Atomic Rockets also has useful pages on:Vapor-core NTRsOpen-cycle Gas-core NTRsClosed-cycle Gas-core NTRs
https://ntrs.nasa.gov/citations/19920001892https://ntrs.nasa.gov/citations/19680012569https://beyondnerva.wordpress.com/2020/03/21/the-nuclear-lightbulb-a-brief-introduction/https://en.wikipedia.org/wiki/Nuclear_lightbulbNote the nuclear lightbulb is closed cycle, but there are also open cycle designs. See: https://en.wikipedia.org/wiki/Gas_core_reactor_rocket
Another great video by Scott Manly. He answered one question I'd been interested in, core has life of about 10 trips to moon after that its is new core or more ĺikely complete new engine with core. NB rocket is refuelled with LH each trip. If you want nuclear rocket with next level performance ( 7000ISP-480,000) with F1 thrust levels, watch his one on nuclear salt rocket. Will need remote lunar base to develop. StarShip has DV of about 8km/s, powered by 7000ISP engine and its more like 150km/s.
your alternative propellant ... ends up gaining the same velocity as the hydrogen, not because of its motion due to temperature but because it is at rest wrt to the average velocity of the hydrogen particles around it
Quote from: KelvinZero on 06/04/2024 01:18 amyour alternative propellant ... ends up gaining the same velocity as the hydrogen, not because of its motion due to temperature but because it is at rest wrt to the average velocity of the hydrogen particles around itIt won't gain "the same velocity," because the rock dust (of course) steals some of the momentum. You can only neglect this fact if the mass flow of dust were insignificant compared to the mass flow of hydrogen, but then in that case the benefit would be insignificant too so what's the point?
Quote from: Twark_Main on 06/04/2024 02:15 amQuote from: KelvinZero on 06/04/2024 01:18 amyour alternative propellant ... ends up gaining the same velocity as the hydrogen, not because of its motion due to temperature but because it is at rest wrt to the average velocity of the hydrogen particles around itIt won't gain "the same velocity," because the rock dust (of course) steals some of the momentum. You can only neglect this fact if the mass flow of dust were insignificant compared to the mass flow of hydrogen, but then in that case the benefit would be insignificant too so what's the point?I added an edit (possibly while you were replying):"the tube would be heated the whole way, so the hydrogen particles dont just have the energy from when they enter. They could keep losing energy from bouncing off the rock dust and gaining it again from the temperature of the sides the whole way down."
Depending on the requirements, it seems like an ISRU propellant solution that doesn't require NTR class Isp. Isp of 500 from rock dust and minimal hydrogen could easily be a win in resource poor exploration targets. Also seems possible that an engine could be developed that doesn't care too much what it eats.Taking it a bit further, could the hydrogen propellant in the concept drive a heavier molecular weight gas that happened to be available? Argon, CO2, etc?
Im trying for a magic trick where you get the same ISP as hydrogen without the massive hydrogen tank, but its likely im flunking some basic physics principle somewhere.
Quote from: redneck on 06/04/2024 08:07 amDepending on the requirements, it seems like an ISRU propellant solution that doesn't require NTR class Isp. Isp of 500 from rock dust and minimal hydrogen could easily be a win in resource poor exploration targets. Also seems possible that an engine could be developed that doesn't care too much what it eats.Taking it a bit further, could the hydrogen propellant in the concept drive a heavier molecular weight gas that happened to be available? Argon, CO2, etc?Im trying for a magic trick where you get the same ISP as hydrogen without the massive hydrogen tank, but its likely im flunking some basic physics principle somewhere.I did wonder if some other material might be more convenient than rock dust, which I was really just using as an example of something totally inert. Maybe oxygen, since it is much more storable than hydrogen+ you probably got the hydrogen from electrolysing water + the horrific corrosive effects of superheated oxygen may not matter if the heavier reaction mass was kept away from the rocket walls.
Quote from: KelvinZero on 06/04/2024 10:46 amIm trying for a magic trick where you get the same ISP as hydrogen without the massive hydrogen tank, but its likely im flunking some basic physics principle somewhere.Yes. It's called conservation of momentum. The hydrogen gas won't transfer its velocity to the dust, it will transfer momentum. Isp is proportional to exhaust velocity. By adding heavier particles to the propellant mix, you're slowing down the exhaust, thereby lowering the rocket's efficiencty but possibly increasing thrust (that depends on other factors, too).
Quote from: Bizgec on 06/04/2024 11:21 amQuote from: KelvinZero on 06/04/2024 10:46 amIm trying for a magic trick where you get the same ISP as hydrogen without the massive hydrogen tank, but its likely im flunking some basic physics principle somewhere.Yes. It's called conservation of momentum. The hydrogen gas won't transfer its velocity to the dust, it will transfer momentum. Isp is proportional to exhaust velocity. By adding heavier particles to the propellant mix, you're slowing down the exhaust, thereby lowering the rocket's efficiencty but possibly increasing thrust (that depends on other factors, too).I understand that heavier particles at the same temperature have the same average kinetic energy and thus lower velocity. But I am not attempting to transfer kinetic energy to the heavier particles through temperature.
Think of each dust particle more like a feather in a gale. A feather is far more massive than an air particle, but it ends up moving the same velocity as the wind carrying it.
I think if there is a flaw in this idea, it is in misunderstanding how the sides of the tube will heat and move the hydrogen, and return energy to them after the drag of the particles removes energy from them. For example I dont have an expander nozzle. Will the heat of the walls still drive the hydrogen particles forwards towards their ideal ISP with a long enough tube?. Will injecting the liquid hydrogen be so hard that im not really gaining anything from the expansion? Something like that.
Quote from: KelvinZero on 06/04/2024 12:24 pmWill the heat of the walls still drive the hydrogen particles forwards towards their ideal ISP with a long enough tube?. Will injecting the liquid hydrogen be so hard that im not really gaining anything from the expansion? Something like that.EDIT: To clarify another misconception: the heat of the tube walls will heat the gas near the walls, making it expand. It will not "push the gas down the tube", the gas will expand in all directions.
Will the heat of the walls still drive the hydrogen particles forwards towards their ideal ISP with a long enough tube?. Will injecting the liquid hydrogen be so hard that im not really gaining anything from the expansion? Something like that.
Hi, watching the new episode of Scott Manley, he mentioned this future nuclear thermal propulsion (minute 20:05), somebody have a paper to know more about this technology?And what do you think?
Quote from: Bizgec on 06/04/2024 03:46 pmQuote from: KelvinZero on 06/04/2024 12:24 pmWill the heat of the walls still drive the hydrogen particles forwards towards their ideal ISP with a long enough tube?. Will injecting the liquid hydrogen be so hard that im not really gaining anything from the expansion? Something like that.EDIT: To clarify another misconception: the heat of the tube walls will heat the gas near the walls, making it expand. It will not "push the gas down the tube", the gas will expand in all directions.I'll expand on that a bit... ahem. Your "long hot tube nozzle" is less efficient. By heating the gas further down the tube you're reducing the pressure differential and actually slowing the gas. There's a reason why rocket engines have expansion nozzles stuck onto the combustion chambers and the shapes of the nozzles aren't parabolic just to be asthetically pleasing.