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NK ICBM -- amateur analysis


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On 8/25/2017 at 11:46 PM, sevenperforce said:

http://thebulletin.org/north-korea’s-“not-quite”-icbm-can’t-hit-lower-48-states11012

Interesting. According to this assessment, which seems pretty detailed, NK's new ICBMs don't have enough dV to reach the continental United States, and may not even be able to hit Alaska.

Evidently, the lofted trajectory we saw would only have been possible with almost no payload; the off-the-shelf Russian engines NK has stockpiled don't have enough thrust to get the demonstrated trajectory unless the rocket itself is fairly small, which in turn means the payload is much lower than the 500-600 kg they'd need to field a warhead. [snip]

The analysis is based on questionable assumptions. This article goes through better than I could.

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Aaaand, more posts removed.

Folks, I realize that it may be a vain hope that this discussion can stay focused on the technical aspects of NK's rockets, given the intense political climate around North Korea.  However, if we want to keep talking about this here in the forum, it needs to stay on-topic.

To be totally clear:

  • What's okay to post in this thread:  Technical aspects of North Korea's rockets.
  • What's not okay to post in this thread:  Pretty much anything else.  Some examples of out-of-bounds areas include,
    • anything about North Korea's politics
    • anything about anyone else's politics, either
    • whether, when, or at whom NK might shoot these things
    • any other countries' past or possible future responses

This thread has gone off the rails enough time that it's starting to look as though it can't stay on.  Please don't make us lock this, folks.  Thank you for your understanding.

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I saw reports that the missile launched yesterday landed in three separate pieces. Is this likely to be an indication of something having gone wrong or would it deliberately have split up. In that case what might the pieces be?

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It doesn't really mean anything, a missile of this range is going to break up on re-entry. All that matters is if the RV survives. We've no word one way or the other, but based on how it handled the HS-14 tests it probably did.

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9 hours ago, tomf said:

I saw reports that the missile launched yesterday landed in three separate pieces. Is this likely to be an indication of something having gone wrong or would it deliberately have split up.

There appears to have been a problem.   The announced range is inconsistent with [short of] the range shown in a propaganda picture showing Kim Jong-un observing a map of the planned trajectory.

Of course, there's always the question of whether the photo is intended to be truthful in the first place, or whether they were lying to the Great Leader, or whether he was in on the deception.  They know full well that outside observers pore over those picture with a fine toothed comb, and misleading them is not without value.
 

9 hours ago, tomf said:

In that case what might the pieces be?


The engine compartment of the second stage, the tankage, any instrument/control compartment, the RV...  the 'three pieces' could be any combination of these.  Since the bird lacks an post-boost vehicle, one would expect only two intentional pieces.

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1 hour ago, DerekL1963 said:

There appears to have been a problem.   The announced range is inconsistent with [short of] the range shown in a propaganda picture showing Kim Jong-un observing a map of the planned trajectory.

Burn time was shorter than the successful may test, so seems to have been an engine failure. Exactly how much shorter is not really established, but probably 10 seconds or so given trajectory.

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58 minutes ago, Kryten said:

Burn time was shorter than the successful may test, so seems to have been an engine failure. Exactly how much shorter is not really established, but probably 10 seconds or so given trajectory.


Or the guidance/flight control system commanding an early shutdown.  Or an eff-up in the propellant level sensing system.  Or...  many possible scenarios.

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More on the science side than the spaceflight side, but still entirely without political discussion....

Here's the purported physics package claimed to be a hydrogen bomb:

21231635_1918299031825541_49038376814195

From a pure physics perspective: what the heck is that? Are they trying to do a Teller-Ullam device with two primaries on either end to squeeze together a dry-fuel fusion core? Is the pipe on the back end a tritium supply hose to make one of the primaries a gas-boosted fission device?

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Afaik, the secondary doesn't has to be exactly a cylinder, and also it can have an additional fission belt around. So, it just looks bulky.
Btw, a poster behind the left man's shoulder displays the scheme.

(Or this is just a mockup made of nice looking pipes).

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4 hours ago, sevenperforce said:

From a pure physics perspective: what the heck is that? Are they trying to do a Teller-Ullam device with two primaries on either end to squeeze together a dry-fuel fusion core? Is the pipe on the back end a tritium supply hose to make one of the primaries a gas-boosted fission device?


Spherical primary at one end, spherical secondary at the other.  The experts I've seen think the left hand side is the primary.  The gas hose could connect to the primary, or internally to both.  (But most likely to the primary as a nice healthy compact primary makes everything else easier.)

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http://nuclearweaponarchive.org/Nwfaq/Nfaq4-5.html

Quote

4.5.1.4 Two Chamber Designs

At some point, the development trend toward a separate radiation case around the primary lead to a full two chamber design for the weapon, with some means of regulating radiation flow between the chambers (like a temporary radiation barrier). With better control over the radiation flux around the secondary, a reduced standoff with a reduced secondary diameter (and perhaps a lighter pusher/tamper) became possible.

This could also be conveniently combined with a spherical secondary design. This has been described as the "peanut design" - two spherical hollow chambers joined at the waist, with a primary sphere in one, and a spherical sphere in the other. Alternatively, a two chamber - spherical secondary design can be used with a modulated primary.

This approach offers the inherent advantages of spherical implosion - a smaller radius change for compression in 3-dimensions to attain a given density compared to two. Smaller radius change translates directly into faster implosion, an important consideration in a smaller, lighter, higher pressure weapon design which would be prone to disassemble faster.

In a spherical secondary the radiation shield between the primary and secondary would evolve into a baffle between the two chamber to prevent the primary from directly (and thus unevenly) heating the side of the secondary facing it, forcing the radiation flux to diffuse into the channel around the secondary.

The primary in a two-chamber design may be effectively encased in a heavy, close fitting uranium shell that can act as an implosion tamper. By trapping the explosive gases, this shell can act as the wall of a spherical piston, forcing the expanding gases to transfer all of their energy to the inward moving beryllium/plutonium shell, and minimizing the amount of explosive required. Such a primary may use a thin uranium or tungsten tamper between the beryllium and plutonium shell layers to enhance inertial confinement of the fissile mass.

 

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