Countermeasures for hypersonic weapons

What possible countermeasures could you envision against hypersonic weapons? These are missiles that travel in excess of 1.5 km/s.

It seems that conventional interceptor missiles would have to be hypersonic themselves, and even more nimble, to be able to intercept incoming hypersonic missiles. Furthermore, there will undoubtedly be issues with mounting sensors for terminal guidance on interceptors.

Lasers may not work given the plasma sheath and leading shockwaves around hypersonic missiles, which would absorb and disperse the energy you dump onto the missile.

neanderthalphysics said:

It seems that conventional interceptor missiles would have to be hypersonic themselves

Why? The interceptor doesn't chase the target from behind, it intercepts the target from ahead of its path. A football player who intercepts a pass does not have to run faster than the football flies.

You've touched on some very real physics challenges in countering hypersonic weapons. But I'll note that anyone with actual knowledge of real efforts to overcome these issues is highly unlikely to be allowed to talk about it in a setting like this.

anorlunda said:

Why? The interceptor doesn't chase the target from behind, it intercepts the target from ahead of its path. A football player who intercepts a pass does not have to run faster than the football flies.

Two reasons really:
1. Unless you are able to put interceptors everywhere, you want your interceptors to be fast so that a few launch sites can cover a wider area.
2. Incoming hypersonic missiles would themselves be highly agile, which means your interceptors must be able to do large course corrections at short notice.

@boneh3ad: Not looking for specifics but broad "coffee break physics" discussions. I note there are many articles in the public domain that discuss hypersonic weapons as a disruptive technology.

neanderthalphysics said:

Incoming hypersonic missiles would themselves be highly agile

Are you sure about that? Sounds like an oxymoron to me, but I'm not an expert in missile technology.

There is a lot of hype about hypersonic weapons. There are not very many cases where it is currently cost effective to stop a non-hypersonic weapon.

neanderthalphysics said:

These are missiles that travel in excess of 1.5 km/s.

That's not all that "hyper". The 3"/76 on the FFG-7 class is over 0.9 km/s. That gun is 50 years old. (And the ship class is 45 years old)

neanderthalphysics said:

Incoming hypersonic missiles would themselves be highly agile

I very much doubt this. If a body is moving twice as fast, it takes twice the impulse to change the direction a given amount.

neanderthalphysics said:

Unless you are able to put interceptors everywhere,

Have you looked at how this works today? See https://en.wikipedia.org/wiki/Close-in_weapon_system and references therein.

berkeman said:

Are you sure about that? Sounds like an oxymoron to me, but I'm not an expert in missile technology.

It is. If you listen to any stories from Vietnam War fighter pilots, many had to dodge dozens of SAMs, and it was possible precisely because being fast made them less manoeverable; a 400kt fighter jet can out-maneuver a machine 3 missile.

neanderthalphysics said:

Two reasons really:
1. Unless you are able to put interceptors everywhere, you want your interceptors to be fast so that a few launch sites can cover a wider area.

Interceptors tend to be based near the target they are protecting. Typically the goal is to fly away from the target, toward the threat. They are fast and their range is fairly short.

berkeman said:

Are you sure about that? Sounds like an oxymoron to me, but I'm not an expert in missile technology.

Well there are two main ways to achieve a course change in a missile - by aerodynamic surfaces or thrust vectoring. Maybe other exotic flow control mechanisms may be relevant in hypersonic missiles, such as plasma flow control, but let's not get into that :)

But if we go back to aerodynamic surfaces - even a slight protrusion or asymmetry in a hypersonic object would cause large differences in the axisymmetry of the shocks around it, and therefore the shock-induced drag forces.

In hypersonic weapons I believe the upper limit on maneuverability would be set by structural limitations and not the ability to generate those forces by control surfaces.

Vanadium 50 said:

That's not all that "hyper". The 3"/76 on the FFG-7 class is over 0.9 km/s. That gun is 50 years old. (And the ship class is 45 years old)

Most guns top out at about 1 km/s, with a projectile that has its maximum velocity at the muzzle and decays henceforth. In this context hypersonic weapons are those which are capable of sustained powered flight. We may include ballistic re-entry vehicles but those are really a separate class of targets where their velocities are sustained by their fall and they do not have a hypersonic scramjet that would permit them to maneuver substantially.

Have you looked at how this works today? See https://en.wikipedia.org/wiki/Close-in_weapon_system and references therein.

Yes, and they would be bad for defending cities or populated regions against hypersonic weapons. Firstly you're spraying ordnance around and what goes up, must come down...hopefully it does not hit anyone who happened to be in the wrong place at the wrong time. Furthermore, a certain small but non-zero percentage of the shells fired by CIWS fail to self-destruct. Which means kids playing in the park after a successful interception may pick up a live CIWS shell..yikes. Fired over the ocean that is less of a problem, unless in a busy shipping waterway (another can of worms).

Also, with an effective range of a few km, let's say we want to defend a large city, it is going to take a lot of batteries doing nothing most of the time until that one time you must use it, and then Murphy's Law says some guy will probably have forgotten to turn on the radar then.

russ_watters said:

Interceptors tend to be based near the target they are protecting. Typically the goal is to fly away from the target, toward the threat. They are fast and their range is fairly short.

Generally the rule of thumb for an efficient interception course for a steady target is to maintain your target at the same bearing but while closing the distance.

If your target is dancing around and moving randomly? Then things get interesting...

neanderthalphysics said:

In this context hypersonic weapons are those which are capable of sustained powered flight. We may include ballistic re-entry vehicles but those are really a separate class of targets where their velocities are sustained by their fall and they do not have a hypersonic scramjet that would permit them to maneuver substantially.

Yes, and they would be bad for defending cities or populated regions against hypersonic weapons. Firstly you're spraying ordnance around and what goes up, must come down...hopefully it does not hit anyone who happened to be in the wrong place at the wrong time. Furthermore, a certain small but non-zero percentage of the shells fired by CIWS fail to self-destruct. Which means kids playing in the park after a successful interception may pick up a live CIWS shell..yikes. Fired over the ocean that is less of a problem, unless in a busy shipping waterway (another can of worms).

Also, with an effective range of a few km, let's say we want to defend a large city, it is going to take a lot of batteries doing nothing most of the time until that one time you must use it, and then Murphy's Law says some guy will probably have forgotten to turn on the radar then.

Maybe it would help if you told us a specific weapon and attack scenario you are interested in, because this is all very vague and seems to be a moving target.

For example, the only hypersonic missile technology I know of that attacks cities is an ICBM. It's a very different scenario from, for example, an ASM attacking an aircraft carrier.

Weapons technologies have evolved to be highly specific.

neanderthalphysics said:

achieve a course change in a missile - by aerodynamic surfaces or thrust vectoring

Well think about it. When you design a missle for hypersonic flight, the larger the control surfaces the higher the drag (and the lower the speed). Hypersonic missles would typically have very small/sleek control fins at the rear...

Vanadium 50 said:

If a body is moving twice as fast, it takes twice the impulse to change the direction a given amount.

Plus what V50 said ^^^^^^

russ_watters said:

, because this is all very vague and seems to be a moving target.

I saw what you did there.

The classic countermeasure for any weapon (hypersonic or not) is to take it out or to suppress activation before it has a chance to fire. Go on the offensive.

https://www.rand.org/content/dam/rand/pubs/monograph_reports/MR1408/MR1408.ch3.pdf
COALITION SCUD-HUNTING IN IRAQ, 1991

boneh3ad said:

You've touched on some very real physics challenges in countering hypersonic weapons. But I'll note that anyone with actual knowledge of real efforts to overcome these issues is highly unlikely to be allowed to talk about it in a setting like this.

Thanks for this reminder.

Trans- and Hypersonic vehicles are hardly new. The terms apply within fluids; the Earth's atmosphere in this case. Interception implies detection and ranging; a curious term that assumes information about the vehicle's position, motions and course. Information 'travels' at, and is limited by, some fraction of the speed of light.

While vehicle velocity remains interesting, even sensational; speed and direction are not primary limiting factors in target acquisition, identification and tracking.

berkeman said:

Well think about it. When you design a missle for hypersonic flight, the larger the control surfaces the higher the drag (and the lower the speed). Hypersonic missles would typically have very small/sleek control fins at the rear...

Precisely because you do not need much deflection or surface area to generate large moments at those speeds.

russ_watters said:

Maybe it would help if you told us a specific weapon and attack scenario you are interested in, because this is all very vague and seems to be a moving target.

For example, the only hypersonic missile technology I know of that attacks cities is an ICBM. It's a very different scenario from, for example, an ASM attacking an aircraft carrier.

Weapons technologies have evolved to be highly specific.

Ballistic re-entry vehicles are already starting to incorporate terminal maneuvering features, such as the SS-27 missile. Previously their terminal trajectories were fairly predictable and yet they still posed difficult targets due to their speed.

It's an open/general discussion, so feel free to cite examples and targets as you see fit. The CIWS solution was raised, and what I'm saying is that it has its problems.

nsaspook said:

The classic countermeasure for any weapon (hypersonic or not) is to take it out or to suppress activation before it has a chance to fire. Go on the offensive.

https://www.rand.org/content/dam/rand/pubs/monograph_reports/MR1408/MR1408.ch3.pdf
COALITION SCUD-HUNTING IN IRAQ, 1991

I like that philosophy, but in the case of fast moving weapons I am not sure it is applicable.

Obviously the greatest strength of hypersonic (let's even include supersonic for completeness) missiles is their speed. Therefore role playing as the enemy, if you're going to use them, you will use them in a circumstance that maximizes their surprise and minimizes your opponent's ability to respond to them.

There's no need to start with hypothetical hypersonic weapons. It is a better question to ask how the SR-71 escaped more than 1300 interception attempts, including missiles. (I'm not certain if that 1300 number is factual or a rumor. But some number whose actual value is probably classified.)

neanderthalphysics said:

I like that philosophy, but in the case of fast moving weapons I am not sure it is applicable.

Obviously the greatest strength of hypersonic (let's even include supersonic for completeness) missiles is their speed. Therefore role playing as the enemy, if you're going to use them, you will use them in a circumstance that maximizes their surprise and minimizes your opponent's ability to respond to them.

Going on the offensive is always applicable. Weapons are the tip of the spear, there is a lot of infrastructure to support any weapons operation even if you can't directly target the weapon. You kill the builders of the weapon, kill the operators, then bomb the logistics, crater the roads, etc.. This all has an effect on the amount of defensive countermeasures needed at the targeted end. Thinking one directional, in a defensive position, is how you lose in a fight to the death.

Even ballistic missiles are hard to defend against and they are very predictable. Any maneuvering at hypersonic speeds would go a long way, both in g's and in the difficulty of intercepting. I think that a directed-energy system of some sort is the only feasible way.
That being said, there is still the possibility of "mutually assured destruction" to consider.

neanderthalphysics said:

Ballistic re-entry vehicles are already starting to incorporate terminal maneuvering features, such as the SS-27 missile. Previously their terminal trajectories were fairly predictable and yet they still posed difficult targets due to their speed.

It's an open/general discussion, so feel free to cite examples and targets as you see fit. The CIWS solution was raised, and what I'm saying is that it has its problems.

This approach is problematic because it's your thread and premise. It looks to me like the consensus so far is that the premise is flawed; the problem you are seeking to address may not even exist. So what you are doing is inviting us to present scenarios that illustrate your premise, when we don't necessarily think there are. And then when we present scenarios where the existing technology works fine (like CIWS), you change the scenario to one where it doesn't work and was never claimed to. That's unfair.

I think it would be worth considering that the problem you think exists might not. And that you should probably put some thought into identifying such a scenario, then re-examine your understanding if you can't. Otherwise I don't think this will be productive; a wild goose chase to solve a problem that hasn't even been defined and may not exist.

Vanadium 50 said:

I very much doubt this. If a body is moving twice as fast, it takes twice the impulse to change the direction a given amount.

That's true, and its even worse than that for the missile; since it is covering twice the distance in the same time as its target, it may also have to turn twice as fast.

russ_watters said:

This approach is problematic because it's your thread and premise. It looks to me like the consensus so far is that the premise is flawed; the problem you are seeking to address may not even exist. So what you are doing is inviting us to present scenarios that illustrate your premise, when we don't necessarily think there are. And then when we present scenarios where the existing technology works fine (like CIWS), you change the scenario to one where it doesn't work and was never claimed to. That's unfair.

I think it would be worth considering that the problem you think exists might not. And that you should probably put some thought into identifying such a scenario, then re-examine your understanding if you can't. Otherwise I don't think this will be productive; a wild goose chase to solve a problem that hasn't even been defined and may not exist.

There are already hypersonic missiles fielded.

https://www.defenceiq.com/defence-t...issiles-what-are-they-and-can-they-be-stopped

neanderthalphysics said:

There are already hypersonic missiles fielded.

https://www.defenceiq.com/defence-t...issiles-what-are-they-and-can-they-be-stopped

IMO the biggest hazard with hyper-sonic weapons is the hazard for taxpayers.

russ_watters said:

I think it would be worth considering that the problem you think exists might not. And that you should probably put some thought into identifying such a scenario, then re-examine your understanding if you can't. Otherwise I don't think this will be productive; a wild goose chase to solve a problem that hasn't even been defined and may not exist.

nsaspook said:

IMO the biggest hazard with hyper-sonic weapons is the hazard for taxpayers.

Absolutely. OOOOhhhh look out their weapons are hypersonic. Hell a V-2 missile was hypersonic. Nothing new here.. nothing to see...move along folks.

russ_watters said:

This approach is problematic because it's your thread and premise. It looks to me like the consensus so far is that the premise is flawed; the problem you are seeking to address may not even exist. So what you are doing is inviting us to present scenarios that illustrate your premise, when we don't necessarily think there are. And then when we present scenarios where the existing technology works fine (like CIWS), you change the scenario to one where it doesn't work and was never claimed to. That's unfair.

I think it would be worth considering that the problem you think exists might not. And that you should probably put some thought into identifying such a scenario, then re-examine your understanding if you can't. Otherwise I don't think this will be productive; a wild goose chase to solve a problem that hasn't even been defined and may not exist.

The problem exists. It's kind of silly pretending it doesn't. If you want a hypothetical weapon, maybe the Chinese DF-17. Or the Russian Tsirkon. Or myriad others in development. The precise system hardly matters for this discussion because, at the moment, no one can effectively defend against any of them.

Also, citing examples about F-5s evading SAMs over Vietnam is hardly relevant. It was 50+ years ago and missiles have advances substantially since then.

Right now all US missile defenses publicly released are designed for either the terminal phase of a fast but non-manuevering weapon or the midcourse phase when it's still pretty vulnerable in space. All of our tracking systems are designed for that, too. A weapon that flies under our midcourse defenses and can maneuver in the terminal phase is currently undefendable and we are effectively relying on deterrence.

See: https://fas.org/sgp/crs/weapons/R45811.pdf

boneh3ad said:

The problem exists. It's kind of silly pretending it doesn't. If you want a hypothetical weapon, maybe the Chinese DF-17. Or the Russian Tsirkon. Or myriad others in development.
[emphasis added]

Does it exist or is it hypothetical? Whatever; To have a productive discussion about this, we need a specific weapon/capability and a target to evaluate the scenario for how to defend against it. Rather than just guessing. This isn't my thread; I would rather not do the guessing, I'd rather the OP provide the topic/scenario to discuss.

But I'll bite; the Tsirkon is an anti-ship missile. So you tell me; could CIWS shoot it down? Is the OP's question of chasing it relevant/useful? The difficulty in out-maneuvering a defense system is that ultimately the missile has to fly towards its target. But if you know of a problem, let us know and we can discuss it.

Also, citing examples about F-5s evading SAMs over Vietnam is hardly relevant. It was 50+ years ago and missiles have advances substantially since then.

Fortunately or unfortunately we haven't had a lot of examples of significant air combat since then. Maybe the first Gulf War -- a lot of SAMs were fired then too, and they were mostly Vietnam war era. But I don't think that's the scenario the OP was after anyway. Also; I'm not sure what the cutoff is, but we're still deploying 40+ year old weapons systems. Surprisingly little has changed, probably because the physics hasn't changed. But again, whatever; this isn't my thread, so don't blame me for a poor guess when I shouldn't have to be guessing in the first place.

russ_watters said:

But again, whatever; this isn't my thread, so don't blame me for a poor guess when I shouldn't have to be guessing in the first place.

Chill, there is no specific correct answer because I am indeed asking generally and because I don't know the answers either. All guesses are welcomed, Vanadium proposed CIWS and I'm telling you some of the disadvantages. This thread is intended to brainstorm at a physics-level and not go into any details like specific scenarios.

In fact I think if we start focusing on specific examples it would derail the point of brainstorming.

neanderthalphysics said:

Chill

You might lose the 'tude, dude. Or is it "d00d"? I can't remember.

What you see as "brainstorming" we see as "figuring out what the hell you are talking about." It's also not clear that whatever it is you have in mind actually exists. But let's look at the history.

Message #1 was about hypersonic (using a slower than typical definition).
Objections were raised.
In message #4 you say "no, no, these aren't just hypersonic, they are hyper-agile."
More objections were raised, and a naval counter-example was provided.
In message #10, you say "no, no, I'm talking about cities"

This quickly becomes a very dull game for everybody but you. Don't be surprised if people quickly tire of playing. If you don't want that, you should respond to requests to be clearer about what you have in mind.

By the time a hypersonics middle got in range of the CIWS it would have probably less than a second before impact. Any damage done would maybe knock out guidance or control but kinetic energy alone from the ensuing impact would still cause substantial damage. You'd have to spray and hope you damaged it enough to cause an outright miss.

Also, for what it's worth, nothing about what @neanderthalphysics has said screams to me that he or she is still "figuring out what the hell [they] are talking about." It's a valid line of discussion and it's one that does not have a defined answer at this time.

What's the target profile of a hypersonic weapon? It's high-value, very well defended target like an nuclear aircraft carrier far at sea surrounded by multi-layered defenses so weapons like an advanced CIWS with nearly free fire capability on any tracked target are possible without worrying about duds and Collateral damage. It's basically a dooms-day first-strike weapon (even conventionally armed hypersonic weapons would still be seen as a strategic if they could sink carriers) because if we can track where the weapon came from you can bet your last dollar something heavy will be headed in that direction if 5000+ people were dead from a destroyed ship.

The actual usage of a hypersonic weapons on high-value targets is IMO suicidal.

Some thoughts on CIWS, because it doesn't work the way people seem to think it does. Most of my experience is with the Phalanx.

It has a range of 6000 yards. It does not decide there is a target, carefully aim, and fire a single bullet at it, like a sniper. Ever try and hit a stationary target with a rifle at even 1000 yards? I can tell you, it's real damn hard. Now imagine something six times farther out, moving, and from a platform that is not only moving, but also pitching.

No, the way the Phalanx works is it sprays as much lead as it can in the general direction of the target. Most of the time, the lead density isn't high enough to make a hit on the target until it is substantially closer. Like maybe 1000 yards. Sometimes less. Indeed, it normally does not fire at its maximum range, preferring that the target get closer. It takes luck to take out the target at 4000 yards, but not as much as at 6000 yards.

Once the Phalanx starts firing, missile speed is of no advantage. Think of it as walking through a (land) minefield. If you ran instead, the risk is exactly the same. ("But...I'm only spending half as much time in it!")

Targets are usually tracked for many tens of seconds before the Phalanx fires. It is true that a faster missile reduces this time. However, there are other ways to reduce this - fly low and slow and stay out of the target's radar horizon for as long as you can, and stay close to the surface clutter. If you do it with speed, you build in a disadvantage: just as the target has less time to respond to the missile, the missile has less time to respond to the target: it was fired where its operators thought the target would be by the time the missile got there. It might be there. It might be somewhere else.

Flak as a countermeasure as been around since the beginning of aviation.


Modern Flak example:

nsaspook said:

What's the target profile of a hypersonic weapon? It's high-value, very well defended target like an nuclear aircraft carrier far at sea surrounded by multi-layered defenses so weapons like an advanced CIWS with nearly free fire capability on any tracked target are possible without worrying about duds and Collateral damage. It's basically a dooms-day first-strike weapon (even conventionally armed hypersonic weapons would still be seen as a strategic if they could sink carriers) because if we can track where the weapon came from you can bet your last dollar something heavy will be headed in that direction if 5000+ people were dead from a destroyed ship.

The actual usage of a hypersonic weapons on high-value targets is IMO suicidal.

This is all conjecture, of course, and defends on the nature of the weapon. The US Department of Defense, for example, has expressed a desire for tactical type hypersonics weapons (as opposed to strategic) and in numbers where they aren't super special to actually use. The idea would be to be able to hit SAM sites prior to a larger scale air assault or heavily defended targets like mobile ballistic missile launchers before they can launch.

These are not necessarily doomsday first strike weapons (at least as the US envisions them). They're more like Tomahawk missiles, only considerably faster. Of course there will be strategic systems as well, but not exclusively.

To address the OP's original question a bit more, have a look at the field of aero-optics. It has to do with the optical path distortion (OPD) created by aerodynamic flow features (e.g., shocks and expansion fans, turbulent boundary layers and wakes, wakes and shear layers, separation bubbles). At high speed these all involve density fluctuations and sometimes chemistry that will set up gradients in the index of refraction. This obviously has important implications on the ability to hit something with directed energy, but also the ability to see out from or communicate with said vehicle.

Most work in this field is in the transonic regime intended to characterize OPD around, for example, radomes. In hypersonics flows it's all relatively new and/or hidden behind a black curtain.