North pole guidance

[Loren Pechtel]

There's going to be a minuscule variation in direction due to the changing angular momentum as your missile gets closer to the pole, and a countervailing minuscule variation as it gets closer to the equator, having passed the pole.

For an object as small and fast as a ballistic missile, that variation would be truly tiny, but it's going to be present in any launch not exactly parallel to the equator.

Why would there be any Coriolis effect once you're out of the atmosphere?

The atmosphere has nothing to do with it.

It's a conservation of angular momentum effect.

But once you're clear of the atmosphere how does the Earth's rotation have any effect on the missile? The velocity of the launch platform simply becomes one component of the missile's orbit. (And, yes, it's an orbit--it's just the periapsis is below the surface.)

 

[bilby]

There's going to be a minuscule variation in direction due to the changing angular momentum as your missile gets closer to the pole, and a countervailing minuscule variation as it gets closer to the equator, having passed the pole.

For an object as small and fast as a ballistic missile, that variation would be truly tiny, but it's going to be present in any launch not exactly parallel to the equator.

Why would there be any Coriolis effect once you're out of the atmosphere?

The atmosphere has nothing to do with it.

It's a conservation of angular momentum effect.

But once you're clear of the atmosphere how does the Earth's rotation have any effect on the missile? The velocity of the launch platform simply becomes one component of the missile's orbit. (And, yes, it's an orbit--it's just the periapsis is below the surface.)

The frame of reference is defined by the positions of the launch platform and target, that is, the Earth's surface. Which is rotating, at a velocity that varies with latitude.

If you prefer to use the frame of the missile, there is no force - but then the target is moving, so you miss anyway.

Both perspectives are equally valid, and neither involves the atmosphere.

 

[steve_bank]

To be pedantic....in FO gyros there are no moving parts compared to electromechanical rotating gyros.

 

[Loren Pechtel]

There's going to be a minuscule variation in direction due to the changing angular momentum as your missile gets closer to the pole, and a countervailing minuscule variation as it gets closer to the equator, having passed the pole.

For an object as small and fast as a ballistic missile, that variation would be truly tiny, but it's going to be present in any launch not exactly parallel to the equator.

Why would there be any Coriolis effect once you're out of the atmosphere?

The atmosphere has nothing to do with it.

It's a conservation of angular momentum effect.

But once you're clear of the atmosphere how does the Earth's rotation have any effect on the missile? The velocity of the launch platform simply becomes one component of the missile's orbit. (And, yes, it's an orbit--it's just the periapsis is below the surface.)

The frame of reference is defined by the positions of the launch platform and target, that is, the Earth's surface. Which is rotating, at a velocity that varies with latitude.

If you prefer to use the frame of the missile, there is no force - but then the target is moving, so you miss anyway.

Both perspectives are equally valid, and neither involves the atmosphere.

You have to aim your missile for where the target will be when it comes down. That's how orbital mechanics work, I don't see how you attribute it to the Coriolis force.

 

[bilby]

There's going to be a minuscule variation in direction due to the changing angular momentum as your missile gets closer to the pole, and a countervailing minuscule variation as it gets closer to the equator, having passed the pole.

For an object as small and fast as a ballistic missile, that variation would be truly tiny, but it's going to be present in any launch not exactly parallel to the equator.

Why would there be any Coriolis effect once you're out of the atmosphere?

The atmosphere has nothing to do with it.

It's a conservation of angular momentum effect.

But once you're clear of the atmosphere how does the Earth's rotation have any effect on the missile? The velocity of the launch platform simply becomes one component of the missile's orbit. (And, yes, it's an orbit--it's just the periapsis is below the surface.)

The frame of reference is defined by the positions of the launch platform and target, that is, the Earth's surface. Which is rotating, at a velocity that varies with latitude.

If you prefer to use the frame of the missile, there is no force - but then the target is moving, so you miss anyway.

Both perspectives are equally valid, and neither involves the atmosphere.

You have to aim your missile for where the target will be when it comes down. That's how orbital mechanics work, I don't see how you attribute it to the Coriolis force.

What do you imagine the Coriolis force to be?

Because that is exactly what it is.

In the rotating reference frame of an earthbound observer, a missile fired at a target north or south of the launch platform appears to deviate. You can say that this deviation is due to a force, which, like centrifugal force, doesn't exist from the perspective of a non-rotating frame. Or you can take that non-rotating perspective, and say 'aim for where the target will be' - which is determined by the difference in latitude between launch point and target.

Both descriptions are of the exact same phenomenon - a rotating sphere has different angular velocity and angular momentum at different distances from the poles - and this phenomenon is called the Coriolis Effect.

It's a force if you want it to be, and not if you don't. But either way, it's a real effect that needs to be accounted for in a guidance system, though it may well be small enough to ignore. For short flight times, the deviation is very small.