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Breaking the Kill Chain |
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Air Power
Australia - Australia's Independent Defence Think Tank
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Air Power Australia NOTAM 27th January, 2009 |
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Su-35
demonstrator #709 displays a mix of R-27 Alamo and R-77 Adder BVR
missiles (KnAAPO).
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Air
combat relies almost completely on the
effectiveness of missiles. Yet for
a missile to down an aircraft there must be an unbroken ‘kill-chain’ of
events
terminating in the explosion of a warhead in close proximity to a vital
part of
the target aircraft. Some
people believe that missiles have near perfect
chance of killing a target. While
modern missiles are technological marvels of modern warfare, they have
faults
and weaknesses, not the least being critical phases of the kill-chain. The
mathematics is quite simple. Sort the
kill-chain into a sequence of
events, starting with the missile on its launch rail and ending with
its
warhead exploding. Assign a ‘Likelihood
of failure’ at each step. Then
take the previous link in the kill-chain’s Hit Probability, subtract
the
Likelihood of Failure from one, and multiply. This
analysis is perhaps best illustrated by the
potentially lethal game of ‘Russian Roulette’ where one round is loaded
into a
six-shot revolver, the cylinder is spun to stop at a random chamber,
the muzzle
is placed against the forehead and the trigger pulled.
The following is the player’s chance of
survival after a series of plays:
What
is may seem to be intuitively obvious to some –
a player will be certain to die after 6 turns of Russian Roulette - is
actually
untrue. Even after twelve plays
where each chamber has a chance of being selected twice, and taking
into
account a 5% unreliability of the weapon, the player still has a 12%
chance of
surviving. Developmental
AIM-120A round destroys a QF-102 drone (U.S. Air Force photo)
Air
Combat Kill Chains
Modern
air combat is a high-tech, high-competency,
deadly business. Each side tries
to maximise the performance, reliability and survivability of each step
in its
kill-chain, while maximising their own ability to disrupt one or more
steps in
the enemy’s kill-chain. These
actions take place simultaneously, at high speed and at times under
high
stress, so it is often a case of ‘the survival of the fastest and the
fittest’ Breaking
a Beyond-Visual-Range Kill Chain
The
following describes a typical kill-chain, and
how an enemy might seek to disrupt it. After
reading the steps in the chain, assign
representative values to
the Kill-Chain Analyst model at the end of the NOTAM to make an overall
assessment of the reliability of a BVR missile. Active
Missile Confirmed on Launch Rail. The pre-flight check shows an active
missile on the launch rail. Or is
it? Has an inert round been loaded
by mistake, or has the round sabotaged on the way to the flight-line? Search and Track Radar Jammed. Electronic Counter Measures (ECM) are
designed to prevent the enemy’s radar finding, ‘locking’ and tracking
an
aircraft. Modern air-intercept
radars are ‘jam resistant’ but not ‘jam-proof’. Launch
or Missile Failure. Missiles are often carried for several sorties
before
being fired or
returned to a maintenance depot for test and refurbishment. Air combat places a high stress on
missiles, especially in harsh climates. As
an example, in Vietnam the Pk (kill
probability) of the
AIM-7E was less than 10%, with low reliability being one of the largest
sources
of poor performance. Guidance
Uplink Jammed. Jamming the missile guidance uplink is not
considered very
effective, as
such links are directional and the missile antenna is usually pointed
away from
the target. In future warfare
where aircraft are spread out and Network Enhancements are in place, it
may be
possible to a ‘buddy’ looking across a launch to disrupt the missile
guidance
by jamming it with AESA radar or a high-power microwave device. Seeker
Head Jammed or Diverted. This
way of disrupting a kill-chain has a higher chance of success, as the
missile’s
radar small radar seeker requires high sensitivity to produce
acceptable
autonomous operational ranges. Digital
Radio Frequency Memory jammers record and replay
the missiles
emission – but in a way designed to deceive the missile into computing
a
false location of its target. Flankers
often carry the KNIRTI L005-S Sorbtsya wingtip jammer
pods. In more advanced jammers,
this configuration is capable of generating ‘cross-eye’ jamming which
introduces an angular error into the missile seeker. Chaff or
Decoys Seduce Seeker. Generally, chaff is considered ineffective
against modern
missiles, is
the internal signal Doppler processing discriminates chaff returns once
they
stop moving. What if the chaff
moves at about the same rate as the aircraft? Forward
firing, slow burn rockets or perhaps a modified
round fired from the targets gun (e.g. the GSH-310 30 mm,) could draw a
missile
away. Seeker
Chooses Towed Decoy. Towed
decoys work. If they did not, why
fit them to vulnerable aircraft like the F/A-18E/F Super Hornet? Flankers may use a KEDR towed
decoy. Used in conjunction with a
Missile Approach Warning System (MAWS) the pilot can present the towed
decoys
to the missile before it reaches the aircraft – e.g. about 140 degrees
off the nose. With DRFM replays of
the missile seeker head emitted pulses, decoys can be very effective at
making
the missile track away from the aircraft, disrupting the kill-chain. Aircraft
Out-Manoeuvres Missile. Why
fit a MAWS to a fighter aircraft? Is it to
give the pilot a chance to mutter a quick prayer
or curse
before dying, or to provide a chance to ‘duck’ the incoming missile? The physics are that G-Forces in a ‘tracking’
turn of a given radius are a square of the speed. A
typical engagement has the fighter doing Mach 0.9 and the
Missile is arriving at Mach 3.6 - four times as fast as the fighter. If the fighter can generate a 5 G turn,
the missile must track at 16 times the G to follow the aircraft, an 80
G
turn. BVR missiles generally max-out
at about 40G, so depending on the aspect, cannot track, so fly past the
aircraft and miss. Fuse or
Warhead Failure. Even at
the end of a long kill-chain, the warhead must fuze
and explode close enough its target to kill or inflict serious damage. Here is another opportunity for failure
or hostile jamming. Su-35 demonstrator displaying the R-172/AAM-L, the R-27ET1 Alamo and the R-77 Adder at MAKS 2007 (KnAAPO).
So,
putting all the steps together in the ‘Kill-Chain
Analyst’ model, and providing reasonable estimates for the likelihood
of
disrupting each step in a modern engagement, this is the result – less
than a 20% kill probability, or put another way, four out of five
missiles
fired will miss. Is
this a reasonable result? Analyses
done elsewhere have shown that the history
of the AIM-120 in BVR engagements has been 6 kills from 13 shots, a
kill
probability of 46%. However, the
targets were ‘straight and level,’ un-alerted aircraft, not fitted with
electronic counter measures. One
was a helicopter. So, for
modern warfare when the enemy is network enabled, fully cognisant of
the
tactical situation, and takes every opportunity to break the
kill-chain, a
sub-20% kill probability for BVR missiles is likely to be the new
reality. The latest generation of Western WVR
missiles employ Focal Plane Array seekers with target recognition
capability and high resistance to infrared countermeasures. Depicted
imagery from the seeker of a Raytheon AIM-9X missile, which uses an
Indium Antimonide bandgap detector array. Russian industry is working
on such an FPA seeker, what is unclear is whether it will employ
bandgap detector or superior two colour QWIP technology. When it enters
production it is likely to become a block upgrade and new production
item for BVR missiles such as the R-27ET and R-77T.
Breaking
a Within-Visual-Range Kill Chain
In
recent times, some people have had such
(over)confidence in their BVR weapons, they have not paid much
attention to
within-visual-range contests. The
exception is those unfortunate to be trapped in ‘Low Density / High
Demand’
craft that don’t have the ability to escape from a fighter –
transports,
tankers and airborne early warning aircraft or other Intelligence
Surveillance
Reconnaissance aircraft. Some of
these make a half-hearted attempt at self-defence by fitting flares and
chaff
dispensers, and Directed Infra-Red Counter Measures (DIRCM) systems. As
with the WVR case, read the steps in the chain,
assign representative values to the Kill-Chain Analyst model at the end
of the
NOTAM to make an overall assessment of the reliability of a WVR missile. Active
Missile Confirmed on Launch Rail. As before, is this a real round or a
dud? Launch
or Missile Failure. Failures are possible as with BVR missiles,
but WVR
missiles tend to be
designed for higher G loadings and have fewer parts to fail, so expect
the
launch reliability to be higher. Directional
Infrared Countermeasures Effective. DIRCM is
rarely fitted to fighters, so
if none is present, the effectiveness is set to zero. Seeker
Head Jammed or Diverted. Older
Infra-Red missiles like the early Sidewinders used a simple tracking
device
that could be diverted by a frequency-modulated signal – the head would
slew away and break track. No such
luck with modern, imaging seekers, where internal digital signal
processing
detects and disregards such measures. Flares
or Decoys Seduce Seeker. Generally, simple flares are considered
ineffective
against modern
missiles. What of the future? Moving flares and decoys might have a
chance, except an imaging seeker head will be looking for a large
object, and
will reject point sources. Two colour seekers will look at the
blackbody
characteristics of the infrared targets and since flares are hotter
than
tailpipes, reject them. Seeker
Chooses Towed Decoy. While
there have been plans to include infra-red emitters in a towed decoy,
this play
could be defeated by an imaging seeker. Aircraft
Out-Manoeuvres Missile. ‘Dogfight’
WVR missiles have been designed to fly close, high-G ‘knife fights’. They have turning capabilities of about
80G and have attack profiles that reduce closing speeds making it
possible to
track a high-G target. Generally, it will be rare for a fighter to
‘duck’ an
incoming WVR missile. Fuse or
Warhead Failure. Reliability is still an issue, but the smaller
size of the
WVR missile
also means the warhead is smaller. Large
aircraft like the Flankers have armour-like
structures around the
engines, which are widely spaced, so a hit might damage, but fail to
kill this
type of aircraft.
This
is a result that looks a lot more like the
Manufacturer’s brochure and promises. Apart from the reduction of kill
probability arising from the size of the warhead, the WVR kill-chain
has fewer
links and less areas of vulnerability to attack, so a WVR missile
launched
within its engagement envelope may well kill at this rate. This
result matches the record of AIM-9L firings in
the Falklands conflict where 26 missiles
were fired for 19 kills – a Pk of 73%. Those LD/HD aircraft that fit a DIRCM effective about 50% of the time will still have to endure a kill-probability of about 40% per missile. And if the missiles miss, there are still guns to shred large, slow and soft aluminium structures. Su-30MK launching an R-77 (KnAAPO) The
Bottom Line Most
fighter pilots rightfully fear a merge
followed by a knife fight where WVR missiles are loose.
These missiles may be unable to
discriminate between friend and foe, and like a rabid dog, will attack
the
nearest target they find. ‘Mutually
Assured Destruction’ (MAD) is possible, as the engagement ranges of WVR
missiles are often about the same, so each side might fire a missile
and down
the opposition. An
inconvenient though inevitable and accurate assessment
of this analysis would be that as BVR missiles lose kill probability
because of
disruption of the kill chain, merges and WVR engagements are more
likely, with
higher losses all-round. If
future air combat, those with the most BVR
rounds, the ability to egress a fight before a merge, and flying tough,
multi-engine aircraft that can take a WVR missile hit and still get
home, will
be the winners. |
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Related ReadingF/A-18E/F Super Hornet vs. Sukhoi Flanker Analysis [Click for more ...] Sukhoi Flanker Analysis [Click for more ...] F-22A Raptor Analysis [Click for more ...] Joint Strike Fighter Analysis [Click for more ...] |
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Air
Power Australia Website - http://www.ausairpower.net/ Air Power Australia Research and Analysis - http://www.ausairpower.net/research.html |
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