“TOWARDS Sustained Self-reliance in Accessing Space” announced a huge poster on a wall in the cabin of S. Ramakrishan, the first Project Director of the Geosynchronous Satellite Launch Vehicle–Mark III (GSLV-MkIII). It was October 2002 and only five months earlier, in May, the Central government had approved the development of the GSLV-MkIII. Frontline was visiting the Vikram Sarabhai Space Centre (VSSC) in Thiruvananthapuram, on whose vast campus was situated, by the seashore at Thumba, a small building that housed Ramakrishnan’s cabin on the ground floor where the GSLV-MkIII project was taking shape. The massive vehicle, as I saw in the poster, was called “gsLVM3”, or launch vehicle Mark 3, India’s “Next Generation Launch Vehicle”.

On October 2, 2002, K. Kasturirangan, then Chairman of the Indian Space Research Organisation (ISRO), had formally constituted the GSLV-MkIII project with Ramakrishnan as Project Director. The primary objective was to develop a launch vehicle that would put a four-tonne satellite into the geosynchronous transfer orbit (GTO, with a perigee of about 180 km and an apogee of about 36,000 km). The rocket would be a “totally new, powerful animal”, Ramakrishnan told Frontline on that 2002 visit.

Fifteen years later, the gigantic GSLV-MkIII D1, weighing 640 tonnes, roared into the sky at 5:28 p.m. on June 5 from its launch pad at Sriharikota in what was its first developmental flight (D1). The heaviest rocket that ISRO has built was well and truly on its way to making history as its two strap-on motors, each guzzling 200 tonnes of solid propellants and together producing 800 tonnes of thrust, worked with gusto. “Strap-on motors’ performance normal”, “L-110 [liquid engine] ignited” came the voice from the Mission Control Centre (MCC) situated seven kilometres from the launch pad. “Strap-on motors separated”, “L-110 performance normal”, “heat shield separated”, “plus four minutes”, and “L-110 core stage separated” were the other announcements from the MCC. Then came the announcement that everyone was waiting for: “Cryo stage ignited”. Its performance too was normal. Finally, at the end of the mission that lasted 16 minutes and 20 seconds came the all-important announcement that “GSAT-19 [the satellite] has separated”.

It was a remarkable success for a totally new vehicle on its debut flight. As ISRO’s top brass stressed, it was a vehicle built indigenously from scratch: its strap-on motors, its core liquid stage, its cryogenic upper stage and the ogive-shaped payload fairing (heat shield) with a massive diameter of five metres. Each of these was conceived, designed, developed, realised and tested in India. Each of the three stages was the largest that ISRO has built so far. The crucial cryogenic upper stage had no reference to the Russian cryogenic engines of the GSLV-MkI series of vehicles. At 640 tonnes, the GSLV-MkIII D1 was 50 per cent heavier than GSLV-MkII, which weighed 414 tonnes.

The 43.43-metre-long GSLV-MkIII D1 had a simple configuration with only three propulsion stages. The two solid strap-on motors, called S-200, clung on to the core liquid stage, called L-110, on either side. The liquid stage, four metres in diameter, used more than 110 tonnes of liquid propellants. Above the core liquid stage sat the cryogenic stage called C-25, which used 28.3 tonnes of cryogenic propellants, that is, liquid oxygen and liquid hydrogen in the mission. On top of the cryogenic stage sat the GSAT-19 surrounded by the payload fairing, which was 10.3 metres tall and five metres in diameter.

The importance of the cryogenic stage in the mission that lasted 16 minutes and 20 seconds can be gauged from the fact that its engine performed with precision for 10 minutes and 40 seconds (640 seconds). Of the total velocity of 10.5 km a second needed to put the 3,136-kg GSAT-19 into the GTO, the cryogenic engine contributed more than 5 km a second.

The triumph signalled India’s self-reliance in space technology with a robust, cost-effective vehicle made possible by its mastery over the cryogenic technology that is needed to put heavier communication satellites into their initial orbit.

The GSLV-MkII rockets, with indigenous cryogenic engines, could put satellites weighing 2.2 tonnes into a GTO. Now ISRO does not have to depend on Arianespace to put its four-tonne satellites into orbit. The GSLV-MkIII can also put satellites weighing 10 tonnes into low-earth orbits. The vehicle can carry a crew module with two or three astronauts into space or even segments of a space station.

The success broke the jinx that had plagued ISRO’s earlier generations of vehicles. Be it the Satellite Launch Vehicles (SLV-3s), the Augmented Satellite Launch Vehicles (ASLVs), the Polar Satellite Launch Vehicles (PSLVs), the GSLV-MkIs (with Russian cryogenic stage) or the GSLV-MkIIs (with Indian cryogenic stage), in all of them the first flight failed. But an extraordinary confidence prevailed in the various ISRO centres when it came to the GSLV-MkIII D1 mission.

Those failures were seen as stepping stones to success. The failure of the first GSLV-MkII flight with an indigenous cryogenic engine on April 15, 2010, was followed by four consecutive successes for the vehicle from January 2014.

ISRO had also drawn its lessons from the LVM3-X/CARE Mission of December 18, 2014. The crew module atmospheric re-entry experiment (CARE) mission was a replica of GSLV-MkIII D1 but with a crucial difference. It carried a C-25 stage which did not fire. The vehicle carried a 3.75-tonne CARE module. At a height of 126 km, the module separated from the dummy cryogenic stage and went into a sub-orbit. It started descending immediately and splashed down near the Andaman archipelago where it was recovered by the Coast Guard. The entire mission from lift-off to splashdown lasted about 20 seconds and the strap-ons and the core liquid stage performed exceedingly well.

Given this background, the relaxed atmosphere at the MCC on June 5 was not surprising. The mission was so flawless that a journalist covering it could not help commenting, rather inappropriately, that “there was no thrill” in reporting it.

ISRO Chairman A.S. Kiran Kumar called it “a historic launch” and “the culmination of a large amount of work done over decades”. About 200 tests had been done on the vehicle’s various systems since 2014 and ISRO was, therefore, confident about the mission’s outcome, he said. “But there were some butterflies in the stomach,” he conceded. The GSLV-MkIII needs one more successful developmental flight before it can be declared an operational vehicle, and this flight will take place in less than a year, Kiran Kumar announced.

The just-concluded mission came about in a year and a half. K. Sivan, Director, VSSC, called it “a marvellous technological achievement” made possible by the meticulous planning by various ISRO centres and the “very fast” fabrication of hardware by industries.

The mission had “no technological element borrowed or adapted from anybody”, asserted S. Somanath, Director, Liquid Propulsion Systems Centre (LPSC). “I am proud to say that the ISRO team has mastered the cryogenic technology” with this success, he added.

The success of the “advanced vehicle” also lay in the fact that it put into a perfect orbit GSAT-19, “an advanced communication satellite”. It carries Ka/Ku-band “throughput communication transponders” that have “no physical presence” and are “virtual transponders”. It uses multiple frequency beams to send down data and is hence called a throughput communication satellite. The satellite carries a payload called Geostationary Radiation Spectrometer (GRASP) to study the nature of charged particles and the influence of space radiation on satellites and their electronic components.

Tapan Misra, Director, Space Applications Centre, ISRO, Ahmedabad, which made the payloads in the satellite, called it “a game changer communication satellite for India”. The satellite was tantamount to a constellation of six or seven communication satellites of earlier generations.

P.K. Gupta, Project Director, GSAT-19, called the satellite “a test laboratory in space” because it carried 15 critical technologies that would be validated during its lifespan in space. These technologies would form the mainstay of the next generation, heavier satellites. GSAT-19 was integrated at the ISRO Satellite Centre, Bengaluru, whose Director is M. Annadurai.

It was a networking of various ISRO centres and industries that led to the GSLV-MkIII D1 mission’s success. The VSSC designed the vehicle and developed its two powerful solid motors. The LPSC developed and realised the core liquid engine stage and the upper cryogenic stage before the ISRO Propulsion Complex (IPRC) at Mahendragiri, Tamil Nadu, was hived off from the LPSC on February 1, 2014. It was in the sophisticated test stands of the IPRC, after it became a separate facility, that the liquid stage and the cryogenic stage were tested and qualified. The three stages of the vehicle and the satellite were married up on a massive mobile platform in the Vehicle Assembly Building of the second launch pad at Sriharikota.

Ramakrishnan, who went on to become Director, LPSC, and also Director, VSSC, asserted that the GSLV-MkIII D1 was “a totally new vehicle because all the systems, including the S-200 stage, the L-110 stage and the C-25 stage are new”. The C-25 stage with its cryogenic engine called CE-20 underwent only two tests—it was fired for 50 seconds on January 25, 2017, and it underwent a full, flight-duration test for 640 seconds on February 17. “We started work from scratch on this cryogenic engine. It is not similar to the cryogenic upper stage of GSLV-MkII. It has no reference to the Russian cryogenic engines used in the GSLV-MkI flights. It is a totally indigenous cryogenic engine,” Ramakrishnan asserted.

In an interview to Frontline in his office at the VSSC on May 27, Sivan explained why the GSLV-MkIII D1 was a totally new vehicle and why ISRO developed it. While the PSLV could put a 1.1-tonne satellite into the GTO, the GSLV-MkII, with an indigenous cryogenic upper stage, had double that capacity. However, 10 years ago, building a new class of communication satellites that weighed four tonnes became the norm.

“Augmenting the capacity of the existing vehicles will not solve the problem. Doubling the capacity is huge. So we had necessarily to go in for a new vehicle,” Sivan said.

ISRO was clear that the new vehicle should be able to reduce the cost of the launch. “The cost of the launch vehicle may be more, but it should be able to take a heavier satellite into orbit so that the cost of launching per kg of satellite will come down. This was the main criterion,” Sivan said.

Secondly, the vehicle’s design should be simple and it should be a reliable vehicle. Reliability entailed that the vehicle should have the minimum possible number of propulsion stages to put a four-tonne satellite into orbit.

An area of major concern was the launch constraint imposed by the location of Sriharikota, India’s space port. The launch had to take place eastward from the island to put a communication satellite into the GTO. This did not offer “full freedom” because after the vehicle cleared the Bay of Bengal, the Indonesian land mass appeared on the scene. The launch vehicle debris—from the jettisoned stages—should not be allowed to fall over Indonesia.

Sivan said: “We had seen that when the vehicle reached a velocity of more than 5 km a second, the Indonesian land mass came in. So we had a requirement of designing a launch vehicle that will have a capacity of reaching [a velocity of] 5 km a second. But it is the lower stages that should produce that velocity of 5 km a second. We then needed one more stage which will produce another 5 km a second of velocity. There cannot, however, be an intermediary stage. [A total of 10.2 km a second velocity is required to put a four-tonne satellite into the GTO.] After the vehicle crosses the land mass, its stages should not come down. They should continuously burn and go into orbit. That means we should have a stage that should give another 5 km a second after the vehicle crosses the land mass. So we had to necessarily go in for a cryogenic stage that will give 5 km a second at a stretch and carry the four-tonne satellite into orbit. To put a 2.2-tonne satellite into orbit, we had a cryo stage with 12 tonnes of liquid oxygen and liquid hydrogen. But to put a four-tonne satellite into orbit, we needed a cryogenic stage which will use 25 tonnes of propellants. That is how the C-25 stage came into the picture.”

In other words, while the vehicle’s lower stages will provide a velocity of about 5.2 km a second, the cryogenic stage will provide another 5 km a second. Thus, the entire vehicle would generate a velocity of 10.2 km a second to put a four-tonne satellite into the GTO.

Since ISRO wanted to build a vehicle with a minimum number of stages and minimum complexity, “we prepared a configuration with two S-200 strap-on motors around the core liquid stage which uses 110 tonnes of liquid propellants and a third, cryogenic upper stage which uses 25 tonnes of propellants. This configuration can carry a four-tonne satellite into GTO,” Sivan said. In fact, the core liquid stage had two Vikas engines.

(In comparison, the GSLV-MkII had seven propulsion motors: four liquid strap-on motors around the core solid stage, then the liquid stage, followed by the cryogenic upper stage to put a 2.2-tonne satellite into orbit.)

Sivan added: “Thus, we configured a simple system with the general requirement of reducing cost, increasing reliability, using the systems already developed and taking less development time. All these combined together, we arrived at this configuration.”

“We have two strap-ons in GSLV-MkIII which are among the most massive strap-ons in the world,” said S. Somanath, Director, LPSC. “Though they are called the strap-ons, they are the primary propulsive stages. They provide the entire lift-off thrust. Unlike in the PSLVs and the GSLVs, the strap-ons in GSLV-MkIII are the primary propulsion stages. That way the basic design of the vehicle is different.”

But the introduction of such big boosters, each of which used more than 200 tonnes of solid propellants, entailed problems. In the PSLVs and the earlier GSLVs, the performance of the strap-on motors “was not very critical” to the mission and “a slight difference in their performance would not make an issue”, the LPSC Director said. However, in GSLV-MkIII D1, since the two strap-on motors were extremely powerful, their performance was very critical to the mission and they had to produce identical thrust. “The entire vehicle will topple if the thrust-level is not identical. They have 400 tonnes of propellants. Their matched performance is very critical,” said Somanath. The thrust differential should not exceed plus or minus ten tonnes.

What also set apart GSLV-MkIII DI from the PSLV and the earlier GSLVs was “the philosophy” of the core liquid stage taking over from the two strap-on motors. All the three fire together for some time before the solid strap-on motors burn out and the core liquid stage fully takes over. What happens is this: after the S-200s erupt into life on the ground at T-minus zero, the L-110 starts firing one minute and 54 seconds later. The three together fire for 26 seconds before the two strap-ons separate. The liquid engine continues to fire until five minutes and 17 seconds after the blast-off.

Somanath said: “When the four motors are working together, we have algorithms which can make use of all four nozzles. Two solid motors are working. Two liquid Vikas engines in the liquid stage are working. All of them are under control. The moment the S-200s are shut down, you have to change the algorithm and transfer the control to the liquid stage motor. It should be done smoothly, without any jerk or problem.”

What made the GSLV-MkIII D1 different was that instead of using explosive separation bolts or springs to push down/jettison the spent stages, ISRO used six small motors in each of the strap-on stages to kick out the spent solid stages. “Here we cannot use the springs because the motor weight itself in each strap-on is 35 tonnes. We have, therefore, used six small motors in each strap-on to push the 35 tonnes away. The motors have to be fired at the moment the strap-ons have to be separated,” the LPSC Director said.

G. Ayyappan, Mission Director, emphasised that after the LVM3-X/CARE mission in December 2014 “we made this vehicle more robust in terms of aerodynamics”. As the launch vehicle climbs into the atmosphere, it experiences turbulence, so ISRO developed a new kind of payload fairing, called ogive payload fairing, to protect the satellite inside. Ayyappan explained: “During the atmospheric phase of the flight, the loads experienced by the vehicle are directly proportionate to the dynamic pressure and the angle of attack. Our aim was to reduce as far as possible the dynamic pressure and the angle of attack so that the vehicle will have a smooth passage through the atmosphere.”

Sivan called the atmospheric phase of the flight “very crucial for any launch vehicle mission”. As the launch vehicle ascends the atmosphere, its velocity builds up fast. But the atmospheric density comes down. Winds would be large. The dynamic pressure acting on the vehicle would be the maximum. When the loads acting on the vehicle are large, the disturbance will try to tilt the vehicle. “When this disturbance is trying to tilt the vehicle, the vehicle’s control systems will work in the opposite direction to correct it. So a breaking effect will be there. The vehicle will break as if it were a stick,” the VSSC Director said.

Besides, the ebb and flow occurring over the vehicle will create a lot of acoustic noise. The acoustics will be so high that they could harm the sensitive instruments in the satellite which is seated inside the payload fairing. It should be ensured that the acoustic level outside the vehicle is benign. So the payload fairing of the GSLV-MkIII D1 was modified, after the LVM3-X/CARE mission in December 2014, to withstand severe aerodynamic loads. “Our aim was that internal acoustics for the satellite should be benign. The payload fairing was changed to an ogive-shaped curve,” Ayyappan said. The normal “straight-on” nose cones of the strap-on booster stages were modified to slanted types. “The shape and size of the payload fairing and the head-end segment of the solid motors were modified so that there will be minimum disturbances acting on the vehicle. The launch vehicle was thus made more aerodynamically robust,” said Ayyappan, who is also the Project Director, GSLV-MkIII.

As P.V. Venkitakrishnan, Director, IPRC, Mahendragiri, said, the GSLV-MkIII D1 turned out to be “a grand vehicle in terms of everything”: in its high-performance cryogenic engine, the smooth functioning of its two solid strap-on motors, the firing of its liquid engine and, of course, its capability to put a four-tonne satellite into GTO. And, above all, in terms of realising the dream of “sustained self-reliance in accessing space”.