MISSILE DEFENCE:

CONCEPTS AND TECHNOLOGIES

Anand Sharma

During the 1950s, counter-force attack was the only effective solution against
ballistic missiles, i.e. by destroying them while they were still in silos or on
launchers. However, efforts were progressing to develop some sort of anti-
missile shield to counter the ballistic missiles that were launched. As the
research and development (R&D) of anti-ballistic missile systems continued
gaining effectiveness and advance capabilities, counter-measures to missile
defence also matured and were outflanking the efforts. This offence–defence
play-off brought ballistic missile defence into prominence in security
planning. Many technologies have come to the fore to provide defence against
annihilating ballistic missile attacks.
A great deal of political, technical and public debate is persistently focussed
on the extreme issue of efficacy of missile defence. The answer in the extreme
is ‘no’; however, it is appreciated that though the phenomenal technological
growth and advancement may not provide foolproof security, missile defence
still has its importance in mitigating the effects of a preemptive strike and
deterring the adversary from believing that a ballistic missile attack can
provide him a clear military or political advantage.

* Wing Commander Anand Sharma is a Research Fellow at the Centre for Air Power Studies,New
Delhi.

79 AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March)

 MISSILE DEFENCE: CONCEPTS AND TECHNOLOGIES

Defending against The scope of this paper is to study the

ballistic missile concepts and various technologies which have
attacks is a challenging evolved to provide a useful defence against ever
technical task. The improving, sophisticated offensive threats. The
defensive system needs paper reviews the characteristics of the relevant
to hit a warhead smaller technologies and outlines the key uncertainties
than an oil drum that concerning those technologies’ potentials.
is travelling in space It researches the imperatives of defences in
at speeds greater than various phases of missile flight and against
18,000 km/hr. numerous counter-measures.

Initial Endeavours
From the late 1950s till 1970, both the superpowers developed the anti-ballistic
missile systems using nuclear tipped missiles as interceptors. US efforts
included the Nike, Spartan, Sprint and Sentinel missiles. When using nuclear
tipped interceptors, difficulties could spring up from collateral damage or
blinding of the defence’s own radar tracking system and communications.
The Soviet Union’s missile defence programme also progressed through
their ABM-1 to ABM-4 systems, namely, the Griffon Galosh, Gazelle, and
Gorgon. The USSR missile defence capabilities were successful and remained
operational with nuclear warheads till the late 1980s.
Given the concerns about using nuclear tipped interceptors, in the 1980s,
the US Army began studies about the feasibility of hit-to-kill vehicles, where
an interceptor missile would destroy an incoming ballistic missile just by
colliding with it head-on. The first successful programme, which actually tested
a hit-to-kill missile interceptor was the army’s homing overlay experiment 1
(HOE), which used a kinetic kill vehicle (KKV)2 on June 10, 1984, intercepting
1. A.Fenner Milton,M.Scot Davis, John Parmentola, Making Space Defense Work: Must the Superpowers
Cooperate? (UK: Pergamon-Brassey’s International Defense Publishers Inc., 1989), Ch.1, p. 8.
2. The KKV was equipped with an infrared seeker, guidance electronics and a propulsion system.
Once in space, the KKV could extend a folded structure similar to an umbrella skeleton of 4
m (13 ft) diameter to enhance its effective cross-section. This device would destroy the ICBM
reentry vehicle on collision.<www.nationmaster.com/encyclopedia/National-missile-
defense#Homing_Overlay_Experiment>

AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March) 80

 Anand Sharma

the Minuteman RV (reentry vehicle) with a Ideally, it is preferable

closing speed of about 6.1 km/s at an altitude to intercept ballistic
of more than 160 km. The feasibility of kinetic missiles as far away
energy intercept technology as demonstrated from their intended
subsequently became the most matured basis target and as early in
of ground-based defence system concepts. their flight trajectory as
The beginning of the second era coincided possible while offering
with the origins of the Strategic Defence the opportunity for
Initiative (SDI) programme, which had, as its multiple shots.
goal, the development of non-nuclear missile
defences. Much of the technologies that Reagan proposed for the system were
at the very edge of technology. They included space and ground-based lasers,
rail-gun kinetic energy interceptors, space sensors, particle beam weapons,
etc. The concepts of ballistic missile defence have been evolving with each of
these technologies.

Concepts of Ballistic Missile Defence

Defending against ballistic missile attacks is a challenging technical task. The
defensive system needs to hit a warhead smaller than an oil drum that is
travelling in space at speeds greater than 18,000 km/hr. Counter-measures
such as decoy warheads further complicate the problem of intercepting targets.
It is essential to exploit the particular vulnerabilities that a ballistic missile
presents during the phases of its flight: boost phase, mid-course phase, and
terminal phase. The characteristics of different phases of the ballistic missile
trajectory are as shown in Table 1 below:

Table1: Phases of Ballistic Missile Trajectory

Phase Duration Description
Boost Phase 1-3 minutes for tactical Powered flight of the rocket boosters
short range missiles. lifting the missile payload into a ballistic
3-5 minutes for long range trajectory.
missiles.

81 AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March)

 MISSILE DEFENCE: CONCEPTS AND TECHNOLOGIES

Post-Boost 10s of second to 10s of Most intercontinental ballistic missiles

Phase minutes. (ICBMs) now have a “post-boost vehicle”
(PBV), an upper guided stage that ejects
multiple, independently targetable reentry
vehicles (MIRVs) into routes to their targets.
If these RVs are to be accompanied by
decoys to deceive ballistic missile defence
(BMD) systems, the PBV will dispense
them as well.

Mid-Course About 20 minutes (less RVs and decoys continue along a ballistic
Phase for sea-launched ballistic trajectory, several hundred to 1,000 km up
missiles (SLBMs). in space.

Reentry 30-100 seconds. RVs and decoys reenter the earth’s

Phase atmosphere, decoys first slow down in
upper atmosphere, then burn up because of
friction with the air and RVs are protected
from burning up in friction by means of an
ablative coating,
At a preset altitude, their nuclear warheads
explode.

Ideally, it is preferable to intercept ballistic missiles as far away from their

intended target and as early in their flight trajectory as possible, while offering
the opportunity for multiple shots. To interdict a missile and its warhead in
any phase of its flight i.e. boost, mid-course or terminal, requires an ability
to detect and intercept the attack within a very few minutes or to track and
destroy the attacking missiles and their warheads during their longer mid-
course journey through space before their reentry into the atmosphere so that
the debris will burn up on reentry. Finally, the last ditch attempt would be to
destroy the attacking missiles as they reenter and pass through the atmosphere
to the target in their terminal phase.
Each of these phases furnishes intercept opportunities, but also has inherent
limitations that must be taken into account in the design and deployment of
the missile defence architecture, as shown in Table 2.

AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March) 82

 Anand Sharma

Table 2: Implications of Intercepting Ballistic Missiles During Different Phases

Phase Advantages Disadvantages
Boost Missile’s thermal signature Time available for intercept
is large. Easy detection and is short (about three to five
tracking. minutes).
Booster is large physical Interceptor must be
target and missile is positioned close to country
vulnerable due to slower from which missile is
speed, large cross-section. launched.
Decoys are difficult to Rocket plume can obscure the
deploy. missile’s body
Multiple engagement Missile’s acceleration
opportunity. complicates the tracking
solution.
Hitting the booster can leave
a live warhead that falls short
of its target.

Ascent/Early Ascent Missile is still large and Warhead separation on the

(Post-Boost) hot. missile being targeted may be
Extends the time available very rapid.
for intercept. Interceptor must be
Missile mostly would be positioned close to country
flying a predictable ballistic from which missile is
trajectory. launched.
Interceptor must destroy
warhead because warhead
has enough speed to reach its
target.

Mid-Course Longest time is available for Missile’s thermal signature is

intercept. small, making it difficult to
Missile is probably flying detect and track.
a predictable ballistic
trajectory. Warhead is small physical
Defences can be positioned target.
in the oceans. Decoys can dilute defences

83 AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March)

 MISSILE DEFENCE: CONCEPTS AND TECHNOLOGIES

Terminal Most decoys are stripped Time available for intercept is

away during atmospheric very short.
reentry.
Forward deployment is Debris from the intercept may
unnecessary. fall on defended territory.

Layered Defence
As anti-missile capabilities emerge from R&D programmes and progress made
to date in missile defence development efforts, it can be reasoned out that the
best way to counter even a limited number of missiles attacks is through defence
in depth3. Multiple defensive layers, with system elements working together
synergistically are central to the approach.4
To achieve a high Promising technologies and approaches include
probability of ballistic space-based detection sensors, ground-based
missiles’ destruction and seaborne early warning and tracking sensors
in flight, a layered and also include kinetic energy (hit-to-kill) and
defensive approach is directed-energy interception systems with various
imperative. land, sea, air and space basing.
To achieve a high probability of ballistic missiles’
destruction in flight, a layered defensive approach is imperative. Layered
defences are built on the premise that although technological limitations might
keep any one layer from having an adequate chance of successfully intercepting
its target, multiple layers could together provide an effective defence. The
layered approach provides multiple opportunities to engage the warheads from
detection in the boost phase till the reentry phase, thus, reducing the burden on
any single layer of defence. Further, layered defences complicate the design of the
adversary’s offensive systems as the offensive systems have to cater to multiple
layers of defences, demanding complex counter-measures, thus, reducing the
payload capacity or compromising in attributes such as range and speed.

3. Defence in depth means there will be a number of opportunities to destroy missiles as they are
launched and transit through the various stages of their flight paths or trajectories.
4. Milton, et. al, n.1, Ch 2, pp 24-32.

AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March) 84

 Anand Sharma

However, there are drawbacks as well to layered Sensor and

defences. The most obvious problem is that more data processing
layers will cost more—especially if the layers are technologies
completely independent. are crucial to an
Second, the degree to which the layers can advanced ballistic
combine to produce high effectiveness will depend on missile defence
how independent the layers are. To take an extreme system.
example, if all the layers depend on the same sensor system and that sensor
system fails, all the layers will fail. The layers must be able to take advantage of
the other layers without being overly dependent on them.
Third, the robustness of the system against the loss (or severe degradation)
of one layer will depend on how much capacity is built into the system to
compensate for that loss. For example, if boost and post-boost defences permit
twice the expected number of objects to reach mid-course, and if that in turn
substantially degrades the mid-course defence’s ability to sort objects, the
mid-course may let through not only the additional RVs but also many of the
ones it would otherwise have intercepted.5
There is a wide variety of technologies which could, in principle be integrated
to form a comprehensive ballistic missile defence (BMD) system. Each technology,
however, is limited by physical laws. These limitations complicate, but do not
eliminate, the possibility of a working system based on that technology. For
example, the limitation on the distance travelled in the time available, due to
finite velocities (kinetic energy weapons); inability of the energy-delivery device
to penetrate the atmosphere effectively (particle beams, X-rays, possibly kinetic
energy); the curvature of the earth (pop-up systems). The relevant criteria used
to determine the usefulness of the different technologies mostly concern their
ability to neutralise targets in a shortest possible time (seconds, at the most).
Sensor and data processing technologies are crucial to an advanced
ballistic missile defence system. The chain of operations which each layer
must perform as individual tasks are surveillance and acquisition, discrimination

5. Richard L.Garwin, “Enforcing BMD Against a Determined Adversary?” in Bhupendra Jasani,

ed., Space Weapons and International Security (SIPRI, Oxford University Press , 1987), pp.73-74.

85 AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March)

 MISSILE DEFENCE: CONCEPTS AND TECHNOLOGIES

of actual missiles and warheads from decoys and other debris, pointing and
tracking with precision as required by the weapon designated to destroy that
target, target destruction and kill assessment. In addition, if it can be determined
why a targeted warhead was not destroyed (for example, incorrect pointing),
the analysis can be used for a subsequent attack.

Fig. 1 Layered Integrated Ballistic Missile Defence Architecture

-

Airborne

-
Air borne

Air borne

R -

-
Infrared

S -

Air borne

AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March) 86

 Anand Sharma

Kinetic Energy Interception

As early as 1962, the concept of ballistic missile intercept through interceptor
rockets was developed which would catch up the attacking missiles and
get close enough to kill them by exploding nuclear warheads. By the mid-
1980s, small, light, accurate guidance systems made it possible to do away
with warheads altogether6, and to create actual collisions between interceptor
rockets and missiles.
Kinetic weapons for targeting objects Kinetic weapons for
in space flight i.e. anti-satellite or anti-ballistic targeting objects in space
missiles, need to attain a high velocity so that flight i.e. anti-satellite
they can destroy their target with their released or anti-ballistic missiles,
kinetic energy alone.7 The force of the impact need to attain a high
destroys the attacking missile or warhead, velocity so that they can
renders it inoperable, or diverts it from its destroy their target.
intended target without the potential collateral
effects of nuclear warhead explosions inherent in earlier BMD systems. Absence
of a warhead saves weight and there is no detonation which is required to be
precisely timed. This method, however, requires direct contact with the target,
which requires a more accurate trajectory because a near-miss has the same effect
as a large miss. This places greater demand on the homing guidance system,
the amount of fuel required for homing and the required peak acceleration to
transfer maximum kinetic energy at the point of impact.
The ‘eyes’ of a kill vehicle typically include seekers (basically, one or more
sensors) that ‘acquire’ the target and help guide the interceptor to the final
impact point. Initially, the KKV must home in on the rocket plume, and then
switch to home in on the missile body near the impact point. Seekers may
be active or passive. There are passive seekers for a broad portion of the

6. Eric Croddy, James J. Wirtz, Weapons of Mass Destruction: An Encyclopedia of Worldwide Policy,
Technology, and History (Oxford, UK: ABC-CLIO, 2005), p. 216.
7. Compare the energy of TNT, 4.6 MJ/kg, to the energy of a kinetic kill vehicle with a closing
speed of 10 km/s, which is 50 MJ/kg and, hence, explosives are not necessary. i.e. it has about 12
times the energy of a high explosive such as TNT. Anything that gets in the way of the attacking
missile—even a plain rock—is likely to destroy it.

87 AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March)

 MISSILE DEFENCE: CONCEPTS AND TECHNOLOGIES

Designers could electromagnetic spectrum, including short,

compensate for a system medium, and long-wave infrared as well as
that took longer to ultraviolet and visible wavelengths. Active
commit by producing seekers may include conventional radar or
faster interceptors, or laser imagers or rangers.
they could make up for Exo-atmospheric and endo-atmospheric
slower interceptors by kill vehicles design and requirements are
speeding up a system’s quite different because the aerodynamic
commit time. drag and lift forces on an endo-atmospheric
kill vehicle will substantially affect its
performance. An endo-atmospheric kill vehicle requires a shroud to reduce
the aerodynamic drag and a window to protect the infrared sensors from
overheating. However, endo-atmospheric kill vehicles have an advantage
that they can manoeuvre with aerodynamic lift forces, thus, requiring less
fuel for divert manoeuvre.

Boost Phase Interception

The missile boosters are accelerating targets. The time available for intercept,
coupled with the distance that an interceptor must travel to reach its target,
which results from the geography of a particular scenario, determines the
response time and interceptor speed needed for a boost phase interceptor.
A boost phase interceptor engagement can be conceptually divided into
two stages. The first is the commit stage, which lasts from when the threat
missile is launched until the interceptor is fired. During the commit stage, the
system must detect its target, track it, and decide to commit an interceptor to
an engagement. The second stage is the fly out stage, which lasts from when
the interceptor is launched until it reaches and destroys its target.
Designers could compensate for a system that took longer to commit by
producing faster interceptors, or they could make up for slower interceptors
by speeding up a system’s commit time. Alternatively, the total time available
for an intercept might be extended by incorporating the capability to hit a
missile in its early-ascent phase.

AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March) 88

 Anand Sharma

During the boost phase, however, a ballistic Ballistic missiles can

missile’s signature comprises both the missile body manoeuvre during
itself and the large rocket plume. At high altitudes, their boost phase,
the plume ‘blooms’ around the missile—in effect, thus, introducing
creating a smokescreen of hot exhaust gas that, errors in the predicted
depending on the kill vehicle’s angle of approach, intercept point.
can obscure the body of the rocket. A kill vehicle
must be able to detect and hit the missile within the plume. Light detection
and ranging (LIDAR) systems that use a laser to penetrate the plume and
locate the missile body have been developed for that application. However, a
LIDAR system’s potential to improve the probability of hitting the target must
be weighed against its disadvantages, which include increased complexity,
weight, and costs relative to other alternatives.
More importantly, ballistic missiles can manoeuvre during their boost
phase, thus, introducing errors in the predicted intercept point. The divert
and altitude control system (DACS) is the propulsion package that not only
gives the kill vehicle, manoeuvring capability for the intercept but also keeps
it balanced and pointing in the right direction.
The characteristics of ballistic missiles against which the defences have
to be developed influence the performance of the defensive systems. For
example, the type of booster used in an intercontinental ballistic missile
(ICBM) is particularly important to designers of boost-phase intercept
systems. Solid-fuel ICBMs usually have shorter boost phases than liquid-fuel
ICBMs. Thus, a boost phase interception (BPI) system designed to counter
solid-fuel ICBMs will need higher performance because its interceptors will
have a short time window for intercept. The effectiveness of interceptor
rockets would require that interceptors be based in near vicinity of the
possible boost-phase flight paths of attacking missiles. In general, because
less time is available to reach the target, more BPI sites are needed so that
interceptors can have a shorter fly out distance. The size and location of
potential threat countries play a role in determining the effectiveness of a
BPI system by determining the distance that an interceptor must fly to reach

89 AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March)

 MISSILE DEFENCE: CONCEPTS AND TECHNOLOGIES

its target.
Similarly, because of the short engagement time, engagement should
include two interceptor shots (salvo) to increase the probability of a successful
intercept. Some surface-based boost phase interceptors could be based at sea
on the navy’s surface combat ships, thus, extending the reach of interceptors
in the boost phase.
It is widely believed that the best basing mode available is a submarine
as it offers a lot of flexibility. It enables positioning of the interceptor missile
closer to the enemy’s launch site, thus, offering a huge advantage in the boost
phase intercept. With submarine basing, one has the advantage of ambiguous
presence because the enemy is always uncertain about their location.
The performance of space-based interceptors is less sensitive to geographic
factors; however, geography is an important factor in determining the number
of space-based interceptors needed in the defensive system. Orbital dynamics
requires that the higher the latitude of the country to be covered, the more
the interceptors that must be deployed. Space basing provides an advantage
of access to any point on earth, including the interiors of very large countries
that could never be reached with a surface-based interceptor launched from
an adjacent country.
The space-based kinetic energy experiment (KEE) has its origins in the
Brilliant Pebbles of the Reagan era. While geostationary orbit is an attractive
location for continuous observation and defence, it is too far away from earth
(about 35,000 km) to be useful for any practical weapon system. Thus, a space-
based system would be a constellation of interceptor satellites located in low-
earth orbit at an altitude of about 250 to 300 km. A kill vehicle near the missile
launch site would then use its onboard propulsion and sensors to accelerate
out of its orbit and home in on the target missile. Satellites in inclined low-
earth orbits are not fixed over one spot and instead follow a sinusoidal ground
track as they move over the earth. Thus, providing full coverage of a specific
threat country requires a constellation of space-based interceptors (SBIs)
with their orbits positioned such that at least one SBI is capable of reaching
the threat at any given time. At lower orbits, however, satellites would have

AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March) 90

 Anand Sharma

shorter life spans because of atmospheric The orbit of these space-

drag. The number of space-based interceptors based interceptors
needed to cover a threat country depends would be at low altitude
on the performance of the system (which and predictable, leaving
determines the coverage area, or footprint, of them vulnerable to
each satellite) and the latitude of the country. attack by inexpensive,
Further, the shorter burn time of solid-fuel short-range missiles.
ICBMs results in a smaller effective footprint
for each space-based interceptor which means that the size of the constellation
must increase.
A 2003 American Physical Society study showed that many hundreds or
thousands of space-based interceptors would be required to provide limited
global coverage against ballistic missiles and given the technology expected
for the next decade, each SBI would weigh a ton or more. As a result, deploying
such a system would be hugely expensive.8
On the negative side, the orbit of these space-based interceptors would
be at low altitude and predictable, leaving them vulnerable to attack by
inexpensive, short-range missiles. By eliminating only those few relevant
interceptors, an attacker could create a hole in the defence. The defence could
also be defeated by simultaneously launching multiple missiles from one
location, overwhelming the system. In short, a defence based on deploying
hundreds or thousands of space-based interceptors, at enormous cost, could
be defeated by a handful of enemy missiles.

Mid-Course Interception
The mid-course phase provides a longer time-frame for interception of the
missile or its payload. For an ICBM, this phase may account for as much as
80 percent of the missile’s total flight time. Therefore, the mid-course phase
allows the longest window of opportunity to intercept an incoming missile.
Conversely, a longer intercept window also provides an opportunity to the

8. “The Missile Defence Space Test Bed”<www.ucsusa.org/global_security/space_weapons/

space-test-bed.html>

91 AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March)

 MISSILE DEFENCE: CONCEPTS AND TECHNOLOGIES

A sea-based system attacker to deploy counter-measures against the

might be more defensive system.
expensive to procure The principal disadvantage of interception
than an equivalent during the mid-course phase is that the RVs and
ground-based system. decoys would have already been dispensed,
increasing by a factor of up to 10 the real number
of targets. Approximately, 10 to 100 mid-course decoys can be deployed
at the expense of one RV. These decoys travel alongside the RVs and pose
an enormous challenge of discrimination of decoys from RVs. Very good
decoys travelling on the right trajectory with the right shape, radar signatures
and thermal properties take up more space and consume valuable time in
discriminating the decoys and also make the other task of battle management
(surveillance, tracking and kill assessment) perplexing.
Countries capable of fielding an ICBM would be capable of developing
counter-measures and these counter-measures would have a significant
impact on the effectiveness of ground-based mid-course defence (GMD).
Rather than focussing on making decoys resemble a warhead, they
configured the warhead to make it look like a decoy, which would be a
simpler prospect. Also, the warhead can be covered in a liquid nitrogen-
cooled metal shroud, which will make it more difficult for the interceptor
kill vehicle to detect in time to manoeuvre into its path.
A multiple kill vehicle (MKV) 9 launched from interceptor missiles will
counter complex ballistic missile threats during their mid-course phase. MKV
payloads do not require the BMD system to pinpoint a single lethal object
within a threat cluster. Instead of pairing one kill vehicle with one interceptor
missile, the MKV payload allows a single interceptor missile to deliver several
kill vehicles that can attack multiple threat objects within the threat cluster.
This arrangement of MKV dramatically increases the probability of destroying
the lethal object within a threat cluster.10

9. Missile Defence Agency Factsheet <www.mda.mil/mda.info@mda.mil>

10. “Multiple Kill Vehicle” < www.mda.mil >

AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March) 92

 Anand Sharma

Sea-based mid-course interceptor platforms At reentry, the defence

will be intrinsically mobile and highly dispersed, can discriminate
and would offer the opportunity to engage the the warhead
threat early in its trajectory, possibly as early as unambiguously and
in its ascent phase of mid-course cruise, thereby, launch interceptors
reducing the susceptibility to counter-measures. with greater confidence.
Sea-based systems also can be operated in
forward (i.e. overseas) locations in international waters, without the need for
negotiating basing access and without restrictions from foreign governments
on how they might be used.
Conversely, a sea-based system might be more expensive to procure than an
equivalent ground-based system due to the potential need to engineer the sea-
based system or fit it into a limited space aboard a ship. Also a sea-based BMD
system operating in a forward location might be more vulnerable to enemy
attack than a ground-based system, particularly a ground-based system sited
in a rear location. Defending a sea-based system against a potential attack
would increase the cost of defence by means of additional ships.
An integrated (combined land and sea) architecture could provide more
operational flexibility and robustness than architecture that relies solely on
sea-based interceptors or on a single land-based interceptor site. This would
provide an additional defence layer that can engage the threat ahead of the
land-based interceptors, and, thus, provide a multi-tiered defence architecture
that has the potential for more robust and more confident protection.

Terminal Phase Interception

The terminal phase provides missile defence systems with a last shot
opportunity. During this phase, the warhead, along with decoys or chaff,
reenters the atmosphere at an altitude of about 100 km, creating a bright infrared
signature. Atmospheric drag then produces dramatically differing behaviour
for lighter as compared to heavy objects. Decoys decelerate significantly
and burn up, but the warhead does neither. Thus, at reentry, the defence
can discriminate the warhead unambiguously and launch interceptors with

93 AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March)

 MISSILE DEFENCE: CONCEPTS AND TECHNOLOGIES

greater confidence. The terminal phase has many advantages compared to

other phases such as the reaction time provided by the early warning is long.
Second, both sensors and interceptors can be based within a geographic area,
thus, reducing the cost. Third, ranges are short, thus, small, high frequency,
hardened or mobile radars can be used for tracking instead of larger radars
which are expensive and vulnerable. Finally, the penetration aid problem
(counter-measures) is manageable.11
However, terminal defence presents severe challenges resulting from the
very high speed of the offensive warhead and the very short time in which
terminal defence operates. The terminal phase is the last one or two minutes
of a ballistic missile’s flight. Several counter-measures are available to combat
a terminal-phase defence:
• Speed: Early reentry vehicle designs used blunt shapes which caused
them to decelerate significantly during reentry. Modern reentry vehicles
are cone shaped to minimise aerodynamic drag, providing high-speed re-
entry. It carries the collateral benefit of reducing the duration of exposure
to terminal missile defences.
• Trajectory and Manoeuvres: A ballistic missile can follow a lofted
trajectory or a depressed trajectory. A lofted trajectory gives less time
for engagement, thus, complicating the terminal phase defence. Further,
it is possible to design a reentry vehicle that will perform simple but
unpredictable and intense manoeuvres upon reentry. This can be done
by using a slightly bent nose, a small fin at the rear, or an internal weight
that is moved laterally during reentry. In the 1970s, the US developed a
manoeuvring reentry vehicle, the Mark 500, for the Trident 1 submarine-
launched ballistic missiles (SLBM). Its tests were successful and
included 200G manoeuvres that would severely challenge any defence.
Manoeuvring reentry vehicles of this type sacrifices some accuracy and
payload; however, these are not significant.
• Ladder Down: A nuclear warhead exploding in the upper atmosphere
would create a cloud of ionised gas that would be opaque to a radar for
11. Milton, et al., n.1, Ch.2, p. 43.

AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March) 94

 Anand Sharma

several minutes. One tactic available to the offence would be to use such
a precursor explosion to mask a following reentry vehicle. The reentry
vehicle would become visible after passing through the cloud, but the
time remaining for the defence would be significantly reduced.

Directed Energy Weapons (DEWs)

The advanced technology has raised the possibility of countering an ICBM
attack through the directed-energy weapons, which possess profound lethality
and unmatchable key features. Their ability to
fire shots at or near the speed of light (186,000 The advanced
miles a second), which would seem like relatively technology has
freezing even high-speed targets in their motion; raised the possibility
their ability to engage multiple targets very of countering an
rapidly; and their very long range (thousands of ICBM attack through
kilometres in space) are the key features. There the directed-energy
are three principal forms of directed-energy weapons.
weapons: the particle-beam weapons, high power
microwave (HPM) weapons and the high-energy laser.
By virtue of their cost and unique capability, development of DEWs may
provide truly transformational war-fighting capabilities, which may signal a
revolution in military hardware; perhaps more so than the ballistic missiles.
Some unique characteristics which mark them as potentially revolutionary
are:
• First, the speciating facets are speed and distance. There is a clear advantage
to propagating lethal energy over militarily significant distances within a
blink of an eye. That means many of the problems associated with aiming
and firing existing weapons are effectively eliminated, because virtually no
time elapses between firing a directed-energy weapon and its impact on the
target.
• Second, the cost of discharging such weapons is typically a small fraction
of what it costs to fire a missile, because the method of destruction is pure
energy. Although directed-energy devices may require a major investment

95 AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March)

 MISSILE DEFENCE: CONCEPTS AND TECHNOLOGIES

in weapons technology development and support infrastructure, the price

of intercepting a missile or aircraft may be only one or two percent of
what conventional munitions would cost. A DEW provides an efficient
alternative wherein it costs only a few thousand dollars per shot to achieve
equivalent or superior probability of kill. For comparison, procurement
costs of the join direct attack munition (JDAM) are US $ 21,000 (tail kit
only); for the joint stand-off weapon (JSOW) $ 660,000; for the joint air-
to-surface stand-off missile (JASSM) $ 300,000; and for the advanced
medium range air-to-air missile (AMRAAM) $ 386,000. Even the basic
Maverick can cost $ 152,000. By contrast, the fuel required per shot of the
large laser in the airborne laser (ABL), costs approximately $ 10,000. For a
100 kilowatt (KW) solid state laser, the cost of the fuel required to generate
electricity for each shot is less than a dollar.12
• Third, directed-energy weapons provide war-fighters with surgically
precise and discriminate firepower. While indiscriminate damage is
certainly within their capability, it is possible to employ directed-
energy weapons in ways that generate no collateral damage at all.
A related feature of DEW technology is the ability to customise
the weapon by adjusting the amount of energy incident upon
targets. This allows for a wide range of results: lethal or non-lethal,
destructive or disruptive.
• Fourth, directed-energy devices potentially enable war-fighters to rapidly
engage many different targets, because of their instantaneous effects and
the relative ease of reaiming them.
• Energy beams are essentially immune to gravity which also frees them from
the kinematics and aerodynamic constraints that limit more traditional
weapons. Hence, the complex calculations required to determine ballistic
trajectories and other flight characteristics of conventional munitions are
irrelevant to directed-energy devices
• Finally, another feature contributing to their multi-target capability is the
12. Richard J. Dunn, “ Operational Implications of Laser Weapons”, (Analysis Centre Papers,
Northrop Grumman, September, 2005), <http://www.analysiscenter.northropgrumman.com/
files/Operational_Implications_of_Laser_Weapons.pdf>

AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March) 96

 Anand Sharma

compactness and low cost of the fuel that drives them. Directed-energy
weapons could be based on a variety of platforms, and they come in a
wide range of power levels.

While DEWs are technologically revolutionary, their associated

requirements will have to develop in a similar fashion. Such weapons also
have unique disabilities. The lethal power of their beams may quickly degrade
on interaction with the surrounding medium, such as when a laser beam passes
through water vapour or dust. In the absence of reflectors, they are strictly line-
of-sight weapons. But their weaknesses, like their strengths, contribute that
directed-energy weapons are fundamentally different from past technologies
of war, and are potentially transformational.
Particle beam weapons work by accelerating a stream of atoms or sub-
atomic particles near to the velocity of light and projecting them in a beam.
Particle beam weapons can be divided into neutral particle beam weapons
and charged particle beam weapons. Both electrons and protons can be
used to form this beam, and would be the choice for a weapon to be used
within the atmosphere. Hydrogen atoms are the preferred choice for an
extra-atmospheric weapon—they have a neutral charge, and, thus, the beam
wouldn’t be deflected by the earth’s magnetic field, or scattered by the
mutual repulsion of similar charged particles.
Particle beam weapons increase the kinetic energy of a large number of
individual atomic or sub-atomic particles which are propagated at essentially
the speed of light and then direct them collectively against a target. Every
particle in the beam that strikes the target will transfer a fraction of its kinetic
energy to the target material. If enough particles hit the target in a short time,
the deposited energy would be sufficient to burn a hole in the skin of the
device, detonate the chemical explosives, disrupt the electronics inside or result
in damage from the swift temperature increase and possibly an explosion; for
example, the effects of a lightning bolt—which is essentially a charged particle
beam—and this gives an idea of how destructive such a weapon could be.
However, particle beam weapons are yet to be practical because of the

97 AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March)

 MISSILE DEFENCE: CONCEPTS AND TECHNOLOGIES

Since its invention huge power requirement i.e. of millions or even

in the early 1960s, billions of watts, in a very short time as a powerful
the laser has proved burst, necessary to create destructive pulses.13 The
to be an extremely technology to create such a power source already
useful device not exists; the problem is in making it small and light
only for the scientific enough to be portable. Since the beam is strongly
and commercial affected by passage through the atmosphere and
communities, but also also due to the earth’s magnetic field, precision is
for the military. questionable in practicality.
High-power microwave (HPM) weapons are
also known as radio frequency weapons and ultra-wideband weapons. HPM
weapons have been in development in the United States, Russia, and China
for decades. An HPM device employs electromagnetic radiation as its weapon
effect. Not as powerful as nuclear electromagnetic pulse (EMP) weapons,
HPM weapons create a narrower level of microwave electromagnetic radiation
as the atmosphere is generally transparent to these frequencies. As a rough
point of comparison, HPM systems produce 100-1,000 times the output
power of modern electronic warfare (EW) systems14. For example, a high-
power microwave device can be aimed at an aircraft, immediately upsetting its
onboard electronics and sending it into a fatal dive without firing a projectile
or even leaving evidence of its use. Such a weapon was successfully field
tested by the US in April 2001, and reported to have been deployed during
Operation Iraqi Freedom.15
The laser is perhaps the most important optical invention in the last
several decades. Since its invention in the early 1960s, the laser has proved
to be an extremely useful device not only for the scientific and commercial

13. “Neutral Particle Beam” <http://www.fas.org/spp/starwars/program/npb.htm>

14. “Space Operations: Through The Looking Glass,” A Research Paper presented to “Air Force
2025
”<http://csat.au.af.mil/2025/volume3/vol3ch14.pdf>
15. Stuart Millar, article published in the Guardian on March 19, 2003 < www.guardian.co.uk/
profile/stuartmillar>

AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March) 98

 Anand Sharma

communities, but also for the military. 16 At first, it was considered to be “a

solution without a problem,” and today, the laser is at the heart of an extensive
array of military applications: range finders, satellite communications systems,
remote sensing, target designation, and laser radar-based navigational aids.
The employment of laser-guided munitions in Operation Desert Storm
brought new meaning to the idea of “precision engagement,” and represents
just one example of how the laser has shifted to become “a solution.”  In fact,
numerous countries are now developing their own laser technologies for
weapons applications. Since the early 1990s, lasers have demonstrated the
capability to produce sufficient energy to merit serious consideration, even by
the most ardent sceptics, as potential weapons against the ballistic missile threat.  
There are four fundamental approaches to high—and medium—power laser
energy: chemical lasers, solid-state lasers, fibre lasers, and free electron lasers.17
In the case of lasers, intense beams of monochromatic light can be
precisely aimed across hundreds or thousands of kilometres to disable a
16. Lasers are extremely flexible weapons, producing effects that cover the full “spectrum of force.”
At low power, laser beams can be used as battlefield illumination devices, to designate targets
from space, blind sensors in the laser’s optical band, ignite exposed flammable objects, raise the
temperature in localised regions, perform as an emergency high-bandwidth laser communication
system, and serve as a laser probe for active remote-sensing systems. At slightly higher powers,
the enhanced heating produced by the laser can be used to upset sensitive electronics (temporarily
or permanently), damage sensor and antenna arrays, ignite some containerised flammable and
explosive materials, and sever exposed power and communications lines. The full power beam
can melt or vaporise virtually any target, given enough exposure time. With precise targeting
information (accuracy of inches), a full-power beam can successfully attack ground or airborne
targets by melting or cracking cockpit canopies, burning through control cables, exploding
fuel tanks, melting or burning sensor assemblies and antenna arrays, exploding or melting
munitions pods, destroying ground communications and power grids, and melting or burning
a large variety of strategic targets (e.g., dams, industrial and defence facilities, and munitions
factories)—all in a fraction of a second. <http://csat.au.af.mil/2025/volume3/vol3ch14.pdf>
17. Chemical lasers can achieve continuous wave output with power reaching multi-megawatt
levels. Examples of chemical lasers include the chemical oxygen iodine laser (COIL), the
hydrogen fluoride (HF) laser, and the deuterium fluoride (DF) laser. Diode-pumped solid-state
(DPSS) lasers operate by pumping a solid grain medium (for example, a ruby or a neodymium-
doped YAG crystal) with a laser diode. Combining the outputs of many fibre lasers (100 to
10,000) is a possible way to achieve a highly efficient HEL. Free-electron lasers (FELs) use a
relativistic electron beam (e-beam) as the lasing medium. Generating the e-beam energy requires
the creation of an e-beam (typically in a vacuum) and an e-beam accelerator. This accelerated
e-beam is then injected into a periodic, transverse magnetic field (undulator). By synchronising
the e-beam/electromagnetic field wavelengths, an amplified electromagnetic output wave is
created.

99 AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March)

 MISSILE DEFENCE: CONCEPTS AND TECHNOLOGIES

Multi-megawatt class wide range of targets, from missiles to satellites

lasers (much larger to aircraft to ground vehicles and even people.
than any system They can also be reflected off mirrors in space
under development to hit targets not visible from their source while
today) would be retaining much of their initial fluence. These
required to defeat special features make it possible to focus the
the faster and much laser energy with mirrors into narrow beams
harder targets. characterised by small divergence angles.
Thus, a laser with 1 micrometre (=1 micron)
wavelength projected with a 1 metre mirror could have at best a 1.2 micro
radian divergence angle, making a spot 1.2 metres wide at a range of
1,000 km. A 10 metre mirror with a hydrogen fluoride (HF) laser beam
would yield a 0.32 micro radian divergence angle and create a laser spot
1.3 metres in diameter at a range of 4,000 metres. The distribution of 20
megwatts (MW) over the laser spot would create an energy flux of 1.5
kilowatts per square centimetre (KW/cm2). The laser spot would need to
dwell on the target for 6.6 seconds to create the nominal lethal energy of 10
kilojoules per square centimetre (kJ/cm2). At a range of 2,000 metres, the
destruction of the booster would require 1.7 seconds of illumination. This
perfect performance is called the diffraction limit18.
Laser light can damage boosters in two distinct ways. With moderate
intensities and relatively long dwell times, the laser simply burns through the
missile skin and is called thermal kill. The second mechanism requires very high
intensities but only one short pulse, the high intensity causes an explosion on
and near the missile skin, and the shock from the explosion injures the booster.
This mechanism, called impulse kill, is more complex than thermal kill.19
DEW systems can be land-based, sea-based, or space-based. Since lasers
can theoretically defeat artillery and missile attacks, any group fielding
an effective laser system will gain decisive advantages in ground, air and

18. Matthew Mowthorpe, “The Revolution in Military Affairs and Directed Energy Weapons,” Air
& Space Power Chronicles, March 8,2002 < www.iwar.org.uk>
19. Stephen D. Rockwood, “Technical Issues for Strategic Defence Research,” in Jasani, ed., n.5, pp.63-65.

AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March) 100

 Anand Sharma

space combat. Under radar control, lasers have shot artillery shells in flight,
including mortar rounds. 20

Ground-Based Directed Energy Weapon

Ground-based lasers are well suited to terminal point defence of critical
targets. These lasers can fire tens of shots against offensive missiles very
quickly, making them difficult to overwhelm. The chemicals consumed per
shot cost much less than the millions of dollars for defensive missiles. Thus,
even taking into account the initial cost of the laser weapons, laser-based BMD
may prove to be a highly effective and more affordable means of adding an
additional layer of defence against theatre ballistic missile (TBM) attack.
They can complement missile defence against longer range missiles.
Megawatt-class chemical lasers could defeat a TMB. Multi-megawatt class lasers
(much larger than any system under development today) would be required
to defeat the faster and much harder targets. In both cases, the effectiveness of
a laser defence would depend on developing systems concepts that overcome
the potential effects of clouds, fog or dust storms. For example, aircraft basing
would allow the laser weapon to operate above these weather effects.
The ground-based laser architecture may consist of multiple ground stations
with high-energy lasers placed in different regions of the country. Lasers are not
all-weather systems. Clouds absorb and scatter laser light, removing power from
the beam and distorting the beam’s ‘footprint’. Thus, the ground-based lasers
systems must be located in regions that have good weather all year round.
Each of the ground systems would include a high-energy laser, beam
director, adaptive optics21, acquisition and tracking systems, and related
20. India Daily, “The Race for Developing Deadly Solid-State Laser Weapons that can Change the
Future battlefield,” March 10, 2005, < http://www.indiadaily.com/editorial>
21. Adaptive optics techniques such as the Guide Star System have been developed to correct
atmospheric distortions to low-power laser beams projected from earth to space and back again.
Adaptive optics systems developed to date depend primarily on deformable mirrors—mirrors
with small actuators that change the mirror’s shape to pre-compensate the beam and correct
anticipated or pre-measured distortions. Further advances will be required in this technology,
both in terms of bandwidth and number/size of actuators, to make this technology work for
weapons class lasers. < “Space Operations: Through The Looking Glass”,http://csat.au.af.
mil/2025/volume3/vol3ch14.pdf>

101 AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March)

 MISSILE DEFENCE: CONCEPTS AND TECHNOLOGIES

support systems. The laser beam is transmitted through the atmosphere to a

constellation of mirrors in space. Changes in the altitude of the space mirrors
will affect the diameter required for the beam director’s primary mirror, relay
mirrors, and mission mirrors, and as well as the number of space mirrors. A
total of four relay mirrors in geosynchronous orbit would provide the necessary
worldwide coverage. One of these mirrors would be positioned as close as
possible to the zenith of the ground lasers to minimise atmospheric effects.22

Space-Based Directed Energy Weapon

For the boost phase intercept, the Strategic Defence Initiative Organisation
(SDIO) proposed several hundred satellites armed with powerful
(>100MW) lasers. Microwave and particle beams were also considered but
lasers remain the more developed technology. Space-based lasers (SBLs)
can be located on satellites placed in low-earth orbit. The satellite needs
to be at an altitude sufficient to enable it to intercept the farthest boosting
missile it can see.23
In the late 1990s, SBL planning was based on a 20-satellite constellation,
operating at a 40° inclination, intended to provide the optimum tactical missile
defence (TMD) threat negation capability. At this degree of deployment, kill
times per missile will range from 1 to 10 seconds, depending on the range from
the missile. Retargeting times are calculated at as low as 0.5 seconds for new
targets requiring small angle changes. It was estimated that a constellation
consisting of only 12 satellites can negate 94 percent of all missile threats
in most theatre threat scenarios. Thus, a system consisting of 20 satellites is
expected to provide nearly full threat negation.24

22. Lt Col William H. Possel, USAF, “Lasers and Missile Defence: New Concepts for Space-based
and Ground-based Laser Weapons,” Occasional Paper, No. 5 Centre for Strategy and Technology
Air War College, July 1998.< http://www.fas.org/spp/starwars/program/docs/occppr05.
htm>
23. Matthew Mowthorpe, “The Revolution in Military Affairs and Directed Energy Weapons,” Air
& Space Power Chronicles, March 8,2002 < www.iwar.org.uk>
24. “Space-Based Laser” [SBL] < http://www.globalsecurity.org/space/systems/sbl.htm>

AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March) 102

 Anand Sharma

Air-Based Missile Defence

Ballistic missile defence components can also be mounted in or on aircraft.
Sensors can be interconnected into the missile defence network and aircraft
can carry the means of intercepting ballistic missiles, particularly early in their
flight, while their rockets are still burning. The means of intercept can employ
either directed energy (lasers) or kinetic energy.
The airborne laser (ABL) is the avant-garde of a revolution. While the
phrase “revolution in military affairs” is overused, the emergence of systems
utilising directed energy for tangible war-fighting applications is worth noting.
Efforts during the 1970s provided that it was possible for an airborne laser to
intercept aerial targets and confirmed that lasers had weapon potential. Iraq’s
use of the Scud missile as a terror weapon during the Gulf War exposed a
potential mission. This led the United States Air Force (USAF) to propose an
ABL weapon system that would be capable of locating, tracking, and destroying
such missiles in their boost phase. A 747 aircraft, an advanced detection and
tracking system, adaptive optics, and a revolutionary high-energy laser, are all
being integrated into a single weapon system for the first time.
The ABL is among the first generation of deployable directed energy
weapons with potential to present the US not only a new capability to destroy
ballistic missiles, but, more importantly, a foundation of an entirely new
defence architecture. The ABL is also being evaluated for its suitability to
perform other adjunct missions. These include cruise missile defence (CMD),
intelligence, surveillance and reconnaissance (ISR) and protection of high
value airborne assets (PHVAA).
Under cloud-free line-of-sight conditions the ABL’s infrared surveillance
system can detect both aircraft and TBM, and acceleration and altitude will
permit discrimination among target types. However, identifying them as
positive hostile targets will require off-board confirmation such as airborne
warning and control system (AWACS) warning. The ABL can destroy aircraft
before they penetrate close enough to fire their air-to-air missiles. Cruise
missiles, though similar to aircraft, are more difficult targets, particularly those
flying low-level profiles. Detecting and identifying cruise missiles as hostile

103 AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March)

 MISSILE DEFENCE: CONCEPTS AND TECHNOLOGIES

will be the ABL’s most challenging target and probably require off-board help.
Flying low to avoid the ABL’s high energy laser (HEL) will shorten the ABL’s
effective range. Obviously, this capability has gaps that can only be filled by
the traditional weapon, the fighter, and its long-range eyes, the AWACS.

Ballistic Missile Defence Sensors (BMDS)

BMD sensors detect, identify, track and assess the missile launch and generate
accurate targeting coordinates and stimulate a target shootdown. New and
innovative approaches to these requirements are being developed which
include not only detecting and tracking of targets but also discriminating
targets from decoys and debris.
For a layered BMDS, multiple sensors, with the different characteristics,
are essential. This would provide information using network-centric ability
by gathering data from various land-based, airborne, sea-based and space-
based sensors. Multiple sensors will not only provide redundancy but also
utilise important characteristics of various sensor systems like radar, infrared
sensors, optical sensors or laser detection sensors. For example, the boost
phase detection is ideal for an infrared seeker whereas during the mid-course
phase, RVs emit little energy and detection would be difficult by infrared
sensor but would be a better target for a radar sensor system.
The resolution and accuracy of the sensor system are also worked out as
per the weapon system being used for interception. For a DEW system, the
resolution required is of a few centimetres so as to keep the laser focussed
on one spot. The KEI system would require less accurate information from a
remote sensor because a homing sensor onboard an interceptor would give
the fine resolution needed in the last few seconds to
For a layered approach and collide with the target.
BMDS, multiple Resolution improves with reduction in distance
sensors, with to the target. Therefore, a sensor satellite placed in
the different geostationary orbit at 36,000 km surveys the entire
characteristics are earth but the resolution will not be of practical
essential. value. Even a constellation of satellites at altitudes

AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March) 104

 Anand Sharma

around of 4,000 km would not be adequate for Kill assessment

DEWs. Further, the vibration and jitters would is an important
preclude the transmission of target position to the factor for sensors.
weapon platform with 10 cm accuracy. Therefore, Missed targets
each DEW would need its own sensor to provide have to be
final pointing accuracy. retargeted and
Kill assessment is an important factor for sensors. disabled targets
Missed targets have to be retargeted and disabled should be ignored.
targets should be ignored. Though KEI weapons’
kill assessment is mostly simple and straightforward, in the case of partial
damage of a booster, leaving the missile intact, it will be a precarious situation
as the kill assessment would be affirmative.
In the case of DEW, assessment of damage of the target is a difficult process.
A laser or a neutral particle beam might burn through the critical component
without detectable damage and divert the missile from its intended course.
For surface-based radars, BMDS relies on fixed and transportable radar.
These radars include X-band radars in the form of the sea-based X-band
(SBX) radar. An X-band (wavelength 2.5-4 cm; frequency 8-12 GHz) radar
can search, detect, and track missiles, and distinguish between warheads and
counter-measures. The SBX radar is built upon a movable sea platform that
will improve the ability to acquire, track, and discriminate counter-measures
during the mid-course phase of flight. The ground-based mid-course
defence system also includes the upgraded early warning radar (UEWR)
and the L-Band (Cobra Dane) radar. These radars provide long-range missile
surveillance, acquisition and tracking, and object classifications, as well as
update information for the BMDS exo-atmospheric kill vehicles.
Space sensors fulfill five functions in supporting the BMDS. First, ‘situational
awareness;’ second, sensors send a wake-up call—‘the early warning’; third,
‘sensor-to-sensor cueing,’ which allows a sensor with a threat missile in track
to pass pertinent information on that missile to another sensor; the fourth and
fifth functions are ‘launch’ and ‘engage’. Sensor accuracy, timing, information
latency, coverage, and availability are all system attributes that determine if

105 AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March)

 MISSILE DEFENCE: CONCEPTS AND TECHNOLOGIES

a possible sensor system is capable of supporting these five functions. For

example, highly accurate information that is too late or timely information
that is inaccurate can negatively affect the execution of the BMDS mission.
This balancing act between accuracy and timeliness is one of the major design
traits that dominates the sensor capability analysis. The space sensor assets
that can most readily be incorporated into BMDS are overhead non-imaging
infrared assets. Future systems with advanced radar technologies to improve
system robustness, reduce cost, and enhance radar performance parameters
for all-weather missile tracking are under development.
The enemy can try to degrade the BMDS performance in several ways.
Reduction of observables of RV i.e. stealth, by the shape of the RVs such that it
gives minimum radar signatures, using either super lofted or super depressed
trajectories so as to avoid the search volume, etc. However, such tactics are relatively
easily countered by expanding the sensor search volume. Infrared sensors can be
degraded either by reducing the signal originating from the target (cooling the
target) or by increasing the competing signal coming from the background.25

Command, Control, Battle Management and

Communications (C2BMC)
The C2BMC programme is a key enabler for implementation of the missile
defence system in all three phases of flight. Responding to ballistic missile
threats presents an unprecedented challenge of speed, precision, and
coordination among numerous weapon systems, sensors, and war-fighters.
Decision cycles are reduced to minutes, and, in some cases, seconds, during
which air, ground, sea, and space sensor-interceptor-communications elements
must be orchestrated into engagement scenarios that seamlessly detect, track,
target, and engage incoming missiles. Unlike the other elements, this is not
primarily a hardware issue, but rather a software development challenge. The
C2BMC element is the critical tool that links the various individual sensor-
interceptor-communications elements into one coordinated system utilising

25. Stephen Weiner, “System and Technology,” in Ashton B. Carter, David N. Schwartz, ed., Ballistic
Missile Defense (Washington, DC: 1984), Ch.3. pp.49-59.

AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March) 106

 Anand Sharma

the best offensive/defensive attributes of each element, ensuring the highest

BMDS capability for protection against all types of ballistic missile threats in
any phase of flight. C2BMC can be thought of as ‘middleware’ linking decision-
makers, weapons, and sensors together in a networked environment.
C2BMC is an evolutionary concept that integrates modelling and simulation,
deliberate planning and analysis algorithms together in a time constrained
manner to ‘propose’ solutions and engagement sequences to the decision-
makers. It is a method of data processing and comprehensive algorithms that
describes, organises and provides prioritisation to a multitude of variables—
most of which change rapidly in an operational situation.

C2BMC Functional Attributes

C2BMC must be able to see, understand, analyse and prioritise the threats
and it must do so in compressed timelines commensurate with the nature of
the threat. Once C2BMC validates the threat, it begins to formulate the BMDS
response.C2BMC has the following functions:26
• Planning capability to optimally locate sensors and weapon systems to
counter identified threats.
• Situational awareness of the evolving battle and status of defensive assets
at all leadership levels. Situation awareness tools and intelligence updates
will provide indications and warning to allow decision-makers to move
the BMDS to higher states of alert when necessary.
• Networking and integration of sensors, weapon systems, and war-
fighters.
• Provision of automated, real-time, multi-source information to project
a single, near real-time command and control (C2) picture to allow
commanders to quickly assess missile threats and execute coordinated,
immediate responses.
• Missile detection and battle management to optimally pair sensors and
shooters for effective and efficient BMDS asset utilisation and engagement
of multiple threats for the highest probability of kill.
26. <http://www.lockheedmartin.com/products/c2bmc/index.html>

107 AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March)

 MISSILE DEFENCE: CONCEPTS AND TECHNOLOGIES

One of the problems • Efficiently manage and distribute essential data

is that there are in support of advanced strategic planning and
numerous ways supporting military echelons 24x7. Additionally,
that offence can C2BMC must perform the above activities for each
attack, thus, making threat and continuously iterate them when new
it impossible to information is received and assessments made
achieve the desired Peace-time activities include the day-
confidence in the to-day operations of the system, including
defensive system. planning updates, training, maintenance, asset
management, logistics and data base updates,
including intelligence. These updates, to the greatest extent possible, should
be automated.
Engagement control (EC) incorporates the traditional capabilities of
command, control and battle management, and recognises the evolutionary
and transformational capabilities that are different from traditional C2BM
but are required for successful C2BMC. Engagement control will use and
support two distinct C2 paradigms: traditional C2 requiring approval
before continuance, and management by exception (MBE). Traditional C2 is
the accepted human-in-control paradigm where the human makes the key
decisions regarding execution plans, weapons engagements and re-tasking.
MBE, on the other hand, represents the C2BMC computers, prosecuting the
engagement by proposing and executing all necessary products and decisions
automatically. In MBE, the human operator will review the proposed plans
and engagement sequences and has to manually stop the C2BMC process to
make changes.
Additionally, the C2BMC capability must have the adaptability to take
inputs from the combat commander regarding changes to defended assets
and changes to priorities, and automatically cascade these changes through
the situational awareness and planning tools.
The communications capability required for C2BMC must necessarily be
robust, interoperable, collaborative, and provide connectivity to the entire
community of interest. It will be net-centric and allow for common access to

AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March) 108

 Anand Sharma

BMDS data sets and databases. It will provide connectivity across operational
echelons and geographic locations. C2BMC communications are a foundational
element and key enabler for all the other C2BMC key capabilities.
The attributes of an effective communication system would include:
• Adequate band width and range.
• Reliability.
• Tolerance of component damage.
• Security from interception or take-over.
• Tolerance of nuclear effects.
• Jamming or spoof resistance.

Operational Imperatives
With the ever progressing technologies, many innovative systems and
approaches to missile defence will evolve. So is the case with the offensive
missile technologies which are improving consistently in range, accuracy
and lethality. This offence-defence challenge is the key factor to analyse
the requirement of a comprehensive missile defence system. For a country
to appropriate a missile defence system, the decision has to rest on serious
assessment in terms of its effectiveness against offensive missiles capabilities
and counter-measures, its survivability, its affordability not only for acquisition
but also for operation as well as maintenance and also its completeness to
provide a comprehensive defence with known and trusted limitations.
Testing of missile defence systems is especially difficult. The basic reliability
of individual components can be ascertained but for the system as a whole,
is a challenging task. One of the problems is that
there are numerous ways that offence can attack, Preemptive
thus, making it impossible to achieve the desired attack against the
confidence in the defensive system. Simulation components of the
may provide a near realistic picture but estimation defence is most
of leakage is the challenge. Similarly, simulation of likely and one of the
counter-measures may not be realistic and, thus, most deadly counter-
correct assessment of defensive effectiveness may offensive actions.

109 AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March)

 MISSILE DEFENCE: CONCEPTS AND TECHNOLOGIES

A well integrated, not be valid in the actual scenario.

layered, defensive The survivability of a defensive system
system using different can be challenged through many means. For
technologies and basing example, the defensive system can fall apart
methods depending if its sensors have been nullified or destroyed.
on geography, threat Preemptive attack against the components of
perception, envisaged the defence is most likely and one of the most
capability and cost deadly counter-offensive actions. Blinding the
analysis is the only satellite sensors can be achieved with a laser
answer. based on a high altitude aircraft. The simplest
form of counter-defence attack can come from
an anti-satellite (ASAT) interceptor launched from the ground. Measures like
hardening, manoeuvrability, self-defence and redundancy could be used to
protect the defensive system against ASAT systems.
Completeness of a missile defence system can be said to be achieved if
it can address the vulnerability to attacks not only from ballistic missiles
but also from other weapons such as cruise missiles, bombers or unmanned
aerial vehicles (UAVs). For this, BMD must also support the conventional air
defences while integrating each other’s assets.
Notwithstanding the limitations and vulnerabilities, ballistic missile defence,
even with imperfect defence, can drastically alter the calculus of military
planning of the adversary by introducing an extra element of uncertainty and
raising the cost of destroying important military targets. A partial defence may
also be able to reduce casualties, particularly in the event of limited attacks. Thus,
even partially effective defence would strengthen deterrence by reducing the
confidence of the adversary that the attacks would not achieve their objectives.

Summary
As discussed in the preceding paragraphs, missile defence is a ‘system-of-
systems’ comprising various technologies and concepts. The distributed
nature of the system-of-systems described above can be its greatest strength
or its greatest weakness. The system-of-systems must be designed carefully

AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March) 110

 Anand Sharma

to minimise or eliminate all critical nodes. Critical nodes that cannot be

eliminated must be protected by deception, added defences (hardening,
placement within a secure environment), or redundancy.
Such capability acquisition by a country must be based on various important
attributes such as timeliness, responsiveness, precision, survivability,
reliability, selective lethality and cost. Various methods of basing of weapon
systems, i.e. ground-based, sea-based or space-based systems, all have their
inherent unique advantages and limitations. (For example, space strike
weapons are currently not possible without reliable and affordable access to
space.)
As we carefully study the characteristics and capabilities of various
candidate weapon systems, it becomes evident that there is no ‘super weapon
system’ that can provide complete defence. A well integrated, layered,
defensive system using different technologies and basing methods depending
on geography, threat perception, envisaged capability and cost analysis is the
only answer.
The overall architecture should have the desired flexibility and adaptability
of integrating future advance technologies, [for example, airborne weapon
system, transatmospheric reusable aerial vehicle (TAV), etc.], new offence
tactics and new offensive weapon counter-capabilities.

111 AIR POWER Journal Vol. 4 No. 1 spring 2009 (January-March)