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Post by zuthal on Nov 22, 2016 9:53:41 GMT
Also, running a reactor with supercritical coolant isn't really that big a problem in principle, besides needing to contain the necessary pressure.
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Post by zuthal on Nov 22, 2016 2:15:22 GMT
See, the one issue I have with that is the ability of the coating to stay on while the turbopump is spinning at several thousand rpm. But I guess the engine does only need to last for a minute or two of total burn time. For fluorine-based capships, I'll use more reasonable materials, though... then again, what the hell even IS compatible with fluorine, and also with hot (if diluted in hydrogen) HF, if the engines use a preburner cycle?
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Post by zuthal on Nov 22, 2016 1:24:06 GMT
Most materials with fluorine - you can without problem pump fluorine through a lithium turbopump, for example. According to my knowledge of chemistry, the turbopump should rapidly and violently combust.
Also, being able to make guns out of plastic - because the temperature at the inside of the barrel wall would probably be enough to melt/decompose it.
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Post by zuthal on Nov 21, 2016 23:02:37 GMT
More from Julia Ecklar... though I am not sure why you would make wings out of tungsten, tungsten is way too heavy!
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Post by zuthal on Nov 21, 2016 20:06:07 GMT
In the same sort of musical style, but more humorous - especially Rocket to the Moon and Space Opera are space-themed.
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Post by zuthal on Nov 21, 2016 0:52:40 GMT
-snip- I have 3 variations of this gun on almost all my vessels. This is the largest version - what varies is mostly the angle and the lighter versions have shorter barrels both to save weight. Its quite effective in its role and can also cut enemy vessels in two at up to 100km, if they don't move. Its probably a bug... . I don't think the cutting ships in half is that unreasonable - you are tossing 216.45 g of iron per second at the enemy ships, going at 3.32 km/s - that is equivalent to about 12 MW in kinetic energy!
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Post by zuthal on Nov 19, 2016 22:13:16 GMT
I think the main use case of resistojets is that its power can be shared with other modules (like weapons) when they are not in use, while the power of NTRs can't. I use them mostly for turning around in tactical combat. Also, resistojets do not pose any radiation hazard, unlike NTRs - meaning that you can put them in places that are not behind a shadow shield.
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Post by zuthal on Nov 19, 2016 1:41:07 GMT
LOX/Methane is actually the cheapest fuel per kilogram, and doesn't square up too badly in terms of cost-specific impulse. It is still a lot worse in volumetric impulse than Fluorine/Hydrogen and Fluorine/Methane though (like everything is), and its exhaust velocity is only about two-thirds that of fluorine-hydrogen, meaning that you will only get about two-thirds the delta-V out of the same mass ratio. If you do not want to use Fluorine for whatever reason, and still want to use a chemical engine, I would suggest LOX/LH2, as that has the best exhaust velocity and volumetric impulse out of all the non-fluorine fuel mixtures.
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Post by zuthal on Nov 18, 2016 22:50:07 GMT
I made a spreadsheet of all chemical fuels currently in the game.From that, it is clear that Fluorine-Hydrogen, with bests in three categories (exhaust velocity, average density and volumetric impulse) is by far the best, followed by Fluorine-Methane (second-best volumetric impulse and best cost-specific impulse). However, it does not seem possible to create a viable HF engine at the MN-scale. There are similar, albeit less extreme, problems with Hydrogen-Methane. I would suggest to, if you can make your vessel have sufficient acceleration with them, use HF engines over Methane or Decane NTRs. However, this will likely not be viable for anything except for missiles, drones and small capships. EDIT: In light blue, I have included, for comparison purposes, Methane and Decane NTRs.
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Post by zuthal on Nov 18, 2016 7:08:20 GMT
Propellants - Chemical:
Hydrogen/Fluorine is the best propellant mix ingame. Delivers up to 5.1 km/s of exhaust velocity (at stoichiometric ratio), while being denser than all of the common NTR fuels (At an 18.8:1 Fluorine:Hydrogen ratio by mass, the average density of both is (18.8*1696+70.85)/19.8=1614 kg/m^3, compared to 422.62 kg/m^3 for methane and 730.05 kg/m^3 for decane). HF rockets are, however, not really viable for MN-scale engines, due to combustion chamber heat issues. Additionally, the inconvenient mixture ratio constrains the minimum total fuel mass to 2 kg. Also, the realism is sketchy, due to both a limited supply of Fluorine in the solar system and the rather... difficult chemistry of fluorine, especially when hot. PTFE tanks should realistically be able to hold it, though (as PTFE is already maximally fluorinated).
EDIT: Also, volumetric impulse (how much impulse you get out of one cubic meter of propellant, calculated as exhaust velocity times propellant density) for an optimal HF chemical engine (5100 m/s exhaust velocity) is 8.23 MN*s*m^-3, or the normalised volume usage as used by apophys, is 0.122 m^3*MN^-1*s^-1. Thus, if your ship is small enough to use them, HF chemicals clearly beat any NTRs.
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Post by zuthal on Nov 14, 2016 14:51:02 GMT
Some issues with this. 1) None of the reactors in game run at Carnot efficiency. Doing so is thermodynamically impossible, and all reactors run below that. 2) You're assuming the final goal is to minimize radiator area. This is not necessarily the case. For instance, colder radiators can take laser and nuclear damage far better than hotter ones. Additionally, colder radiators will yield overall less waste heat, which can be a major consideration for flare decoys. 3) You can't necessarily assume you can set your output temperature arbitrarily. One such limitation is thermocouple stress. Having too great of a temperature may not be possible, or the materials might be too expensive to do so. 4) The reactors bleed power out of both turbocompressors. This further drags your efficiency down from the Carnot efficiency, even possibly bringing it negative. Arbitrarily controlling the output temperature can cost you more power than it gives you back. TL;DR Your ideas work if your reactor is a spherical cow. The details end up being a touch messier. Edit: Forgot about one more thing. Radiators do not perfectly follow the Stefan-Boltzmann law, because you can't simply pump 2000 K coolant in and suddenly your radiator is 2000 K. They have an additional efficiency coefficient based on a slew of factors like the heat transfer coefficient, thickness, coolant, etc. So again, radiators are not spherical cows either. 1) True, though I am assuming (somewhat naïvely) that reactor efficiency as a percentage of Carnot efficiency is roughly constant with temperature - though I will be open to being corrected on that. 2) They can indeed, but materials are available (like the various allotropes of carbon) which have a margin over the typical coolant temperatures at the high-temperature end (on the order of 2500 K) of over 1000 K before they melt/sublimate. And needing less radiator area allows you to have more redundant radiators, allowing them to sustain more damage before your reactor is disabled. 3) Indeed, that is an issue especially at the high-temperature end - a tantalum-tungsten thermocouple, which is the standard high-temperature solution, seems to have a maximum temperature drop of ~500 K, though due to the nature of quartic functions, that is still close to the optimum radiator area. 4) They do indeed, and increasing coolant flow to reduce output temperature does increase the amount of power needed for the turbopumps. However, in my experience, it seems that the turbopumps only take up a small percentage of the total output power for large (multi-MW and beyond) reactors. And regarding the non-ideal radiators, that is true, however experiments have shown that as the game is currently, if you use materials that have sufficiently high heat transfer coefficients, you can achieve significant additional armour thickness without losing efficiency - for example, a 1 mm thick diamond radiator keeps its full efficiency up to an additional armour thickness of ~7 mm. Though I feel that diamond's transparency should have an impact on its use as a radiator - you would in effect have significant emission directly from the coolant.
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Post by zuthal on Nov 12, 2016 11:24:52 GMT
I don't get this, shouldn't the energy density of the reactor, area density of the radiator, and the total size of your craft be factors of consideration? If total radiator mass needed is tiny relative to the craft, you'd opt for low temperature outlet because weight penalty wouldn't matter much but increased thermocouple efficiency means a smaller reactor is needed. If total radiator mass needed is huge relative to the craft, you'd opt for high temperature outlets to minimize radiator size in order to increase payload. If you have a certain reactor design (core mass, moderator mass, control rod mass), you can adjust the available thermal power almost freely via the neutron flux, and increasing or decreasing the turbopump speed (to regulate core temp) is almost free too, in general. The radiators will usually end up making up the majority of the mass of your power system. qswitched wrote on his blog that: I respectfully disagree, if you make sufficient assumptions. These are that the thermocouple exit temperature can be adjusted more or less freely for a given core temperature and electric output power, without significant mass penalties. Solving the Carnot efficiency equation and the Stefan-Boltzmann law yields these graphs. A few conclusions are readily apparent: 1) You should always run your core as hot as possible 2) There is a single optimum radiator temperature, and it is always three quarters of the thermocouple inlet temperature. Thermocouple stresses from thermal expansion limit the maximum delta T available across the thermocouple, and thus the efficiency. I think most people have settled on Tungsten + Tantalum thermocouples with about 500K delta T. This... actually gets surprisingly close to the optimum you computed. Of course, you sadly cannot reach that optimum at the reactor temperatures that would be most ideal (not that a reactor that is only 100 K away from meltdown would ever be approved by any safety officer anyways). Though fortunately, due to the quartic scaling in the Kevin-Boltzmann law, the region of "acceptable" radiator efficiency isn't too narrow.
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Post by zuthal on Nov 11, 2016 21:17:27 GMT
qswitched wrote on his blog that: I respectfully disagree, if you make sufficient assumptions. These are that the thermocouple exit temperature can be adjusted more or less freely for a given core temperature and electric output power, without significant mass penalties. Solving the Carnot efficiency equation and the Stefan-Boltzmann law yields these graphs. A few conclusions are readily apparent: 1) You should always run your core as hot as possible 2) There is a single optimum radiator temperature, and it is always three quarters of the thermocouple inlet temperature.
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Post by zuthal on Nov 11, 2016 19:52:05 GMT
For semiheavy water (HDO), it shouldn't really, at least I don't see why from the game data... Semiheavy water has a bond dissociation energy of 931.68 kJ/mol, compared to 927.01 kJ/mol for just water. So... no clue. The only thing that might be it is what qswitched mentioned on his blog for hydrogen deuteride, that the Gibbs free energy of formation for monoatomic deuterium is lower than for monoatomic hydrogen.
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Post by zuthal on Nov 10, 2016 17:15:16 GMT
I would like to be able to attach muzzle brakes to conventional cannons.
This is because the reaction force from the expanding combustion gases makes up a significant fraction of the recoil, and a muzzle brake would serve to significantly reduce it (and thus the beam deflection stress).
In addition, I would like, for all guns, for both the recoil impulse (in kN*s) and the average recoil force while firing at the maximum fire rate to be displayed.
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