Minimum target speed for air to air missiles

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garrya

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Unread post14 Jan 2016, 07:56

As i understand AIM-120 , R-77 , Meteor's seeker user doppler processing to distingush target from chaff and ground reflection ,
so what is the minimum target speed that their seeker can detect ?
Can the radar guide air to air missiles hit a stationary (hover ) helicopter or F-35B ?
Can radar guider missiles hit a fast moving truck or a fast moving tank , ship ?
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hornetfinn

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Unread post14 Jan 2016, 10:51

Doppler processing is not the only way missile seekers distinguish the target. All those missiles employ monopulse radars with doppler processing. Monopulse radar can get precise coordinates of target with just one received echo. This way the missile seeker will get the pretty precise information from target, chaff and ground and be able to measure the relative speed of each to distinguish which one is which. This is very reliable and effective way of distinguishing targets from unwanted returns.

A lot depends on how high the target is flying. Any higher altitude target can be pretty easily distinguished from ground returns due to being closer. A very low altitude or ground target which is stationary or moving very slowly would be difficult to distinguish from ground returns. It's possible due to difference in echo strength and echo properties but detection/tracking probability would likely be lower than against relatively fast moving high altitude target. Of course hit probability would be very high if target is detected and tracked. Chaff is a problem mainly due to large number of echoes it generates which can mask the real target.

Helicopters would be relatively easy targets due to their rotor blades turning would create doppler shift in target returns. Material and shape of rotor blades would dictate how well the rotors would be visible to missile seeker. F-35B would likely be much more difficult target depending on aspect angle due to stealth features and having very small and well buried lift fan turning during hover and low speed. Of course getting to shoot F-35B when it's hovering would be very unlikely event.

Radar guided air-to-air missiles can likely hit fast moving ground targets with some success. They are not optimized for it and thus are not likely be used unless in very rare cases. There are cases where for example Sea Sparrow missile has hit a ship (Turkish destroyer in 1992). Of course that's a semi-active radar homing missile but I don't see any reason why active radar homing missiles couldn't hit same targets especially if guided close enough with fighter sensors.
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garrya

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Unread post14 Jan 2016, 12:54

hornetfinn wrote:Doppler processing is not the only way missile seekers distinguish the target. All those missiles employ monopulse radars with doppler processing. Monopulse radar can get precise coordinates of target with just one received echo. This way the missile seeker will get the pretty precise information from target, chaff and ground and be able to measure the relative speed of each to distinguish which one is which. This is very reliable and effective way of distinguishing targets from unwanted returns.

How can monopulse radar get precise coordinates of target with just one received echo ? What the difference with pulse Doppler radar ? Why don't aircraft use monopulse radar if they are very accurate
hornetfinn wrote:Helicopters would be relatively easy targets due to their rotor blades turning would create doppler shift in target returns. Material and shape of rotor blades would dictate how well the rotors would be visible to missile seeker. .

Wouldnt the different of doppler reflection between heli blade confuse the missiles processor ?
Blade that going opposite with missiles direction will has different Doppler return from blades that go in the same direction as missiles
hornetfinn wrote:Radar guided air-to-air missiles can likely hit fast moving ground targets with some success. They are not optimized for it and thus are not likely be used unless in very rare cases. There are cases where for example Sea Sparrow missile has hit a ship (Turkish destroyer in 1992). Of course that's a semi-active radar homing missile but I don't see any reason why active radar homing missiles couldn't hit same targets especially if guided close enough with fighter sensors.

As i understand it SARH missiles will home on anything that have continues wave reflection so as long as the illuminator pointing at something ,SARH missiles can home on in ( similar to SAL )
That is not the case with Active radar guide AIM-120
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hornetfinn

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Unread post14 Jan 2016, 14:22

garrya wrote:
hornetfinn wrote:Doppler processing is not the only way missile seekers distinguish the target. All those missiles employ monopulse radars with doppler processing. Monopulse radar can get precise coordinates of target with just one received echo. This way the missile seeker will get the pretty precise information from target, chaff and ground and be able to measure the relative speed of each to distinguish which one is which. This is very reliable and effective way of distinguishing targets from unwanted returns.

How can monopulse radar get precise coordinates of target with just one received echo ? What the difference with pulse Doppler radar ? Why don't aircraft use monopulse radar if they are very accurate


I'm sure all modern fighter(and other tracking radars) radars use monopulse techniques to improve target tracking resolution. It's a technique that can be used with pulse-doppler radars to improve target angular information (more precise position information). You can read about monopulse technique easily as there are numerous web pages describing it.

garrya wrote:
hornetfinn wrote:Helicopters would be relatively easy targets due to their rotor blades turning would create doppler shift in target returns. Material and shape of rotor blades would dictate how well the rotors would be visible to missile seeker. .

Wouldnt the different of doppler reflection between heli blade confuse the missiles processor ?
Blade that going opposite with missiles direction will has different Doppler return from blades that go in the same direction as missiles


No they would not be confused as there are two separate Doppler effects in action. One is the change in frequency in returned signal depending on targets relative speed to radar. Another is the micro-Doppler effect which changes the radar signal frequency modulation and comes from target parts having their own Doppler effect. Micro-Doppler is the effect which is generated by helicopter blades or by jet engine turbine blades rotating fast enough. Most modern radars can handle both Doppler and micro-Doppler effects coming from target. Range for getting micro-Doppler is generally quite a bit shorter than where target Doppler can be got.

garrya wrote:
hornetfinn wrote:Radar guided air-to-air missiles can likely hit fast moving ground targets with some success. They are not optimized for it and thus are not likely be used unless in very rare cases. There are cases where for example Sea Sparrow missile has hit a ship (Turkish destroyer in 1992). Of course that's a semi-active radar homing missile but I don't see any reason why active radar homing missiles couldn't hit same targets especially if guided close enough with fighter sensors.

As i understand it SARH missiles will home on anything that have continues wave reflection so as long as the illuminator pointing at something ,SARH missiles can home on in ( similar to SAL )
That is not the case with Active radar guide AIM-120

[/quote]

No but the mechanism is pretty similar. Main difference is that the target illumination does not come from separate radar but missile radar does the illumination part also. I don't see any reason why any target can't be illuminated by missile seeker just as much as fighter radar.
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Unread post15 Jan 2016, 01:00

It probably depends on the missile's software. I'm not sure how they determine targets, but I'm guessing they aren't programmed to stop tracking a fighter just because it turns to zero relative velocity (at least not in the absence of chafe).
Though an AA warhead is unlikely to do much to a tank.
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Unread post15 Jan 2016, 07:59

count_to_10 wrote:It probably depends on the missile's software. I'm not sure how they determine targets, but I'm guessing they aren't programmed to stop tracking a fighter just because it turns to zero relative velocity (at least not in the absence of chafe).
Though an AA warhead is unlikely to do much to a tank.


They are definitely not programmed to stop tracking but tracking gets more difficult if target has the same speed as other objects (like ground or chaff) the missile sees. It's however very unlikely scenario against airborne targets as having zero relative velocity would be very special flight condition. Helicopters might be hovering but like I said, their rotor blades still create recognizable Doppler signature which can be pretty easily detected. Aircraft might have that in some maneuvers, but it would last only very short time period and unless perfectly timed, would make the aircraft easy target afterwards due to having no speed and energy. Ground targets can have zero velocity and are more difficult to distinguish from ground. Air to surface missiles usually have some type of imaging radar seekers to do the job.

Using Air-to-air missile against a tank would be some kind of last resort measure in some very special case. It might give a mission kill depending on where the missile hit and at what point it detonates.
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sferrin

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Unread post16 Jan 2016, 05:03

More of an interesting factoid than anything but back in the day, the Nike Hercules was designed to be able to hit targets at 150,000 feet. They demonstrated it by knocking down a balloon at 150,000 feet.
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Unread post17 Jan 2016, 03:17

hornetfinn wrote:
No but the mechanism is pretty similar. Main difference is that the target illumination does not come from separate radar but missile radar does the illumination part also. I don't see any reason why any target can't be illuminated by missile seeker just as much as fighter radar.

IMHO Garry is correct
The processor of SARH missiles doesn't have to figure out whether the reflection come from a fighter or a ship or chaff , that the job of the missiles carrier radar , After launch SARH will always home on CW reflection ( very different from pulse reflection , on ship you can see that the illuminator is not the same as main fire control radar ) regardless whether target is stationary or moving , By contrast ARH seeker have to process it reflection so that it doesn't hit chaff or ground .

most if not all SARH can be used in air to surface mode Ex RIM-7 , ESSM ...etc
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Unread post17 Jan 2016, 03:22

count_to_10 wrote:.
Though an AA warhead is unlikely to do much to a tank.

AIM-120 warhead has more explosive than a 150 mm artillery rounds and according to tanker a direct hit from 150 mm would give crew of any tank a very bad days

hornetfinn wrote:
They are definitely not programmed to stop tracking but tracking gets more difficult if target has the same speed as other objects (like ground or chaff) the missile sees. It's however very unlikely scenario against airborne targets as having zero relative velocity would be very special flight condition. Helicopters might be hovering but like I said, their rotor blades still create recognizable Doppler signature which can be pretty easily detected. Aircraft might have that in some maneuvers, but it would last only very short time period and unless perfectly timed, would make the aircraft easy target afterwards due to having no speed and energy. Ground targets can have zero velocity and are more difficult to distinguish from ground. Air to surface missiles usually have some type of imaging radar seekers to do the job.

Aren't some helicopter have composite rotor blade ? ( RAH-66 )
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sferrin

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Unread post17 Jan 2016, 18:37

eloise wrote:Aren't some helicopter have composite rotor blade ? ( RAH-66 )



Why would that matter? Composites show up on radar just fine.
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Unread post18 Jan 2016, 02:01

eloise wrote:
count_to_10 wrote:.
Though an AA warhead is unlikely to do much to a tank.

AIM-120 warhead has more explosive than a 150 mm artillery rounds and according to tanker a direct hit from 150 mm would give crew of any tank a very bad days.

A HE 150 mm howitzer shell is going to make a whole lot of noise if it gets a direct hit on a tank, but shouldn't do much more than cosmetic damage to the tank itself unless it drops right on the roof where the armor is thin. An AA warhead will be even more inefficient in a direct hit (assuming it has a fail safe to make sure it actually detonates upon pancaking itself on the tank's armor), as it is designed to focus it's energy sideways. There is also the issue of the proximity sensor, which may trigger from the ground before actually getting to the target.
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Unread post18 Jan 2016, 07:17

sferrin wrote:

Why would that matter? Composites show up on radar just fine.

Normally reflectivity of composite is much less than metal , some composite is transparent to radarwave if I remember correctly
Given the fact that RAH-66 was designed as a stealth heli Iam sure designer has thought about it
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Unread post18 Jan 2016, 07:22

count_to_10 wrote:

A HE 150 mm howitzer shell is going to make a whole lot of noise if it gets a direct hit on a tank, but shouldn't do much more than cosmetic damage to the tank itself unless it drops right on the roof where the armor is thin

Not according to this
http://sill-www.army.mil/famag/2002/NOV ... S_8_11.pdf

http://forum.worldoftanks.eu/index.php? ... s/#topmost

count_to_10 wrote: . An AA warhead will be even more inefficient in a direct hit (assuming it has a fail safe to make sure it actually detonates upon pancaking itself on the tank's armor), as it is designed to focus it's energy sideways. There is also the issue of the proximity sensor, which may trigger from the ground before actually getting to the target.

Actually I think the design of AAM may give it an advantage , Because it focus energy on the side , if the missiles hit the turret the energy will focused at driver hatch
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Unread post18 Jan 2016, 10:05

eloise wrote:
hornetfinn wrote:
No but the mechanism is pretty similar. Main difference is that the target illumination does not come from separate radar but missile radar does the illumination part also. I don't see any reason why any target can't be illuminated by missile seeker just as much as fighter radar.

IMHO Garry is correct
The processor of SARH missiles doesn't have to figure out whether the reflection come from a fighter or a ship or chaff , that the job of the missiles carrier radar , After launch SARH will always home on CW reflection ( very different from pulse reflection , on ship you can see that the illuminator is not the same as main fire control radar ) regardless whether target is stationary or moving , By contrast ARH seeker have to process it reflection so that it doesn't hit chaff or ground .

most if not all SARH can be used in air to surface mode Ex RIM-7 , ESSM ...etc


That's somewhat true but all current fighter radars are also pulse-doppler radars and they have to track the target anyway. SARH missiles do not always home on CW reflections as they can also be designed to use pulsed operation. For example AIM-7M (and later), RIM-7M (and later), Skyflash, Standard SM-2, R-27R/ER all use (inverse) monopulse seekers which means they use pulsed signals rather than CW signals. Older SARH missiles did use CW signals with their conical scan seekers and required CW illumination. RIM-7M and SM-2 at least have shown they can hit ground or sea targets at least as well as earlier missiles. Ships use illuminator radars so that main fire control radar is not tied to illuminating targets and main radar is used to search and track other targets. It has nothing to do with CW or pulsed operation.

Both SARH and ARH seekers have to process the radar reflections whether they are CW or pulsed. Both later SARH seekers and current ARH seekers use pulsed operation as it has several advantages (like being better against ECM and clutter). The missile still needs to figure out the reflections coming from chaff, ground and the actual target. The fighter radar (or separate antenna) transmitting either CW or pulsed signals will transmit beam that is couple of kilometers wide 50 km away from radar. This means there will be returns from a lot of sources and the missile seeker will have to do a lot of work to figure out which one is the actual target from all of those returns.
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Unread post18 Jan 2016, 11:35

eloise wrote:
sferrin wrote:

Why would that matter? Composites show up on radar just fine.

Normally reflectivity of composite is much less than metal , some composite is transparent to radarwave if I remember correctly
Given the fact that RAH-66 was designed as a stealth heli Iam sure designer has thought about it


There are basically limitless types of composites as any two or more constituent material put together is a composite by definition. This means there is also limitless ways how they show up on radar. Some absorb radar waves really well and some are the opposite and reflect radar waves even better than pure metal. Composites are used in many LO applications as they can combine many useful features like light weight, strength and radar absorbing features. Many materials with good properties to absorb radar waves are not that great otherwise (for example have poor strength or can not withstand heat) especially for aircraft applications. Using them in composite materials can give both the benefits and avoid drawbacks to large extent. RAH-66 used all composite main rotor and other parts to reduce all kinds of signatures (acoustic, radar and IR) while being strong and durable enough for the task.
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