Talk:Pulsed nuclear thermal rocket

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Reword the explanation for Isp amplification to avoid implying the engine defies thermodynamics

Heat transfer via relativistic neutrons should still comply with the second law of thermodynamics. The neutrons released by fission have a (large) amount of kinetic energy, and fly off in random directions. They interact with the propellant by means of exchanging kinetic energy with it. The neutrons aren't converted into anything. Once the nucleons of propellant are all moving randomly around with the same momentum as the neutrons, shouldn't they be at equilibrium? Isn't average kinetic energy the definition of temperature? How are the neutrons exempt from the second law of thermodynamics?

With an average neutron speed of about 20,000 km/s, I will admit that the chances this becomes a limiting factor in an engine is pretty slim, but I still think saying it's unconstrained by the second law gives the wrong impression. The neutrons and the fuel both exchange heat in the same way, it's just that the neutrons are much hotter and more mobile. Felix Bardner (talk) 13:17, 4 October 2022 (UTC)[reply]