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Propulsion system proposal - comments?
Imagine a V-shaped notch in a thin diamond layer - 100nm across at the top, 1000nm deep, with a drop of liquid hydrogen (or helium or other liquid) injected in the bottom 200nm. Imagine that notch being closed at 12000m/s - the speed of sound in diamond. The liquid hydrogen would be driven out at roughly 100km/sec - ~8x faster than the velocity the notch is closing. (My choice of 100nm wide and 1000nm deep was rather arbitrary. It might be possible to scale it up to handle a larger volume of reaction mass, or change the notch aspect ratio to get greater exhaust velocities.)
The notch would be closed by directing an intense pulse of sound through the diamond - compressing it very slightly. If two pulses are (VERY!) precisely timed to meet at the notch, the closure time could be halved, doubling the exit velocity to around 200km/sec - roughly 5x the exhaust velocity of an ion engine. (The timing precision required is probably too great to be practical - but there may be a way for a single pulse to do the job.)
This would use tiny amounts of reaction mass per pulse, but the notch could be made longer to increase the amount of reaction mass ejected in each pulse.
It should be possible to set up a resonating sound wave with enough energy to do the required compression, and then feed in just enough power to replace energy lost to exhaust and heat. If the pulse is injected from 1cm away, it might cycle at around 600khz, for example.
It might also be necessary to use an "anvil" approach - with the sound pulse injected into a thicker diamond that narrows down to the notch, concentrating energy into a smaller area.
This could be nuclear or beam powered. I doubt it could ever be made to fly out of a gravity well, but for manned interplanetary exploration, where flight time is more critical than amount of energy expended, it might be useful.
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Imagine a V-shaped notch in a thin diamond layer - 100nm across at the top, 1000nm deep, with a drop of liquid hydrogen (or helium or other liquid) injected in the bottom 200nm.
If all you need is a liquid, you should use something dense and non-cryogenic rather than hydrogen.
The notch would be closed by directing an intense pulse of sound through the diamond - compressing it very slightly. If two pulses are (VERY!) precisely timed to meet at the notch, the closure time could be halved, doubling the exit velocity to around 200km/sec - roughly 5x the exhaust velocity of an ion engine. (The timing precision required is probably too great to be practical - but there may be a way for a single pulse to do the job.)
In electric engines, since they are usually energy-limited rather than propellant-limited, higher isp/exhaust velocity is not always better. The things you use to compare electric engines are efficiency, power density, reliability/durability, and what range of isp values it can throttle through.
If the diamond engine is efficient, reliable, able to use a lot of power for its size, and capable of operating at exhaust velocities lower than its maximum without loosing much efficiency, then it might be better than ion engines. If it fails any of those requirements, then it probably will not be better.
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Sounds awfully fragile to me, and I doubt you could achieve signifigant thrusts without a MASSIVE diamond pore plate.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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I don't know about fagile, but it would seem you would need a fairly large plate to achive a signifigant amount of thrust per blast.
How do you fill the wells back up with hydrogen after you blast it off, or is it a one shot only kind of deal?
He who refuses to do arithmetic is doomed to talk nonsense.
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Also for the same trust how does the weight compare to electric engines.
Dig into the [url=http://child-civilization.blogspot.com/2006/12/political-grab-bag.html]political grab bag[/url] at [url=http://child-civilization.blogspot.com/]Child Civilization[/url]
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Taking to the extreme, the piezo electric inkjet printer fires ink droplets.
Similarly, a piezo effect on carbon nanotubes,
creating an atomic gun for helium atom bullets, held inside the barrel.
Nanotube miniature particle accelerator ?
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Powered by the Suns solar energy this could work.
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Doesn't matter where the energy comes from, only how well the engine performs versus other electric engines.
Problems I see with it:
-Difficulty in making it big enough for useful thrust
-Difficulty in getting it to withstand extended use even at extreme temperature
-Difficulty in reloading with LH2 between cavity cycles
-Difficulty in getting the diamond to withstand LH2 exposure for extended periods
It might push your rocket, but I think it has a tall list of things against it.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Nano technology is the wave of the future though I wonder about ION style propulsion. Power is also in great need of advancement and it would seem that at least some are looking to do better than batteries.
Power on a Chip tiny jet engines
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In space travel, its all about energy density and energy conversion... that is, you want to maximize the amount of energy available per mass and you want to use that energy as efficently as possible.
A combustion turbine of any kind cannot produce more energy then is available to it from its fuel, which has an unchangeable maximum, so even with 100% efficency you can squeeze no more energy from it.
For all chemical combustion fuels, the Hydrogen/Oxygen reaction has the highest energy density where the componets are easy to handle, but even these aren't that great as far as density goes. Modern chemical rocket engines already operate at >85% of the maximum theoretical efficency, so using nanotechnology to squeeze out the last few percent isn't very useful, even if you could convert this energy into propulsive force as easily as a rocket could.
The solution is not to try and squeeze a little more efficency out of exsisting chemical fuels, that will yeild little bennefit, but to use different sources of energy, like Solar/Ion arrangements or one of an array of Fission sources and engine combinations.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Problems I see with it:
-Difficulty in making it big enough for useful thrust
-Difficulty in getting it to withstand extended use even at extreme temperature
-Difficulty in reloading with LH2 between cavity cycles
-Difficulty in getting the diamond to withstand LH2 exposure for extended periodsIt might push your rocket, but I think it has a tall list of things against it.
There are two possible types of objections: objections from physics, and objections from engineering. These are mostly engineering issues - they may prove difficult (or easy) to overcome, but the only way to tell is to try to design a specific system and analyze/test it.
Objections from physics would, if properly done, kill the concept outright - e.g. if the scheme tried to produce more thrust than a given amount of reaction mass and energy allowed. I'd say that it's more useful at this point to look at possible physics objections - but:
- big enough - ion engines also produce relatively tiny thrust - the point is to produce as much thrust with as little mass as possible, for maximum delta V on long flights.
- extreme temperatures - I've done no study of this - but one reason to use diamond is to be able to rapidly conduct away waste heat.
- reloading LH2 - really detailed technical issue. You might as well say that pumping fuel and oxidizer into the high pressure chamber of a rocket poses a problem - of course it does, but there are technical solutions. One simple approach - the rear of the notch, when it is fully expanded, opens onto a high pressure source of LH2, admitting a small droplet, and then closes off before the larger end of the notch, trapping the droplet.
- Diamond withstanding LH2 - I would expect diamond to react with LH2 at the surface, creating a hydrated (correct term?) boundary layer. If pressure rips some hydrogens away from that surface, the next cycle will probably replace them. On the other hand, if the hydrogen does NOT react with the diamond, that's probably almost as good, as it means there'd be no chemical modification of the notch surface, leaving the issue of potential mechanical ablation of the carbon.
I'm more concerned with a physics issue - can the notch possibly be made to close suddenly rapidly enough? Having a high speed of sound doesn't help if the sound is 1hz (no matter how powerful) and takes a full second to close and open the notch. Some sort of instantaneous impulse - like that of hitting it with a hammer - is more likely to create the desired effect - but that would likely waste most of the input energy as heat.
Piezo-electrics? Someone suggested Surface Acoustic Wave devices - but I'm not familiar enough with the benefits of those to comment. To me it looks like SAW technology just looks like it is supposed do signal filtering / conversion - perhaps the idea is to convert a powerful high frequency signal into an acoustic square wave pulse?
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