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Lasers
Oct 6, 2016 0:03:08 GMT
Post by apophys on Oct 6, 2016 0:03:08 GMT
To get your irradiance, I need a 9m aperture, which needs a 20m radius turret to hold it.
Can cut mass by using diamond reaction wheels (11 kt), but then they eat an entire 700MW of power themselves. Cadmium is more reasonable, but the mass becomes 26kt. Not great mass either way.
Even with diamond, ~90% of the thing's mass is reaction wheel, with ~10% being the 6cm boron armor. Everything else is drowned out.
What I really want to do is shove more than 1 GW into a laser.
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Lasers
Oct 5, 2016 23:04:51 GMT
Post by apophys on Oct 5, 2016 23:04:51 GMT
Very awesome.
That 74.7 kt weight though... makes it 0.1 irradiance per ton at 240km . I wonder how much the radiators weigh, too...
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Post by apophys on Oct 5, 2016 21:59:23 GMT
Big upgrade. The effect of aperture is way bigger than I expected. I grew it from 0.5 to 2.4 meters, changing basically nothing about the lasing components (grew the turret to match; that made it 6 times heavier at 89.8t, and the diameter 10.3m).
This is now a proper siege laser.
Distance Irradiance (MW/m^2) 20km >60,000 30km 34,600 40km 19,600 50km 12,600 60km 8,650 70km 6,400 80km 4,900 90km 3,840 100km 3,150 110km 2,590 120km 2,160 130km 1,860 140km 1,600 150km 1,380 160km 1,230 170km 1,080 180km 961 190km 868 200km 781 210km 712 220km 647 230km 590 240km 545 250km can't see... :P
That's about 4 times the irradiance of the 1GW stock laser while being ~6,550 times lighter and ~480 times smaller cross section.
6 irradiance per ton at 240km, and the small radiator area it needs, makes it practical.
New lasersnipe meta? xD
LaserModule 1.000 GW Nd:YAG Green Laser ArcLamp GasComposition Krypton EnvelopeComposition Diamond PowerSupplied_W 1e+009 Radius_m 0.01 CavityWallComposition Molybdenum CavityCoolantComposition Hydrogen CavitySemimajorAxis_m 1 CavitySemiminorAxis_m 0.99 GainMedium Nd:YAG OpticalNodes 5000000 LasingRodRadius_m 0.023 Mirror Composition Molybdenum OutputCoupler Composition Diamond CoolantTurbopump Composition Boron PumpRadius_m 0.9 RotationalSpeed_RPM 400 CoolantInletTemperature_K 2200 FrequencyDoubler NonlinearOptic Composition Silver Gallium Selenide OpticLength_m 0.026 OpticRadius_m 0.025 ApertureRadius_m 2.4 FocusingMirror Composition Silver Turret InnerRadius_m 5.1 ArmorComposition Boron ArmorThickness_m 0.06 ReactionWheels Composition Iridium RotationalSpeed_RPM 73 EngagementRange_km 250 TargetsShips true TargetsShots true
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Lasers
Oct 5, 2016 20:13:46 GMT
Post by apophys on Oct 5, 2016 20:13:46 GMT
Added. But that's with an aperture of 0.5m ; if you're fine with a smaller targeting angle than 70 degrees you can arbitrarily increase the aperture (and the turret once it gets too big for that) for crazy irradiance.
Doubling the aperture and doing minor tweaks, I get 670 at 90km range. But targeting angle drops to 47 degrees.
Probably worth it, now that I think about it...
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Lasers
Oct 5, 2016 19:38:17 GMT
Post by apophys on Oct 5, 2016 19:38:17 GMT
My first stab at it:
LaserModule 1.000 GW Nd:YAG Green Laser ArcLamp GasComposition Krypton EnvelopeComposition Diamond PowerSupplied_W 1e+009 Radius_m 0.01 CavityWallComposition Molybdenum CavityCoolantComposition Hydrogen CavitySemimajorAxis_m 1 CavitySemiminorAxis_m 0.99 GainMedium Nd:YAG OpticalNodes 4000000 LasingRodRadius_m 0.022 Mirror Composition Molybdenum OutputCoupler Composition Diamond CoolantTurbopump Composition Boron PumpRadius_m 0.9 RotationalSpeed_RPM 400 CoolantInletTemperature_K 2200 FrequencyDoubler NonlinearOptic Composition Silver Gallium Selenide OpticLength_m 0.026 OpticRadius_m 0.025 ApertureRadius_m 0.5 FocusingMirror Composition Silver Turret InnerRadius_m 2.2 ArmorComposition Boron ArmorThickness_m 0.06 ReactionWheels Composition Lithium RotationalSpeed_RPM 320 EngagementRange_km 100 TargetsShips true TargetsShots true
Screw efficiency, 2240K or bust (which is the limit set by the Nd:YAG). Produces 19.6 MW output, weighs 15.9 tons.
Coincidentally, the weight is close to the 15.6t of the reactor to feed it. Not sure about radiators though.
Update: Irradiance table:
5km off the chart 10km 13100 20km 3400 30km 1490 40km 840 50km 541 60km 375 70km 275 80km 211 90km 166 100km can't see because the scrollbar's in the way, ~135
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Post by apophys on Oct 5, 2016 11:23:36 GMT
Updated the 1GW reactor with a version lighter by 4 tons.
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Post by apophys on Oct 5, 2016 6:54:25 GMT
Try vanadium-chromium steel or osmium for reaction wheels. With high loads, those are my go-to materials. Also try increasing the internal radius of the turret to put more mass on the reaction wheel.
Still, I'd definitely like a turret option to push against the main ship for its aiming.
On a related note, chemical rockets and NTRs do not use power for their reaction wheels. What's up with that? ...
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Post by apophys on Oct 4, 2016 13:13:05 GMT
I tried to make a gigawatt reactor, and i don't think its possible with the current materials. I could probably shave some mass, but it exists. UPDATE: Now weighs only 15.6 tons. Same output and dimensions. ThermoelectricFissionReactorModule 1.01 GW Thermoelectric Fission Reactor ReactorCoreDimensions_m 0.1 0.1 NuclearReactor Coolant Sodium Moderator Diamond ModeratorMass_kg 4 Fuel U-235 Dioxide FuelMass_kg 10 FuelEnrichment_Percent 0.97 ControlRodComposition U-233 Dioxide ControlRodMass_kg 9 NeutronReflector Diamond ReflectorThickness_m 0.597 AverageNeutronFlux__m2_s 2e+020 InnerTurbopump Composition Amorphous Carbon PumpRadius_m 1 RotationalSpeed_RPM 570 ThermocoupleInnerDimensions_m 5 6.3 Thermocouple PTypeComposition Tungsten NTypeComposition Tantalum Length_m 0.001 ThermocoupleExitTemperature_K 2500 OuterCoolant Sodium OuterTurbopump Composition Calcium PumpRadius_m 0.5 RotationalSpeed_RPM 600
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Post by apophys on Oct 4, 2016 12:31:14 GMT
To see how fuel density really affects mission capability, I'll use math, because math is awesome.
A UHMWPE methane tank has a mass ratio of 400 (this is wet mass / dry mass). In other words, the ratio of propellant to propellant wall is 399. A UHMWPE hydrogen tank has a mass ratio of 67. The ratio of propellant to propellant wall is 66.
Taking your hypothetical 10 km/s mission, your methane wet mass is 20 kt and dry mass 3.98 kt. You are lugging 16.02 kt of propellant. Your propellant wall weighs 0.04 kt, so you actually have 3.94 kt of functional dry mass. Your hydrogen wet mass is 20 kt and dry mass 6.17 kt. You are lugging 13.83 kt of propellant. Your propellant wall weighs 0.21 kt, so you have 5.96 kt of functional dry mass. This is a 51% increase in usable dry mass by switching to GEICO, I mean hydrogen. Good.
But what if you decided to have more than a sheet of paper separating you from a fuel spill? Let's make a modest change to approximate – instead of UHMWPE tanks, we'll use amorphous carbon, a good all-around damage-resistant material, and still decently light.
An amorphous carbon methane tank has a mass ratio of 38. Propellant to wall is 37. An amorphous carbon hydrogen tank has a mass ratio of 7.3. Propellant to wall is 6.3.
The methane ship has 0.43 kt of propellant wall, leaving it with 3.55 kt of functional dry mass. The hydrogen ship has 2.20 kt of propellant wall, leaving it with 3.97 kt of functional dry mass. A 12% increase in usable mass.
At the cost of a 498% increase in propellant volume.
Of course, the more thickly you armor, the worse this gets, and soon you'd have actually been better off with methane.
I'd say an unarmored dump-and-escape carrier or silo ship would benefit significantly from hydrogen fuel, but a brawler type would not. I will probably start using some hydrogen deuteride due to this (as it has all the benefits of hydrogen with less of the density issue). Thanks for the thread (and I hope I'm not coming off as spammy...).
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Post by apophys on Oct 4, 2016 9:03:53 GMT
To build on the fuel density point:
a bunch of maximally lengthened 10kt fuel tanks built from UHMWPE for each of the following fuels gives the following ultimate dV caps (using stock engines because I'm lazy):
Hydrogen deuteride -> 42.7 km/s Hydrogen -> 37.9 km/s Methane -> 36.8 km/s Decane -> 34.4 km/s
Decane using my cool new resistojet -> 41.7 km/s
The dV advantage that hydrogen has is actually rather small due to its horrible density. In real life it's actually a bit worse, because hydrogen will slowly leak right through materials due to how small the H2 atoms are. Hydrogen deuteride looks pretty good though.
EDIT: Helium MPD -> 116 km/s Xenon MPD -> 84.1 km/s
MPDs would be gamebreaking if you could get reasonable thrust out of them... something to try later I suppose.
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Post by apophys on Oct 4, 2016 6:53:53 GMT
I'm solidly on team Decane. Having tested NTR fuels in the module designer (tweaking to a core temp of around 3100 K for all fuels), the one that gave the lowest volume usage per second (normalized to 1 MN of thrust) was nitromethane, which had an absolutely terrible exhaust velocity. Number two (a very close second) was decane, which is fully respectable at around 5.4 km/s. To a large degree, fuel density determines how much useless structural dry mass you require, and that eats into your mass allowance. The mass of tank walls and supporting struts is a serious concern for hydrogen in particular (armor less so, because you can armor just the front and still make a functional ship). If you use hydrogen, you are certainly going to have issues with random stray shots blowing tanks, as well as nukes that go off to your side, and you had better make sure that you point directly at the target consistently (which brings up the point of turnabout times on long ships...). On a side note, earlier today I tested out resistojets. Here's what I managed to cook up: Yeah, that's an exhaust velocity equal to a quality methane NTR, with acceptable thrust to back it. This needs more experimentation, for sure, but it looks very promising. It'll take a little extra mass in reactors & radiators, but with the fuel density of decane and the mass savings it otherwise brings, that's fully affordable. I also tested every other fuel for resistojets, and nothing else came even remotely close in performance. Edit: the code - ResistojetModule 6.38 km/s 10.0 MW Decane Gimballed Resistojet PowerSupplied_W 1e+007 Propellant Decane CoilComposition Tantalum Hafnium Carbide ChamberLength_m 0.1 CoilRadius_m 0.0001 ThermalRocket ChamberComposition Diamond ThroatRadius_m 0.01 ChamberWallThickness_m 0.015 ChamberContractionRatio 8 NozzleExpansionRatio 88 NozzleExpansionAngle_degrees 6.9 RegenerativeCooling_Percent 1 Injector Composition Amorphous Carbon PumpRadius_m 0.095 RotationalSpeed_RPM 790 Gimbal InnerRadius_m 0.14 ArmorComposition Amorphous Carbon ArmorThickness_m 0.05 ReactionWheels Composition Vanadium Chromium Steel RotationalSpeed_RPM 15000 GimbalAngle_degrees 17
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Post by apophys on Oct 1, 2016 22:46:21 GMT
Huh. That diamond trick is pretty cool. Very useful on all but the tiniest reactors. I'd say it's especially useful for the smallest reactors, which do not have shielding around the core due to self-imposed size limitations. 10 kg of diamond moderator, with U-233 dioxide control, brings your minifridge down to ~179 W of radiation without increasing size. Still not safe, but definitely safer.
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Post by apophys on Oct 1, 2016 20:06:05 GMT
So, I've managed to get a power density of over 7 MW / m 3 on a reactor with output temp at 2500 K. As a side benefit, it's lighter and cheaper than any stock reactor, while outputting more raw power than any stock reactor. Stock reactors appear hilariously bad now. I call it the Thermos. Because it looks like one. Diamond moderator is stuffed in there to reduce radiation leakage (this is why I use U-233 dioxide control instead of boron nitride; it's denser, leaving room for moar diamond). A moderator is also required for the design, as without any the range would not reach criticality and the fuel would not last long enough. 4kg is the bare minimum for diamond. And yeah, that's a lot of power from a single kg of fuel. Calcium is used for the outer turbopump because it's lighter and cheaper than amorphous carbon. Not that the difference is very large. Total cost is 51.9 kc (the screen isn't big enough to show that). Copy/paste design code (from my UserDesigns.txt file to yours): ThermoelectricFissionReactorModule 71.0 MW Thermoelectric Fission Reactor ReactorCoreDimensions_m 0.1 0.11 NuclearReactor Coolant Sodium Moderator Diamond ModeratorMass_kg 11 Fuel U-235 Dioxide FuelMass_kg 1 FuelEnrichment_Percent 0.97 ControlRodComposition U-233 Dioxide ControlRodMass_kg 1 NeutronReflector Diamond ReflectorThickness_m 0.7 AverageNeutronFlux__m2_s 1.4e+020 InnerTurbopump Composition Amorphous Carbon PumpRadius_m 0.34 RotationalSpeed_RPM 1200 ThermocoupleInnerDimensions_m 0.79 2.4 Thermocouple PTypeComposition Tungsten NTypeComposition Tantalum Length_m 0.001 ThermocoupleExitTemperature_K 2500 OuterCoolant Sodium OuterTurbopump Composition Calcium PumpRadius_m 0.34 RotationalSpeed_RPM 1000
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Post by apophys on Oct 1, 2016 18:02:18 GMT
As I understand it, the actual reason to burn on the sun side is because of the direction of the particular orbit the craft starts in. Let me explain.
In general, to catch up to a target, you want to burn retrograde (which happens to be away from your target), to slow down and drop your orbit closer to the body you're both orbiting (here, the sun). Because you're going to be burning fuel to escape your planet anyway, you might as well make that burn also go toward your next goal; this means matching up the burn point in the orbit around Mercury that points in the same direction as your next burn. The backward direction of the point in the orbit around Mercury happens to be sun-side in this case. If the orbit was reversed, you'd want to escape Mercury on the side away from the sun.
I cleared using 12.9 km/s, at 2 months 10 days. (I swap my frame of reference to always be the nearest body I'm orbiting, in this case Mercury -> Sol -> L4. I've never used the target as a reference, way too confusing.)
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Post by apophys on Jul 31, 2016 12:28:46 GMT
I assumed the radiator-armor could be easily sectioned and oversized to account for losing sections to damage. Material strength decreasing with temperature I didn't consider, though. Seems like the long thin radiator idea running the full length of the ship (perpendicular to the armor) is what I'll mostly use, then. About the angled armor, a full cylinder would have the best slope, as only a small section would be close to 0 degrees. With the rounded prisms, anytime the enemy is side-on, a full section of the ship is close to 0 degrees. Shouldn't it be possible to always roll the edge towards the enemy while in range of combat? Reaction wheels should be enough to roll. You even mention pointing radiators edge-on. Unless the case of having multiple enemies from multiple directions happens more often than I'm expecting. Thanks for the responses. I'm really looking forward to being able to test things ingame when it becomes available. Another thing I thought of: Would it be possible to make laser apertures of 100m or more with a thin umbrella mirror around the ship (aim by moving the ship itself, focus by deforming the umbrella)? I'm aware this would be an enormous target to shoot at, but the greater effective range of the laser could be worth it. Long-range artillery would allow kiting tactics, and thus the complete abandonment of armor. I was thinking a metal coating on a semi-rigid tensile membrane with tubular support structure (i.e. literally a shiny umbrella), but this might work too for much less mass: www.obs-hp.fr/www/preprints/pp136/PP136.HTML
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