DRDO RUDRAM - 1 NGARM

INTRODUCTION

Neutralising enemy's radar and SAM systems is one the primary tasks performed by an attacking force. Doing SEAD/DEAD without an Anti Radiation missile is extremely dangerous and costly even with light aircarfts. Indian Airforce with an aim to bolster it's strike capabilities is spearheading development of many air launched bombs and missiles. In similar line the Airforce has taken multiple agencies in the country primarily the DRDL, ARDE, DLRL, HEMRL, RCI, TBRL, NTAF for development of NGARM Next Generation Anti Radiation missile, now named Rudram-1. Surface to Air missiles may not be 100% perfect but guarantee a strong deterrence against air raids. Chinese have made immense progress in this particular area. The deployment of SAM puts a no flying zone over a land mass. Unless air superiority is achieved an attack or defence on surface is useless.

Air Marshal (retd.) Daljit Singh, a former IAF fighter pilot and highly respected electronic warfare expert, broadly welcomes the IAF’s NGARM acquisition, although he warned MONCh that, “to be really relevant and effective, the ARM would have to be capable of multimode operations. It must also be upgradable to match emerging radar technologies.”

He stressed that the missile’s seeker must be capable of detecting and locking onto contemporary radar threats employing a myriad of low probability of deception/interception and electronic counter-countermeasure tactics and techniques to hide in the ether. AM Singh also urges the IAF to invest in escort jammers for strike packages, an area he argues where the air force is currently deficient.

DESIGN

DRDO NGARM / RUDRAM-1 is the effect of stringent requirements laid out by the Indian Air Force. It can be launched from a height ranging from 500 m to a height of 15 km and speeds ranging from Mach 0.6 to Mach 2.0 .Its overall range is 200 km. The Missile weighs 600 kg and it approximately 5.5 M long. Drop Flight Trial (DFT) was completed by December 2016 with the missile released by Sukhoi Su-30MKI at a speed of 0.8 Mach, from 6.5 km altitude. The Front section of the missile contains the passive homing head needed there to seek enemy RF waves, behind it their is navigation system. The fixed cruciform wings are attached to the motor casing. In the aft section we have dual pulse Solid rocket motor. Popular journalist Saurav Jha said that design is similar to dual pulse propulsion of LRSAM and both LRSAM and NGARM's rocket motors are manufactured by the same company named Primier Explosives Limited. At the end their is a nozzle surrounded by what looks like actuators for control and stabilisation. Their is almost zero information and pictures about the control mechanism that moves the missiles fins for maneuvering. Basically just an enlarged Astra mk1 with nozzle.

The Passive homing head ( PHH ) tracks sources of radiation of a wide range of frequencies. It is also equipped with a MMW seeker transmitting on frequencies of 30 Ghz or higher, to seach locate and hit moving emitters. It can lock into a target not only before launch but also after it has been launched.

The combination of Passive Homing Head , MMW seeker and INS-GPS guidance system allows RUDRAM-1 to not only engage relocatable air defence targets like mobile SAM systems but other emitting targets equipped with shutdown capability. This means that even if the enemy shuts down the radar / emitter after the missile is launched, it will still find and hit the target.

MMW seeker is especially used, if the target is a mobile SAM system which has shutoff it's emissions and is attempting to scoot. In this case the multimode seeker will fly under GPS/inertial control to a search footprint, within which the MMW seeker will search for the target, allowing a precision homing attack. Existing MMW seeker technology has the ability to recognise a specific target type by shape and fine Doppler modulations. The operational deployment of multi sensor NGARM will spell the end of the mobile SAM system, as it effectively nullifies the shoot and scoot and the go off the air tactics.

NAVIGATION SYSTEMS.

The Navigation systems usage on an Anti Radiation missile which most people believe goes in the direction of RF source is a bit tricky. In one of the operational modes of Lock On After Launch, where the location of the target is known, NGARM would fly in a area of intrest and turn on it's receives afterwards, such an operation needs guidance from other sensors. In a dense EW environment where sidelobes of the target radar and other waves from other sources limit the ability of NGARM to follow the path of generated tracks, GPS-INS guidance helps in to implement successive position corrections until the missile is near enough to see the target waves clearly. Their are a lot of technicalities in implementing a satellite based navigation system combined with inertial navigation system. The inertial navigation system provides input and output for course correction during flight. The exact photo and design details of the type of GPS-INS guidance to be used in NGARM hasn't been revealed by DRDO yet.

There is another reason why inertial navigation is needed in an ARM. ARMs are designed to home primarily upon the mainlobe and other sidelobes, mainly horizontal sidelobe and backlobe emissions of the target, attacking the target in a shallow dive trajectory. Modern radars with very low sidelobe antennas will thus present a "blinking" target to an approaching ARM, which must estimate the real position of the target from the intervals of active emission, when the antenna is radiating in the direction of the inbound missile. In the terminal phase of the NGARM's flight, a slow rotating antenna on the target may be looking away from the missile virtually emitting nothing from the source. The NGARM will follow an inertially steered trajectory based upon previous measurements of the radar's position. As a result the missile will not smash the target directly, but pass within few metres of the target, employing its proximity fuse to set off the warhead. This is why apart from satellite navigation systems whose accuracy vary for various geographical locations we also need inertial navigation in an Anti Radiation Missile.

Ejector Launch type launcher of NGARM.

WARHEAD

The NGARM has a 60 Kg pre fragmented warhead. In a typical DRDO designed PF warhead their are tungsten fragments packed in such a way that the surround an explosive filled column and wound by filament which acts as a casing. The explosive column made by filling a new explosive called DENTEX inside a FRP tube. It is detonated to disperse the high density tungsten fragments in surrounding causing severe damage. These warheads are lethal even at large distances. The high density tungsten alloy fragments are manufactured using powder metallurgy techniques. DENTEX is a new explosive DRDO which is a mixture of RDX and TNT and other substances. DRDO through these years have designed many warheads of this type and developed testing methodologies and mathematical models to predict the performance of PF warheads.

By seeing at photos of brochures available on various blogs, it seems that warhead design is highly similar to the 65 kg PF warhead of Akash SAM.

LASER PROXIMITY FUSE.

The Fuse of NGARM is very unique, and employs a laser rangefinder to asses it's distance from target. It looks like Rudram-1 is designed to dive down vertically and pass a beam on the target emitter, this specialised fusing arrangement is designed to measure the altitude of the missile precisely, and trigger the warhead detonator as the missile passes near the radar's antenna. This ensures that the warhead is as close as possible to the target when it is fired. The exact information on design of DRDO'S laser proximity fuel is not available, I tried my best to find it.Because of certain unpredictability in calculating the exact position of RF frequency source and drifting of the missile from that source due to inertia, the missile never directly smashes itself on the target. It only goes as close as possible. Because of this proximity fuses are employed to detonate the warhead once they are sufficiently close to cause damage.

AN EXAMPLE OF WORLD WAR 2 ERA OPTICAL PROXIMITY FUSE

Typically such devices consist of optical ranging apparatus where a laser generates light pulses illuminating a surface. The mirror arrangement inside enables a single lens to emit and receive a reflection of these pulses. An optical fiber bundle is used for delaying the optical reference pulses to correspond to a predetermined distance from the target. The optical ranging apparatus includes circuitry for providing a first signal depending upon the light pulses reflected from the target, a second signal depending upon the light pulses from the optical delay fiber bundle, and an output signal when the first and second signals coincide with each other. The output signal initiates circuitry that would enable detonator. An additional circuit clarifies difference between received laser pulse and any other light reflected by target surface. The system knows type of radar it is attacking, and therefore also knows what the elevation of the antenna is above the ground. This information is then used to select the most suitable altitude for warhead firing.

Su-30 MKI armed with Astra Mk1, NGARM and BrahMos ALCM, a typical DEAD configuration.

PROPULSION

NGARM uses dual pulse Solid rocket motor. The dual pulse solid rocket motor design consists of two burning chambers, separated by a bulkhead, designated as pulse separation device (PSD) and a nozzle. The pulse separation device protects the propellant grain in the second pulse chamber against high temperature and pressure impact during the first pulse operation. At initiation of the second pulse, the PSD reliably opens for the gas flow and the combustion gas from the second pulse chamber passes through the empty first pulse chamber and the nozzle. This design allows the initiation of the second pulse at any time after burn out of the first pulse. The use of one central nozzle for both pulses and the avoidance of lateral nozzles help the missile to show outstanding aerodynamic stability in manoeuvres during the second pulse phase. Number of dual pulse rocket motors were designed, manufactured and successfully tested in missile flights and the utility of this technology is demonstrated.

The first pulse chamber is filled with a fin-o-cyl shaped aluminized composite propellant. It has a moderate burn rate. moderate. In the second pulse chamber a star-shaped low aluminized composite propellant is cast. Its burn rate is high. Both chambers are screwed together. Between both chambers the PSD is jammed. A nozzle is attached to the rear of the first pulse chamber. Typical thrust time curve of a dual pulse rocket motor is shown in diagram below.

Pic posted by Saurav Jha on twitter.

The Dual Pulse Rocket motor of NGARM is similar in design with LRSAM and is manufactured by same company.

PASSIVE HOMING HEAD

The NGARM has a passive homing head. It means that this seeker doesn't emit any radio frequency emissions it only receives them. The direction and distance of the received emissions are accurately detected and the head homes in or goes towards that direction in an attempt to hit the source of that radio frequency emission. The PHH is a wide band system with compact front end made of medium monolithic integrated circuit for identification of RF waves.

The Passive homing head on NGARM has been developed by DLRL and Astra Microwave based in Hyderabad. The passive homing head performs complex functions of detecting, direction finding and generating tracks for each target that has been detected. It has been designed to identify military operated radars in spectrum of 1 to 10 and 6 to 18 Ghz. The system has a typical design of cavity backed spiral antennas that is usually found in other passive homing heads of other nations Anti Radiation Missiles. Their is a Digital Instantaneous Frequency Measurement DIFM receiver which is used to measure frequency characteristics of target emitter. Their is also a processor which helps in direction finding, electronic support measures. It measures emitter parameters like pulse repeatation frequency, amplitude, azimuth/elevation and time of arrival. It then performs de-interleaving and generates emitter tracks identified targets.

In terms of radars Interleaving is the calculation done to find the least error value of all the multiple values collected, it is done by spacing the consecutive data collected by emitter. It is a continuous process and makes radar beams more focused. Deintreleaving puts data back into original sequence. The pulse repeatation frequency is the number of pulses repeated per unit time. The change of a variable value in a single period is called amplitude, it is the highest value achieved by wave's Crest(peak) if you see a wave on graph. Azimuth is a horizontal angle measured clockwise from a north base line or meridian and elevation is the distance of target from horizon.

OPERATION

The operation of Rudram 1 or NGARM can be predicted by the fact the most of the technologies point towards western design trends. The west speaks primarily about their experience of their wars in west asia. As per reports that have come until now talks about Lock On Before Launch LOBL and Lock On After Launch LOAL. NGARM is likely to be programmed with threat liabriers of known Radar parameters, operation modes, fusing altitudes and a program that prioritizes certain targets over others. The LOAL and LOBL may have sub-modes classified amongst them.

Lock On Before Launch-
A Lock-on-before-launch (LOBL) mode uses missile receiver before launch to acquire the target. This mode allows off axis attacks on emitters within the field of view of the seeker. It is typically used as an by non-dedicated strike aircraft to suppress emitters. Non dedicated strike aircraft do not carry specific emitter locator podded hardware with them and rely on RWR or missile sensor to locate enemy emitters. In LOBL defensive mode, which is a short to medium range mode NGARM engages targets within 360 degrees of the launch aircraft. The missile receives target information from aircraft's RWR and given a prioritised list of threats. The highest priority threat will be engaged after launch. Usage of RWR instead of missile sensor provides a larger FOV of emissions across the battle space.

Lock On After Launch -

A Lock On After Launch (LOAL) mode is used for standoff maximum range attacks on emitters of a known type and location, within several degrees of the missile boresight. In this mode an onboard sensor of aircraft gets information about identity, type, etc of the radar and uploads the information into missile constantly while missile is in flight. The launch aircraft will then hurls the missile to impart the best possible range. The missile flies on inertial guidance until it acquires the target, and then homes to impact. During a dense EW environment a specific mode may be applied that is more accurate in terms of target selection, and can engage off axis if required, but requires more precise target position information than the baseline LOAL mode. The de Interleaving and selection of target frequency would be more precise and the launch would likely happen at closer ranges than normal LOAL modes.

Once the missile begins terminal phase it doesnt matter which mode it had selected previously. In terminal phase it begins homing in directly and it's performance solely depends upon the homing algorithm. The optical fuse would be armed from this point and incase emitter shutoff GPS/INS and millimetres wave seeker would be used for further trajectory correction. The overall performance of this missile thus largely depends upon operation conditions and the type of aircraft used. If an aircraft podded with dedicated EW-ESM emitter detection capability the missile can be launched from a larger standoff range. The missile can also recieve data from data links.

THE DRDO NGARM RUDRAM-1 WILL BRING A PARADIGM SHIFT IN INDIAN FORCE AND MAKE IT A TRUE STRIKE CAPABLE FORCE WITH ABILITY TO CONDICT WARTIME AND PEACETIME OFFENSIVE MISSIONS AGAINST ANY TYPE OF CHINESE RADARS. NGARM WILL FURTHER ENHANCE MISSILE TECHNOLOGY IN INDIA MATURING THE ALREADY FLOURISHING MISSILE MAKING INDUSTRY.

Sources :-

https://www.strategicfront.org/forums/threads/indian-missiles-and-munitions-discussion.75/page-37

http://www.ausairpower.net/alarm-armat.html

https://defenceforumindia.com/threads/indigenous-next-generation-anti-radiation-missile-thread.75954/page-2

https://www.monch.com/mpg/news/ew-c4i-channel/5402-nargm.html

http://www.ausairpower.net/API-AGM-88-HARM.html

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