sevenperforce

NK ICBM -- amateur analysis

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There are US reports that they caught this being fuelled immediately before the launch. It's likely not intended to stay fuelled long term.

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Posted (edited)

On 07.07.2017 at 1:40 PM, Kryten said:

There are US reports that they caught this being fuelled immediately before the launch. It's likely not intended to stay fuelled long term.

And probably that means acid, not NTO.

7 hours ago, insert_name said:

apparently the main engine closely resembles an RD 250, the main engine for the R 36 and Tskylon rockets. 

Surprise. DPRK can into google photos.
Or they have KSP with Real Engines/Soviet Engines mod installed - and just copy.

Edited by kerbiloid

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2 hours ago, kerbiloid said:

And probably that means acid, not NTO.

With this performance? That's not at all likely.

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42 minutes ago, Kryten said:

With this performance? That's not at all likely.

ICBMs were powered with nitric acid, too.

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24 minutes ago, kerbiloid said:

ICBMs were powered with nitric acid, too.

Yeah, at about three times the size of this one.

 

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Posted (edited)

On ‎10‎.‎07‎.‎2017 at 0:56 PM, Kryten said:

Yeah, at about three times the size of this one.

Well, what are our other options? No sense to fuel at launch site with NTO, cryogens are pretty easily detected (see link), and I still don't believe NK can manage ClF3.

http://i.imgur.com/mN39W6R.gifv

Edited by DDE

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Posted (edited)

On 10.07.2017 at 0:56 PM, Kryten said:

about three times the size of this one.

Because they were first generation ICBM, 1950s
They would be so large even with NTO.
While acid is even a little more dense (1.5 vs 1.44) and has 3 O per 1 N, while NTO has 2:1.

Edited by kerbiloid

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Posted (edited)

On ‎10‎.‎07‎.‎2017 at 0:56 PM, Kryten said:

Yeah, at about three times the size of this one.

Or more.

Spoiler

1000px-R-16U.svg.png

However, a lot hinges on how light a nuke NK have or think they're going to have. That thing above had old electronics and a megaton-class payload.

On ‎10‎.‎07‎.‎2017 at 9:36 AM, kerbiloid said:

And probably that means acid, not NTO.

Does it really? I know US Type III IRFNA can be kept fuelled for decades, and I've never understood why there's all this incessant dancing around with Soviet АК-27И being loaded and unloaded between every bomber sortie.

Edited by DDE

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3 hours ago, DDE said:

Well, what are our other options? No sense to fuel at launch site with NTO, cryogens are pretty easily detected (see link), and I still don't believe NK can manage ClF3.

 It'll have to be fuelled at the launch site. Yeah, it's not ideal; neither is using liquid fuel for a mobile ICBM in the first place. Ideally they'd want to use this thing by poking it out of a cave, fuelling it, and launching it, like DF-3 and DF-4 used to deployed, but modern recon systems+the size of NK+modern precision weapons makes that impossible.

 You can't really move a liquid missile this size fuelled regardless of what fuel you use, it just won't have the structural integrity. The closest that's actually been done are some Soviet SLBMs, but that was over short distances and used a special supportive missile container.

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Posted (edited)

5 hours ago, DDE said:
On 10.07.2017 at 0:56 PM, Kryten said:

Yeah, at about three times the size of this one.

Or more.

Ancient anti-aircraft missiles fueled with acid are much smaller.

(Do not get me wrong, I'm not claiming that they necessarily use acid. I just can't see why not.)

5 hours ago, DDE said:

Does it really? I know US Type III IRFNA can be kept fuelled for decades,

And was replaced because was too unstable without special measures (including NTO mixing) and choking pipes?

Are you sure DPRK and USA chemicals quality is similar? They could just not bother with storable acid and use cheaper one for tests.

Edited by kerbiloid

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6 hours ago, kerbiloid said:

(Do not get me wrong, I'm not claiming that they necessarily use acid. I just can't see why not.)

It's just a matter of performance. Check the charts here; https://www.38north.org/2016/12/musudan122016/ NTO v. IRFNA gives you 200km extra range for a Musudan, effectively for free; the difference would be greatly exacerbated in a multi-stage design like this one.

6 hours ago, kerbiloid said:

Are you sure DPRK and USA chemicals quality is similar? They could just not bother with storable acid and use cheaper one for tests.

The chemical industry is one of the most advanced in the DPRK. Something like NTO or IRFNA is child's play to people who mass-produce VX.

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Thanks for the link.

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7 hours ago, kerbiloid said:

And was replaced because was too unstable without special measures (including NTO mixing) and choking pipes?

Are you sure DPRK and USA chemicals quality is similar? They could just not bother with storable acid and use cheaper one for tests.

I imagine it was because of the added safety of a propellant that doesn't leak onto the deck.

Inhibitants aren't difficult to produce - it takes just 0.6% of hydrofluoric acid.

Hey, @kerbiloid, @Kryten, riddle me this: why does MIL-P-7254 specify IRFNA having NO2 content while Soviet AKs are specified as containing N2O4?

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2 minutes ago, DDE said:

IRFNA having NO2 content while Soviet AKs are specified as containing N2O4?

Maybe because

Quote

The liquid is also colorless but can appear as a brownish yellow liquid due to the presence of NO2 according to the following equilibrium:

N2O4 ⇌ 2 NO2

So, one of them likes to count what they pour, another one prefers to measure what's inside.

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1 hour ago, kerbiloid said:

So, one of them likes to count what they pour, another one prefers to measure what's inside.

Reportedly, it's worse. Really, really worse.

Quote

But things didn't turn out that way. There were the expected difficulties (only they were worse than expected) that stemmed from the corrosive nature of the acid and its fumes, both of which did their best to chew up the black box. But then something much more disconcerting showed up. White would take a sample of acid which was, as far as he could tell, absolutely anhydrous, with no water in it at all. And the IR absorption band was still there, as large as life, and twice as natural. Nitric acid appeared to be a somewhat more complicated substance than most people thought.
It is. Take 100 percent nitric acid—pure hydrogen nitrate. (I won't go into the question of how you go about getting such a substance.) Does it appear as HNO3, period? It does nothing of the sort. Studies by Ingold and Hughes, by Dunning, and by others during the 30's and 40's had shown that there is an equilibrium:
2HNO3 = NO2 + NO3 + H2O
so that there is some —not much, but some —"species" water present even in absolutely "anhydrous" acid. So the relation between "analytical" water, which was what people were interested in, and optical absorption is not linear, and you have to analyze dozens of samples of acid in order to establish a calibration curve. White embarked upon the calibration.

...

And there was another reason. RFNA had been domesticated. Two things had done it: A series of meticulous studies at Ohio State University and at JPL solved the problem of decomposition and pressure buildup, and a completely unexpected breakthrough at NARTS reduced the corrosion problem to negligible proportions. With these problems solved the acid could be "packaged" or loaded into a missile at the factory, so that it didn't have to be handled in the field. And that solved the problem of those toxic fumes, and eliminated the danger of acid burns.

By the beginning of 1951 the nature and behavior of nitric acid had become comprehensible. True, it was a fiendishly complicated system —one could hardly call it a substance —but some sense could be made out of it. The monumental work of Professor C. K. Ingold and his colleagues, published in a series of articles in 1950, had clarified the equilibria existing among the various species present in the system, and Frank and Schirmer, in Germany, in the same year, explained its decomposition. Briefly, this is what their work showed:

First, in very strong nitric acid, there is an equilibrium:

(1) 2HNO3 = H2NO3 + NO3.
However the concentration of H2NO3 is extremely small at any time, since it, too is in equilibrium:

(2) H2NO3 = H2O + NO2

so that for all practical purposes we can write:

(3) 2HNO3 = NO2 + NO3 + H2O

and ignore the H2NO3. In dilute acid, the equilibrium is

(4) H2O + HNO3 = H3O + NO3

Thus, in acid containing less than about 2.5 percent of water, NO2 is the major cation, and in acid containing more than that, H3O takes that role. Exactly at 2.5 percent water, very little of either one is present, which very neatly explains the minimum in the electrical conductivity observed there. If NO2 is the active oxidizing ion in strong acid (and in the course of some corrosion studies I made a couple of years later I proved that it is) the effect of water on ignition delay is obvious. Equation (3) shows that adding water to dry acid will reduce the concentration of NO2 which is the active species. The addition of NO3 will do the same thing —which explains the poor combustion observed with acid containing NH4NO3.

The nitronium (NO2) ion would naturally be attracted to a negative site on a fuel molecule, such as the concentration of electrons at a double or triple bond —which goes far to justify Lou Rapp's remarks as to the desirability of multiple bonds to shorten ignition delay.

The NO2 cation also explains the instability of nitrites in strong acid by the reaction:

NO2+ + NO2- = N2O4

If N2O4 is present in strong acid, another set of equilibria show up.

2NO2 = N2O4 = NO + NO3

The result of all of this is that (even neglecting solvation) in strong acid containing N2O4 have appreciable quantities of at least seven species:

HNO3 NO2+
N2O4 NO+
NO2 and
H2O NO3-

Plus possible traces of H3O+ and H2NO+. And all of them in interlocking equilibria. But this didn't explain the pressure buildup. Nitric acid decomposes by the gross reaction.

4HNO3 -> 2N2O4 + 2H2O + O2

But how? Well, Frank and Schirmer had shown that there is yet another equilibrium present in the system, and another species:

NO3 + NO2 = N2O5

And N2O5 was well known to be unstable and to decompose by the reaction.

2N2O5 = 2N2O4 + O2

Then as O2 is essentially insoluble in nitric acid, it bubbles out of it and the pressure builds up and your acid turns red from the NO2.

...

It was D. M. Mason and his crew at JPL and Kay and his group at Ohio State who undertook —and completed — the heroic task of mapping the phase behavior and equilibrium pressure and composition of the nitric acid-N204-H20 system over the whole composition range of interest, up to 50% N2O4 and up to 10 percent or so H 2Oand from room temperature up to 120°C. By the time these groups were finished (all of the work was published by 1955) there was nothing worth knowing about nitric acid that hadn't been nailed down. Thermodynamics, decomposition, ionetics, phase properties, transport properties, the works. Considering the difficulties involved in working with such a miserable substance, the achievement can fairly be classified as heroic.

I hope my high school chemistry teacher is proud, because I didn't understand a thing.

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One small notice: except impurities, N2O4 doesn't contain any H.

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