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Post by anonymous on Jun 6, 2019 17:37:41 GMT
childrenofadeadearth.wordpress.com/2016/07/12/stealth-in-space/In this post, qswitched said he would talk about a hypothetical nuclear rocket design whose exhaust temperature would be as low as just 30 K. It has been almost three years, and no update on this. I haven't been able to find mention of such an engine anywhere other than his blog. Does anyone have any links to said idea, or similar designs?
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Post by airc777 on Jun 6, 2019 18:03:43 GMT
How would you even any Delta V? Cold gas thrusters aren't exactly the bleeding edge of hypothetical high specific impulse designs.
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Post by AtomHeartDragon on Jun 6, 2019 19:21:59 GMT
This might be about this: toughsf.blogspot.com/2017/01/expansion-cooled-curved-nozzle-stealth.htmlRocket nozzles are basically devices for converting chaotic motion of gas atoms/molecules (temperature) into ordered one (exhaust velocity), and in vacuum exhaust temperature can get almost arbitrarily low, if you can bear having massive, sufficiently expanded nozzle. The main innovation in the post linked is using curved nozzle to block line of sight to hot interior of combustion chamber.
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Post by anonymous on Jun 7, 2019 1:10:14 GMT
How would you even any Delta V? Cold gas thrusters aren't exactly the bleeding edge of hypothetical high specific impulse designs. I think the idea is that, as it expands, the exhaust reaches 30 K by the time it exits the nozzle, not that it would start off being 30 K. This might be about this: toughsf.blogspot.com/2017/01/expansion-cooled-curved-nozzle-stealth.htmlRocket nozzles are basically devices for converting chaotic motion of gas atoms/molecules (temperature) into ordered one (exhaust velocity), and in vacuum exhaust temperature can get almost arbitrarily low, if you can bear having massive, sufficiently expanded nozzle. The main innovation in the post linked is using curved nozzle to block line of sight to hot interior of combustion chamber. Interesting article, I never heard of curving nozzles before. Wouldn't making your exhaust colder than the universal background radiation be less efficient than having it at exactly the background radiation temperature? Or do I misunderstand how temperature factors into efficiency?
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Post by AtomHeartDragon on Jun 7, 2019 7:55:37 GMT
Wouldn't making your exhaust colder than the universal background radiation be less efficient than having it at exactly the background radiation temperature? Or do I misunderstand how temperature factors into efficiency? 30K is well above background radiation.
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Post by qswitched on Jun 26, 2019 21:33:27 GMT
childrenofadeadearth.wordpress.com/2016/07/12/stealth-in-space/In this post, qswitched said he would talk about a hypothetical nuclear rocket design whose exhaust temperature would be as low as just 30 K. It has been almost three years, and no update on this. I haven't been able to find mention of such an engine anywhere other than his blog. Does anyone have any links to said idea, or similar designs? I was referencing the design that toughsf went over. After what he wrote, I felt no need to elaborate.
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Post by anonymous on Jul 12, 2019 23:06:43 GMT
\I was referencing the design that toughsf went over. After what he wrote, I felt no need to elaborate. Do you have a link for this? I cannot find it with Google and if it's linked on the blog post then I must be blind because I can't find it anywhere.
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Post by lucubratory on Jul 12, 2019 23:47:52 GMT
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Post by eternalsorrow on Apr 16, 2020 21:45:31 GMT
Anybody succeeded at reproducing it in-game? I have no luck with creating such a low-emission engine in game with reasonable dV.
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Echo
Full Member
Posts: 141
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Post by Echo on May 21, 2020 8:58:47 GMT
To lower the nozzle temperature, try increasing the nozzle expansion ratio. Increasing the nozzle expansion angle won't make the exhaust colder, but will reduce the rocket dimensions and mass at the expense of exhaust velocity and thrust.
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Post by Rocket Witch on May 24, 2020 0:25:46 GMT
Anybody succeeded at reproducing it in-game? I have no luck with creating such a low-emission engine in game with reasonable dV. IIRC hydrogen NTRs can get around 31-37K exhaust at the end of the nozzle. It may require a comedy nozzle extension ratio of over 1000, but some very small engines with tiny throats actually don't get particularly big with such ratios. Being able to expand beyond 1000 may help you here. To that end there is a line in Limits.txt (found in %AppData%\Roaming\CDE\Mods\Data) called NozzleExpansionRatio — if you change the second number it will change the maximum setting available ingame.
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Post by eternalsorrow on May 24, 2020 10:21:25 GMT
My mistake was trying to make a water engine, which mostly suck. Slightly modified my HD engine and got a decent result.
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Post by cipherpunks on May 24, 2020 18:39:01 GMT
Slightly modified my HD engine and got a decent result. I guess You can do better weight-wise. Anyway, here's "semi-stealth" 1 kt craft example with my take on HD NTR from 2 years ago:
RadioisotopeThermoelectricGeneratorModule 10.0 kW Radioisotope Thermoelectric Generator UsesCustomName false FuelPellet Fuel Strontium-90 Mass_kg 48.23 Height_m 0.1058 Thermocouple PTypeComposition Gadolinium NTypeComposition Nickel Chromium Cobalt Length_m 0.0321 ExitTemperature_K 275 Coolant Hydrogen Turbopump Composition Polyethylene PumpRadius_m 0.00877 RotationalSpeed_RPM 860
CrewModule 26 Crew Module MgAlZn 9 UsesCustomName true CrewCapacity 26 Decks 9 StructureMaterial Magnesium Aluminum Zinc ShellThickness_m 0.000802
RadiatorModule 3x6 Amorphous Carbon Radiator UsesCustomName false Composition Amorphous Carbon PanelWidth_m 1 Height_m 6.2 Thickness_m 0.001 ArmorThickness_m 0.001 Panels 3 FrontTaper_radians 0 BackTaper_radians 0 SurfaceFinish Diamond
RadiatorModule 6x1 Boron Nitride Radiator UsesCustomName false Composition Boron Nitride PanelWidth_m 1 Height_m 1 Thickness_m 0.001 ArmorThickness_m 0.0005 Panels 6 FrontTaper_radians 0 BackTaper_radians 0 SurfaceFinish null
PropellantTankModule 880 t Hydrogen Deuteride Steel Tank UsesCustomName true Propellant Hydrogen Deuteride StructureComposition Vanadium Chromium Steel ReactionMass_kg 8.8e+05 HeightToRadiusRatio 25.6 AdditionalArmorThickness_m 0
NuclearThermalRocketModule 9.51 km/s Hydrogen Deuteride Gimballed Nuclear Thermal Rocket UsesCustomName false ReactorCoreHeight_m 0.1634 NuclearReactor Coolant Hydrogen Deuteride Moderator Lithium-6 ModeratorMass_kg 0 Fuel U-235 Dioxide FuelMass_kg 17 FuelEnrichment_Percent 0.97 ControlRodComposition Titanium Diboride ControlRodMass_kg 42.3 NeutronReflector Pyrolytic Carbon ReflectorThickness_m 0.649 AverageNeutronFlux__m2_s 5.6e+19 ThermalRocket ChamberComposition Diamond ThroatRadius_m 0.06 ChamberWallThickness_m 0.003849 ChamberContractionRatio 6 NozzleExpansionRatio 930 NozzleExpansionAngle_degrees 8.2 RegenerativeCooling_Percent 0 Injector Composition Polyethylene PumpRadius_m 0.23 RotationalSpeed_RPM 907.8 Gimbal InnerRadius_m 0.4237 ArmorComposition Amorphous Carbon ArmorThickness_m 0.04 AttachmentCount 1 MomentumWheels Composition Vanadium Chromium Steel RotationalSpeed_RPM 38710 GimbalAngle_degrees 15
CraftBlueprint Cool HD 1 Modules 9.51 km/s Hydrogen Deuteride Gimballed Nuclear Thermal Rocket 1 0 null 0 0 880 t Hydrogen Deuteride Steel Tank 1 0 null 0 0 26 Crew Module MgAlZn 9 1 0.5 null 0 0 10.0 kW Radioisotope Thermoelectric Generator 1 -0.5 null 0 0 6x1 Boron Nitride Radiator 12 144.13 26 Crew Module MgAlZn 9 0 0 3x6 Amorphous Carbon Radiator 8 8.1595 10.0 kW Radioisotope Thermoelectric Generator 0 0 50.0 cm x 0 m Spacer 2 143.86 null 1.5708 1 Armor Shape Dodecagonal Concave true ArmorLayers Nickel Phosphorus Microlattice 0.0005 0 0 1 1 0 Graphite Aerogel 0.018 0 0 1 1 0
20.2 km/s ΔV, 0.1 gee min.acceleration, spare radiators (to close most and orient some w.r.t. adversary LoS). Vantablack finish would be more proper, but that's a mod. Crew requirements are silly, though: 3 radiator technicians? WTF. Comm officers can't double as sensor officers? C'mon. I should binary-patch this nonsense some day. p.s. Proper stealth craft would need at least a different S-nozzle, as in modern stealth aircraft - NTR throat orifice should not be seen.
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Post by eternalsorrow on May 24, 2020 18:59:29 GMT
Yes, I've read the article. I think it's better to stop there, since the game doesn't support stealth in any manner. I've already described somewhere, that the assumption "spy sats everywhere" is a good simplification for such a game, but won't be true for some more deep space conflict description.
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Echo
Full Member
Posts: 141
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Post by Echo on May 26, 2020 9:04:37 GMT
Increasing the nozzle expansion angle won't make the exhaust colder, but will reduce the rocket dimensions and mass at the expense of exhaust velocity and thrust. But it will also expose the hot chamber to a wider solid angle (portion of the sky), thus it will make it easier to be spotted by a spy satellite. OTOH, deacreasing the nozzle expansion angle will balloon the nozzle mass and size.
There is still the problem of hot radiators for capships though.
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