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Post by Peterthesmall on Feb 12, 2017 13:49:18 GMT
Here's the paper: u.nya.is/lxewyl.pdfIt doesn't look very promising. From table 1, at least 93% of the energy is going into the fuel instead of the propellant (via the fission fragments, which don't, AFAIK, easily pass through solid matter). So to get the propellant hotter than the fuel, you have to get rid of that heat somehow. Up to the max service temperature of the fuel, you could use regenerative cooling. But that would only get the propellant a little hotter (about 7.5% hotter) than you could in a conventional NTR. To get a substantial improvement in Isp, you'd have to get rid of the fission fragment heat somewhere else, i.e., with radiators. You can still use some regenerative cooling, but the higher you want to push the Isp, the more of the heat going into the propellant has to come from neutron collisions. This could make a decent hybrid design, if you used the heat to generate power and run an MPD. Assuming you design such that the MPD and the pulsed NTR have the same ISP, it looks like half again as much thrust than the MPD alone. But we have magical near-Carnot efficiency thermoelectrics, so IRL it would probably be a lot more useful. The paper claims this could be used to increase thrust as well, by increasing the average power of the reactor and using greater mass flow, but I don't see why that's better than running the reactor at higher power in stationary mode. Either way you have to to get the heat out of the fuel and into the propellant. Thanks for the paper RiftandRend, After reading this, yes, it is as you say seems that you need to get rid of that heat somehow. But, after all is Isp that you are looking for. I think that Isp is like gold, If we want a kilogram of gold we need to remove tons and tons of soil, etc.. but this is the price I suppose we need to pay, and after all we are talking of human exploration. I think that the pulsed solid-NTR has a little philosophical ground, I mean sounds strange that you are using fission energy and then you are not using precisely the fission fragment and only the energy from neutrons which is only around 5%, but if really you can get the Isp mentioned before, I think that could be worthy. The thrust, I am not understanding well in the paper, but as far I can grasp, you can increase the thrust by increasing the power much like a pushing the accelerator pedal in your car? The documentation I have seen describes an active cooling system separate from the propellent flow. |
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Post by The Astronomer on Feb 12, 2017 13:53:07 GMT
The documentation I have seen describes an active cooling system separate from the propellent flow. Why are you writing in others' quotes? It is confusing and misleading sometimes. |
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Post by Rachelwhite on Feb 12, 2017 14:20:29 GMT
Is a solid-NTR? Hi guys, it is really a solid-NTR with this Isp? I thought that NTRs were almost dead in evolution since the NERVA projects since the NTR was stuck because the limit of melting point of the materials around 3000K and the famous 800 sec Isp. I am reading the up-to-date at www.projectrho, and then this interesting topic. I agree that it requires a lot of work, it is not as simple as Triga reactor, but then again we are talking about space travel it cannot be expected a very simple solution. If I understand well a pulsed- solid-NTR solve the problem of Orion project by not releasing fission products? in a bi-modal fashion. But I am skeptical on the capability of fission fragment heat evacuation, I mean it will require a very large heat exchanger perhaps on 300 to 500 square meters. or like a disc with 10 meters of radius, assuming that heat is released by radiation to the environment (empty space), but as also discussed, seems that some heat could be used. It will be interesting to see if this heat can be stored in someway. |
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Post by apophys on Feb 13, 2017 19:05:39 GMT
As we can see with MPD-based ships in the game, when your exhaust velocity is high, you can afford to carry more mass. Large radiators would not be a problem here.
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Post by newageofpower on Feb 17, 2017 23:43:19 GMT
As we can see with MPD-based ships in the game, when your exhaust velocity is high, you can afford to carry more mass. Large radiators would not be a problem here. We still require a non-trivial amount of thrust to dodge stuff, but a pulsed NTR or Fission Fragment propulsion system both offer more thrust than a MPD/Reactor setup. |
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Post by darthroach on Mar 3, 2017 16:21:34 GMT
As we can see with MPD-based ships in the game, when your exhaust velocity is high, you can afford to carry more mass. Large radiators would not be a problem here. We still require a non-trivial amount of thrust to dodge stuff, but a pulsed NTR or Fission Fragment propulsion system both offer more thrust than a MPD/Reactor setup. FFRs provide more thurst? I've only seen designs with thrust on the order of tens of newtons, which is hardly sufficient for a combat ship massing kilotons. |
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