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Post by mavericksawyer on Sept 29, 2016 7:41:15 GMT
Agreed. Even with neutron reflectors and a fast-neutron reactor, that core for the NTR wouldn't get the kind of reaction rates needed to get hot enough to actually WORK.
EDIT: 97% enriched fuel? Christ on a crutch, that's not an NTR, that's a BOMB!
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Post by blothorn on Sept 29, 2016 8:02:29 GMT
Actually, with no neutron reflector I would think it so far sub-critical as to be an RTG---critical mass of unconstrained U235 is about 15kg, and it would be spread out (somewhat) in a reactor. Both reactors and NTRs seem to ignore the neutron reflector for the reactor calculations (only using it for radiation emission calculations).
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Post by mavericksawyer on Sept 29, 2016 8:11:18 GMT
Yeah, it doesn't make sense. But, exploit it while you can! XD
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Post by jonatanhedborg on Sept 29, 2016 8:20:17 GMT
I slapped that engine on a stinger (removed the fluorine tank). The results are... Well. dl.dropboxusercontent.com/u/340238/microntr.png73% of the acceleration but 40% of the mass, 66% of the price and 149% of the delta-v. Also 59% of the length. Just crazy. Bugged, or just good?
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Post by RA2lover on Sept 29, 2016 8:29:14 GMT
Even more broken:
NuclearThermalRocketModule 4.18 km/s Heavy Water Nuclear Thermal Rocket ReactorCoreHeight_m 0.15 NuclearReactor Coolant Heavy Water Moderator Diamond ModeratorMass_kg 1 Fuel U-235 Dioxide FuelMass_kg 1 FuelEnrichment_Percent 0.97 ControlRodComposition Boron Nitride ControlRodMass_kg 1 NeutronReflector Diamond ReflectorThickness_m 0 AverageNeutronFlux__m2_s 1.7e+020 ThermalRocket ChamberComposition Boron ThroatRadius_m 0.02 ChamberWallThickness_m 0.0013 ChamberContractionRatio 4.6 NozzleExpansionRatio 15 NozzleExpansionAngle_degrees 11 RegenerativeCooling_Percent 0.24 Injector Composition Lithium PumpRadius_m 0.3 RotationalSpeed_RPM 24 GimbalAngle_degrees 0
246kN in a 9.6kg package for 2.54k TWR - doubt you can get that with a chemical engine.
In any case, designing a NTR for TWR is basically getting as much heat as possible from your reactor, then passing as much coolant as possible through it so it doesn't vaporize itself, while using as lightweight of a pump as possible for that task.
The design uses heavy water as reaction mass in order to collect as much heat as possible from the reactor per unit of mass flow. The higher propellant density and full dissociation of the water into hydrogen are just a bonus.
A not-so-obvious choice here for the pump material is Lithium. At the pump's scale stresses aren't that big of a concern, and you're not pumping reaction mass at temperatures hot enough to melt it.
The reactor is a pretty interesting one. 1kg of diamond as moderator, 1kg of U-235 dioxide and 1kg of boron nitride for criticality control. The U-235 isotope is used instead of the cheaper U-233 because it needs less total reactor mass to attain criticality. The moderator here has as function mantaining the reactor working for longer; this allows it to output 514MW over just a bit over 6 months, which wouldn't be attainable using 2kg of fissiles and no moderator.
The rocket engine chamber and nozzle use boron, which fits in a sweet spot spot between RCC(which can't withstand the chamber pressures used) and Diamond(which although doesn't need regenerative cooling to be used is heavier than this design requires to attain optimal TWR). Its chamber was sized to fit the reactor - Any smaller would make it not fit, whereas any larger would cause the reactor to be less efficient.
On a side note, a way this design could be made lighter would be by inserting control rods to make the reactor go supercritical instead of removing them so you can save in moderator mass, though i haven't had success in designing a high-temperature design that can do this in less than 3kg of components.
EDIT: seems like methane is also a good choice of fuel that i didn't initially consider, though this might depend on how much space you're willing to spend on fuel tanks - heavy water is about 3 times as dense. I've gotten TWRs of 2.95k by adapting the engine above to use methane, and this can probably be optimized to 3k.
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Post by concretedonkey on Sept 29, 2016 12:02:29 GMT
So... super effective small NTRs are an exploit or are realistic? Frankly, even if things like super effective rail guns might be fun, its kind of defeating the purpose of the game, I'd like to keep it as realistic as possible. With the chemical propellants, read a bit why fluorine is not so popular and may switch to lox/methane for the same reason.
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Post by jonatanhedborg on Sept 29, 2016 13:36:53 GMT
Even more broken: NuclearThermalRocketModule 4.18 km/s Heavy Water Nuclear Thermal Rocket ReactorCoreHeight_m 0.15 NuclearReactor Coolant Heavy Water Moderator Diamond ModeratorMass_kg 1 Fuel U-235 Dioxide FuelMass_kg 1 FuelEnrichment_Percent 0.97 ControlRodComposition Boron Nitride ControlRodMass_kg 1 NeutronReflector Diamond ReflectorThickness_m 0 AverageNeutronFlux__m2_s 1.7e+020 ThermalRocket ChamberComposition Boron ThroatRadius_m 0.02 ChamberWallThickness_m 0.0013 ChamberContractionRatio 4.6 NozzleExpansionRatio 15 NozzleExpansionAngle_degrees 11 RegenerativeCooling_Percent 0.24 Injector Composition Lithium PumpRadius_m 0.3 RotationalSpeed_RPM 24 GimbalAngle_degrees 0
246kN in a 9.6kg package for 2.54k TWR - doubt you can get that with a chemical engine. In any case, designing a NTR for TWR is basically getting as much heat as possible from your reactor, then passing as much coolant as possible through it so it doesn't vaporize itself, while using as lightweight of a pump as possible for that task. The design uses heavy water as reaction mass in order to collect as much heat as possible from the reactor per unit of mass flow. The higher propellant density and full dissociation of the water into hydrogen are just a bonus. A not-so-obvious choice here for the pump material is Lithium. At the pump's scale stresses aren't that big of a concern, and you're not pumping reaction mass at temperatures hot enough to melt it. The reactor is a pretty interesting one. 1kg of diamond as moderator, 1kg of U-235 dioxide and 1kg of boron nitride for criticality control. The U-235 isotope is used instead of the cheaper U-233 because it needs less total reactor mass to attain criticality. The moderator here has as function mantaining the reactor working for longer; this allows it to output 514MW over just a bit over 6 months, which wouldn't be attainable using 2kg of fissiles and no moderator. The rocket engine chamber and nozzle use boron, which fits in a sweet spot spot between RCC(which can't withstand the chamber pressures used) and Diamond(which although doesn't need regenerative cooling to be used is heavier than this design requires to attain optimal TWR). Its chamber was sized to fit the reactor - Any smaller would make it not fit, whereas any larger would cause the reactor to be less efficient. On a side note, a way this design could be made lighter would be by inserting control rods to make the reactor go supercritical instead of removing them so you can save in moderator mass, though i haven't had success in designing a high-temperature design that can do this in less than 3kg of components. EDIT: seems like methane is also a good choice of fuel that i didn't initially consider, though this might depend on how much space you're willing to spend on fuel tanks - heavy water is about 3 times as dense. I've gotten TWRs of 2.95k by adapting the engine above to use methane, and this can probably be optimized to 3k. I tried building this one, and everything lined up (I think) but I got the "won't fit"-error (can't look up the exact phrase now). Could you post a screenshot of your setup? I must have missed something
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Post by RA2lover on Sept 29, 2016 14:50:44 GMT
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Post by RA2lover on Sept 30, 2016 3:40:53 GMT
I've gotten a butane-based design to a TWR of 4.67k, although it's starting to be a bit too big for missile scales due to pump scaling: Performance is mostly limited by reactor mass efficiency at this point - you want to maximize neutron flux to use up as much fissiles as possible while using the least amount possible of moderators/control rods and fitting within the 6-month use barrier. Honestly, a run time of 1 hour is more than enough for this type of design. EDIT: removing the moderator on that design allows it to hit a TWR of 4.8k, still didn't do chamber tweaking to take advantage of that. EDIT2: nope, seems like i hit a dead spot between chamber pressure and overheating, while increasing the throat radius worsens up overall TWR. can't use regenerative cooling to cool this anymore either. EDIT3: more fiddling with control rod/fuel mass, gotten an even larger design to 5.64k, though i guess this is mostly NTR scaling at this point. The chamber/nozzle is now a nightmare to work with, though. Can't find a more mass-efficient neutron absorber than boron nitride(except for lithium-6, though its use would kill thermodynamic efficiencies). There's also an upper limit where building a pump out of lithium isn't feasible anymore.
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Post by concretedonkey on Sept 30, 2016 6:40:51 GMT
Guys, I'll steer clear of you ungodly miniaturized NTRs for the moment . Switched to bi propellant missiles then switched to LOX/Decane to avoid the fluorine, also switched to nukes for the defensive and multi functional missiles ironically the pure offensive one stayed with a flak warhead Pure interceptor 53G, 1.7 km/s delta V, 7.2 kt nuke no armor to speak of. Multi functional interceptor 36G, 2.65 km/s delta V , again 7.2 kt nuke, a minimal layer of basalt composite (thanks to blothorn's thermal armor post). First strike missile 5G, 5 km/s delta V, 75 kg flak and 4 mm of basalt composite. Out of pure laziness standardized everything - same diameter for tanks , the same engine on all of them. Ironically the nuke warhead is actually lighter than the conventional one - 66 kg vs 75 , but the flak still works better for the initial strike. Less fratricide for the missiles and the cone works better in this case.
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Post by RA2lover on Oct 1, 2016 17:09:10 GMT
No nuclear rockets? No problem! You don't need a NTR to get crazy thrust-mass ratios:
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Post by concretedonkey on Oct 2, 2016 15:45:15 GMT
hahah , I'm actually also starting to get quite fond of diamond chambers ... other than that I'm playing with drones now... armed with micro nukes... one is firing a small 2.45kt missile and the other has a spinal conventional cannon firing the same warhead... its a bit of a FPS killer frankly when your drones spew 20 missiles each... also distracts the defensive lasers and the drones are free to pound with cannons...
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Post by nerd1000 on Oct 2, 2016 15:57:31 GMT
Even more broken: NuclearThermalRocketModule 4.18 km/s Heavy Water Nuclear Thermal Rocket ReactorCoreHeight_m 0.15 NuclearReactor Coolant Heavy Water Moderator Diamond ModeratorMass_kg 1 Fuel U-235 Dioxide FuelMass_kg 1 FuelEnrichment_Percent 0.97 ControlRodComposition Boron Nitride ControlRodMass_kg 1 NeutronReflector Diamond ReflectorThickness_m 0 AverageNeutronFlux__m2_s 1.7e+020 ThermalRocket ChamberComposition Boron ThroatRadius_m 0.02 ChamberWallThickness_m 0.0013 ChamberContractionRatio 4.6 NozzleExpansionRatio 15 NozzleExpansionAngle_degrees 11 RegenerativeCooling_Percent 0.24 Injector Composition Lithium PumpRadius_m 0.3 RotationalSpeed_RPM 24 GimbalAngle_degrees 0
246kN in a 9.6kg package for 2.54k TWR - doubt you can get that with a chemical engine. In any case, designing a NTR for TWR is basically getting as much heat as possible from your reactor, then passing as much coolant as possible through it so it doesn't vaporize itself, while using as lightweight of a pump as possible for that task. The design uses heavy water as reaction mass in order to collect as much heat as possible from the reactor per unit of mass flow. The higher propellant density and full dissociation of the water into hydrogen are just a bonus. A not-so-obvious choice here for the pump material is Lithium. At the pump's scale stresses aren't that big of a concern, and you're not pumping reaction mass at temperatures hot enough to melt it. The reactor is a pretty interesting one. 1kg of diamond as moderator, 1kg of U-235 dioxide and 1kg of boron nitride for criticality control. The U-235 isotope is used instead of the cheaper U-233 because it needs less total reactor mass to attain criticality. The moderator here has as function mantaining the reactor working for longer; this allows it to output 514MW over just a bit over 6 months, which wouldn't be attainable using 2kg of fissiles and no moderator. The rocket engine chamber and nozzle use boron, which fits in a sweet spot spot between RCC(which can't withstand the chamber pressures used) and Diamond(which although doesn't need regenerative cooling to be used is heavier than this design requires to attain optimal TWR). Its chamber was sized to fit the reactor - Any smaller would make it not fit, whereas any larger would cause the reactor to be less efficient. On a side note, a way this design could be made lighter would be by inserting control rods to make the reactor go supercritical instead of removing them so you can save in moderator mass, though i haven't had success in designing a high-temperature design that can do this in less than 3kg of components. EDIT: seems like methane is also a good choice of fuel that i didn't initially consider, though this might depend on how much space you're willing to spend on fuel tanks - heavy water is about 3 times as dense. I've gotten TWRs of 2.95k by adapting the engine above to use methane, and this can probably be optimized to 3k. You made a water pump from lithium? IRL your pump (and a portion of the incoming water) would turn to lithium hydroxide and hydrogen gas shortly after the inlet valve was opened, evolving quite a bit of heat in the process. CODE needs a materials compatibility mechanic. No alkali metals with water, no hot carbon in contact with hydrogen, no fluorine with, well, practically anything really- so on and so forth. Otherwise we'll keep seeing designs that are literally impossible.
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Post by blothorn on Oct 2, 2016 18:37:51 GMT
hahah , I'm actually also starting to get quite fond of diamond chambers ... other than that I'm playing with drones now... armed with micro nukes... one is firing a small 2.45kt missile and the other has a spinal conventional cannon firing the same warhead... its a bit of a FPS killer frankly when your drones spew 20 missiles each... also distracts the defensive lasers and the drones are free to pound with cannons... Yep. Something needs to be done about AI laser targeting priorities; payloads can be made a lot more laser resistant than drones, so it is almost always going to be better to kill of drones before trying to target their payloads. Right now just one of these can kill a handful of laser frigates (200 10kt nukes):
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Post by concretedonkey on Oct 2, 2016 18:50:56 GMT
Wow , almost 9MWs on a drone ... what is the muzzle velocity on that cannon ?
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