BEHIND the success of the GSLV-MkIII D1 lay 15 years of developmental efforts of the vehicle’s massive strap-on motors, the core liquid stage and the crucial cryogenic stage. At 640 tonnes, it is the heaviest vehicle ISRO has built so far. It required the setting up of brand new infrastructure facilities at various ISRO centres, chiefly the Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram; the Liquid Propulsion Systems Centre (LPSC), Valiamala, 30 km from Thiruvananthapuram; the ISRO Propulsion Complex (IPRC) at Mahendragiri near Nagercoil in Tamil Nadu; and the Satish Dhawan Space Centre (SDSC) at Sriharikota.

The mission also led to ISRO fabricating a payload fairing, or heat shield, that was five metres in diameter and 10.7 metres tall, the largest composite hardware realised by ISRO so far. It protects the satellite inside during the vehicle’s ascent into the atmosphere.

When the mission turned out to be a spectacular success on June 5, a big slice of the credit belonged to the IPRC. A key centre for the mission, it had realised, tested and qualified the vehicle’s cryogenic stage (C-25) and the core liquid stage. Besides, it was here that the cryogenic and liquid propellants needed for the mission were made. “Our ISRO Propulsion Complex” is the “Jet Propulsion Laboratory [JPL, Pasadena, U.S.] of India,” declared P.V. Venkitakrishnan, Director, IPRC. “It is a world-class facility in terms of its integration centres and massive test stands. These facilities are tailor-made for India. They cannot be copied from elsewhere and set up here,” he told Frontline on May 30, six days before the launch.

According to S. Ramakrishnan, the first Project Director of GSLV-MkIII, as early as 2000 the Launch Vehicle Design Group (LVDG) at the VSSC was giving shape to the GSLV-MkIII. The LVDG’s report described the GSLV-MkIII as “a vehicle capable of launching four to 4.5 tonnes into GTO or about ten tonnes into low-earth orbit. The vehicle will use efficient boosters and stages with state-of-the-art materials and design methods to realise a rugged, least-cost and reliable launcher.”

The payload fairing that encases the four-tonne satellite has a diameter of five metres. “It was the first time we were going to make a payload fairing with a diameter of five metres. But there were no facilities in India, including machining works, to handle a heat shield of such a diameter and height,” said Venkitakrishnan, who was associated with the GSLV-MkIII D1 development from its inception to the end at the VSSC, the LPSC and the IPRC.

The entire infrastructure for a vehicle of this mass and size had to be developed for the first time, and Indian industries rose to the occasion. They included private industries such as Walchandnagar Industries Limited (WIL); Larsen & Toubro; Godrej; MTAR Technologies Private Limited, Hyderabad; and public sector undertakings such as MIDHANI, Hyderabad; and HAL, Bengaluru.

MIDHANI equipped itself to handle the four-metre class hardware for the liquid L-110 stage which was developed by 2006. “It was done in record time,” said Venkitakrishnan. Drawings, civil works, equipment facilities, hardware fabrication and validation of hardware were all done in four years. By 2010, the LPSC had developed the massive core liquid stage, and the big test stand in the IPRC had fired and tested it. The static test of the two solid booster motors were done at Sriharikota. By then, Ramakrishnan had become Director, LPSC, and N. Narayanamoorthy had taken over as Project Director, GSLV-MkIII. The development tests of the booster motors and the liquid stage were done under Narayanamoorthy’s leadership.

Qualifying the liquid stage and the strap-on motors was not an easy job. “The L-110 core liquid booster of the vehicle uses two Vikas engines. They should perform identically. There should not be any differential thrust between them. If the thrust between them differs, the vehicle will topple. The same is true with the two strap-on motors. Their performance should be identical,” said Venkitakrishnan.

From 2010 to 2015, Venkitakrishnan was in charge of the development and testing of the cryogenic stage at the LPSC. This demanded development of several strategic materials and superalloys used in the fabrication of the cryogenic engine. These materials were developed indigenously with a number of participating industries. The aerospace division of HAL, Bengaluru, provided the propellant tanks for the cryogenic stage. Soon the cryo engine development was completed and stage engineering done.

In fact, a special titanium-alpha alloy developed to make the helium gas bottles used in the vehicle led to a lot of weight being saved. This, in turn, led to a gain of 60 kg in payload (satellite) weight. The development of the gas bottles using the titanium alloy was done at the LPSC, said Venkitakrishnan.

Massive infrastructure was built at the SDSC, Sriharikota, to augment the capacity of the Solid Propellants Space Booster Plant (SPROB) to cater to the requirements of GSLV-MkIII class vehicles. A new Solid Propellants Plant (SPP) was built to produce the S-200 motors exclusively for GSLV-MkIII vehicles. It has now been made versatile in terms of enabling the production of solid motors for the PSLVs and the GSLV-MkII vehicles. The Solid Stage Assembly Building (SSAB) at Sriharikota, where the solid motors of the GSLV-MkIII are integrated, has also been made versatile. It has been modified for the integration of the first stages of the PSLVs and the GSLV-MkII vehicles. Besides, big facilities have come up at the launch pad to service the cryogenic stage of GSLV-MkIII vehicles with liquid oxygen and liquid hydrogen. They include refrigeration, pipelines, engine chilling, liquid oxygen tanks and so on. All these have state-of-the-art safety features.

P. Kunhikrishnan, Director, SDSC, Sriharikota, said that during the lift-off of the GSLV-MkIII D1 an acoustic suppression tower built at the second launch pad sprayed 600 tonnes of water in order to reduce the noise levels that might damage the rocket and the satellite inside the heat shield. (When the GSLV-MkIII lifts off, its two strap-on motors together generate a thrust of more than 800 tonnes. The sheer volume of noise produced then can damage the rocket and the satellite.)

Kunhikrishnan said a second Vehicle Assembly Building (VAB), three times bigger than the present one, would be ready in some months. Once the second VAB is ready, the frequency of launches would go up.

What gave Team ISRO the confidence about the GSLV-MkIII D1 mission was the first successful firing of the cryogenic stage for 50 seconds on January 25, 2017, at the towering test stand at Mahendragiri. “If any problem were to be there, it would show within the first 50 seconds. After that, the engine will stabilise. There will be combustion stability,” said Venkitakrishnan. After this test, the flight stage, that is, the D stage, was prepared with minor modifications using the results of the 50-second test. This stage was fired successfully for the full flight duration of 640 seconds on February 17, 2017. It was this stage that went into the actual flight on June 5.

V. Narayanan, Project Director, C-25 Cryogenic Project, and Associate Director, LPSC, said: “We are one of the few countries to have developed this cryogenic technology. The cryogenic engine used in the GSLV-MkIII D1 mission was totally indigenously conceived, designed, developed, realised, tested and qualified. This gives us a great advantage.”

After the GSLV-MkIII D1 success, Venkitakrishnan said: “In 2002, we were wondering how to make a heat shield with a diameter of five metres, how to make the machines for it and so on. This vehicle had more swadeshi elements than any other vehicle. The superalloys and strategic materials needed for the vehicle were made here.

All the machines were conceived, designed and realised by our industry. We have gone on the right path from the beginning in 2002.”

T.S. Subramanian