Select Committee on Defence Memoranda

Further Memorandum from the Ministry of Defence


  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 1998[4].

  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 them[5].

  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 been reported.

1.1  What was the purpose of TRRAP?

  As reported to Parliament in 1999[6], 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 missiles;

    —  the performance of radar and other sensors; and

    —  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.


  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.


  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.

BelarusSCUD-B, SS-23
BulgariaSCUD-B, SS-23
ChinaCSS-2, CSS-3, CSS-4, CSS-5, CSS-6, CSS-7
Czech RepublicSS-21
KazakhstanSCUD-B, SS-21
South KoreaNHK-1
Saudi ArabiaCSS-2
SlovakiaSS-21, SS-23
SyriaSCUD-B, SCUD-C, SS-21
UkraineSCUD-B, SS-21
YemenSCUD-B, SS-21

Figure 2: Countries Operating Ballistic Missiles[7]

  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 each threat.

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[8]

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 profile.

  Detailed assessments of potential threat characteristics cannot be publicly disclosed for national security reasons.


  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.
—  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.[9] 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:

    —  Radar—Antenna, Generator Unit, Air-conditioning Unit and Communications Equipment Unit plus generators and prime movers;

    —  Launcher—Interceptor 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 plus generators;

    —  Support—Maintenance 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 Franco/Italian SAMP/T.


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 long-range threats.

  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:

    —  Radar—Antenna Element, Electronic Unit, Power Production Unit, Communications Equipment Unit and Cooling Unit plus generators and prime movers;

    —  Launcher—Interceptor Pallet Vehicle with pallet, a Launcher Control Station and a Communications Relay Vehicle plus generators;

    —  C3—Tactical Operations Centre and an Antenna/cable vehicle plus generators;

    —  Support—Maintenance 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 are:

    —  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 increases.

    —  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[11]).

    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.

February 2002

4   "The UK Ballistic Missile Defence Pre-Feasibility Programme Report Executive Summary". June 1998. DERA/WX9/6/173/1/3/3/2.0. Back

5   SDR Supporting Essay 5, paragraph 45. Back

6   Official Report, 27 July 1999, Column 203W. Back

7   Source: US DoD, Missile Defense Agency. Back

8   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

9   Interception outside the atmosphere (exo-atmospheric) was regarded as beyond the scope of TBMD. Back

10   WAN- the Wide Area Network required to support widely distributed platforms by the inter-platform communication of threat data. Back

11   Defence Science and Technology Laboratory, a MoD agency formed after DERA PPP in July 2001. Back

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