Reply To: Site availability is poor

[Joeviocoe]

Francisl is correct. Newton’s laws of motion govern this idea.

There is no way to recover the momentum of the ball/projectile (to recollect the propellant material), without also applying that momentum to the spacecraft in the opposite direction…. negating any previous momentum in the positive direction. What you’ve come up with, is a very complex vibrator.

Whether it is a magnetic plate, using ferromagnetic fluid, or anything else… as the relative velocity of the ball slows (in relation to the craft)… the other side of the magnet will get the momentum. Magnetism is an invisible force, but it ultimately transfers all force in the same way as a physical connection. No different than firing a bullet into a spring/buffer to recapture it. The gun will move back, but connecting the spring or magnet that is capturing the bullet, to the gun… will always produce the equal and opposite effect. Making the net momentum 0.

This is a “closed system” even if material seems to move freely through the vacuum of space. If the whole thing could be put inside a finite container without changing anything else… it would be more obvious to an observer… but still the same closed system.

No, there is no way any object can just “reduce its velocity with itself (using magnetic fluid)”. Remember, velocity is relative to something.
Read Newton’s 1st law:

Every body persists in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed.

https://upload.wikimedia.org/wikipedia/commons/5/51/First_law.ogg

In an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a net force.

The ball cannot change it’s velocity relative to the spacecraft or its attached recovery mechanism…. without acting upon said mechanism. If the ball slows down because of a magnet force (spin or otherwise).. the magnet pushes on the recovery mechanism and will slow down the spacecraft. There is no free ride.

Think about it, if a spinning metal ball could change it’s linear velocity with its self contained ferromagnetic fluid… then why need the gun, the electromagnets, or the spacecraft? Just put the cargo/passengers inside a scaled up ball, and go.

Magnetism is misunderstood enough, that is it conveniently used to obscure part of the equation. Many a perpetual motion machine has used it.
Take out the magnetic middleman, and just use a mass off center on a spinning axis. When the mass is going in the –> direction, the motor assembly / spacecraft will move <--, but that mass always recovered by remaining physically attached to the motor shaft. So as the mass makes its way back <-- to restart the cycle... the momentum is reversed and the spacecraft moves back -->. The common vibrator!
That is essentially the same as your idea, without all the magnetism stuff which doesn’t change anything other than making it easy forget or misapply Newton’s laws.