Questions involving ballistic missiles

[Tio Barnabe]

With high tensions involving North Korea, I wonder

1 - Why can't they in principle just pick up some kind of brake on the missile in order to slow it down so that it doesn't break apart during its re-entry?

2 - They usually claim to have developed a miniaturized nuclear bomb. Wouldn't this require testing such device during its development? How can they actually claim they have a thing they have never tested at all?

Or is it possible to test it without perturbing the neighboring area, i.e. without the knowledge of the other countries?

 

[phinds]

1 - Why can't they in principle just pick up some kind of brake on the missile in order to slow it down so that it doesn't break apart during its re-entry?

Putting a "brake" on it would definitely make it break up

2 - They usually claim to have developed a miniaturized nuclear bomb. Wouldn't this require testing such device during its development? How can they actually claim they have a thing they have never tested at all?

Apparently you don't read the news. They have tested numerous nuclear bombs.

 

[Tio Barnabe]

Putting a "brake" on it would definitely make it break up

Why? Stress would increase if the speed is reduced?

Apparently you don't read the news. They have tested numerous nuclear bombs.

Even the miniaturized one?

 

[phinds]

Why? Stress would increase if the speed is reduced?

The process of reducing the speed would induce stress

Even the miniaturized one?

How would we know?

 

[Tio Barnabe]

How would we know?

Given the physics involved. That's what I meant to ask in the opening post.

 

[davenn]

Or is it possible to test it without perturbing the neighboring area, i.e. without the knowledge of the other countries?

no
The one they tested today was recorded by many seismic stations. It was equivalent to a M 6.3 earthquake
see my thread in the Earth section of the forum

2 - They usually claim to have developed a miniaturized nuclear bomb.

a M 6.3 producing quake WASNT a miniature bomb blast !


Dave

 

[phinds]

Given the physics involved. That's what I meant to ask in the opening post.

Well, is not WHAT you asked. I answered what you asked. I'm not a mind reader. The only thing we can measure is the YIELD. The actual physical size of the bomb is unknown, although I'd agree w/ davenn that this most recent test is unlikely to have been of a miniaturized one.

 

[Drakkith]

1 - Why can't they in principle just pick up some kind of brake on the missile in order to slow it down so that it doesn't break apart during its re-entry?

You could certainly design a ballistic missile that doesn't break up when it falls from its suborbital flight, but what would be the point? Any ballistic missile is launched with the knowledge that there's essentially zero chance of recovering it, so it's not worth the extra time, money, and effort spent to create a missile that survives re-entry.

 

[Tio Barnabe]

You could certainly design a ballistic missile that doesn't break up when it falls from its suborbital flight, but what would be the point? Any ballistic missile is launched with the knowledge that there's essentially zero chance of recovering it, so it's not worth the extra time, money, and effort spent to create a missile that survives re-entry.

The reason should be obvious. If you want to hit a city with the missile, you need to have it intact until it reach the soil.

 

[Drakkith]

The reason should be obvious. If you want to hit a city with the missile, you need to have it intact until it reach the soil.

I'm not certain how shorter ranged ballistic missiles work, but ICBM's do not work this way. The warheads are released from the missile while it is above the atmosphere and they enter the atmosphere separately from the missile to head to their targets. If shorter ranged ballistic missiles do not separate their warheads from their missile bodies, then the missile body must obviously remain intact.

 

[russ_watters]

1 - Why can't they in principle just pick up some kind of brake on the missile in order to slow it down so that it doesn't break apart during its re-entry?

Like retro-rockets? Sure, they could -- but that would be difficult and there wouldn't be much point to it.

2 - They usually claim to have developed a miniaturized nuclear bomb. Wouldn't this require testing such device during its development? How can they actually claim they have a thing they have never tested at all?

Anyone can claim whatever they want.

Or is it possible to test it without perturbing the neighboring area, i.e. without the knowledge of the other countries?

No. We've monitored all of their nuclear bomb tests.

 

[jerromyjon]

If you want to hit a city with the missile, you need to have it intact until it reach the soil.

I am pretty sure nuclear bombs are much more effective detonated far above the surface...

 

[phinds]

Russ, I made a statement earlier that I'm not now so sure about, and that is that since it is only the yield that we can detect indirectly (via seismograph) we could not tell if the bomb being tested was a physically small one or not. What do you think about that?

 

[phinds]

I am pretty sure nuclear bombs are much more effective detonated far above the surface...

I think "far above the surface" in this case means perhaps a mile or two (unless you're trying for EMP damage as opposed to direct physical destruction). That is an insignificant amount of the total reentry.

 

[Nugatory]

Why can't they in principle just pick up some kind of brake on the missile in order to slow it down so that it doesn't break apart during its re-entry?

An airbrake, the device we use to slow things moving through the atmosphere, operates by increasing air friction, turning the kinetic energy of the object into heat as it slows. The missile reentry problem is that the object is moving so fast when it reenters the atmosphere that air friction (and the associated turbulence) is going to burn it up. Thus, an airbrake would just make things worse, by further increasing the friction.

Instead, we would have to slow slow it before it reenters the atmosphere. That means retrorockets firing backwards (because nothing else works in space), and the fuel required for these would all come at the expense of payload. To get a sense of how dramatic this effect can be, compare a picture of a typical ballastic missile with a picture of something like the Saturn rockets that carried Gemini astronauts into space along with the fuel they needed to brake for a safe reentry. The former is a practical weapon, the latter is not.

 

[jerromyjon]

That is an insignificant amount of the total reentry.

What I was commenting about wasn't in regards to re-entry, only that it detonates above the "soil".

you need to have it intact until it reach the soil.

 

[russ_watters]

Russ, I made a statement earlier that I'm not now so sure about, and that is that since it is only the yield that we can detect indirectly (via seismograph) we could not tell if the bomb being tested was a physically small one or not. What do you think about that?

I think we can tell by the size of the earthquake what the yield was.

http://science.howstuffworks.com/nuclear-detection.htm

 

[Nugatory]

I am pretty sure nuclear bombs are much more effective detonated far above the surface...

It depends on the effect that you are trying to produce. Air bursts produce substantial overpressures and radiant heat effects over a relatively large area (for those who are curious, the area subject to a given overpressure goes more as less as the two-thirds power of the explosive yield); these will burn and smash ordinary building, factories, industrial infrastructure (as well as inflicting appalling burns on everyone in line of sight of the explosion). So if you want to wreck an economy and visit untold suffering on an entire society... Yes, that's the most murderously efficient of doing it.
Othe other hand, air bursts are relatively ineffective against properly hardened military targets which can survive very high atmospheric overpressures and aren't exposed to direct flash effects. Attacking these requires detonations at ground level to set up shock waves in the ground itself. Ground bursts also produce more and worse fallout.

However, none of this matters much when we're talking about a megaton range bomb going off anywhere near a major city. Even the "inefficient" ground burst would be an unprecedented catastrophe, something along the lines of all of the destruction of the second world war compressed into twenty seconds.

 

[jerromyjon]

From wikipedia:
The Tsar Bomba detonated at 11:32 Moscow Time on 30 October 1961, over the Mityushikha Bay nuclear testing range (Sukhoy Nos Zone C), north of the Arctic Circle over the Novaya Zemlya archipelago in the Arctic Ocean. The bomb was dropped from an altitude of 10.5 km (6.5 mi); it was designed to detonate at a height of 4 km (13,000 ft) over the land surface (4.2 km (14,000 ft) over sea level) by barometric sensors.

The largest bomb ever tested, 10 times the power of all conventional weapons used in WWII.

 

[Tio Barnabe]

An airbrake, the device we use to slow things moving through the atmosphere, operates by increasing air friction, turning the kinetic energy of the object into heat as it slows. The missile reentry problem is that the object is moving so fast when it reenters the atmosphere that air friction (and the associated turbulence) is going to burn it up. Thus, an airbrake would just make things worse, by further increasing the friction.

Instead, we would have to slow slow it before it reenters the atmosphere. That means retrorockets firing backwards (because nothing else works in space), and the fuel required for these would all come at the expense of payload. To get a sense of how dramatic this effect can be, compare a picture of a typical ballastic missile with a picture of something like the Saturn rockets that carried Gemini astronauts into space along with the fuel they needed to brake for a safe reentry. The former is a practical weapon, the latter is not.

@Nugatory Oh, I see

Thank you all. I'm enjoying your responses here.

 

[phinds]

I think we can tell by the size of the earthquake what the yield was.

http://science.howstuffworks.com/nuclear-detection.htm

Exactly, but that's not my question at all. My question is, can we tell the physical size of the device. I think not, but I don't know for sure.

 

[russ_watters]

Exactly, but that's not my question at all. My question is, can we tell the physical size of the device. I think not, but I don't know for sure.

Oh...i would think no.

 

[Tracey3]

Why can't they in principle just pick up some kind of brake on the missile in order to slow it down so that it doesn't break apart during its re-entry?

Unfortunately slowing down an ICBM would be like feeding someone 'spoons with a cake'. What I mean is that the whole point of an ICMB warheads is to reach maximum velocity to reduce response time and make it really hard to shoot it down on its trajectory. Generally a fire doctrine for ICMBs is that of a 'Mass Raid' where let's say you fire 10 ICMBS with 10 warheads each. That would give you effectively 100 targets that can reach speeds of Mach 20 depending on re-entry angle.

Why this type of attack is effective in the end? Its because it overwhelms the system. It might take 2 or 3 missiles to take out 1 warhead and even if you catch most of them out, you only need a few to hit positions of strategic importance i.e Nuclear Power plants, Airbases. Ow did I also mention that some ICMBs can be packed with decoys?

Notes: http://space.au.af.mil/au-18-2009/au-18_chap18.pdf