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Post by subunit on Nov 1, 2016 18:02:21 GMT
In the bipropellant recommended reading entry, it states that bipropellant chemical mixes are superior to monopropellants because one can get more chemical energy out of a bipropellant than a monopropellant. I found this confusing. I don't really know anything about inorganic chemistry or rocket propellants, but my understanding is that generally reaction energies are dependent on bond strengths between atoms in the fuel molecules. Since a bipropellant mix necessarily contains dissimilar molecules, naively reasoning about this seems to indicate that a monopropellant tank of the higher-energy bipropellant component would have more potential chemical energy than the bipropellant mix itself. Can someone tell me what I'm missing here?
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Post by captinjoehenry on Nov 1, 2016 18:31:44 GMT
In the bipropellant recommended reading entry, it states that bipropellant chemical mixes are superior to monopropellants because one can get more chemical energy out of a bipropellant than a monopropellant. I found this confusing. I don't really know anything about inorganic chemistry or rocket propellants, but my understanding is that generally reaction energies are dependent on bond strengths between atoms in the fuel molecules. Since a bipropellant mix necessarily contains dissimilar molecules, naively reasoning about this seems to indicate that a monopropellant tank of the higher-energy bipropellant component would have more potential chemical energy than the bipropellant mix itself. Can someone tell me what I'm missing here? It is the chemical reaction between the two propellants that release the energy. Such as oxidation and fire. Or all explosives when they are detonated undergo a very exothermic and high energy reaction with the oxidiser. Normal that is the oxygen in the atmosphere. Same thing with combustion engines and jets. In space you do not have any oxygen so you bring an oxidizer along. Therefore giving you bipropellant. A fuel and oxidiser. Which is the primary reaction that powers the world these days. I don't have the chemical equation but that is my best shot at explaining why it works without going into the chemistry.
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Post by ross128 on Nov 1, 2016 18:43:13 GMT
Essentially, fun with electronegatives. Monopropellant reactions generally work by taking an unstable molecule, like hydrogen peroxide, and decomposing it into its more stable components (oxygen and water, in this case). The change in energy of decomposition reactions is generally fairly small, because you're taking a molecule that has already formed bonds and breaking it into some slightly more stable molecules.
Most bipropellant fuels are oxygen plus another reactant, though some of the more energetic ones use fluorine as an oxidizer. Oxygen and fluorine are both very electronegative, which means they like to steal electrons from other atoms to form bonds. So if you can find them something that has a weak hold on its electrons, like hydrogen, they can react to form very stable molecules (like water) and release a ton of energy in the process. Because they can only release energy by forming those bonds, the energy is all locked up unless you mix both propellants together.
So why don't you have both propellants already mixed in the same tank? Well, oxygen and fluorine REALLY like stealing electrons, especially fluorine. And your reactant will have a really weak hold on its electrons, you picked it like that to get lots of energy. Which means that as soon as they mix, they're likely to start reacting whether you want them to or not. So you have to keep them separated, and only mix the amount that you want to be exploding at the moment.
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Post by subunit on Nov 1, 2016 18:44:09 GMT
In the bipropellant recommended reading entry, it states that bipropellant chemical mixes are superior to monopropellants because one can get more chemical energy out of a bipropellant than a monopropellant. I found this confusing. I don't really know anything about inorganic chemistry or rocket propellants, but my understanding is that generally reaction energies are dependent on bond strengths between atoms in the fuel molecules. Since a bipropellant mix necessarily contains dissimilar molecules, naively reasoning about this seems to indicate that a monopropellant tank of the higher-energy bipropellant component would have more potential chemical energy than the bipropellant mix itself. Can someone tell me what I'm missing here? It is the chemical reaction between the two propellants that release the energy. Such as oxidation and fire. Or all explosives when they are detonated undergo a very exothermic and high energy reaction with the oxidiser. Normal that is the oxygen in the atmosphere. Same thing with combustion engines and jets. In space you do not have any oxygen so you bring an oxidizer along. Therefore giving you bipropellant. A fuel and oxidiser. Which is the primary reaction that powers the world these days. I don't have the chemical equation but that is my best shot at explaining why it works without going into the chemistry. Now I'm confused- oxidizer is not propellant, is it? If so, then why describe "monopropellants" at all, since they're unusable?
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Post by subunit on Nov 1, 2016 18:46:52 GMT
Essentially, fun with electronegatives. Monopropellant reactions generally work by taking an unstable molecule, like hydrogen peroxide, and decomposing it into its more stable components (oxygen and water, in this case). The change in energy of decomposition reactions is generally fairly small, because you're taking a molecule that has already formed bonds and breaking it into some slightly more stable molecules. Most bipropellant fuels are oxygen plus another reactant, though some of the more energetic ones use fluorine as an oxidizer. Oxygen and fluorine are both very electronegative, which means they like to steal electrons from other atoms to form bonds. So if you can find them something that has a weak hold on its electrons, like hydrogen, they can react to form very stable molecules (like water) and release a ton of energy in the process. Because they can only release energy by forming those bonds, the energy is all locked up unless you mix both propellants together. So why don't you have both propellants already mixed in the same tank? Well, oxygen and fluorine REALLY like stealing electrons, especially fluorine. And your reactant will have a really weak hold on its electrons, you picked it like that to get lots of energy. Which means that as soon as they mix, they're likely to start reacting whether you want them to or not. So you have to keep them separated, and only mix the amount that you want to be exploding at the moment. Ah, gotcha. I think I was thinking that bipropellants are decomposed in the same way as monopropellants. Thanks! e: it occurs to me that the RR entry I'm referring to would be more easily comprehensible if it simply mentioned that monopropellant reactions are generally lower-energy decomposition reactions and bipropellant reactions are normally higher-energy oxidations rather than indicating that the chemical energy of the propellants themselves differ
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Post by ross128 on Nov 1, 2016 18:55:41 GMT
I suppose if you wanted to be really crazy, you could use dioxygen difluoride (charmingly known as FOOF) as your oxidizer. The FOOF itself would rapidly decompose into oxygen and fluorine as soon as it got above -160C, and would also also violently oxidize whatever else you put in the reaction chamber, so you'd get a strong decomposition immediately followed by a violent redox reaction. I don't know whether it would technically count as a bipropellant or a tripropellant though.
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Post by captinjoehenry on Nov 1, 2016 19:01:23 GMT
It is the chemical reaction between the two propellants that release the energy. Such as oxidation and fire. Or all explosives when they are detonated undergo a very exothermic and high energy reaction with the oxidiser. Normal that is the oxygen in the atmosphere. Same thing with combustion engines and jets. In space you do not have any oxygen so you bring an oxidizer along. Therefore giving you bipropellant. A fuel and oxidiser. Which is the primary reaction that powers the world these days. I don't have the chemical equation but that is my best shot at explaining why it works without going into the chemistry. Now I'm confused- oxidizer is not propellant, is it? If so, then why describe "monopropellants" at all, since they're unusable? Ah rocket terminology. In a chemical rocket you have reaction mass which is the stuff that is thrown out the back and then you have fuel. For chemical rockets they are the same thing. Nuclear rockets the nuclear rods are the fuel that heat up and expel the reaction mass which can be pretty much anything. Bipropellant engines almost always has an oxidizer and something else. They are mixed together in an oxidation reaction releasing lots of energy and throws the products of the reaction out of the rocket nozzle at fairly decent velocities. One thing I am not sure I have the totally correct names for the things but I definitely described them correctly
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Post by subunit on Nov 1, 2016 19:19:13 GMT
Now I'm confused- oxidizer is not propellant, is it? If so, then why describe "monopropellants" at all, since they're unusable? Ah rocket terminology. In a chemical rocket you have reaction mass which is the stuff that is thrown out the back and then you have fuel. For chemical rockets they are the same thing. Nuclear rockets the nuclear rods are the fuel that heat up and expel the reaction mass which can be pretty much anything. Bipropellant engines almost always has an oxidizer and something else. They are mixed together in an oxidation reaction releasing lots of energy and throws the products of the reaction out of the rocket nozzle at fairly decent velocities. One thing I am not sure I have the totally correct names for the things but I definitely described them correctly Yeah, sorry, it sometimes takes me a couple of people telling me similar things in different ways to understand Is anything like this simulated in-game? I haven't got to rocket design yet so I don't really know how deep the propellant simulation is.
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Post by RA2lover on Nov 2, 2016 3:06:54 GMT
As of now, you don't have FOOF as an oxidizer ingame. Theoretically, you can add its chemical properties and reactions by editing the game's data through text files, assuming you've somehow managed to actually get your measuring equipment to resist the damn thing in real life long enough to get data on them.
In any case, monopropellants are used due to density and simplicity. They're denser than most bipropellants(not that big of a concern in space as you don't have to deal with drag, though hydrogen still isn't very viable for combat craft because it needs so much space for tankage it's nigh impossible to armor), and don't need complicated injection/ignition equipment to start them(hypergolics still need proper mixing despite spontaneously reacting when in contact with eachother, while more stable bipropellants tend to require an ignition source). The latter isn't represented in COADE as the game assumes you've got proper mixing and ignition systems for your thrusters already. On the other side, they're unstable and tend to have their tanks explode if provoked(say, by a high velocity projectile which managed to penetrate the tank) and are not very energetic(which limits the engine's exhaust velocity).
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Post by Rocket Witch on Nov 3, 2016 17:38:08 GMT
I suppose if you wanted to be really crazy, you could use dioxygen difluoride (charmingly known as FOOF) as your oxidizer. The FOOF itself would rapidly decompose into oxygen and fluorine as soon as it got above -160C, and would also also violently oxidize whatever else you put in the reaction chamber, so you'd get a strong decomposition immediately followed by a violent redox reaction. I don't know whether it would technically count as a bipropellant or a tripropellant though. What if... FOOF+LH2+Li tripropellant. Is that now a quadpropellant (and engine exploding with the force of a thousand suns)?
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