MISSILES OF इंडिया, PART-1

PRITHVI MISSILE (पृथ्वी मिस्सिले)

The Prithvi (Earth) is a single stage, dual engine, liquid fuel (red fuming nitric acid as an oxidiser, with a 50/50 mix of xylidiene and triethylamine as fuel), road-mobile, short-range ballistic missile which began design in 1983 and was first tested in 1988. The missile has a length of 9 metres, a diameter of 1.1 metres and a weight of 4000 kg. It has a unique appearance, with four delta-shaped wings midway down the fuselage. The missile’s volatile liquid fuel launch mode must be loaded immediately prior to launch, which might prove to be a disadvantage in the field. However liquid fuel gives better accuracy and the missile crews who operate them undergo intense training in three general phases; missile sub-system, handling & maintenance. An advanced simulator has been developed to train the missile crews in it’s operation. Liquid fuel also provides the capability, for in-flight manoeuvring; the missile is capable of being manoeuvred up to 15º in flight.

Prithvi has a distinctive design, using a particular gyro system with a uniquely configured software. When the flight is in progress, the drift can be monitored through the on-board computer. It has other innovations as well; the type of thrust termination is so innovatively configured that for a multiple payload, multiple ranges can be achieved. The strap-down inertial guidance system has a twin microprocessor-based computer integrated with interrupt-driven, real time software. Its navigation system guides it to the target within a CEP (Circular Error Probable) equal to .01% of its range. During one test, the missile reportedly achieved a high accuracy rate, which suggests that guidance system may include the capability of feeding GPS inputs into its inertial navigation system.

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Test flight of the Prithvi SS-250
Some of Prithvi’s warheads

Initially two variants were developed at DRDO, one for the Army and the other for the Air Force, but presently the SS-250 is only variant being produced at Bharat Dynamics Limited (BDL), Hyderabad. The Army version, designated as the SS-150 had a range of 150 km and could carry up to a maximum of a 1000 kg as its payload. The Air Force version, designated as the SS-250 had a range of 250 km and could carry up to a maximum of a 500 kg as its payload. By using boosted liquid propellant to generate more thrust-to-weight ratio, DRDO has increased the payload of the SS-250 to 1000 kg. The Prithvi reportedly has the highest warhead-weight to overall-weight of any missile in its class.

The missile can carry a variety of conventional warheads such as pre-fragmented explosives, bomblets, incendiary, cluster munitions, sub-munitions, fuel-air explosives and high-explosives. The nuclear tests conducted in May 1998 proved that miniaturized nuclear warheads of various yields can also be fitted and Dr. APJ Abdul Kalam, the then-incumbent Scientific Advisor to the Government and DRDO Chief, stated that a few days after the Shakti-98 n-tests. However, after the Agni-I MRBM test in January 2002, K. Santhanam - former RAW officer, DRDO technical advisor, nuclear scientist and presently IDSA Director - stated that the Prithvi missile was never meant to carry nuclear warheads under normal circumstances. This indicates that the solid-fuelled Agni has completely taken over the ‘nuclear’ role from the liquid-fuelled Prithvi.

The missile is strengthened against ABM defences with a guidance system that can be programmed to follow up to six different trajectories so as to avoid interception. Another defence the missile has, is the application of a special type of radar absorbing paint to reduce radar signature. For field operations, the missile will be transported on an all-terrain, eight wheel Kolos Tatra 4×4 truck. The missile is deployed from the vehicle and fired from a simple launcher. Each battery of four Prithvi carrier vehicles will be accompanied by a missile re-supply & loading vehicle, a propellant tanker and also a command post to provide target data to the missile’s guidance system before launch. It also has an integrated surveillance & mission support capability and other support vehicles & equipment.

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The Prithvi’s support vehicles
Prithvi SS-150 at the Republic Day

By October 1995, 20 pre-production Prithvi SS-150s were delivered to the Army to form the 333rd Missile Group based in Secunderabad. Two more have been formed since, 444 and 555. The former has been raised and trained and should receive its equipment soon, while the latter exists only on paper and is yet to be raised. Each group will have 12 launchers, with possibly another three more acting as reserves. Around 120 Prithvis (both variants) have been produced to date, at BDL, with 40-50% of them being the SS-250 and is now the only production version at BDL. Various technical tests of the SS-250 variant have been carried out and a recent one on 31 March 2001, reportedly carried multiple payloads over 250 km and was solid-fuelled. On 18 April 2001 in Parliament, then-incumbent Defence Minister Jaswant Singh stated that the SS-250 was being inducted into the IAF, but apparently the IAF plans to use it only for familiarisation training.

The last Prithvi test occurred on 12 December 2001 and was reportedly liquid-fuelled. The test was flawless and the missile impacted at the intended target point accurately. This Prithvi was provided with a homing facility and was a more advanced version than the one tested in March 2001. Significantly in December 1998, the Army deployed the SS-150 in a major military exercise for the first time since its induction. Code-named Shiv-Shakti, the military exercise signified that the Prithvi had been further inducted into the military doctrine. If the missile is deployed in states like Kashmir, Punjab and Gujrat which border Pakistan, it would place the cities of Islamabad, Lahore, Karachi, Hyderabad and many of Pakistan’s strategic military installations within its range. An unspecified number of Prithvis are rumoured to be based near Jalandhar, northern Punjab, for use as a tactical battlefield missile against Pakistan.

AGNI I (अग्नि प्रथम)

The Agni-I (Fire) is a 15-metre tall, 12-ton, single-stage, solid-fuelled, medium range ballistic missile. The missile is smaller than its big brother - the Agni-II IRBM - in dimensions and range, but can still carry a one ton nuclear payload to most targets in Pakistan without having to be deployed at the borders. The core and triggers can be swiftly assembled by BARC (Bhaba Atomic Research Centre) and DRDO (Defense Research & Development Organisation) - within India’s avowed no-first-use paradigm. Agni-I is also designed to be launched from a rail-based mobile launcher; one that can move on a standard broad-gauge rail system and also from a road-mobile launcher system. DRDO’s Ahmednagar-based VRDE (Vehicle Research & Development Establishment) and the Pune-based R&DE (Research & Development Engineers) played important roles in validating the tractor-cum-transporter-cum-launcher. A mobile missile system reduces vulnerability and allows for greater operational flexibility, while critics feel that the cost of these mobile systems could be higher and that they greatly increase the time for moving from one place to another.

DRDO’s Chief Controller of R&D (Missiles), Dr. A.S. Pillai, stated that Agni-I incorporates new guidance & control systems and there was also significant improvements in its re-entry technology and manoeuvrability. With only one stage, the weight is less but the thrust is the same, giving the missile more acceleration. As to it’s name of Agni-I, Dr. Pillai said it was christened so because it had a shorter range. When DRDO started the Agni project, it was part of the Integrated Guided Missile Development Program (IGMDP) and the first flight was intended as a technology demonstrator. After its successful completion, the Agni-II program was taken up. Since the range of the new missile lay between that of Prithvi-II and Agni-II, it was called Agni-I. The series is now called Agni, Agni-II and Agni-I, according to Dr. Pillai.

The requirements for the shorter range were met with some modifications to the Agni-II and instead of developing a new missile from scratch, DRDO decided to scale down the Agni-II, which has two solid stages. It used only the first stage and thus range has been reduced. Test and evaluation assumed more importance in the design of the missile, in concept validation and in terms of proving the systems for production of the missile. The first test, from a road-mobile launcher, was conducted on 25 January 2002 to a range of 700 km and was termed an accurate and successful flight which met its mission objectives. Additional tests may not be required, as the re-entry vehicle has been rigorously tested in its previous flights over all dynamic parameters, and the system may already be cleared for operational use. This strategic missile will join the Army and reportedly a Agni missile regiment is being raised for the purpose.

The Agni-I (photos left and right) mounted on a road-based mobile tractor-cum-transporter-cum-launcher. The diagram (above) shows the range of the Agni-I against Pakistan, at ranges of 700 km, 860 km and 1200 km. Being road and/or rail mobile, the missile won’t be prone to pre-emptive strikes and solid fuel ensures a quick and safe launch. All these combine to ensure a sound second strike capability.

During the test, the Agni-I missile was launched at a sub-optimal trajectory to reach an altitude of 300 km on a range of 700 km, corresponding to launch angle of 67º. The missile re-entered the atmosphere and splashed down in the Bay of Bengal. For the optimal 45º launch angle, the maximum altitude would be ~185 km and travel a range of 860 km in about seven minutes. With a special weapons load, Agni-I can reach 1200 km. The Agni-I MRBM missile has following operational superiority as compared to the Agni-II IRBM:

1. Lower cost: of unit procurement, ancillary support (trucks & storage building), maintenance and deployment (upgrading bridge, rail-stock).
2. Simplicity of single stage rocket: higher mission reliability improved safety, handling, operation, training & up-time (% time ready to be used).
3. More mobile: Easier & flexible deployment options.
4. More accurate (as compared to two-stage missile, i.e. Agni-II): higher effectiveness.
5. Stealth features: Smaller less conspicuous main and support vehicles, and a stealthy re-entry vehicle (RV) - which is very difficult to detect and defeat by a first generation ABM system - makes it an effective second strike weapon.

New Data Points & Technical Aspects:

1. Unlike the Agni-II, the RV of Agni-I does not have fins, indicating use of a new method for RV manoeuvring.
2. The re-entry velocity is significantly lesser than the Agni-II and thus there is more room for terminal manoeuvrability, or conversely for original degree of manoeuvrability albeit with a heavier payload.
3. The shorter-range missile does not require additional velocity from RV-thrusters, saving fuel space & weight for additional electronic gear, decoy or bigger payload.
4. The single-stage Agni-I with 12 ton GLOW (Gross Launch Overall Weight), is estimated to have combined RV & Payload weight of 2T, which appears heavier than the Agni-II. This may be useful for additional avionics, decoys or a heavier conventional payload.

Performance Aspects:

a) Given the strategic role of Agni-I, lack of fins on the RV and from item 2 above, the missile RV-body has greater terminal flight control envelop for better overall accuracy, not to mention additional improvement due to better navigational accuracy at shorter ranges.
b) From items 1 & 4 above, the Agni-I likely has a RV thruster for re-entry control and terminal steering, enabling a wider flight control envelope for better accuracy.
c) From item 1 above, the Agni-I is expected to have a smaller RCS signature, which makes detection by radar even more difficult.

Strategic Aspects of Agni-I Evolution:

On political aspects, the decision to develop Agni-I was the result of a discussion on the need to have a intermediary range missile between the short range Prithvi-II (250 km) and the longer range Agni-II (2500 km). The discussion was initiated in June 1999 at the height of the Kargil imbroglio. The concern was that advanced deployment of the Prithvi could be misinterpreted as lowering the nuclear threshold. Yet press reports after the crisis was resolved, indicated that four Prithvis and one Agni were activated. Obviously the misinterpretation would not have happened if sufficient Agni missiles were around for the task or these were tasked for other targets. Also there is the question of minimum range for the Agni which precluded more of them being tasked as a result of the Kargil crisis. Hence the need for the intermediary missile.

Soon after in late June 1999, Prime Minister Nawaz Sharif went to Washington D.C. and agreed to withdraw Pakistani troops from the heights of Kargil. The decision was taken in October 1999, which is a full three months after the discussion was initiated. This period must have been spent in trade studies to determine the feasibility of designing such an intermediary missile. K. Santhanam in an interview to ‘Times of India’ stated that it took 15 months to develop the missile and its road-mobile launcher. This indicates Agni-I development was over by December 2000. News reports indicate that the missile was ready for testing in December 2001 but was postponed twice to ease tensions. Either this was a development flight to qualify the missile or was done to proof the batch by confirmatory testing. It could be the latter as a statement by DRDO after this test, suggested speedy deployment in the armed forces.

On technical aspects, Agni-I design is said to have used existing sub-assemblies of the Agni-II vehicle with modifications. In addition the closed loop guidance scheme for the missile trajectory was worked out. Some of the airframe and sub-assemblies were reworked due to the higher boost phase accelerations for this intermediary missile compared to the Agni-II. This is true for the RV on Agni-I, since it will see much higher accelerations due to the reduced overall mass of the vehicle. We can infer that the RV has been qualified now for higher accelerations than on the Agni-II and this has implications for the planned longer-range missiles (Agni-III). It has been stated that Agni-III is in development and is rail-mobile as opposed to road-mobile and has a range of 3500 - 4000 km and its first test may occur in late 2003. Experts have commented on the reactive nature of the Indian system in developing this missile. However the IGMP was successful due to its close interaction with the armed forces and the fact that the low range of the Prithvi could be viewed as de-stabilizing is an indication of the cursory nature of strategic assessment by various interests - DRDO and the armed forces.

Since arms control issues were involved it would be interesting to find out the involvement of the MEA experts in this matter. Another issue to pick a bone with is the reason for the Prithivi program. From “Wings of Fire” (by Dr. APJ Abdul Kalam) it is clear that the project was implemented as a morale booster for disheartened scientists in DRDL who had worked on a previous program named Devil. And after the first flights it developed its own constituency. It is a sorry state of affairs when a weapons system implemented as a morale booster, ended up creating heartburn about lowering the nuclear threshold. Someone higher up should have stepped in long ago and come up with a less destabilizing system. It only goes to show that special weapons are complex systems and have deeper ramifications that have to be understood before proceeding.

Summary:

1. India has an intermediary range missile which can be deployed far away from pre-emptive strike zones and could be activated without lowering the nuclear threshold. It is based on a solid fuel vehicle, which reduces the time factor for assured retaliation. Thus it enhances the credibility of the deterrent.
2. India has an RV and sub-assemblies that have been qualified for higher accelerations than the Agni-II vehicle. This implies these can be used on longer range vehicles as needed.
3. Agni-I is very accurate as it uses the Agni-II guidance sub-systems over shorter range, and better RV configuration for extended flight control envelope.
4. The Indian system can and does react in a quick manner to immediate threats. It has to strengthen its review process and ensure participation of all stakeholders.

AGNI II

The Agni (Fire) is an Intermediate Range Ballistic Missile which had begun development in 1979. It became part of India’s Integrated Guided Missile Development Program (IGMDP) in 1983. The first Agni test occurred on 22 May 1989, and two more tests were conducted on 29 May 1992 and 19 February 1994. These tests were technology test-beds (TTBs) for developing vehicle structure, integration, navigation and control, flight dynamics and re-entry vehicle technology. The TTBs achieved a maximum range of 1500 km, however the main drawback was the missile’s solid-liquid propulsion configuration, which seemed unsuitable for an operational IRBM. Thus the Agni-II was developed, which had a length of 20 metres, a diameter of 1.3 metres and weighs 16 tonnes, and is an improvement over its predecessor which had a length of 21 metres and weighed 19 tonnes.

The first prototype of an operational variant, the Agni-II, was tested on 11 April 1999 at 9:47 a.m. IST (Indian Standard Time). The missile was tested to a range of ~2100 km, taking 11 minutes to reach target and was a perfect textbook launch. This first test of Agni-II occurred exactly 11 months after India’s nuclear tests on 11 May 1998. A second Agni-II test occurred on 17 January 2001 at 10:01 a.m. IST (Indian Standard Time) and was tested to a range greater than 2100 km. After the second test, Agni’s Program Director - Professor P.N. Aggarwal - said, “The flight test results have indicated that mission objectives were met satisfactorily.” Although this was the second Agni-II test, it was for the first time that the missile was test-fired in its final configuration. Reportedly, the focus of the test was to observe the accuracy at an increased range. An official, connected with the Agni-II program said, “The re-entry control and guidance technology have already been tested, but accuracy at increased ranges was to be tested.” A maximum range of 3000 km can be achieved, using specific payloads.

Test flight of the Agni TTB

Test flight of the Agni-II

Both stages of the Agni-II have a solid propulsion system, which allows the missile to be mobile and flexible. This was confirmed, as the test which was conducted on 11 April 1999, was a rail-based missile launcher. The solid-fuel motor in the first stage of Agni-II, is similar to the first stage in the technology test-bed, itself based on the SLV-3 Space Launch Vehicle. However the solid-fuel motor in the second stage of Agni-II, has been reportedly designed anew for the missile. For manoeuvrability and thrust control, the second stage has a flex nozzle which enables small changes in the thrust vector direction in flight. The flex nozzle can be exploited with the help of an on-board closed-loop guidance & control system. Till now, the flex nozzle has been used only in the third-stage motor of the PSLV. At a range of 2000+ km, Agni-II has an apogee (the farthest point from earth) of 405 km, a re-entry speed of 3.9 km/second and a boost phase of 110 seconds. The re-entry vehicle uses its manoeuvring fins to porpoise the warhead, to avoid missile defenses while manoeuvring to its target, employing a terminal guidance radar operating in the C- and S-bands.

The then-incumbent Scientific Advisor to the Government and DRDO Chief, Dr. Abdul Kalam, has said that what is unique about the Agni-II is the trajectory shaping and guidance that is possible through software. Agni-II, has appropriate on-board thrusters fitted on the second stage of the missile. This is because solid fuel is allowed to burn completely, which means that the velocity increment achieved before re-entry could be more or less from the mission perspective. Further, there is considerable dispersion or variation in the burn and thrust time of solid fuels. Any compensation that is given to the missile during its ballistic phase (which happens once the second stage is fully burnt out) should be based on the on-board sensor data and should be amenable to being adjusted reactively. These on-board thrusters are driven by liquid-fuel and provide small increments in the appropriate directions to shape the trajectory depending upon the target of the mission. It is these thrusters that give the manoeuvrability during the missile’s re-entry phase. This has apparently been optimised through on-board software which, based on the initial trajectory fed in, does an appropriate velocity trimming. In effect this is a hot gas active velocity correction system.

Agni-II, on a road-mobile launcher, at the 1999 and 2000 Republic Day Parades

Agni’s Project Director, Avinash Chander, said the effort to operationalise the missile system was complex, as it involved reducing the host of computer’s processing information, both inside the missile and ground control systems, to a single control system. To ensure greater reliability of the missile, they reduced the mass of over 600 different sets of communications channels, involving 24 km of cabling, to just 10 pairs requiring one-eighth of the original wiring. A new concept has been adopted for the on-board navigation system, which is the 1553 Data Bus. It is the standard that is adopted in civilian aircraft (circuit routing and device mounting) and all the software in the Agni-II has been designed around this bus. DRDO sources claim that this reduces the number of connectivities and also making the missile a little more rugged. However, certain missile analysts feel that a standard bus may not be the best path to follow. They say that a customised bus is better because in a standard bus, one tends to use off-the-shelf electronic devices whose performance may not be optimal. However most modern missiles are moving towards digital buses using commercial off-the-shelf technology and which enables affordable sub-system replacement. A customized bus would lead to more delays and increased costs which should be avoided to prevent needless expenditure.

Another major feature in terms of operational configuration is that Agni-II is designed to be launched from a rail-mobile launcher; one that can move on a standard broad-gauge rail system. The technology test-beds, however, had been designed as a road-mobile system. There are pluses and minuses to this change. A rail- and/or road-based missile system reduces vulnerability and allows for greater operational flexibility, while critics feel that the cost of these mobile systems could be higher and that they greatly increase the time for moving from one place to another. Considering that except in some parts - for instance, India’s north-eastern region - road infrastructure is available wherever rail tracks are available, the decision to become rail-mobile could mean, in strategic terms, that deployment in India’s north-eastern region is to be considered a serious possibility. Assuming that Agni-II is to be deployed in India’s north-eastern region and even given a 2,000+ km range, Agni-II can still not reach vast parts of China - including Beijing, which is over 3000 km away. Therefore, a longer-range Agni variant may well be required if the need for a deterrent against China is being seriously felt.

Agni-II’s various flight stages

Agni-II on the launch pad

While a new and longer-range system can certainly be developed if the Services require it, the present configuration is in operational mode, says Dr. Kalam. Range, he adds, could be optimised by appropriately configuring the payload mass. According to him, a road mobile version would also be available and it would be then left to the Services to choose according to their operational convenience. He also says that additional tests are not needed to operationalise the Agni-II. This indicates that the re-entry vehicle has been rigorously tested in its previous flights over all the dynamic parameters and is qualified. If inducted, Agni-II will reportedly always be in a ready-to-fire mode and can be launched within 15 minutes as compared to almost half a day of preparation for the technology test-beds. A longer-range version, designated Agni-III, is being planned and K. Santhanam - former RAW officer, DRDO technical advisor, nuclear scientist and presently IDSA Director - stated that Agni-III is indeed in the developmental stage. The missile will be rail-mobile, with a range of 3,500 - 4,000 km and a first test may occur in 2003.

Reports of the missile having a GPS (Global Positioning System) is not true, as Dr. Kalam has said, and adding that it depends on several external influencing factors and this would make the system vulnerable to external interference. However, many tactical missiles the world over do use GPS systems. DRDO officials say that the use of GPS had been considered for Agni-II at some point of time. It is possible that, GPS augmented mode could be used for conventional versions to increase accuracy. A Japanese newspaper report stated that Agni-II achieved a Circular Error Probable of 40 metres. This however, has yet to be confirmed from reliable sources. If true, it certainly is an improvement since the technology test-beds reportedly had a CEP of ±100 metres. DRDO’s Chief Controller of R&D (Missiles), Dr. A.S. Pillai, stated after the Agni-II test, “We have improved accuracy by a factor of at least three. It is a far more lethal missile now.” He also said that the missile would have a unique on-board energy management system and an on-flight guidance process using navigational sensor technology.

The rail-mobile Agni-II being wheeled out of a hangar
The road mobile Agni-II in front of India Gate at New Delhi

Dr. Kalam, said that the complete re-entry hypersonic flow was simulated in the Computational Fluid Dynamics, on a super-computer. Import content in the Agni-II is less than 10%, as stated by Dr. Kalam. Cost estimates for the Agni-II vary and are subject to change depending on the number produced. Many conventional warheads have been developed for use with the strategic missile, everything from bomblets to guided munitions to even fuel air explosives. The low CEP is thus needed for the conventional mission. The most important warhead the Agni-II is designed to and will carry is a one-tonne nuclear device, using a thermonuclear design, which was tested successfully on 11 May 1998. Dr. Kalam confirmed that nuclear warheads can be fitted on the Agni-II in April 1999.

Although the Indian Government denies that the Agni-II will be nuclear-armed, many Indian analysts point out, that the missile costs too much to develop for just delivering conventional payloads. Reportedly Bharat Dynamics Limited (BDL), Hyderabdad, is planning to manufacture 10 to 12 Agni-IIs annually. In May 2001, and again in July 2001, the then-incumbent Defence Minister Jaswant Singh informed the Cabinet Committee on Security (CCS) that the Agni-II is operational, limited production had begun and induction being planned during 2001-2002. On 14 March 2002, Defence Minister George Fernandes informed Indian Parliament that the Agni-II has entered the production phase and is under induction.