Indian Missile News And Discussion

[osman]

http://www.frontline.in/stories/20120518290912400.htm



Frontline on Agni V. A lot of details. Did not post the entire article. Just technical details.



At 8-07 a.m., as the Agni-V shot out smoothly from its launch pad, roared into the sky and built up a powerful thrust, there was no doubt about the mission's success. The three stages ignited on time and their separation was clean and precise. The missile climbed to a height of about 600 km before starting to descend. The powered flight, with the three stages igniting and separating, lasted about 220 seconds. As each stage fired and decoupled, the MCC and the adjacent hall reverberated with applause. There was a long gap between the third stage separation and the re-entry vehicle knifing into the atmosphere at an altitude of 100 km.After the third stage separated and the re-entry vehicle was ejected at a velocity of about six km a second, the mood in the MCC was relaxed.



The DRDO's missile technologists were sure that “the re-entry vehicle will not go anywhere”. Even if no data were available after the powered flight phase got over, “we would have known precisely where the re-entry vehicle had gone”, they said. In fact, when the third stage ejected the re-entry vehicle at a velocity of 6 km a second, it became the fastest travelling object made by India, speeding at 25 Mach, or 25 times the speed of sound.



“The third stage separation was the determining point,” Sekaran explained later. “After that, gravity takes over. Subsequently, nothing will happen. Nothing can happen also. It [the re-entry vehicle] is a free body travelling under gravity. It becomes what you call a ballistic flight.”



The re-entry vehicle itself is a technological marvel, housing the missile's avionics and the nuclear warhead. Indeed, it houses all the electronics systems for navigation, guidance and control and the on-board computers. The avionics are within the missile's nose cone, which is made of carbon-carbon composites. The re-entry vehicle is protected by a heat shield, which is made out of carbon composite fibre. In this mission, the Agni-V carried a warhead that mimicked a nuclear bomb but without the radioactive material. {full test sans the radioactive material to test the survivability of the trigger}



The re-entry itself is a critical manoeuvre for the vehicle should slice itself into the atmosphere at the correct angle. The levels of deceleration should be perfect although the loads acting on the re-entry vehicle are very high. Besides, the survival of the re-entry vehicle is important. Its carbon composite tiles, a couple of inches thick on its outer surface, should withstand scorching temperatures of more than 5,0000 Celsius as it slices into the atmosphere. But the temperature inside the re-entry vehicle should not be more than 500C{50?} so as not to harm the electronics equipment in the nose cone. “At that stage, the outer layer starts burning and the package inside should survive and be functional at 500C…. Over a few inches of thickness, the temperature drops from 5,0000C to 500C,” Chander explained.



After about 20 minutes of flight, when the dummy warhead carrying explosives erupted into a fireball and hit the waters of the Indian Ocean somewhere between Australia and Madagascar, another round of applause rang out in the MCC. The re-entry vehicle's impact point in the Indian Ocean was more than 5,000 km from Dhamra in the Bay of Bengal. The fireball was captured by cameras on three naval ships stationed downrange near the impact point. Agni-V was a spectacular success on its maiden flight itself.



Sekaran argued that “the critical, deciding factor was the propulsion” system used in the three stages of the missiles. This was the first time that the DRDO was test-firing a three-stage missile, all powered by solid propellants. {better thrust for given weight?}



According to Chander, Agni-V was “a game-changer in many ways”. First, he said, “You can reach all targets of your interest from deep inside India. You have got a system which allows you to reach the farthest corners where you want to exert your influence while you have sufficient protection for yourself.” Secondly, it can be launched from a canister and a road-mobile launcher, that is, a massive truck with a trailer. “It will give you ‘a stop and launch' capability,” the DRDO Chief Controller said. The road-mobile launcher can stop at a roadside, fire the missile and go away. So it will be difficult to intercept it, beat it or defeat it during its launch phase because its mobility will be high.



Thirdly, the composite motors of the size used in Agni-V has given the DRDO the confidence to go for missiles with larger motors and manoeuvring warheads because the motor casings, made out of composites, will be light in weight but provide a higher performance.{was that the reason for conical motors? Will the mirv also have these manoeuvering motors on warheads?}



Although the DRDO's missile complex in Hyderabad comprising the DRDL, the ASL and the Research Centre, Imarat (RCI) played important roles in developing the components, systems and subsystems for Agni-V, the ASL's contribution stood out. The ASL, which Sekaran heads, designed and developed the Agni-V, built the powerful propulsion systems for its three stages, developed the light-weight rocket-motor casings made of composites and the heat shield too. Chander praised Sekaran's role in designing and developing the heat shield.



While Agni-III missiles ejected the re-entry vehicle at a velocity of 4.2 km a second, Agni-V ejected it at a velocity of 6 km a second. “This is a new dispensation in terms of higher velocity. At the end of the day, you have to survive the re-entry and then only you can deliver. The particular heat shield we made for Agni-V is the strength of the ASL,” the ASL Director said.



As the re-entry vehicle comes down through the atmosphere from an altitude of 100 km to a lower altitude, the atmosphere's density keeps increasing. Once the density increases, the re-entry vehicle's deceleration breaks and the heat generated keeps shooting up. It is akin to speeding in a car when brakes are suddenly applied and people seated in the car lurch forward. “In this case, the systems are qualified for 100 G. The survivability of the re-entry vehicle is a critical area,” Sekaran said. (The re-entry phase lasts 40 seconds to 50 seconds.) {Hmmz 220 seconds of powered flight to third stage separation, re-entry time of 40 to 50 seconds. 24 minutes total flight time ? Am I missing something here?}



In a civilian mission – for instance a mission of the Indian Space Research Organisation (ISRO) – the heat shield protects the satellite from intense heat and friction during the rocket's ascent phase into the atmosphere and later splits down its seams and falls away. The role of a heat-shield protecting the re-entry vehicle of a missile is different. And, the satellite goes into empty space. But in a military mission, as the re-entry vehicle enters the atmosphere, the heat shield not only protects the re-entry vehicle but goes down with it. “The heat shield does not jettison at all,” a DRDO engineer said.



Although the ASL had made heat shields for previous Agni missions including that of Agni-III, the shape, size, diameter and angle of the heat shield for Agni-V was different. The heat shield's diameter in Agni-V was 1.5 metres, while it was 1.2 metres for Agni-III.



Another strength of the ASL lay in designing and developing motors propelled by solid fuel for Agni missions. For the Agni-V test flight also, the ASL designed and developed solid motors for its three stages. Besides, it developed the all-important light-weight composite for the second- and third-stage motors, which led to a reduction in their weight but far better performance. A crucial step towards developing Agni-V was taken when the ASL developed in 2007 a large rocket motor casing made entirely of carbon-filament wound composite. This casing, developed indigenously, formed the third upper stage of Agni-V. The casing went through full qualification trials in 2007.



“We never went out. The static testing of the motors was done in the same organisation [in various units of the ASL]. This is a formidable combination,” said Sekaran. The ASL also established its expertise in high-performance composites. It developed the composites for the missile motor casings and nose cone and established the process parameters for them. Then the technology was transferred to the industry for fabricating these composites. “The nose cone was fully made out of carbon composites developed by the ASL. It withstood a temperature of more than 5,0000C. You cannot make it out of metal. If you do so, the weight will shoot up,” he added. {Indigenous carbon-filament wound composite.}



Systems engineering is also one of the strengths of the ASL because it specialises in building up from what it already has. With the addition of a third upper stage and with minor modifications, the two-stage Agni-III metamorphosed into an awesome Agni-V. Yet the weight remained the same for both vehicles despite the addition of a third upper stage to Agni-V because the second- and third-stage motor casings were made out of light-weight composites. A lighter missile can be easily transported by rail or on road. Besides, it can carry a payload over a longer range.



In an interview to Frontline in May 2008, Chander pointed to the DRDO developing a large rocket motor casing made entirely of carbon-filament wound fibre and said, “This is a major breakthrough because it provides us the key technology for going into longer missions with light-weight missiles.... We have flight-tested Agni-III twice successfully. When we want to go in for missiles with higher ranges, one key technology is the rocket motor casing. That has been developed now” ( Frontline, June 06, 2008).



The RCI developed the navigation system for Agni-V, and its architect was the young G. Satheesh Reddy, Associate Director, RCI. “Our navigation for Agni-V was different from the one used for Agni-IV. It was a redundant, reliable system with high-performance and accuracy,” he said. Agni-V had two navigation systems: ring-laser gyro-based system and a micro-navigation system with good accuracy. Fault-tolerant features were incorporated into the navigation system and on-board computers. “Our on-board computers have been developed in such a way that they can recover transient failures. Besides, the entire data computation in avionics is highly reliable and robust,” he said. {In case of blackouts during re-entry the system will recover. Even the space shuttle has crucial communications blackout. Does this mean all ICBMS go through a navigational blackout during re-entry?}



The important technology of the inertial navigation system, guidance and control used in Agni-V was the brainchild of the RCI, said S.K. Chaudhury, its Director. All the systems were validated by advanced simulation at the RCI. The DRDL's role in the mission was to characterise the vehicle.



The DRDO's attention is now focussed on the next Agni-V launch from a canister and a road-mobile launcher in early 2013. The Shourya and the BrahMos missiles were launched many times from a canister. Chander said the DRDO had set up a facility at Shamirpet, near Hyderabad, for missile ejection tests using a gas-generator from a canister. The road-mobile launcher would be ready in May. With Agni-V scheduled to be inducted into the Army by 2015, there would be six flight tests, including three pre-induction trials.