SURFACE-TO-SURFACE MISSILES
Columnist IMRAN SHAH details the characteristics.
Introduction
Surface-to-surface missiles have a role of projecting offensive power in the strategic sense. There are two types of surface-to-surface missiles. The first is cruise missiles and other is the ballistic missile. Cruise missile is like an aircraft with wings and a jet propulsion system. Ballistic missile is a missile that does not rely on lift provided by wings and it flies under the action of gravity after the thrust termination. The world’s first cruise missile was V-1 Doodlebug and the first ballistic missile was V-2. Both V-1 and V-2 were made and used by Germany in World War 2. They were relatively inaccurate and were used as terror weapons and had area targets like cities. London was the main target for these new weapons. In WW2, there was no counter to ballistic missiles but British fighters succeeded in intercepting some cruise missiles.
Accuracy of Missiles
Accuracy of missiles is measured by a quantity called Circular Error Probability (CEP). The CEP of a missile is the radius of a circle in which 50 percent of the missiles fired at a target shall impact. A ballistic (or cruise) missile with a conventional high-explosive warhead and a CEP of 1 km would not normally be expected to destroy or disable fixed military targets such as a Command and Control facility or an air base. A ballistic (or cruise) missile with a CEP of 1km would, however, be effective against a soft and area target such as a city. The German V-2 ballistic missiles fired at London between September 1944 and March 1945 had a conventional high-explosive warhead and a very large CEP of some 17km. Yet the 518 V-2s which hit London succeeded in causing thousands of casualties. However, if a ballistic (or cruise) missile has a nuclear, biological, chemical or radiological (NBCR) warhead, the missile can destroy or disable fixed military targets even if it has a large CEP such as 1 km.
Classification by Range
The surface-to-surface missiles are usually classified by their range. But as cruise missiles are generally of short to medium range, therefore this terminology is used mostly for ballistic missiles. The categories used to subdivide ballistic missiles of differing ranges vary from user to user but those used by US Dept of Defence are given below.
SRBM.........................less than 1,100 km.
MRBM............................1,000-2,750 km.
IRBM.............................2,750-5,500 km.
ICBM...................................5,500+ km.
Here SRBM stands for Short Range Ballistic Missile, MRBM stands for Medium Range Ballistic Missiles, IRBM stands for Intermediate Range Ballistic Missile, and ICBM stands for Inter-Continental Ballistic Missile.
Warheads
Warheads fitted on the surface-to-surface missiles can be of conventional, nuclear, biological, chemical or radiological (NBCR) nature. The NBCR warheads are also called “The Devil’s Brews”. The conventional warheads can further be divided into High Explosive (HE), Fragmentation, Fuel Air Explosive (FAE), Earth penetration, Electromagnetic Pulse (EMP), anti-armour, anti-runway and anti-personnel. Earth penetration warheads are used to attack the hardened underground facilities. NBCR weapons come under the category of Weapons of Mass Destruction (WMD). Much has been said and written on nuclear weapons. We shall discuss briefly the chemical and biological weapons.
Chemical weapons release toxic gases or liquids that attack the body’s nerves, blood, skin or lungs. They may produce surface effects such as tears, blistering, or vomiting, or cause loss of nervous control. Chemical attacks can contaminate an area for between several hours and several days, forcing troops to wear highly restrictive protective clothing (reducing their efficiency). Chemical attacks cause widespread panic amongst both civilian and military populations, and their terror effects on civilians are potent.
Biological weapons are hundreds to thousands times more potent than the most lethal chemical agents, meaning that a few kilograms could be used with devastating effect, whereas hundreds or thousands of tons of chemical agents could be required for militarily significant operations. Biological agents contain either living organisms or their derivatives, such as toxins, which cause disease or death. Living organisms can multiply within the living targets to produce their effects, while toxins can’t reproduce themselves. Toxins are generally more lethal, and act relatively quickly causing incapacitation or death within minutes or hours.
Living organisms require incubation period of 24 hours to 6 weeks.
The high stresses, gravitational forces and heat generated by the acceleration and re-entry of ballistic missiles make them a less-than-ideal method of delivering live biological agents. Mounting biological dispersal systems onto cruise missiles may overcome the disadvantages associated with ballistic missile delivery systems. Biological warheads can be used to disable a large ship such as an aircraft carrier that can
withstand several conventional hits. An attack on the ship would contaminate the ship and crew, reducing or destroying its operational efficiency.
Launch Platforms
Both ballistic and cruise missiles can be launched by a number of platforms. Ballistic missiles can be launched from Silos, mobile launch vehicles, railway system, and submarines. Cruise missiles can be launched from aircraft, ships, submarines, and missile launchers on the ground. Cruise missiles that are launched from the ground and ships need booster rockets for take-off and those from aircraft do not need boosters.
Silos are the underground vertical launch stations, built mostly for Inter-Continental Ballistic Missiles (ICBMs). Silos have steel doors and complete control room deep underground.
Other vehicles associated with mobile ballistic missile launcher are command and control vehicle, meteorological vehicle, site-surveying vehicle, missile transport vehicle, warhead transport vehicle, maintenance vehicle and mobile missile test vehicle. The mobile launchers should be capable of driving over rough terrain and for the short-range missiles the launcher should preferably be amphibious.
Cruise Missiles
As the strategic nuclear competition enters an environment of increasingly effective ballistic missile defence, the importance of aerodynamic attack systems shall increase. Cruise missile is one of these aerodynamic attack systems. A study of recent conflicts shows that US used its Tomahawk cruise missiles for attacking land targets with high precision. After World War II, ballistic missiles have not been used
much but played a role in maintaining balance of power among nations.
A cruise missile can provide surgical strike, if equipped with some sort of terminal guidance system. Just Inertial Navigation will be unable to provide the necessary high accuracy because of drift that comes with time in IN-armed missiles. Today, GPS is being used to improve the accuracy of guided weapons. GPS is controlled by USA and it can thus introduce more error (still there is some error) in this system and they can also shut it down. Moreover, GPS is also prone to jamming efforts. A solution to this can be the adoption of GLONASS (Global Navigation Satellite System) system, which is the Russian equivalent of GPS. If signals from both of these are used, then the error can be minimized.
The other solution can be the installation of some kind of terminal guidance system like the DSMAC (Digital Scene Matching and Area Correlation) system used on BGM-109 Tomahawk. Further Laser Ring Gyroscopes or Fibre-Optic gyroscopes should replace the spinning wheel mechanical gyroscopes used in navigation systems for more accuracy. A cruise missile needs booster (which is always of solid fuel) for initial take-off but if the
cruise missile is launched from the aircraft, like USAF AGM-86 ALCM (Air-Launched Cruise Missile), then there is no need of booster. Cruise missiles can be launched from ground, ships and aircraft and thus are best suited for forward deployment and can be used against a variety of targets. Cruise missiles can fly low to avoid radar detection, can adopt defensive routing to avoid air defences, can be launched from aircraft and can give best accuracy if equipped with terminal guidance system. They can fly at different altitudes. They can fly low to avoid air defence systems and if there is no threat, can fly at medium altitude to conserve fuel.
Intercepting a cruise missile is not easy. Foremost is the fact that the cruise missile is small – much smaller than a fighter aircraft. It travels fairly fast and at very low level, where ground returns can seriously affect air intercept radars. Its RCS can be extremely small – 0.1m2 being considered achievable by today’s generation of missiles. Even an AWACS, with its much larger radar, would be able to detect a cruise missile of 0.1m2 RCS at only 50 NM.1
Today, we have satellite imagery of good resolution (0.5 m is a good resolution), which is necessary for providing digital maps to the cruise missiles. Stealthy cruise missiles also have been produced. AGM-129 is a stealth cruise missile with much reduced RCS (Radar Cross Section). This reduced RCS makes it very difficult to be detected on radar and thus engaged for interception. The nose-profile of AGM-86 ALCM (Air-Launched Cruise Missile) of USAF was re-designed to reduce its RCS. The infrared signature of cruise missile is also less because of use of turbojets or turbofans instead of rocket motor. If turbofan is used then its IR signature can be further reduced because of high-bypass ratio of turbofan engine.
SBIR (Space-Based InfraRed) satellites are used by USA for surveillance of ballistic missiles. SBIR (high) is used to detect the launch of a ballistic missile by its exhaust plume and then track it by SBIR (low). This system takes two minutes to report the location of a ballistic missile launcher and then this information is passed on to the nearest allied fighters, which can attack these sites. Thus the ballistic missile launcher
should change its position soon after the missile launch. This will not be a serious concern
for cruise missiles because of their lower IR signature. The Microturbo (now owned by Snecma of France) and Williams International of US are dedicated for designing small gas turbine engines for cruise missiles and UAVs.
Ballistic Missiles
For ranges more than 2,500 km, ballistic missiles are preferred because the time taken by a cruise missile will become too much due to low-speed of present cruise missile as compared to a ballistic missile. However, in future we may see hypersonic cruise missiles with scramjet power plants. The advantage of ballistic missile is that it offers greater range and more speed than present cruise missiles. A ballistic missile can carry a given payload to its target in shortest possible time.
Ballistic missiles are excellent weapons for nuclear deterrence. But the greatly increased accuracy now attainable from the ballistic missile not only increases its potency as a nuclear delivery vehicle, but also opens up some extremely interesting possibilities in the conventional field. Given accuracies of within about 30m, the technology now available in the design and construction of conventional warheads brings a whole range of targets, strategic and tactical, into the view of the conventional force planner.2 But the growing defence against the ballistic missiles is a matter of concern. The trajectory of a ballistic missile makes it very vulnerable to defences. The 1st successful interception of ballistic missiles was demonstrated during Operation Desert Storm (1991), in which 45 Iraqi Scuds were intercepted by Raytheon MIM-104 Patriot SAM system.
The Strategy
We must also set the strategy for using our ballistic missiles. During the war, the mobile missile launchers will be a high priority for both the air forces of India and Pakistan. Therefore, the air defence element for the mobile missile launchers should also be taken into consideration. Each caravan of mobile missile launchers of four to five vehicles should be protected at least by a SPAAG (Self-Propelled Anti-Aircraft Gun) system and possibly a SHORAD (Short-Range Air Defence) missile system. The number of ballistic missiles that are to be fired against a target should also be worked out. It shall depend upon the importance, size and defences of the target.
As Pakistan Air Force has no air-to-air refuelling capacity, therefore all those targets fall within the domain of ballistic missile force that are out of range of PAF fighter jets. The strike radius of PAF fighters with some payload is up to 600km inside India, so targets that are at a distance of more than 600kms are the main targets for the ballistic missile force of Pakistan. For conventional strikes, the CEP (Circular Error Probable) of these 600+ Km range missiles should not be more than 100 metres.
Ballistic missiles of range less than 600km should be used if the target is heavily defended and difficult for the air force to destroy it without heavy losses or there is no air support available from the air force at some particular time. Ballistic missile attacks can also be used in conjunction with air force strikes with proper planning. Air force strike formation should reach the target area shortly after the missile strike. If fragmentation or sub munitions are used in warhead, then they can wipe out some of the air defences of the target like an air base.
Conventional ballistic missiles strikes in the area where PAF can also operate should be coordinated with the PAF. Missile strikes should not coincide with air force strikes. Like the air force, which carries out regular BDA (Battle Damage Assessment) of its strike missions, BDA missions should also be designed for missile strikes. These missions can be carried out either by UAVs or by air force recce missions.
During the Iran-Iraq war, both sides used ballistic missiles in the war of cities, with no significant gains.
Accuracy Matters
A small weapon, delivered accurately, can have the same effect as a much larger weapon delivered less accurately. If the accuracy of delivery can be increased by a factor of two, the yield of a warhead can be reduced by a factor of ten.4 If the CEP of a missile is not good, then it can only be used against enemy population centres as a terror weapon with no significant military gains. A ballistic missile having a
CEP of almost 100 metres can be used against bridges, command and control centres and other strategic and tactical military targets.
Many factors are responsible for inducing error in the missile impact. These include mis-alignment of the accelerometer or inertial platform error, incorrect assessment of wind velocity on re-entry, inaccurate assumptions of air density and geophysical conditions above and around target area and algorithmic errors in missile computer programming.5
The CEP of a ballistic missile can be decreased substantially by incorporating a terminal guidance system, which starts to operate after the re-entry. The common method of terminal guidance is the radar comparison terminal homing system. This type of terminal guidance was used in US Army Pershing-2 IRBM, called RADAG (Radar Area Guidance).
RADAG gave Pershing-2 a CEP of 50 metres. In such a system, the onboard radar takes a look at the terrain around the target point during terminal phase and compares this digital radar picture with one stored in its memory and makes necessary adjustments in its trajectory by matching both pictures. This radar shall not need much power because it shall be operated just to take a snapshot of the theoretical target point. The SS-23 Spider ballistic missile of Russia also employs active radar homing, giving it a CEP of 30 metres. The SS-23 has a maximum range of 500 km and a minimum range of 50 km.6
Anti-Missile Defences
The strategy of employing ballistic missiles should take into account the effect of anti-missile defences. If the ballistic missile attack is based on air force attack style, then it will be able to penetrate defences. Air force strike formations first tries to neutralize enemy air defences and then other targets. Some special jamming or EMP (Electro-Magnetic Pulse) warheads should be developed to disrupt the fire control radars of the
missile defence systems.
An EMP-armed missile should be followed after 2-3 seconds by two or three other conventional ballistic missiles. Other solution is that a missile should also carry some jamming or EMP payload, which will be activated after the re-entry phase. Another technique to penetrate ballistic missile defences is to use very high-speed missiles. High speed is especially required in re-entry phase, when it is intercepted.
Most anti-ballistic missiles systems intercept missiles in the terminal phase, so we require high speed in the terminal phase. This can be achieved by fitting a solid rocket motor in the Re-Entry Body that starts operating after the re-entry and imparts the missiles a speed of up to mach 10. The US Army Pershing-2 IRBM had a re-entry speed of mach 8.
An alternative or complementary to the high-speed can be manoeuvrability in the terminal phase. The Russian SS-21 SRBM has the capability to make pre-programmed manoeuvres during the terminal phase of the flight to make interception more difficult. Today, long-range SAMs are being modified to improve their capability of engaging the short-to-medium range ballistic missiles. Some surface-to-air missiles are being solely
designed as dedicated anti-ballistic missile defence systems like Arrow 2 of Israel.
In response to this, the ballistic missiles should also be modified accordingly. The installation of decoy system in ballistic missiles has become necessary. If a strategic asset is defended by anti-ballistic missile defence system, then it defences should be saturated by launching more missiles than its fire control radar can handle. Dummy warheads can also be installed to make the job of defences more difficult.
But if the decoys or dummy warheads are ejected after the re-entry, then their IR signature will be different than that of actual warhead. An Imaging IR sensor in an interceptor missile will be able to distinguish between dummy warhead and actual one because actual one has gone through extreme heating during re-entry.
If both actual and dummy warheads are ejected at the same time from the RV, then both warheads shall represent the same IR signature. But conventionally, warhead remains the part of RV till impact. Both chaff and flare decoys should be carried within the re-entry body to fool the dual-seeker anti-ballistic missiles. The time at which the chaff and flare payloads are to be released should be optimized. These decoys should be used only if some radar has locked on the missile. This can be monitored by fitting a Radar Warning Receiver (RWR) in the RV (Re-entry Vehicle).
The threat library of this RWR will include the frequencies of only those radars that are a part of an ABM (Anti-Ballistic Missile) system. The RWR shall identify the threat and the electronic system shall control the release of decoys. Moreover, if a system is there in the ballistic missile, which separates the Attitude Correction Mechanism (ACM) from the warhead, then the ABM system shall have an extra target to worry about. The separation of ACM is more suitable for medium and intermediate range ballistic missiles. Multiple warheads or multiple re-entry vehicles should be incorporated in the intermediate to long-range ballistic missiles and all separated after re-entry to represent same IR signature.
For a more realistic evaluation of a ballistic missile or missiles, a few missile tests can be conducted in the presence of an ABM system. This ABM system in our case should be the Russian S-300 system, which India has acquired. These tests shall demonstrate the ability and limitations of such anti-missile system and the modifications required in the hardware and trajectory software of the ballistic missiles. Another useful feature, used mostly with ICBMs, is Multiple Independently Targeted Re-entry Vehicles (MIRVs). MIRV-capable ballistic missiles are very difficult to counter because ABM system has to counter many RVs. The US MIRV-capable Trident D-5 ICBM carries eight MIRVs. These MIRVs are carried in the Post-Boost Vehicle (PBV). The third stage of the motor is usually attached to the PBV. The US Peacekeeper ICBM carries ten Advanced Ballistic Re-Entry Vehicles (ABRVs).7
The next stage in the sophisticated warhead design after the MIRVs is the MARVs, which stands for Manoeuvrable Re-entry Vehicles. A MIRVed missile can deliver several warheads against separate targets and after ejection from the missile they follow predetermined and predictable courses. A MARVed missile, on the other hand, would eject as many warheads, each also destined for a separate pre-selected target, but which would follow a variable and changing course, making them much harder for ballistic missile defences to destroy.
Second Strike Capability
It is the ability to survive a first nuclear strike with sufficient resources to deliver an effective counterblow. The strategic nuclear policy should be to maintain a deterrent second strike capability; that is to maintain nuclear forces in such numbers and variety that no first strike could prevent a retaliatory strike that would inflict unacceptable damage to the aggressor. Second strike capability can be achieved by diversifying the delivery means of nuclear weapons. Land-based ballistic missiles usually provide the first strike capability. Submarine-Launched Ballistic Missiles and bomber aircraft can provide second strike
capability.
References
1,2,4,5-“Strategic Offensive Air Operations” by Air Chief Marshal Sir Michael Knight.
3-www.cdiss.org (Lancaster University)
6-,7-Jane’s Strategic Weapons, 2001.
8-“Security Implications of the SDI”, edited by Jeffrey Simon.
9-Dictionary of Military Science published by Facts on File.
No comments:
Post a Comment