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Post by Enderminion on Sept 10, 2017 15:25:02 GMT
you don't hardly need 3Mm/s of Dv to travel around a star system though, 10km/s is enough to do a Holman transfer to jupiter, with 30000km/s of Dv you can get their faster yes, but how much faster? also their is a thing of too much specific impulse And what do you think is cheaper? A few kilotons of fusiles generated from seawater and borax for a few cents per kilo or highly enriched uranium? Depends on how much water is availible |
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Post by Kerr on Sept 10, 2017 15:27:08 GMT
And what do you think is cheaper? A few kilotons of fusiles generated from seawater and borax for a few cents per kilo or highly enriched uranium? Depends on how much water is availible The universe is awash in water. |
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Post by The Astronomer on Sept 10, 2017 15:31:49 GMT
Wow... You don't even know how the rocket equation works? One of the most basic parts in rocket science. Example: Delta-v: 1Mm/s Mass ratio 2.77 Delta-v: 2Mm/s Mass ratio 7.7 Delta-v 3Mm/s Mass ratio 21 Delta-v: 4Mm/s Mass ratio of 60 Delta-v: 6Mm/s Mass ratio 456 Delta-v: 30Mm/s (0.1c) Mass ratio 19711924989665, if you use 10 Stages instead you have the same speed with an mass ratio of 26600 Delta-v: 30Mm/s Mass ratio 21 using an fuel with an specific impulse of one million seconds. See how an increase in Isp by ten decreases the mass ratio by 900 billion? The tyranny of the rocket equation. you don't hardly need 3Mm/s of Dv to travel around a star system though, 10km/s is enough to do a Holman transfer to jupiter, with 30000km/s of Dv you can get their faster yes, but how much faster? also their is a thing of too much specific impulseWhat the hell is too much specific impulse |
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Post by Kerr on Sept 10, 2017 15:39:01 GMT
you don't hardly need 3Mm/s of Dv to travel around a star system though, 10km/s is enough to do a Holman transfer to jupiter, with 30000km/s of Dv you can get their faster yes, but how much faster? also their is a thing of too much specific impulseWhat the hell is too much specific impulse An urban legend told between the uncivilized . |
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Post by Enderminion on Sept 10, 2017 16:00:28 GMT
you don't hardly need 3Mm/s of Dv to travel around a star system though, 10km/s is enough to do a Holman transfer to jupiter, with 30000km/s of Dv you can get their faster yes, but how much faster? also their is a thing of too much specific impulseWhat the hell is too much specific impulse if you can't accelerate enough, buring half way there and then slowing down could be slower then a freefall trajectory |
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Post by Kerr on Sept 10, 2017 16:14:17 GMT
ironclad6Apparently you can make your engine's work out at rather smaller dimensions than expected. "LUKE CAMPBELLS BLADE SHIELDS" Gives an interesting insight in how small you can actually make your fusion drive. The distance of the blade shields in a 10TW D-He³, if your blade shields operate at 3000K, is 1.5m in radius. This means that if you have graphene blade shields you can run them at 4000K reducing the distance to 1m. An 1PW drive therefor needs 10x higher radius. The magnetic coils need to have an 10x stronger current. Meaning an 10x larger cross-section. If you have an high-tech room-temperature superconductor with the critical current of YBCO you can generate an 30T magnetic field in the middle with an coil 15 cm in diameter. Carbon Nanotube superconductor could lower this to 5 cm diameter coils. So I use your Crater class as an example. An 1PW p-B11 drive produces 200MN, providing your ship with roughly 2m/s acceleration, which is really more than enough to cruise around. Because after an day of burning you already reached velocities of 170km/s. Higher acceleration would only mean you've had to burn shorter, at the cost of less Delta-v. If you go into combat you can start injecting tungsten pellet, reducing your exhaust velocity and increasing your mass flow. The same 1PW can now produce 1G of acceleration at 2000km/s. Or 2G at 1000km/s. And let's close the magnetic nozzle/fusion drive problem with this and continue with other stuff. Your blade shields/coils 1. Glow white-hot 2. Are angled in a special way to reflect x-rays and scatter neutrons down to 1%. 3. Are internally cooled with an Thermal-nanofluid 4. Have to be checked and repaired once a week for an hour or two for safety.
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Post by Kerr on Sept 11, 2017 15:16:22 GMT
Upon further reflection I've found out that using an tungsten/uranium shell has a few more advantages.
First of which is the reduced x-ray and neutron source. Having 1.85cm tungsten can stop 90% of X-rays. And (assumption) 50% Neutrons.
This means it can heavily reduce reduce waste heat by turning neutral radiation into thermal radiation.
D-D: 50% X-rays -> 5% X-rays, 40% Neutrons -> 20%. This turns D-D ,a very messy fusion fuel, into an fuel which has is produces as much waste heat as an full powered D-He³ engine.
p-B11: 64% X-rays -> 6.5%. Makes p-B11 and very clean fuel again.
D-He³: 20% X-rays -> 2% X-rays, 5% Neutrons -> 2.5%. Only 4.5% will leave as waste heat now. Which means that not only you get more thrust per watt because of lower exhaust velocities, but that you can run your fusion drive at over 5x more thrust power with equal waste heat (Ignoring the ignition system).
Secondly, I and probably matterbeam forgot about the compression, PuFF (Pulsed Fission Fusion) compresses it's fuel pellet by a factor of 10x. Which increases density of its uranium-235 and D-T.
Tungsten/Depleted Uranium and D-He³ are very like their counterparts used in PuFF. An 10x compression factor would increase the density of the outer shell by 10x. If absorption scales linearly with density then the needed thickness of the uranium/tungsten shell has to be roughly 2mm for 90% X-ray absorption. The same 45g D-He³ matterbeam proposed would thereby reach exhaust velocities up to 1.2Mm/s. Using heavier pellet might increase this value up to 2.5Mm/s realistically at the same 10% Burn efficiency. At 10% Burn efficiency a pure D-He³ drive would reach exhaust velocities of only 8.3Mm/s. Meaning that using a tungsten shell increases the thrust by 45x at equal amounts of blade shield waste heat.
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Post by matterbeam on Sept 12, 2017 0:51:22 GMT
Upon further reflection I've found out that using an tungsten/uranium shell has a few more advantages. First of which is the reduced x-ray and neutron source. Having 1.85cm tungsten can stop 90% of X-rays. And (assumption) 50% Neutrons. This means it can heavily reduce reduce waste heat by turning neutral radiation into thermal radiation. D-D: 50% X-rays -> 5% X-rays, 40% Neutrons -> 20%. This turns D-D ,a very messy fusion fuel, into an fuel which has is produces as much waste heat as an full powered D-He³ engine. p-B11: 64% X-rays -> 6.5%. Makes p-B11 and very clean fuel again. D-He³: 20% X-rays -> 2% X-rays, 5% Neutrons -> 2.5%. Only 4.5% will leave as waste heat now. Which means that not only you get more thrust per watt because of lower exhaust velocities, but that you can run your fusion drive at over 5x more thrust power with equal waste heat (Ignoring the ignition system). Secondly, I and probably matterbeam forgot about the compression, PuFF (Pulsed Fission Fusion) compresses it's fuel pellet by a factor of 10x. Which increases density of its uranium-235 and D-T. Tungsten/Depleted Uranium and D-He³ are very like their counterparts used in PuFF. An 10x compression factor would increase the density of the outer shell by 10x. If absorption scales linearly with density then the needed thickness of the uranium/tungsten shell has to be roughly 2mm for 90% X-ray absorption. The same 45g D-He³ matterbeam proposed would thereby reach exhaust velocities up to 1.2Mm/s. Using heavier pellet might increase this value up to 2.5Mm/s realistically at the same 10% Burn efficiency. At 10% Burn efficiency a pure D-He³ drive would reach exhaust velocities of only 8.3Mm/s. Meaning that using a tungsten shell increases the thrust by 45x at equal amounts of blade shield waste heat. The D-D reaction would quickly become the most favourable one due to the wide availability of the fuel compared to He3 or Boron11. Nice find on the compression density. One thing I forgot was that molecular compounds can have a rather high density but still allow for relatively high exhaust velocity when they dissociate into ions after the fusion ignition heats everything into plasma. My first thought was uranium oxide. Pure uranium has a density of 19g/cm3, uranium dioxide has a density of 10.9g/cm^3, so you'd need roughly twice as much uranium dioxide than pure uranium to absorb the same fraction of X-rays... but Uranium's molar mass of 235g/mol severely restricts the possible exhaust velocities while UO2 dissociates into a plasma with average molar mass (235+16+16)/3: 89g/mol, which is 2.6 times lower. |
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Post by ironclad6 on Sept 12, 2017 4:39:56 GMT
Switching topic momentarily, is laser pumping efficiency a function of the relationship between pumping band and the medium's transition wavelength?
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Post by Kerr on Sept 12, 2017 11:37:14 GMT
Switching topic momentarily, is laser pumping efficiency a function of the relationship between pumping band and the medium's transition wavelength? |
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Post by matterbeam on Sept 12, 2017 13:03:53 GMT
Switching topic momentarily, is laser pumping efficiency a function of the relationship between pumping band and the medium's transition wavelength? My knowledge on laser mechanics is woefully lacking. |
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Post by Kerr on Sept 12, 2017 13:10:24 GMT
My knowledge on laser mechanics is woefully lacking. Huh, welcome to the club. |
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Post by Kerr on Sept 12, 2017 14:39:51 GMT
I've created a new fusion ship to fill a niche between heavy multi-kton ships and drones. While also being an high acceleration craft.  The Intermediate class is a light destroyer having an armament of 8x 100MW/41.7MW Lasers with 1-10Mm effective range (depending on target type) 8x Colloid guns launching small charged colloids at 0.01c. Having an effective range of 20Mm. 4x 330kW Missile launchers able to deploy 40x Hyperion KKV Mk VI per second, each missile has 29km/s Dv, 30s Burn, 5kg mass, 60c cost. It's propulsion system is an 10TW ICF Fusion Drive using DD pellet in a thin tungsten shell, it produces 35MN Thrust at a exhaust velocity of 570km/s. |
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Post by ironclad6 on Sept 12, 2017 16:04:39 GMT
That looks nasty.
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Post by Kerr on Sept 12, 2017 16:32:11 GMT
Yea, they are usually used in medium-heavy destroyers/dreadnaughts as small engagement fighters. Connected with hydraulic/electromagnetic decouplers and easily deployable, up to 8 in a dreadnaught. Being able to deploy 80,000x Hyperions. These ships can also perform an Tactical Hellfire-Assist, where the craft accelerated to 80km/s relative velocity, launch their missile with 29km/s of Delta-v, and end up with thousands of Micro Missiles, each moving at 100km/s and having 9km/s Delta-v for Jinks. Seven of them could overwhelm a dreadnaught (given 21x kills per second), then decelerate, go back to their mothership, restock fuel and weaponry and be re-used. Their lasers are rather pathetic compared to yours, they are 80% efficient 77nm pulsed quantum dots lasers, mainly used to destroy missiles or damage sensors. Their Colloid guns deal fairly good damage. Having an firerate of 3000 RPS and each projectile having 20kJ of kinetic energy. Each able to drill through 18cm Graphene every second. Although this craft is not very common because of fairly high production and maintenance costs. Filling a role similar to stealth bombers today. |
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