|#1533||2308||March 15, 2016||By Radhakrishna Rao|
In a major breakthrough in the quest of the Indian Space Research Organisation (ISRO) to build a heavy lift capability, the cryogenic engine, forming a part of the upper stage of the next generation, high performance Geosynchronous Satellite Launch Vehicle (GSLV) Mk-III successfully passed its qualification test on 19th Feb 2016. This engine, designated CE -20, was test fired for a duration of 640-seconds at the Mahendragiri based Liquid Propulsion Systems Centre (LPSC) of ISRO. Following this landmark test, the design of the cryogenic engine is being frozen for its use in GSLVMK-III orbital missions. This most critical test has cleared the decks for the maiden orbital mission of GSLVMk-III planned for December 2016.
The three stage, GSLVMk-III, with a lift off weight of 640-tonne, is designed to place a 4-tonne class satellite payload into a geostationary transfer orbit. The GSLVMk-III launch capability, twice as heavy as that of GSLV-MKII, is equipped with a home grown upper cryogenic engine stage. The three stage GSLVMk-II with a lift-off weight of 416-tonne, having gone through the two successful flights is now close to attaining the operational status. The GSLVMK-II, while helping India attain self-reliance in launching satellites in 2-2.5-tonne weight class would also boost the prospects of Indian commercial space launch service being offered by Antrix Corporation, the commercial arm of the Indian space programme.
The GSLVMk-III cryogenic engine, stuffed with 27 tonnes of propellant in the form of liquid oxygen and liquid hydrogen, is capable of generating a thrust of186-kN. Also known as LVM 3, GSLVMK-III features two identical, solid boosters with 200-tonnes of fuel each to provide the massive lift-off thrust for the vehicle. The core stage of the vehicle is the re-startable liquid propellant system with 110-tonne propellant loading. Both the solid boosters and liquid core stage have been fully well qualified.
The maiden flight of GSLVMk-III will launch an advanced Indian communications satellite, named GSAT-19. Significantly, GSLVMk-III is also tipped to serve as the vehicle for the proposed manned flight mission yet to be approved by the Indian Government. As part of pre-project activities of the manned flight mission, ISRO is now busy developing a range of critical technologies including environment and life support system, space suite and crew vehicle required for the manned flight.
As it is, the first experimental, suborbital mission of GSLVMk-III was successfully accomplished in December 2014. During this mission, the vehicle equipped with a passive cryogenic stage carried a 3775-kg Crew Module Atmospheric Re-entry Experiment (CARE) to the intended height of 126-kms following which CARE successfully re-entered the earth’s atmosphere and soft-landed into the waters of Bay of Bengal, twenty minutes after the take off. Of course, the primary objective of this flight was to evaluate the performance of the two solid fuel boosters as well as the liquid core stage with a Vikas engine at its heart. This experimental flight will also help ISRO perfect the technique of atmospheric re-entry which is crucial for the successful accomplishment of the manned flight.
The upper cryogenic engine stage of GSLV Mk-III marks the scaling up of the cryogenic propulsion technology—based on liquid oxygen and liquid hydrogen-- successfully developed by ISRO for the GSLV-Mk-II. The biggest technological challenge involved in developing the cryogenic engine system is handling oxygen which remains liquid only at minus 183 degree Celsius and hydrogen which remains liquid at below minus 243 degree Celsius.
Basically, the cryogenic engine stages of both GSLVMk-II and GSLVMk-III fall back on the staged combine-cycle technology, which makes for a partial burning of the hydrogen with a little oxygen in the gas chamber. The hot gases which drive the fuel booster turbo pumps are injected at high pressure into the thrust chamber where the rest of the 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 where the temperature increases abnormally high when the engine is fired. However, in case of the CE-20 engine of GSLVMk-III, a gas generator cycle system has been introduced to improve performance. The staged combine technology adopted for the cryogenic stages of GSLVMk-II and GSLVMk-III are characterised by the way the engine is started and steering engines are used for controllability.
Interestingly, ISRO had launched experimental studies on cryogenic propulsion system way back in 1980s. ISRO’s cryogenic engine team had suggested the development of a 120-kN cryogenic engine for the GSLV with a 10-kN subscale engine for data generation to aid evolution of the vehicle design. The first experimental hot test was carried out on a single injector element thrust chamber using gaseous hydrogen and gaseous oxygen for a duration of five seconds in 1987.
But then by late 1980s, ISRO deemed it fit to acquire cryogenic engine technology from Russia with a view to speed up the development of the GSLV. Accordingly in 1991, ISRO signed an agreement with the Glavkosmos space agency of the erstwhile Soviet Union for the supply of two cryogenic engine stages along with the transfer of relevant technology. However, USA citing the provisions of MTCR (Missile Technology Control Regime), coerced an economically emaciated and politically unstable Russia that had emerged out of the disintegration of the Soviet Union to cancel its commitment of transferring the cryogenic engine technology to India. The argument of USA was that transfer of cryogenic engine technology, which is a dual use system, was not allowed under MTCR.
At the end of the day, the Indo-Russian agreement was diluted to the supply of seven cryogenic engine stages sans technology transfer. These Russian engine stages were meant to sustain the flights of GSLV till such time India's own cryogenic engine were ready for operational use. Against this backdrop, ISRO launched the Cryogenic Upper Stage Project (CUSP) in the first half of the 1990s.
The technology of cryogenic engine is quite complex and challenging. India happens to be the sixth nation to have mastered this technology which is a closely guarded preserve of advanced space-faring countries. As it is, the cryogenic propulsion system is capable of delivering a heavier payload into orbit compared to non-cryogenic propellants as the specific impulse generated by the cryogenic fuel is much higher than the conventional solid and liquid fuel systems.
The realization of GSLVMk-III will make India self-reliant in launching home grown satellites in the weight class of 4-tonne and above. Currently, India is dependent on the commercial launch service of the European space transportation company, Arianespace for getting its heavier class INSAT/GSAT satellites off the ground at an enormous cost to the pubic exchequer. Further into the future, an augmented version of GSLVMk-III will help India deliver a 6-tonne class payload into GTO. GSLVMk-III will also help India to be a competitive player in the multi-billion dollar global market for launching satellites on commercial terms. Indeed, with GSLVMk-III in operational trim, the Indian commercial launch business is expected to move into a higher orbit.
As part of the strategy to bring down the cost of accessing space, ISRO is developing a semi-cryogenic rocket engine for realizing a future heavy lift Unified Launch Vehicle (ULV) and Reusable Space Vehicle (RLV). The LPSC of ISRO is the lead agency for developing the semi cryogenic engine stage. The semi cryogenic engine stage operates based on the use of a combination of liquid oxygen and ISROSENE (propellant grade Kerosene) which are eco-friendly and cost-efficient propellants. In comparison, the liquid hydrogen used in a cryogenic stage is not only costly but also difficult to handle. Of course, the semi-cryogenic engine technology is by no means a latest innovation and USA and Russia have been using this propulsion technology for many years now.
By replacing the core stage of the existing launch vehicles with the semi-cryogenic engine stage, it would be possible for considerably enhancing the payload carrying capability of the vehicle in a cost efficient manner. Such unified launch vehicles are considered ideal for deep space missions including planetary probes and sample return missions to the moon. As things stand now, the Indian semi-cryogenic engine stage is expected to be ready before the end of this decade. It was originally planned to be ready by the middle of this decade.
Looking beyond the conventional space launch systems, ISRO is planning to develop a reusable space vehicle with a view to reduce the cost of accessing space and also to make space missions a routine exercise. The first technology demonstration flight to prove the concept of Indian reusable space vehicle is planned to take place sometime this year, 2016.
India, which began its space journey in a modest way with the launching of a 9-kg sounding rocket in November 1963, is now poised to hit the higher orbit as a prelude to reinforcing its leadership position in the exploration of the final frontiers.
Views expressed by the Author are personal.