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Post by Kerr on Sept 2, 2017 12:22:29 GMT
I've did some math on the 90% UTB NSWR.
For 1MN thrust your NSWR will put out 2.3TW. If 20% of the energy is absorbed (given that the peak fission rate happens outside the ship) you need an engine bell that can give off 460GW of heat. Using graphene we can operate the engine bell at 4000K, emitting 28.5MW per square meter. The needed area for this is 16,000m2. Which translates into an bell diameter of 72m. At 0.1mm thickness the bell would weight 3.7t. All of that for an single meganewton.
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Post by Kerr on Sept 2, 2017 12:45:45 GMT
matterbeamDo you know a way to estimate bremsstrahlung? At 100kev D-He3 produces 20% X-rays because at these temperatures ion and electrons collide. And the ignition temperature of p-B11 is 200kev.
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Post by matterbeam on Sept 2, 2017 13:08:50 GMT
matterbeam Do you know a way to estimate bremsstrahlung? At 100kev D-He3 produces 20% X-rays because at these temperatures ion and electrons collide. And the ignition temperature of p-B11 is 200kev. Look at this table: www.projectrho.com/public_html/rocket/fusionfuel.php#id--Fusion_Reactionsp-B11 is noted as releasing of its energy 0% as electromagnetic radiations. It therefore does not produce bremsstrahlung. But, that source could be wrong, as could be ignoring the interaction between a hail of charged alpha particles and a cloud of inert hydrogen propellant. Rapidly slowing down any charged particle produces high-energy radiations, which is what bremsstrahlung is. |
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Post by matterbeam on Sept 2, 2017 13:19:36 GMT
I've did some math on the 90% UTB NSWR. For 1MN thrust your NSWR will put out 2.3TW. If 20% of the energy is absorbed (given that the peak fission rate happens outside the ship) you need an engine bell that can give off 460GW of heat. Using graphene we can operate the engine bell at 4000K, emitting 28.5MW per square meter. The needed area for this is 16,000m2. Which translates into an bell diameter of 72m. At 0.1mm thickness the bell would weight 3.7t. All of that for an single meganewton. This is a bad solution! Graphene is extremely fragile at 4000K and random temperature fluctuations means it is constantly sublimating away into space. It is better to use active cooling. A coolant flow against the engine bell carries away the heat to radiators. An even more mass-effective solution is to dump the heat into the propellant being fed to the engine. We don't want to boil the salted water before it enters the reaction chamber, so we will try to increase its temperature from 4 degrees celsius (maximum density point BTW) and 80 degrees. Heat capacity of water tells us that one kilo will take away 318kJ. If we keep the engine bell at 2000K, it will radiate at 90kW/m^2. Also, there is a thing as too much exhaust velocity. Doubling the non-salted water flow cuts exhaust velocity in half and gives us 2MN thrust and so on. I don't have the mass flow right now, but putting all these together, plus minimal radiators, will drastically cut the engine size and mass. |
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Post by Kerr on Sept 2, 2017 13:21:17 GMT
matterbeam Do you know a way to estimate bremsstrahlung? At 100kev D-He3 produces 20% X-rays because at these temperatures ion and electrons collide. And the ignition temperature of p-B11 is 200kev. Look at this table: www.projectrho.com/public_html/rocket/fusionfuel.php#id--Fusion_Reactionsp-B11 is noted as releasing of its energy 0% as electromagnetic radiations. It therefore does not produce bremsstrahlung. But, that source could be wrong, as could be ignoring the interaction between a hail of charged alpha particles and a cloud of inert hydrogen propellant. Rapidly slowing down any charged particle produces high-energy radiations, which is what bremsstrahlung is. It wouldn't make sense that bremsstrahlung just goes away in p-B11 but not in other reactions. And I know what bremsstrahlung. Heck, the name even describes it pretty well. "brems" derived from "bremsen" meaning slowing down or to brake. And "strahlung" which means radiation. |
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Post by Kerr on Sept 2, 2017 13:29:00 GMT
I've did some math on the 90% UTB NSWR. For 1MN thrust your NSWR will put out 2.3TW. If 20% of the energy is absorbed (given that the peak fission rate happens outside the ship) you need an engine bell that can give off 460GW of heat. Using graphene we can operate the engine bell at 4000K, emitting 28.5MW per square meter. The needed area for this is 16,000m2. Which translates into an bell diameter of 72m. At 0.1mm thickness the bell would weight 3.7t. All of that for an single meganewton. This is a bad solution! Graphene is extremely fragile at 4000K and random temperature fluctuations means it is constantly sublimating away into space. It is better to use active cooling. A coolant flow against the engine bell carries away the heat to radiators. An even more mass-effective solution is to dump the heat into the propellant being fed to the engine. We don't want to boil the salted water before it enters the reaction chamber, so we will try to increase its temperature from 4 degrees celsius (maximum density point BTW) and 80 degrees. Heat capacity of water tells us that one kilo will take away 318kJ. If we keep the engine bell at 2000K, it will radiate at 90kW/m^2. Also, there is a thing as too much exhaust velocity. Doubling the non-salted water flow cuts exhaust velocity in half and gives us 2MN thrust and so on. I don't have the mass flow right now, but putting all these together, plus minimal radiators, will drastically cut the engine size and mass. And? The point of my post is to show the many flaws of 90% UTB and that it isn't really practical for a missile. You also have to qudruple mass flow to cut the exhaust velocity in half |
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Post by matterbeam on Sept 2, 2017 13:33:23 GMT
This is a bad solution! Graphene is extremely fragile at 4000K and random temperature fluctuations means it is constantly sublimating away into space. It is better to use active cooling. A coolant flow against the engine bell carries away the heat to radiators. An even more mass-effective solution is to dump the heat into the propellant being fed to the engine. We don't want to boil the salted water before it enters the reaction chamber, so we will try to increase its temperature from 4 degrees celsius (maximum density point BTW) and 80 degrees. Heat capacity of water tells us that one kilo will take away 318kJ. If we keep the engine bell at 2000K, it will radiate at 90kW/m^2. Also, there is a thing as too much exhaust velocity. Doubling the non-salted water flow cuts exhaust velocity in half and gives us 2MN thrust and so on. I don't have the mass flow right now, but putting all these together, plus minimal radiators, will drastically cut the engine size and mass. And? The point of my post is to show the many flaws of 90% UTB and that it isn't really practical for a missile. You also have to qudruple mass flow to cut the exhaust velocity in half Engine power output: Thrust x Exhaust Velocity /2 Thrust and exhaust velocity vary linearly for the same engine output. I was just trying to point out that 90% NSWR is a very risky choice of propulsion, but engine bell size is not one of the major contributors to this fact. Passive cooling would make practically any high-powered engine nearly impossible. Heck, even chemical rockets today need actively cooled rocket nozzles! |
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Post by Kerr on Sept 2, 2017 13:49:45 GMT
And? The point of my post is to show the many flaws of 90% UTB and that it isn't really practical for a missile. You also have to qudruple mass flow to cut the exhaust velocity in half Engine power output: Thrust x Exhaust Velocity /2 Thrust and exhaust velocity vary linearly for the same engine output. I was just trying to point out that 90% NSWR is a very risky choice of propulsion, but engine bell size is not one of the major contributors to this fact. Passive cooling would make practically any high-powered engine nearly impossible. Heck, even chemical rockets today need actively cooled rocket nozzles! 1Mm/s 1MN equals to 1kg/s and 500GW thrust power. 500km/s 2MN equals to 4kg/s and 500GW. If your amount of 90% Enriched uranium stays constant you'll have to increase mass flow by 4 to reduce exhaust velocity by 50%. The amount of active cooling needed would be too enourmous for an missile to handle. The major flaws of NSWR are, danger of fuel detonation, high radiation and very high fuel costs. |
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Post by Enderminion on Sept 2, 2017 14:02:07 GMT
two of those "flaws" are pretty good for missiles
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Post by Kerr on Sept 2, 2017 14:04:16 GMT
two of those "flaws" are pretty good for missiles Exploding in a mega-gigaton explosion when hitting a grain of sand is an advantage? |
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Post by Enderminion on Sept 2, 2017 14:43:39 GMT
two of those "flaws" are pretty good for missiles Exploding in a mega-gigaton explosion when hitting a grain of sand is an advantage? well, when you say it like that... but nuking on impact with the enemy ship seems like a good thing |
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Post by The Astronomer on Sept 2, 2017 14:46:05 GMT
You really should try multiple-direction engagement. If one missile explodes it would cause no damage to the other missiles. Maybe.
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Post by Kerr on Sept 2, 2017 14:59:35 GMT
You really should try multiple-direction engagement. If one missile explodes it would cause no damage to the other missiles. Maybe. Or just use kinetic energy. They should be more practical at 0.01c. Because their blast is directed, meaning nearly 100% go into the target instead of an omnidirectional explosion which has pn impact 50% coupling. 1kT vs. 1.37kT effective yield. And this is if you used an 1kg clump of pure zubrol compared to an 1kg Submunition which could have 100g MH and get 1750m/s Dv to track the target and to perform dodge burns. |
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Post by ironclad6 on Sept 2, 2017 15:08:58 GMT
I've concluded that if you have fusion power but not magnetic confinement nozzles MPDT outperforms NSWR while avoiding all of that tedious messing about with rare fissiles that explode when you look at them the wrong way.
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Post by The Astronomer on Sept 2, 2017 15:16:22 GMT
You really should try multiple-direction engagement. If one missile explodes it would cause no damage to the other missiles. Maybe. Or just use kinetic energy. They should be more practical at 0.01c. Because their blast is directed, meaning nearly 100% go into the target instead of an omnidirectional explosion which has pn impact 50% coupling. 1kT vs. 1.37kT effective yield. And this is if you used an 1kg clump of pure zubrol compared to an 1kg Submunition which could have 100g MH and get 1750m/s Dv to track the target and to perform dodge burns. If your missile's going too fast the whole thing will blast through the enemy ship, leaving a hole, and some, if not most of the kinetic energy will still be on the missile. |
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