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Post by dichebach on Oct 28, 2017 13:44:51 GMT
First off, it appears there was not "helium tanker" in the stock designs, and when I've created one "add refueler" does not seem to function. Secondly, I'm a bit unclear on the role that these various fuel elements play in propulsion, given the machines are all powered by nuclear reactors. ADDIT: Ah! more efficient! Nuclear thermal rocket. Interesting. So what is the actual status of this technology? Is it viable for cheaper surface to orbit costs too? Being as my physics comprehension is fairly rudimentary, I'm slightly baffled at the plethora of fuels; are there any general principles there? Like for example, it appears that the very few helium based designs yield the highest dV?
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Post by Enderminion on Oct 28, 2017 14:04:45 GMT
you have to create a helium refueler in module design IIRC, or click on one of the Helium tanks then go to the sidebar and click "Add Refueler" and select one from the drop down. your lack of rocket science shows, Helium is not fuel, it is propellant, propellant is what you shoot out the back of the space craft, fuel is what you burn to make propellant go faster. Nuclear Thermal Rockets are decent for surface to orbit launch but chemical rockets are better as you need thrust not specific impulse on launch, also people are deathly afrid of the N word and R word so no nuclear launches )-; which is a shame because the best surface to orbit launcher involes detonating a series of ~200 sub kiloton atomic bombs
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Post by The Astronomer on Oct 28, 2017 14:09:37 GMT
First off, it appears there was not "helium tanker" in the stock designs, and when I've created one "add refueler" does not seem to function. Secondly, I'm a bit unclear on the role that these various fuel elements play in propulsion, given the machines are all powered by nuclear reactors. ADDIT: Ah! more efficient! Nuclear thermal rocket. Interesting. So what is the actual status of this technology? Is it viable for cheaper surface to orbit costs too? Being as my physics comprehension is fairly rudimentary, I'm slightly baffled at the plethora of fuels; are there any general principles there? Like for example, it appears that the very few helium based designs yield the highest dV? If you don't have a helium refueler, just design one. 'Fuel' in rocketry refers to substance which produces energy to push reaction mass (remass). In case of combustion rocket, 'fuel' is the remass itself. In nuclear thermal rockets, fuel is that radioactive matter in the core you used to heat up the fuel.
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Post by dichebach on Oct 28, 2017 15:14:39 GMT
I suspect this distinction between "propellant" and "fuel" will take me about as long to comprehend as the distinction b/w mass and weight! (which did click pretty quickly to be honest) Setting that aside for the moment . . . It appears on superficial glance that the most efficient propulsion systems (in terms of endurance, how much dV you get per mass of machinery and expendable) is helium with xenon coming in second? Does that sound in the ballpark? Made it up to the Thermis to Mars mission so I was taking the time to fiddle with the ship designer a bit and see about designing a super long-range civilian ship. Wound up with a ship I called "Strider" powered by Xenon and with one sniper coil gun on the nose, but then I backed up and made a "Strider Q" version to make it feasible for the mission. Left everything else identical so I have a design that is long-distance, reasonable performance, heavily armored and can easily switch between an armed and unarmed version without any need for changes to crew facilities, radiators, etc. I figure the extra 24 crew bunks are for passengers in the civilian configuration. Holy crystallography Major Tom, the plethora of materials for armors is mind blowing! I opted for an inner layer of some time of composite referred to by an inch long acronym (UHCFHMPM or some such) which is extremely pricey and melts pretty quick but has good strength it seems. I then put an outer layer of depleted uranium, which compensates for the low melting point of the composite stuff. Well, off to build a fence
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Post by Enderminion on Oct 28, 2017 15:22:26 GMT
UHMWPE, its plastic, like shopping bag plastic, just like 10x longer. Depeleted Uranium is more expensive, less dense, and weaker then Osmium. IIRC Neon is the best propellant for Magnetoplasmadynamic (MPD) thrusters, Hydrogen Duetruide is good for MPDs as well, for Resistojets anything works, Hydrogen and Hydrogen Dueturide are good for Ev and RP-1 can get you lots of thrust. for NTR use it's Hydrogen and Hydrogen Dueturide or RP-1 for Ev or thrust. most materials are pointless, there is a short list of laser armour, kinetic armour, propellant tanks, nuclear materials, propellant, explosives, armor, etc.
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Post by newageofpower on Oct 28, 2017 15:22:52 GMT
Generally speaking, Hydrogen offers the highest dV, but the lowest thrust and lowest storability. We'll ignore cost for now.
Most fuels fall onto this line of thrust & volumetric density vs maximal dV.
Given that CDE nuclear rockets can dump almost all their waste heat into the exhaust plume, we can overcome low thrust (in nuclear rockets, that is) by simultaneously adding more nuclear fuel to the core and increasing fuel-flow rate, it's recommended you optimize around dV & storability; especially for military vessels.
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Post by Enderminion on Oct 28, 2017 15:26:33 GMT
Generally speaking, Hydrogen offers the highest dV, but the lowest thrust and lowest storability. We'll ignore cost for now. Most fuels fall onto this line of thrust & volumetric density vs maximal dV. Given that CDE nuclear rockets can dump almost all their waste heat into the exhaust plume, we can overcome low thrust (in nuclear rockets, that is) by simultaneously adding more nuclear fuel to the core and increasing fuel-flow rate, it's recommended you optimize around dV & storability; especially for military vessels. we only use one fuel here, U-233 Dioxide
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Post by treptoplax on Oct 28, 2017 15:43:46 GMT
I suspect this distinction between "propellant" and "fuel" will take me about as long to comprehend as the distinction b/w mass and weight! (which did click pretty quickly to be honest) Setting that aside for the moment . . . It appears on superficial glance that the most efficient propulsion systems (in terms of endurance, how much dV you get per mass of machinery and expendable) is helium with xenon coming in second? Does that sound in the ballpark? Made it up to the Thermis to Mars mission so I was taking the time to fiddle with the ship designer a bit and see about designing a super long-range civilian ship. Wound up with a ship I called "Strider" powered by Xenon and with one sniper coil gun on the nose, but then I backed up and made a "Strider Q" version to make it feasible for the mission. Left everything else identical so I have a design that is long-distance, reasonable performance, heavily armored and can easily switch between an armed and unarmed version without any need for changes to crew facilities, radiators, etc. I figure the extra 24 crew bunks are for passengers in the civilian configuration. Holy crystallography Major Tom, the plethora of materials for armors is mind blowing! I opted for an inner layer of some time of composite referred to by an inch long acronym (UHCFHMPM or some such) which is extremely pricey and melts pretty quick but has good strength it seems. I then put an outer layer of depleted uranium, which compensates for the low melting point of the composite stuff. Well, off to build a fence Sounds like pretty reasonable armor; there are some good threads on that you can find here (and of course many people who doubt the utility of armor at all, but that's another discussion...). A gap of a few tens of centimeters (maybe a meter?) between that uranium and UHMWPE (ultra high molecular weight polyethylene) will help, allowing ultra-high-speed projectiles broken up by the uranium to disperse before hitting the inner armor. You could fill the gap with something really light (one of the aerogels) if you like. For budget-conscious craft right now I'm using a thin layer of tin (dense, cheap, soft! - the spalling from breaking it can't easily penetrate the inner layers), half-a-meter or more of graphite aerogel (cheap, light, heat-resistant), and then a thin layer of amorphous carbon (hard, heat resistant) backed by silk (! - cheap, light, strong). Different attacks are best stopped by very different sorts of armor. Large low-speed (less than 4 Km/s?) projectiles, you just want lots of something hard (steel, some kind of carbon lattice - diamond, amorphous carbon, reinforced carbon-carbon), backed by something with high tensile strength if you're feeling fancy, ideally at a high slope angle relative to the shooter. High speed projectiles that works but not nearly as well; you want a layer about as thick as the projectile of something dense and soft, then a gap, then something to catch the cone of plasma and high-speed fragments resulting from the outer impact. Nuke flash I think you mostly want a thin layer of something temperature resistant - ceramics, carbon-based stuff. Lasers are odd; you can go, again, with high-temperature stuff, but also consider the aerogels (I think their semi-opaqueness and huge surface area makes them hard to melt??), or certain organic polymers that take huge amounts of energy to ablate (PTFE and nitrile rubber are both bizarrely effective against lasers). YMMV, void where prohibited.
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Post by treptoplax on Oct 28, 2017 16:16:14 GMT
First off, it appears there was not "helium tanker" in the stock designs, and when I've created one "add refueler" does not seem to function. Secondly, I'm a bit unclear on the role that these various fuel elements play in propulsion, given the machines are all powered by nuclear reactors. ADDIT: Ah! more efficient! Nuclear thermal rocket. Interesting. So what is the actual status of this technology? Is it viable for cheaper surface to orbit costs too? Being as my physics comprehension is fairly rudimentary, I'm slightly baffled at the plethora of fuels; are there any general principles there? Like for example, it appears that the very few helium based designs yield the highest dV? So, here's my 5c: From the point of view of a spaceship designer, there are really only two engine metrics you care about. One is exhaust velocity; how fast you throw the reaction mass out the back. Total delta-V (acceleration) is proportional to this, so it's a big win to increase it. (But be aware of the weight of fuel *tanks*). One is thrust/weight ratio; how massive is the engine itself compared to the thrust it generates? Unfortunately, these tend to work against each other. Increasing exhaust velocity requires lots of power, which increases weight. Pumping more mass at the same power increases thrust but decreases exhaust velocity. A key note on all thermal engines (that spray hot gasses out the back): speed of gas molecules is proportional to their temperature, and inversely proportional to their mass. At somewhere around 4000-5000C, just about any engine you can build will start to melt, at least if any appreciable amount of mass is going through it. Chemical engines get their power by heating chemicals with a chemical reaction, then shooting it out the back. You want an energetic reaction with really light products - HF is the best you can do. Of course, HF may actually be too hot for large engines (more prone to overheating than small ones), and H and F are both really bulky, so if you're armoring those tanks, maybe you want to try a hydrocarbon instead? It depends. Nuclear thermal engines heat up something by pumping it through a nuclear reactor (!) and shoot it out the back; you can get it as hot are your reactor and engine bell will stand without melting. Hydrogen is lightest, so it'll go fastest at that temperature (or maybe a hydrogen-deuterium mix for reasons I don't quite understand - it's less likely to reform h2 molecules I think??). But then again, it's buiky; at those temperatures most hydrocarbons, or water, will fly apart into individual atoms anyway, although many will be carbon, which is heavier, so... Resistojets work a lot like a NTR and use the same sorts of reaction mass, but use an electrical heating coil to heat the propellent; because your heating system doesn't also have to work as a nuclear reactor they may be able to get marginally hotter than a NTR, and they can be more compact (powered by a reactor elsewhere on the ship), but they're less energy-efficient (you have to convert to electricity and then back to heat, so you need to pair them with a reactor much bigger than a comparable NTR would be). MPDs are different; they use electrical fields to accelerate gas molecules. This works better with heavier atoms, but uses enormous amounts of power. My advice, FWIW: chemical engines (probably HF) is for small drones/missiles, or maybe larger craft where cost is the main concern. If you want a fast warship, NTR is the easy choice. MPDs give enormous range, even for interplanetary maneuvers, but are very limited in combat maneuvering. Resistojets are mostly useful as maneuvering thrusters (for helping large craft turn quickly) or as a secondary combat propulsion system on a ship where the main engines are MPD.
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Post by The Astronomer on Oct 28, 2017 16:19:24 GMT
So, here's my 5c: From the point of view of a spaceship designer, there are really only two engine metrics you care about. One is exhaust velocity; how fast you throw the reaction mass out the back. Total delta-V (acceleration) is proportional to this, so it's a big win to increase it. (But be aware of the weight of fuel *tanks*). One is thrust/weight ratio; how massive is the engine itself compared to the thrust it generates? Unfortunately, these tend to work against each other.Of course, because the thrust power (which should be less than input power) is (thrust*exhaust velocity)/2. If you want to increase exhaust velocity while keeping the thrust power the same, you must trade thrust for that (as seen in MPDs), and vice versa. The only way to increase both value is to increase the thrust power.
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Post by Rocket Witch on Oct 28, 2017 16:54:51 GMT
most materials are pointless Hydrogen is lightest, so it'll go fastest at that temperature (or maybe a hydrogen-deuterium mix for reasons I don't quite understand - it's less likely to reform h2 molecules I think??). Q discussed this on the blog. In fact that might be a good place for dichebach to start: childrenofadeadearth.wordpress.com/But H2 being cheaper than HD hasn't held up in any release version of the game, due to H2 boiloff being factored into the cost (I think), so HD is both better and cheaper, except I think in MPD engines.
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Post by Enderminion on Oct 28, 2017 17:19:36 GMT
most materials are pointless wtf are you gonna use Iron or Titanium for when Steel (any type) and Beta Titanium are superior? U-235? Plutonium in general? RCC? Boron? Gadolinium? UHMWPE? etc.
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Post by The Astronomer on Oct 28, 2017 17:25:20 GMT
wtf are you gonna use Iron or Titanium for when Steel (any type) and Beta Titanium are superior? U-235? Plutonium in general? RCC? Boron? Gadolinium? UHMWPE? etc. You know, Rocket Witch is the material forger of the Children of a Dead Earth community. If you talk trash of the myriads of the materials out there, they'll be the first person to deliver a punch in your virtual face.
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Post by Kerr on Oct 28, 2017 17:41:21 GMT
wtf are you gonna use Iron or Titanium for when Steel (any type) and Beta Titanium are superior? U-235? Plutonium in general? RCC? Boron? Gadolinium? UHMWPE? etc. Don't wrong the material god/ess Rocket Witch! Or you shall suffer an fate worse than Boron the Almighty!
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Post by RiftandRend on Oct 28, 2017 18:58:08 GMT
wtf are you gonna use Iron or Titanium for when Steel (any type) and Beta Titanium are superior? U-235? Plutonium in general? RCC? Boron? Gadolinium? UHMWPE? etc. I imagine most of the materials are going to be pointless to you if you still don't care about cost. Titanium is good for reaction wheels and pumps. Iron has applications for reaction wheels and chemical gun projectiles. Most of the steels are very cost ineffective, along with Beta Titanium. U-235 and Plutonium are admittedly novelties, along with RCC and Boron (rip). Gadolinium can be used for lightweight forcers in launchers. Most materials have some situation where they outperform everything else. These situations may be incredibly niche, but they do exist.
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