Author Topic: North Korea's failed ICBM test  (Read 7495 times)

Offline Admiral Thrawn

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North Korea's failed ICBM test
« on: 07/15/2006 02:22 am »
I read that the Taepodong-2 failed after 42 seconds.

Any idea what altitude and speed the rocket would have reached in this time?

I assume an ICBM has a better power / weight ratio than the STS system, for example. Even though the STS has halved its weight after 1.5 minutes.

Also ICBMs only have to achieve an elliptical orbit, unlike the STS which has to gain both altitude and orbital velocity.

How would the ascent into orbit and the orbital path itself of an ICBM differ between one aimed at a close target (e.g. North Korea to Shanghai) versus a very long range target (e.g. North Korea to the US)?

Offline edkyle99

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RE: North Korea's failed ICBM test
« Reply #1 on: 07/15/2006 06:01 am »
Quote
Admiral Thrawn - 14/7/2006  9:09 PM

I read that the Taepodong-2 failed after 42 seconds.

Any idea what altitude and speed the rocket would have reached in this time?

I assume an ICBM has a better power / weight ratio than the STS system, for example. Even though the STS has halved its weight after 1.5 minutes.

Also ICBMs only have to achieve an elliptical orbit, unlike the STS which has to gain both altitude and orbital velocity.

How would the ascent into orbit and the orbital path itself of an ICBM differ between one aimed at a close target (e.g. North Korea to Shanghai) versus a very long range target (e.g. North Korea to the US)?

Using guesstimate vehicle specs from this site
http://www.globalsecurity.org/wmd/world/dprk/td-2-specs.htm
I calculate (guesstimating, mind you) that a Taepodong 2 would have reached about 10-ish km (6+ miles) high at somewhere above 400 m/s (about 900 mph) velocity at the 40 second mark.  To me, this sounds like the vehicle didn't quite make it to "max-q", the portion of the ascent where it would have experienced maximum dynamic pressure from atmospheric drag, which is a common failure point for new rockets with design flaws.  

As far as ascent paths, my understanding is that ICBMs and space launchers look alike during the initial climb out of the lower atmosphere, but after that the ICBMs usually pitch over less rapidly and reach substantially higher apogees than low-earth orbit launch vehicles.

 - Ed Kyle

Offline Admiral Thrawn

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RE: North Korea's failed ICBM test
« Reply #2 on: 07/15/2006 10:16 am »
Thanks for the info.

So it didn't get very high at all.

After 42 seconds STS-121 had reached 19,340ft (5.9km, 3.66miles) at 694mph (310m/s, 1117km/h, Mach 0.91), so I guess your estimate reflects an ICBMs better power/weight ratio.

Btw, how did you estimate your figures?

Offline edkyle99

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RE: North Korea's failed ICBM test
« Reply #3 on: 07/15/2006 03:28 pm »
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Admiral Thrawn - 15/7/2006  5:03 AM

Thanks for the info.

So it didn't get very high at all.

After 42 seconds STS-121 had reached 19,340ft (5.9km, 3.66miles) at 694mph (310m/s, 1117km/h, Mach 0.91), so I guess your estimate reflects an ICBMs better power/weight ratio.

Btw, how did you estimate your figures?

I wrote a Javascript program a while back that does a two-dimensional, piecewise, second-by-second estimate of serial-stage rocket ascents.  It basically figures out how much ideal velocity is added each second, then subtracts gravity losses.  It isn't perfect, but it usually provides a good rough estimate for my purposes.  

 - Ed Kyle

Offline Avron

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Re: North Korea's failed ICBM test
« Reply #4 on: 07/17/2006 03:55 am »
How much short of MaxQ, pct wise?

Offline edkyle99

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Re: North Korea's failed ICBM test
« Reply #5 on: 07/17/2006 07:22 pm »
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Avron - 16/7/2006  10:42 PM

How much short of MaxQ, pct wise?

I haven't incorporated aerodynamic forces into my model (yet), so I can only guess based on my very-guesstimated altitude and speed.  It seems likely that the Taepodong was still on the uphill side of the pressure curve, but not too far from the maximum.  It may have made it to something like 80% of maximum dynamic pressure.

 - Ed Kyle

Offline Avron

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Re: North Korea's failed ICBM test
« Reply #6 on: 07/18/2006 01:56 am »
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edkyle99 - 17/7/2006  3:09 PM

Quote
Avron - 16/7/2006  10:42 PM

How much short of MaxQ, pct wise?

I haven't incorporated aerodynamic forces into my model (yet), so I can only guess based on my very-guesstimated altitude and speed.  It seems likely that the Taepodong was still on the uphill side of the pressure curve, but not too far from the maximum.  It may have made it to something like 80% of maximum dynamic pressure.

 - Ed Kyle

great... so 80% loading.. 20% to go.. based on Pareto 20 % done.. 80% to go..

Offline Admiral Thrawn

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RE: North Korea's failed ICBM test
« Reply #7 on: 07/20/2006 03:52 am »
How exactly do you calculate Max Q?

Isn't it determined by the shape and attitude of the spacecraft?

Max Q during the STS-121 ascent occured 64 seconds after launch, 6 seconds after the go at throttle up.

Acceleration Gs were 2.17, altitude 42,778ft, speed 1058mph (~Mach 1.39), pitch angle 56.90 degrees.

Offline Jim

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RE: North Korea's failed ICBM test
« Reply #8 on: 07/20/2006 07:37 am »
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Admiral Thrawn - 19/7/2006  11:39 PM

How exactly do you calculate Max Q?

Isn't it determined by the shape and attitude of the spacecraft?

Max Q during the STS-121 ascent occured 64 seconds after launch, 6 seconds after the go at throttle up.

Acceleration Gs were 2.17, altitude 42,778ft, speed 1058mph (~Mach 1.39), pitch angle 56.90 degrees.

Nothing to do with the shape and orientation of the launch vehicle.  

dynamic pressure (q) is  1/2 rho times velocity squared, where rho is the density of air.    The density of air is a function of temperature and altitude.  

While it seems like an easy equation,  it has many more variables that don't allow an easy solution

Offline guidanceisgo

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RE: North Korea's failed ICBM test
« Reply #9 on: 07/21/2006 03:57 am »
[/QUOTE]
As far as ascent paths, my understanding is that ICBMs and space launchers look alike during the initial climb out of the lower atmosphere, but after that the ICBMs usually pitch over less rapidly and reach substantially higher apogees than low-earth orbit launch vehicles.

 - Ed Kyle[/QUOTE]

ICBM's typically have a higher thrust to weight ratio off the pad relative to space launch vehicles.   They can implement a kick turn very shortly after liftoff due to this effect.   This minimizes the gravity loss and optimizes range.  The missile burns out at a flight path angle of approximately  30-35 degrees versus a space launch vehicle which attempts to acquire a 0 degree flight path at burnout (assuming a circular orbit).   ICBM's don't use coast phases because of the intent to get the vehicle through boost phase as quickly as possible.  This makes launch detection harder ( and interception in today's world).  Space launch vehicles use coast phases to get to orbit apogee to do insertion burns, etc.

Offline kevin-rf

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RE: North Korea's failed ICBM test
« Reply #10 on: 07/22/2006 02:18 am »
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guidanceisgo - 20/7/2006  10:44 PM

ICBM's typically have a higher thrust to weight ratio off the pad relative to space launch vehicles.   They can implement a kick turn very shortly after liftoff due to this effect.   This minimizes the gravity loss and optimizes range.  The missile burns out at a flight path angle of approximately  30-35 degrees versus a space launch vehicle which attempts to acquire a 0 degree flight path at burnout (assuming a circular orbit).   ICBM's don't use coast phases because of the intent to get the vehicle through boost phase as quickly as possible.  This makes launch detection harder ( and interception in today's world).  Space launch vehicles use coast phases to get to orbit apogee to do insertion burns, etc.

I thought the higher thrust to weight ratio was more a result of using solids (usually ICBM's, except North Korea) vs. using Liquids (usually Space Launchers).

It was interesting reading the analysis on globalsecurity.org which was based on statements by the various goverments (US,Japan,S. Korea) to the press. Sounds like something fell off the missile early in flight leading to the upper stages seperating from the first stage, but they think the first stage continued firing until fuel depletion. Must have done some pretty cool loops in the sky.
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