Below presented a concept for a electromagnetic thruster.
Suppose you have two identical current carrying solenoids, Solenoid A and Solenoid B that are firmly mounted to the inside of a container.
The solenoids are aligned along the x axis, have current flowing in the same direction and have a separation distance d, as shown in Figure 1.
Let the force on Solenoid A due to the magnetic field of Solenoid B be denoted as $F_a$, the force on Solenoid B as $F_b$. It follows that $F_a – F_b = 0$ and the container holding the solenoids is initially at rest.
At a certain time $t_0$, Solenoid’s B current flow is disrupted. The magnetic field generated by Solenoid B will start to decay, decreasing the attraction force $F_b$ to a lower value of $F_b’(t) < F_b$. Due to the finite propagation speed of electromagnetic waves, the information bubble will reach Solenoid A only at $t_1 = d / c$.
In the time interval $T = t_1 – t_0$, Solenoid A is “unaware” of the change and will continue to experience force equal to Fa in the positive x direction. The net force acting on the container during interval $T$ must be $F = F_a – F_b’(t) > 0$ i.e. force in the positive x direction as shown in Figure 2. that should propel to container to the right.
After the information bubble will propagate to reach Solenoid A, the force will stop.
Scheme for a Continuous Motion
It is possible to adjust the mechanism above to create continuous force production by periodically changing the current in the solenoids with frequency $f=c/d$ and a phase difference of half a cycle.
instead of disrupting the current in Solenoid B, we change the current's direction and in doing so, change the polarity of the solenoid.
This will further increase the magnitude of $F = F_a – F_b’(t)$ compared to the basic scheme above, because now $F_b'(t) < 0$ and Solenoid B is pushed by the field of Solenoid A in the positive x direction.
In order for solenoid A to continue to produce force to the right, when the information bubble will reach it after period $T$, we switch it's polarity.
this will produce two effects:
1. Solenoid A will be pulled to the right
2. We create an information bubble that will propagate towards Solenoid B
after another period of $T$ we switch the polarity of Solenoid B, which will push solenoid B to the right.
we can continue this alteration of polarities to produce force in a "push-pull" configuration.
Is it physically possible to produce thrust using this setup?
it is clear that there are many specific issues that where neglected such as transient effects, difficulty of crating high frequency alternating currents in solenoids and many others.
but can it fly? :)