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Post by dwwolf on Mar 22, 2017 13:36:34 GMT
Abysmall dV judging from your 9.86Mt missile.
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Post by Inglonias on Mar 22, 2017 14:15:41 GMT
Abysmall dV judging from your 9.86Mt missile. ¯\_(ツ)_/¯. Seems to work well enough for my purposes. But yeah, you're right. I treat these things like I would treat the best bi-propellant combustion rockets with the bonus of not having to carry two propellants around at once. Put them on things where mass is a limiting factor, but you want high acceleration, such as in missiles and drones. If you've got a high efficiency rocket that also provides high acceleration and TWR...well, I'd love to see it.
(As a side question - Do resistojets still break physics?)
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Post by bigbombr on Mar 22, 2017 15:47:04 GMT
Abysmall dV judging from your 9.86Mt missile. ¯\_(ツ)_/¯. Seems to work well enough for my purposes. But yeah, you're right. I treat these things like I would treat the best bi-propellant combustion rockets with the bonus of not having to carry two propellants around at once. Put them on things where mass is a limiting factor, but you want high acceleration, such as in missiles and drones. If you've got a high efficiency rocket that also provides high acceleration and TWR...well, I'd love to see it.
(As a side question - Do resistojets still break physics?) Try RP-1 as a propellant, it's fairly dense and gives decent thrust but a higher exhaust velocity than sodium.
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Post by vegemeister on Mar 22, 2017 17:13:28 GMT
I've started experimenting with sodium propellant NTRs because of sodium's impressive results in cooling reactors and results appear very promising. The exhaust velocity is nothing to write home about (best I can do is 2.5 to 2.7 km/sec) but the TWR is INSANE (I was easily able to get engines with 500 to 1 TWR). When you need crazy acceleration for things like drones and knifefight range missiles, these engines appear to be superior to chemical rockets in every respect except for the kilowatts of radiation they spew everywhere, but they're for remote controlled vehicles so who cares?! I've only made 1 and a half engines with this design so far (1 engine, and I tweaked it so my flak missile wouldn't have 38g acceleration, which I don't think the AI can handle) but I hope to continue my experimentation later. It is good to experiment. However, exhaust velocity is really important. Recall the Tsiolkovsky rocket equation. If you rearrange it to get the required mass ratio as a function of Δv, you find this: mass_ratio = e^(Δv / v_exhaust) Exponentials grow *really* fast. So if you have a 5 km/s engine, and you want 5 km/s of Δv, you need a mass ratio (that's the weight of the rocket with fuel in it divided by the weight of the rocket without fuel in it) of 2.72. If you have a 2.5 km/s engine, you need a mass ratio of 7.39. Even if you manage to stuff in all that extra fuel without increasing the dry mass of the rocket at all, the wet mass has increased by a factor of e, about 2.72 times. If you want to keep the same acceleration, you have to increase the thrust of your engine by that much. Which itself adds dry mass, requiring even more fuel. This effect is sometimes called, "the tyranny of the rocket equation". The other thing is, when you're building a missile with a thrust:mass ratio of, say 10 g_0, and you're choosing between engines with TMR of 500 g_0 or 1000 g_0, whichever one you choose, the engine is only going to be a small part of the missile's mass. It matters even less with drones (say, 4-5 g_0) and capital ships (say, <2 g_0). But even so, chemical engines in this game can be made with very high mass ratios. For example:
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Post by Inglonias on Mar 22, 2017 18:48:42 GMT
It is good to experiment. However, exhaust velocity is really important. Recall the Tsiolkovsky rocket equation. If you rearrange it to get the required mass ratio as a function of Δv, you find this: mass_ratio = e^(Δv / v_exhaust) Exponentials grow *really* fast. So if you have a 5 km/s engine, and you want 5 km/s of Δv, you need a mass ratio (that's the weight of the rocket with fuel in it divided by the weight of the rocket without fuel in it) of 2.72. If you have a 2.5 km/s engine, you need a mass ratio of 7.39. Even if you manage to stuff in all that extra fuel without increasing the dry mass of the rocket at all, the wet mass has increased by a factor of e, about 2.72 times. If you want to keep the same acceleration, you have to increase the thrust of your engine by that much. Which itself adds dry mass, requiring even more fuel. This effect is sometimes called, "the tyranny of the rocket equation". The other thing is, when you're building a missile with a thrust:mass ratio of, say 10 g_0, and you're choosing between engines with TMR of 500 g_0 or 1000 g_0, whichever one you choose, the engine is only going to be a small part of the missile's mass. It matters even less with drones (say, 4-5 g_0) and capital ships (say, <2 g_0). But even so, chemical engines in this game can be made with very high mass ratios. For example: I should have specified monopropellant rockets. My sodium NTRs are better than monopropellant chemical rockets. Sorry about that. I also feel that because my missiles are so light, I can get away with a lower exhaust velocity and go with raw power, which missiles need anyhow for terminal maneuvers. Perhaps you're right and I should look at bipropellant chemical rockets, which I admit that I sort of dismissed out of hand. Incidentally, I refuse to use fluorine because I have a good head on my shoulders. That chemical rocket you put up is impressive, but hydrogen fluoride gas will melt your everything and the less said about fluorine oxygen mixtures, the better.
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Post by RiftandRend on Mar 22, 2017 19:40:22 GMT
LOX H2 rockets are not quite as good but are still a viable replacement if you refuse to use fluorine.
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Post by Inglonias on Mar 22, 2017 21:37:35 GMT
Despite the higher delta-V offered by the fluorine hydrogen (hypothetical!) engine, the loss in acceleration and the increase in mass and size is just not worth it to me. I am sorry. I did try it your way, and in most respects it's better! Certainly far more scaleable. I could use a flourine hydrogen rocket for drones! But the fact of the matter is that at this extremely small size of vessel, I need the raw power a sodium NTR offers me.
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Post by RiftandRend on Mar 22, 2017 21:46:20 GMT
Despite the higher delta-V offered by the fluorine hydrogen (hypothetical!) engine, the loss in acceleration and the increase in mass and size is just not worth it to me. I am sorry. I did try it your way, and in most respects it's better! Certainly far more scaleable. I could use a flourine hydrogen rocket for drones! But the fact of the matter is that at this extremely small size of vessel, I need the raw power a sodium NTR offers me. You can just add more combustion engines for almost no cost. 3 more should easily overpower the NTR for 1 10 th the cost and provide more Delta-V.
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Post by RiftandRend on Mar 22, 2017 22:17:07 GMT
I could use a flourine hydrogen rocket for drones! But the fact of the matter is that at this extremely small size of vessel, I need the raw power a sodium NTR offers me. I made a LOX H2 engine that outperforms that NTR. It is a bit wide though so you may want to customize it.
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Post by Inglonias on Mar 22, 2017 22:37:09 GMT
I could use a flourine hydrogen rocket for drones! But the fact of the matter is that at this extremely small size of vessel, I need the raw power a sodium NTR offers me. I made a LOX H2 engine that outperforms that NTR. It is a bit wide though so you may want to customize it. I do like that engine. Sure beats the pants off of anything in KSP, that's for sure. But scaling it down by a factor of two may be challenging if I want to keep that performance. For now I'll save it as the RiftAndRend ECD-10. I'll fiddle with it. Thanks! EDIT: I fiddled with it. It's now small enough that I can use it, but also weighs more than the one you posted. I swapped out the boron for a diamond chamber, and thickened it up some to handle the higher heat and pressure. CombustionRocketModule RiftAndRend 3.99 km/s ECMD-10B LOX LH2 Rocket UsesCustomName true Reaction LOX LH2 StoichiometricMixtureRatio 1.008 ThermalRocket ChamberComposition Diamond ThroatRadius_m 0.04 ChamberWallThickness_m 0.003 ChamberContractionRatio 5.3 NozzleExpansionRatio 58 NozzleExpansionAngle_degrees 18 RegenerativeCooling_Percent 0 Injector Composition Potassium PumpRadius_m 0.19 RotationalSpeed_RPM 200 Gimbal InnerRadius_m 0.28 ArmorComposition Boron ArmorThickness_m 0.0001 MomentumWheels Composition Potassium RotationalSpeed_RPM 3500 GimbalAngle_degrees 4
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Post by RiftandRend on Mar 22, 2017 22:41:46 GMT
I made a LOX H2 engine that outperforms that NTR. It is a bit wide though so you may want to customize it. I do like that engine. Sure beats the pants off of anything in KSP, that's for sure. But scaling it down by a factor of two may be challenging if I want to keep that performance. For now I'll save it as the RiftAndRend ECD-10. I'll fiddle with it. Thanks! Glad I could help. If it is too large and can't be scaled down without affecting performance then you can pull the armor forward so the gimbals doesn't make the missile too wide.
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Post by Inglonias on Mar 22, 2017 22:56:47 GMT
I do like that engine. Sure beats the pants off of anything in KSP, that's for sure. But scaling it down by a factor of two may be challenging if I want to keep that performance. For now I'll save it as the RiftAndRend ECD-10. I'll fiddle with it. Thanks! Glad I could help. If it is too large and can't be scaled down without affecting performance then you can pull the armor forward so the gimbals doesn't make the missile too wide. I'm really starting to think the very low fuel density is hurting performance. The missile is 1.5 times the length, weighs more, and costs more than the Sodium NTR version without offering significant dV increases.
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Post by Enderminion on Mar 22, 2017 22:58:46 GMT
thats getting into the range of my H-F missiles... but I get twice the DV and acceleration as you with 30.5mm of armour
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Post by Inglonias on Mar 22, 2017 23:11:31 GMT
thats getting into the range of my H-F missiles... but I get twice the DV and acceleration as you with 30.5mm of armour I'm trying to keep my nuclear missiles smaller than you are, I think... bigbombr your idea to substitute RP-1 instead of sodium was exactly what I needed
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Post by Enderminion on Mar 22, 2017 23:13:03 GMT
I do have smaller warheads (3x1.33MT w/50kg NEFP) and heavier armour
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