Using a plasma arc instead of fission for a reactor style rocket

[matthekc]

Gas core reactor rockets use nuclear gas reacting to super heat and therefore pressurize hydrogen. They operate at about 25000 C.

Why not use a high intensity plasma arc which routinely operate at about 13,000 C but if designed to can go much higher by at least several fold.

I got bored today and found myself curious about the progress in ion and pulsed laser ion propulsion systems and some how found myself here.


I think it may be feasible solid core rockets were desirable because of the heat produced well that and the heat producer was it's own energy source. People are funny though tell them you want to launch a bunch of nuclear fission rockets and they think you've gone mad. --I'm pretty sure that's quotable.

Plasma arcs can produce a lot of heat but the downside is they require a fair amount of electricity to do so.

http://en.wikipedia.org/wiki/Gas_core_reactor_rocket

for anyone who isn't up on a gas core rocket and wondering what I'm talking about.
Oh and I know wikipedia = not real research.

 

[Renge Ishyo]

I think you answered your own question, if you don't go nuclear you have to generate the heat entirely with electricity which is expensive. One you get a nuclear reaction going it can generate large amounts of heat on its own.

 

[matthekc]

The question really isn't if its less good than a fission gas rocket but if it could be as good or better than a conventional rocket. Could the gains in thrust offset the extra needed weight?

 

[vanesch]

I have to say I had never seen a crazy idea like that before reading this!

What I wonder is, how do you make a nozzle which can guide a gas of 30 000 degrees ? Or is this some magnetic confinement thing ? I might expect a little tad of material engineering problems...

 

[matthekc]

well technically it will loose some heat as it expands... Although the pressure should be impressive.

 

[Tominator]

I know this is kind of off-topic, but if we have nuclear reactor on board can't we use some kind of non-propellant propulsion? I have heard about Emdrive, does anybody know more about it?

 

[russ_watters]

EMdrive and other reactionless drives are a violation of the most basic principle in physics: conservation law. They are the domain of crackpottery only.

 

[Tominator]

EMdrive and other reactionless drives are a violation of the most basic principle in physics: conservation law. They are the domain of crackpottery only.

I do not think so. If you have EM generator in nozzle made of material able to reflect the EM waves, it can be considered EM drive and it ceartainly does not violate any laws of physics. On the other hand I meant something else. Recently I saw this video: [crackpot link deleted]
This guy talks about something similar, but I did not understand him so well to say, he is right. He mentioned, that there is EMdrive by SPR Ltd, which works:
[crackpot link deleted]
Do you know something more about it?

edit: [crackpot link deleted]
I found this only now, but it will certainly interest you.

 

[russ_watters]

I do not think so. If you have EM generator in nozzle made of material able to reflect the EM waves, it can be considered EM drive and it ceartainly does not violate any laws of physics.

Do you know something more about it?

You found some good crackpottery there, and that's it. It's pretty simple: if your rocket ship goes this way and nothing goes that way, you've generated momentum from nothing. That's a straightforward violation of conservation of momentum. No, these devices you've found really don't work. We also don't discuss or give free advertising to crackpot ideas here, so please don't bring them up again.

 

[Topher925]

What I wonder is, how do you make a nozzle which can guide a gas of 30 000 degrees ? Or is this some magnetic confinement thing ? I might expect a little tad of material engineering problems...

Well, a magnetic nozzle is probably possible at those temps but I think the greater challenge would be designing a material that can handle the transition from gas to plasma when the engine is initially activated. Sounds like another mad scientists pipe dream to me. When are we going to have space elevators?

 

[.:Endeavour:.]

First, a nuclear rocket will not be an effective rocket; furthermore if it uses fission or fusion. Rockets don't have a high reliablility than a conventional airplane flight. A rocket like that will be too heavy to lift of the ground with all the shielding needed for radiation to be contained for a fission rocket. The temperature that you are talking about is 13,273.15 Kelvin. No nozzle or combustion chamber will actually operate at that high temperature without melting first or bursting from the high pressure.

 

[Astronuc]

well technically it will loose some heat as it expands... Although the pressure should be impressive.

The pressure of any system is constrained by the stress limitations of the structure enclosing the pressure. As the temperature increases, the strength of a material decreases, and creep becomes an issue.

At temperatures > 3300 K, and certainly in the range of 10000 K, one would have to use a magnetic field, but that also requires some amount of ionization in the fluid being confined, since neutrals simply diffuse or leak through magnetic fields.

With a fixed limit on pressure, P, one then has to trade of the particle (ion/electron) density, n, with temperature, T, by virtue of P = nkT where k is Boltzmann's constant.


At the moment, no one of credibility has proposed using nuclear based rockets for surface to orbit transfer. So far, the only credible proposals have been for orbital transfer.


Plasma arc systems have been considered since the 1950's, and there are various forms of EM (with propellant) and MPD devices. All require some power source, whether its nuclear or solar based.


Propellantless EM systems needs some large mass to push against or pull. To move, force has to be excerted on something, be it propellant or some large effectively infinite mass, in order to achieve a force that can be used to accelerate the mass of a spacecraft .

 

[Tominator]

You found some good crackpottery there, and that's it. It's pretty simple: if your rocket ship goes this way and nothing goes that way, you've generated momentum from nothing. That's a straightforward violation of conservation of momentum. No, these devices you've found really don't work. We also don't discuss or give free advertising to crackpot ideas here, so please don't bring them up again.

Do you consider Solar sail a crackpottery? It also reflects only EM waves. Well in real, also particles of solar wind, but it would work even without them. As long as I know, EM waves carry momentum, so you won't generate momentum out of nothing. On the other hand the acceleration, you will get is mizerable.
So by throwing off the EM waves=energy, you will get acceleration in the oposite direction. In another words you will "throw off" energy to gain momentum of the opposite direction. Is this violation of conservation? If no, than I do not see any crackpottery in EM drives.

Propellantless EM systems needs some large mass to push against or pull. To move, force has to be excerted on something, be it propellant or some large effectively infinite mass, in order to achieve a force that can be used to accelerate the mass of a spacecraft .

I do not understand you, if they need a mass to push against-propellant, they can no longer be considered propellantless. What do you mean by large effectively infinite mass? You mean something like to push off the magnetic field of a planet?

 

[Astronuc]

Do you consider Solar sail a crackpottery? It also reflects only EM waves. Well in real, also particles of solar wind, but it would work even without them. As long as I know, EM waves carry momentum, so you won't generate momentum out of nothing. On the other hand the acceleration, you will get is mizerable.
So by throwing off the EM waves=energy, you will get acceleration in the oposite direction. In another words you will "throw off" energy to gain momentum of the opposite direction. Is this violation of conservation? If no, than I do not see any crackpottery in EM drives.


I do not understand you, if they need a mass to push against-propellant, they can no longer be considered propellantless. What do you mean by large effectively infinite mass? You mean something like to push off the magnetic field of a planet?

Yes, for electric or magnetic fields, there needs to be some larger object like a planet or moon.

Now if one is meaning photons when one refers to EM (propellantless), then certainly one can use photons (e.g. from the sun) with a solar sail. That's attractive because the sunlight is there. The drawback is that the momentum per photon is very low, p = E/c, and the available thrust falls of with distance from the source. In terms of energy per force or change in momentum, it would make no sense to use an on board power source to use a laser (propellantless EM device) for propulsion. The thrust is simply way too low to be practical for a large spacecraft , especially one in orbit, i.e. bound in a gravity field.

 

[.:Endeavour:.]

The solar sail concept for a new way to propel a spacecraft to other planets, like Mars, will take too long to reach. But to travel to a celestial body like a comet or farther than a soar sail will be good to use because it continue to increase as long as there is light, from the Sun for this case. The thrust produced will be too small to propel a spacecraft fast enough to reach another planet. Another drawback is the surface area that a solar sail has to be exceeding the capacity of a rocket's payload. The more surface area a sail has the more thrust it will produce. For example, radiation pressure is about 1^-6 Pa at 1 AU.

F_thrust = P * A
P = 1 * 10^-6 Pa
A = the surface area of the sail

Lets say that we have a sail with length and width of 5 meters or 25 meters².

F_thrust = 1 * 10^-6 Pa * 25m²
F_thrust = 25 µN

But if the surface area was 1,440,000 meters²:

F_thrust = 1 * 10^-6 Pa * 1,440,000m²
F_thrust = 1.44 N

The more surface area the sail the more thrust it will produce, but a rocket has a limited capacity in carrying something that big into orbit.

 

[Astronuc]

But then one has to look at the mass of the sail, e.g. say it has a mass of 0.1 kg/m², which then yeilds an acceleration of

a = 1.44 N/144000 kg = 1 E-5 m/s²

or if one can manage 0.01 kg/m², then one could achieve an acceleration of 0.0001 m/s².

Slow accelerations are fine if one is not in a stronger gravitational field, and it does matter if one take decades, centuries or millenia to get to the destination.


The other complication is that solar flux falls of as 1/r², and that means acceleration falls off similarly.

 

[.:Endeavour:.]

But if you want to have a manned mission to another planet, you want to get and come back in specific time frame, but for a unmanned mission it will depend. An ion engine sounds better because it yields more thrust than a solar sail. If can live on the moon, that's the perfect place to create a sail with a high surface area, if it can be done there.