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Post by apophys on Nov 1, 2016 11:01:53 GMT
Also, boron in your armor and/or crew module will basically negate thermal neutrons, which are the type it's leaking most (ethane coolant takes care of the fast neutrons).
If you're still worried about it, you can max the enrichment % and lower neutron flux to match (tweak other settings). It'll lower the leakage by a factor of about 70, but will increase cost by 30% because U-233 is quite a bit more expensive than U-238. I don't consider this trade to be worth it for a disposable munition when boron shielding is so easy.
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Post by apophys on Nov 1, 2016 6:05:52 GMT
For something that follows the original premise of the thread, a 100GW MPD with TWR at 122 kg 0 (just because I can): Attachment DeletedIt's probably not very interesting for standard use, because mercury is dead weight in combat (mercury NTRs are bad). Also the TWR is utterly meaningless, because the power generated requires 1,510 tons of reactor alone with my mass-efficient 10GW design. Side note: 100GW through a 10cm disk; it's not a superconductor, so why is it not melting? Now, on the other hand, you can use decane with regular NTRs and/or resistojets, so this 100 MW thing here makes sense out of combat, considering its negligible weight & cost (and 90 o gimbal means it's even mountable radially on the sides to provide forward thrust): Attachment DeletedCode:
MagnetoplasmadynamicThrusterModule 17.6 km/s 100 MW Decane Gimballed Magnetoplasmadynamic Thruster CathodeRadius_m 0.0042 ChamberThickness_m 0.045 AnodeThickness_m 0.001 ThrusterLength_m 0.01 CathodeComposition Vanadium Chromium Steel AnodeComposition Vanadium Chromium Steel InsulatorComposition Polyethylene Propellant Decane Current_A 76000 Injector Composition Lithium PumpRadius_m 0.032 RotationalSpeed_RPM 310 Gimbal InnerRadius_m 0.047 ArmorComposition Silica Aerogel ArmorThickness_m 0.04 ReactionWheels Composition Polyethylene RotationalSpeed_RPM 23000 GimbalAngle_degrees 90
Note: From what I've seen, at the upper end of power, you can basically use any propellant at all to get to a desired thrust/exhaust velocity/power usage point that any other propellant can reach. So it makes sense to use propellants that are inherently interesting (mercury is superdense; decane is dense and very versatile).
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Post by apophys on Nov 1, 2016 3:18:58 GMT
Regarding the original point of this thread, building crew modules out of boron (and/or having boron main armor, which is common) gives them excellent rad shielding against thermal neutrons, and wrapping the innermost part of the armor belt around crew with a little lithium-6 will stop fast neutrons. So neutron bombs, or even a fringe possibility of highly radioactive drones coming close, are not very difficult to block and ignore. Yes, everyone please use my 1GW and 10GW reactors, and my 1GW laser, too. I love seeing them proliferate. I'm an arms dealer now. xD
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Post by apophys on Nov 1, 2016 2:30:43 GMT
Here's what I came up with for a 1 MW disposable reactor. Probably better than whatever the OP was going to use. Code: ThermoelectricFissionReactorModule 1.02 MW Thermoelectric Fission Reactor ReactorCoreDimensions_m 0.1 0.1 NuclearReactor Coolant Ethane Moderator Boron Nitride ModeratorMass_kg 0 Fuel U-233 Dioxide FuelMass_kg 1 FuelEnrichment_Percent 0.016 ControlRodComposition Boron Nitride ControlRodMass_kg 1 NeutronReflector Diamond ReflectorThickness_m 0 AverageNeutronFlux__m2_s 1.3e+020 InnerTurbopump Composition Amorphous Carbon PumpRadius_m 0.12 RotationalSpeed_RPM 390 ThermocoupleInnerDimensions_m 0.12 0.41 Thermocouple PTypeComposition Tungsten NTypeComposition Tantalum Length_m 0.001 ThermocoupleExitTemperature_K 2500 OuterCoolant Sodium OuterTurbopump Composition Lithium PumpRadius_m 0.05 RotationalSpeed_RPM 290
Comparison to stock 1 MW reactor: 300 times lighter and 800 times cheaper. My god, stock designs are terrible. Attachment Deleted
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Post by apophys on Nov 1, 2016 0:14:00 GMT
Here's mine. Same thrust; much lighter. I like large gimbal angles, so it's bigger, but you can easily tweak that down. 6.39 km/s exhaust, 25.8 kN thrust & 1.37 kg (1920 TWR). Cost 6.59c. Attachment DeletedCode:
ResistojetModule 6.39 km/s 1.00 MW Decane Gimballed Resistojet PowerSupplied_W 1e+006 Propellant Decane CoilComposition Tantalum Hafnium Carbide ChamberLength_m 0.01 CoilRadius_m 0.0001 ThermalRocket ChamberComposition Diamond ThroatRadius_m 0.0013 ChamberWallThickness_m 0.0016 ChamberContractionRatio 5.4 NozzleExpansionRatio 100 NozzleExpansionAngle_degrees 7 RegenerativeCooling_Percent 1 Injector Composition Lithium PumpRadius_m 0.098 RotationalSpeed_RPM 72 Gimbal InnerRadius_m 0.14 ArmorComposition Silica Aerogel ArmorThickness_m 0.0001 ReactionWheels Composition Lithium RotationalSpeed_RPM 2500 GimbalAngle_degrees 20 Need a reactor?
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Post by apophys on Oct 31, 2016 20:17:23 GMT
I'd expect those things to have a coating (or multiple coats) of things inert to both the structural material and the fluid. Such a coating is thin enough to be ignored for mass.
Of course, if you get a crack in it...
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Post by apophys on Oct 31, 2016 19:19:02 GMT
Another option would be to grow algae or other plants on Mars (probably under some domes), using the plentiful CO2 from the ice caps to make complex molecules via photosynthesis, then running the biomass through an anaerobic digester for methane. As a plus, such infrastructure would be excellent support for colonization, and probably cheaper for electricity than massing solar panels over the surface (nuclear reactors are great, but sourcing fuel for long-term installations may be troublesome; not sure about the geology of Mars or the viability of importing fuel).
Trace methane in the atmosphere makes me think of biological activity. It's possible that there are bacteria living deep underground on Mars feeding on something (and another bacterium is turning their dead remains into methane). If this is the case, we might actually discover some methane deposits under the surface with exploratory drilling.
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Post by apophys on Oct 31, 2016 12:15:16 GMT
The ones I've got that beat your records:
1. Distress Call at Luna Time: 9h 30m dV spent: 405 m/s (exploiting a bug - if you line things up perfectly, you basically don't spend dV on the join)
3. Predatory Opportunism Time: 10h 16m
9. Uranian Cargo Run Time: 2d 3h dV spent: 3.89 km/s
Haven't really spent time perfecting things yet, though.
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Post by apophys on Oct 31, 2016 6:20:01 GMT
In addition to increasing the maximum (to maybe 10 tons), decrease the minimum mass of fuel and control rods in reactors and NTRs, by at least an order of magnitude. It's hindering optimization with regard to mass.
Increase the maximum power input to lasers and resistojets, by at least an order of magnitude. If I can make a functioning 10 GW MPD, I want to do the same for other components which would benefit from it.
Increase the maximum settable engagement range of lasers to 10 Mm. We're seeing affordable laser ships at very high power levels that are pushing the 250 km distance limit really hard, and it's a serious combat limitation (because they don't have enough time to burn things when they should be able to).
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Post by apophys on Oct 31, 2016 5:40:01 GMT
I'm guessing the decane MPDs are used for main thrust out of combat, so that it can actually go places. Slowly.
It would probably be better to edit it with a double line of broadside-oriented main thrust, which can actually be efficient because it isn't limited to a count of 20.
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Post by apophys on Oct 31, 2016 4:51:45 GMT
That kind of output would certainly require a way bigger power draw than it's pulling. Can't wait for rail and coil guns to get fixed.
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Post by apophys on Oct 29, 2016 13:04:44 GMT
Though I do gotta say that I stole your design above, Lawson, and am absolutely loving the 1GW reactor - I've not been able to fiddle around with it quite yet to make it more temperature efficient, but it makes for an excellent test reactor for my weapons testing. Ahem... You may not have noticed the quote block there, but it's actually my reactor, and Lawson is commenting on it.
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Post by apophys on Oct 10, 2016 10:23:14 GMT
Hi all. I would like to post pics of some of my design but sadly Ctrl PrtScn give me black screen, problably because of my dual screen. Just play in windowed mode, and do a printscreen & paste in MS Paint or GIMP or other equivalent.
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Post by apophys on Oct 7, 2016 20:18:35 GMT
Any idea for the radiators? Diamond, carbon and graphite all seem great all around materials, but probably there's more to it. I'm thinking relatively thin amorphous carbon with a diamond finish. Amorphous carbon is light, strong, has great specific heat, and is tested to be acceptably resistant to lasers on its own (much more so than solid diamond, for the weight). A diamond surface should help shatter/ricochet projectiles (extreme shear modulus) and spread nuke/laser heat across the radiator (excellent thermal conductivity). Graphite is a bit more laser-resistant due to its lower thermal conductivity, but this also makes it a worse radiating material, so it has to be even thinner (or else it faces efficiency losses). The lower melting point & strength, and higher density, don't help. With laser radiators at 1234K, boron is a valid option for cheapness and strength. It hits efficiency losses pretty quickly, though, so it has to be really thin. I see multiple people using diamond radiators (for reactors, not lasers), and that's probably because you can get them really thick without losing efficiency. The weight associated with that tactic makes me think it isn't really worth it. I have not tested any radiator scheme, though.
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Post by apophys on Oct 7, 2016 18:06:00 GMT
Wait a minute... 1.01 GW and 71 MW? Those must be my reactors! Glad they're seeing use. Your 100 MW design is a fantastic improvement, but this one might have a few flaws. The mass breakdown is 50% boron armour, 45% lead reaction wheels, 5% other stuff, and the cost breakdown is 70% boron 20% lead. Cutting down on armour allows a switch to lithium reaction wheels, which are stupidly cheap and lightweight. Using lithium and keeping the armour results in minuscule rotation speed (2-3 degrees per second) which might be acceptable considering the range this thing should work at, and basically halves the weight. I am going to try 4mm of amorphous carbon and 100rpm lithium, let's hope it fares well My thought process justifying it is as follows. You can swap boron to UHMWPE and wheels to cadmium fairly easily; this results in a bit over 30t weight. But the cost skyrockets due to 3cm of UHMWPE (may or may not be worth it, but I'm stingy). Lighter reaction wheels while leaving the armor alone require far higher power to sustain at this targeting speed. Your preferred power balance may differ, and you may accept a lower speed. I'm uncomfortable lowering the armor on the turret further than this, since it represents a pretty sizable investment on the ship (1GW of reactor, plus assorted radiators for both reactor and laser, plus ship armor wrapping the reactor, plus dV to move all this). The weight is already 50% lighter than an equivalent 10 of my 100MW lasers, while having more power and higher intensity than such a collective.
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