Method to discriminate ICBM decoys? decoys are useless?

[RyanC]

No, but we could add chaffs and jammers, and corner reflectors to make radar picture of decoy cloud extremely confusing.

US Jammers actually did go to sea with Polaris Boats...and then they got withdrawn because they were extremely temperamental to keep in service.

Again, this isn't as easy as waving your hand and saying "jammers".

 

[RyanC]

Honestly, the only reason ABM systems aren't more widespread is because of arms control treaties limiting the major developers (US/Russia) from widely deploying them from 1972-2002.

(There is some evidence the Russians did cheat by deliberately not cooling down their advanced heavy SAM systems from the 1970s onwards. By contrast, PATRIOT was cooled down during development to avoid running afoul of the ABM treaty -- a lot of the Gulf War era anti-tactical ballistic missile stuff that had been just added to PATRIOT at the time of the Gulf War had been originally proposed during system definition back in the late 1960s / early 1970s).

 

[Trident]

You have to inflate it fast enough so as not to be rejected by the defenders as an obvious, slowly inflating decoy.

Or you hide the inflation process in a dense cloud of chaff, so the defenders don't get to observe it. Individually, any deception technique is liable to be defeated, but in the real world the attacker would not give you the luxury of tackling each in isolation.

This means you need a thick, rugged decoy skin that can withstand the stress of rapid inflation.

Sounds downright trivial relative to the proposed attempts at reliably measuring minuscule effects at ranges in the hundreds to thousands of kilometres.

Second is that you need some method to provide the gas for inflation.

If you try using compressed gas, as the gas expands to fill the decoy, it cools.

If you try using a solid propellant gas generator, the chemical reactions to generate the gas are going to be rather hot, particularly if you want a lot of gas volume generated in a short time to fool radar; leading to a rather hot gaseous interior.

How big are these effects compared to other influences such as solar heating or clutter when the sensor views the targets/decoys against the background of the earth? What about the exhaust of fairing separation & warhead spin motors and aerosol clouds from explosive squibs? Does it simply disappear in the noise of signature variations between individual warheads and decoys?

Will it still be discernible enough for terrestrial sensors to discriminate in poor weather, strong atmospheric distortion or high dust content from warhead detonations nearby? Just because the math says a certain marker should be substantial enough to be discernible in perfect conditions, and it can perhaps even be demonstrated in the lab, doesn't mean it works that way in the field.

A certain Mr. Petrov would have a thing or two to say about unanticipated complexities in discrimination. And the Oko satellite in 1983 wasn't even trying to sort out warheads from decoys deliberately designed to mimic them, it was confusing sunlit cloud layers for missile exhaust plumes!

"In 1987 we had the AIM-9P, which was designed to reject flares, and when we used US flares against it would ignore them and go straight for the target. We had the Soviet flares – they were dirty, and none of them looked the same – and the AIM-9P said 'I love that flare'.

"Why’d that happen? We had designed it to reject American flares. The Soviet flares had different burn time, intensity and separation. The same way, every time we tried to build a SAM simulator, when we got the real thing it wasn’t the same.

"I use the AIM-9P because it is out of the system and I can talk about it. The same thing happened to a lot of things that are still in the system and that I can’t talk about."

More recently, in Syria several AIM-9X with their imaging seekers designed to defeat conventional flares succumbed to legacy Soviet decoys fired by a tired old Su-22. Meanwhile, the current state of the art is multispectral charges, sometimes with measures to temporarily counter aerodynamic drag to defeat algorithms that expect flares to lag behind the target aircraft:

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aviation21.ru

Finally, in one test of the GBI interceptor, the entire mission was a "failure" because the target missile couldn't deploy decoys successfully.

If decoys were really a cheap and solved problem from the 1960s, how could decoy deployment failure occur?

If jet airliners were really a safe and sound mode of transport from the 1960s, why do they continue to crash to this day? Sh*t happens occasionally, even with long established and generally bullet-proof systems. Didn't a couple of BMD tests get scrubbed simply because the target missile failed to launch altogether? If missiles cannot be counted upon to launch, what does that imply for the ABM interceptors? (Playing devil's advocate here, obviously.)

With this?

While we're on the subject of blithe hand waving...

US Jammers actually did go to sea with Polaris Boats...and then they got withdrawn because they were extremely temperamental to keep in service.

Again, this isn't as easy as waving your hand and saying "jammers".

Yet jammers evidently made a comeback on Trident. Maybe the specific implementation on Polaris was simply poor, and thus does not reflect a fundamental difficulty with the basic concept? Quite apart from the fact that "temperamental to keep in service" is not the same as "ineffective at spoofing radars".

Even if the US had never deployed a successful jammer, that wouldn't necessarily mean everybody else must inevitably run into the same problems. The US never cracked LOx/RP-1 staged combustion rocket engines and indeed was inclined to treat the whole notion with incredulity until it was able to test Soviet engines of the type after the Cold War. Or the saga of VTAS/AIM-95 versus Sura-K/R-73 - sometimes it's as banal as one side missing the boat.

 

[Dilandu]

And you can't shield against neutrons easily -- at least not without significant mass penalties.

You only need to shield enough for warheads not to be knocked in a bunch. As long as the opponent need to individually target the warheads with nuclear ABM missiles, you won.

 

[zen]

Yes. But since midcourse is the most lenghty stage - tens of minutes - protection here especially important.

Not uniform densities of atmosphere, altitude varies.

Yes, a bit.

No 'a bit' it is yes, it is absolute. For X fuel of Y isp you get Z discrete weight outcome. Irrespective of what the objectives are, orbit or ballistic trajectory for a given altitude and velocity.
No free launch.
No free mass.
Everything is paid for in fuel or you trade altitude, velocity and with them distance on a ballistic trajectory.

You seems to forget, that warheads are coated in the thermal isolation covering.

You must be forgetting the facts about the laws of thermodynamics.
Insulation is not perfect reflector of heat. A RV has a thermal signature. A distribution of thermal emissions not easily or perfectly replicable by a heater in a balloon.

Require enormous energy, not reliable on long ranges, easy to confuse by just adding reflectors into the decoys.

How enormous the battery on Brimstone must be then....

 

[zen]

Or you hide the inflation process in a dense cloud of chaff, so the defenders don't get to observe it. Individually, any deception technique is liable to be defeated, but in the real world the attacker would not give you the luxury of tackling each in isolation.

Risk of chaff piercing a balloon. Would be embarrassing to puncture your decoy with your own chaff....

 

[zen]

And you can't shield against neutrons easily -- at least not without significant mass penalties.

You only need to shield enough for warheads not to be knocked in a bunch. As long as the opponent need to individually target the warheads with nuclear ABM missiles, you won.

Cost of lofting interceptor less than bus and RVs. Much less.

 

[zen]

And you can't shield against neutrons easily -- at least not without significant mass penalties.

You only need to shield enough for warheads not to be knocked in a bunch. As long as the opponent need to individually target the warheads with nuclear ABM missiles, you won.

But you still traded mass.

 

[Dilandu]

You must be forgetting the facts about the laws of thermodynamics.
Insulation is not perfect reflector of heat. A RV has a thermal signature. A distribution of thermal emissions not easily or perfectly replicable by a heater in a balloon

One "small" question. How exactly the other side could know what is the distribution of thermal emission in my warheads?

Exactly.

They couldn't. And since they couldn't, all I need is that thermal signatures were all different, so they could not establish any patterns. So randomly placed heaters of random output solve the whole problem. The enemy observe a bunch of signatures, each of them is different from another. No easy-to-recognize patterns.

 

[Dilandu]

Risk of chaff piercing a balloon. Would be embarrassing to puncture your decoy with your own chaff...

...You dont know what chaff is? Its a piece of metal foil. How exactly it is supposed to penetrate the baloon?

 

[zen]

Risk of chaff piercing a balloon. Would be embarrassing to puncture your decoy with your own chaff...

...You dont know what chaff is? Its a piece of metal foil. How exactly it is supposed to penetrate the baloon?

In vacuum you presume sharp edges cannot cut?

 

[zen]

You must be forgetting the facts about the laws of thermodynamics.
Insulation is not perfect reflector of heat. A RV has a thermal signature. A distribution of thermal emissions not easily or perfectly replicable by a heater in a balloon

One "small" question. How exactly the other side could know what is the distribution of thermal emission in my warheads?

Exactly.

They couldn't. And since they couldn't, all I need is that thermal signatures were all different, so they could not establish any patterns. So randomly placed heaters of random output solve the whole problem. The enemy observe a bunch of signatures, each of them is different from another. No easy-to-recognize patterns.

So short answer is they can only really have precise data of their own....unless..... guess

But generally speaking, the relatively solid structures of an RV have a notably different pattern of thermal emissions to a balloon.
Heaters....and the batteries to power them cost mass and again mass impacts fuel or other weights or range.
No escape from the cost benefit of for missile of X throw weight to Y range.

 

[Firefinder]

You must be forgetting the facts about the laws of thermodynamics.
Insulation is not perfect reflector of heat. A RV has a thermal signature. A distribution of thermal emissions not easily or perfectly replicable by a heater in a balloon

One "small" question. How exactly the other side could know what is the distribution of thermal emission in my warheads?

Exactly.

They couldn't. And since they couldn't, all I need is that thermal signatures were all different, so they could not establish any patterns. So randomly placed heaters of random output solve the whole problem. The enemy observe a bunch of signatures, each of them is different from another. No easy-to-recognize patterns.

That is actually pretty simple.

THERMAL IMAGERS are getting better all the time, heck standard visual image recognition is getting up there as well.

We are getting up to the point were the interceptors can actually see the difference between an RV and a balloon or metal reflector the same way we can. Well most of the time, the software still have a few bugs that need working out.

Through of course you can start adding laser dazzlers to the RV bus to mess with that...

Honestly the best intercepter may as well be a guided flak shell/claymore mine. Get the front point onto the general direction of the RV's and let her rip, it might not instant kill the warhead, but it make its reentry out right impossible which is just as good. Or go with that one SDI idea of basically a Spartan ABM missile with the Warhead being a Casaba Howitzer if you really want to kill the RVs, which as all the same issues of the regular nuke ABMs.

 

[major-1]

There are decoys made of metal mesh (cones that are inserted into each other). This average between heavy decoys and mylar balloons

 

[Dilandu]

We are getting up to the point were the interceptors can actually see the difference between an RV and a balloon or metal reflector the same way we can. Well most of the time, the software still have a few bugs that need working out.

Sigh. How interceptors are supposed to know what thermal signature are my RV supposed to have? All I need to do is to add random heat emitters on RV's and decoys, so no one thermal signature would be like other. Because your processing software have no idea what signature exactly my RV is supposed to have, it would be completely incapable to discriminate.

You are making a mistake, assuming that situation would be something like that:



With modern decoys, it would be like that:



Feel free to guess, which color correspond with RV, and which with decoy. All are different. All are random. There are no pattern. My heat emitters gave each object its unique heat signature, and since they all random, you could not possibly discriminate anything.

 

[Firefinder]

We are getting up to the point were the interceptors can actually see the difference between an RV and a balloon or metal reflector the same way we can. Well most of the time, the software still have a few bugs that need working out.

Sigh. How interceptors are supposed to know what thermal signature are my RV supposed to have? All I need to do is to add random heat emitters on RV's and decoys, so no one thermal signature would be like other. Because your processing software have no idea what signature exactly my RV is supposed to have, it would be completely incapable to discriminate.

You are making a mistake, assuming that situation would be something like that:

View attachment 660320

With modern decoys, it would be like that:

View attachment 660321

Feel free to guess, which color correspond with RV, and which with decoy. All are different. All are random. There are no pattern. My heat emitters gave each object its unique heat signature, and since they all random, you could not possibly discriminate anything.

Thats nice but it doesnt work like.
And you dont need to know the thermal signature, just the size and shape.

Put it this way.

I'm thinking of the Aim-9X camera.

You seemly thinking the Aim-9L/M sensor.

Basically this is the sensor that I am talking about.

View: https://www.youtube.com/watch?v=AzyH0M4C8TY


Changing how the decoys and RV will emitter thermal radaition will not change how it looks on a thermal camera. Enough tests done by Darpa and the like over the years for the thermal seeking missiles have shown that. They have try all the tricks in the book including you random thermal pattern trick, on tanks, aircraft, ships, and likely even RVs to see if they can spoof a thermal camera.

Then Answer been not unless you make the decoy look exactly the same physically or have a hotter thermal back drop to blind the sensor. Or have laser blind it.

Or the recongitizion software fitzs out, but I'm not counting that since that be like counting on the similar odds of a warhead not working.

For ICBMs this means you need to have several full size decoy RVs mixed into you real ones that limit the amount you can have. Which makes the intercept job slightly more easier since you going from like 56 targets to 14 targets per missile. Only way to incase that is to make the RV smaller, likely, or the missile bigger, unlikely since you have to rebuild all the silos to fit.

Which is the main kicker of this plan.

It gives you too few decoys to warhead ratio. You better off just spamming warheads so at least one will get thru.

Normally this was fine, but launch costs are dropping faster then an RV does. So a Brilliant Pebbles* style system is not out of reach like it was 30 years back which will solve the question of which one is real the same way one does a Gordian knot.

Hit both, we got pebbles to spare.

Before someone says something about cost, Starlink is basically a civilian version of the systems, it has the same numbers and launch cycle needs.

 

[Dilandu]

Thats nice but it doesnt work like.
And you dont need to know the thermal signature, just the size and shape.

Newsflash: inflatable decoys are in size and shape of actual warheads. Specifically for that reason.

Normally this was fine, but launch costs are dropping faster then an RV does. So a Brilliant Pebbles* style system is not out of reach like it was 30 years back which will solve the question of which one is real the same way one does a Gordian knot.

Brilliant Pebble was a BOOST-PHASE INTERCEPT SYSTEM! It was never ever supposed to intercept warheads! It was supposed to intercept boosting missiles, homing on their enormous, impossible-to-camouflage, heat plume!

Seriously, Firefinder!

 

[Kat Tsun]

I'd imagine the resolution an IR sensor like SBIRS from 35,000 kilometers away would be so poor it would really only be able to tell you a target is there by its massive exhaust plume anyway, since SBIRS-GEO is a replacement for the DSP missile launch detectors. Since midcourse transit produces zero exhaust there's not a lot of stuff to look at, so special heaters and thin film covers for an RV are probably unnecessary.

At the moment there's simply no practical way to target an incoming RV reliably, or discriminate a target in midcourse in orbit. SBIRS-LO can theoretically do it (I guess, it was supposed to be the Brilliant Eyes component for midcourse tracking) but there's only two of them on oddball orbits on NRO buses, so not exactly ideal. At best it can do a pass once and tell you there are some clouds of decoys and warheads before you get turned into radioactive dust. Maybe in a few decades if the USSF ever decides to deploy a major space tracking network for anti-ABM purposes, but that would require air defense systems to be several orders of magnitude more effective against high speed and VLO ballistic missile targets (incoming conical RVs and crossing IRBMs are notoriously hard targets no matter what is being used) than they are now.

 

[RyanC]

You must be forgetting the facts about the laws of thermodynamics.
Insulation is not perfect reflector of heat. A RV has a thermal signature. A distribution of thermal emissions not easily or perfectly replicable by a heater in a balloon

One "small" question. How exactly the other side could know what is the distribution of thermal emission in my warheads?

Both sides in the Cold War (and today) had MASINT (measurements intelligence) aircraft flying in international airspace, or "fishing trawlers" in international waters loaded to the gills with sensors for precisely this purpose.

Also; you've got your own nuclear warheads that you can put on a pedestal in vacuum chambers and look at with whatever sensors you have. While the configurations may be different between a US warhead and a Russian Warhead, the materials science of fissile material implosion and the heat of hypersonic re-entry limits you to staying within certain known configuration ranges.

 

[RyanC]

And you can't shield against neutrons easily -- at least not without significant mass penalties.

You only need to shield enough for warheads not to be knocked in a bunch. As long as the opponent need to individually target the warheads with nuclear ABM missiles, you won.

Officially it's been revealed that the neutron flux from the 10 KT warhead on the BOMARC missile would have been able to mission kill a nuke on an enemy bomber at 300 ft (91m) distance.

Given that space doesn't have an atmosphere to attenuate neutron flux; and that SPARTAN had the first neutron bomb warhead design (of 5 MT yield), along with the fact that:

Lead or steel do not shield against neutrons.

You need

10" of Regular Concrete
or
8" of Polyethylene
or
9" of water

to attenuate neutrons by a factor of 10.

You can do the basic math on how bad a 5 MT enhanced neutron warhead would be for the enemy RV(s) in an incoming threat cluster.

 

[RyanC]

Aviation Week & Space Technology. March 25, 1974

Improved Galosh, a follow-on Soviet anti-ballistic missile defense system with the capability of loitering aloft while sorting out U. S. intercontinental ballistic missile penetration aids from warheads, is under advanced development.

The Improved Galosh has the capability of stopping and restarting its motor at upper altitudes four or five times to provide the loiter capability.

The Improved Galosh has already been flight-tested by the Soviets. While the two-stage missile coasts with its motor off, ground radar stations and data processing units can track incoming reentry vehicles and compute the warhead's trajectory. The engine then can be restarted to maneuver the missile for an Intercept.

The delay enhances the Soviets' capability to determine which reentry vehicles are penetration aids and which actual nuclear warheads.

The actual warhead behaves differently over a long flight path than do penetration aids because of weight differences. By extending the flight time of Improved Galosh, and providing a restart capability for maneuvering, the Soviets provide more time to track and determine actual warheads for interception.

Improved Galosh is operated as a terminal reentry vehicle interceptor and has a slant range of 200 to 400 naut. mi. The original Galosh missile has been deployed to defend large area targets and not for defense of specific missile fields. Galosh is deployed around Moscow, with four sites having 64 launchers.

The U. S. so far has been limited to studies of a loiter-mode anti-ballistic missile Interceptor using an Improved Bell Laboratories/Western Electric Spartan XLIM-49A missile. This version of the Spartan would have a nuclear warhead in the 1-megaton class for loiter-mode operations instead of the present 5-megaton class warhead.

Soviets are expected shortly to begin adding 36 more Galosh launchers to the Moscow site. A second large radar will be added to a large target acquisition and tracking radar already in operation, with four sets of smaller engagement radars.

Miami News - February 28 1972; repeating a NYT Article "New Missile is Designed to Manouver"

The advanced system, coupled with a new satellite equipped with special Infra-red sensors, would also offer increased capability against small numbers of Soviet missiles carrying sophisticated defense penetration devices, according to senior Pentagon officials.

...

The Defense Department, he said, has successfully tested "infra-red sensors aboard spacecraft" that have detected the path of missiles and warheads "in mid-course flight."

Foster also noted the successful test-firing of an anti-missile missile that can fly out into space, stop its engine, then start again and maneuver to reach its target.

...

Heretofore, the principal factors limiting missile defense were the relative short ranges at which data could be received on the precise flight path of the incoming warheads, and on the limited range of interceptor missiles.

The longest-range American interceptor, the Spartan missile, now has a range of about 400 miles.

But sources say the advanced programs should enable American defenders to accurately predict the flight path of an enemy missile shortly after it has been launched some 5,000 to 7,000 miles from the United States.

Work on a much improved Spartan, the sources add, would permit interception to take place roughly 2,000 miles from the United States.

...

"If we should decide it's still desirable to have a China-oriented defense," one Pentagon source said, "the ability to be able to predict the exact flight path of an incoming missile several thousand miles away, and to be able to effect Intercept at least 2,000 miles from our launch site, should permit country-wide defense from almost anywhere in the United States."

By going out 2,000 miles or so and then coasting, the improved Spartan could employ special sensors to sort out the actual warhead from the decoys; it would then restart its engines and go after the real thing.

The Soviet Union, intelligence sources say, has been testing at least two versions of an advanced anti-missile missile with a similar stop-start feature. It is assumed a missile of this type will be deployed at sites around Moscow where the Russians last year resumed construction activity after a lapse of several years.

Aviation Week & Space Technology. May 6, 1974

The Army's Homing Intercept Technology (HIT) is now in its third stage and will be ground-tested in a chamber under contract with LTV Aerospace Corp. to determine if the small, lightweight (a few pounds) warhead can home on simulated targets and deploy its kill mechanism for point detonation.

Prior to the signing of the anti-ballistic missile treaty and interim offensive ICBM weapons agreement in May, 1972, the Army was developing the Homing Intercept Technology program for use as multiple independently-targetable interceptors.

The ABM treaty prohibits multiple interceptors in a single booster, even if the work is merely a feasibility study of the concept, according to a Pentagon official. The Army reviewed the program in light of the provisions of the ABM treaty prohibiting development, test or deploy-ment of ABM interceptors for the delivery of multiple warheads.

The Homing Intercept Technology program developments now under contract are not prohibited by the treaty and are continuing, a Pentagon official said. He added that the final phase originally planned, launching cluster warheads, has been canceled.

Homing Intercept Technology is designed to provide an optically-guided, non-nuclear warhead. "Such a warhead, if successfully demonstrated in a ballistic missile defense environment; would permit the NORAD [North American Air Defense] commander, for example, to commit an interceptor without requiring the presidential nuclear release authority, which is inherent in current systems. In addition, a non-nuclear warhead eliminates the problems associated with nuclear explosions, such as radar blackout or distortion, interceptor fratricide [friendly interceptor killing another] and perturbed environment in general," an Army official said.

Homing Intercept Technology is adaptable to mass-production without requiring the use of nuclear materials and more economical "than a system providing equal effectiveness but using nuclear warheads. HIT, as-a non-nuclear warhead concept, offers the promise of very high lethality, without the need for complicated fuzes, auxiliary sensors, or sophisticated communication links," Army officials added.

Its propulsion system is a cluster of small rocket tubes wrapped around the optical sensor package containing a small digital computer and control mechanism. The rocket tubes also function as the kill mechanism for point contact with a reentry vehicle. The entire package is spin stabilized at a very high spin rate, according to Defense Dept. officials. The warhead's terminal homing device detects the target, and the computer maneuvers the device by firing the rockets to conduct the intercept. On signal, the rods are placed in the path of the incoming reentry vehicle, destroying it.

Under the original concept, or if the treaty is abrogated by either party, a large number of the small warheads would be used on an improved Spartan interceptor and they would provide a "cumulative probability" of detecting, tracking and destroying reentry vehicles, a Pentagon official said. Because the treaty prohibits multiple warheads on a single booster, "they could be developed for use on a much smaller booster and HIT will likely be tested with a single warhead on a small booster," the official added.

Under the Homing Intercept Technology concept, the interceptor would be command-guided by ground-based radar until reaching a high altitude.

Under the multiple concept, which officials' stress is not being developed, a large optical sensor would be operated on the Spartan to detect targets at very long ranges. On command the smaller warheads would be deployed with their smaller optical sensors used for terminal homing. The large electro-optical system is designed to have the capability of discriminating reentry vehicles from chaff, penetration aids or decoys, officials said. They added that the technology could also be used in an anti-satellite mission.

...

A non-nuclear warhead could be one of several types, including a rod flechette or pellet configuration. "Not much warhead design effort is in progress now, but a fair amount of effort has gone into them in the past. It is a straightforward approach—with an RV traveling at about 24,000 fps. All we have to do is to put a-pattern like buckshot in front of that RV and it "provides the necessary velocity for destruction. The major warhead effort now is to establish homing devices that will insure a high probability of kill and deployment of the warhead at very small miss distances," a Pentagon official said.

"We are talking about warhead particles that weigh about 100 grains and depleted uranium is one example of a good substance to use. It makes a good kill mechanism. We can calculate the pattern and probability of a hit on an RV that presents a certain cross-section," he added.

Foreign Relations of the United States, 1969–1976, Volume XXXIV, National Security Policy, 1969–1972
Notes of Defense Program Review Committee Meeting
Washington, December 20, 1969

HAK: Why improve Spartan?

Foster: Old Spartan relied on large yield to attack large volume of objects. Subsequent to that, we saw we could get loiter capability. It can loiter 50–60 seconds. With last min. info, so you direct it, you don’t need as much yield, and you can get greater ranges. So you could have fewer sites.

HAK: I don’t understand. Original 12 sites gave you defense less easily spoofed, less subject to pen aids. What does it cost to get Improved Spartan?

Starbird: $450 million.

HAK: Why do we want it?

Foster: You can deal with advanced pen aids.

HAK: What you should do with advanced one is add more sites.

Starbird:
—The sites can reinforce each other, so fewer sites needed.
—If he uses depressed trajectory, big Spartan can’t catch depressed trajectory.
—Improved Spartan gives you loiter, 150 mile effectiveness against advanced pen aids. Don’t have to use Sprints.

HAK: We have major doctrinal problem. Chinese won’t have SLBMs. If rationale is China, aren’t you better off with old Spartan.

Starbird: No, with old, you get non-overlapping coverage. With Improved Spartan you have overlap. This is important as numbers build up.

Found at the Dwight D Eisenhower Library in a letter to DDE circa 10 December 1958:

Dear Mr. President;

I am pleased to forward herewith the progress report on the Anti-Ballistic Missile Weapon System Program for the quarter ending 15 October 1958.

During this period our supporting research programs yielded substantial contributions. Our confidence in the radar designs for the NIKE-ZEUS defense system and the Ballistic Missile Early Warning System has increased as a result of experiments performed as a part of the HARDTACK nuclear test series. Theoretical considerations indicated the possibility that radars would be unable to penetrate the nuclear cloud associated with a weapon detonation. Preliminary test data indicate that some attenuation of radar signals will occur but this attenuation is not sufficiently serious to require a redesign of the radars in question.

 

[RyanC]

And here's a biggie

https://static.history.state.gov/frus/frus1969-76v34/pdf/frus1969-76v34.pdf

National Security Policy 1969-72 Volume XXXIV page 54 minute 16

Minutes of National Security Council Meeting
Washington, March 5, 1969

...Spartan—kill radius of 20 mi. (later said 12 mi for soft targets, 4 mi for hard targets)....

Page 409

Notes of Defense Program Review Committee Meeting1
Washington, January 15, 1970.
At the meeting were: Henry Kissinger, McCracken, Helms, Richardson, Alexis Johnson, Wheeler, Packard, Smith, Lynn, Schlesinger

...The scientific panel discussed the issue at length.5 It has taken us 10 years to penaids. The preponderance of opinion is that the Chinese won’t have the capability in 1974–80 to develop technical measure to degrade system. The people who know most about missile technique say that simple penaids like chaff and balloons won’t work. Need more sophisticated devices...

Page 408
MEMORANDUM ON THE SAFEGUARD SYSTEM, 12 JAN 1970

The Chinese, because of their limited economy and lack of the very expensive, sophisticated range instrumentation needed to develop penetration aids, are not expected to be able to deploy penetration aids like our Mk 1a or “Antelope” system for many years after they deploy simple ICBM’s. When they do begin to deploy sophisticated penetration aids we will find ourselves in a technology (rather than force level) race, which we should be able to win. Our advanced ballistic missile defense research program now includes the kind of work needed to counter the later Chinese threat. For example, we are investigating the use of long wavelength infra red (LWIR) optical sensors for both surveillance and long-range ABM interceptor homing. The LWIR sensors can detect a reentry vehicle in the presence of chaff because chaff does not resemble a reentry vehicle at infra red wavelengths.

 

[Dilandu]

You can do the basic math on how bad a 5 MT enhanced neutron warhead would be for the enemy RV(s) in an incoming threat cluster.

Sigh. Three-dimensional quartz phenolic.

 

[Dilandu]

You can do the basic math on how bad a 5 MT enhanced neutron warhead would be for the enemy RV(s) in an incoming threat cluster.

Basic math strongly urges to remember inverse-square law. By reducing the intensity of radiation, we also proportionally reduce the distance on which it may cause harm. We do not need tenfold reduction to drastically reduce warhead efficient range.

 

[zen]

Simple logic.
Nuclear devices can be optimised for neutron release. Ergo a conventional nuclear device of 10MT may not produce the same level of neutron output as an optimised device of 5MT.

 

[Have Blue]

This video may be of interest:

View: https://youtu.be/LxZS_Zrd5NM

 

[Forest Green]

Of some relevance.

New Missile Defense Radar Passes Key Stage: Lockheed LRDR - Breaking Defense

As anxiety rises over North Korean rocket tests, the Missile Defense Agency needs better radar to tell threats apart. Which of those distant blips is an InterContinental Ballistic Missile (ICBM) warhead capable of hitting the US? Which is a burnt-out rocket boaster coasting harmlessly through...

breakingdefense.com