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PostPosted: Tue Oct 07, 2008 11:56 am 
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There is a lot of confusion about the various different types of multiple-headed missiles and I thought it would be helpful if they were examined in a bit more detail. Usually, these three are considered to be onward developments of the same basic theory which is quite incorrect. In reality, they were all developed independently for different reasons.

Multiple Re-Entry Vehicles (MRVs)

Why they exist When Polaris was introduced in 1959, it was an extremely inaccurate missile, so much so that there was a very real possibility that it would miss a large industrial target completely. In order to overcome this problem, the first thought was to install a larger warhead. The problem was that the destructive power of a warhead is proportional to the cube root of its explosive power - in other words, to double the destructive power one has to increase the explosive power by a factor of eight. It quickly became obvious that was a losing game, it was much more effective to use three smaller warheads aimed so that they would form a triangle with their destructive radii touching. That offered maximum destructive power. So, a design was created where three warheads were installed on a bus that would release them over the target.

How it works So, a missile is fired at a target. The bus then separates and, at the appropriate time, it releases it's three warheads (there can be more or fewer but three is optimum) and they descend to for the triangle around the target.

There was a problem. When delivering RVs, it's not possible to have a major change of course of the RV as it comes down through the atmosphere. Thus the angle through which the MRVs can be scattered is restricted. This, in turn affects the dispersion pattern of the warheads. If they are released from the bus too late, they don't get enough dispersion to form the proper destructive pattern. If they are released too early, the inherent inaccuracy of the system means that the dispersion pattern is too great - its quite possible that the target in the middle of the triangle would be untouched. Thus, the bus has to release its warhead in a very tight altitude band, low enough for accuracy, high enough for proper dispersion.

Effects on ABM MRVs are often promoted as a way of beating an ABM defense by "swamping it", apparently on the assumption that each descending RV would have to be destroyed individually. In fact, this was not the case. Using nuclear-tipped ABMs, the relatively tightly clustered MRVs would be taken out by a single shot. However, even that wasn't necessary. The restricted release heights for the bus meant that the bus would be well within range of the ABM long before it released its MRVs and would be destroyed before it did so, either by a nuclear proximity burst or a direct hit on the bus. MRVs had no relevence to ABMs and did not affect the efficiency of an ABM screen. One ABM still took out one inbound missile, regardless of whether that missile had one warhead or ten.

Multiple Independently-Targeted Re-Entry Vehicles (MIRVs)

Why they exist Although MIRVs are often regarded as a development of MRVs, in fact they come from a totally different logic. In a ballistic missile site, the missile itself represents only a small proportion of the cost of the system (usually 10 - 20 percent). The bulk of that cost is represented by the silo and the command control system that goes with it. That cost is dorectly related to the number of missiles, not the number of warheads on each missile. Therefore, it is much less expensive to built 100 missiles with ten warheads each that 1,000 missiles with one warhead each. All the money saved can be invested in making the silos much harder and thus more difficult to destroy (meaning the enemy must fire more missiles at them to guarantee their destruction).

How it works The missile bus containing the warheads is designed so that it can make changes in its attitude and pitch between discharging warheads. It is then programmed so that, at the appropriate time, it can make those changes before discharging a warhead and can, thus, aim each warhead at a separate target. In theory it can aim all its warheads at different targets, in reality things are much more complex.

The problem is that the system has to discharge its warheads one at a time. It cannot discharge the whole lot at once. This puts a limit on how many it can discharge in the time available. Also, the degree of manoeuvering is strictly limited. So, the targets engaged by a single MIRV missile are limited toa relatively restricted footprint. Also, there are a lot more variable, many random and unpredictable, in aiming and discharging the MIRV bus which mean that MIRV missile-delivered RVs are a LOT less accurate than unitary RVs. So much so that if the launch distance is too far back from the target, the MIRVs are likely to miss by so much that they will be useless. So the distance at which the MIRV can discharge is severely limited. It should also be noted that the MIRV bus is very complex and very sensitive.

Effects on ABM MIRVs are also often promoted as a way of beating an ABM defense by "swamping it", apparently on the assumption that each descending RV would have to be destroyed individually. In fact, this is, again, not the case. Using nuclear-tipped ABMs, the relatively tightly clustered MIRVs would be taken out by a single shot. However, the simplest technique of eliminating MIRVs is, once again, to kill the bus before it discharges its warheads. This needs some extended range - the effect of MIRVs on the Nike-Zeus program was to upgrade the Zeus interceptor so that it had the range necessary to kill the MIRV bus before it discharged its warheads. That's why the range was increased from 250km (more than adequate to kill an MRV bus) to 740km (way more than adequate to kill any projected MIRV bus. Also, as a bonus, it needed only tiny amounts of damage or disturbance to render the MIRV bus ineffective. Far from being a way of beating an ABM defense, MIRVs were only credible in the absence of ABMs of adequate range.

Manoeuverable Re-Entry Vehicles (MARVs)

Why they exist In the late 1970s and early 1980s, there came to be a lot of interest in hitting very precise targets with ballistic missiles. Existing systems just didn't - and by the laws of physics couldn't have that accuracy. The only way around it was to give the RV some form of homing device. This requires a much bigger and more complex RV that has course correction devices, fuel, sensors etc etc. By and large MARVs are either incompatible with multiple warhead missiles or at most, only a few such warheads can be carried.

How it works The most common guidance system for a MARV is either radar or optical terrain matching. This system makes limited corrections to the RVs trajectory in its final stage of descent to correct its aim. By so doing, they have accuracies in terms of a few feet. Stories of "radically-manoeuvering MARVs" are the realm of science fiction, like spinning ICBMs and some other proposed devices, they do not and probably cannot be built. A MARV corrects is aim as it goes down, that's all.

Effects on ABM Essentially none. The course corrections made by the MARV are not sufficient to evade an interceptor and to an interceptor, there is no difference between a unitary RV arriving in an unguided ballistic arc and a MARV. Both are essentially predictable targets.

Thus it can be seen that neither MRVs, MIRVs or MARVs pffer any real problem to a properly-designed ABM system. As long as the interceptor has the range to hit the bus before it unloads its warheads (a condition met by both Zeus-XE and Sentinal) then the missiles remain just targets. MARVs are not relevent to a missile defense. There are ways of making an anti-missile systems life more complex, but these aren't it.

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Scott Brim Re: MRVs, MIRVs and MARVs #1

Quote:
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Thus it can be seen that neither MRVs, MIRVs or MARVs offer any real problem to a properly-designed ABM system. As long as the interceptor has the range to hit the bus before it unloads its warheads (a condition met by both Zeus-XE and Sentinal) then the missiles remain just targets. MARVs are not relevent to a missile defense. There are ways of making an anti-missile systems life more complex, but these aren't it.
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Could one of those ways be the future development of a new generation of supersonic manned bomber operating within a linked network of strategic weapons systems which employ both aircraft and ballistic missiles?


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Seer Stuart Re: MRVs, MIRVs and MARVs #2

Quote:
Could one of those ways be the future development of a new generation of supersonic manned bomber operating within a linked network of strategic weapons systems which employ both aircraft and ballistic missiles?


That's one. Another is to develop a missile warhead that skims the atmosphere in a very depressed trajectory and can manoeuver as it comes it. That's a lot easier to write than to do. The Russians are testing (or attempting to develop, the degree of progress is uncertain) a warhead design that can do it but it certainly isn't in service yet. It can be done using a manned vehicle - that's essentially what the Dynasoar bomber was - but doing it automatically is a real pain. Also, simply doing a depressed-trajectory is enormously fuel-expensive; an RV like that needs a large booster and is essentially a single-shot proposition one warhead per missile). Since suitable boosters could carry between eight and fourteen normal RVs, that means the defense has virtually "shot down" seven and thirteen RVs without firing a shot. Doing a manoevering depressed trajectory shot is even more fuel-expensive and inflicts even more penalties.


Scott Brim Re: MRVs, MIRVs and MARVs #3

Whether its missile defense on the one hand, or prosecuting the war on terror on the other, both seem to have something in common at a very deep level: Those who eventually prevail will be those who can most efficiently play the game of managing their available resources to maximum total effect.

MarkSheppard Brainflash moment concerning Decoys... #4

I just realized this just now reading the posts this time:

The fact that MIRV busses deploy their RVs one at a time over a period of time completely defeats any attempt to "swamp" the radar with decoys, unless you release them at the same rate as real RVs.

You can't just spam out 10 decoys at once; that's too obvious, and the ABM system will say "hahaha, who do you think you are fooling?" and reject it as an obvious fake.

All this is another strike against decoys; they just take up space and are ineffective; better to either:

1.) use space from decoy deletion to add more MIRVs
2.) use space from decoy deletion to add more fuel to the missile to make it fly a "hotter" flight trajectory, shaving a minute or perhaps two off the overall trajectory between launch and impact.

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Zen9 #5

Stuart, is it necessary to have the bus as such? All this presupposes the bus on seperation from the booster does the flying to a release point, which it seems as you describe it to be quite a distance and time for the bus 'flight'.

Assuming you produced MARVs the extra effort, cost and weight might be clawed back by uping the fuel in the MARVs and making them do the exoatmospheric flight completely. The logic of multiple RVs per booster in inescapable, but once their up out of the atmosphere why keep them nice and neatly together for a single interceptor to knock the lot out?

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drunknsubmrnr #6

You need the bus for a reasonably accurate MARV delivery.

If you want to substitute a full-up maneuvering warhead for the MARV's, you won't be able to carry more than one of them.

Kevin

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gifted one22 #7

Some missiles carry over ten warheads. Wouldn't you need more than one bus for that many? I'd think that some of these missiles could carry more than one MARV, though only two or three or so. Still, putting destructive power on target is the issue. If one warhead replaces ten, but can still destroy the target, have you lost much?

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Seer Stuart #8

gifted one22 wrote:
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Some missiles carry over ten warheads. Wouldn't you need more than one bus for that many? I'd think that some of these missiles could carry more than one MARV, though only two or three or so. Still, putting destructive power on target is the issue. If one warhead replaces ten, but can still destroy the target, have you lost much? No, one bus does for the lot. The problem with MARVs is that they need a lot more volume than a normal RV so they are one per.

If one warhead replaces ten, what does one lose? The other nine targets that would have been hit.

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Seer Stuart #9

Zen9 wrote:
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Stuart, is it necessary to have the bus as such?

Oh yes, very much so. Its the bus that does the manooeuvering to aim the RVs at their targets


Quote:
Assuming you produced MARVs the extra effort, cost and weight might be clawed back by uping the fuel in the MARVs and making them do the exoatmospheric flight completely. The logic of multiple RVs per booster in inescapable, but once their up out of the atmosphere why keep them nice and neatly together for a single interceptor to knock the lot out?


One simple word, accuracy. The accuracy of the RVs degrades dramatically with range. Remember the RV from a MIRV has no independent manoeuvering capability; one its been launched it is set. So the further it is aimed from its target, the less accurate it is.

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MarkSheppard #10

Stuart, are there any uhm.......publications that might talk about all this that have been declassified? If you have to wait until you're relatively close to the target to release your warheads because of kilotonnage (225 kt) and accuracy requirements; then it means you're very vunerable to an ABM system knocking down all of your warheads.

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PostPosted: Tue Jul 04, 2017 5:48 am 
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Stuart, question for you.

What is it that the GMD system does, that NIKE- ZEUS didn't... aside from actually (barely) existing nowadays?

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PostPosted: Tue Jul 04, 2017 9:20 am 
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Craiglxviii wrote:
Stuart, question for you.

What is it that the GMD system does, that NIKE- ZEUS didn't... aside from actually (barely) existing nowadays?

Uses non-nuclear warheads is the primary one. Zeus was designed to use a nuclear warhead that would provide an area effect on the presumption that getting a direct hit was difficult. In fact, it later proved that getting skin-to-skin hits was significantly easier (ie Zeus could do it) than expected. GMD was designed to use non-nuclear means of destruction from the start.

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PostPosted: Tue Jul 04, 2017 9:29 am 
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Francis Urquhart wrote:
Craiglxviii wrote:
Stuart, question for you.

What is it that the GMD system does, that NIKE- ZEUS didn't... aside from actually (barely) existing nowadays?

Uses non-nuclear warheads is the primary one. Zeus was designed to use a nuclear warhead that would provide an area effect on the presumption that getting a direct hit was difficult. In fact, it later proved that getting skin-to-skin hits was significantly easier (ie Zeus could do it) than expected. GMD was designed to use non-nuclear means of destruction from the start.


Soooo... current missile defence is still at 60s levels of effectiveness?

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PostPosted: Tue Jul 04, 2017 9:47 am 
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Craiglxviii wrote:
Soooo... current missile defence is still at 60s levels of effectiveness?

In some ways, it's quite a bit less. Battle management capability is a lot better, target discrimination is much better, number of interceptors is a lot lower. A better way of saying it would be that the current missile defense system is a mere shadow of what we would have had if we'd gone ahead with our planned defenses in the mid-1960s. A very faint and insubstantial shadow. You see, once a system is established, its much easier to keep updating it and keeping pace with the offense than to start again from a higher technology level.

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PostPosted: Tue Jul 04, 2017 10:12 am 
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Thank you Stuart, I had those feelings in me waters but nice to have them confirmed.

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