"sm3 missile versus sub launched ballistic missile" Topic

if a us cruiser armed with sm3 missiles was in range of a soviet of chinese sub armed with ballistic missiles .and said sub launched those missiles would the sm3 be capable of taking them out in the assent stage

Short answer is "probably", though a number of factors come into play. The boost phase of an ICBM is it's most vulnerable, however given the fact the launch first has to be detected and tracked, then an interceptor (such as the SM-3) launched towards the target. Range from the launch is essential, as the further away the target, and longer it has been in boost phase before reaching midcourse phase, the harder it is to intercept.

So let's say a Russian Delta IV launches an R-29 missile, and an Aegis equipped ship (either a Burke DDG or Bunker Hill CG) happen to be within 200nm from the launch. The Aegis system would quickly pick up the R-29 ascending, and at that point the SM-3 should have a good chance of interception, since the SM-3 is faster than the ICBM in boost phase.

However, since most "enemy" SSBN's (particularly Russian) operate in bastions guarded by surface and air assets, it would be highly unlikely that an Aegis ship would get that close.

It's a small window, since they're both accelerating mostly in the "same" direction, but it should be at least possible.

SM-3 is not really an ascent stage interceptor, though.
-Kle.

However, it would be *possible* for the SM3 to take out the re-entering warheads. After all, one did swat a satellite at what you'd assume was close to the limits of the system.

As Kle said, that's a pretty tight window for launch, probably less than 10 seconds wide just due to the range difference between an SM3 and a SLBM. An ascent-stage interceptor is something best dropping down from low orbit, or needs to be obscenely fast.

No chance of intercepting a warhead on its way to impact!! It would be travelling far too fast and be a very small target (esp if a MIRV)…The best anti missile missile system is the Sea Wolf--And that can only occasionally intercept a 4.5inch shell in flight…A MIRV would be travelling much faster..
Also if we are talking about a large nuclear strike then an EMP detonation in the upper atmosphere would give enough time for warheads to sneak through…

In the launch stage ICBM's may be vulnerable but a ship would have to be very close to the sub to have a chance of interception--The sea is a very very big place and the horizon is only about 20 miles away max so to catch a bird in flight is a million to one shot at the best!!!

The sea is a very very big place and the horizon is only about 20 miles away max so to catch a bird in flight is a million to one shot at the best!!!

So you are saying there's a chance.

Uh, you do know that the Mk4 Reentry Body is roughly 5 feet long and a foot in diameter, right? Not to mention that it's coming down in a radar-reflective plasma that's the size of a pallet and about a mile long?

While moving obscenely fast towards the ground, it's an enormous radar target, and causing an RB to tumble will destroy it due to the huge forces involved in re-entry. It doesn't take much damage to keep an implosion nuke from going off. Even a slight deformation of the frame will prevent the fission reaction from starting. Unfortunately, an object the size of a Mk4 RB is heavy enough to deliver a serious amount of KE to whatever it lands on (~100kt, seriously), so you want that to land on water, not on land or even close to land.

The radar horizon for an Aegis ship is closer to 70 miles, but that's still a little area in a big ocean.

To game it? Roll d1000 to see if your Aegis ship happened to be in an spot to see the launch and do something about it other than phone home. On a roll of 000, you were. Then roll a d% to see if you launched in time, on a roll of 00, you did. Then roll another d%, this one has better chances: 50 or better, you intercepted successfully. Chances are roughly 5 in a million.

Well in WW2 a Tempest did manage to shoot down a V2 and in Korea a Centurion shot down a MiG15 with its main gun!!--However how you would put a million to one shot into a game is difficult..

A Tempest shot down a V2?! I've never heard of that one! Have you got any more details?

No it was one of those things I read somewhere!! Essentially a V2 took off at just the same time the Tempest flew past and he did a snap shot and blew it up!!!

thanks folks
so this new idea of putting sm3 missiles on land would be the same result

Yes--basically nice and pretty fireworks that would in all likelyhood miss completely!!
In the 50's and 60's the Soviets did look seriously into an anti ballistic missile system but by the time they had got anywhere with it the US had introduced MIRV's which rendered it far too difficult to interceptincoming warheads--Even when using H bombs as warheads themselves!!

Lion,
I'm interested in your statement that the radar horizon of an Aegis ship is 70 miles. I assume that we are talking surface to surface radar horizon, compared to the five fourths of the line of sight horizon , or about 24 miles, that is normal given for surface radar.
I know that the Russians, Chinese, Indians and Italians have radars that either operate on troposcopic scatter or on radar ducting to give active and passive OTH capability, and I have incorporated that into my rules. It makes sense considering that Souvremmenys, Nanuchkas as Tarantuls are armewd with missiles that have a range far longer than theie normal radar horizon. It has always struck me as odd for the Americans to be behind in such an important area as OTH surface search radar.Are you saying that Aegis operates in the same way?

Cheers,
Bertie

I couldn't tell you. I wasn't an Aegis tech, and even if I was, that's probably something that I would have 'forgotten' when I left the service. Thing is, most American deployments have an airborne search radar, so who needs ship-borne OTH capabilities. Besides, I've seen pictures of the OTH-B radar rigs, they're not particularly portable.

Distance (in miles) = square root of (1.5*height in feet). At ~10 feet above the surface, you can see something like 6000 yards (3nm) to the water's surface, plus however long the other guy's masthead horizon is. Aircraft carriers end up with about a 18 mile masthead horizon, for example.

So, the true horizon distance for a Tico (using a radar antenna height of 150 feet, which I don't think is correct) is "only" 15 miles, but I can detect the masthead of a ship on the other side of the horizon, so there's ~30 miles between my antennas and your ship, and the bigger the ships the farther those distances are.

SPY-1 radar sets can track high(er) altitude objects at 200 miles or more (remember that ASAT demonstration?), so that backtracks to object heights of about 23,000 feet when they pop into the scanned radar sphere (and give the radar operator a brown-shorts moment). That is still where some orbital rockets are subsonic, so *IF* the SM3 is fast enough, you might be able to catch an ascending SLBM 200 miles away. Obviously, the interception envelope varies with the SLBM's relative trajectory, with shots going over the head of the Aegis ship being intercept-able at a much longer 'range' than a true stern chase.

At this point, I don't know enough details about target and SM3 acceleration to be able to give even a rough guess for the max detect-and-engage range.

Thanks Lion,
I'm no expert either.
The problem is that SPY 1 being so big, it is fitted quite low on the superstructure of Aegis ships, not on the masthead. The ability to fit the Briish Samson system higher than SPY 1 is touted as one of its advantages as this extends horizon range against surface targets and sea skimmers.
On the OTH issue it occurs to me that the Russian and Italian shipborn OTH radars must be permanently atuned to take advantage of the radar ducting conditions that they expect to experience. This, presumably, makes them less efficient in other circumstances.
Equally presumably, and this is just guesswork on my part, one of the advantages of a computer controlled phased array such as SPY 1 is that it could be quickly, (perhaps even automatically,)reconfigured to take advantage of any ducting conditions that occur. So it may not be optimum, but it would be more flexible.
Lots of "presumablies" here but I can't see why this shouldn't be so.
In rules terms I've just decided to treat radar ducting conditions as a variable natural phenomena that you may, or may not, have in a scenario, just like weather conditions for visibility, or bad acoustic conditions for sonar.
Cheers,
Bertie

True, but the superstructure of a Tico is pretty dang tall to make up for the lack of masthead antennas. The Burke's aren't as tall, but again, they're primarily an air-search set, not a surface-search.

Again, when the US deploys with a flying AWACS (with secondary surface-search mode), there's not much reason to have a ship-borne OTH radar.

Also, at least the US Over the Horizon-Backscatter radars have an enormous minimum range in order to get the right bounce angle off the ionosphere, something like 500nm.

lion in the stars
so that backtracks to object heights of about 23,000 feet when they pop into the scanned radar sphere .am i reading this right that from surface to 23000 at range? below that point missile cannot be seen . you probably covered that in square root thingy my maths capability just about cover 1+1=2.was actually thinking about the dead zone as earth surface drops away from radar.the bmw early warning radars in alaska have range 3000 miles .how far up would russian missiles have to ascend to pop on to radar scope

Yup, you're reading that correctly. At 200 miles, even Aegis isn't tracking stuff below 23,000 feet altitude.

DEW radar ranges of 3000 miles, squared, then divided by 1.5, will give you target altitude in feet. 6,000,000 feet altitude… That's 1136 miles up.

That's not counting any atmospheric bounce weirdness like the OTH-B radars use. Those radars use a weird atmospheric effect that makes the upper atmosphere act like a mirror, so they're actually getting a look 'down' at the earth from about half the distance, but you need big antennas (each element is multiple wavelengths, not the usual 1/4 wave antenna) and very high amplification to get a usable signal back out of it.