Electron Rocket

[dansmith170]

TL;DR Summary

Why not build an electron rocket?

Hi all,

Why not build an electron rocket? Why won't this idea work? Seems like someone could just hitch an electron gun onto a spaceship. Boom! Electron Rocket.

I was thinking about ion thrusters. These use ions to achieve thrust. They are problematic for achieving a high delta V because they have a low exhaust velocity (meaning they would require an enormous amount of fuel for high speeds - see the Rocket equation).

With Newton's Second Law, a = F/m. There are two ways to increase acceleration: 1. increase force 2. decrease mass. So, thinks I, let's just lower the mass by using electrons instead of ions as propellant. And, turns out, electrons in electron guns can achieve speeds of up to 10% the speed of light. Exhaust velocity problem solved.

Note: the application for electron gun rockets would be interstellar travel. Say we want to go to Alpha Centauri (4.2 Lightyears away) in about 50 years. Then we'll need to go 10% the speed of light for most of the trip. I think an electron rocket could achieve this with an amount of fuel that is perhaps not unreasonable (at least not as unreasonable as the amount of fuel needed for an ion thruster for the same trip).

Note 2: there are electron microaccelerators that could be part of the rocket design - this would further increase exhaust velocity and further cut down on the amount of fuel required.

It's true that we would need A LOT of electrons, although that seems like more of a practical problem than a theoretical infelicity.

Anyways, do you think this idea has any merit? And if not, why not?

Thanks.

 

[PeroK]

The photon rocket is theoretically more efficient than a rocket with massive particles as propellant.

 

[Bystander]

You might see "coulombic explosion."

Summary:: Why not build an electron rocket?

why not?

See above.

 

[Astronuc]

Summary:: Why not build an electron rocket?

Anyways, do you think this idea has any merit? And if not, why not?

In our part of the universe, there is usually, for every electron, there is a positively charged nucleus nearby. So if one is shooting off electrons, from some mass, there will be a net positive charge developing.

When ions are used for propulsion, there is a method for exhausting electrons to neutralize the propellant stream.

One also has to consider the available thrust and thrust-to-mass ratio.

 

[Vanadium 50]

I think an electron rocket could achieve this with an amount of fuel that is perhaps not unreasonable

You might calculate this.

You might also compare the thrust from this with the force your spaceship will experience when it enters even a weak electric field.

 

[mfb]

Ion thrusters are already expelling electrons as well to stay neutral.

Ion thrusters can achieve an even higher I_sp without too much difficulty, but that needs more power per thrust. Focusing on the electrons is only making things worse. For an ideal efficiency you would want to eject both at the same speed, in practice the electron speed doesn't matter as long as it's not too high.