Further Memorandum from the Ministry of
Following the use by Iraq of ballistic missiles
against coalition forces during the Gulf War, it was realised
that consideration should be given to the means of active defence
of forces in overseas theatres. Active measures also represent
a safeguard against the continuing proliferation of ballistic
missile technology. A Theatre Ballistic Missile Defence (TMBD)
Pre-Feasibility Study was carried out, primarily in industry,
and an unclassified summary of the work was made available in
In 1998, the Strategic Defence Review (SDR)
noted that BMD technologies were changing rapidly, and that it
would be premature to decide on acquiring such a capability. The
UK would, however, monitor developments in the risks posed by
ballistic missiles and in the technology available to counter
The detailed technical assessments undertaken
by the TRRAP drew upon sensitive intelligence material. Clearly
it is in the public interest for there to be a proper appreciation
of the nature of TBMD and the technical challenges it presents.
However, it would be undesirable to proliferate to the designers
of potentially hostile missile systems any information that could
increase the risks faced by UK allied personnel. For this reason,
various points of detail established during the TRRAP have not
1.1 What was the purpose of TRRAP?
As reported to Parliament in 1999,
following the SDR the MoD established a three-year study to:
(i) to monitor developments in the potential
threat and the technologies available to counter it, and
(ii) to establish a position from which a
national requirement for fielding an active Ballistic Missile
Defence (BMD) system could be developed, should one become necessary.
1.2 How did we go about TRRAP?
The TRRAP programme of analysis was led by DERA
with extensive industry participation from Alenia Marconi Systems,
BAe Systems, Hunting Engineering and Matra BAe Dynamics. The work
was completed in August 2001 at a cost of £12.5 million.
The focus of the TRRAP was the Theatre Ballistic
Missile Defence of deployed forces. It did not address defence
of national territory against longer-range ballistic missile threats.
The programme focussed on:
the characteristics of ballistic
the performance of radar and other
the guidance of interceptors, and
their potential to defeat ballistic missile warheads, including
those containing biological or chemical agents.
Supporting activities were broken down into three "Research
Objectives" (ROs) and a further 11 "Technical Areas"
(TAs), as shown in Figure 1. Each TA was jointly led by a DERA
and an industry representative, with funding being equally divided
between DERA and industry. To ensure adequate integration, various
sub-groups were also formed across this structure.
Figure 1: TRRAP ACTIVITIES
Detailed computer modelling and observations
carried out by the technology focused TAs were used in the assessment
of the various systems capabilities in a "one-on-one"
performance context (ie single weapon system engaging a single
threat). The key issues governing one-on-one performance were
derived in three stages:
A detailed understanding of weapon
system capability was derived by examining defended area sensitivity
to those key drivers identified by the sensor and interceptor
focused TAs. This analysis used performance trade-offs between
the weapon system elements to assess the overall system robustness.
Information on the lethality and
post-engagement effects was integrated with the weapon system
performance to provide an "end-to-end" assessment.
Ownership and operational issues
which could affect the weapon system performance were identified,
as a precursor to examining the weapon system performance in the
context of illustrative scenarios.
TRRAP then made use of a Military Advice Panel
through the effectiveness and operational analysis TA. This provided
valuable input to the study in terms of how, when and where a
BMD system is likely to be deployed.
2. THE EMERGING
Ballistic missiles were used against the UK during the Second
World War and have been used in several conflicts over the last
20 years, most notably the Iraqi SCUD-type weapons during the
Gulf War in 1991. Many countries now possess ballistic missile
capabilities, including those shown in Figure 2.
|China||CSS-2, CSS-3, CSS-4, CSS-5, CSS-6, CSS-7
|India||PRITHVI I, PRITHVI II, DHANUSH, AGNI II
|Iran||SCUD-B, SCUD-C, CSS-8, SHAHAB-3
|Iraq||AL SAMOUD, AL HUSSEIN
|Israel||JERICHO 1, JERICHO 2
|North Korea||SCUD-B, SCUD-C, NO-DONG, TAEPO-DONG 1
|Pakistan||HATF-I, HATF-II, CSS-7, SHAHEEN, GHAURI
|Syria||SCUD-B, SCUD-C, SS-21
Figure 2: Countries Operating Ballistic Missiles
TRRAP examined six systems (Fig 3) that were considered representative
of the ballistic missile threat that could be encountered by deployed
UK forces. Various characteristic details were identified for
Figure 3: TRRAP BM Threats
In modelling the threat systems several threat characteristics
were estimated including signatures, payloads, and trajectories.
The nominal trajectory characteristics of these systems are shown
in Figure 4.
Figure 4: Illustrative BM Threat Trajectories
2.1 Technical Evolution of the Threat
The threat definition within the TRRAP aimed to characterise
possible threat systems to the year 2015. This included descriptions
of possible countermeasures that could be engineered by the designers
of potentially hostile BMs. Many countermeasure options were considered
and categorised and a number selected for further analysis. Each
option was assessed by a panel of experts, in terms of the regime
in which the measure would be designed to operate, the availability
of the technology, and the perceived effectiveness against the
defence systems postulated for the TRRAP study.
Current BM threats were assessed to be of relatively low
accuracy, meaning that unitary High Explosive (HE) warheads would
be of limited military utility. It was assessed that improvements
to the guidance system of missiles could increase accuracy and
hence tactical military utility.
For the majority of the threat systems considered in the
TRRAP, various designs of payload that could evolve were assessed:
for example, unitary high explosive and chemical, and chemical
and biological sub-munitions. In each case, the mass characteristics
of the warhead were generated, which allowed an assessment of
the effects of the differing configurations on the trajectory
Detailed assessments of potential threat characteristics
cannot be publicly disclosed for national security reasons.
3. MODELLING BMD SYSTEMS
The main emphasis of the TRRAP was on BMD systems utilising
surface-based interceptors to counter the potential effects of
TBM warheads and payloads. To appreciate the problems involved,
it is necessary to consider a likely engagement sequence. A typical
sequence is set out below.
|THEATRE MISSILE DEFENCE ENGAGEMENT ||
| Engagement commences when the threat is detected by a dedicated sensor, usually an Early Warning (EW) type radar and a space-based radar or infra-red sensor.|
| A cue is passed which will allow the BMD weapon system Fire Control Radar (FCR) to acquire the threat with a minimum of search.|
|The Fire Control Radar initiates a track
| Once a track has been initiated it may be necessary to undertake an identification activity, during which specialised waveforms are used to distinguish between re-entry vehicle (RV) carrying the payload, the booster and any separation debris. Some threats addressed by the TRRAP do not have separating RVs, in which case there should be no such requirement.|
| Once an accurate predicted intercept position (PIP) has been established, which in most cases requires a significant tracking period, the interceptor is launched.|
|Guidance commands are uplinked to the interceptor in-flight
| These are based on additional track data provided by the FCR continuously tracking the threat throughout the engagement process.|
| Finally, the target is impacted by the interceptor. The whole engagement process is "time critical" because the interceptor has to be launched as soon as possible in order to intercept threats at high altitudes and hence achieve optimal defendable areas.|
To assess the feasibility and technical risks associated
with Theatre Ballistic Missile Defence the TRRAP work centred
on two generic types of interceptor system, operating at low and
high altitudes within the earth's atmosphere.
These are referred to as the Low Endo-atmospheric (LENDO) and
High Endo-atmospheric (HENDO) TBMD systems, respectively.
3.1 The Generic Low Altitude Endo-Atmospheric TBMD System
Figure 5 shows a land-based LENDO system, comprising a fire
control radar, an interceptor and launcher and a Tactical Operations
Centre (TOC), in which the engagement process is initiated via
an external early warning derived from either a satellite or a
Ground Based Radar. Typical LENDO engagement altitudes are between
8 km and 24 km, with interceptor times of flight up to 40 seconds.
Typically, this weapon system will engage short and medium range
threats. Against the short-range threats, the LENDO Weapon System
radar could perform limited autonomous surveillance, subject to
a priori knowledge of the likely threat arc.
The LENDO interceptor is controlled by making use of the
forces produced by aerodynamic surfaces. It has a single stage
booster and a sustain motor and utilises a radio frequency seeker.
The generic LENDO radar adopted in the TRRAP was conceptual, based
on multifunction electronically scanned adaptive radar technology.
A LENDO fire-unit would consist of the following items:
RadarAntenna, Generator Unit, Air-conditioning
Unit and Communications Equipment Unit plus generators and prime
LauncherInterceptor Pallet Vehicle
(IPV) with "pallet" containing 10 interceptors, an Engagement
Control Station and a Communications Relay Vehicle plus generators;
Command Control and Communication (C3)
Control Reporting Station and an Antenna/cable vehicle
SupportMaintenance Centre, wrecker/crane,
Field Repair Centre, Fuel Bowser and Recovery Trailer plus generators
and a prime mover.
The complete LENDO Weapon System should be deployable into
theatre using either air or sea lift. Two systems of this type
currently available or in development are the US PAC-3 and the
Figure 5: LENDO Engagement Process[ 10]
3.2 The Generic High Altitude Endo-Atmospheric TBMD System
Figure 6 shows a HENDO system, comprising a long-range fire
control radar, an interceptor and launcher and a TOC, in which
the engagement process is initiated via an external EW cue derived
from a satellite or ground-based radar. The lower intercept altitude
lies between 40 and 50 km, while the maximum intercept altitude
is of the order of 200 km. Typical times of flight are between
50 seconds and 150 seconds, depending on the flyout range to be
covered. Typically, this weapon system will engage medium and
This land-based HENDO interceptor makes use of a separating
Kill Vehicle (KV) to achieve hit-to-kill intercepts. A Divert
Attitude Control System acting via thrusters provides KV control
acceleration. It uses a single stage booster. The separating KV
has an infra-red seeker. The radar's narrow beam width results
in a very limited surveillance capability, so an external cue
is essential to ensure optimum performance.
A HENDO fire-unit would consists of the following items:
RadarAntenna Element, Electronic
Unit, Power Production Unit, Communications Equipment Unit and
Cooling Unit plus generators and prime movers;
LauncherInterceptor Pallet Vehicle
with pallet, a Launcher Control Station and a Communications Relay
Vehicle plus generators;
C3Tactical Operations Centre and
an Antenna/cable vehicle plus generators;
SupportMaintenance Centre, wrecker/crane,
Field Repair Centre, Fuel Bowser and Recovery Trailer plus generators
and a prime mover.
The equipment for the HENDO fire unit is larger than for
the LENDO Fire Unit and this will mean that deployment considerations
are more stressing.
The best-known system of this type is the US Theater High
Altitude Defense System (THAAD), currently in the Engineering,
Manufacture and Development (EMD) phase and not yet deployed as
an operational system.
Figure 6: HENDO Engagement Process
3.3 Other Systems
As well as using land basing, TBM interceptors could be located
on naval and airborne platforms. Some limited analysis was performed
during the TRRAP on systems of this kind. The technology of an
airborne high energy laser operating at high altitude and destroying
BMs early in flight (boost phase) was not assessed.
3.4 Technical Issues
Against this background, the technical issues addressed by
the TRRAP included sensors and discrimination, guidance and control,
seekers and lethality. The study investigated the requirements
and robustness issues for active BMD systems to meet the specified
threats. Various trade-offs between the components of a BMD system
were explored and their interactions appreciated. Such trade-offs
included radar array size, the extent of tasks to be discharged
(eg surveillance, tracking etc) and the performance of various
combinations of guidance techniques and missile agility used in
closing the interceptor on its target. In addition, the performance
and effectiveness of weapon systems against the defined threat
was assessed. An understanding of the sensitivities and links
between the technical issues, system attributes and overall effectiveness
was derived using a fully integrated analysis approach.
Operation of both LENDO and HENDO systems are highly dependent
on the performance of sensors, particularly radars, and their
ability to discriminate between the real target and other objects.
For example, threat BMs may employ a separation mechanism, by
which a re-entry vehicle (RV) is separated from the spent booster
before motors are fired to impart a spin to the RV for stabilisation.
The separation event would probably result in debris objects being
produced that could take up defensive radar resources and have
an adverse effect on system discrimination performance.
As a result of the TRRAP studies it was concluded that surface-based
interceptors employing hit-to-kill are a feasible mechanism to
counter TBM systems and payloads.
In summarising the performance of the generic LENDO and HENDO
systems against the specified threats, the following conclusions
have been drawn:
The generic LENDO system is capable of intercepting
and negating shorter-range BMs armed with unitary warheads (HE,
bulk CW and bulk BW). Different threats will have different "ideal"
intercept altitudes. A worthwhile defended ground area for deployed
force elements would be achievable.
The generic HENDO system is capable of intercepting
and negating longer-range missiles armed with unitary warheads.
The intercept region will lie between 50 km and 150 km altitude
and a larger defended ground area for deployed force elements
would be achievable.
The relative merits of interceptors with either hit-to-kill
vehicles or warheads were considered. A warhead is less demanding
in terms of miss distance but may be less well-suited to destroying
targets containing multiple sub-munitions, if these were to emerge.
In the situations examined by the TRRAP, it was concluded that
hit-to-kill is the preferred option.
The TRRAP recorded a number of the remaining key technical
and system risks. The main points are:
The final stage of threat engagement is very demanding
of radio frequency seeker performance. Alternative seeker technologies
need to be identified and their integration into the interceptor
guidance and control loop should be assessed.
The capability of BMD systems to negate sub-munition
warheads (if these were to emerge) is more difficult to quantify
than for unitary warheads. This is due to the problems associated
in estimating the number of sub-munitions that might survive the
impact. Even after successful interception there may still be
casualties on the ground depending on the altitude of intercept,
sub-munition dispersal, and the type of agent contained.
Timeline studies have shown that, if the threat
missiles employ sensor countermeasures, there is a limited amount
of time available for discrimination. Increased sensor performance
can only go so far in redeeming the situation, as the threat has
a finite time of flight. The discrimination problem is of main
concern for a HENDO intercept region, but cannot be completely
ignored for LENDO intercepts.
Effective support to the planning and co-ordination
activities is important at all levels and stages of a campaign.
The deployment strategy, lay down and tasking processes are all
key to maximising the probability of first time success. The management
of Battle Management, Command, Control, Communication, Computers
and Intelligence (BMC4I) during the deployment process is critical,
as its structure and communications topology is likely to evolve
as deployment proceeds. A particular concern is the need to ensure
timely distribution of intelligence information to the appropriate
planning cells to provide the best possible basis for developing
the deployment strategy and laydown.
Four main technical risk areas have been identified, these
Threat Projection. It was recognised that
the threat will evolve, not only in terms of more advanced technology
to improve, for example, accuracy, but also in response to the
deployment of active BMD systems. It was recommended that further
work on threat projection be conducted, particularly on countermeasures.
Discrimination. The use of threat countermeasures
may result in: an extended RV discrimination period; a delayed
interceptor commit; and an inability to acquire the RV at seeker
handover. In order to collect the necessary data for discrimination,
it is important to ensure that the correct sensor characteristics
are available. A key uncertainty is in predicting what countermeasures
might be used. The system functionality and technical and operational
requirements may alter significantly as the threat complexity
Engagement. Intercepting threats in the
LENDO region requires seekers to operate close to performance
limits. Further examination of seeker characteristics, supported
by hardware demonstration, is required.
Lethality. Any consideration of lethality
in its widest context must be influenced by: interceptor guidance;
miss distance assessment; closing velocity; engagement geometry;
intercept altitude; threat payload definition.
The requirement is to minimise ground effects, usually casualty
levels, either by destroying the BM payload or by deflecting it
away from the intended ground target. The damage caused at impact
was assessed using vulnerability and lethality codes. These codes
seek to approximate the underlying impact physics and therefore
have a margin of error in predicting the size of the damage zone.
For unitary warheads this is not a concern, but in the case of
sub-munitions, if these were to emerge, it is critical, as there
is uncertainty in the number of sub-munitions destroyed. In particular,
even a few surviving sub-munitions containing biological agents
might be capable of causing appreciable casualties on the ground.
Deflecting the payload may, in any case, only transfer the problem
to a different location, which may or may not be a desirable outcome.
The purposes of the TRRAP were:
To monitor developments in the potential threat to deployed
forces and the technologies available to counter it.
There are a number of areas that need to be considered together
when postulating defence against a BM attack. These are active
defence, passive defence, deterrence, counter-force and political
measures. The TRRAP study has concentrated solely on the technology
issues associated with active defence.
By exploring the performance of conceptual BMD systems it
has been shown that ground-based interceptors employing hit-to-kill
are a feasible mechanism to counter Theatre Ballistic Missile
systems. The Key technical risks are the possible evolution in
the sophistication of TBM systems, especially if countermeasures
are introduced; and the lethality against sub-munitions.
Throughout the TRRAP, analysis of the overall system challenges
highlighted the need for a "mission" definition, considered
to be essential in providing a framework for the technical analysis
of active BMD solutions. On completion of TRRAP, most of the techniques
and methodologies are better understood. Where there were "knowledge
gaps", steps have been taken to fill these. The UK is also
in a much stronger position to assess the operation and performance
of active BMD systems, when required.
To establish a position from which a national requirement for
fielding an active theatre BMD system could be developed, should
one become necessary.
TRRAP has greatly improved the techniques and methodologies
available within the UK to evaluate Ballistic Missile Defence
options. The integrated assessment approach adopted by DERA and
the industrial participants is considered to have been extremely
beneficial. It took all the findings from the individual technology
and system areas and combined them into an overall assessment,
demonstrating clearly the capability of an active BMD system.
Such a methodology is essential if the impact of key technical
issues on the overall effectiveness of a system is to be assessed.
The base of understanding that the UK has acquired is integrated
but spread through industry as well as DERA (now Dstl).
The UK is now in a position to participate in the NATO Feasibility
Study and also to take informed judgements on what protection
might be offered to allied forces from any future TBMD system
should such a requirement arise. MoD is continuing to monitor
developments both in the potential threat and in the rapidly evolving
technology available to counter it.
"The UK Ballistic Missile Defence Pre-Feasibility Programme
Report Executive Summary". June 1998. DERA/WX9/6/173/1/3/3/2.0. Back
SDR Supporting Essay 5, paragraph 45. Back
Official Report, 27 July 1999, Column 203W. Back
Source: US DoD, Missile Defense Agency. Back
Source: DERA: The NO-DONG and SHAHAB-3 trajectories are
thought to be similar so the latter is not shown. The NO-DONG
and TAEPO-DONG missiles are longer range than most theatre BMs
but were included as developments in the threat and as useful
for BMD technical evaluation. Back
Interception outside the atmosphere (exo-atmospheric) was regarded
as beyond the scope of TBMD. Back
WAN- the Wide Area Network required to support widely distributed
platforms by the inter-platform communication of threat data.
Defence Science and Technology Laboratory, a MoD agency formed
after DERA PPP in July 2001. Back