Refitting existing planes with liquid hydrogen is essentially impossible. The fuel tanks are far too small and are not designed to hold a cryogenic fuel.
Yes, the fuel in the shuttle ET had a lot of energy. This is a necessary property of rocket propellants. Hydrogen, kerosene, whatever would have burned to produce a large energy release in the Challenger accident. Note that the hydrogen there did not *explode* in the sense of detonating, it just burned rapidly (without a detonation wave being produced). And this burning did not cause the accident, or destroy the orbiter -- the orbiter was torn apart by being thrown sideways into a supersonic airstream.
The weight to energy density of hydrogen is much better than jet fuel. The tanks would have to be larger, however, because of the lower volumetric efficiency.
Hydrogen also allows new engine cycles since it has substantial cooling capacity, which can reduce the power diverted to the compressor (intercooling).
> Basically to start a fusion reaction you
> basically need a huge energy burst, essentially
> a nuke.
Basically, you're full of shit. That statement is completely wrong. The energy content of the plasma in a fusion reactor will be measured in megajoules, not the terajoules of even a small nuclear weapon.
No, the energy spent in the magnets is not what keeps fusion reactors from reaching breakeven. What keeps them from reaching breakeven is the distressing tendency for the energy to leak out of the plasma. BTW, this is also why fusion reactors tend to be big -- energy escapes less readily from a larger plasma.
You do get 3He from the decay of tritium produced in the blanket of a DT fusion reactor.
However, most of the tritium produced in that blanket has to be recycled back as fuel for the DT reactor. The net reaction is D + 6Li --> 2 4He. To make 3He you need extra neutrons from (n,2n) side reactions. As a result, the 3He output will only be a sideshow, a minor byproduct of an energy system that produces most of its energy from DT reactions.
To have a system that is primarly D3He fueled, you need to be able to mine 3He somewhere. The moon has been suggested (but at 10 ppb the economics are dubious). Beyond that, Uranus may be a good source, and maybe we can mine 3He from the thin atmosphere of some as-yet undiscovered Kuiper Belt Object. A body the density of Pluto with a radius of ~2800 km and a temperature of 30K could retain 3He in its atmosphere. It would be about 3% of the mass of the Earth, about half the mass of Mars.
> Also, fusion will be MUCH cheaper than gasoline.
This is nonsense. Fusion promises to be very expensive. Oh, sure, *deuterium* is cheap, but deuterium by itself isn't useful. You need this big expensive reactor to get energy from it.
This kind of economic illiteracy shows up often in naive talk about energy. Sunlight is free, wind is free, does that make electricity generated from these sources free? Of course not.
Farnsworth achieved fusion in the sense that his device produced fusion reactions, emitting neutrons. It did NOT achieve anywhere close to breakeven. Noone has ever achieved close to breakeven in an electrostatic device of the kind he proposed, and there's good reason to think it would be hard.
Achieving fusion reactions is *easy*. Anyone can do it with some deuterium and some electrodes in a discharge tube with a very high voltage power supply. This was first done in the lab in the 1930s. Heck, the 'Amateur Scientist' column in Scientific American showed how the layman could do it decades ago. The hard part is achieving breakeven, which these simple basement schemes cannot do.
In fact, the rate at which man is using primary energy is about 1/10,000th the rate at which solar energy is hitting the earth. Four orders of magnitude, not eight.
The same argument could be made in 10 years. Why even bother with space at all???
In 10 years (or 20, or 100), other technologies
may have developed that make space more sensible.
It's silly to think it's 'now or never'. Your complaint will have weight only when all other
technological progress has stagnated.
IMHO it's an extremely near sighted view. Research in microgravity can possible yeild new medicines, alloys, etc.
The scientific yield from microgravity
research has been meagre and shows no sign
of being anything but meagre. If it were
forced to compete with other ways to spend
science dollars it would not be funded.
Microgravity research is a rationalization
at best, and a fraudulent justification at
worst, for building the space station.
Wasn't there an online poll just a few weeks ago asking what visitors thought about such a raise?
Two comments:
First, online polls are worthless, as are
any self-selected polls.
Second, when competent polling organizations
ask questions that rank public support for various
federal spending programs, the space program comes
in near the bottom, below even farm subsidies.
Let's say we managed to get to 10Bn, which is less than double. A lot more of us would be eating a lot more tofu.
And if we move these people into space, they're going to be eating hamburgers? Just how easy do you think it is to raise cattle in space? For the same cost, you could blanket the Earth with climate controlled greenhouses and feed hundreds of billions of people.
Sometime in the near future, the Earth will
not be able to accomodate everybody. This is almost guranteed with thecurrent rate of population increase.
Sorry, but this is not the case. Current
projections have the world population not
reaching even double the current level before
leveling off or declining. This is well below
the level the planet can support.
There's no good evidence that an industrial civilization can even maintain its population, let alone grow the population over the long term. The fertility
rate is well below replacement in most of the
industrialized world.
Anonymous coward's comments display a stunning
ignorance of atmospheric physics.
Yes, most CFCs are released in the northern
hemisphere. But their atmospheric lifetime is
much longer than the mixing time of the
lower atmosphere, so the concentration in
the southern hemisphere is only slightly
lower.
Given that, why is the hole in the south? Because of the lower temperature and presence
of ice crystals in the stratosphere there pulls
NOx out, deinhibiting the chlorine radicals.
(There are also some reactions of the chlorine
radicals themselves on the ice crystals, enhancing
their effectiveness at destroying ozone.)
This chemistry is well understood now.
The willful ignorance of the CFC apologists
reminds me of the idiocy of young-earth creationists. The intellectual content
is about the same.
Actually, the cost of propellant in general, and liquid oxygen in particular, is a negligible fraction of the cost of a launch with current launch vehicles. And using a nuclear rocket would *increase* the propellant cost, not decrease it, since you'd replace cheap oxygen with more expensive liquid hydrogen. And let's not talk about the difficult of refurbishing and reusing a nuclear rocket with hot reactor core.
Space fans like to think of alternatives, but there's good reason everyone uses chemical rockets. A shame; it would be nice if there were a technological magic bullet for reducing launch costs.
Air breathing engines have been looked at for years, for the reasons you give. But they always turn out to be a bad idea. There are several reasons for this.
First, liquid oxygen is cheap. Really cheap. It's pennies per pound, the second cheapest industrial liquid (after water). Putting in complex machinery to save LOX doesn't make sense. For jet engines like scramjets that use liquid hydrogen, the propellant costs can actually be higher than for a rocket-based vehicle, since more LH2 is needed for engine/vehicle cooling/drag compensation.
Second, rocket engines have much higher thrust/weight ratios than jet engines. They're also simpler, and therefore cheaper.
Third, the air breathing engines are only sort of practical early in the launch, at low mach number. So it's a waste to carry them to orbit (especially since they're so heavy). But if you stage them early then the Isp of the first stage is not very important. You might as well use a big, dumb, cheap rocket stage.
The idea of using 3He from the moon is pretty old. It's like the Hungarian recipe for ham and eggs: "If we had some ham, we could make ham and eggs, if we had some eggs." If we had 3He, we could run D3He fusion reactors, if we had the reactors.
There are serious problems. We don't know how to build D-3He fusion reactors. The 3He is present on the moon embedded in the regolith at a concentration of maybe 10 ppb. You have to heat the regolith to get it out. The energy required for the heating is significant, maybe 10% of the energy you get from the fusion. So, if you want to produce 300 GW of power on earth you'll need to have processing equipment on the moon handling in the neighborhood of 30 GW. Needless to say, this would be extremely expensive.
So, this idea is going to stay in the realm of science fiction for the foreseeable future. Fortunately, accelerator-driven fission reactors seem easier to build, can operate on the thorium-uranium cycle without separation of plutonium, and can destroy their own long-lived fission products and actinides. And there's enough thorium on Earth to supply the energy demand here for billions of years.
I'm not sure this nanomagnet scheme would be feasible. When the domains get small enough, they can flip between states by quantum mechanical tunnelling.
A scheme that *does* look feasible is storing of individual electrons in nanometer-scale metal particles. This would be electrostatic rather than magnetic storage (but would still be on the surface of a rotating disk). The read head would be a "single electron transistor" with a head/disk spacing similar to current hard drives. See the most recent Proceedings of the IEEE for an article on this.
While the notion that EPIC allows one to throw more cpus at a problem is silly, this does bring up the related idea of chip level multiprocessing. That is, if you *do* have a program that can be run well on an SMP machine, then you can use a computer that has two or more conventional cores on a single chip, sharing an L1 cache. This may be a better way to use a transistor budget than fancy VLIW schemes. The shared cache would make interprocessor communication very fast.
Linux programmers should try to make their programs SMP-friendly.
Slashdot Mirror
Refitting existing planes with liquid hydrogen is essentially impossible. The fuel tanks are far too small and are not designed to hold a cryogenic fuel.
Yes, the fuel in the shuttle ET had a lot of energy. This is a necessary property of rocket propellants. Hydrogen, kerosene, whatever would have burned to produce a large energy release in the Challenger accident. Note that the hydrogen there did not *explode* in the sense of detonating, it just burned rapidly (without a detonation wave being produced). And this burning did not cause the accident, or destroy the orbiter -- the orbiter was torn apart by being thrown sideways into a supersonic airstream.
The weight to energy density of hydrogen is much better than jet fuel. The tanks would have to be larger, however, because of the lower volumetric efficiency.
Hydrogen also allows new engine cycles since it has substantial cooling capacity, which can reduce the power diverted to the compressor (intercooling).
Yes, fusion is repeating the same mistake as the fission breeder reactor program: using expensive capital equipment to replace cheap fuel.
Ordinary fission burner reactors with once-through fuel cycle can be used for centuries. And we have these now, not 'real soon now'.
> Basically to start a fusion reaction you
> basically need a huge energy burst, essentially
> a nuke.
Basically, you're full of shit. That statement is completely wrong. The energy content of the plasma in a fusion reactor will be measured in megajoules, not the terajoules of even a small nuclear weapon.
No, the energy spent in the magnets is not what keeps fusion reactors from reaching breakeven. What keeps them from reaching breakeven is the distressing tendency for the energy to leak out of the plasma. BTW, this is also why fusion reactors tend to be big -- energy escapes less readily from a larger plasma.
You do get 3He from the decay of tritium produced in the blanket of a DT fusion reactor.
However, most of the tritium produced in that blanket has to be recycled back as fuel for the DT reactor. The net reaction is D + 6Li --> 2 4He. To make 3He you need extra neutrons from (n,2n) side reactions. As a result, the 3He output will only be a sideshow, a minor byproduct of an energy system that produces most of its energy from DT reactions.
To have a system that is primarly D3He fueled, you need to be able to mine 3He somewhere. The moon has been suggested (but at 10 ppb the economics are dubious). Beyond that, Uranus may be a good source, and maybe we can mine 3He from the thin atmosphere of some as-yet undiscovered Kuiper Belt Object. A body the density of Pluto with a radius of ~2800 km and a temperature of 30K could retain 3He in its atmosphere. It would be about 3% of the mass of the Earth, about half the mass of Mars.
> Also, fusion will be MUCH cheaper than gasoline.
This is nonsense. Fusion promises to be very expensive. Oh, sure, *deuterium* is cheap, but deuterium by itself isn't useful. You need this big expensive reactor to get energy from it.
This kind of economic illiteracy shows up often in naive talk about energy. Sunlight is free, wind is free, does that make electricity generated from these sources free? Of course not.
Sheesh.
Farnsworth achieved fusion in the sense that his device produced fusion reactions, emitting neutrons. It did NOT achieve anywhere close to breakeven. Noone has ever achieved close to breakeven in an electrostatic device of the kind he proposed, and there's good reason to think it would be hard.
Achieving fusion reactions is *easy*. Anyone can do it with some deuterium and some electrodes in a discharge tube with a very high voltage power supply. This was first done in the lab in the 1930s. Heck, the 'Amateur Scientist' column in Scientific American showed how the layman could do it decades ago. The hard part is achieving breakeven, which these simple basement schemes cannot do.
In fact, the rate at which man is using primary energy is about 1/10,000th the rate at which solar energy is hitting the earth. Four orders of magnitude, not eight.
In 10 years (or 20, or 100), other technologies may have developed that make space more sensible. It's silly to think it's 'now or never'. Your complaint will have weight only when all other technological progress has stagnated.
IMHO it's an extremely near sighted view. Research in microgravity can possible yeild new medicines, alloys, etc.
The scientific yield from microgravity research has been meagre and shows no sign of being anything but meagre. If it were forced to compete with other ways to spend science dollars it would not be funded.
Microgravity research is a rationalization at best, and a fraudulent justification at worst, for building the space station.
Two comments:
First, online polls are worthless, as are
any self-selected polls.
Second, when competent polling organizations
ask questions that rank public support for various
federal spending programs, the space program comes
in near the bottom, below even farm subsidies.
And if we move these people into space, they're going to be eating hamburgers? Just how easy do you think it is to raise cattle in space? For the same cost, you could blanket the Earth with climate controlled greenhouses and feed hundreds of billions of people.
Sorry, but this is not the case. Current projections have the world population not reaching even double the current level before leveling off or declining. This is well below the level the planet can support.
There's no good evidence that an industrial civilization can even maintain its population, let alone grow the population over the long term. The fertility rate is well below replacement in most of the industrialized world.
If you had read that paper, you'd see that the way Mt. Pinatubo depleted ozone was by making the chlorine (from CFCs) more effective.
Anonymous coward's comments display a stunning
ignorance of atmospheric physics.
Yes, most CFCs are released in the northern
hemisphere. But their atmospheric lifetime is
much longer than the mixing time of the
lower atmosphere, so the concentration in
the southern hemisphere is only slightly
lower.
Given that, why is the hole in the south? Because of the lower temperature and presence
of ice crystals in the stratosphere there pulls
NOx out, deinhibiting the chlorine radicals.
(There are also some reactions of the chlorine
radicals themselves on the ice crystals, enhancing
their effectiveness at destroying ozone.)
This chemistry is well understood now.
The willful ignorance of the CFC apologists
reminds me of the idiocy of young-earth creationists. The intellectual content
is about the same.
Space fans like to think of alternatives, but there's good reason everyone uses chemical rockets. A shame; it would be nice if there were a technological magic bullet for reducing launch costs.
First, liquid oxygen is cheap. Really cheap. It's pennies per pound, the second cheapest industrial liquid (after water). Putting in complex machinery to save LOX doesn't make sense. For jet engines like scramjets that use liquid hydrogen, the propellant costs can actually be higher than for a rocket-based vehicle, since more LH2 is needed for engine/vehicle cooling/drag compensation.
Second, rocket engines have much higher thrust/weight ratios than jet engines. They're also simpler, and therefore cheaper.
Third, the air breathing engines are only sort of practical early in the launch, at low mach number. So it's a waste to carry them to orbit (especially since they're so heavy). But if you stage them early then the Isp of the first stage is not very important. You might as well use a big, dumb, cheap rocket stage.
There are serious problems. We don't know how to build D-3He fusion reactors. The 3He is present on the moon embedded in the regolith at a concentration of maybe 10 ppb. You have to heat the regolith to get it out. The energy required for the heating is significant, maybe 10% of the energy you get from the fusion. So, if you want to produce 300 GW of power on earth you'll need to have processing equipment on the moon handling in the neighborhood of 30 GW. Needless to say, this would be extremely expensive.
So, this idea is going to stay in the realm of science fiction for the foreseeable future. Fortunately, accelerator-driven fission reactors seem easier to build, can operate on the thorium-uranium cycle without separation of plutonium, and can destroy their own long-lived fission products and actinides. And there's enough thorium on Earth to supply the energy demand here for billions of years.
I'm not sure this nanomagnet scheme would
be feasible. When the domains get small
enough, they can flip between states by
quantum mechanical tunnelling.
A scheme that *does* look feasible is storing
of individual electrons in nanometer-scale
metal particles. This would be electrostatic
rather than magnetic storage (but would still
be on the surface of a rotating disk). The
read head would be a "single electron transistor"
with a head/disk spacing similar to current
hard drives. See the most recent Proceedings
of the IEEE for an article on this.
While the notion that EPIC allows one to
throw more cpus at a problem is silly, this
does bring up the related idea of chip level
multiprocessing. That is, if you *do* have
a program that can be run well on an SMP
machine, then you can use a computer that
has two or more conventional cores on a single
chip, sharing an L1 cache. This may be a
better way to use a transistor budget than
fancy VLIW schemes. The shared cache would
make interprocessor communication very fast.
Linux programmers should try to make their
programs SMP-friendly.