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BEYOND THE VISUAL RANGE AIR TO AIR MISSILES
PAST, PRESENT AND THE FUTURE
1. INTRODUCTION: A BVR missile is a missile which can be fired at the target which is
outside the visual bubble of the pilot. In case of a BVR, it is the AI radar that acts as the fighter
eyes and enables the pilots to acquire an opposing aircraft. It also feeds the required parameters
to the onboard computer and produces an aiming solution. Pilot can then launch the missile
without having seen the target. But lack of positive identification is a heavy constraint on BVR
options. If one studies the development of BVR, the major factor that stands out as the main
driver of its evolution was the threat analyzed as a single strategic bomber, carrying a nuclear
payload, which could destroy cities or anything else. This threat was more effective than
formations of heavy bombers in the World War II. To understand the phenomenon of their
development we must go back in time and see how it all happened.
THE PAST
2. The first aerial guided missiles were developed in the World War I but only against the
surface and the naval targets. The concept of AAM had hardly dawned at the start of the World
War II, largely because of the extreme difficulty of developing a workable system. The first to be
attempted, which were built in large numbers, and were nearly deployed in service, were the
German HS 298 and X-4. Both had basic shortcomings. After the World War II, the technology
made rapid progress. Atom bombs and other nuclear weapons effectively demonstrated to the
world, the superiority of science and technology over the human efforts in the realm of armed
conflict. It was during that time the bold concept of the BVR developed. It was reasoned that
since the aircraft were flying too fast for the pilot to use his guns, a missile that can catch a fast
flying aircraft, without the launch aircraft coming very close to the target, needs to be developed.
Unfortunately, bold as the concept was, the ground situation was substantially different. The
BVR engagements in the various conflicts after the World War II were few and also they were
not accurately documented and analyzed. The performance of the BVR missiles in different
conflicts is reviewed in the subsequent paragraphs.
3. In the Vietnam War, the aircraft and missiles used were designed in 1950's. Two main
missiles used were AIM-9 sidewinders for close combat and AIM-7 Sparrow III’s for the BVR
engagements. US Navy preferred AIM-9 over AIM-7, because the delicate mechanism of AIM-7
came in for heavy punishment during carrier landings and caused a lot of malfunctions. During
the conflict the USAF brought down 137 Mig-17's, Mig-19's and Mig-21's. 88 out of these were
accounted for by the aircraft missiles.
(a) AIM-9 - 34 - 24.8%
(b) AIM-4D – 04 - 02.9%
(c) AIM-7 - 50 - 36.4%
(d) GUNS - 42 - 30.6%
(e) UNACCOUNTED – 7 - 05.1%
4. As a major weapon system of 60's and 70's the F-4 Phantom's total kills in all wars have
been reasonably well documented. The main weapons of F-4 were AIM-7 and AIM-9. Guns
being the complimentary armament. The breakdown of 227 kills achieved by the F-4 are:
(a) AIM-9 - 96 - 42.19%
(b) AIM-4 - 04 - 01.75%
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(c) AIM-7 - 64 - 28.13%
(d) GUNS - 22 - 09.89%
(e) UNACCOUNTED – 41 - 18.02%
5. If we compare the data given in the two tables we come to the following conclusions:
(a) USAF kills with close combat weapons in Vietnam - 58.3%.
(b) USAF kills by the BVR AIM-7 - 36.4%.
(c) Total kills by F-4 using close combat weapons - 53.83%.
(d) Total kills by F-4 using AIM-7D, E, E-2 - 28.13%.
6. The result of both the studies seems to point towards a similar conclusion about kill rates
of different weapons. Though the AIM-7E was rarely used in the manner it was designed to.
Decisions about the targets, weapons and tactics were made far away in Washington. Men in the
field had no say whatsoever. All the targets had to be visually identified before launching. Hence
there were very few BVR engagements. Most of the Sparrows were launched at the manoeuvring
targets at the commencement or at the end of a visual engagement. This may lead to an erroneous
conclusion that kill rate by the BVR would have gone up markedly had the missiles been used in
its designed role. There was no choice but to visually identify the targets due to the lack of
adequate IFF technology.
7. During the Arab-Israeli conflict about 2/3 of the IAF kills of 335 Arab aircraft were
attributed to guns. The remaining 113 kills were claimed by AIM-9 or by Shafrir CCMs. In the
BEKKA valley operations most of 84 kills were achieved by use of AIM-9L or Shafrirs. Thus the
role of the BVR in these conflicts was almost negligible.
THE PRESENT
8. Most of the Air Forces now have acquired BVR missiles. A typical BVR missile is the
SUPER 530D which is available with the Indian Air Force. The salient features of this missile,
which can be launched by the MIRAGE 2000 are given in subsequent paragraphs.
9. Description: The Matra Super 530D is a semi active BVR air to air missile with a very
good snap up and snap down capability. The missile is equipped with a semi active
electromagnetic unit utilising Doppler processing. This missile can be carried on the Mirage
2000 and coupled with the RDM radar forms a formidable weapon system.
10. Construction: This missile is of conventional cruciform shape and can be broken down
into five main sub assemblies.
(a) Seeker: It is of semi active electro-magnetic type working on the Doppler
principle. The seeker receives and processes signals transmitted by the illuminator and
reflected by the target. It operates on the X band and is integrated with the RDM radar.
The local oscillator can be tuned to three different frequencies which can be selected
only on the ground hence we have three different types of homing heads available with
different frequency bands to allow for changes in frequency (ECCM). There is a rear
reception antenna which enables the seeker to receive directly the signal from the
illuminator during the missile free flight. The antenna axis has a max deflection of 100'
cone and once the seeker is locked on, seeker antenna axis is slewed to the direction of
the target.
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(b) Proximity and Impact Fuse: Proximity fuse is of an active electromagnetic type
and is energised 1.45 seconds after the missile is launched. The detection range of the
proximity fuse is 34 Mt. It has two sets of beams whose radiation pattern is fairly conical
and centred on the missile centreline with a 60' apex angle. The processing of the signal
is so done that this fuse does not operate on ground clutter for height less than 60m.
Impact fuse is for instantaneous explosion controlled by the impact detonation assembly.
(c) Warhead: It is a 30 Kg fragmentation charge containing 10 Kg of explosive. The
numbers of fragment per square metre are 3400 and it has a max lethal zone of 10 Mt at
low levels and 15Mt at high levels. The explosive is 88% Hexogen and 12% Polybutane.
(d) Booster Engine: The total impulse is 19800 DaN. It has two phases of
combustion, initial acceleration on the boost phase which lasts for 2 seconds and cruise
phase that lasts for 8.5 seconds with a total burn out time of 11 seconds. It gives a
velocity gain of 4.5M which makes it the fastest air to air missile.
(e) Guidance: To carry out proportional navigation, the missile has a steering
computer which receives data from the seeker, accelerometer, rate gyros and control
position sensors. It also calculates the warhead firing delay as a function of closing speed.
The missile is highly manoeuvrable under all roll presentation angles and high AOA and
can manoeuvre upto 30 `g'.
11. Operation: The S 530-D missile requires to be harmonised before launch in direction,
frequency and closing speed in order to identify the target. This takes place in three steps.
(a) Harmonisation in direction: It consists of aligning the axis of the gyroscope and
of the seeker antenna on the axis of the radar antenna. The seeker antenna is always
aligned to the target tracked by the radar even when the missile mode is not selected.
(b) Harmonisation in frequency: It is carried out in two steps.
(i) When the S 530D missile mode is selected the missile tunes the local
oscillator frequency to the illuminator frequency.
(ii) As soon as the radar is in tracking mode, the local oscillator is set in
frequency from a microwave sample taken from the illuminator source and
transmitted via a special link.
(c) Harmonisation in closing speed: This is carried out by setting the tracking gate to
the seeker frequency matching with the Doppler frequency corresponding to the target
closing speed computed by the radar tracking mode.
12. Once the harmonisation is completed the seeker can detect and lock on to the designated
target. Effective lock will trigger an audio warning tone indicating to the pilot that the missile
has locked on. 2.8 seconds after the missile is launched the warhead gets armed. During its flight
the target should be illuminated at all times. The explosion thereafter is controlled by either the
impact fuse or the proximity fuse.
13. Performance: The performance characteristics are:
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(a) Min launch range - Tail on - 700Mt. Head on- 2.2 to 20km.
(b) Min target altitude - 250'.
(c) Max firing range - Tail on - 5km. Head on- 25km.
(d) Max launch altitude - 50,000'.
(e) Max launch speed - 700kts.
(f) Min launch speed - 250kts.
(g) Boresight angle at launch - + 45'.
(h) Manoeuvring target `g' - 6-8 `g'.
(j) Max missile `g' - 30 `g'.
(k) Max flight altitude of missile - 24km.
(l) Self destruction time - 45 seconds.
(m) Snap up/ snap down - 30,000'.
14. Guidance Characteristics:
(a) Bore sight - + 45'.
(b) Seeker tracking speed - 10'/sec.
(c) Miss distance 20,000' - 10 Mt. 60,000'- 15 Mt.
(d) Lock on range homing head - 34 km.
(e) SSKP - 85%
15. ECCM: The missile has certain counter measures for ECM.
(a) The homing head can be selected to three different frequencies.
(b) The homing head works on the principle of Doppler shift in the frequency
transmitted by the aircraft radar. Homing head with the help of a very narrow band filters
receives only the Doppler shift frequency. Hence it is very difficult for the jammer to
produce the same `Doppler shift frequency'.
(c) The missile has a home on jammer facility so the jammer cannot be on
continuously.
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(d) Passive jamming chaff is disregarded as there is no lock on if closure speed is <
+ 50 m/s.
(e) Ground clutter is totally eliminated as the Doppler frequency from the ground is
different from that of the moving target.
(f) Signal / Noise ratio is very high thereby increasing the sensitivity of the homing
head.
16. Limitations:
(a) Min target height is 250'.
(b) Min fighter altitude is 600'.
(c) Battery heating takes 3' 45" which increases the scramble time.
(d) Autonomous multiple launch not possible.
(e) Look down in clutter has search limitations.
(f) Tracking warning is always given to the target.
(g) Loss of missile in case of radar break lock.
THE PRESENT DRAWBACKS AND LIMITATIONS
17. Need to illuminate continuously: Current generation of BVRs are generally of the semi-
active class. This in itself is a major drawback as the mother aircraft has to continuously
illuminate the target aircraft till the missile impact. During this period the mother aircraft is
totally blind to any other aircraft. The continuous illumination required also limits the launch
aircraft's manoeuvre during the engagement and keeping track of the tactical situation becomes
difficult. In other words there is no launch and leave capability. This drawback can be overcome
by using radars which have Track While Scan facility in the true sense or by providing active
homing capability to the missile.
18. F-POLE: F-Pole is the closest a fighter comes to the target at the time of the impact. This
range has a major tactical significance in front quarter attacks. The launch aircraft, which has to
perforce continue illuminating the target, ends up at a close distance, wherein he is entering the
visual bubble of the target aircraft just before missile impact. This gives the target aircraft an
opportunity to launch its own missile which may be an all aspect missile. So even though the
target aircraft gets shot up, the launch aircraft may also get shot. Such a ratio of 1:1 is not
acceptable in any conflict hence the use of BVR missile is restricted.
19. IFF: One of the biggest drawbacks of utilising the BVR missile is that of IFF. As
engagements are beyond the visual range, some method of identifying the target aircraft as an
enemy aircraft must exist. During the Vietnam conflict, USAF and US Navy F-4's had to resort to
visual identification of the target aircraft before firing. This was because of lack of a IFF system.
Hence Sparrow missiles were never utilised for the role they were designed for. IFF continues to
be a grey area in today's environment. Identification is necessary and is a critical issue if the
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BVR missiles are not to be as lethal to one's own side, as to the enemy. The west is relying on
advancement in technology, careful mission planning, use of C3I assets such as AWACS & AEW
aircraft, real time electronic surveillance and JTIDS (Joint Tactical Information Distribution
System) to provide an answer to the IFF problem. In addition, methods such as high speed radar
signal processing to analyse characteristic signatures, are being used by the USAF. Northrop has
developed a device called TISEO (Target identification Stabilised Electro Optical), which
presents a telephoto picture of the target to the weapon system's operator in the F-14. An
improved follow up to this system is the AXX-1 TCS (Television Camera Set) which is used on
the F-14D. The most important change, however, is the adoption of very fast programmable
signal processors in advanced radars such as Hughes APG-70 & APG-71 (F-15C/D and F-14D).
These can analyze radar returns to identify characteristics of individual aircraft types, such as the
beat imparted to the returns by the engine compressor blades.
20. Jamming: Before launching a semi- active BVR missile, the launch aircraft has to carry
out a radar search and then lock on to the target aircraft. By doing this, the launch aircraft gives
away his position the moment he begins to radiate, thereby making him vulnerable to jamming.
Most modern fighters carry self protection jammers which react instantly to lock on indications,
thereby degrading the performance of the aircraft radar, which in turn degrades/prevents the
employment of the semi-active BVR missile.
THE FUTURE
21. Having seen the capabilities of one the best BVR missile available in the market today
and also the drawbacks and weaknesses of the present generation BVR missiles it is quite obvious
that the BVR technology is still in its infancy. The main drawbacks are being an absence of a
foolproof IFF system and the nature of semi-active guidance. With semi-active guidance, the
fighter is forced to hold the target in the radar scan. This has two important effects. Firstly, it
takes the fighter closer the target than the pilot may wish. Secondly, it prevents the crew from
attacking subsequent targets until after the missile impact. What the modern missile
development seeking is, therefore a means of overcoming these drawbacks. The next generation
of Medium Range AA Missile seeks to combine the launch and forget characteristics of Phoenix
with the size and weight of S530D, while at the same time improving the BVR capability. The
Hughes AIM 120 AMRAAM, now under going development for the USAF, is the prime example
of this approach.
22. AMRAAM: The AMRAAM (Advanced Medium Range Air to Air Missile) is designed
to succeed the Sparrow missile. The Sparrow missile has been a standard BVR missile for more
than thirty years. It entered service in 1958. The air war over Vietnam soon uncovered several
deficiencies. The AIM-7's minimum range was too great for the type of air engagements taking
place. There was too long a delay between radar lock on and missile firing and the Sparrow's
performance against agile targets was poor. Between 1965 and 1969 fewer than 10% of the
Sparrows fired hit their target. However many modifications were made, which showed a marked
improvement in both reliability and kill rate. The latest Sparrow AIM-7M has a monopulse
seeker, digital electronics, better auto pilot and an active proximity fuse. However, these
improvements were not good enough hence a new missile AMRAAM was developed.
23. Hughes AIM-120 AMRAAM has 2/3 the weight of Sparrow. Its maximum speed is much
higher, in the range of Mach 4 to 4.5. It can be launched automatically on inertial mid course
guidance without the need for illuminating the target. Its terminal homing is done by a small
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active seeker. It has a high impulse motor, which provides rapid acceleration. It has three distinct
guidance phases:
(a) Command
(b) Inertial
(c) Autonomous
24. The targets are detected by the aircraft fire control radar in the track while scan mode.
The ten highest priority targets are kept in the memory and the top eight are presented to the pilot
on his radar display. When the pilot designates a target for attack, its position is automatically
loaded into the missile upto the launch. After the launch, only the aircraft knows the target's
latest position. The missile continues on inertial guidance until close enough to switch on its
active radar seeker. If the target is manoeuvring, its position as stored in the missile memory must
be updated and this is done by the aircraft's fire control radar. Command in the critical mid-
course guidance allows upto eight AMRAAMs to be guided simultaneously to eight different
targets while the radar continues to scan to detect new targets Time to go to active radar switch
on is displayed to the pilot, allowing him to cease updating and so break off the attack once the
missile has acquired the target.
25. AMRAAM's x-band radar seeker has a choice of modes depending upon the type of
target. High PRF transmission is used for long range look up targets and medium PRF for look
down attacks. If target resorts to ECM the missile can be launched onto mid-course guidance,
and terminal radar home-on jam guidance. For short range attacks where the pilot acquires his
target visually, the AMRAAM can be fired along the aircraft bore sight, directly into active
radar work. This provides launch and leave capability in close combat. Even after all these
innovations, the problem of IFF still remains.
26. ADVANCED AIR TO AIR MISSILE (AAAM): It is a long range missile which is being
developed to replace AIM-54 PHOENIX. Phoenix holds the distinction of being the most costly
and sophisticated AAM in the world. Its weight is 447kgs and a range of around 200km. It has
semi-active homing phase initially. The terminal phase guidance is by a pulse Doppler seeker
head. Due to its size it is carried only by the F-14.
27. AAAM is lighter and is easily carried by the F-18, the F-16 and the ATF (Advanced
Tactical Fighter). It has a greater range than the Phoenix and has a weight which is 1/3 that of
Phoenix. This drastic improvement is made possible by the use of a new guidance technology. Its
speed is around Mach 4 and has a two stage power plant. The sustainers burn through out the
flight. It is likely to enter service by end 1991.
28. Thus it is seen that the trend is to keep the mother aircraft safe by providing fire and
forget capability. Though the development in this field has been quite rapid it is unlikely that a
fool proof will be deployed in the near future because of IFF constraints.
29. Conclusion: The rapid improvement in the capability of the BVRs is changing the shape
of future air combat. However, it must not be assumed that any of the foregoing technology will
prevent the pilot from getting into close combat. The BVR will be used mainly to improve the
odds before close combat and for disrupting the enemy's formations. Lastly, one big advantage of
the BVR is its deterrence value as an unseen threat will scare any potential intruder.
GLOSSARY OF TERMS
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1. AAAM: Advanced Air to Air Missile
2. AMRAAM: Advanced Medium Range Air to Air Missile
3. BOOSTER: Propulsion motor imparting large thrust for a short time to give high
acceleration at the beginning of the flight.
4. BURN OUT: Point at which the missile propellant has been totally consumed.
5. BVR: Beyond Visual Range
6. DOPPLER RADAR: Radar whose operation depends on the apparent change of
frequency caused by relative velocity between the radar and the target.
7. ECM: Electronic Counter Measures
(a) Active: The impairment of enemy electronic detection, control or
communication devices/systems through deliberate jamming or deception.
(b) Passive: Electronic countermeasures based on the reflections, absorption or
modification of the enemy's electromagnetic energy.
8. ECCM: Electronic Counter-Counter Measures.
9. FREQUENCY AGILITY: Radio or radar operating frequency automatically hops or
jumps to confuse the enemy or which can be positively controlled in accordance with a prior
programme.
10. HOMING GUIDANCE: In homing guidance, the missile itself is provided with a device
for looking at the target. The accuracy of the missile is improved as it nears the target.
(a) Active Homing System: The missile is equipped to transmit radio signals in the
direction of the target. It receives the reflected signals and directs itself on the target.
Once launched the missile is independent.
(b) Semi-active Homing System: The target is tracked by a transmitter outside the
missile. The missile receives the reflected signals and uses them as in the case of an
active homing system.
(c) Passive Homing System: All objects emit infra red radiations which could be
used by the missile homing system. The missile seeks these signals and homes on to the
target. Most passive homing systems in airborne missiles use IR heat seeking cells. Other
systems use electromagnetic emission from radar.
11. MONOPULSE: A radar technique in which four overlapping beams (two in azimuth and
two in elevation) give zero output voltage for a target exactly in the centre.
12. TWS (TRACK WHILE SCAN): In this method of target tracking, the radar is capable of
scanning within a defined angular volume and at the same time a computer (part of the radar)
memorises the co-ordinates of targets and anticipates their positions on successive scans.
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