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Post by The Astronomer on Apr 11, 2017 11:13:16 GMT
Why don't you guys reduce the neutron flux?
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Post by Enderminion on Apr 11, 2017 11:22:28 GMT
mo powah, hotter engines run exhaust faster, so having the bare minmium of fuel and using neutron flux to heat it the rest of the way gets you the highest TWR
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Post by sevenperforce on Apr 17, 2017 12:50:37 GMT
A quick and dirty build with the Tantalum Hafnium Carbide pellet/liquid fissile metal design allows me to extract 5.44 km/s from plain water at 12 meganewtons while maintaining 260 TWR, while maintaining a core meltdown margin of 10k. I am using a aluminum injector and amco nozzles for safety reasons, and the CoADE simulation does not allow for composite nozzle design, so an IRL NTR could easily surpass this design. I can probably improve this, but as a proof of concept it's proven it's point. Smaller thrusters can comfortably pass 5.52 km/s, but for an SSTO design we need multi-meganewton setups. Question for you -- when you say you got a TWR of 260 (!!!), what does that entail? Is that the thrust divided by the weight of the NPBR core alone, or are you including the mass of the nozzle or turbopump assembly? Trying to get a rough idea of how heavy this would be IRL.
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Post by Enderminion on Apr 17, 2017 13:23:08 GMT
thrust divided by weight, then divide what you get till its in newtons, if on a planet its thrust divided by (weight*gravity)
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Post by sevenperforce on Apr 17, 2017 13:35:58 GMT
thrust divided by weight, then divide what you get till its in newtons, if on a planet its thrust divided by (weight*gravity) Yes, lol, I know how TWR is calculated. I was trying to figure out what weight newageofpower was using for his engine. E.g., is 260 the thrust divided by the weight of the fuel alone? The weight of the fuel and the casing and the containment cylinder? The weight of the fuel, casing, containment cylinder, turbine, and nozzle?
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Post by Enderminion on Apr 17, 2017 13:47:31 GMT
the mass listed in the engine design is the mass of the nozzle, reactor, turbopump, and gimbal
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Post by sevenperforce on Apr 17, 2017 13:54:11 GMT
the mass listed in the engine design is the mass of the nozzle, reactor, turbopump, and gimbal Damn. Hot damn...literally. That's insane. I mean, we've still got to add in the masses of shielding and associated systems, but still...that's an incredible amount of thrust. Do you know in what ways it differs from what could readily be constructed in real life?
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Post by Enderminion on Apr 17, 2017 14:16:45 GMT
safety, margin of error, boron suffers when exposed to air, lack of composite materials and variable thickness which could lead to a higher TWR, sanity checks, ummm, the launch might have a fairly large minimum safe distance and you should wait until the wind blows AWAY from anything you like otherwise they're may be fallout, I think we were talking about NTRs
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Post by newageofpower on Apr 17, 2017 16:52:38 GMT
safety, margin of error, boron suffers when exposed to air, lack of composite materials and variable thickness which could lead to a higher TWR, sanity checks, ummm, the launch might have a fairly large minimum safe distance and you should wait until the wind blows AWAY from anything you like otherwise they're may be fallout, I think we were talking about NTRs I am designing with quite a bit of margin. IIRC @deskjester passed 4,000 TWR with his Decane Nuclear Drives with his ludicrous minmax.
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Post by Enderminion on Apr 17, 2017 17:18:59 GMT
sorry I didn't know
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Post by bigbombr on Apr 17, 2017 17:19:50 GMT
safety, margin of error, boron suffers when exposed to air, lack of composite materials and variable thickness which could lead to a higher TWR, sanity checks, ummm, the launch might have a fairly large minimum safe distance and you should wait until the wind blows AWAY from anything you like otherwise they're may be fallout, I think we were talking about NTRs I am designing with quite a bit of margin. IIRC @deskjester passed 4,000 TWR with his Decane Nuclear Drives with his ludicrous minmax. If you're willing to use modded materials (graphene nozzles, 3D-graphene turbopumps, U-233 encapsulated in graphene, boron nitride encapsulated in graphene) and to go big, it's possible to reach TWR's of over 10000. (RP-1 NTR with an exhaust velocity of 6.7 km/s, a thrust of 385 MN, a mass of 3.76 t, thrust to mass ratio of 10500 G, a cost of 972 kc).
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Post by newageofpower on Apr 17, 2017 17:27:13 GMT
I am designing with quite a bit of margin. IIRC @deskjester passed 4,000 TWR with his Decane Nuclear Drives with his ludicrous minmax. If you're willing to use modded materials (graphene nozzles, 3D-graphene turbopumps, U-233 encapsulated in graphene, boron nitride encapsulated in graphene) and to go big, it's possible to reach TWR's of over 10000. (RP-1 NTR with an exhaust velocity of 6.7 km/s, a thrust of 385 MN, a mass of 3.76 t, thrust to mass ratio of 10500 G, a cost of 972 kc). Right, but we don't actually have MP mass assembly of nanomaterials, and the OP indicated we are to use a SSTO design with currently achievable technology; must have non-trivial safety margins and must be stable in atmosphere. So I used a Aluminum Injector and Amorphous Carbon nozzle/chamber, with a Tantalum Hafnia Carbide/Liquid Uranium core. We could probably use a Lithium injector (plated with PTFE) and taper the nozzle (and use regenerative cooling/boron fiber reinforcement) for significant weight savings IRL. The boron would be imbedded in the carbon, of course.
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Post by sevenperforce on Apr 17, 2017 19:54:43 GMT
safety, margin of error, boron suffers when exposed to air, lack of composite materials and variable thickness which could lead to a higher TWR, sanity checks, ummm, the launch might have a fairly large minimum safe distance and you should wait until the wind blows AWAY from anything you like otherwise they're may be fallout, I think we were talking about NTRs I am designing with quite a bit of margin. IIRC @deskjester passed 4,000 TWR with his Decane Nuclear Drives with his ludicrous minmax. In your design you said it was a 12 MN thruster but that isp would come up with a smaller thruster -- what about something in the 17 kN range? Or is that too small? I'm thinking about the minimum-size airbreathing water-prop crew shuttle...like, 7 people or so.
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Post by darthroach on Apr 19, 2017 10:25:05 GMT
This is military situation I think we all know what an actual military necessity would create... i.imgur.com/Nfnu0YL.png
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Post by RiftandRend on Apr 19, 2017 16:25:02 GMT
On this topic, I wonder how small you can make an Orion Drive.
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