# Could a spacecraft be propelled by a 180 degree deflection of two charged particle beams?

I am wondering if the electrostatic deflection of two charged particle beams could create enough thrust, via the Lorentz Force, to propel a spacecraft.

This conceptual propulsion design would make use of deflection plates, similar to those used in a CRT, to create an electric field. A positively-charged particle beam entering into this field would by design be deflected 180 degrees, and at the same time a negatively-charged particle beam entering this field would by design be deflected 180 degrees. This hardware setup would be installed on the stern of the spacecraft so that the two charged particle beams would be traveling in the opposite direction of the spacecraft.

The positively-charged particle beam could be created by a Proton Gun and the negatively-charged particle beam could be created by an Electron Gun. If both of these charged particle guns are high-voltage devices, and the electric field of the deflection plates is also high-voltage, I believe that the resultant Lorentz Force could be capable of propelling the spacecraft.

Also, I believe that the charged particles flowing in the Sun's solar wind would also be deflected away once entering into this electric field, providing an additional thrust to that being created by the charged particle guns.

Could a spacecraft be propelled by a 180 degree deflection of two charged particle beams?

• Are the proton and electron gun in this model part of the spacecraft, or are they back home providing a beam to propel the spacecraft? – Steve Linton Jan 7 '19 at 20:03
• @Steve Linton, they would be a part of the spacecraft. – user28781 Jan 7 '19 at 21:01
• Why don't you just shoot the beams out the back of the ship and cut out the deflection field? – Organic Marble Jan 7 '19 at 21:15
• This feels like a bootstrap lifter but I'll let someone who actually knows about electromagnetics weigh in. – Organic Marble Jan 7 '19 at 22:27
• If the deflection is being acheived by a magnetic field, then it will not change the amount of thrust from the guns at all, just the direction. An electric field that was accelerating them to higher energies would help, of course. Basically, though this is an ion drive with extra complications – Steve Linton Jan 7 '19 at 23:16

The diagram in the question shows the trajectories of equal magnitude magnetic rigidity particles (but opposite sign) in a magnetic field pointing out of the page. Charged particle orbits in magnetic fields are circular.

The diagram does not show the trajectories of charged particles in an electric field. If they entered the field in the direction of the gradient, they would be undeflected. Once inside the volume of higher but constant electrostatic potential, they would still continue to move in straight lines.

However, if they entered the region of higher electrostatic potential at an angle then they would be deflected in opposite directions.

Either way: (electric or magnetic or even both) the fields could help transfer momentum from incident particles. However they won't do anything more than what a mirror would do.

This is a similar question to an earlier one about a spacecraft with a laser and a mirror both mounted on it. In that case the laser pointed backward produces a force $$F_0$$. If you point it forward, you get $$-F_0$$ but bouncing it backwards with the mirror produces $$+2F_0$$ and so the net force is still $$-F_0$$.

So as mentioned in @SteveLinton's comment

...it will not change the amount of thrust from the guns at all, just the direction.

and so @organicmarble's comment is spot on:

Why don't you just shoot the beams out the back of the ship and cut out the deflection field?

There's nothing mysteriously "powerful" about the Lorentz force. Momentum is conserved and there's no difference in net force between shooting out the back, and shooting forward and reflecting with a magnetic field. The field won't add any extra thrust.

Here is something different but related. In this case the electric field is pointing in the plane of the page (unlike the field direction shown in the question.

The Dipole Drive described in Paul Gilster's Centauri Dreams, Imagining and Planning Interstellar Exploration is also based on differential deflection of oppositely charged particles. However, based on the title of my question Is this description of the “dipole drive” and how it would work physically correct? I am not convinced this is physically sound either.

https://i.stack.imgur.com/9gwTU.png

• Can you add a tl;dr for us electromagnetically challenged folks? Like, will it work or not? – Organic Marble Jan 7 '19 at 23:22
• @OrganicMarble I've added some, starting at Either way: Thanks – uhoh Jan 7 '19 at 23:44
• @OrganicMarble I didn't see that at first, but yes that summarizes it nicely. edited again. – uhoh Jan 8 '19 at 0:03
• Great! now even I can understand it. Thanks. – Organic Marble Jan 8 '19 at 0:05
• @uhoh, thank you very much for that explanation. I would upvote your answer, but I don't have a high enough reputation score to do so at this time. – user28781 Jan 8 '19 at 0:55