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Post by zuthal on Nov 4, 2016 16:31:14 GMT
So, it seems that Fluorine-Hydrogen combustion rockets are competitive with, or even possibly superior too, methane and decane NTRs even for capship usage. This of course poses a possible logistical problem: How do you get that much Fluorine? Hydrogen, methane and decane are little problem, since hydrogen and carbon are quite abundant in the solar system, but Fluorine isn't - Carbon is ~4800 times more abundant in the Solar System than Fluorine is.
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Post by nerd1000 on Nov 6, 2016 10:42:47 GMT
So, it seems that Fluorine-Hydrogen combustion rockets are competitive with, or even possibly superior too, methane and decane NTRs even for capship usage. This of course poses a possible logistical problem: How do you get that much Fluorine? Hydrogen, methane and decane are little problem, since hydrogen and carbon are quite abundant in the solar system, but Fluorine isn't - Carbon is ~4800 times more abundant in the Solar System than Fluorine is. You dig up flourite and make flourine from it. Reserves on Earth alone are estimated at 230 million tonnes, and we have an entire solar system to mine for the stuff. |
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Post by shurugal on Nov 6, 2016 14:16:47 GMT
So, it seems that Fluorine-Hydrogen combustion rockets are competitive with, or even possibly superior too, methane and decane NTRs even for capship usage. This of course poses a possible logistical problem: How do you get that much Fluorine? Hydrogen, methane and decane are little problem, since hydrogen and carbon are quite abundant in the solar system, but Fluorine isn't - Carbon is ~4800 times more abundant in the Solar System than Fluorine is. You dig up flourite and make flourine from it. Reserves on Earth alone are estimated at 230 million tonnes, and we have an entire solar system to mine for the stuff. 230 MT is not very much at all. There are ship designs that use kilotons of the stuff. Would only take a few years of s couple fleets like that running around to deplete the supply, especially when you consider how much of it must be used to lift it into orbit. |
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Post by wafflestoo on Nov 6, 2016 15:21:39 GMT
You dig up flourite and make flourine from it. Reserves on Earth alone are estimated at 230 million tonnes, and we have an entire solar system to mine for the stuff. 230 MT is not very much at all. There are ship designs that use kilotons of the stuff. Would only take a few years of s couple fleets like that running around to deplete the supply, especially when you consider how much of it must be used to lift it into orbit. This is precisely why I treat the stuff as strategic material; I use it for drones and maybe a few special missile types so I use tons at a time instead of kilotons. |
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Post by ross128 on Nov 6, 2016 16:20:38 GMT
Yeah, I basically use it for micromissiles and small drones. The extra 2-3 km/s (6-7 vs 4) of exhaust velocity that a methane NTR can give you is nothing to sneeze at, so I don't really see F/H as a real alternative for heavy lifting unless you have a strong aversion to fissiles.
I only use chemical rockets in applications where ~20kg of fissiles and reactor components would be a dealbreaker. For anything over a ton or two, that extra engine weight is entirely worth the thrust and exhaust velocity an NTR will give you.
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Post by zuthal on Nov 6, 2016 17:17:42 GMT
Also, fluorine isn't really viable, I feel, for large (>5 kt or so) capships, I found, because making very high-thrust fluorine/hydrogen engines simply doesn't appear to be feasible - the blasted stuff just puts out too much heat.
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Post by docfizzix on Nov 6, 2016 22:14:20 GMT
Also, fluorine isn't really viable, I feel, for large (>5 kt or so) capships, I found, because making very high-thrust fluorine/hydrogen engines simply doesn't appear to be feasible - the blasted stuff just puts out too much heat. Cluster your engines! Also, large capships are overrated vs. stock ships IMO. If you need me to, I'll go ahead and share some o my big thruster designs. |
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Post by jageriv on Nov 6, 2016 23:16:42 GMT
So, it seems that Fluorine-Hydrogen combustion rockets are competitive with, or even possibly superior too, methane and decane NTRs even for capship usage. This of course poses a possible logistical problem: How do you get that much Fluorine? Hydrogen, methane and decane are little problem, since hydrogen and carbon are quite abundant in the solar system, but Fluorine isn't - Carbon is ~4800 times more abundant in the Solar System than Fluorine is. You dig up flourite and make flourine from it. Reserves on Earth alone are estimated at 230 million tonnes, and we have an entire solar system to mine for the stuff.Is Is that 230 million tonnes of flourite or flourine? Because it its Flourite less than half that weight is Flourine, reducing the reserves to about 100 million tons. |
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Post by apophys on Nov 7, 2016 7:17:12 GMT
The extra 2-3 km/s (6-7 vs 4) of exhaust velocity that a methane NTR can give you is nothing to sneeze at, so I don't really see F/H as a real alternative for heavy lifting unless you have a strong aversion to fissiles. For fissile aversion, decane resistojets even give a little more exhaust velocity than methane NTRs (and with nice thrust, unlike MPDs). The 1 GW limit on energy input means I can only go up to 25.8 MN of thrust with individual decane resistojets, but that'll certainly cover most uses. |
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Post by nerd1000 on Nov 7, 2016 7:32:09 GMT
You dig up flourite and make flourine from it. Reserves on Earth alone are estimated at 230 million tonnes, and we have an entire solar system to mine for the stuff. 230 MT is not very much at all. There are ship designs that use kilotons of the stuff. Would only take a few years of s couple fleets like that running around to deplete the supply, especially when you consider how much of it must be used to lift it into orbit. Good point, I wasn't thinking of people using kilotons of fluorine in a single ship. If we take into account the industrial consumption of the stuff there's probably not much left for using it as propellant. Of course from a logistics standpoint there's not much sense in using flourine as a propellant at all- it's simply too toxic, corrosive and cryogenic. Outside of edge cases (like really tiny missiles) the extra performance simply isn't enough to justify using fluorine rather than oxygen (which is very easy to come by). What might be slightly more sensible is chlorine trifluoride. While it's just as toxic and corrosive as fluorine it does have the very nice property of being a liquid at a little below room temperature, which makes storage far easier. |
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Post by RiftandRend on Dec 19, 2016 3:04:00 GMT
Chlorine trifluoride ignites almost every known material and cannot be extinguished. It is far too dangerous to use in drones, as any tank rupture would lead to the carrier being totally destroyed.
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Post by kjakker on Dec 19, 2016 4:49:37 GMT
Given the Chlorine TriFluoride mention I thought I should post this.
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