North pole guidance

[Keith&Co.]

When i was six, i saw a stuntman jump dtraight up off the hood of a speeding pickup, over the cab, and land in the cargo area of the same truck.
Dad explained that inertia meant he traveled with the truck, but lost speed, so he didn't jump over the cab as much as it slid under him.

Next day on the playground i had the idea that i could jump up on the merry-go-round bench and i'd come down on the next bench. Four guys were pushing the MGR for all they were worth, i let go of the bar, jumped straight up, and hit Mrs. Kleinkopff at at pretty good clip. She was just walking over to say something about safety. (Steel equipment on concrete. 1967 satey was playground monitors shouting, 'Don't die!' One adult per 70 children... yeah, not sure how we lived).
Dad never got around to explaining the flaws in my physics, he couldn't stop laughing.

This comes up because a friend of my cousin, who is trying to orgaanize a protest at Subbase Kitsap, has numerous criticisms of the missile program. One is that in case of war, our missiles will be flying over the North Pole. There's apparently 'no telling' how the guidance system will be affected, as all our test shots go west to east, not north to perfect north.

I'm thinking the GS should not give a rat's ass, right?
Once we launch, it becomes an independent body. It has inertia based on what Earth was doing when it let go of the bar, but it won't be continuing in the rotation. Like jumping off the merry-go--hurt, it'll take its speed at time of launch into consideration, but it no longer cares about Earth's axis or spin.

Or am i missing something?

More importantly, though, the chance of a viable target being exactly opposite the pole from the weapon assigned to it is vanishingly small. We'd have yo work really hard to shoot a missile over that small a target.

Far, far more importantly, powered flight is a small fraction of missile flight. Never mind how TV and James Bond make it look like the missile is intact right up to impact, the GS is done way before it gets that far. Not an issue.

 

[steve_bank]

Sounds like a question someone asked about the wind. The wind blows, but it is a vector in line with the with the rotation of the Earth.

If a rocklifts off exacatly normal to the Earth and hovers without any latral thrust and comes down will it chnange position?

I forget the name. There was a woman mathematician around the second century who dropped weights from the mast of a moving ship to see if it landed in a different spot.

In mechanics there is a 'free body diagram'. Draw a small circle on a paper and sketch in all the force vestors acting on it. Then add the vectors to derive direction.

I think the polar path is because it is the shortest flight time from our mid west silos to Moscow.

A lot of info for ballistic missile trajectory

https://www.idc-online.com/technical_references/pdfs/mechanical_engineering/The_rotation_of_Earth_effect_for_ballistics.pdf

THE ROTATION OF EARTH EFFECT
FOR BALLISTICS
The simulation displays ballistic trajectories near the Earth. The panel on the
left shows the trajectory and its trace with respect to the inertial coordinate
system, the panel on the right shows the trajectory and its trace as seen from
a point of view that is co-rotating with the Earth. The values for the rotation
rate and gravitational acceleration (g) are not preset to match to the
circumstances on Earth. Rather, the defaults settings were selected to give a
vivid display. Air resistence effects are not included, so the results are valid
only for celestial bodies with no atmosphere.
In ballistics, two distinct rotation-of-Earth effects are at play.
A. The total velocity after the launch comes from two contributing factors:
- The velocity the projectile already had as it was co-rotating with the
Earth.
- Additional velocity imparted by the launch.
B. After the launch the missile/projectile moves along an orbital trajectory.
The Earth rotates underneath that trajectory. As seen from a co-rotating
point of view there is apparent deflection.

Figure 2. A free body diagram of the aerodynamic forces on a...

Download scientific diagram | A free body diagram of the aerodynamic forces on a maneuvering missile. The diagram includes all terms necessary for analysis of the free response of the short-period approximation. from publication: Integrated Guidance Navigation and Control Using High-Order...

www.researchgate.net

Drawing Free-Body Diagrams

The motion of objects is determined by the relative size and the direction of the forces that act upon it. Free-body diagrams showing these forces, their direction, and their relative magnitude are often used to depict such information. In this Lesson, The Physics Classroom discusses the details...

www.physicsclassroom.com

 

[Loren Pechtel]

This comes up because a friend of my cousin, who is trying to orgaanize a protest at Subbase Kitsap, has numerous criticisms of the missile program. One is that in case of war, our missiles will be flying over the North Pole. There's apparently 'no telling' how the guidance system will be affected, as all our test shots go west to east, not north to perfect north.

I'm thinking the GS should not give a rat's ass, right?
Once we launch, it becomes an independent body. It has inertia based on what Earth was doing when it let go of the bar, but it won't be continuing in the rotation. Like jumping off the merry-go--hurt, it'll take its speed at time of launch into consideration, but it no longer cares about Earth's axis or spin.

Or am i missing something?

More importantly, though, the chance of a viable target being exactly opposite the pole from the weapon assigned to it is vanishingly small. We'd have yo work really hard to shoot a missile over that small a target.

Far, far more importantly, powered flight is a small fraction of missile flight. Never mind how TV and James Bond make it look like the missile is intact right up to impact, the GS is done way before it gets that far. Not an issue.

The guidance cares about the launch situation until it has cleared the atmosphere. Winds aloft can shove it a bit. Once it's in vacuum, though, the Earth is basically just a mass. The North Pole is completely irrelevant to the physics of the missile but in theory there could be a software bug. AFIAK substantial bugs have been found in flying too far below sea level and in crossing the equator. A missile that freaked out about crossing the pole is not beyond the realm of possibility.

My impression is that modern warheads have some terminal guidance capability. That wouldn't be doing anything when it crossed the pole unless the missile was aimed at something very close to the pole though. Aimed at Russia it would have plenty of time to recover if it were programmed well. (It should be designed to restart if it freaks out--whether it is or not is another matter. I'm thinking of the first Ariane V launch that freaked out due to sensor input beyond what the software could understand, resulting in the controls getting stuck at maximum deflection and the rocket breaking up as a result.) Even if it was totally freaked out the terminal guidance won't have a lot of cross range capability anyway, it's still coming down near it's target.

 

[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.

Passing directly over the pole maximises this tiny effect, but I would guesstimate that it's far smaller even in that worst case scenario than other perturbations routinely handled by the guidance system, such as wind shear, variations in gravity, and the motion of the launch platform. Without doing the maths, I would wager that the coriolis effect would cause a deviation of the order of less than a metre in even the most extreme situation; I doubt that's enough to care about for a nuclear warhead. Missing Vladimir by a metre with a thermonuclear device is not going to make him noticeably less dead.

There's nothing particularly special about trans-polar ballistic flight that would need correction that wouldn't be required by any flight entailing a change of latitude.

Perhaps your cousin's friend has heard about compass navigation issues close to the magnetic poles, and is vaguely recalling that navigation is difficult at high latitudes. Which it is, if you are a nineteenth century explorer who is dependent on magnetic compasses; But is not if you are a ballistic projectile that completed its boost phase at low latitudes and/or had modern navigational capabilities such as GPS or even HFDF to refine or replace simple magnetic compass bearings.

 

[Keith&Co.]

(It should be designed to restart if it freaks out--whether it is or not is another matter.

There is a reboot function if it detects an EMI pulse. Everything shuts down and comes up again.
There are warheads with some post-release guidance capability. Must just wait to reach their determined boom parameters, either X seconds after release, or altitude of Y, or impact, or impact plus Z.

 

[Keith&Co.]

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.

Hmmm. At the (unclassified) range of 4000nm, that could be detrimental. Depends on where it hits. We calculated that a 100-arc-second error at launch would be a miss by 2.9nm at range, if uncorrected for.

Passing directly over the pole maximises this tiny effect, but I would guesstimate that it's far smaller even in that worst case scenario than other perturbations routinely handled by the guidance system, such as wind shear, variations in gravity, and the motion of the launch platform.

Air density at target, measured inaccuracies in the GS itself, Time of Day (and Corrected Universal Time), time since last external fix for Navigation sydtem, lever arms, missile misalignment, lauch depth, yeah.

Perhaps your cousin's friend has heard about compass navigation issues close to the magnetic poles, and is vaguely recalling that navigation is difficult at high latitudes.

Really think it's something he heard from someone else, regurgitates whst he kinda remembers.

He started the conversation talking about those evil bastards on subs, and thrrir goals, and she asked if he'd ever met one, since she's related to me and i never once HOPED to shoot in earnest.

 

[steve_bank]

The missiles undoubtedly have inertial guidance these days if for nothing else as a backup to GPS.

Measure accretion and integrate to derive direction, distance, and speed. Subs use inertial navigation.

All the warhead needs to do is to come down in a general area, terminal guidance takes over. I have no idea what state of the art is. It can include radar, thermal video, and visible video to ID and track to a target.

The Nazis used crude electromechanical gyros to guide missiles to hit London.

BTW, is somebody building a ballistic missile in the back yard? We all need to do our part against those pesky Ruskies.

 

[Keith&Co.]

The missiles undoubtedly have inertial guidance these days if for nothing else as a backup to GPS.

Thenes i work on are strickly inertial. At the time of their design, GPS was in infancy, and concerns were about the satellites being shot down.
And SSP hates change. They really do.

Measure accretion and integrate to derive direction, distance, and speed. Subs use inertial navigation.

Backed up by GPS when we come to periscope depth.
There are also ways to use sonar to fix our location on a map of the sea floor.

All the warhead needs to do is to come down in a general area,

That's a negative. We only target hardened military targets with nukes, by treaty. We need precision, not neighborhood.

I have no idea what state of the art is. It can include radar, thermal video, and visible video to ID and track to a target.

You're flexing over to Tomahawk. We use radar, air pressure, a clock, impact (the k-dirt relay), impact plus clock (for max penetration before boom).

 

[steve_bank]

The missiles undoubtedly have inertial guidance these days if for nothing else as a backup to GPS.

Thenes i work on are strickly inertial. At the time of their design, GPS was in infancy, and concerns were about the satellites being shot down.
And SSP hates change. They really do.

Measure accretion and integrate to derive direction, distance, and speed. Subs use inertial navigation.

Backed up by GPS when we come to periscope depth.
There are also ways to use sonar to fix our location on a map of the sea floor.

All the warhead needs to do is to come down in a general area,

That's a negative. We only target hardened military targets with nukes, by treaty. We need precision, not neighborhood.

I have no idea what state of the art is. It can include radar, thermal video, and visible video to ID and track to a target.

You're flexing over to Tomahawk. We use radar, air pressure, a clock, impact (the k-dirt relay), impact plus clock (for max penetration before boom).

Are you on active duty? In the 80s I worked for Kollmorgen on miniature IR cameras that went into periscopes, they also made the periscopes. I was familiar with laser fiber optic gyros that went into subs.

I worked on an anti tank weapn that used mm wave radar imaging. Details were classified but Honeywell had a global terrian data base that coud be downloaded to a weapon.

In the Navy in the 70s I trained as a tech on the old A6 Intruder fire control systems. It could fly a hands off mission profile.

Terminal guidance means accuracy. Artillery munitions have it.

I was not aware of that treaty issue. If NK nukes Tokyo we can't drop on the NK capitol?

 

[Keith&Co.]

The missiles undoubtedly have inertial guidance these days if for nothing else as a backup to GPS.

Thenes i work on are strickly inertial. At the time of their design, GPS was in infancy, and concerns were about the satellites being shot down.
And SSP hates change. They really do.

Measure accretion and integrate to derive direction, distance, and speed. Subs use inertial navigation.

Backed up by GPS when we come to periscope depth.
There are also ways to use sonar to fix our location on a map of the sea floor.

All the warhead needs to do is to come down in a general area,

That's a negative. We only target hardened military targets with nukes, by treaty. We need precision, not neighborhood.

I have no idea what state of the art is. It can include radar, thermal video, and visible video to ID and track to a target.

You're flexing over to Tomahawk. We use radar, air pressure, a clock, impact (the k-dirt relay), impact plus clock (for max penetration before boom).

Are you on active duty? In the 80s I worked for Kollmorgen on miniature IR cameras that went into periscopes, they also made the periscopes. I was familiar with laser fiber optic gyros that went into subs.

I worked on an anti tank weapn that used mm wave radar imaging. Details were classified but Honeywell had a global terrian data base that coud be downloaded to a weapon.

In the Navy in the 70s I trained as a tech on the old A6 Intruder fire control systems. It could fly a hands off mission profile.

Terminal guidance means accuracy. Artillery munitions have it.

I was not aware of that treaty issue. If NK nukes Tokyo we can't drop on the NK capitol?

I was an FTB, 1981 TO 1995, MT 1995 to 2000.
Working at GD since.
Our Guidance systems just started upgrading to gyros with no mobing parts. Every time an engineer explains them, i come away with, "Magic."
I work a tiny bit with Tomahawk (SSGN Launch Control). The options for terminal guidance are many, and much of it's also used to gauge each shot's effectiveness.

As to the tresty, NK is not a signatory of the treaty, i don't believe. Still, before we drop a nuke on them, we'd have to justify it with everyone who might get upset to detect a missile launch. More likely we'd just saturate an area with, Tomahawks off a task force or a sub.

 

[bilby]

Hmmm. At the (unclassified) range of 4000nm, that could be detrimental. Depends on where it hits. We calculated that a 100-arc-second error at launch would be a miss by 2.9nm at range, if uncorrected for.

Sure, but this isn't an angular error at launch; Rather it's a tiny lateral force applied throughout the flight - and reversing as the N/S component of the flight reverses (if the trajectory crosses the equator).

The worst case, a missile launched on the equator and targeting the opposite equatorial position via the pole you're still not going to see a particularly large deviation. Back of the envelope figures get me around 200 metres for such a scenario (about 0.1nm), though I wouldn't be surprised if that was wrong, because my mental arithmetic is shit.

The angular deflection is tiny at the poles, and is zero at the equator, increasing as the latitude increases. That's a lot less significant than a constant angle of launch error, which continually increases in direct proportion to the total distance flown.

Note that my earlier post says (incorrectly) that passing the pole reverses the direction of the deflecting force; In fact this point reverses the increase in that force. Reversal of its direction occurs if the missile crosses the equator. The size of the deflection force is greatest at the pole.

 

[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?

 

[Loren Pechtel]

I was an FTB, 1981 TO 1995, MT 1995 to 2000.
Working at GD since.
Our Guidance systems just started upgrading to gyros with no mobing parts. Every time an engineer explains them, i come away with, "Magic."
I work a tiny bit with Tomahawk (SSGN Launch Control). The options for terminal guidance are many, and much of it's also used to gauge each shot's effectiveness.

No moving parts? My understanding is that the moving "part" is light rather than mechanical. That doesn't mean it's not moving, though. (Send the light around a ring. Rotation around the axis of the ring will doppler shift the light.)

 

[Keith&Co.]

I was an FTB, 1981 TO 1995, MT 1995 to 2000.
Working at GD since.
Our Guidance systems just started upgrading to gyros with no mobing parts. Every time an engineer explains them, i come away with, "Magic."
I work a tiny bit with Tomahawk (SSGN Launch Control). The options for terminal guidance are many, and much of it's also used to gauge each shot's effectiveness.

No moving parts? My understanding is that the moving "part" is light rather than mechanical. That doesn't mean it's not moving, though. (Send the light around a ring. Rotation around the axis of the ring will doppler shift the light.)

Sure, sure, light moves.
But going from two spinning frisbee on flexible shafts that detect torque on two axes each, overlapping to measure 3D movement
TO
three solid state single one axis inputs, meets my (admittedly uneducated) standard for 'no moving parts.'

 

[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.

 

[steve_bank]

I was an FTB, 1981 TO 1995, MT 1995 to 2000.
Working at GD since.
Our Guidance systems just started upgrading to gyros with no mobing parts. Every time an engineer explains them, i come away with, "Magic."
I work a tiny bit with Tomahawk (SSGN Launch Control). The options for terminal guidance are many, and much of it's also used to gauge each shot's effectiveness.

No moving parts? My understanding is that the moving "part" is light rather than mechanical. That doesn't mean it's not moving, though. (Send the light around a ring. Rotation around the axis of the ring will doppler shift the light.)

A common sensing method in fiber-optic sensors is using a small interferometer to detect phase changes between two paths. The interferometers are common and are sold conectorized for FO.

The other is micro-bending. Bend a fiber optic cable and some light will leak proportional to bending..

 

[Shadowy Man]

I was an FTB, 1981 TO 1995, MT 1995 to 2000.
Working at GD since.
Our Guidance systems just started upgrading to gyros with no mobing parts. Every time an engineer explains them, i come away with, "Magic."
I work a tiny bit with Tomahawk (SSGN Launch Control). The options for terminal guidance are many, and much of it's also used to gauge each shot's effectiveness.

No moving parts? My understanding is that the moving "part" is light rather than mechanical. That doesn't mean it's not moving, though. (Send the light around a ring. Rotation around the axis of the ring will doppler shift the light.)

Sure, sure, light moves.
But going from two spinning frisbee on flexible shafts that detect torque on two axes each, overlapping to measure 3D movement
TO
three solid state single one axis inputs, meets my (admittedly uneducated) standard for 'no moving parts.'

Yes. this is what "no moving parts" means. No mechanisms to wear out, nothing with mass moving around. I don't know anyone who wasn't simply dealing in pedantry who would consider the light in a optical gyroscope as a "moving part".

 

[Keith&Co.]

I don't know anyone who wasn't simply dealing in pedantry who would consider the light in a optical gyroscope as a "moving part".

I think he's teasing me. Which is not to discount the charge of pedantry, but...context.

 

[steve_bank]

I understand the police run stings on the net to expose pedantic-try.

 

[Loren Pechtel]

I was an FTB, 1981 TO 1995, MT 1995 to 2000.
Working at GD since.
Our Guidance systems just started upgrading to gyros with no mobing parts. Every time an engineer explains them, i come away with, "Magic."
I work a tiny bit with Tomahawk (SSGN Launch Control). The options for terminal guidance are many, and much of it's also used to gauge each shot's effectiveness.

No moving parts? My understanding is that the moving "part" is light rather than mechanical. That doesn't mean it's not moving, though. (Send the light around a ring. Rotation around the axis of the ring will doppler shift the light.)

Sure, sure, light moves.
But going from two spinning frisbee on flexible shafts that detect torque on two axes each, overlapping to measure 3D movement
TO
three solid state single one axis inputs, meets my (admittedly uneducated) standard for 'no moving parts.'

The movement of the light is critical to it's function, I would consider that a moving part. It's not like most solid state devices where it's the electric fields that matter, not movement.