Agni-II

Agni (अग्नि fire), is a strategic ballistic missile. The Agni missile family is envisaged to be the mainstay of the Indian missile-based strategic nuclear deterrence. The Agni-II is a medium range ballistic missile (MRBM) with two solid fuel stages and a Post Boost Vehicle (PBV) integrated into the missile's Re-entry Vehicle (RV). The Agni's manoeuvring RV is made of a carbon-carbon composite material that is light and able to sustain high thermal stresses of re-entry, in a variety of trajectories. The Agni-IIA is a more advanced version of Agni-II, albeit with more sophisticated and lighter materials, yielding a better range and operating regime. Agni-IIA was later renamed as Agni-IV plugging the gap between Agni-II and Agni-III. While the first test of Agni-IV in December 2010 was a failure, the second test flight in November 2011 was a success Agni-II, developed as part of medium and long range Agni series of missile systems, has already been inducted into the Armed Forces.

On 17 May 2010, the trial was conducted with a special strategic command force (SSC) of nuclear-capable Agni-II ballistic missile, with a range of 2,000 kilometres from the Wheelers Island off Orissa coast thus making Agni-II missile operational by army. The missiles are operated by the 335 Missile Group at Secunderabad using 12 TEL vehicles.

Preface: Evolving Indian Security Environment
During the 1990s, India's security situation gradually worsened with security challenges from China, blatant Chinese nuclear and missiles proliferation to Pakistan, and mutual proliferation between Pakistan and North Korea. The strategic redline was crossed in 1998 when Pakistan tested nuclear capable Ghauri missile, that could threaten India's heartland. The international complicity in allowing nuclear proliferation by proxy into the hands of Pakistan and ability to deliver it over long ranges, obtained by trading in black-market North Korean No-Dong missiles, in return for Pakistani nuclear design and enrichment equipment by the nuclear and missile black-market run by Pakistani scientist A.Q. Khan and the Pakistani Military. These developments forced India to go fully nuclear, resulting in the Pokhran-II nuclear test series and its weaponisation by developing the Agni family of ballistic missiles that could deliver a variety of payloads over long ranges.

Quick deployment of the Agni-II was possible, by building on the earlier Agni-TD program that provided proven critical technologies and designs required for long range ballistic missiles. Thus when the decision was made to build the Agni weapon system, some quick optimisation and ruggedisation was done to the basic '1980 vintage' design, including a solid fuelled second stage. The re-entry vehicle (RV) and avionics were brought up to state-of-the-art levels. The Pokhran-II nuclear test proved a family of more powerful and lighter nuclear weapons; the 200 kt thermonuclear weapon is far lighter compared to 1,000 kg earlier budgeted for the 200 kt boosted nuclear weapon. Thus a high yield weapon configuration now assumes a payload of 500 kg, including weapon and RV. However, in the interest of rapid development, the basic design that was earlier developed continued to be used, keeping the future option open for more optimised missile design and lighter payload.

Testing
The Agni-II was first tested on 11 April 1999 at 9:47 am IST (Indian Standard Time), from a converted rail carriage, with a carriage roof that slides open to allow the missile to be raised to the vertical for launch by two large hydraulic pistons. The launch process is controlled from a separate railcar. The missile was launched from the IC-4 pad at Wheeler Island, Balasore. Splash down was 2,000 – 2,100 km. down range in the Bay of Bengal, on a trajectory designed to simulate a range of 2,800 – 3,000 km. The Agni-II missile can also be launched from a road TEL vehicle, as demonstrated in the second test flight on 17 January 2001, at 10:01 am IST (Indian Standard Time) to a range of 2,100 km. This missile has a theoretical maximum range of some 3,000 km with a 1,000 kg payload (conventional or strategic).

Tested to range of over 2,000 km, the Agni-II has an all-solid propellant system. After the 17 January test, the missile was cleared for production and it is possible that a production capacity (under-utilised at present) exists for 12 Agni-II missiles per year. On 17 January test, the missile was alleged to have covered a range of over 2,100 km with a 700 kg warhead. The Agni-II is designed to be launched from a rail-mobile launcher, but it is also available in road-mobile configuration. This lends flexibility and reduces vulnerability to first strike.

The Agni-II is always in a ready-to-fire mode and can be launched within 15 minutes as compared to the almost half-of-a-day preparation time for the previous generation Agni-TD. 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 missile 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. Agni-II is made by BDL in Hyderabad, with a production capacity of 18 missiles/year and costs about ₹ 35 crore for each missile. On 19 May 2009, user trial of Agni-II was undertaken by Indian Army, while DRDO scientists provided required logistical support. The Agni-II missile was tested at 1006 hrs IST from a defence base in Orissa. The missile was test fired from launch pad-4 from Integrated Test Range. Integrated Test Range is the missile testing facility on the Wheeler Island, near Dhamara in the district of Bhadrak. Initially it was announced by Indian media that India has successfully tested the nuclear capable Agni-II missile from a defence base in Orissa. According to official sources, the aim of the test was to give the Indian Army confidence to fire the missile on its own. The May 2009 test however ended in failure of the Agni II when the second stage failed to operate correctly and the missile started to veer wildly off course. In a subsequent re-test at night time on Nov 2009, the missile once again failed completely at the second stage, this time dropping directly into the sea. On 17 May 2010, the missile was flight-tested successfully from Wheeler Island off the Orissa coast. The flight lasted 660 seconds, with the missile achieving its full range, after which it splashed into the sea at the predesignated target. A new navigation system which provides better accuracy as well as the capability, to manoeuvre and defeat anti-ballistic missiles was tested during the trial. This was a training trial by the Indian Army. On 30 September 2011 another successful launch of Agni-II was conducted from Balasore, Orissa. The missile was fired from a rail mobile launcher and struck target 2000 km away within 10 minutes of launch, meeting all the performance parameters of the mission such as velocity, terminal phase, trajectory and destruction of the warhead. Another test was done on 9 August 2012, when the missile was successfully launched from Orissa by the Strategic Forces Command as a part of a training exercise.

On Sunday, 7 April 2013, India again test fired Agni-2 ballistic missile with range of more than 2000 km, from Wheeler Island, Odisha at 10:20 AM. The test was carried out by the Strategic Forces Command of the Indian Army as part of training exercise with logistic support provided by the DRDO. The test was a complete success as per Mr. Prasad, the director of Integrated Test Range.

Propulsion
First Stage: The Agni-II's first stage uses solid fuel propellant.

Second Stage: The Agni-II's second stage weighs around 4,200 kg and uses solid fuel propellant. The case is presumably made of the same material, (high-strength 15CDV6 steel) as the booster stage for ease of manufacturing. This solid propellant stage has flex nozzles for thrust vectoring, enabling precise trajectory control. Unlike the Agni-TD, the solid fuel second stage does not require retro motors for proper stage separation. It uses a vented inter-stage.

Manoeuvring Re-Entry Vehicle: Agni RV Mk 2
The 1980-vintage RV was reportedly designed to be able to carry a BARC-developed, boosted nuclear weapon of 200 kt yield weighing 1,000 kg, also of 1980 vintage design. After making room for new and lighter Indian thermonuclear weapon payload, of 1995 vintage design, the MRV has room for about 200 kg (estimated) liquid fuel in pressurised vessels. Although for velocity correction, approximately 50 to 80 kg is estimated to be sufficient. At least one MRV variant type uses a set of solid fuelled cartridges for velocity trimming. The RV is reported to have an attitude control system and aerodynamic manoeuvre fins. Unlike the Agni-II, the RV of Agni-I does not have fins, indicating use of a new method for RV manoeuvring, presumably to make missile defence more difficult. Reports suggest that an improved optical or radar terminal phase correlation system has been developed to provide accuracy of around 40 meters CEP, although later reports have suggested that the accuracy was around 100 to 200 meters CEP. The RV largely inherits the basic shape, design and technology of the earlier Mk.1 RV of the Agni-TD.

Agni is unlike long-range missiles developed by western missiles where the RV is a passive ballistic load, whose accuracy depends on the launching vehicle's exact insertion into the sub-orbital trajectory. A large inaccuracy associated with the first generation RV involved spinning the RV for greater stability during re-entry. Second generation western missiles were mostly MIRV (Multiple Independently targetable Re-entry Vehicle) and the accuracy was greatly improved by the payload bus with HAM velocity correction package for more accurate sub-orbit insertion. It also allowed individual MIRV payloads to impart different velocities, so that each can be independently targeted to a different target, albeit in nearby vicinity of each other. As before, the RV continued to be passive and purely ballistic. The Agni-RV Mk 2 is more advanced than the western RVs, because it embodies proposition, navigation and control all the way to the target. The RV re-enters at an altitude of 100 km, at a shallow angle, with a gliding trajectory. However it does not carry a MIRV payload, which is not to be intended to mean that India does not have the technology: the country launched and accurately placed ten satellites in a single launch in 2007, on its PSLV space vehicle, which was the first evidence of the country having revealed its expertise in this arena.

Key Features of the Agni-RV Mk 2

 * 1) The manoeuvring fins that allows it to;
 * 2) *Execute a non-ballistic trajectory to make interception more difficult.
 * 3) *Overcome any perturbation due to high altitude atmospheric disturbance.
 * 4) *Enable use of body lift at hypersonic velocity to glide the missile over longer ranges, thus reducing the thermal and physical stress at a modified Max-Q point.
 * 5) *Trajectory error to be determined late into the flight and corrected using aerodynamic force during re-entry.
 * 6) *Terminal manoeuvre dive for a more acute target interdiction angle, reducing the CEP (Circular Error Probable).
 * 7) *Support a wider range of payload weight and configuration.
 * 8) Integrated velocity correction package for greater precision; has a set of solid fuelled cartridge(s) that are used to correct impulse variances of solid fuelled stages and subtle launch trajectory perturbation.
 * 9) Integrated High Altitude Motor (HAM) which is liquid fuelled. Depending on the actual payload configuration, the HAM fuel load can be increased to trade range for a lighter and more compact weapon.
 * 10) Larger internal volume allows more sophisticated ABM (anti-ballistic missile) counter-measures.

Avionics, Navigation and Control
The Agni family of missiles uses a strap-down INS system for flight control and navigation. Necessary inertial sensors were indigenously developed for the purpose, including laser rate gyros.

Agni-II introduced a new concept in missile control system by adopting MIL-STD-1553 databus for all on-board communication and control device interconnection mainly INS system, Flight Control Computer, actuators and sensors. It is the standard that is adopted in new civilian & military 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 connections and also makes the missile more rugged. However, some missile analysts feel that a standard databus may not be the best path to follow. It is said that a customised databus is better because in a standard databus, one tends to use off-the-shelf electronic devices whose performance may not be optimal. However most new missiles are moving towards digital buses using commercial off-the-shelf technology and which enables affordable sub-system replacement.

Accuracy
The Agni-II's navigation and aiming uses an advanced ground based beacon system using a TDOA (Time Delay Of Arrival) technique, similar to a GPS system, that constantly provides missile flight position and velocity updates and has been proven in test flights. The TDOA system reportedly improved the accuracy by three times. India has demonstrated a measure of mastery in navigation sensors and flight control through its space program. The placement accuracy in GTO (involving powered flight of 1,000 seconds much of it in sub-G or gravity free environment) is far more complicated and delicate than that of the sub-orbital trajectory of an IRBM. Thus the GSLV-D2 and F01 GTO Apogee accuracy of 1965 PPM and 361 PPM respectively that compares with Agni-II's 40 meter CEP at IRBM ranges with 13 PPM accuracy.

It is worthwhile to note that INS error differs for a ballistic missile versus an aircraft. Ballistic missile accuracy is only dependent on the INS accuracy up to the point when rocket fuel is expended (100 seconds for Agni-II) and it exits the atmosphere (> 90 km altitude), after that the trajectory is purely ballistic that is predetermined and easily computed. INS in a combat aircraft requires continuous operation of IMU and navigation computer throughout the flight during which the error keeps building as IMU sensors drift. A ballistic missile that can update its position and velocity from auxiliary means, can completely eliminate the built up error from INS and continue flight at a precise predetermined path, if necessary correcting the launch error by using:
 * 1) Small velocity correction thruster package and/or
 * 2) Aerodynamic manoeuvring during re-entry (this requires active RV configuration with integrated INS and control system).

The Agni-II missile reportedly makes use of both the above techniques. The Agni-II exits atmosphere and expends the second stage at an altitude of 120 km and at a distance of about 150 km. This allows the ground based TDOA system to operate well within Indian Territory and at close range (i.e. robustness against Electronic Warfare interference). The missile maintains LOS (line of sight) well beyond apogee. The overall accuracy is the cumulated sum of:
 * 1) Accuracy of determining geographic coordinate of target and launcher.
 * 2) Accuracy of hitting the designated coordinates that is determined by missile's navigation and control system.

Launching the Agni from a surveyed site is one aspect of item 1 above. The sub-meter target coordinates, using national surveillance assets, (aerospace, sensors, etc.) would largely address the accuracy of target coordinate designation. A long-range ballistic missile (passive RV) targeting error is typically spread in a highly elliptic pattern. The CEP is thus adversely biased by a wide error spread in a longitudinal axis (due to shallow incidence angle). The Agni's active manoeuvring RV with onboard IMU (INS) and control system can perform terminal manoeuvre to correct errors and make a more accurate top attack profile using greater incidence angle significantly reducing the longitudinal spread and overall CEP.

While earlier test versions of the missile had a CEP of ±100 metres, the latest versions will have a CEP of around 30 metres.

Range
The Bharat Rakshak website has extensive data and analysis that uses public domain data and ballistic calculations to show that the range is greatly influenced by use or non-use of thrusters on the RV (required for velocity trimming) for propulsion as a HAM (High Altitude Motor). There seems to be room in the RV for about 200 kg fuel (solid or liquid) after allowing for a long but lightweight thermonuclear weapon. This RV integrated HAM is referred to as the half stage after the two solid fuelled stages. This stage provides a disproportional increase in range for a lighter RV payload. Thus development of lightweight nuclear weapons is paramount to the missile's range.

When the Agni-II was first launched, then Defence Minister George Fernandes indicated that the maximum range of the Agni-II was 3,000 km. Since then, ranges from 2,000 km to 2,500 km have been stated, while Dr. Kalam, at Aero India '98, stated that Agni-II had a maximum range of 3,700 km. The missile was tested to 2,300 km in 1999 and 2,100 km in 2001, with an apparently lighter payload.

It would appear that Agni-II has a theoretical ability to hit a target 3,000 km away with a 1,000 kg overall payload, a 250 kg RV with a 750 kg warhead. It is suggested that a 200 kiloton boosted fission warhead was earlier developed for the Agni system when it was on the drawing board in the late 80s, however after the Pokhran-II series of nuclear test in May 1998, the 200 kt boosted fission design has clearly given way to a 200 – 300 kt two stage thermonuclear design that is expected to be much lighter. Range changes can be made by either varying the payload or by altering the engine configuration.

Greater range with a lighter payload however requires the RV to be qualified for higher re-entry velocity and corresponding Max-Q for thermal stress.

Conclusion
As the backbone of the Indian land-based nuclear deterrent, the real significance of the Agni-II is the fact that it is both road and rail mobile. This is an indication of India's desire not to put its missiles into vulnerable silos. The mobility of the Agni-II, combined with the sheer physical size of India renders the mobile IRBM a very secure and survivable delivery system. Its range of strategic weapons payload and good accuracy make this strategic weapon useful for counter value as well as first strike role.