THE Defence Research and Development Organisation (DRDO) achieved a technological breakthrough in September-October 2007 when it developed and tested a large rocket motor whose casing was made entirely of carbon filament-wound composite. The qualification and static tests were successful. The motor casing was developed indigenously by the Advanced Systems Laboratory (ASL), Hyderabad, a unit of the DRDO, and realised by industry.

“This is a major breakthrough because it provides us the key technology for going into longer missions [for instance, the Agni-V missile] with lighter missiles,” said Avinash Chander, Director, ASL. The advantages of rocket motor casings made of composites that are light but strong are manifold. The ultimate ambition of the ASL is to build a missile made totally of composites with no metal in them.

Today, most rocket motor casings in the civilian and defence sectors in India are made out of steel. Maraging steel, made by the public sector undertaking MIDHANI, has special strength. However, weight is a critical factor in missiles. A lighter missile can be easily transported either on a railway track or by a truck and thus can be launched from any part of India. Besides, light-weight missiles are able to carry payloads over a longer distance. Therefore, the trend all over the world is to make rocket motor casings out of composites.

The ASL is a premier missile laboratory working on composites. It achieved a breakthrough several years ago by developing a heat shield made of carbon composite without any metal back-up. It is the heat shield that protects the warhead and avionics from the 2,500-degree Celsius temperature generated during the missile’s re-entry into the earth’s atmosphere. This heat shield, made of composites, is being used in the Agni family of missiles.

Avinash Chander said: “But a composite motor [that is, motor casings made of light-weight composites] was one area where we were struggling to find our own capability because nobody gives you this technology. We had no access to any machinery or equipment to make the composites. Only the Russians, the Americans and the European consortium EADS [European Aeronautics Defence and Space Company] have this capability.”

The advantages of building rocket motor casings out of composites are manifold. Composites reduce the weight of the missile stage by 40 per cent. That is, if the composite motor casing leads to a weight reduction of 200 kg compared to a casing made of metal, the warhead’s weight can go up correspondingly, by 200 kg. This is a huge amount for a payload. Or the range of the missile can be stepped up. Alternatively, a combination of both can be had.

Besides, the missile can operate at much higher pressures. “We are able to increase the operating pressure and reduce the burn duration so that the missile will have a short time of operation and we can make it more efficient,” the ASL Director said.

A composite motor casing is also cost-effective. It costs half as much as a metallic motor casing. Thus, the performance of the motor is two times more efficient at half the cost. Composites are non-corrosive and thus have a longer storage life than metallic motors. Since missiles have to be stored, the non-corrosive nature of a composite rocket motor is an advantage.

But it was not a smooth journey for the young team comprising K. Jayaraman, Director, Composites, and Manoj Kumar Buragohain and Pradeep Thakkar, both scientists, to develop and test the rocket motor casing. This ASL team had to do non-destructive evaluation of motors. “An entire set of evaluation techniques using X-rays and ultrasonics that are applicable to this class of systems was developed,” said Jayaraman.

Today, the ASL has come up with a frontier technology from a zero base, and this involved the development of material processes, evaluation techniques, design tools, fabrication techniques and so on. It is equally important that all these have been transferred to medium-scale industries specialising in composite structures, and the ASL receives its products from them.

Avinash Chander said: “For all our long-range missions, this is a key technology. This will enable building upper stages for missiles with greater ranges. In the long run we will have an all-composite missile. We have already developed payloads made of composites. We have made inter-stages out of composites. They have gone through qualification trials and we are ready to use them. With this development of motor casing made of composites, we will practically have no metal in our missiles.”

This development would be an avoidable requirement when India wants to build missiles with multiple warheads or a missile that is launched from under water. “That is the basic importance of this event,” he added.

T. S. Subramanian