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Post by rgmadsimon on Jan 26, 2024 0:54:56 GMT
Real life NERVA had a TWR of 1.4 (just engine, no propellant) and a NERVA ship would never make it to orbit on its own power.
But NTRs in the game have a TWR comparable to chemical rockets (The 9.1 Km/s Hydogen deuteride one has a TWR of 28, others range from 10 to 65 (!) ).
You can design a civilian ship in COADE that would reach orbit (10+ Km/s dv) taking off with a TWR of like 1.3 (thin alumin armor, no weapons). That's nuts.
Is the game getting ahead of reality or is NERVA just old, unnecessarily heavy junk?
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Post by kerikbalm on Jan 29, 2024 19:20:59 GMT
en.m.wikipedia.org/wiki/Project_TimberwindNerva was the first and only NTR ever built (not flown). Like a lot of first generation technology, there was a lot of room for improvement. The timberwind project expected to be able to achieve a 30:1 TWR with a 9.8 km/sec exhaust velocity - so the NTRs in this game seen fine to me. Actually, a bit underpowered, because I can't make a molten core NTR, where the molten uranium is encased in a tantalum halfnium carbide shell, so it still acts like a solid core NTR, except for a much higher melting point. You can sort of get this in game using a tantalum halfnium carbide (or just tantalum, or just tungsten, I forget what works) heating element in a resisto-jet Except now you have the inefficiency of the thermocouple, and all the excess mass of the radiators for the reactor that powers the resistojet
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Post by rgmadsimon on Jan 30, 2024 20:29:52 GMT
Cool find!
All those silly youtubers never mentioned this additional development. Good to know.
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Post by kerikbalm on Feb 2, 2024 19:45:27 GMT
Keep in mind that Nerva was actually built and tested, Timberwind never left the drawing board.
Who knows if they could have actually achieved th design specifications - but at least they thought such performance was reasonable and could be achieved
Fyi, I managed to make a small methane NTR (for mini missiles) that had a 270:1 TWR, in that case, I think the game's equations were deviating quite far from reasonable, but I don't know
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Post by 20crewmodule on Apr 8, 2024 7:04:22 GMT
However,although 10kmps deltaV with TWR 1.3 sounds somehow "realistic" in CDE, It's still impossible in real world.
The problem is not engine dead mass, but massive cyrogenic containers. CDE hasn't simulated thermal-isolating shell outside LH2 tanks, so it's normal to see such thing happen.
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Post by kerikbalm on Apr 8, 2024 15:03:01 GMT
Vacuum is a great insulator.
If you're in the orbit of Neptune, you don't need active cooling for a while.
Mercury is another issue
Another issue is time: if you're going to use the propellant right away for a big ejection burn, you don't really need to worry about insulation.
Active cooling and propellant boil-off might be nice to have
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