On the face of it, the August 27 successful launch of the three-stage Indian launch vehicle GSLV(Geosynchronous Satellite Launch Vehicle) seems yet another routine orbital mission pulled off by the Indian Space Research Organisation (ISRO). The flawless GSLV-D6 mission has helped the Indian space agency validate the performance of the domestically made critical upper cryogenic engine stage for the second time after the successful maiden test flight of GSLV equipped with an indigenous cryogenic engine stage in January 2014.

The technologically complex cryogenic propulsion system is the zealously guarded preserve of only a handful of advanced space-faring countries which are not willing to transfer the technology of this crucial rocket propulsion system. India is the sixth country in the world to have mastered the cryogenic propulsion system, which provides more thrust for every kg of fuel burnt in comparison to the solid and earth storable liquid propellants.

By successfully demonstrating the capability of the indigenous cryogenic engine stage that is driven by liquid hydrogen and liquid oxygen at extremely low temperatures, ISRO has overcome a major technological barrier in so far as building a domestic heavy lift launch capability is concerned. Indeed, the 630-tonne heavy lift GSLV-MKIII capable of placing a 4-tonne class satellite payload into a geostationary transfer orbit is now being subjected to a slew of qualification trials as a prelude to its maiden flight in 2016. The current Mark-II version of GSLV has been designed to orbitsatellite payload weighing upto 2.5-tonne. The message of the successful GSLV-D6 mission is that no technology, however complex and challenging it might be, is beyond India's capability to develop and deploy.

With a lift off weight of 416- tonne, the 49-metre-tall GSLV-MK II showcases the painstaking endeavours of the Indian space agency spread over two decades. It precisely injected 2,117-kg. GSAT-6 communications satellite designed for multi-media services into its intended orbit. This satellite, equipped with an unfurlable, S-band antenna, the largest so far deployed on an Indian satellite, will be used by the Indian defence forces for “strategic purposes”. In addition, it will also be deployed for search-and-rescue missions and disaster mitigation and emergency response.

As it is, the routine deployment of GSLV would free India from its dependence on the Ariane-5 vehicle of the European space transportation company, Arianespace, for getting its two-tonne plus GSAT/INSAT satellites off the ground. This “launch independence” would save Indian exchequer the enormous cost involved in paying for a commercial launch service. It costs around $90-million for launching a communications satellite in 3.5-tonne weight class through a procured commercial space vehicle. India can also consolidate its position in the global commercial launch market by offering the services of GSLV-MKII for launching the satellites of international customers on commercial terms. Of course, India has made modest forays in the satellite launch market by promoting its four-stage space workhorse PSLV(Polar Satellite Launch Vehicle) as a cost-efficient space platform for launching light weight satellites into a variety of orbits for a fee. PSLV has set an excellent track record of reliability by launching as many as 45 satellites from 19 countries. However, it is only a heavy-lift vehicle like GSLV-MKIII that could add “real muscle” to the Indian launch service business. Clearly, a home-grown, high- performance launch vehicle capable of meeting Indian needs for launching heavier class satellites makes for strategic sense because it could insulate the country from “whims and uncertainties” that the multi-billion dollar global space launch market could face in the future due to shifting political, geo- strategic priorities. Further, with a heavy-lift capability under its thumb, there is no need for India to worry about the notorious technology denial regime as exemplified by the US trade sanctions and technology embargo.

Despite the tall talk of Indo-US strategic cooperation, the US continues to be suspicious about India's intention of mastering the nuances of advanced technology elements. The success of GSLV clearly reflects the Indian defiance of US sanction regime. The ISRO,which in the 1980s, had carried out experimental studies on the feasibility of developing a cryogenic propulsion system, deemed it prudent to acquire the cryogenic engine technology from the erstwhile Soviet Union so that the GSLV — the first two stages of which are derived from PSLV—will be propelled by a home-grown upper cryogenic engine stage, without much loss of time. Accordingly, in 1991 the ISRO signed an agreement with Soviet space agency, Glavkosmos, for the supply of two flight-ready cryogenic engine stages, along with the transfer of the sensitive cryogenic engine technology. This was before the breakup of the USSR.

As it is, the cryogenic engine stage the erstwhile Soviet Union agreed to provide was a modified version of the N-1 rocket stage. Following the breakup of the Soviet Union, US found it rather easy to blackmail a politically turbulent Russia into dropping its commitment of transferring the cryogenic engine technology to India. The argument of US was that the transfer of dual use technology of cryogenic engine constituted the violation of the provisions of Missile Technology Control Regime(MTCR). The US logic did not make any sense since cryogenic propulsion is never a preferred choice for driving a strategic missile system.

The Indo-Russian agreement was diluted down to the supply of just seven flight-ready cryogenic engine stages to sustain the flights of GSLV till such time as a home-grown cryogenic engine stage gets ready. Out of these seven, six have already been used by ISRO for GSLV flights. Out of the six GSLV flights with Russian-supplied upper cryogenic engine stage, three have been a failure. Like its Russian counterpart, the Indian cryogenic engine also works on “staged combustion cycle” technique wherein hydrogen is partially burnt with a little oxygen in the gas generator. The hot gases, which drive the fuel-booster turbo pump, are injected at high pressure into the thrust chamber where the rest of oxygen is introduced to facilitate the fuel combustion. Before going to the gas generator, the incredibly chilly liquid hydrogen is used to cool the thrust chamber whose temperature rises abnormally high when the engine is fired.

The challenge involved is sustaining the functional efficiency of the turbo pump that rotates at 40,000 rpm(revolution per minute) in order to send upto 18-kg of propellant every second into the thrust chamber in the face of the sharp temperature gradient. Not surprisingly, for ISRO the development of cryogenic engine was really a tough and painstaking job involving as it does the mastery of materials technology, operation of turbo pumps that operate at cryogenic temperature, along with the challenges involved in handling liquid hydrogen and liquid oxygen.

ISRO is now developing cost-efficient and eco-friendly, semi-cryogenic engine stage capable of developing 2,000-kN thrust. By replacing the core stage of the existing launch vehicles with the semi-cryogenic engine stage, it would be possible to considerably enhance the payload carrying capability of the vehicle in a cost-efficient manner. Such unified vehicles are considered ideal for deep space probes, including sample return mission to moon. To render orbital missions both affordable and routine, ISRO has now focussed its attention on developing the advanced air-breathing propulsion system in tandem with reusable space vehicle technology.

The writer is a Bangalore-based analyst, specialising in space technology, defence and terrorism-related issues.