Plasma Thrusters Enhanced with Chemical Rockets

[Cheif Operations Director]

2 minutes ago, Nothalogh said:

You'd better hope it doesn't, or it won't make it through the mag accelerator.

It goes through that first, then I cool it down in a "pre-chamber" so by the time it gets to the chemical combustion chamber where the two ion streams meet It is a gas. Im pretty much giving the chemical fuel speed boost

12 hours ago, Cheif Operations Director said:

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Something like this (excuse the bad sketch) the purple is your run of the mill plasma thruster, the it pushes the ionized fuel (purple) into the combustion chamber where a small amount of LOX is added for combustion.

 

[farmerben]

I'm pretty sure it works better the other way around.  Chemically react cold stuff, and then use electromagnetic forces to push the hot stuff.  

 

[Cheif Operations Director]

1 hour ago, farmerben said:

I'm pretty sure it works better the other way around.  Chemically react cold stuff, and then use electromagnetic forces to push the hot stuff.  

 

I mean it may work better but you would need to ionize the products of the chemical reaction.

[KerikBalm]

On 8/14/2019 at 1:56 AM, Cheif Operations Director said:

normal plasma thrust based off of this (https://en.m.wikipedia.org/wiki/Ionization_energy)

No, plasma thrust is not based on ionization energy. It is based on the ability of ionized particles to interact with magnetic fields. Atoms must first be ionized, and that takes energy. Low Ionization energy means less energy goes into ionizing the atom, so if you have a limited supply of power, you can use more energy to accelerate the ions if you use an element with a lower ionization energy.

Now, chemical reactions are based on electron swapping, and ionizing stuff is stripping the electrons off of them, so there's that problem. However, a larger problem is simple the sheer difference in power levels.

Consider a single RS-25/SSME, 452 Isp, 2280 kN. Exhaust velocity is basically 4.44 km/sec. Now to generate 1 kilonewton of thrust by expelling mass at 1 km/sec, you need to expel 1 kg per second. The SSME would be expelling mass at 4.44 km/sec, and for 2280 kN needs to expel  513 kg of propellant per second. The kinetic energy of propellant per second is determined by 1/2 MV^2, so 0.5*513*(4440)^2= 5056538400 W or 5.06 GW. To increase Isp by 1% would require a 2% increase in propellant energy (1.01^2 = 1.0201). 2% of 5.056 GW is 2% of 5056 MW, or  101 MW.

You'd need 100 MEGA watts of power to increase the SSME's Isp by 1% 300 MW for all 3. You think the dry mass of that machinery is going to be worth a 1% increase in Isp? This is of course assuming 100% efficiency. FWIW, solar energy at earth is about 1 KW/square meter, and the most efficient solar cells are about 30% efficient. The most efficient ion engines are around 70-80% efficient.. lets say 80%. So for increasing propellant KE by 100 megawatts, you'd need to capture 100/0.3 /0.8 = 416 MW of solar energy. This would then require 416,000 square meters of solar panels. So a 644 x 644 meter solar panel would do it... to increase 1 of 3 SSME engine's Isp by 1%.

On top of that, Ion engines are more efficient the faster they eject material, because that way more energy goes into KE of the propellant, and less (as a %) into ionizing the propellant. An engine increasing SSME exhaust velocity by 1% would barely be giving the propellant a nudge, but would have to spend a lot of energy ionizing all that propellant. Energy efficiency would plummet (your solar panel area or nuclear reactor size would skyrocket... your rocket would not)

You'd have a hard time supplying that much power with a nuclear reactor, solar panels are out of the question. Ion engines only work for very long burn times, with low power output and low TWR. Chemical engines are the opposite. Combining them will have the strengths of neither. You'll have poor TWR, still have a poor Isp, and your dry mass will be terrible resulting in reduced dV.

If you're going to go with a nuclear reactor for power, use an NTR. If you're going to go with solar, you won't be able to accelerate any meaningful amount of reactants from a chemical reaction. Even using a tiny tiny tiny chemical engine with a massive solar array won't work well because you aren't using propellant optimized for use in an ion engine, nor an optimal ion engine design.

Really, if you want high Isp and high thrust, nuclear or antimatter reactions are pretty much the only way to do it. Beamed power can be interesting too, but wouldn't work in deep space/the ship wouldn't be independent.

Edited August 15, 2019 by KerikBalm

[Cheif Operations Director]

7 hours ago, KerikBalm said:

No, plasma thrust is not based on ionization energy. It is based on the ability of ionized particles to interact with magnetic fields. Atoms must first be ionized, and that takes energy. Low Ionization energy means less energy goes into ionizing the atom, so if you have a limited supply of power, you can use more energy to accelerate the ions if you use an element with a lower ionization energy.

Now, chemical reactions are based on electron swapping, and ionizing stuff is stripping the electrons off of them, so there's that problem. However, a larger problem is simple the sheer difference in power levels.

Consider a single RS-25/SSME, 452 Isp, 2280 kN. Exhaust velocity is basically 4.44 km/sec. Now to generate 1 kilonewton of thrust by expelling mass at 1 km/sec, you need to expel 1 kg per second. The SSME would be expelling mass at 4.44 km/sec, and for 2280 kN needs to expel  513 kg of propellant per second. The kinetic energy of propellant per second is determined by 1/2 MV^2, so 0.5*513*(4440)^2= 5056538400 W or 5.06 GW. To increase Isp by 1% would require a 2% increase in propellant energy (1.01^2 = 1.0201). 2% of 5.056 GW is 2% of 5056 MW, or  101 MW.

You'd need 100 MEGA watts of power to increase the SSME's Isp by 1% 300 MW for all 3. You think the dry mass of that machinery is going to be worth a 1% increase in Isp? This is of course assuming 100% efficiency. FWIW, solar energy at earth is about 1 KW/square meter, and the most efficient solar cells are about 30% efficient. The most efficient ion engines are around 70-80% efficient.. lets say 80%. So for increasing propellant KE by 100 megawatts, you'd need to capture 100/0.3 /0.8 = 416 MW of solar energy. This would then require 416,000 square meters of solar panels. So a 644 x 644 meter solar panel would do it... to increase 1 of 3 SSME engine's Isp by 1%.

On top of that, Ion engines are more efficient the faster they eject material, because that way more energy goes into KE of the propellant, and less (as a %) into ionizing the propellant. An engine increasing SSME exhaust velocity by 1% would barely be giving the propellant a nudge, but would have to spend a lot of energy ionizing all that propellant. Energy efficiency would plummet (your solar panel area or nuclear reactor size would skyrocket... your rocket would not)

You'd have a hard time supplying that much power with a nuclear reactor, solar panels are out of the question. Ion engines only work for very long burn times, with low power output and low TWR. Chemical engines are the opposite. Combining them will have the strengths of neither. You'll have poor TWR, still have a poor Isp, and your dry mass will be terrible resulting in reduced dV.

If you're going to go with a nuclear reactor for power, use an NTR. If you're going to go with solar, you won't be able to accelerate any meaningful amount of reactants from a chemical reaction. Even using a tiny tiny tiny chemical engine with a massive solar array won't work well because you aren't using propellant optimized for use in an ion engine, nor an optimal ion engine design.

Really, if you want high Isp and high thrust, nuclear or antimatter reactions are pretty much the only way to do it. Beamed power can be interesting too, but wouldn't work in deep space/the ship wouldn't be independent.

You make very good points. I was not thinking something on the scale of the SSME. I was thinking something more on the scale of an RCS thruster to a Goddard sized liquid rocket engine. Then it would actual have more an effect. I’m trying to take the fact that these gases are ionized to my advantage. Since they will chemically react easier when they are not balanced, why not add in a chemical reaction to the process? Instead of having or plasma thrust have two. Then have them meet in a combustion chamber. This would take the extra heat and pressure of these small streams of ionized gases to even more advantage. 

 

Is is it possible to “reverse ionize something” (in this context) for similar thrust. Instead of striping electrons giving them?

Edited August 15, 2019 by Cheif Operations Director

[FreeThinker]

You might want to read

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.471.9416&rep=rep1&type=pdf

[Cheif Operations Director]

1 hour ago, FreeThinker said:

You might want to read

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.471.9416&rep=rep1&type=pdf

I will thanks I need better wifi though

[farmerben]

 

Does anyone know why the arcjet cathode and anode are this way and not the reverse?  

 

[Nuke]

you got things like arcjets that can take a normal chemical engine and boost the isp so i dont see how it would be impossible. of course its going to boost the weight of your engine and require a beefier power source. but its possible. 

microwaves are a good way to heat water, which is what the exhaust products of a lh2+lox engine are. a bunch of megatron's pointed into the combustion chamber might do something. 

maybe you can come up with a fuel mixture that results in ionized products with a quasi decent isp that can be boosted magnetically. 

[Cheif Operations Director]

3 minutes ago, Nuke said:

you got things like arcjets that can take a normal chemical engine and boost the isp so i dont see how it would be impossible. of course its going to boost the weight of your engine and require a beefier power source. but its possible. 

microwaves are a good way to heat water, which is what the exhaust products of a lh2+lox engine are. a bunch of megatron's pointed into the combustion chamber might do something. 

maybe you can come up with a fuel mixture that results in ionized products with a quasi decent isp that can be boosted magnetically. 

Will that just not form a larger compound?

[Nuke]

7 minutes ago, Cheif Operations Director said:

Will that just not form a larger compound?

idk. i really dont know enough about chemestry. all i know is that some reactions create ions. not sure if any rocket fuels would do that or not. 

[sevenperforce]

Getting a reaction with a workably ionized exhaust stream is...tricky.

[Cheif Operations Director]

1 hour ago, sevenperforce said:

Getting a reaction with a workably ionized exhaust stream is...tricky.

why?

[kerbiloid]

Probably because of lack of electrons.

[Cheif Operations Director]

1 hour ago, kerbiloid said:

Probably because of lack of electrons.

Is it possible to reverse ionize something? I mean in the rocketry context, I know you can add an electron. My design require them to not have electrons. I’m trying to make these fuel spontaneously react like a hypergolic fuel. If the plasma jet leaves the nozzle normally at such high temperatures, I read somewhere that it could be about 1,000,000. (I think it was the the VASMIR article ) Why not harness that waste heat in a combustion chamber. Yes I know it will melt... Very quickly, that being said things can be done to fix this such as pulsing the engine or using the fuels to cool it down, Etc. 

On 8/15/2019 at 12:12 PM, FreeThinker said:

You might want to read

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.471.9416&rep=rep1&type=pdf

Sorry I have not gotten a chance to read that yet sorry I’m sure it relates based off of the skimming I did of it but I need to in-depth more.

Edited August 17, 2019 by Cheif Operations Director

[kerbiloid]

At temperatures ~10 kK and greater the atoms get ionized in any case due to the frequent atomic collisions.
So, unlikely any chemistry is available when any molecule gets broken once it appears.

[sevenperforce]

13 hours ago, Cheif Operations Director said:

15 hours ago, sevenperforce said:

Getting a reaction with a workably ionized exhaust stream is...tricky.

why?

For an exhaust flow to be ionized in a way that would allow it to be manipulated my magnetic fields, you'd need to rip the electrons away in an organized fashion. You can't just annihilate the electrons, either. You'd almost need to have a tripropellant reaction, with one exhaust flow being net-positive and the other being net-negative.

What I really want to see is a Hall Effect thruster (or other electrostatic thruster) which can have a working fluid injected into it to amp up the thrust at the expense of isp.

[farmerben]

10 hours ago, Cheif Operations Director said:

Is it possible to reverse ionize something? I mean in the rocketry context, I know you can add an electron. My design require them to not have electrons. I’m trying to make these fuel spontaneously react like a hypergolic fuel. If the plasma jet leaves the nozzle normally at such high temperatures, I read somewhere that it could be about 1,000,000. (I think it was the the VASMIR article ) Why not harness that waste heat in a combustion chamber. Yes I know it will melt... Very quickly, that being said things can be done to fix this such as pulsing the engine or using the fuels to cool it down, Etc. 

Sorry I have not gotten a chance to read that yet sorry I’m sure it relates based off of the skimming I did of it but I need to in-depth more.

Let me get this straight.  You want to ionize O₂ so that radical oxygen ions react suddenly with fuel.  There is a device which does exactly this.  

https://en.wikipedia.org/wiki/Spark_plug

There is some debate about whether boosting the ionization (by adding two spark plugs per cylinder, etc) provides any benefit.  In general the answer is no, or almost negligible, but the double spark plugs may resist corrosion and contamination longer.  

Would there be any benefit to keeping to keeping the reactants ionized before mixing them together?  I think you would have to supply energy during this time, for no net benefit.  

The arcjet appears to simply heat the exhaust products.  The electric force is pointed the wrong way.  Reversing the anode and cathode would give more boost.  Maybe doing so would make the engine more massive?  I don't really understand why the electric force in an arcjet is pointed opposite what makes sense.  

 

Edited August 17, 2019 by farmerben

[Cheif Operations Director]

@sevenperforce

@farmerben

Im idea(not the full topic of the thread just this one point of it ), is to transfer the electrons from one of the chemicals to the other proplleant. Causing both of these atoms to be ionized then combining them for a chemical reaction. The hope is that the heat reduced from the first ionization process can cause the gases in the combustion chamber to be hotter, thus expanding more, thus creating more pressure. I'm trying to forcibly strip the electrons from an otherwise stable fuel and apply it to the other, then re-combining them in the combustion chamber they will spontaneously react like hypergolic fuels. I do realize that take the electrons away in the first place cost energy.

 

So I am not adding/creating energy. (only adding this because the way I worded it, it seems like a free energy machine, my bad, i'm not sure how else to word it at the moment I will edit this out if I do)

 

Probelms:

-Heat

-A ton of energy to power the ionization process.

[Nuke]

16 hours ago, kerbiloid said:

At temperatures ~10 kK and greater the atoms get ionized in any case due to the frequent atomic collisions.
So, unlikely any chemistry is available when any molecule gets broken once it appears.

i was thinking using chemical energy to do the ionization for you so that you are left with a magnetically accelerated exhaust. but i dont know of any high energy reactions that would produced charged exhaust products. but again my lack chemistry knowhow leaves me scratching my head. as far as i know most research into rocket fuels has been about more thrust or more isp,  rather than creating charged exhaust.

Edited August 17, 2019 by Nuke

[sevenperforce]

17 hours ago, Nuke said:

i was thinking using chemical energy to do the ionization for you so that you are left with a magnetically accelerated exhaust. but i dont know of any high energy reactions that would produced charged exhaust products. but again my lack chemistry knowhow leaves me scratching my head. as far as i know most research into rocket fuels has been about more thrust or more isp,  rather than creating charged exhaust.

You can't have a chemical reaction that produces charged exhaust with only two reactants, because you need a charge sink. You can't just delete charge; it has to go somewhere. Any system that produces charged exhaust would accumulate electrostatic charge on itself.

What you could do, conceivably, is have a multichamber tripropellant engine that produces two exhaust streams, one positively-charged and one negatively-charged. Maybe do it with an annular thrust chamber, like an aerospike engine inside a de laval. Then your net charge flux is zero and you can use magnetic fields to further accelerate one of the two charged exhaust streams..

[farmerben]

Ugh.  Magnetic forces do no work.  Magnetic force cannot increase exhaust velocity.  Only electric force can do that.

During a chemical reaction, the reactants are ionized.  

When the electrons reach a new ground state in the reaction product they give us a precise amount of energy, the temperature does not effect this amount of energy.

Temperature is the limiting factor in solid rocket nozzles.  Magnetic nozzles can handle unlimited temperature, but they only work on ions not neutral molecules.

Electron guns are simple devices.  So the effort should be to accelerate positive ions.  Neutralizing the charge behind the rocket is not so difficult.

Here is an ion engine.  Putting these types of electromagnetic fields around a chemical reaction would be much better than an arcjet, or the thing that COD is describing IMHO.  

[KerikBalm]

On 8/15/2019 at 6:04 PM, Cheif Operations Director said:

You make very good points. I was not thinking something on the scale of the SSME. I was thinking something more on the scale of an RCS thruster to...

Ok, I looked up the RCS of the space shuttle for comparison:

https://en.wikipedia.org/wiki/Space_Shuttle_Orbital_Maneuvering_System

3.87 kN instead of 2280 kN. I don't want to redo all the other calculations because of different Isps, so I'm just going to assume its a tiny SSME variant. In this case for a 1% increase to Isp, assuming 80% efficiency of the electric "boost" system, and 30% solar power efficiency, we only need 0.0017x the solar panel area.

So instead of 416,000 square meters of solar panels, you'd need about 700 square meters. So a 26.5 x 26.5 square meter solar panel would do it. The ISS would have the area to boost 3 RCS thrusters Isp by 1%. Actually, they only supply max 120 kW from 2500 m^2. I was assuming they'd supply 750 kW with 30% total efficiency... obviously 30% total efficiency is optimistic (really only achieved in lab settings in narrow EM bands).

So scratch that, the entire power array of the ISS wouldn't be enough to boost the Isp of a single such 3.87 kN thruster by 1%. It could manage a 1% boost to a 2.2 kN thruster, if that boost system was 80% efficient.

Now... in such a scenario, is the dry mass of all the ISS solar arrays worth a 1% increase in Isp? I'm going to guess that is a no, and you dV goes down a lot due to that mass.

The time-span for thrusting by chemical reactions is too short for a solar power boost system to contribute useful amounts of energy to the propellants.

A hybrid engine makes no sense. There is no suitable power source or energy storage device that would be able to offset its own mass penalty... except nuclear, but in that case a NTR outcomepetes it, so again, a hybrid engine like this thread describes makes no sense as far as I can tell.

[sevenperforce]

2 hours ago, KerikBalm said:

The time-span for thrusting by chemical reactions is too short for a solar power boost system to contribute useful amounts of energy to the propellants.

A hybrid engine makes no sense. There is no suitable power source or energy storage device that would be able to offset its own mass penalty... except nuclear, but in that case a NTR outcomepetes it, so again, a hybrid engine like this thread describes makes no sense as far as I can tell.

In theory, you could have an NTR which produces an ionized exhaust stream with an open-cycle coolant loop acting as the charge sink. The coolant loop would generate power, which could be used for an electromagnetic nozzle to accelerate the exhaust stream faster. The big problem with an NTR is temperature: you can only make the propellant move faster by making it hotter, and at some point you melt the reactor. A pure hydrolox rocket burned at stoichiometric ratio produces heat not significantly lower than the temperature of a solid-core NTR; the advantage with an NTR is that you're only pushing hydrogen, not that nasty and heavy oxygen, and so your specific impulse goes up.

By accelerating the NTR exhaust products after they leave the chamber, you don't have to worry about overheating the reactor. If you could make it work.

[KerikBalm]

Sure, nuclear-electric propulsion and such is interesting, but a Chemical-Electric hybrid seems just plain dumb to me