Astra BVR missile - deadly weapon of Vayusena.

Beyond Visual Range combat may not be a new phenomenon but seeing the modern doctrines of air to air combat , it can be considered to be the most effective tactic for achieving a kill in an air to air duel. Since the basic tactic of seeing the enemy and killing the enemy by our own self being out of enemy's reach is what the latest trend stimulates us to follow, nations across the world intending to achieve self sufficiency in weapon development are pursuing the development of missiles that are capable of hitting the target which is even away from the line of sight of naked eyes.

The era of Beyond Visual Range combat began with introduction of Sparrow missiles of the USAF. These missiles were simply semi active guided, where radar of the fighter would 'paint’ the target with high power radio waves which when reflected from enemy fighter would be used as 'feed’ for the seeker of the missile. To achieve this, radars would need to achieve a 'lock-on’ on the enemy fighter. As a counter tactic against a lock on by the enemy a defending fighter would then try to out maneuver the missile by flying close to ground through valleys and mountains to break lock-on. With passage of time newer missiles having 'infrared guidance’ came into existence which would home-in on reflected radiation coming from heated parts of a target aircraft, the most significantly heated part was the exhausts of jet engine. These kind of missiles relieved the launcher aircraft from following the missile, because earlier for missiles using radar guidance it was needed that target should be constantly painted in an order to guided the air to air missile. Now with heat seeking missiles available one can just shoot and scoot. But heat seeking missile's drawbacks came into foray when flare decoys were introduced. The flare decoys were heated balls of fire released by the defending aircraft in an order to divert the attention of heat seeking missiles to the flare and hence get saved. This problem could be addressed only when if we have a radar guided missile which does not need constant guidance from the aircraft which is firing it.

Fire and forget​

To overcome the drawbacks stated above an entirely new series of missiles with active seekers came into existence. These new “fire and forget” kind of missiles were able to seek the target on their own. They were equipped with terminal active seeker.This relieved the launch platform of the need to illuminate the target until impact putting it at risk. This was also the first time, multiple enemy aircrafts could be targeted at one same time. The F-14 Tomcat became a horror amongst it's adversaries all because of this. Now taking this to a new evolution modern BVR missiles like R-77 and AIM-120 AMRAAM came into existence. These missiles instead used an inertial navigation system (INS) combined with initial target information from the launching aircraft and updates from a one or two-way data link in order to launch beyond visual range, and then switch to a terminal homing mode, typically active radar guidance. These types of missiles have the advantage of not requiring the launching aircraft to illuminate the target with radar energy for the entire flight of the missile, and in fact do not require a radar lock to launch at all, only target tracking information. Having two way data links means the target information can also be provided by another aircraft or an AWACS.

Introduction

Astra is an active radar homing beyond-visual-range air-to-air missile (BVRAAM)developed by the Defence Research and Development Organisation (DRDO), India. With the development of Astra India have developed such sleek missiles capable of detecting, tracking and destroying highly-agile hostile supersonic fighters packed with ``counter-measures'' at long ranges.The highly agile, accurate and reliable missile features high "single-shot kill probability" (SSKP) and is capable of operating under all weather conditions. Length of the weapon system is 3.8m, while its diameter is 178mm, and an overall launch weight is 154kg. Its low all-up weight provides high launch range capability and the system's airborne launcher can be used with different fighter aircraft.

Development of Astra missile

In the late 60s India realised that if they have to defend their nation against a heavy aggression of hostile and expansionist neighbours they would need to have a formidable indigenous defence technology that can be mass produced within the nation independently. The simplest way of doing so was going forward with an integrated program for development of a wide range of tactical and strategic missiles. Hence Integrated Guided Missile Development Program was launched under the leadership of Dr A.P.J. Abdul Kalam. Except Nag missile anything that came from this program was a world beating success that any Indian would be proud of. One such success is Astra missile. DRDO carried out mission analysis, system design, simulation and post-flight analysis of the weapon system. The Mk-I variant of the Astra missile was first tested in May 2003.

The initial design had wings on rear side of the body.

But as a later development, the wings moved more towards middle section of the body.

The Astra Missile development like any usual DRDO program faced multiple challenges primarily because of sanctions against India after nuclear tests. Moreover Indian Air Force came under fire from the Comptroller and Auditor General of India for the ‘not so worthy’ purchase of few AAMs, which did not home in on targets during evaluations or failed ground tests because they were ageing much before their shelf lives. No doubt, the failed missile test has affected the “operational preparedness” of the IAF. There are too many conflicting requirements for an air-to-air missile such as stability and safe release coupled with high agility during engagement against the target aircraft. Astra project is a tech-treat considering the miniaturization of the systems, including on-board computer, data links for transmitter/receiver and rotary electro-mechanical actuators. A smokeless, non-metalized high-specific impulse propellant was developed for the rocket motor.

In the latest Configuration Astra’s mid body wings are shortened and clipped.

All this development involved over 50 private Indian companies partnering with DRDO. Captive flight trials (a total of eight) have been conducted on the aircraft in 2010-11 for establishing the structural integrity of the aircraft with the missiles for the complete flight envelope. After which successive firing trial the latest one conducted in sep 2017 were termed a success.

Warhead

The warhead is 177mm in diameter and 288mm in length. It contains 2050 cuboids each of dimensions 6x8x4.5mm. The total weight of warhead is 15kg. During tests this warhead cuboid sub-projectiles moved away at 20m distance from core housing and penetrated through 8mm MS plate. Total 4.8kgs of explosives used. The explosive used is HMX called High Melting Explosive sometimes also Her Majesty's Explosive. IUPAC name
1,3,5,7-Tetranitro-1,3,5,7-tetrazocane.

The Astra contains a high explosive pre-fragmented warhead which has a radio proximity fuse. This type of warhead design may differ from country to country but have one same principle behind them. A set of small sub projectiles is packed around a big explosive device. As the warhead nears the target, the explosive blows out the sub-projectiles sharply penetrating into target aircraft’s body. This damages the streamline body, control surfaces and engine parts also which are highly critical for continued stable flight. Thus effectively destabilising the aircraft and making it fall down.

Effects of cuboid sharpnel on a fighter aircraft’s body.

The radio proximity fuse here is used to trigger the explosive device. Radio proximity fuze is a unit combining a miniature radio transmitter and a receiver. The transmitter begins emitting radio waves, which are reflected by the target and are picked up by the receiver in the fuze. The reflected signals differ from those radiated in frequency and amplitude, and, as a result, an error signal is produced. When the distance between projectile and target becomes sufficiently short, the error signal exceeds the triggering threshold of the detonator mechanism; a current is generated through the electric detonator, and the projectile explodes.

This RPF used in Astra weighs approximately 2.5kg and has a detection range of up to 30m, a detonation range of 20m and a missile target velocity between 100m/s and 1,600m/s.

Rocket Motor

Astra is a single stage solid propulsion fuel based missile. It uses HTPB as fuel. HTBP is a very interesting fuel.HTPB is a mixture rather than a pure compound. It binds the oxidizing agent and other ingredients into a solid but elastic mass. The cured polyurethane acts as a fuel in such mixtures. It is used by ISRO’s PSLV and also Japanese SLV called M5. JAXA describes the propellant as "HTPB/AP/Al=12/68/20", which means, proportioned by mass, HTPB plus curative 12% (binder and fuel), ammonium perchlorate 68% (oxidizer), and aluminium powder 20% (fuel).

HTPB is a non-metalized high-specific impulse propellant developed for the rocket motor. This all makes Astra a smokeless missile. The missile's maximum speed is Mach 4.5+ and can attain maximum altitude of 20 km. The missile can handle 40 g turns near sea level while attacking a maneuvering target.

Solid rocket motor comprises of a cylindrical casing enclosing a propellant grain, a combustor/igniter at either ends of the cylinder and a nozzle to force out hot gases burnt after combustion. The igniter can be mounted either at the nozzle end or at head end. There can be one or many nozzles. The shape of the cross section of propellant grain is very significant, because it influences the manner in which burning would take place. When ignited, the propellant grain burns out radially outward forcing the hot gases through nozzle. The nozzles are designed to maintain some level of chamber pressure inside the casing, and casing design should also be in accordance to that.

Dual Pulse Rocket Motor.

The Astra mk2 will use a dual pulse rocket motor which will be a major technology upgrade.

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 flights1-6 and the utility of this technology is demonstrated

The first pulse chamber is filled with a finocyl-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.

Seeker.

As we know Astra uses a terminal active radar seeker, let's see the philosophy behind it. Other seekers are only receivers, but the one used in Astra is a transceiver a transistor cum receiver, it is basically a mini radar itself radars can be fooled and can be deceived , but the more a radar is closer to the target the lesser are the chances of fooling it. Since terminal guidance stage goes active when it is 'enough near’ the target the question weather the terminal active seeker be spoofed, jammed or decoyed is a big question. To counter the spoofing and jamming their is an effective technique, which is passive radiation homing. Spoofing the active seeker means using the radio waves coming from it and showing a false target, Jamming means shooting heavy pulses at an antenna in an order to overload and burn it from inside.

Astra's Russian Seeker

Here in both spoofing and jamming the enemy would be giving radio waves and the technique of passive radiation homing uses these same waves as 'feed’ and homes in on a target. During tests in March 2016 conducted near Pune, Astra Missile was tested, it was sought to be jammed to see how it performs in such a scenario at the time of war when the enemy tries to jam its operation. The ECCM (electronic counter-countermeasure) features of the missile to overcome any jamming were evaluated. “The trials were vigorous. But the state-of-the-art missile did very well,” said a source that reported this event.

Astra used 9B-1103M seeker which is used in R-77 missile variants. It is a multi-function doppler-monopulse active radar seeker. The seeker features two modes of operation, over short distances, the missile will launch in an active "fire-and-forget" mode. Over longer distances the missile is controlled by an inertial guidance autopilot with occasional encoded data link updates from the launch aircraft's radar on changes in spatial position or G of the target. As the missile comes within 20 km (12 mi) of its target, the missile switches to its active radar mode. The host radar system maintains computed target information in case the target breaks the missile's lock-on. Later on DRDO’s RCI developed an indigenous seeker it is a Ku band seeker which is manufactured by VEM technologies. During tests this new seeker performed very well and hit the PTA Lakshya. DRDO has now mated the Astra missile with indigenous KU-band Active radar seeker which is a miniaturised version of the seeker which DRDO developed some time ago for PAD.
​

Indigenous seeker for Astra

In India, R & D work began in 2016 for developing AESA-based X-band and Ku-band active seekers for both the XR-SAM long-range surface-to-air missile and the SFDR-powered Astra-2 BVRAAM, with Hyderabad-based Astra Microwave already having developed two types of such seekers, with work now underway on developing their Ka-band successors that too will be compatible with the Meteor BVRAAM. The Ka-band seeker with an active phased-array antenna (with 20km-range) and a secondary X-band passive channel will replace existing Ku-band seekers (with 6km-range) and provide higher resolution and countermeasures resistance. Such seekers can effortlessly work across multiple frequencies simultaneously, which makes them not only better at finding objects, but are also more difficult to detect. In addition, electronically steered antenna beams also offer other improvements: it is possible to perform an adaptive antenna beam-forming based on antenna sub-group transmit (Tx) and receive (Rx) channels or even adjusting all the single antenna transceiver elements. This put us into a position to use algorithms of super resolution in order to recognise and localise jammer sources while concurrently conducting target acquisition and tracking.

Range of a BVRAAM

The range of BVRAAMs given in the brochures don't tell the whole truth about them. Actually range of any BVRAAM isn't one single fixed value. The range is different at different altitudes of the launching aircraft. It increases with increase in altitude as the air at upper atmosphere is thin and offers least resistance in the form of drag. Their is an exponential relation here between launch altitude and range of a BVRAAM. So the range of any BVRAAM stated in the brochure is range at a standard service ceiling of a particular fighter aircraft.

Now the success of any BVRAAM depends on it's kinematics, is an important factor universally ignored by western military enthusiasts / analysts (except those who designed F-22 Raptor). The impact of the launch aircraft's kinematics at the point of missile launch. A supersonic Su-35 sitting at Mach 1.5 and 45,000 ft will add of the order of 30 percent more range to an R-27 or R-77 missile. High speed of the launch platform adds-on to the speed and range of the missile fired by it. This isn't something controversial, it is plain basic newtonian physics taught in school. The fighters which have lower speed during launch of missile, or which have lower kinematic performance at all do not enjoy this advantage of add-on increased range. So a missile fired by low performance fighter is dependent wholly upon whatever fuel it has got and on the mercy of correctness of it's mid-course guidance algorithms who should direct the missile towards its target without wasting time and energy.

The Astra is designed to be capable of engaging targets at varying range and altitudes allowing for engagement of both short-range targets (up to 20 km) and long-range targets (up to 80 km).It uses smokeless propulsion system to evade enemy detection and has the capacity to engage in multi-target scenario. Astra can reach up to 110 km when fired from an altitude of 15 km, 44 km when launched from an altitude of 8 km and 21 km when fired from sea level.

Astra is believed to have a “No Escape Zone” of 30kms at ideal conditions. Based on seeker technology and missile kinematics the no escape zone is adjudged. This zone is defined as a conical shape with the tip at the missile launch. The cone's length and width are determined by the missile and seeker performance. No Escape Zone isn't practically an area where hit is guaranteed, it's just that when enemy is in your NEZ he/she cannot outrun the missile, but may outmaneuver it. Astra also have a high offbore-sight capability of +-45° by which it can shoot down enemy at a wider level.

Indian BVR combat tactics.

Earlier MiG-21 was the poster boy of Indian Airforce and Indians surrounded their tactics based on what MiG-21 can do the best. We see the developed nations have got strategies and they design their weapons according to these strategies, but developing countries tweak and adjust their strategies based on whatever weapons they manage to receive from developed nations. Although late but Indians decided to make their own strategies and tweak the foreign weapons suiting that. That's why the baseline Su-30mk was modified to MKI.

Induction of MKI brought new dominance for the IAF. Although MiG-29’s induction was the first time in history that IAF clearly knew that they have got a weapon superior than anyone in region. Having gained BVR capability IAF practiced real hard initially during an exercise which was conducted back in time, where all missiles fired missed their targets at high ranges. Those are Russian made R-77 missiles which both India and China operate in heavy numbers but not Russia itself. Unlike this Pakistan have got AIM-120s in the form of BVR and SD-10s as latest. Rising up to the reality IAF went major change in its BVR tactics that were akin to the actual capabilities of its missiles. This is why IAF who have so much loved foreign material is highly admanant of getting an indigenous Astra missile.

Now the tactics differ at different levels for a heavy class fighter like Su-30MKI, IAF choses to fire two missiles in one volley at a time per aircraft. This overwhelmes a usual target that IAF may potentially face. In fact there is a weapon select mode in MKI that makes it fire two missiles but this is only about R-77. While using R-27 it's just one missile in one volley because R-27 is relatively more reliable this is used in a later stage of BVR combat only if the first volley of R-77s have failed because the variants of R-27 used by IAF are semi active and at longer ranges using semi active radar seeking guidance is giving away your position.

If you see the Su-30MKI in air superiority configuration with maximum air to air loadout, it carries some 8 to 12 missiles in total. IAF believes that 'more the number of missiles in one volley more would be the kill probability’ Since if you fire just one missile the enemy have a number of countermeasures to get away and respond. But for a lower tier of fighters like MiG-29 the Navy's MiG-29k, Dassault Mirage 2000 or the latest HAL Tejas IAF puts it's bet on single shot kill probability being so high that a single missile is enough. Both Astra and the currently unnamed SFDR missiles are optimised for future scenarios and would be armed onto Indian 5th generation fighters. This is why IAF has French and Israeli AAMs in their arsenal. If there's any nation that has fired the most number of AAMs in actual combat that is Israel, they have huge experience in this. This is why Python 5 and Derby are some new favorites of IAF and recently tested and integrated with HAL Tejas.

Astra Mark 2

Astra mk2 which will begin testing in the upcoming years, experience with mk1 will come in handy and will boost in meeting the timeline of mk2. Astra mk2 will be using dual pulse rocket motor(cheap alternative of ramjet) which will boost it range to 125km if launched from 12km altitude and will gradually increase the NEZ (no escape zone) of the missile. Astra will be the mainstay of Indian airforce and Navy A2A missile arsenal in the future. Currently about 50 Astra missiles have entered in the initial production will be handed over to the airforce for some more testings, and will be inducted after the all the tests are done and bugs are sorted out. It is also said that mk2 may feature 3D thrust vectoring capability as it won't have those mid body control surfaces.

The main purpose of Astra is to replace the R77 from IAF. Being a fifth generation missile , it would provide true beyond visual range capability with greater strategic depth for the Indian Air Force. Being smoke free and having two way data link it provides very less chances to enemy to be alert about it.

Image Source: Click on the respective images

Info Sources :

http://trishul-trident.blogspot.in/2017/02/aero-india-2017-highlights-2.html?m=1

https://www.google.co.in/amp/s/m.economictimes.com/slideshows/infrastructure/astra-indias-first-indigenous-bvr-air-to-air-missile/astra-drdos-air-to-air-missile/amp_slideshow/35329826.cms

http://www.ausairpower.net/APA-Rus-BVR-AAM.html

https://en.m.wikipedia.org/wiki/Astra_(missile)

http://www.airforce-technology.com/projects/astra-beyond-visual-range-bvr-air-to-air-missile/

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