Author Topic: Gas Core Nuclear Thermal Rocket  (Read 6768 times)

Offline Tywin

Gas Core Nuclear Thermal Rocket
« on: 06/03/2024 03:33 am »
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?

« Last Edit: 06/03/2024 03:34 am by Tywin »
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Offline Twark_Main

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« Last Edit: 06/03/2024 05:16 am by Twark_Main »

Offline TrevorMonty

Re: Gas Core Nuclear Thermal Rocket
« Reply #2 on: 06/03/2024 08:24 am »
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.

Offline RON_P

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Re: Gas Core Nuclear Thermal Rocket
« Reply #3 on: 06/03/2024 08:34 am »
Not exactly a GCNTR but ...
A recent NASA study/proposal on Centrifugal Nuclear Thermal Rocket ( CNTR ) .

https://ntrs.nasa.gov/citations/20230000621

As for GCNTR's

https://anstd.ans.org/NETS-2019-Papers/Track-4--Space-Reactors/abstract-33-0.pdf
« Last Edit: 06/03/2024 08:36 am by RON_P »

Offline edzieba

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Re: Gas Core Nuclear Thermal Rocket
« Reply #4 on: 06/03/2024 10:49 am »

Online Spiceman

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Re: Gas Core Nuclear Thermal Rocket
« Reply #5 on: 06/03/2024 04:51 pm »
Atomic Rockets also has useful pages on:
Vapor-core NTRs
Open-cycle Gas-core NTRs
Closed-cycle Gas-core NTRs

Atomic rockets is a formidable source. Thanks to this website it is possible to make a brief list of nuclear thermal rockets, with different core states.
-solid-core NERVA (= 800 seconds isp)
-solid-core CERMET (= 900 seconds)
-solid-core twisted ribbon (the Soviets: 940 seconds isp)
-pebble-bed core (around 1000 seconds+)
-liquid-core (1200 seconds)
-dropplet core (1300 seconds)
-vapor core (1500 seconds)
-gaseous core (1800 seconds)
-plasma core (2000 seconds+)

My two favorite ones however are "Pulsed NTR" and "Fission Fragment Rocket".

Offline Tywin

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Offline Tywin

Re: Gas Core Nuclear Thermal Rocket
« Reply #7 on: 06/03/2024 08:15 pm »
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.

Wow amazing, I go to watch now...
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Offline KelvinZero

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Re: Gas Core Nuclear Thermal Rocket
« Reply #8 on: 06/04/2024 01:18 am »
Hi.. I watched that video too and had a random thought. (Someone tell me if it violates thermodynamics somehow)

The video discusses using a 'vortex' or something to hold your fissionable material away from the engine walls..

..if it can do that, couldnt it also hold inert propellant mass eg rock dust away from the engine walls?

My idea is that instead of carrying a massive fuel tank of liquid hydrogen, what if you had a much smaller tank, and another easier to store propellant mass, eg rock dust. You allow your very hot hydrogen exhaust to pass down a long tube, reaching the velocity that its temperature produces.. but you also pour your alternative propellant down the center of the tube. It 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.

(edit) 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.

(edit2) Is the flaw that this assumes the hydrogen moving down the tube can gain its full directed velocity without a nozzle? I feel it would still work because the hydrogen would keep feeling pressure accelerating it from behind, but maybe my intuition is flawed. (edit3) maybe this is more like the configuration of a solid booster rocket, where the combustion products pass down a long core in the center?
« Last Edit: 06/04/2024 02:04 am by KelvinZero »

Offline Twark_Main

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Re: Gas Core Nuclear Thermal Rocket
« Reply #9 on: 06/04/2024 02:15 am »
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

It 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?

Offline KelvinZero

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Re: Gas Core Nuclear Thermal Rocket
« Reply #10 on: 06/04/2024 02:30 am »
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

It 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."

Offline redneck

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Re: Gas Core Nuclear Thermal Rocket
« Reply #11 on: 06/04/2024 08:07 am »
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

It 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."

I'm picturing your concept as a shotgun like engine. The gunpowder single boom replaced by continuous heating of the hydrogen working fluid. The birdshot/particles being small enough that particle/propellant acceleration can take place in a reasonable L*. 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?
 

Offline KelvinZero

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Re: Gas Core Nuclear Thermal Rocket
« Reply #12 on: 06/04/2024 10:46 am »
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.

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.

Offline Bizgec

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Re: Gas Core Nuclear Thermal Rocket
« Reply #13 on: 06/04/2024 11:21 am »
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.

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).

Offline Stan-1967

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Re: Gas Core Nuclear Thermal Rocket
« Reply #14 on: 06/04/2024 12:12 pm »
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.

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.


Have you tried deuterium?
« Last Edit: 06/04/2024 01:13 pm by Stan-1967 »

Offline KelvinZero

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Re: Gas Core Nuclear Thermal Rocket
« Reply #15 on: 06/04/2024 12:24 pm »
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.

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.
« Last Edit: 06/04/2024 12:40 pm by KelvinZero »

Offline Bizgec

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Re: Gas Core Nuclear Thermal Rocket
« Reply #16 on: 06/04/2024 03:46 pm »
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.

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.

I said momentum (g = mv), not energy (Ek = mv2/2). Both are conserved.

Quote
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.

Thereby slowing down the wind. You're confused by the relative scales in your example (energy of gale vs energy of feather).

Quote
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.

The flaw is in not understanding basic physics. It doesn't really matter how you heat your tube and how long it is, that just affects the efficiency of your engine. If you inject dust into a stream of gas, the dust will speed up but the gas will slow down. Energy and momentum will be conserved but the speed of your mixture will be lower than the initial speed of the gas.

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.
« Last Edit: 06/04/2024 03:54 pm by Bizgec »

Offline Bizgec

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Re: Gas Core Nuclear Thermal Rocket
« Reply #17 on: 06/04/2024 04:11 pm »
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.

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.
« Last Edit: 06/04/2024 04:12 pm by Bizgec »

Offline Sarigolepas

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Re: Gas Core Nuclear Thermal Rocket
« Reply #18 on: 06/04/2024 10:06 pm »
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?

I think they are such a life hack it's incredible, the energy is coming from the fuel itself and not the engine which means they have film cooling just like chemical rocket engines so the chamber can survive pretty much unlimited temperature and they use nuclear fuel so they also have pretty much unlimited energy density like solid core reactors. The best of both worlds.

There is no reason to believe that they can't reach the same thrust as chemical engines, right now the thrust of chemical engines is limited by chamber pressure, which is limited by the power of the turbopumps and the density of the fuel. It just so happends that hydrogen has a lower density than kerosene which means more volume to pump which is why efficient hydrogen engines have less chamber pressure, but having more specific impulse doesn't necessarily mean less thrust, what happends inside the combustion chamber doesn't affect chamber pressure even at millions of degrees, the chamber pressure is pretty much set at the pumps.

Edit: I think I am confusing nuclear saltwater as a type of gas core nuclear reactor, what's the difference?

« Last Edit: 06/04/2024 10:27 pm by Sarigolepas »

Offline redneck

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Re: Gas Core Nuclear Thermal Rocket
« Reply #19 on: 06/04/2024 10:40 pm »
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.

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.

The gas cannot expand in all directions as it is constrained by the walls and the injection end of the tube. It can only expand in one direction left to it, so it will accelerate. Also, you might want to check on your thermodynamics regarding the claim that further heating of the gas would slow it down.

The KelvinZero concept would seem to derive from light gas gun research more so than rocketry. Accelerating solids, even in particle size, would lend itself to the tube rather than an expansion nozzle.

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