My point is that a gyro fights *torque*, and nothing is torquing a projectile in vacuum once it's left the barrel. If it emerges with a slow spin perpendicular to direction of flight, it will keep that slow spin. The gyro effect won't work against that at all.

Satellites and space probes are gyro-stabilized because over the time scales they operate, tiny torques from e.g. light pressure and tidal effects have time to add up to troublesome levels. A projectile won't have that problem. :)

On Mon, Jun 29, 2015 at 4:14 PM, Ethan McKinney <ethan.mckinney@gmail.com> wrote:

On Mon, Jun 29, 2015 at 2:57 PM, Craig Berry <cdberry@gmail.com> wrote:
The thing is, spin-stabilization of the sort being discussed depends on an atmosphere. What happens is:

If that were true, you couldn't stabilize anything with a gyroscope :)

And that's all a spin-stabilized projectile is: a gyroscope.

Remember the spinning bicycle wheel demonstration in you physics class? No air flow across the bicycle wheel to push it back upright when it started to topple over.

And if you spin a top in a vacuum, it doesn't just fall over immediately. https://www.youtube.com/watch?v=WTt_hoWtMIc (He turns on the vacuum pump around :30--the top stays upright.
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Craig Berry (http://google.com/+CraigBerry)
"Eternity is in love with the productions of time." - William Blake