redflyer
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Question Re Mirv Warheads

Tue Jun 26, 2007 11:43 am

On a MIRV equiped booster, at what point in the trajectory do the independent warheads separate? Is it during the powered boost phase, the non-powered ascent phase, or during the decent phase? Or is it possible to separate and hit diverse targets during any of the three phases of the flight profile?

[Edited 2007-06-26 04:44:02]
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rwessel
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RE: Question Re Mirv Warheads

Tue Jun 26, 2007 3:51 pm

The common design is that the bus which holds all the warheads has a small rocket engine, which it uses shortly after the booster separates to maneuver. At appropriate points it pickles off individual reentry vehicles (RVs and various decoys) so that they hit their independent targets.

This happens soon after the booster separates in order to maximize the possible "spread" of targets.

Some RVs also use aerodynamics to further increase cross range capability.

On a few missiles (Trident D5, for example), the individual RVs have some maneuvering capability ("MARV") after they've separated from the bus, to further fine-tune the trajectory.
 
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kc135topboom
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RE: Question Re Mirv Warheads

Wed Jun 27, 2007 11:54 pm

Quoting RedFlyer (Thread starter):
On a MIRV equiped booster, at what point in the trajectory do the independent warheads separate? Is it during the powered boost phase, the non-powered ascent phase, or during the decent phase? Or is it possible to separate and hit diverse targets during any of the three phases of the flight profile?



Quoting Rwessel (Reply 1):
The common design is that the bus which holds all the warheads has a small rocket engine, which it uses shortly after the booster separates to maneuver. At appropriate points it pickles off individual reentry vehicles (RVs and various decoys) so that they hit their independent targets.

All of the RVs are released before any decent phase, but not during the boost phase. Most are released while the missile reaches orbit.

It is true that some of the warheads are released by a small rocket motor to put them on the correct reentry trajectory towards their targets, others do not need rocket assist.

I think this tread may be getting into areas we shouldn't be talking about. So, this is my last post on this thread.
 
redflyer
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RE: Question Re Mirv Warheads

Thu Jun 28, 2007 2:42 pm

Quoting Rwessel (Reply 1):
The common design is that the bus which holds all the warheads has a small rocket engine, which it uses shortly after the booster separates to maneuver.

If the "Bus" has a small rocket engine, then does its motor burn continuously during its trajectory after booster separation and it releases the RVs at points along that trajectory?

I'm trying to understand how each RV is managed to its independent target. I was under the impression that a ballistic missile is similar to a bullet -- once fired it's pretty much heading in the direction its pointed at (with guidance systems used primarily to keep it on target). So, using the analogy of a bullet, you could have multiple bullets on one cartridge -- such as a shotgun shell with buckshot -- and once fired at a target the individual bullets would spread out (due to aerodynamics) and hit an area around the actual aiming point. I assume that is the process of how MIRV warheads work and that would explain aerodynamics being used to enable cross-range capability. However, is aerodynamics the primary means by which independent targeting is achieved or are their other means, such as the Bus motor? If it's through aerodynamics then does that mean that each MIRV incorporates some form of lifting body?

Quoting KC135TopBoom (Reply 2):
I think this tread may be getting into areas we shouldn't be talking about.

Why?
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rwessel
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RE: Question Re Mirv Warheads

Thu Jun 28, 2007 3:12 pm

Quoting RedFlyer (Reply 3):
If the "Bus" has a small rocket engine, then does its motor burn continuously during its trajectory after booster separation and it releases the RVs at points along that trajectory?

The burn happens (relatively) briefly near the start of the ballistic flight. The idea is to nudge each RV enough so that the extra velocity accumulated over the entire flight time adjust the impact point as desired. That has to be done at the beginning of the flight. Very roughly, let's say you impart a 300mph nudge to an RV at the beginning of a 20 minute coast. That'll move the impact point roughly* 100mi. The same nudge just before reentry might move the impact point 15-20mi.

While some RV do use aerodynamics to further adjust their impact point, the problem that poses for an ICBM RV is that there is very little time when that's effective (only the last two or three minutes of the flight), which severely limits the amount of "spread" you can get. Some early MIRV'd ICBMs used that technique to scatter several smaller warheads around one large target, the idea being that five 100kt warheads spread a few miles apart will do much more damage to a city than a single MT class warhead right in the center. But that's not quite hitting separate targets.

As a counter example, the Indian Agni III is a bit different in that it uses a rather shallow reentry angle, which gives the RV a lot more aerodynamic flight time.

Remember that in any case, the MIRV'd RVs are going to hit in an ellipse no more than a few (3-4) hundred miles across.



*It's rather more complicated than that - the possible impact points from a given delta-V will form something of an ellipse.
 
redflyer
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RE: Question Re Mirv Warheads

Thu Jun 28, 2007 10:51 pm

Quoting Rwessel (Reply 4):

Great insight. Thanks!  Smile
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