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Old 05-19-2019, 11:59 PM
SamuelA is offline
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How do submarine launched ballistic missiles fly when launched from "point blank" ranges?


So if you look at a map of the United States, and try to red team out what a hypothetical Soviet attack might try, you notice an obvious vulnerability.

The Pentagon, the White House, the aircraft that can serve as a mobile command post - all are within just a few miles of the ocean.

An obvious thing for the Soviets to try would be to attempt to sneak a submarine loaded with ballistic missiles right into Chesapeake Bay and fire at basically point blank range.

The Soviets apparently never managed to make their submarines quiet enough to do this, and there are supposedly vast underwater hydrophone arrays in the Atlantic for the specific reason of preventing this kind of attack*, but nevertheless, it makes for an interesting question.

Hypothetically, the Soviets had pulled this off. They have an Akula class submarine with it's pumpjet propulsor in Chesapeake Bay and they open fire.

Would the ballistic missiles be able to hit their targets without first traveling up into space? It seems physically possible to just cant the missile over and use the remaining rocket fuel to get it to the target even faster, reducing the warning time to less than 60 seconds.

Do ballistic missile submarines have the capacity to fire their entire payload all at once, or must they fire each missile individually? The reason this is important is that according to books like Blind Man's bluff, the US managed to tail many of the Soviet submarines while they were on patrol, and would obviously have several torpedo tubes loaded and ready to fire at a moment's notice if they heard the Soviet submarine firing a missile.

But they couldn't tail all that close, and it seems like at least the first missile would escape the submarine before the torpedo coming to kill it could possibly get there...

*this also would explain why the PAL codes were not actually used for years. If the Soviets could plausibly hit in 2 minutes every individual with authorization to order a nuclear launch and destroy every copy of the codes, it would be a vulnerability to have them.

Last edited by SamuelA; 05-20-2019 at 12:01 AM.
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Old 05-20-2019, 12:11 AM
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I'm not an expert, but there are some preparatory steps to launching, like opening the missile launch doors, that a nearby submarine could probably detect and identify.

And I don't believe they can fire all their missiles simultaneously, but they can shoot them off in pretty close succession. For example, here is a Russian Borei-class SSBN firing off four missiles within a few seconds of each other.

But, what good would nuking the White House and Pentagon do anyways? Russia still gets nuked in response, even if they've managed to kill the President, VP, Congress, and the Joint Chiefs.
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Old 05-20-2019, 12:14 AM
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Originally Posted by SamuelA View Post
Would the ballistic missiles be able to hit their targets without first traveling up into space? It seems physically possible to just cant the missile over and use the remaining rocket fuel to get it to the target even faster, reducing the warning time to less than 60 seconds.
I don't know about "less than 60 seconds", even for Washington, D.C., but in general this is referred to as a depressed trajectory launch. This paper* from the early Nineties discusses some of the strategic relevance of the concept.

*About a 7.5 meg PDF file, if that's of any relevance to whatever device you're using to read stuff on the Internet.
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Old 05-20-2019, 12:37 AM
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Originally Posted by HurricaneDitka View Post
And I don't believe they can fire all their missiles simultaneously, but they can shoot them off in pretty close succession. For example, here is a Russian Borei-class SSBN firing off four missiles within a few seconds of each other.

But, what good would nuking the White House and Pentagon do anyways? Russia still gets nuked in response, even if they've managed to kill the President, VP, Congress, and the Joint Chiefs.
Thanks for the video, Ditka. Those launch intervals are so fast as to be basically simultaneous. The Mark 48 torpedo only travels approximately 60 mph - if the trailing submarine is 1 mile away, at the launch rate shown in the video, the boomer is going to be empty before the torpedo arrives.

As for why - if there are a finite number of copies of the nuclear launch codes, and the Russians/Soviets knew where they all were (with spies like Anna Chapman's hot sisters on the case, how could they not?), in principle they could prevent themselves getting nuked in response. A slim chance but not impossible. Sort of like the math during the Cuban missile crisis - if the US had made a devastating first strike with ballistic missiles, especially aimed at the Russian bomber bases, and had been very lucky with their air defense that day, they would in principle have "won" ww3 with just a few million casualties, "depending on the breaks".

Last edited by SamuelA; 05-20-2019 at 12:39 AM.
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Old 05-20-2019, 12:44 AM
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A few megadeaths.
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Old 05-20-2019, 04:38 AM
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Similarly, how effective would a nuclear torpedo be if a submarine launched it at a coastline hoping to do some shoreline damage against nearby buildings?
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Old 05-20-2019, 09:16 AM
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The real trick would be limiting the range. SLBMs are typically solid-fueled rockets, and meant to be launched within a very narrow span of ranges.

Depressed trajectory launches would be made primarily to achieve very short in-flight times- 7 to 10 minutes according to MEBuckner's PDF cite, giving your adversary little time to react, even relative to the ~15 minute normal SLBM time-on-target. Even ICBMs are roughly 30 minutes.

But this is achieved by flying unusual flat trajectories. Even at that, they're still on the order of 1500-3000 km (as opposed to the more typical 7500+ km range of modern SLBMS). What this means is that a SSBN sitting in Chesapeake Bay would be limited to hitting targets somewhere along a minimum range arc that would be defined very roughly by Minneapolis, Des Moines, Kansas City, Springfield, MO, Little Rock, Jackson, MS, and New Orleans.

That range would be great for taking out the bomber bases, but the ICBM fields in the far northern Midwest are still mostly out of range.

If the goal was some kind of nuclear decapitation strike, they'd do better to figure out how to ship a bomb to Washington DC in a shipping container or on a fishing boat or something innocuous like that.
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Old 05-20-2019, 09:24 AM
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Correct me if I'm wrong, but this things are better used as air burst, exploding above the ground. If so it seem like just having it fly over the target then detonating it is trivial.
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Old 05-20-2019, 09:37 AM
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If a Russian submarine were to seek to attack the coasts of the United States, I can't see why it would use a ballistic missile to do so. Russia has developed extremely effective cruise missiles, including submarine-launched ones.

https://nationalinterest.org/blog/bu...missiles-49727
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Old 05-20-2019, 09:55 AM
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Correct me if I'm wrong, but this things are better used as air burst, exploding above the ground. If so it seem like just having it fly over the target then detonating it is trivial.
Sure, but you have to do it at the right height. Just detonating a nuke over something at 100,000 feet isn't going to do much.
The optimal height for the largest nuclear weapon ever designed is a little less than 50,000 feet. For your more everyday nukes, we're looking at more like 10,000 feet.
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Old 05-21-2019, 08:35 AM
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I'm confused by the original post. Here's where. . .

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Originally Posted by SamuelA View Post
An obvious thing for the Soviets to try would be to attempt to sneak a submarine loaded with ballistic missiles right into Chesapeake Bay and fire at basically point blank range.
Why would this be obvious? Why would a competent Soviet sub Captain put his entire payload of ballistic missiles and independent warheads at risk of detection and destruction in near-littoral waters of the United States?

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Originally Posted by SamuelA View Post
The Soviets apparently never managed to make their submarines quiet enough to do this, and there are supposedly vast underwater hydrophone arrays in the Atlantic for the specific reason of preventing this kind of attack*, but nevertheless, it makes for an interesting question.

Hypothetically, the Soviets had pulled this off. They have an Akula class submarine with it's pumpjet propulsor in Chesapeake Bay and they open fire.
The Akula Class is an attack submarine (SSN equivalent) and does not carry ballistic missiles. It does carry cruise missiles. I think you are either confusing weapons or confusing classes of Russian submarines. Clarifiy?

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Would the ballistic missiles be able to hit their targets without first traveling up into space? It seems physically possible to just cant the missile over and use the remaining rocket fuel to get it to the target even faster, reducing the warning time to less than 60 seconds.
No. Ballistic missiles need time to do things prior to detonation--i.e. navigate. Missiles are built for axial load support, not lateral. The missile would be unstable if it just "canted over". Missiles also do not have flight control surfaces to sustain horizontal flight and guidance. Missiles use thrust vectoring to position the payload above the earth, and drop payload items from above. ICBMs are not built for lift generated by airflow, they are built for lift generated by thrust. Cruise missiles are built for lift generated by airflow.

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Please clarify. . .
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Old 05-21-2019, 08:43 AM
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But, what good would nuking the White House and Pentagon do anyways? Russia still gets nuked in response, even if they've managed to kill the President, VP, Congress, and the Joint Chiefs.
I feel like I read somewhere that nuking the other side's leadership was not considered a good strategy because the missiles and bombers would fly anyway, but there would be no one to recall them or shut it down.


Which leads me to wonder what the actual strategies were for nuclear war, aside from the concept of "MAD" and simply having so many nukes that neither side would benefit from starting a war.
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Old 05-21-2019, 09:00 AM
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No. Ballistic missiles need time to do things prior to their weapons’ detonation--i.e. navigate.
Missed the editing window, but I wanted to clarify.

Msmith, read Command and Control. It’s about the Damascus disaster, but it brings up a good point—if you decapitate a government via nuclear strike, who do you negotiate a cease fire with?

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Last edited by Tripler; 05-21-2019 at 09:00 AM.
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Old 05-21-2019, 10:03 AM
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Why would a competent Soviet sub Captain put his entire payload of ballistic missiles and independent warheads at risk of detection and destruction in near-littoral waters of the United States?
Good question. I also donít see why this is a obvious thing to attempt.

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Missiles are built for axial load support, not lateral.
Huh? I mean, the axial loads on a missile during launch are tremendous, yes. But missiles are always launched axially; launching them sideways doesnít seem to work very well. I hear the rule of thumb is to keep the nose cone pointed in the direction of travel.

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The missile would be unstable if it just "canted over".
Why do you say that?

And even if it were true, why arenít ballistic missiles unstable when they cant over just before apogee? Horizontal is horizontal, even 600 miles above the earth. At this altitudeóthe apogee of a Polaris S3óthe earthís gravity is still about 75.5% as strong as it is on the surface at the equator.

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Missiles also do not have flight control surfaces to sustain horizontal flight and guidance. Missiles use thrust vectoring to position the payload above the earth, and drop payload items from above.
ICBMs do thisóthat is, they fly ballistic trajectories after their engines burn out, putting the B in ďICBM.Ē But plenty of non-ballistic missiles fly arbitrary trajectories, whether guided to those trajectories by fins, thrust vectoring or both. External control surfaces arenít necessary to sustain horizontal flight.

The only requirement for horizontal flight is that the missile generate a ~1g acceleration in a direction opposite to the gravity vector, whether thatís done with fins, thrust vectoring or conventional wings.

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ICBMs are not built for lift generated by airflow, they are built for lift generated by thrust. Cruise missiles are built for lift generated by airflow.
Thatís true, but either could fly horizontally and either could fly vertically. The cruise missile may not have the thrust-to-weight ratio to sustain vertical flight for long, but cruise missiles have no inherent inability to fly vertically. Neither is there an inherent barrier to a vectored-thrust missile vectoring its thrust to fly horizontally.
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Old 05-21-2019, 10:10 AM
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... because the missiles and bombers would fly anyway, but there would be no one to recall them or shut it down.
I know you're talking about both, but ICBMs can't be recalled once launched. There's no self-destruct (it would be vulnerable to being used by the enemy).

There's no turning back - if an ICBM were launched [Kiefer Sutherland voice] MILLIONS OF PEOPLE WILL DIE![KSV]

Last edited by Just Asking Questions; 05-21-2019 at 10:10 AM.
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Old 05-21-2019, 10:15 AM
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The Akula Class is an attack submarine (SSN equivalent) and does not carry ballistic missiles. It does carry cruise missiles. I think you are either confusing weapons or confusing classes of Russian submarines. Clarifiy?
Actually, there are two different Akulas - one is the fast-attack SSN, as you mention (but which is designated by NATO as Akula,) and then there is the Typhoon-class ballistic-missile sub, also known as Akula. I am assuming SamuelA meant the Typhoon.
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Old 05-21-2019, 07:48 PM
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Actually, there are two different Akulas - one is the fast-attack SSN, as you mention (but which is designated by NATO as Akula,) and then there is the Typhoon-class ballistic-missile sub, also known as Akula. I am assuming SamuelA meant the Typhoon.
That's what I figured.

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Originally Posted by EdelweissPirate View Post
Good question. I also donít see why this is a obvious thing to attempt.
Thank you. I mean, why put your SLBMs at risk, when you can use a more apporpriate weapon--cruise missiles--and save your SLBMs for second-strike capability?

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Huh? I mean, the axial loads on a missile during launch are tremendous, yes. But missiles are always launched axially; launching them sideways doesnít seem to work very well. I hear the rule of thumb is to keep the nose cone pointed in the direction of travel.

Why do you say that?

And even if it were true, why arenít ballistic missiles unstable when they cant over just before apogee? Horizontal is horizontal, even 600 miles above the earth. At this altitudeóthe apogee of a Polaris S3óthe earthís gravity is still about 75.5% as strong as it is on the surface at the equator.
Combining comments here to address them in one response.

I was speaking in the context of the OP--in the context of ballistic missiles. And my answers are caveatted against his "point blank, less-than-60-seconds-warning" supposition. Yes, all missiles are launched and powered with the pointy end into the direction of travel. However, not all missiles are constructed the same.

In broad brush terms, there are "lift" missiles and "attack" missiles, based on their flight profile (yes, I'm coining those terms for just this discussion). For example, AGM-114 Hellfires and AIM-120 AMRAAMs are fired at their target to 'attack' them. Their flight profiles are more-or-less horizontal to the earth, to deliver their payload to a target in roughly that same plane. "Lift" missiles on the other hand, like the Delta IV, the Minuteman, and the Trident D5 are designed to lift their payload to a higher altitude, in a more-or-less perpendicular flight profile to the earth. This difference in flight profile drives mechanical design difference between the "lift" and "attack" missiles. Lift missiles are obviously larger, and can use their fuel systems to support the mass of the missile against the pull of gravity axially. Attack missiles are constructed with a body structure that resists gravity during handling, loading, and time of flight laterally. Lift missiles go up, but can tip to some degree--not much. They normally just don't have the design features; adding them in would cut back on the range of the missile (the "NASCAR" principle--'less weight, go further').

At apogee (or just before), the missile has shed its first and second stages after they have burned out. The geometry of the flight body has changed, and thus its center of gravity.

Quote:
Originally Posted by EdelweissPirate View Post
ICBMs do thisóthat is, they fly ballistic trajectories after their engines burn out, putting the B in ďICBM.Ē But plenty of non-ballistic missiles fly arbitrary trajectories, whether guided to those trajectories by fins, thrust vectoring or both. External control surfaces arenít necessary to sustain horizontal flight.

The only requirement for horizontal flight is that the missile generate a ~1g acceleration in a direction opposite to the gravity vector, whether thatís done with fins, thrust vectoring or conventional wings.
No, but some sort of control surface or thrust vectoring is necessary to sustain controlled horizontal flight. SLBMs are meant to lift their payload, not fly them roughly perpendicular to the surface of the earth. With the weight of a fully-fueled, just-launched SLBM from its position, it would have one mother truckin' hell of a time maintaining the proper control to fly horizontal.

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Originally Posted by EdelweissPirate View Post
Thatís true, but either could fly horizontally and either could fly vertically. The cruise missile may not have the thrust-to-weight ratio to sustain vertical flight for long, but cruise missiles have no inherent inability to fly vertically. Neither is there an inherent barrier to a vectored-thrust missile vectoring its thrust to fly horizontally.
I disagree. Without control surfaces, the output thrust by the SLBM would be split between two things: maintaining forward velocity, and maintaining it's altitude. Just like the cruise missile would perform poorly flying vertically, the SLBM would perform poorly flying horizontally.

MEBuckner that's a good paper--I read it earlier today. Thank you!

Tripler
There's other factors besides SLBM performance that make the OP a no-go.
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Old 05-21-2019, 10:13 PM
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Tripler, I meant the typhoon class.

As for canting over - this works in Kerbal space program, a notoriously loose simulator for structural dynamics and aerodynamics. So I had a feeling it wouldn't work - but the basic trajectory does work. Basically the ICBM would ascend to just a few thousand feet and immediately use it's thrust vectoring to angle below the horizontal for a ground burst on the white house or Pentagon. I think you are right, the missile would fail from the structural stresses and fixing this would make it a less good ICBM because it would be heavier.

I meant this was an obvious attack in that if Soviet submarines were as difficult to detect as American submarines supposedly are it could sneak there. And firing from point blank means the enemy gets no chance to respond and the various atomic blasts might destroy any aircraft coming to destroy the submarine.

If the missile launch interval is 10 seconds between missiles the sub could empty it's payload and sneak away before anything could be scrambled to stop it.

Again, this assumes stealth on approach -obviously if it's detected this won't work.

Though having the subs fire from the territorial limit doesn't give much warning either does it.
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Old 05-22-2019, 01:31 AM
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With the weight of a fully-fueled, just-launched SLBM from its position, it would have one mother truckin' hell of a time maintaining the proper control to fly horizontal.
Um. What?

Letís think about the relative magnitudes of the vector components of the forces acting on a submarine-launched ballistic missile (SLBM). The gravity vector is trivial compared to pretty much everything else.

If you still disagree, youíre making an extraordinary claim. To coin a phrase, extraordinary claims require extraordinary evidence. What evidence do you have?
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Old 05-22-2019, 07:37 AM
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Um. What?
"Um. . ." let me spell it out for you. The fully-weighted SLBM (a heavy cylinder) with one point of lift (the exhaust), canted over in such a way to achieve a an overall horizontal trajectory, would have to fly in an attitude that would make it look like an drunken sailor, unsteady on his feet, just thrown out of a bar: moving in a direction, but wildly unsteady.

Want an example you can practice? Balance a pen/pencil on your finger, pointy end down, and try to walk to a corner of the room. Tell me how straight of a line you make. . .

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Letís think about the relative magnitudes of the vector components of the forces acting on a submarine-launched ballistic missile (SLBM). The gravity vector is trivial compared to pretty much everything else.
Okay, lets do that. The gravity vector is trivial compared to what, exactly? Gravity is the first and foremost problem you've got. Drag is induced by velocity, and lift is generated by thrust, in which thrust is shared between generating that lift and fighting its induced drag.

And an SLBM is not a single point in space--it is a weighted cylinder with a CG far offset (to the center of length of the cylinder) from its center of lift (the exhaust). Stability is achieved by balancing the CG atop the center of lift, or damned close to it.

These missiles are designed to overcome gravity (and axial drag). Try the afore-recommended pen-on-finger trick.

Quote:
Originally Posted by EdelweissPirate View Post
If you still disagree, youíre making an extraordinary claim. To coin a phrase, extraordinary claims require extraordinary evidence. What evidence do you have?
Extraordinary claims require extraordinary evidence. Are you claiming that gravity is not the first and foremost problem with a missile designed to boost a payload?

Here's a YouTube of a D5 test gone wrong. What happened? Multiple things. This pen didn't make it to the corner (it was command destructed)

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Old 05-22-2019, 07:43 AM
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Do you really want to fire missiles with nuclear warheads "at point blank range"? I guess they could find a crew for a suicide mission for the Motherland.
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Old 05-22-2019, 08:11 AM
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Do you really want to fire missiles with nuclear warheads "at point blank range"? I guess they could find a crew for a suicide mission for the Motherland.
It's not the 1960s any more. Why bother sneaking in a sub as a prelude to Armageddon, if that ever even made sense, when you can send in the nuclear-powered underwater drones, nuclear-powered cruise missiles, accurate FOBS, various hypersonic missiles, etc.?

ETA it is expensive hardware, but it's not like the following year's budget will be an issue.

Last edited by DPRK; 05-22-2019 at 08:13 AM.
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Old 05-22-2019, 08:25 AM
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It's not the 1960s any more. Why bother sneaking in a sub as a prelude to Armageddon, if that ever even made sense, when you can send in the nuclear-powered underwater drones, nuclear-powered cruise missiles, accurate FOBS, various hypersonic missiles, etc.?
Because those technologies aren't actually operational today.
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Old 05-22-2019, 12:53 PM
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Do you really want to fire missiles with nuclear warheads "at point blank range"? I guess they could find a crew for a suicide mission for the Motherland.

Missiles can be lobbed from ~20m underwater and well enough away from the blast zone while still giving only a 5 minute warning to the target. And y'know, at that point the immediate priority will probably not be "track and destroy that submarine !"
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Old 05-22-2019, 01:19 PM
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So, let's say you have a missile that can handle loads and has some lift and the flight control surfaces for it. Normally, it would go at ballistic missile speed in a high arc trajectory but now you have it fly in a shallow trajectory. How fast can it go? If you take an SLBM and have it burn pointing up at 5 degrees or so, what will be its maximum speed and average speed over, say, 100km? You could presumably do this with truck-mounted ballistic missiles aiming at targets 10km away. That's the sort of thing the Soviets would have planned for.
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Old 05-22-2019, 01:42 PM
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Oh where is Stranger on A Train when you need him...

One thing about the SLBM flying in atmosphere vs flying in space is that the aerodynamic loads on the SLBM should be much greater in the former. It's going faster, for one, and unlike its normal flight path, it should still be in atmosphere when it's accelerating much more heavily towards the end of first, and especially second, stage burnout.

For the wiki on the Trident D5, it says that first stage burnout occurs 65 seconds after launch. I don't know, but I'm guessing that the missile is well out of the atmosphere, and aerodynamic pressure consequently much lower, near the end of that burn.

I'd think maxQ for a sideways flight path would be much greater than its design limits, and there'd probably be a loss of vehicle. There's probably an altitude below the Karman Line though where atmospheric pressure could be low enough that maxQ would be within airframe design limits. Though stagnation heating might be an issue?

Ravenman hit it with the idea that an enemy'd use much stealthier cruise missiles for this sort of decapitation strike, even if those were slower than this sideways SLBM. Much lower launch signature too, at least thermally, and probably acoustically too.
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Old 05-22-2019, 01:45 PM
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Although if you want truly stealthy decapitation, besides pre-positioning the warhead on the target, gravity bomb delivery from a stealthy aircraft should yield next to no warning. Which is one reason I think why the Soviets deployed things like Perimeter/Dead Hand.
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Old 05-22-2019, 05:33 PM
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Like any such question you are not going to get a reliable exact answer based on classified information and I believe classification would enter in to an exact answer. However no reference suggests the standard US SLBM has any special depressed trajectory capability. There are public references quoting 2000km as minimum range of Trident D5, and that probably involves an especially *high* trajectory, like the very high trajectories of some North Korean long range BM tests where they wanted to limit the provocation of having the stages and delivery vehicle come down out in the Pacific, so launched them on a very high short trajectory into the Sea of Japan. Despite Trident being a more advanced weapon, I see no reason to assume it has a special low trajectory capability: nothing indicates any design intention to use it for surprise short range strikes.

During the Cold War there was actually speculation that the Soviets had nuclear mines they'd deploy in Western waters before a war broke out, though no post-Soviet info confirms this AFAIK. But the Russian development of a long range nuclear Unmanned Underwater Vehicle recently suggests the general idea could have occurred in Russia before.

Soviet nuclear armed cruise missile subs were also viewed as a risk factor for US installations near the coasts, as were shorter (than Trident) ranged early Soviet SLBM's. SAC largely abandoned bomber bases on the coasts in favor of those in the middle of the country for that reason, more warning time against offshore cruise/BM launches.

Last edited by Corry El; 05-22-2019 at 05:35 PM.
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Old 05-22-2019, 08:29 PM
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Originally Posted by Tripler View Post
[...] some sort of control surface or thrust vectoring is necessary to sustain controlled horizontal flight.
That’s right—and US SLBMs have gimbaled nozzles, so they meet this requirement.

I’m going to step back here for a moment and explain my objection to your claims about horizontal rocket flight, lest this devolve into more of a sneerfest1 than it already has.

I think you might be conflating inherent stability and other definitions of stability. To wit:

Quote:
Originally Posted by Tripler View Post
The missile would be unstable if it just “canted over.”
The missile is inherently unstable from the moment it clears the sub. Lacking inherent aerodynamic stability, a finless SLBM’s attitude is uncontrollable without thrust vectoring. The direction of travel itself has nothing to do with whether the missile’s attitude is controllable.

Missiles with enough fin area aft of the center of mass become inherently stable due to aerodynamic forces once they exceed a certain airspeed, yes, but SLBMS typically don’t have fins.

Contrary to your assertion above, an SLBM is not significantly less stable when flying horizontally than it is when flying vertically. In both cases, it relies on thrust vectoring to maintain a relatively constant attitude. A constant, relatively small acceleration like gravity is not a challenge for a thrust-vectoring attitude control system.

I pointed out that ballistic missiles are “flying” parallel to the earth’s surface at apogee and manage not to tumble out of control or tear themselves apart. In response, you said:

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Originally Posted by Tripler View Post
At apogee (or just before), the missile has shed its first and second stages after they have burned out. The geometry of the flight body has changed, and thus its center of gravity.
Again, you seem to think there’s something about “going up” that provides inherent stability—otherwise, why mention “center of gravity?”

The location of the center of mass is one factor in determining how much thrust-vectoring authority is required to keep the missile pointed in the desired direction. But the missile was controlled with thrust vectoring from launch to apogee, even as the solid propellant burned away and as the stages dropped away, both of which alter the rocket’s center of mass. If your three-stage rocket is controllable with a full fuel load and all three stages (at launch) it’s going to be controllable for the rest of the flight.

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Originally Posted by Tripler View Post
Lift missiles are obviously larger, and can use their fuel systems to support the mass of the missile against the pull of gravity axially. Attack missiles are constructed with a body structure that resists gravity during handling, loading, and time of flight laterally. Lift missiles go up, but can tip to some degree--not much.
It almost sounds like you’re trying to distinguish between axial strength and bending strength. It’s true that a Sidewinder turning at, say, 10 g is going to experience very different loads from an SLBM, and naturally each missile is designed for the loads it will encounter. But at apogee, the gravity vector is perpendicular to the axis of travel, just as it would be any other time the missile is flying parallel to the earth’s surface. And the acceleration of Earth’s gravity isn’t much weaker at 1000 km than it is at 0 km: it’s about 76% as strong as at the Earth’s surface. So no, flying horizontally is not going to automatically tear a Trident II apart.

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Originally Posted by Tripler View Post
SLBMs are meant to lift their payload, not fly them roughly perpendicular to the surface of the earth.
You must mean “parallel,” not “perpendicular” here. Right?

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Originally Posted by Tripler View Post
With the weight of a fully-fueled, just-launched SLBM from its position, it would have one mother truckin' hell of a time maintaining the proper control to fly horizontal.
No, it wouldn’t struggle to maintain control just after launch. The demands on the gimbaled nozzle’s attitude authority under horizontal flight aren’t very different from those demands when flying vertically. The missile is inherently unstable in either case.

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Originally Posted by Tripler View Post
Want an example you can practice? Balance a pen/pencil on your finger, pointy end down, and try to walk to a corner of the room. Tell me how straight of a line you make. . .
I’m not sure what you’re trying to convey here or how you think your example applies to the question at hand. Gimbaled nozzles alone are adequate to maintain attitude control on rockets without inherent aerodynamic stability—who cares if human beings struggle to balance a pencil on end?

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Originally Posted by Tripler View Post
The gravity vector is trivial compared to what, exactly?
The gravity vector is small compared to the other loads applied to the missile. The rocket motor might produce a peak acceleration of 7 g; aero loads can also be very large, and there are bending moments induced by thrust vectoring.

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Gravity is the first and foremost problem you've got.
In terms of structural response, gravity is less than 1/7th the “problem” that aero thrust-acceleration loads are. It’s true that a huge amount of energy is required to accelerate to orbit or to escape Earth’s gravity well; are you maybe thinking of that?

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Originally Posted by Tripler View Post
And an SLBM is not a single point in space--it is a weighted cylinder with a CG far offset (to the center of length of the cylinder) from its center of lift (the exhaust). Stability is achieved by balancing the CG atop the center of lift, or damned close to it.
No, stability is achieved by thrust vectoring and very fast-acting closed-loop control systems. Again, you seem to think that keeping the center of mass “above” the rocket nozzle somehow makes a rocket inherently stable. That’s just not true.

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Originally Posted by Tripler View Post
These missiles are designed to overcome gravity (and axial drag).
For some reason, you seem to be ignoring acceleration loads from the rocket motor. Statements like this make me wonder whether you’re using the word “gravity” to mean “all axial acceleration loads.” Is that what you’re doing here?

It’s true that any given SLBM is designed for a particular peak dynamic pressure (max Q). That max Q assumes that, as acceleration/velocity increase, air density decreases. Since an SLBM flying horizontally encounters a near-constant air density, such a missile could easily encounter peak dynamic pressures well in excess of those for which it was designed. (Gray Ghost stated this upthread, and succinctly. Cheers!)

Furthermore, gimbal movements that would be fine below the designed max Q could well end badly if the dynamic pressure is higher than the designers anticipated. I would never argue otherwise.

But that’s not what you said. You said that an SLBM would be “unstable” if “canted over” to fly horizontally. Then you said that it wouldn’t be unstable, but only at apogee, because the rocket’s center of mass had shifted enough in an unspecified direction. Those were the points I took issue with.





1 I acknowledge that I contributed to the sneering. I regret it, which is why I’m trying to shift the tone.

Last edited by EdelweissPirate; 05-22-2019 at 08:32 PM.
  #30  
Old 05-22-2019, 08:58 PM
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When a Trident (or whatever missile you choose) is at apogee, the payload is conducting its maneuvers to take readings from its star tracker while continuing on its same ballistic flight path.

Talking about a payload traveling perpendicular to the earth while at apogee would seem to me to have literally nothing to do with the depressed trajectory being discussed here... unless you think a D5 could conduct the same maneuvers at <10,000 feet and continue along its flight path.
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Old 05-22-2019, 09:03 PM
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As a side note, this is a special, special case. I'm saying the missile fires from inside the Chesapeake - it's targets are under 10 miles away. The only reason the submarine wouldn't be destroyed by the blast is it's firing from underwater and the water:air impedance interface would probably block most of the overpressure.

So the aerodynamic loads might not be very high because the missile doesn't really accelerate very long. You might also throttle back and have it travel more slowly so it doesn't break up in the atmosphere.
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Old 05-22-2019, 10:06 PM
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As a side note, this is a special, special case. I'm saying the missile fires from inside the Chesapeake - it's targets are under 10 miles away. The only reason the submarine wouldn't be destroyed by the blast is it's firing from underwater and the water:air impedance interface would probably block most of the overpressure.

So the aerodynamic loads might not be very high because the missile doesn't really accelerate very long. You might also throttle back and have it travel more slowly so it doesn't break up in the atmosphere.
You can't throttle back though. SLBMs are solid-fueled these days. So there's no throttling back or stopping the booster burn.

The best you can do is put it into some kind of trajectory that is going to have a lot of atmospheric resistance- more flat and not at all optimal in terms of payload.

But even at that, we're looking at something on the order of 1500-2000 kilometers minimum range, which is SHORT, considering the maximum range is more like 7500-8000 km on a more conventional trajectory.

They'd have to be out in the Atlantic or maybe in the Gulf to hit Washington like that. The real advantage would be that the flight time would reduce from about 15 minutes to about 9 minutes.


https://www.cia.gov/library/readingr...0000500575.pdf
  #33  
Old 05-23-2019, 01:30 PM
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Thanks for the video, Ditka. Those launch intervals are so fast as to be basically simultaneous. The Mark 48 torpedo only travels approximately 60 mph - if the trailing submarine is 1 mile away, at the launch rate shown in the video, the boomer is going to be empty before the torpedo arrives.
I don't think there's enough info in the video to determine that.

Because the question is not whether a torpedo can arrive between the launch of the first missile and the last. The question is whether a torpedo can arrive between the first unambiguously detectable step on the missile-launch procedure and the first (or last) missile launch).
  #34  
Old 05-23-2019, 11:17 PM
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1 I acknowledge that I contributed to the sneering. I regret it, which is why I’m trying to shift the tone.
I realize that I'm not helping the downward glideslope either, and I apologize. I haven't done rocketry since college (20 yrs ago), and have lost a lot of the memory on proper definitions (i.e. Max Q, centers of gravity, centers of lift, etc.). My concepts are clear in my mind, but I've been poorly articulating them through bad anecdotes and analogies. I've also been trying to do this while being rushed, and from a tablet/cellphone, which isn't helping. Please accept my apologies for lending to a poor tone, and I'll try to better describe what I'm proposing. I invite you, (and anyone else that wants to come), to a virtual barbecue restaurant, where we can discuss the OP, like proper Engineers: over a couple 'o' slabs of ribs and heapin' baskets of fries, with beverages of your choice. That being said, please pass the spicy sauce, and I'll re-group some of our quotes into a coherent couple of paragraphs.

I hear you, EdelweissPirate, and you're correct--I now realize where I hadn't remembered a lot of the other forces at play. Let me take a moment to re-frame my thoughts a li'l better:
  • I've probably been confusing some terms, correct me where I'm wrong. I have been using "axially" where I might better off have been using "along the longitudinal axis." From the tip of the nose, to the center of the exhaust, that's what I'd been calling "axially." I have also goofed, and in the one case did mean "parallel."
  • The SLBM, as a system, has a changing Center of Mass (CoM), and what I'd term a "Center of Lift" (CoL). "Unstack 'em" relative to gravity--yer hosed. Bear with me on this one: The payload has it's own CoM, and it's at a fixed point along the longitudinal axis, but it's just one component of the overall system. As motor stages are exhausted and shed from the rest of the missile, the system CoM and CoL shifts closer to the payload, shortening turning moments1. I believe that in a perfectly perpendicular attitude, the CoM (wherever it is during flight) stacked 'above' the CoL in relation to gravity, is the most stable configuration, again, in relation to gravity. I was trying to use that balanced pen/pencil as an example. Any deviation from that perfect "stack" allows gravity to put a turning moment on the flight body. I picture gravity pulling down on a lever arm; gravity acts on the CoM and the fulcrum is where the CoL (the point of thrust) is lifting the body. With the OP's "point blank" shot, I doubt the first stage would have been shed by the time the flight body goes horizontal, creating your biggest moment on that lever arm. If there were fins/wings/canards you could offset that lever with some lift, but the Trident doesn't have them, and I suspect that given enough of a tilt, the whole thing would corkscrew or fall like a tree to the ground.
  • I honestly don't think the thrust can be vectored to enough of an angle, or fast enough to accommodate truly horizontal flight for a "point blank" trajectory. Tridents (or Poseidons) weren't really designed for this kind of flight profile. I can't speak to the control systems, but having been up close and personal with some of these things2, I doubt the pneumatics and hydraulics could keep up with vectoring thrust fast enough for changing conditions. Once it tips over, it has to keep accelerating at least 1 g away from the earth to maintain an attitude towards its target. Granted, it's got 6 g additional3 to accelerate with, but without flight control surfaces . . . I dunno brother, I've got a hard time seeing this making it that far with only thrust. . .
  • Compressive strength through the longitudinal axis of the system is already proven. I doubt lateral shear strength is nearly as good. We've launched these things before, and we continue to do so periodically for flight tests, in their ballistic profiles. Loads are through the longitudinal axis--and you're correct again: I forgot about the longitudinal axis loads from gravity (down) and acceleration (up). And I see and agree with gravity being 1/7th of the problem (on a 7 g acceleration). What I don't think is going to hold together are the mechanical joints between stages in a horizontal attitude, or even the solid fuel itself. Something would buckle and either bend (to induce a turning moment between the CoM and the CoL), or the thing would start mechanically separating in flight.

I think we're in agreement on the concepts, with only differences in opinions.

What hasn't been addressed yet, and what's more important, is how the OP plans to seperate the RVs from the equipment section in such a short span of time, and accurately hit their target. RVs were designed to fall to their target from high above. "Things" need to happen for the warhead to function properly.

1 I vaguely remember that the closer your CoL is to your CoM, the more stable your aircraft is, but because the distance is so short, it's far more nimble (e.g. an F-16).
2 Let's just say that through work, I get to see these things from time to time.
3 I'm just rolling with your "7 g" from earlier.

Tripler
Are you a mustard sauce or vinegar sauce kinda guy?

Last edited by Tripler; 05-23-2019 at 11:19 PM.
  #35  
Old 05-24-2019, 12:38 AM
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[sub]I realize that I'm not helping the downward glideslope either,
What hasn't been addressed yet, and what's more important, is how the OP plans to seperate the RVs from the equipment section in such a short span of time, and accurately hit their target. RVs were designed to fall to their target from high above. "Things" need to happen for the warhead to function properly.
These would be Russian / Soviet warheads. I sorta imagine a crew of technicians with soldering irons bypassing most of the detonation interlocks before the subs depart. And drinking vodka.

But on a serious note, did the warheads ever really get the embedded "weak link" technology USA shared with them? Because if they didn't, just bypassing components or replacing the detonator circuit board with one with modified firmware so that the only safety checks are for launch and perhaps an arming timer sounds feasible.

Obviously the USA could remanufacture their warheads the same way but I suspect it would take longer. Since I understand there are supposed to be electronis buried in the warhead designed to permanently brick themselves if any tampering is detected.

I assume if there were no interlocks the actual warhead needs mere seconds at most to go off.

Last edited by SamuelA; 05-24-2019 at 12:39 AM.
  #36  
Old 05-24-2019, 10:10 AM
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But on a serious note, did the warheads ever really get the embedded "weak link" technology USA shared with them? Because if they didn't, just bypassing components or replacing the detonator circuit board with one with modified firmware so that the only safety checks are for launch and perhaps an arming timer sounds feasible.

Obviously the USA could remanufacture their warheads the same way but I suspect it would take longer. Since I understand there are supposed to be electronis buried in the warhead designed to permanently brick themselves if any tampering is detected.
Warheads are explicitly engineered to "brick" if tampering is detected.

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I assume if there were no interlocks the actual warhead needs mere seconds at most to go off.
If you want a warhead to "go off" at your target point and with expected yield, then this is an incorrect assumption.

Trip

Last edited by Tripler; 05-24-2019 at 10:12 AM.
  #37  
Old 05-24-2019, 03:38 PM
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Warheads are explicitly engineered to "brick" if tampering is detected.



If you want a warhead to "go off" at your target point and with expected yield, then this is an incorrect assumption.

Trip
That leaves one option - begin preparing the warhead to explode while it's still in the submarine.
  #38  
Old 05-24-2019, 04:09 PM
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That leaves one option - begin preparing the warhead to explode while it's still in the submarine.
Warheads mounted to their boost missiles are inaccessible from the interior of/inside the submarine.

Last edited by Tripler; 05-24-2019 at 04:13 PM.
  #39  
Old 05-24-2019, 04:22 PM
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One thing about the SLBM flying in atmosphere vs flying in space is that the aerodynamic loads on the SLBM should be much greater in the former.
I think this is the answer right here. If you fire it at a low angle, it will be travelling through the troposphere at speeds that are meant for the stratosphere (and higher), which will rip it apart. And it can't be throttled back since it's a solid rocket.

Lots of other good replies in this thread but I think this one is the clincher.

Last edited by HMS Irruncible; 05-24-2019 at 04:22 PM.
  #40  
Old 05-24-2019, 04:27 PM
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If memory of Clancy's novels (yes, I know...) is correct the Soviets did have this sort of capacity. It was called FOBS or something similar.
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Old 05-24-2019, 04:37 PM
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If memory of Clancy's novels (yes, I know...) is correct the Soviets did have this sort of capacity. It was called FOBS or something similar.
Thanks, HMSIrruncible.

FOBS, or Fractional Orbit Bombardment System, https://en.m.wikipedia.org/wiki/Frac...ardment_System is a little different than the depressed trajectory shot in the OP. With FOBS, the payload is put in an actual orbit, then deorbited when desired. The advantage is the payload can arrive from an unanticipated direction. Like from over South America.

Disadvantages are it takes extra energy to put something in orbit, the payload needs to be larger to accommodate retro rockets, and its banned by treaty. The wiki also mentions that accuracy was crap; something I believe is no longer valid, given things like the PLA's D-21, ballistic missile with terminal guidance.
  #42  
Old 05-24-2019, 04:55 PM
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For the D-5 Trident SLBM I mentioned in my example, both stages burn for a maximum of 130 seconds total. 65 each. After those burns, there's no more energy save however long the 3rd stage burns and whatever mechanism is used to jettison warheads from the bus. In the normal SLBM flight path, this isn't a problem, as the bus is well out of the atmosphere by this point, with 600 ish miles of altitude and ~8-11,000 MPH of forward velocity. As has already been stated it coasts ballistically to its target.

In atmosphere, and again, this may vary greatly how high in the atmosphere the payload ends up, it can't coast. On the contrary, drag forces are going to be immense on the bus and RVs. I would guess the shroud would be destroyed well before this. Maybe it would work on a system with a unitary warhead, where the exterior of the payload is merely the exterior of the RV?

The rocket would have to launch to some intermediate height (50 miles let's say), tip over horizontal-ish, thrusts with the remainder of the first stage. Then burn all of the second stage while sitting in what would essentially be a reentry-like plasma sheath. Then coast to the target. I can't see a range greater than 600 miles with that kind of flight path, and I really can't see the second stage burning nominally in those conditions. But if you could, you'd have a 600 mileish range rocket, that would be insanely inaccurate, would still achieve a high enough horizon to be seen by early warning radar, but only a 3 minute or so flight time
  #43  
Old 05-25-2019, 02:41 PM
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Warheads mounted to their boost missiles are inaccessible from the interior of/inside the submarine.
I mean the warhead internally is going through whatever particle accelerator power-up/gas injector warmup/other secret nuclear components that are needed to give the warhead it's full yield. You are implying that more than the electronics are needed to arm it, some secret processes are happening inside the bomb that begin during some phase of ballistic missile flight.

It is public knowledge that compact, modern, fission-fusion nuclear warheads have complex components and additional steps than just setting off explosives, although of course the exact details are secret.

Obviously this hypothetical mission requires the warhead to explode with full yield mere seconds after launch with none of the normal phases, so obviously it would need modifications to the firmware to support this.

Last edited by SamuelA; 05-25-2019 at 02:44 PM.
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Old 05-25-2019, 02:46 PM
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Possibly this would be achievable before the submarine departs by simply disassembling the payload of the nuclear missiles, removing the warheads, and replacing whatever circuit boards contain the firmware. If the russians were at least smart enough to disable flashing*, which they might not have done...

*microcontrollers and other embedded processors have pins where you can connect a programming device to them to load a different firmware image. There will be a connector or set of test points on the circuit board that the programmer connects to, or it can be done pre-soldering, this would have been done in the factory for a nuclear weapon. It is possible to set certain bits in the firmware image that locks the chip, which would be the obvious thing to do.

Come to think of it, if I were designing a nuclear weapon, I'd include mechanical safeties. Such as making it where the warhead needs to be ejected from the carrier spacecraft first before the battery in the warhead even completes the circuit. Or other hard safety mechanisms blocking the flow of electric current to the detonators. I'd be very interested in not having the weapon have even the remote possibility of exploding during prototyping or in storage or the factory.

This might be what Tripler was referring to without disclosing any non-public information.

Last edited by SamuelA; 05-25-2019 at 02:50 PM.
  #45  
Old 05-25-2019, 02:55 PM
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Oh where is Stranger on A Train when you need him...

One thing about the SLBM flying in atmosphere vs flying in space is that the aerodynamic loads on the SLBM should be much greater in the former. It's going faster, for one, and unlike its normal flight path, it should still be in atmosphere when it's accelerating much more heavily towards the end of first, and especially second, stage burnout.

For the wiki on the Trident D5, it says that first stage burnout occurs 65 seconds after launch. I don't know, but I'm guessing that the missile is well out of the atmosphere, and aerodynamic pressure consequently much lower, near the end of that burn.

I'd think maxQ for a sideways flight path would be much greater than its design limits, and there'd probably be a loss of vehicle. There's probably an altitude below the Karman Line though where atmospheric pressure could be low enough that maxQ would be within airframe design limits. Though stagnation heating might be an issue?

Ravenman hit it with the idea that an enemy'd use much stealthier cruise missiles for this sort of decapitation strike, even if those were slower than this sideways SLBM. Much lower launch signature too, at least thermally, and probably acoustically too.
So, the makers of the movie The Iron Giant did their homework when showing that a virtual point blank launch will still require a missile like that to go up into the stratosphere...




..darn dust still gets in the eyes.

Last edited by GIGObuster; 05-25-2019 at 02:55 PM.
  #46  
Old 05-25-2019, 03:56 PM
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...I'd be very interested in not having the weapon have even the remote possibility of exploding during prototyping or in storage or the factory.

This might be what Tripler was referring to without disclosing any non-public information.
Go read Eric Schlosser's, "Command and Control..." For the bibliography, if nothing else. It goes into the efforts the US took towards nuclear surety: the idea that the weapon will never detonate unless commanded to by a duly authorized entity, and that the weapon will always detonate once its enabling criteria are met. It's pretty tough to do both at the same time, as it turns out.

Consider that for even a fission bomb of modest efficiency, the explosives that compress the core must be constructed with amazing precision and detonated with great control. Then, an artificial neutron source must bombard the core with a precisely timed pulse of neutrons. Too early, predetonation might occur, and a fizzle. Too late, doublings are lost, and fizzle.

Then consider that, for a staged thermonuclear, the construction of the bomb and timing of explosives must be so precise that radiation from within the bomb case can be harnessed to compress and heat deuterium so that it can fuse. Computer control of timing and detonation can be so precise now, I wouldn't be surprised if the physics packages weren't symmetrical---that they relied on precisely asymmetrical pulses from the timing computer to form a symmetrical implosion wave.

The point is, mess with the timing on any of that, when the timing is encoded within those chips the hackers in your example are trying to bypass, and the bomb either won't detonate at all, or will be basically a dirty bomb. It's not the sort of thing one can hotwire---with exceptions like crude devices, things like SADM, an AIUI, 2-d linear implosion fission device that topped out at 1 kt.
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Old 05-25-2019, 09:22 PM
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The point is, mess with the timing on any of that, when the timing is encoded within those chips the hackers in your example are trying to bypass, and the bomb either won't detonate at all, or will be basically a dirty bomb. It's not the sort of thing one can hotwire---with exceptions like crude devices, things like SADM, an AIUI, 2-d linear implosion fission device that topped out at 1 kt.
The "hackers" are nuclear weapons engineers who are qualified and supported by a nation state. This hypothetical attack would have taken place in the 1980s probably, or perhaps today. I'm saying they know what they are doing, but they do need to make these preparations in secrecy, obviously.

Last edited by SamuelA; 05-25-2019 at 09:23 PM.
  #48  
Old 05-25-2019, 09:56 PM
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The "hackers" are nuclear weapons engineers who are qualified and supported by a nation state. This hypothetical attack would have taken place in the 1980s probably, or perhaps today. I'm saying they know what they are doing, but they do need to make these preparations in secrecy, obviously.
I guess I don't understand what you're asking then. If they are nuclear weapons technicians and designers, I would imagine they'd have the capability to disassemble and reassemble their own country's devices. They'd have the assorted documentation, manuals, engineering drawings, fixtures, and tooling to do the above. Basically what Pantex does. And, if the following article is right, even they screw up occassionally: https://grist.org/article/dept-of-holy/

For another country's devices, lacking the above know how and tooling, I'd think the exercise would be fraught with danger. Tripler, AIUI, does EOD as his day job. I don't know if he could talk about his procedures for securing a foreign, unsecured and possibly arming, nuclear device, but I'm sure they'd be interesting.
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Old 05-25-2019, 10:00 PM
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Oh, if I'm understanding correctly, you mean the possibility of modifying an SLBM warhead to detonate under anything besides after a nominal flight? I don't know, but I can't imagine that's anything capable of being done outside depot-level maintenance, and probably under the auspices of a national laboratory engineering program. IOW, and again, those who know won't say, the guys on the boat won't be able to do it.
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Old 05-25-2019, 10:08 PM
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You are implying that more than the electronics are needed to arm it, some secret processes are happening inside the bomb that begin during some phase of ballistic missile flight.
I am implying nothing of the sort. I am stating that your aforementioned "crew of technicians with soldering irons bypassing most of the detonation interlocks" will not be "preparing the warhead to explode while it's still in the submarine" from inside the submarine.

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Tripler, AIUI, does EOD as his day job. I don't know if he could talk about his procedures for securing a foreign, unsecured and possibly arming, nuclear device, but I'm sure they'd be interesting.
I retired from EOD. I now work in "a small town Northwest of Santa Fe", as a "Device" Engineer (as in "devices of interest in this thread"). I go to Pantex frequently. Modesty and 'discretion in an open message forum' apply to my previous two sentences.

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