Move in Space without mass exchange

[Irvin Atkins]

I did a thought experiment and I can't figure out what the mistake is.

There is a system of 2 electric motors weighing 1 kg each with batteries in the Earth's orbit.
The motors are rigidly connected by a 1-meter-long bar.

If one motor starts rotating in one direction on a signal, the entire system should start rotating in the opposite direction around(???) the motor's rotation axis.
After a while, we start rotating the motor in the opposite direction to stop the system from rotating.
As a result, we have a system in the same state but shifted 1 meter to the side.

Repeat the same with the second motor.

If this works, then you can make the motors' rotation axes perpendicular and move in any direction without exchanging masses.

 

[Helio]

Is this somehow different than how gyro motors work for spacecraft, especially space telescopes?

Gyroscopes

 

[Classical Motion]

Interesting. Don’t stop or reverse the motors. As the arm approaches 180 degrees, start 2nd motor and slow down first motor less than second motor. Rinse and repeat. Step walking the rotational origins.

The oscillations of these motor speeds can be increased for velocity. But it would be one heck of a ride. And probably impossible for navigation. Or bearing.

 

[Questioner]

My layperson's take,

Space is completely fluid.
The aggregate center of mass will stay there.

The motor is imparting a differentiated rotation of masses.
Pushing some mass around one way & pushing the other mass around the opposite way.

As the initiating motor turns whatever turning of the long bar will be compensated by shifting that motor's position complimentarily around the center of mass.

I'm pretty sure the system will stay in its center of mass.
Essentially rotating around it.

just my 2 cents.

 

[Questioner]

Further thoughts,

my guess is the rotation rate of the [active] motor will be proportionally greater by the difference of each quantity of mass perhaps with some radius differential variance

So if the cross bar [structure] is 1/2 a kilogram plus the idle motor's one kilogram there might be 2/3rds rotation of that structure per one complete revolution of the active motor.

A real physicist would be able to give exact predicted values.

 

[Ken Fabian]

Like Questioner said - the center of mass won't move. You can make your contraption rotate, from equivalent counter-rotation within the motors, but it will not make it move.

 

[Questioner]

What's needed is a space 'grabber".
Probably a black hole singularity (which I think may be the event horizon).
But then moving infinite density around becomes a problem.

So some kind of artificial transient singularity might work if anyone can figure out how to produce that.

 

[billslugg]

one motor starts rotating in one direction on a signal, the entire system should start rotating in the opposite direction around(???) the motor's rotation axis.

The assembly will not rotate about the motor axis, but around the assembly's center of mass.