Illustration by C R Sasikumar Illustration by C R Sasikumar

Last Wednesday, the Indian Space Research Organisation (ISRO) opened its launch activities for 2017 by deploying an eye-popping 104 satellites on a single Polar Satellite Launch Vehicle (PSLV), making it seem easy to accomplish. There’s more to come.

The space agency is now gearing up to send the “Satellite for South Asia” on a Geosynchronous Satellite Launch Vehicle (GSLV) next month. This is a satellite that Prime Minister Narendra Modi directed ISRO to produce three years back. The GSAT-9, as it is also known, is intended to provide a range of communication and broadcasting services to neighbouring countries. (Pakistan, however, decided to opt out.)

Far more momentous will be the first developmental flight of the country’s most powerful launch vehicle thus far, the GSLV Mark-III, which is currently expected to take place in the second half of April. This is a massive rocket that weighs one and a half times as much as its predecessor, the GSLV, and, more importantly, will have twice its heft in terms of payload capacity. So it will be able to carry communication satellites that are too heavy for the latter and which ISRO must at present launch abroad at a cost of hundreds of crores of rupees each.

Just two days after the 104-satellite launch, a major milestone was crossed. The final ground test of the Mark-III’s cryogenic stage was successfully completed at the ISRO Propulsion Complex (IPRC) at Mahendragiri in Tamil Nadu. A cryogenic engine burns a highly-efficient propellant combination, liquid hydrogen and liquid oxygen. But their ultra-low temperature, particularly of liquid hydrogen, creates enormous problems when using them in rockets. A cryogenic stage holds the engine as well as insulated tanks for the propellants and all the pipes, valves and other components need to control their flow to the engine.

It is difficult technology to master. In 1991, India had signed a contract with Russia to acquire its technology for a cryogenic engine and stage. But, under pressure from the United States, the Russians backed out of the deal two years later and ISRO was left to develop that capability on its own. The Russians did supply seven flightworthy stages, six of which have flown as the upper stage of GSLV rockets, with the first such flight carried out in 2001. It took ISRO 20 years to produce indigenous equivalents of the Russian engine and stage. The first successful flight of a GSLV equipped with an indigenous “Cryogenic Upper Stage” (CUS) took place just three years back, making India only the sixth nation to possess cryogenic technology.

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The GSLV Mark-III’s CE-20 cryogenic engine and C25 cryogenic stage, on the other hand, are based on a wholly Indian design that is considerably simpler, though a bit less efficient in terms of propellant consumption, than the CUS. Moreover, the CE-20, producing, as its name suggests, 20 tonnes of thrust, is two and a half times more powerful than the CUS engine. It also ranks, according to ISRO, as one of the most powerful upper stage cryogenic engines in the world. Experience with the CUS had greatly aided development of the Mark-III’s cryogenic engine and stage, remarked S. Somanath, director of the Liquid Propulsion Systems Centre (LPSC), which has its headquarters near Thiruvananthapuram in Kerala.

Some elements of the CUS engine and its manufacturing process had, for instance, gone into the Mark-III’s CE-20 engine. Stage development, too, had benefited. In the case of the GSLV, after the Russian engine was indigenised and qualified, a flightworthy CUS took eight years to develop, he pointed out. But for the Mark-III, “the [cryogenic] engine was qualified just six months back and we have tested the stage now,” he said.

The Mark-III’s C25 stage was test fired for 640 seconds, the duration for which it is expected to operate in flight, at Mahendragiri last Friday (February 17). The successful completion of all ground tests means the CE-20 engine and the C25 are now ready to take wing. That in itself is a hugely significant event, further underscoring India’s mastery of cryogenic technology. Assembly of the cryogenic stage for the Mark-III’s first development flight is in progress, according to P.V. Venkitakrishnan, the IPRC director. The stage would be ready for transportation to Sriharikota by the middle of March. The Mark-III’s core stage is powered by twin Vikas liquid propellant engines that are used in the PSLV and GSLV as well. On either side is one of the world’s largest solid propellant boosters loaded with 200 tonnes of propellant. The C25 cryogenic stage goes on top of the core stage.

ISRO flight tested the GSLV Mark-III on an experimental mission in December 2014, using a dummy cryogenic stage. The mission had been carried out to address a number of important questions about the rocket’s performance in actual flight, according to Somanath, who was the Mark-III project director at the time. He claimed that all those questions are answered. “I think we had a beautiful flight,” he said. Now, “we are sure that all the lower stages are going to perform” and so there was greater confidence in the success of the upcoming mission with the actual cryogenic stage.

The GSLV is currently capable of accommodating a communication satellite weighing up to about 2.2 tonnes. However, since 2002, ISRO has launched 11 INSAT and GSAT communication satellites that exceeded that capacity. These satellites, weighing between 2.7 tonnes and 3.4 tonnes, went into space aboard Europe’s Ariane rockets. The cost of launching just one of those satellites, the 3.4-tonne GSAT-18 that flew on the Ariane 5 last October, came to Rs 459 crore.

On its forthcoming flight, the GSLV Mark-III will be carrying a 3.3-tonne communication satellite, GSAT-19. The payload capacity of the rocket could be enhanced in various ways to about 4.5 tonnes, according to K. Sivan, director of the Vikram Sarabhai Space Centre in Thiruvananthapuram, the lead institution for launch vehicle development. ISRO is currently working on a 200-tonne thrust semi-cryogenic engine, running on liquid oxygen and kerosene. A core stage with one such engine would raise the Mark-III’s capacity to 6 tonnes.

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