elukka
Junior Member
Posts: 73 
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Post by elukka on Apr 3, 2017 11:23:11 GMT
Imagine the amount of coolant required to carry away terawatts or petawatts of heat and the square kilometers of radiators it would take ... if your chamber somehow manages to survive. Usually these concepts rely on some way to prevent most of the heat from reaching the ship in the first place. You can have the reaction happen some distance away from the ship (such as with an Orion drive) or you can use an open magnetic nozzle. One idea I like is a magnetic nozzle where the magnet loop is protected by a circular blade facing the reaction, very sharp at the tip and extending at about 3 degrees from there to the magnet loop. The idea is that at that angle the blade will reflect most x-rays. You let like 99% of the heat fly directly to space, but you still have copious amounts of waste heat to deal with. But it does make it more feasible. A point about Orion: Though it doesn't have serious issues with heat, it still has the same fundamental issue of coupling a very high energy reaction to the ship in a constructive manner. It's just not in the form of radiation, but kinetic energy. If the propellant hitting the pusher comes in too fast with too much energy you will no longer have a pusher plate. This is actually what limits the performance of the Orion, and why there's such a huge gulf between practical designs and the theoretical maximum. Available energy is not the issue - you can scale the yield of the nukes almost arbitrarily high - having the ship survive it is. |
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Post by nerd1000 on Apr 3, 2017 11:28:40 GMT
No, I arbitrarily chose 10,000K because I couldn't find a source for p-B11 fusion temperature (in fact it seems that p-B11 cannot sustain a fusion reaction by sheer heat, as the plasma will lose more energy as X-rays due to Bremsstrahlung than the reaction itself produces). I calculated the 'heat of formation' of the fuel by converting the fusion energy (8.7 MeV) to joules and multiplying that by avogadro's number to get the energy per mole of reactant fused. I think the biggest flaw with this 'hackjob' fusion torch is that it assumes all fusion fuel is consumed. In practice it seems unlikely that any reactor could get all of the fuel to fuse before it's ejected through the nozzle, so the possible power output and exhaust velocity should be much lower than we can achieve with this. I see (again  )~ BTW is it possible to make NSWR? Although i don't think it is likely to produce because it produce neutron... NSWR might be possible if we make some (very bad) assumptions, e.g. all neutron energy is lost to space and doesn't heat the propellant. Might be able to fudge the material definitions to simulate less than 100% fission rate and so forth. |
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Post by gedzilla on Apr 3, 2017 12:02:02 GMT
Imagine the amount of coolant required to carry away terawatts or petawatts of heat and the square kilometers of radiators it would take ... if your chamber somehow manages to survive. Usually these concepts rely on some way to prevent most of the heat from reaching the ship in the first place. You can have the reaction happen some distance away from the ship (such as with an Orion drive) or you can use an open magnetic nozzle. One idea I like is a magnetic nozzle where the magnet loop is protected by a circular blade facing the reaction, very sharp at the tip and extending at about 3 degrees from there to the magnet loop. The idea is that at that angle the blade will reflect most x-rays. You let like 99% of the heat fly directly to space, but you still have copious amounts of waste heat to deal with. But it does make it more feasible. A point about Orion: Though it doesn't have serious issues with heat, it still has the same fundamental issue of coupling a very high energy reaction to the ship in a constructive manner. It's just not in the form of radiation, but kinetic energy. If the propellant hitting the pusher comes in too fast with too much energy you will no longer have a pusher plate. This is actually what limits the performance of the Orion, and why there's such a huge gulf between practical designs and the theoretical maximum. Available energy is not the issue - you can scale the yield of the nukes almost arbitrarily high - having the ship survive it is. about Orion, i thought that having the ship survive wasn't actually that big of a challenge. after all, if the nuke is very powerful, just let it detonate further away, the energy drops off as a cube function i think. the challenge was in finding the tiny window of just right, between destruction, and total inefficiency. |
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elukka
Junior Member
Posts: 73
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Post by elukka on Apr 3, 2017 12:23:51 GMT
The radiation from the nuke drops off quickly (which is why it's not a big issue, also the propellant shields the ship) but the kinetic energy imparted on the pusher plate by the cone of propellant plasma doesn't, and that's what you use to propel the ship. You can easily impart more kinetic energy on the propellant by using a higher yield nuke but there are limits to what the pusher plate can survive. It shouldn't be an issue at the performance level they considered, but that was the factor that set its performance at that level in the first place. You could theoretically get much higher performance out of it but having the pusher plate survive is what constrains it.
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Post by gedzilla on Apr 3, 2017 12:59:39 GMT
The radiation from the nuke drops off quickly (which is why it's not a big issue, also the propellant shields the ship) but the kinetic energy imparted on the pusher plate by the cone of propellant plasma doesn't, sure it does. the propellant material (the vaporized plasma of the nuke and its casing) also drops of in a cube, same as any exploding (in a sphere) thing. if you detonate the nuke 10m away, you will get hit by a certain percentage of the vapor, but if you are 30m away, you will get hit by a smaller percentage of that stuff, since you occupy a smaller percent of the nukes "View". Also, I've heard that the Orion Drive has an amazing mass to push ratio (tiny Nuke mass Releasing an enormous amount of energy), so you need less mass for the propellant, and can easily afford to make that plate out of a really dense, strong material like Boron or VCS) |
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Post by nerd1000 on Apr 3, 2017 13:09:32 GMT
The radiation from the nuke drops off quickly (which is why it's not a big issue, also the propellant shields the ship) but the kinetic energy imparted on the pusher plate by the cone of propellant plasma doesn't, and that's what you use to propel the ship. You can easily impart more kinetic energy on the propellant by using a higher yield nuke but there are limits to what the pusher plate can survive. It shouldn't be an issue at the performance level they considered, but that was the factor that set its performance at that level in the first place. You could theoretically get much higher performance out of it but having the pusher plate survive is what constrains it. Hence the 'Medusa' design which uses a gigantic parachute on the end of a long tether as the pusher plate. The energy is spread across a much wider area, and the shock absorber stroke is much longer. |
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elukka
Junior Member
Posts: 73
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Post by elukka on Apr 3, 2017 13:38:12 GMT
Yeah, Medusa handily takes care of maximum power density issues by having a surface area as big as you like. I imagine there's still some limit of propellant velocity until the sail material can't survive it, and I'd be really curious to know what that might be. Also, I'm sorry, I meant to just make a general observation about high power rockets, not derail the thread into Orion talk. The radiation from the nuke drops off quickly (which is why it's not a big issue, also the propellant shields the ship) but the kinetic energy imparted on the pusher plate by the cone of propellant plasma doesn't, sure it does. the propellant material (the vaporized plasma of the nuke and its casing) also drops of in a cube, same as any exploding (in a sphere) thing. if you detonate the nuke 10m away, you will get hit by a certain percentage of the vapor, but if you are 30m away, you will get hit by a smaller percentage of that stuff, since you occupy a smaller percent of the nukes "View". Also, I've heard that the Orion Drive has an amazing mass to push ratio (tiny Nuke mass Releasing an enormous amount of energy), so you need less mass for the propellant, and can easily afford to make that plate out of a really dense, strong material like Boron or VCS) Well yes, but you design it so that you intercept the maximum possible amount of the propellant. If it doesn't hit your ship it's wasted and it doesn't contribute to your thrust power at all, not exactly a solution for avoiding pusher damage. You'd rather have less propellant in the first place. |
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Post by Enderminion on Apr 3, 2017 14:14:15 GMT
I would not want to be anywhere downrange of those rockets...
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Post by gedzilla on Apr 3, 2017 14:38:58 GMT
Yeah, Medusa handily takes care of maximum power density issues by having a surface area as big as you like. I imagine there's still some limit of propellant velocity until the sail material can't survive it, and I'd be really curious to know what that might be. Also, I'm sorry, I meant to just make a general observation about high power rockets, not derail the thread into Orion talk. sure it does. the propellant material (the vaporized plasma of the nuke and its casing) also drops of in a cube, same as any exploding (in a sphere) thing. if you detonate the nuke 10m away, you will get hit by a certain percentage of the vapor, but if you are 30m away, you will get hit by a smaller percentage of that stuff, since you occupy a smaller percent of the nukes "View". Also, I've heard that the Orion Drive has an amazing mass to push ratio (tiny Nuke mass Releasing an enormous amount of energy), so you need less mass for the propellant, and can easily afford to make that plate out of a really dense, strong material like Boron or VCS) Well yes, but you design it so that you intercept the maximum possible amount of the propellant. If it doesn't hit your ship it's wasted and it doesn't contribute to your thrust power at all, not exactly a solution for avoiding pusher damage. You'd rather have less propellant in the first place. I guess we are talking about different Orion pusher plate shapes. You seem to be envisioning a sort of like nozzle shaped pushers plate where you are obsorbing more of the plasma than not. what I was envisioning was more like a flat disk, and less like a Bowl (which when it sorrounds the nuke occupys a large part of its "view"). The disk might only be hit by a far smaller percent of the plasma, but that Would still yield a decent push and Efficiency. Look for the "Deep Space Force - Orion Drive Warship Combat Video" thread. Its on the second page of General Discussion |
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Post by RiftandRend on Apr 3, 2017 21:16:06 GMT
Bit of refining, the auto ignition temperature should be about 1,320,000,000 K. That's supposedly the optimal pressure limited temperature. Alternatively, 6,600,000,000 K is the optimal temperature for reaction rate. The activation energy should be about 239262804 KJ per mol. That's the amount of energy required to heat 1 mol of the p-B mixture to 1,320,000,000 K. It is not possible to achieve the ideal reaction rate temperature with only energy from the fuel. For a more accurate simulation one could calculate the required energy for the reaction rate in their engine and then create a blackbox module that would be active at the same time to consume the required energy. For example, This engine would need 5.114 TW of external power to fuse the 258 g/s fuel flow rate. This all assumes 100% efficiency so a more realistic assumption would be 10.228 TW at 50%. Additional power would be required to operate the magnetic nozzle, loosely represented by regenerative cooling. The power requirements of the nozzle are probably related to the thrust power. If someone can come up with a vague estimate of this I would appreciate it. |
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Post by nerd1000 on Apr 4, 2017 2:29:49 GMT
Good Stuff. The Zubrin NSWR was also requested, so I had a crack at that one too. Material Zubrol
Elements H O U-235 U-238 Br
ElementCount 2 1 0.004 0.016 0.08
Density_kg__m3 1100
EnthalpyOfFormation_kJ__mol 102102
BondDissociationEnergy_kJ__mol 927.01
GibbsFreeEnergyOfFormation_kJ__mol -237.14
BulkModulus_GPa 2.151
MeltingPoint_K 273
BoilingPoint_K 373
ThermalConductivity_W__m_K .609
SpecificHeat_J__kg_K 4183.95
Viscosity_Pa_s 1.0016e-3
Resistivity_Ohm_m 1.8e5
DielectricStrength_MV__m 65
RelativePermittivity 80.1
RelativePermeability .999992
RefractiveIndex Water
Dissociation
Products Monatomic Hydrogen Monatomic Oxygen
ProductCounts 2 1
Material Depleted Zubrol
Elements H O U-235 U-238 Br
ElementCount 2 1 0.00399 0.016 0.08
Density_kg__m3 1100
EnthalpyOfFormation_kJ__mol 0
BondDissociationEnergy_kJ__mol 927.01
GibbsFreeEnergyOfFormation_kJ__mol -237.14
BulkModulus_GPa 2.151
MeltingPoint_K 273
BoilingPoint_K 373
ThermalConductivity_W__m_K .609
SpecificHeat_J__kg_K 4183.95
Viscosity_Pa_s 1.0016e-3
Resistivity_Ohm_m 1.8e5
DielectricStrength_MV__m 65
RelativePermittivity 80.1
RelativePermeability .999992
RefractiveIndex Water
Dissociation
Products Monatomic Hydrogen Monatomic Oxygen
ProductCounts 2 1
I decided to call the fuel 'Zubrol' because it sounded appropriately corporate. Properties are based on the 'example' NSWR described on Atomic Rockets, which assumes an 0.1% fission rate from a 2% aqueous solution of 20% enriched Uranium Tetrabromide, for an specific energy of 3.4 GJ/kg. This config gives 3.5GJ/Kg, which IMO is close enough. ChemicalReaction Zubrin NSWR
Reactants Zubrol
ReactantCounts 1
Products Depleted Zubrol
ProductCounts 1
ActivationEnergy_kJ__mol 0.01
AutoignitionTemperature_K 273
CharacteristicLength_m 0.65
Here's the reaction. And here's an example fuel tank, engine and ship.    What you might have noticed is that the NSWR ship is very expensive (and very light) compared to its NTR counterpart. That's because its fuel/propellant contains a lot of fissiles. The Delta-V is excellent though, and this engine is overall far more believable than the Fusion Torch drive. Another thing to take note of is that because Zubrol is a monopropellant the game correctly classifies it as being explosive. Its energy content is an order of magnitude higher than that of any chemical monopropellant in the game, so I'd advise that you don't let the enemy shoot your fuel tanks- the consequences will be akin to a large nuclear bomb detonating inside your hull. The exhaust velocity came out a lot lower than Atomic Rockets predicted- I suspect that this is because our nozzles are much less efficient than he assumed due to inadequate expansion ratio (even 1000:1 doesn't get the exhaust below 20,000K). |
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Post by RiftandRend on Apr 4, 2017 3:06:55 GMT
It should be noted that the NSWR ship has 2 orders of magnitude higher heat output than the NTR ship. Also, do you think a fission fragment rocket is possible using similar methods?
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Post by Enderminion on Apr 4, 2017 3:08:50 GMT
It should be noted that the NSWR ship has 2 orders of magnitude higher than the NTR ship. Also, do you think a fission fragment rocket is possible using similar methods? higher what? |
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Post by RiftandRend on Apr 4, 2017 3:13:03 GMT
It should be noted that the NSWR ship has 2 orders of magnitude higher than the NTR ship. Also, do you think a fission fragment rocket is possible using similar methods? higher what? Heat output. Whoops. |
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elukka
Junior Member
Posts: 73
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Post by elukka on Apr 4, 2017 3:40:54 GMT
I figure the amount of heat emissions realistically wouldn't really matter. For any reasonable warship drive, even a chemical rocket, it's going to be plenty high enough to detect and seek on, and I'm pretty sure any missile seeker not built in the 60's could trivially choose from any target it sees so it wouldn't draw any more missiles than any other ship. (you'd select the targets based on tactical concerns, not which ship generates the most heat) Of course, as it is now in the game it does matter and that would probably be a heck of a missile magnet. I guess we are talking about different Orion pusher plate shapes. You seem to be envisioning a sort of like nozzle shaped pushers plate where you are obsorbing more of the plasma than not. what I was envisioning was more like a flat disk, and less like a Bowl (which when it sorrounds the nuke occupys a large part of its "view"). The disk might only be hit by a far smaller percent of the plasma, but that Would still yield a decent push and Efficiency. Look for the "Deep Space Force - Orion Drive Warship Combat Video" thread. Its on the second page of General Discussion Any propellant not intercepted by the pusher is just a loss in efficiency (and thus effective exhaust velocity). I was talking about ways to increase the velocity and the energy of the propellant without wrecking the pusher, and, well, having the propellant miss the pusher is not a solution. |
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)~ BTW is it possible to make 
