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Post by geraldmonroe on Oct 10, 2016 3:19:51 GMT
So a nerva engine can be thought of as a cylinder with a cluster of rods. Those rods get very hot from being near each other. Specifically, the rate of heat production is controlled by neutron flux, which in turn you control by the positions of neutron damper rods as well as passive properties of the engine construction.
So if you make 1 gigawatt of heat, then you compute a mass flow rate that will remove 1 gigawatt at a particular temperature. You flow the propellant through, and the superheated propellant carries away the heat, exactly as much heat as you are producing.
The outer shell of the reactor rods stay at an equilibrium temperature so long as propellant is flowing.
So there's a couple of things that fall out from this :
You could preheat propellant in another heat engine before sending it to the NERVA engine. So you could maybe theoretically have a gigantic electric power reactor that is open cycle and much smaller radiators.
You could run a NERVA engine until the propellant is exhausted, then just eject the engine. You don't have the plumbing or any way to cool it after the propellant is gone, so it's literally a nuclear rocket booster.
Are these things possible?
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Post by RA2lover on Oct 10, 2016 5:17:53 GMT
NTRs ingame are cooled through reaction mass and thus don't need radiators. However, there's no fuel line modeling implementation, which effectively prevents you from using a preheater (which isn't necessary because you can just make the reactor output more power to compensate).
Generating power out of a NTR is also impractical. Running turbines basically requires you to create a turbine that can contain a NTR's exhaust and collect energy from it (which would reduce its performance as a rocket). Using a thermopile als. is problematic in that they work on temperature gradients, meaning you still need radiators to keep one side cool. Putting one inside the chamber would likely destroy it due to thermal expansion stresses.
As for NTR boosters - they are possible, but not in a straightforward way. The game doesn't really allow staging (though it allows you to refuel vessels which enables the use of disposable tankers to go along with your fleet). You can also create a launcher to launch other ships, though this significantly limits your launched vessel's size.
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Post by goduranus on Oct 17, 2016 3:01:31 GMT
Is it possible to use NTRs for thermoelectricity though? if it works you can save yourself a dedicated generator.
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Post by RA2lover on Oct 17, 2016 3:08:25 GMT
You need to keep the NTR cooled without expelling coolant and have a thermocouple able to support temp spikes associated with NTR operation. Even adding both an open and a closed loop cooling system is more trouble than its worth. You can try to get power through a expansion cycle turbine, but it's difficult to power anything beyond a turbopump with it.
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feld
New Member
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Post by feld on Oct 18, 2016 15:34:57 GMT
Ummm....actually, generating electrical power off of an NTR appears practical to people who study these things.
Google "bimodal nuclear thermal rocket". There were a bunch of technical papers released in the 2001-2003 timeframe I think by NASA. Other folks there and elsewhere have fleshed out the concept to varying degrees (before and since). Dr. Stanley Borowski is the only author whose name I recall. I *think* ESA has looked at it as well.
A summary powerpoint brief at link below.
www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwiIsreLz-TPAhXGeSYKHeYYCYAQFggpMAE&url=http%3A%2F%2Fntrs.nasa.gov%2Farchive%2Fnasa%2Fcasi.ntrs.nasa.gov%2F20040182399.pdf&usg=AFQjCNFjbFy3NCZ_QMqtEc95XdGcg5SNnQ
Best source of papers I know is on the NASA Technical Reports Server here:
ntrs.nasa.gov/
A search for "bimodal nuclear thermal rocket" there will provide more detail than I can here.
The way you do that is adding a secondary loop that runs through your NTR core and operating the reactor continuously at a low power level (much lower than the level typically used for impulsive thrust). I think that this sort of thing would be a standard feature in (especially military) NTR because it lets you keep the propulsion reactors critical all the time (albeit at a low level), avoiding thermal cycling to increasing service life and also reducing overall spacecraft complexity by combining the power and propulsion systems. That last obviously at the cost of *increasing* the propulsion systems' complexity and cost.
Now the folks at NASA/ESA(?) who were looking at this were obviously not working in the 1000 mT s/c range that CoaDE does. The electrical power output of their designs was in the kW range but more than sufficient for housekeeping power (life support and active cryogen cooling). Given the necessary upscaling in NTR reactors to produce the levels of thrust seen in CoaDE I would think that getting MW off the secondary loop would be feasible. I suspect that you could get enough juice out of it (at the high end) to charge weapons energy storage systems on a military craft.
Of course, to complete the thermodynamic cycle that secondary loop will need radiators downstream of the conversion system and all that massive goodness.
Also, not sure why "it's difficult to power anything beyond a turbopump with it." The TRL of gas-cooled nuclear reactors and high temperature brayton turbines, while not "flight ready", is respectable. No reason to believe that it cannot be done. Especially in a society like that in CoaDE that has mastered reliable re-startable NTRs (implying substantial improvements over our own material science). We have turbines today that operate in the necessary RPM/temperature ranges but operate directly off combustion gases.
On "NTR boosters": would say that you wouldn't do that. You probably want to keep all that (expensive hard to find) fissile material and even the waste products. No reactor achieves 100% fuel burnup. When you get that "spent" reactor back to base, you probably swap out the engines, take the old ones apart and salvage useful materials from them.
v/r
feld
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