Developing a delivery system

Print edition : April 24, 1999

India's National Magazine from the publishers of THE HINDU

The development of Agni-II is of a piece with the nuclear weaponisation process undertaken by the Vajpayee Government.

THE launch of Agni-II on April 11, nearly a year after the Pokhran-II nuclear tests, would seem to be the logical extension of the nuclear weaponisation process that has been set in motion in India. The argument that the country needed to go nuclear for reasons of national security, in the face of a potential nuclear threat from across the borders - namely from Pakistan and China - would demand the development of a delivery system that would be nuclear-capable - which means a payload capacity of about a tonne and capability to reach deep into China. Irrespective of the reality (or lack of it) of the threat from China, having gone nuclear ostensibly on that premise without developing and deploying such missile delivery systems, the argument would lack credibility.

From the above perspective, therefore, the development of Agni-II, with a range capability of 2,500 km, much greater than the 1,000-km-plus of Agni-I, constitutes an essential component of building a credible minimum deterrent against an assumed nuclear threat from China. The Agni-II test, in that sense, marks a shift in the development of this intermediate range ballistic missile (IRBM) into an operational mode. In fact, until its last test flight in February 1994 as part of the Integrated Guided Missile Development Programme (IGMDP) of the Defence Research and Development Organisation (DRDO), Agni was being touted as a 'Technology Demonstrator', and that too one meant to carry only conventional warheads. Then its development was put on hold and its hibernation was perceived in political and strategic circles as being demonstrative of a lack of political will. The recent test would seem to have altered all that.

The launch of Agni-II was carried out from an entirely new launch site on an island, called Wheeler Island, about 2 sq km in area and about 20 km off Orissa's Chandipur coast.

There were reports earlier this year that the Agni-II launch had been scheduled but had been called off owing to external pressures. According to DRDO sources, the launch was on the anvil since January, awaiting a go-ahead from the Government, which came in early March. The marine and aviation agencies were accordingly intimated. At a press conference after the April 11 launch, Defence Minister George Fernandes cited a "technical problem" as a reason for the delay. DRDO sources confirmed that there was a minor technical problem, but said that they could have gone ahead if the Government had wanted them to. According to them, the launch window was available till April 14; if the launch had not been underaken by then, the Meteorological Department would have been required to give another window. The advancing monsoon winds would have made it difficult to give another window.

There had for long been considerable political pressure to operationalise the missile. In August 1996 the DRDO appears to have sent in a proposal to the H.D. Deve Gowda Government to revive the Agni project (into Phase II) following the Prime Minister's Independence Day address in which he stated that the Agni project would be revived. However, the Deve Gowda Government fell within months and the Government headed by I.K. Gujral seems to have put the project on hold. Soon after the BJP-led Government took office in March 1998, a new thrust was given to the project. The Ghauri-1 test by Pakistan in April 1998, which pointed to external assistance for that country's missile technology, coupled with the nuclear tests in May 1998, seems to have proved decisive. A DRDO brochure on the IGMDP, issued in mid-1998, said: "The Agni IRBM has been successfully developed and successfully evaluated in flights, establishing re-entry, guidance and control. Operationalisation is progressing."

Agni-II marks a critical change in the basic rocketry technology it uses. Agni-I was developed as a two-stage vehicle whose first (booster) stage (S1) was essentially the solid-fuel first stage of the Satellite Launch Vehicle SLV-3 and the second stage (S2) is derived from the liquid-fuel short-range surface-to-surface ballistic missile Prithvi, developed as part of the IGMDP. The SLV-3 had been developed by the Indian Space Research Organisation (ISRO) in its efforts to acquire an autonomous satellite launch capability. Its efforts since then have led to the development of the Polar Satellite Launch Vehicle (PSLV); ISRO is moving towards achieving geostationary launch capability by the turn of the century.

One of the critical technologies ISRO mastered in its launch vehicle programme was the solid propellant and solid motor technology. This was the heritage which the ISRO derived from its earlier sounding rocket programme using Scout rockets and solid fuel called Polybutadiene Acrylic Nitrate (PBAN) imported from the United States. During the development of the Augmented Satellite Launch Vehicle (ASLV) after the Missile Technology Control Regime (MTCR) came into force in 1987, the export of PBAN stopped and ISRO had to develop the solid propellant technology on its own. One of the most promising and successful propellants developed was Hydroxy-Terminated Polybutadiene (HTPB), which has come to be the mainstay solid propellant for ISRO's programme.

When Agni was conceived in 1983 as a vehicle based on SLV-3, the choice of solid fuel in its first stage became automatic. However, its second stage is essentially the Prithvi missile, which was being concurrently developed, whose origins went back to the liquid-fuel Devil missile that had been obtained from the Soviet Union. But as an operational system, this solid-liquid mix of propulsion of the missile was a matter of considerable controversy and debate. Simply put, a solid-fuel launcher is a "fire-and-forget" type of system; once ignited, the entire propellant load will have to burn out.

In the liquid fuel system, on the other hand, the propulsion can be controlled by shutting off the supply of fuel to the combustion chamber. For a controlled and guided trajectory, with mid-course corrections and so on, it was argued that liquid-fuel stages were better. However, as an operational system, liquid-fuel missile stages have storage and handling problems. Liquid fuels are corrosive and highly toxic; they are also hypergolic (that is, they do not require ignition but burn immediately on contact with an oxidiser chemical). All these pose operational hazards. Moreover, loading the missile with liquid fuel could take a few hours before each launch which, in a battle-field situation, could render operations ineffective. The debate, however, continues because both kinds of missile systems exist.

From the Indian perspective, however, with an established mastery over solid propellants, it was logical to go in for solid propellants right from the start because even solid propellants, concepts and technologies for thrust termination had emerged. The DRDO seems to have waited to validate other critical technologies in the missile, such as the carbon-composite heat shield, manoeuvrable re-entry of the warhead carrying re-entry stage, homing technologies as well guidance and control systems, before deciding to go fully solid with Agni. This happened once the Technology Demonstrator phase of Agni (Agni-I) was completed and there was a hiatus before the solid second-stage motor was developed. Indeed, the DRDO appears to be well on its way to using solid fuel in a big way; it has, somewhat belatedly, established a facility to produce solid propellants, and the unit is likely to go on stream very soon. It would also seem to make sense to make Prithvi a soild-fuel missile. As of now, however, the solid motors for the missile programme come from ISRO's facilities.

One of the main features of Agni-II, therefore, is that it is a completely solid-fuel missile. According to DRDO sources, the second-stage (roughly 3 m x 1 m) solid motor has been designed anew specifically for the missile. As against the three-segment S1 motor, the S2 motor is a single segment. 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 manipulated with the help of an on-board closed-loop guidance and control system. Till now, the flex nozzle has been used only in the third-stage motor of the PSLV. The DRDO would seem to have adopted this technology for flight control of Agni in a newly designed motor. Agni-I's second stage, being liquid-propelled, used gimballing of the nozzle for thrust vector control, a concept that cannot be used in case of solids.

THE range achievable in a missile launch is a function of the propellant used and the parameter that describes it is called 'specific impulse' (Isp). Isp is a measure of the thrust generated per unit mass of the propellant burnt. Isp for liquid fuels is considerably higher than for solid propellants; this is one more reason why using liquid propellants to launch satellites yields a payload advantage. Also, it depends on the fraction of the propellant loading for a given mission. That is, the higher this fraction, as the fuel gets consumed, the mass to be lifted over a given range is smaller. At the present levels of technology, this fraction is as high as 90 per cent in the best solid motor launchers. The capability in India (going by ISRO's figures) is close to 86 per cent, which is extremely good.

The stated flight time and range for the Agni-II test launch are 11 minutes and 2,000-plus km respectively. However, according to experts, both Indian and foreign, a back-of-the-envelope analysis based on the dimensions of the missile and assuming 86 per cent propellant loading, indicates that the range is likely to have been lower than claimed. However, if a higher loading (say close to 90 per cent) was achieved, a greater range would have been possible. Of course, a higher range can also be achieved by reducing the payload mass. However, DRDO officials confirm that the tested payload was more than one tonne and therefore they claim that the range capability of Agni-II is even more by 200-300 km. But experts discount this claim.

According to A.P.J. Abdul Kalam, who heads the DRDO and the IGMDP, what is unique about Agni is the trajectory shaping and guidance that is possible through software. This is a feature of Agni-I as well as Agni-II. For the liquid-propelled Agni-I, this shaping was conceivably simpler; for Agni-II, it calls for appropriate on-board thrusters on the second stage of the missile. This is because the solid fuel is allowed to burn fully, which means that the velocity increment achieved before re-entry could be more or less from the mission perspective. Further, there is considerable dispersion in the burn 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 on-board sensor data and should be amenable to being adjusted reactively. These small force thrusters are liquid-fuel-driven and provide small increments in appropriate directions to shape the trajectory depending upon the target of the mission. It is these thrusters that give manoeuvrability during the 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".

An altogether new concept has been adopted for the on-board navigation system. The earlier hard-wired part of the system was apparently not the most optimal, according to DRDO sources. In Agni-II, the standard that is adopted in civilian aircraft (circuit routing and device mounting) has been used. It is known as 1553 Data Bus; all the software have been designed around this bus. DRDO sources claim that this is the first time anyone has used the 1553 Bus on a missile; this, the sources say, not only reduces the number of connectivities but it also makes the missile a little more rugged. However, some missile analysts feel that this 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.

THERE have been media reports that Agni-II uses the Global Positioning System (GPS) for control during re-entry. Abdul Kalam, however, denied this; such a system, he said, depends on several external influencing factors and would make the system vulnerable to external interference. However, many missiles the world over do use GPS. Sources say that the use of GPS had been considered for Agni-II at some point of time.

Another major departure 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. Agni-I, on the other hand, had been designed as a road-mobile system. There are pluses and minuses to the change. DRDO officials feel that it reduces vulnerability and lends operational flexibility. Critics feel that the cost of rail-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, the northeastern region - road infrastructure is available wherever rail tracks are available, the decision to become rail-mobile could mean, in strategic terms, that deployment in the northeastern region is to be considered seriously.

However, even assuming that Agni-II is to be deployed in the northeastern region and even given a 2,000-km-plus range, Agni can still not reach vast parts of China - including Beijing, which is over 3,000 km away. Therefore, a longer-range Agni may well be required if the need for a deterrent against China is being seriously felt. The Agni programme does not otherwise make much sense, since Prithvi is an adequate deterrent against a threat from Pakistan. While a new system can certainly be developed if the Services require it, the present configuration is in operational mode, said Kalam. Range, he said, could be optimised by appropriately configuring the payload mass. According to Abdul Kalam, the road mobile version would also be available and it would be left to the Services to choose according to their operational convenience. According to him, no more tests are needed to operationalise Agni-II.

Experts contest this claim, pointing out that the new Russian Topol-M had to go through nine launches before being inducted. Failures, they say, are inevitable in a new system. Some DRDO scientists feel that at least one more test towards the end of the year may be required.

In any case, user agencies have so far not been involved in operationalising the system. In fact, it is not clear which Service - white, blue or olive green - will use Agni. Then, as was the case with Prithvi, user trials have to be undergone; this will certainly call for at least a few test firings. In addition, the solid propellant facility has to go into a production mode. It can be assumed, of course, that Bharat Dynamics Ltd will get into Agni production as well but it does not have the capability to handle solid-fuel motors. The two units have to be appropriately coordinated and all this will take time. Last, but not the least, a credible minimum deterrent is yet to be defined in strategic terms; precisely what the strategic considerations are has not been made clear. Clearly, the Agni-II launch has demonstrated an operational capability; the actual operationalisation of the missile is at least five years away.

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