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Post by RA2lover on Oct 1, 2016 23:52:20 GMT
What i mean is - your conventional gimbal-steered missile ends up losing a significant amount of delta-v while turning so it can thrust at a direction where it can compensate for turning radius properly. A missile with proper RCS thrusters wouldn't have that issue, though the game's limitation on minimum throat size(which leads to a limitation on minimum thruster size as pretty much everything else is based on it) prevents this from being done in a reasonably compact package.
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Post by RA2lover on Oct 1, 2016 21:32:41 GMT
ROFL.
In any case, although proportional navigation is much better than your generic pure pursuit homing(which is so terribad it shouldn't be used at all), it's still not optimized for spacecraft. For one, it assumes your missile has a constant lateral acceleration to its velocity vector, meaning you're losing a lot of delta-v while doing correction turns.
A thing i haven't seen taken advantage of here are nuclear decoys - a ship with a big, inefficient reactor whose only task is powering its massive cooling system.
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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 RA2lover on Oct 1, 2016 17:02:39 GMT
I was trying to make a 105mm cannon-launched missile before. Do note i'm still on 1.0.0(pirated the game - still intending to buy it once it goes on sale though) - so its performance figures should change somewhat if nuke formulas were indeed changed since the initial release: The idea was basically putting the highest yield nuke that could fit in a 10cm diameter cylinder. It really limits the available options though - a 20cm diameter nuke(made because i've confused radius as diameter here) can get to 300kt easily. A few design considerations: - Calcium is probably one of the strongest desensitizers out there, followed by Potassium(which you need less of to make your slow explosive not ignite) - At this scale, the job of your neutron reflector isn't reflecting neutrons, but containing the explosive for as long as possible. In this case, as much density as possible helps. - You need as little explosive as possible to maximize yield, though i've had issues at this as I can't find a slow explosive material that covers the gap between silicon nanothermite(pretty slow by itself, meaning it's easy to build a nuke with it, though it has a low energy density that limits your yield later on if you decide to use it) and nitroglycerin. - Most of this design's efficiency comes from the fission stage, which needs fusion boosting to work properly. Adding more fissiles needs more explosives to compress them, though, and i can't afford it at this size. Does anyone have a slow explosive composition that can bridge the gap between nitroglycerin and silicon nanothermite?
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Post by RA2lover on Oct 1, 2016 16:34:05 GMT
You can manually detonate them, though i guess that's still a chore.
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Post by RA2lover on Sept 30, 2016 15:45:31 GMT
you can make multi-stage missiles by using a launcher to fire your next stage.
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Post by RA2lover on Sept 30, 2016 15:32:59 GMT
There's an use for it - it allows you to increase the space available for the reactor without the associated pressure increase that comes with increasing the chamber wall contraction ratio.
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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 RA2lover on Sept 30, 2016 2:06:45 GMT
It depends on what your tanks are supposed to endure. atmospheric orbital launch conditions are very different from what you would expect on designs made to be only used in microgravity, and you can get away with lighter stuff from the assumptions your tank isn't going to accelerate faster than 1G or resist atmospheric loads. As far as i know, we haven't tried to launch an empty tank and fill it in space(though the ISS might have done that at some point i'm not aware of), and the closest thing of that i've seen proposed was the Lunar Escape System.
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Post by RA2lover on Sept 29, 2016 14:55:11 GMT
What's the efficiency of the laser? Can you replicate the same results with different laser wavelengths? how much does M² affect the results?
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Post by RA2lover on Sept 29, 2016 14:50:44 GMT
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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 RA2lover on Sept 29, 2016 1:52:17 GMT
That's the line bringing coolant from the radiators back to the reactor, which is outside the reactor itself. It's pegged to the melting point of the coolant, though - this might be a bug.
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Post by RA2lover on Sept 28, 2016 22:38:40 GMT
Expanding on material typos, the nickel-chromium-cobalt alloy has a thermal expansion coefficient of 17.8 K^-1, which is several orders of magnitude above everything else.
EDIT: Seems like there's something wrong with the LOX/RP-1 chemical engine performance as well, though i can't exactly point out what. In particular, the reaction's flame temperature is much lower than a quick source search appears to indicate.
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Post by RA2lover on Sept 28, 2016 19:40:25 GMT
xkcd's what-if did some analysis on the effects of overpowered heat sources in a 1x1x1 cube. pumping 1.8MW into it would only heat it to about 1600K.
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