Which kind of target is harder to intercept?

[Ronny]

To attack a destroyer, especially one with good long range air defense, a common tactics used is sea skimming flight, so that aircraft/missiles can get very close to target before they are detected and give the air defense the shortest alert time as possible. For subsonic cruise missile, it is very straight forward, the lower you fly, the shorter the radar horizon will be, and your speed doesn't change significantly with altitude so missile at lower altitude is better. But for supersonic missiles, there is an issue
For example:
P-700: top speed when launched from high altitude: Mach 2.5, top speed when launched from low altitude Mach 1.6
ASMP-A: top speed when launched from high altitude: Mach 3, top speed when launched from low altitude: Mach 2
ASM-3: top speed when launched from high altitude: Mach 3, top speed when launched from low altitude: ? (probably same as ASMP-A)
Rocks: top speed when launched from high altitude: Mach 5, top speed when launched from low altitude: Mach 3? (since it is roughly the same size as ATACMS)
AARGM-ER top speed when launched from high altitude: Mach 4 top speed when launched from low altitude: Mach 2.5-3?
we can see the trend, supersonic missile aren't as fast when launched from low altitude because the high density will cause great drag especially at supersonic speed. However, on the other hand, launching missile from low altitude shorten the warning time and warning distance significantly.
For example:
For a radar on 25 meters high mast, the radar horizon to a target flying at 50 meters altitude is 49.5 km while the radar horizon to a target flying at 8000 meters is 390 km. The distance is 7.7 times shorter, come with that is much shorter warning time, and the speed of interceptor at low altitude is slower as well
So the question is: which is harder for a ship air defense to intercept?
a) very fast target at high altitude, detected from long range
b) slower target at very low altitude, detected from very short range

 

[GARGEAN]

Little corrections: those speeds are not for launch altitudes but for flight altitude. AShM launched from ship can have lo/lo or hi/lo trajectory, same goes for air launched.

As for question - near Mach 2 flying at low altitude and maneuvering is MUCH harder target than high flying Mach 3.5-4. Problems for defender might start at Mach 5 and higher, cuz not a lot of systems today can work with such fast atmospheric targets.

 

[Ronny]

Little corrections: those speeds are not for launch altitudes but for flight altitude. AShM launched from ship can have lo/lo or hi/lo trajectory, same goes for air launched.

I guess, but isn't missile launched from high altitude have additional potential energy to increase its terminal speed

As for question - near Mach 2 flying at low altitude and maneuvering is MUCH harder target than high flying Mach 3.5-4. Problems for defender might start at Mach 5 and higher, cuz not a lot of systems today can work with such fast atmospheric targets.

So with the exception of Rocks, all others missiles in my list are harder to intercept when launched and fly at low altitude?

 

[GARGEAN]

Little corrections: those speeds are not for launch altitudes but for flight altitude. AShM launched from ship can have lo/lo or hi/lo trajectory, same goes for air launched.

I guess, but isn't missile launched from high altitude have additional potential energy to increase its terminal speed

As for question - near Mach 2 flying at low altitude and maneuvering is MUCH harder target than high flying Mach 3.5-4. Problems for defender might start at Mach 5 and higher, cuz not a lot of systems today can work with such fast atmospheric targets.

So with the exception of Rocks, all others missiles in my list are harder to intercept when launched and fly at low altitude?

1: really applies to AAM which have significant ballistic portion in their flight. AShMs are different in being powered during whole flight. High alt launch increases range, but not speed.
2. Basically yes. But as usual it depends on a lot of factors. Some missiles are more maneuverable in terminal phase of flight. Some have own ECM. Some AA systems start to have problems above Mach 3, not Mach 5 and so on. It's always better to look at specific example rather than generalize.

 

[Scott Kenny]

I ran some numbers for the Klub/Kalibr missiles, with their ~Mach 3 terminal phase. Assuming they're detected 90km out, you get two shots at them with ESSMs with time to see effects, one shot with RAM, and then you're down to the CIWS. IIRC, that was Detect at 90km, first interception with ESSM at ~47km, second ESSM interception that was launched 1sec after first fail at ~25km, RAM interception at ~10km, and CIWS opening up at ~2km.

Low altitude supersonics are the most difficult threat to engage, due to limited time.
Low altitude subsonics are still a threat, particularly since they can be a lot stealthier than supersonics.
High altitude missiles can be a LOT faster, but you have so much more time to engage them that they're a lesser threat than low altitude supersonics.

 

[stealthflanker]

CIWS could be out of options for supersonics as such close in intercept risks the ship or the platform being showered by supersonic debris.

The rule of thumb for the minimum range of target destruction is the mach number of the missile in Km. So say Exocet.. can be safely intercepted in 850-900 meters (mach 0.85-0.9) away from the ship. Faster missile demand longer. The missile with Mach 3 endgame is therefore cannot be safely intercepted by CIWS.

 

[perttime]

CIWS could be out of options for supersonics as such close in intercept risks the ship or the platform being showered by supersonic debris.

The rule of thumb for the minimum range of target destruction is the mach number of the missile in Km. So say Exocet.. can be safely intercepted in 850-900 meters (mach 0.85-0.9) away from the ship. Faster missile demand longer. The missile with Mach 3 endgame is therefore cannot be safely intercepted by CIWS.

Still, supersonic debris is the lesser evil, compared with the detonation?

 

[stealthflanker]

Still, supersonic debris is the lesser evil, compared with the detonation?

The debris may still damage the CIWS, or hitting elsewhere in the ship, potentially causing fire.

You cannot think "Lesser evil" here you need to think a better defense against low altitude high speed target. There should be 0 missiles getting in your CIWS range in the first place. Thus why there are things like RAM or something like 76 mm AHEAD or 57mm . That's your CIWS. As those have longer standoff range.

 

[Arjen]

There should be 0 missiles getting in your CIWS range in the first place.

Unfortunately, in war, the enemy gets a vote too. Would you advocate doing without CIWS entirely? I'm guessing 'no'.

 

[stealthflanker]

Unfortunately, in war, the enemy gets a vote too. Would you advocate doing without CIWS entirely? I'm guessing 'no'.

Am i advocate for no CIWS ? Which if you read my post. it's not. To be clear If you're facing supersonic sea skimmers and have to shoot it with CIWS... you want it to be more long ranged.

 

[Arjen]

supersonic debris is the lesser evil

This ^

 

[stealthflanker]

Until it start penetrating the structures, killing radars or the CIWS itself, causing fires and well if there is another missile coming behind. There would be trouble.

 

[TomS]

This paper comparing the utility of subsonic and supersonic antiship missiles looks relevant. It's possibly a bit colored by the fact that it comes from McDonnell Douglas, who had rather a vested interest in subsonic ASCMs at the time. But the math is still worth reviewing.

Naval Engineers Journal Volume 109 Issue 1 1997 J. F. McEachron - Subsonic and Supersonic Antiship Missiles - An Effectiveness and Utility Comparison | PDF | Surface To Air Missile | Mach Number

Naval Engineers Journal. This edition describes design and measure of effectiveness of subsonic and supersonic anti ship missiles. More or less this describes the US approach toward anti ship missiles .

www.scribd.com

 

[Scott Kenny]

Still, supersonic debris is the lesser evil, compared with the detonation?

Still very likely to be a mission kill as the supersonic fragments damage or outright destroy the radar antennas.

This paper comparing the utility of subsonic and supersonic antiship missiles looks relevant. It's possibly a bit colored by the fact that it comes from McDonnell Douglas, who had rather a vested interest in subsonic ASCMs at the time. But the math is still worth reviewing.

Naval Engineers Journal Volume 109 Issue 1 1997 J. F. McEachron - Subsonic and Supersonic Antiship Missiles - An Effectiveness and Utility Comparison | PDF | Surface To Air Missile | Mach Number

Naval Engineers Journal. This edition describes design and measure of effectiveness of subsonic and supersonic anti ship missiles. More or less this describes the US approach toward anti ship missiles .

www.scribd.com

That paper makes a very good case for the next US antiship missile to be something with a supersonic terminal phase like the Kalibr/Klub. Subsonic for range, supersonic for defense penetration.

 

[Arjen]

Still very likely to be a mission kill as the supersonic fragments damage or outright destroy the radar antennas.

Possibly. But a direct hit will likely inflict more damage. What to choose?

 

[stealthflanker]

Not getting hit. Unless maybe one can be sure that's the very last missile in the salvo.

 

[Arjen]

Not getting hit.

That would be best. Against certain weaponry, with your own options limited, that sometimes involves being somewhere else. The opposition - or indeed your own leadership - might not offer that opportunity, and then you make do with what you have. Or refuse the mission - which in some circumstances is another way to commit suicide.

 

[Josh_TN]

Still very likely to be a mission kill as the supersonic fragments damage or outright destroy the radar antennas.


That paper makes a very good case for the next US antiship missile to be something with a supersonic terminal phase like the Kalibr/Klub. Subsonic for range, supersonic for defense penetration.

For better or worse, the US is wedded to subsonic for the rest of this decade (well, excluding SM-6). The one notable advantage is range* - YJ-18 and Tomahawk are in the same weight class, but the latter has 3x the endurance. It does suffer in the end game, but until that last 25nm/45km they are both subsonic. The subsonics also make for much cheaper/lighter decoys - a MALD-N is basically going to look exactly like a subsonic AShM on radar and have a cost and launch weight an order of magnitude lower than LRASM.

*Although probably the more important factor was that Maritime Strike Tomahawk and LRASM were more or less off the shelf conversions of existing missiles that could be pressed into service much more quickly than a purpose built supersonic AShM.

 

[Scott Kenny]

For better or worse, the US is wedded to subsonic for the rest of this decade (well, excluding SM-6). The one notable advantage is range* - YJ-18 and Tomahawk are in the same weight class, but the latter has 3x the endurance. It does suffer in the end game, but until that last 25nm/45km they are both subsonic. The subsonics also make for much cheaper/lighter decoys - a MALD-N is basically going to look exactly like a subsonic AShM on radar and have a cost and launch weight an order of magnitude lower than LRASM.

Agreed, but I'm going to bet that the next AShM will have a supersonic sprint to target.

 

[TomS]

Agreed, but I'm going to bet that the next AShM will have a supersonic sprint to target.

The next gen AShM is currently planned to be totally hypersonic -- HALO is now OASuW Increment 2, apparently.

 

[Scott Kenny]

The next gen AShM is currently planned to be totally hypersonic -- HALO is now OASuW Increment 2, apparently.

Gonna either be huge or have crap for range, then.

Long range AShMs are best served as subsonic with a sprint mode.

 

[Josh_TN]

Agreed, but I'm going to bet that the next AShM will have a supersonic sprint to target.

The USAF and USN are skipping over supersonic altogether and going hypersonic with HACM and HALO.

 

[Josh_TN]

Gonna either be huge or have crap for range, then.

Long range AShMs are best served as subsonic with a sprint mode.

X-51 was a 4000 lb stack empty with only 270lbs of fuel. The HAWC demonstrators both made Mach 5+ for 300 miles. I suspect HACM will be a 3000lb class store that is hypersonic out to several hundred miles. Notably the initial platform will be the F-15, not a bomber.

HALO is a question mark because it has to be CV compatible, which means among other things that it has a 15’ length limit. It will have to use a very different mechanism as a result. But I suspect it will be quite fast and long ranged as well.

 

[Scott Kenny]

X-51 was a 4000 lb stack empty with only 270lbs of fuel. The HAWC demonstrators both made Mach 5+ for 300 miles. I suspect HACM will be a 3000lb class store that is hypersonic out to several hundred miles. Notably the initial platform will be the F-15, not a bomber.

HALO is a question mark because it has to be CV compatible, which means among other things that it has a 15’ length limit. It will have to use a very different mechanism as a result. But I suspect it will be quite fast and long ranged as well.

Oh, you were talking air launched AShMs.

I was talking surface and sub-launched, where there's both a length and a diameter limit.

 

[Josh_TN]

Oh, you were talking air launched AShMs.

I was talking surface and sub-launched, where there's both a length and a diameter limit.

Ah, ok. Yeah, those will likely remain subsonic for longer. Though the fact that HALO will be 15’ might make it a candidate for a Mk72 booster in a vertical cell. If they use some kind of dual mode ramjet/scramjet like the HiFly project, they might adapt it to surface launch with a range reduction. Depends on what method ends up being adopted; I’ve heard USN is agnostic with regards to propulsion so long as speed and range requirements are met.

There also is Sea Dragon, whatever that is. Most open source guesses assume it is a sub launched SM-6, so presumably relatively short ranged.