for a long time, and have been able to produce impressive laboratory samples for a long time, but you don't see spacecraft or suspension bridges built using them yet. I strongly suspect nanotubes will go the same way.
In summary, I don't think we'll have anything safer than rockets to launch with for the medium-term future.
B) if you have a small enough load -- in a remote enough area -- you would radiate a large area 'just a little'... There is radiation all around you now, everywhere, if properly concieved a rocket scheme could produce a risk equal to very mildy raise radiation...
I agree that the per-accident contamination is small if you're using small payloads, but that doesn't change the total amount of contamination that occurs. If you have a 1% catastrophic failure rate, then 1% of your radioactive waste is going to end up dusted across the landscape by the time you've finished launching it all. This is enough that you'll have difficulty convincing any government to approve irradiation of remote forest/ocean/ice-field territory to the required degree.
The mine-shaft approach doesn't involve loss of containment even in a catastrophic accident en route, and can keep waste contained for as long as you care to leave it there. I don't see the attractiveness of the rocket approach with respect to this.
You've made good arguments, though