GSLV flight with indigenous engine likely in 2012: ISRO
During the 90's, India seeking to launch INSATs weighing more than two tonnes, was scouting for cryogenic engines to power its GSLVs. Work on developing India's own cryogenic engine was started by ISRO shortly after the project to develop the GSLV was initiated in 1986. With an initial project cost of about Rs 235 crore, the work for the development of India's own cryogenic engine was jointly carried out by the Liquid Propulsion Systems Centre (LPSC) in Trivandrum, Material Development and Research Centre at Vikram Sarabhai Space Centre (VSSC). Though India has her own plans for developing an indigenous engine, the plan was to fast track development time by procuring technology from outside.
Cryogenic engines are essential to put heavier satellites into geo-synchronous transfer orbits (GTO) at an altitude of 36,000 km. Cryogenic propulsion enables a launch vehicle to put a payload two times heavier than that orbited by a vehicle without a cryogenic upper stage. It was essential that they be employed in GSLV rocket if it were to launch a 2000 kg class INSAT communciation Satellite to geo stationary orbits.
A cryogenic engine is powered by cryogenic propellants - liquid oxygen as oxidiser and liquid hydrogen as fuel. A bi-propellant combination of LH-LOX offers a higher specific impulse than the semi-cryo or fully earth-storable combinations. This implies that a fully cryogenic engine can deliver a higher payload mass for a given weight of on-board fuel. Since they are gases at room temperature, they require use of the cryogenics or techniques and systems at sub-zero temperatures to liquefy them. Liquefying oxygen and hydrogen, maintaining and handling these cryogenic fluids is an extremely demanding and tough task. At such low temperatures, metals become brittle. New welding techniques, new alloys and new types of lubricant are required. Liquid hydrogen and liquid oxygen had to be pumped into the engine in the right proportions.
Initially, General Dynamics (USA) and Arianespace were willing to sell the cryo engine and offered to transfer technology. But the cost was very prohibitive. Then the Russians approached India and a deal was stuck with Glavkosmos in 1991 for Rs.235 crores which included total cryogenic technology transfer and the supply of two KVD-1 engines.
But the U.S. played spoilsport, pressuring Russia not to sell the technology to India on the grounds that it violated MTCR agreements and that the missile-related technology and equipment transfers to non-member countries is restricted . The Pokhran-II nuclear tests in May 1998 further complicated the problem.
Russia backed out from transferring the cryogenic engine technology under American pressure. The 1991 deal had to be renegotiated subsequently in 1994 without technology transfer as per the original deal. Instead Russia agreed to supply ready built and complete cryogenic stages. The Russians also supplied the supporting equipment. ISRO built massive ground facilities to store liquid hydrogen and liquid oxygen.
The cryogenic engine supplied by Russia was tailor made for GSLV and ISRO�s requirements. Russia was prepared to sell India a cryogenic engine stage that developed a thrust of 10 tonnes as againt the current 7.5 tonnes. Though Russia supplied the cryogenic stage, ISRO insisted that it will develop its own electronics, guidance and control systems for the cryogenic stage. A cryogenic stage in a launch vehicle consists of the engine kept in a casing and the associated control, guidance and electronic systems. The thrust chamber is the powerhouse of the engine where combustion of fuel and oxidiser takes place. The burnt gases are ejected through a nozzle, converting the thermal energy of the combusted products into kinetic energy. The cryogenic engine thrust chambers need to be cooled to protect them from high temperatures. Materials of high thermal conductivity such as copper and its alloys are used for chamber construction. The tanks and pipelines are double-walled, insulated and vacuumed. The fuel and oxidiser itself is circlated around the nozzle surface to cool it.
While an entire GSLV flight lasts approximately for 1,050 seconds to inject the satellite into the orbit, the cryogenic engine alone operated for 700 seconds. That�s more than 66% of the entire flight duration. The cryogenic engine hurls the satellite at a velocity of 10 km a second into the orbit. While the earth storable liquid propellants could be loaded easily into the vehicle stages, the cryogenic propellants evaporated easily during storage. So in the GSLV, the cryogenic propellants are loaded just 3-4 hours prior to the launch. The final level is achieved in the last 10 minutes. This ensures that precise conditions needed at the lift-off for the quantity of propellants, their temperature and pressure are met.
In a PSLV, the core liquid motor is ignited first and the vehicle lifts off. Later, the solid strap-on motors are ignited. In the GSLV however, the 4 liquid strap-on motors are ignited first and their performance checked. After a gap of 4.6 seconds, the core solid stage is ignited. This gap is to confirm that all the 4 strap-on motors have developed the required thrust. So in both cases, if the liquid motor does not develop the required thrust, the entire flight is aborted and the liquid motors are shut down. The liquid stage is de-fuelled and defects analysed. One the issue is rectified, they can be re-fuelled and new countdown can be resumed. This is not possible with a solid fuel stage. This was demonstrated during GSLV flight on March 28, 2001 when it was aborted just 1 sec before lift-off.
During a GSLV launch, at T-10 minutes, automatic launch sequence (ALS) computer takes over the operations. At T-4.6 seconds, the 4 liquid strap-on liquid motors containing 42 tonnes of propellant are ignited and their performance checked. At T-0 sec, core first stage, powered by 138 tonnes of solid propellant is ignited. After lift-off, the first stage burnt for 105 seconds and the strap-ons for 148 seconds, taking the vehicle to an altitude of 70 km. The second stage, with 39 tonnes of liquid propellants, ignites at 1.6 seconds before the burnout of the last of the four strap-on stages. The second stage is fired for another 140 seconds, taking the vehicle to an altitude or 130 km, and its velocity to 5.4 km a second. When the vehicle reaches a height of 115 km, it would have cleared the dense atmosphere, The "Heat Shield" which protects the satellite from getting overheated splits down and jettisoned. At around t-290 secs or 292 seconds after lift-off, the third cryogenic stage is ignited. Cryogenic stage, which carries liquid oxygen and liquid hydrogen weighing 12 tonnes together, fires for 704 seconds. The satellite and the equipment bay reach an altitude of 206 km. Then the stage injects the geo-stationary satellite into the required orbit with a velocity of around 10.24 km a second.
The Indian Cryogenic Engine
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The indigenous cryogenic engine develops a thrust of 73 kilo Newtons (kN) in vacuum with a specific impulse of 454 seconds and provides a payload capability of 2200 Kg to Geosynchronous Transfer Orbit (GTO) for GSLV. The engine works on 'Staged Combustion Cycle' with an integrated turbopump running at around 42,000 rotations per minute (rpm). It is also equipped with two steering engines developing a thrust of 2 kN each to enable three-axis control of the launch vehicle during the mission. Closed loop control of both thrust and mixture ratio ensures optimum propellant utilization for the mission.
The Indian Cryogenic Stage
As of 2008, the development of the indigenous cryogenic engine has been completed. Full duration tests, with the engine burning for 1,000 seconds, have been done. The engine is integrated with its stage i:e electronics, guidance, control systems, fuel tanks, fuel supply lines etc. This entire stage has been qualified. ISRO had tested several cryogenic engines for a cumulative duration of 7,500 seconds. The engine now stands tall ready of its first flight in April 2010. A successful launch would make India totally self-reliant in all aspects of space launch vehicle technology
Gaining confidence from its monumental effort, ISRO is also preparing a new cryogenic engine from scratch starting from the drawing board. Codenamed C-25, this all new engine will have 25 tonnes of propellants developing a thrust of 20 tonnes. This will power the upper stage of GSLV-III
India will realize it dream in April 2010 with a successful launch of GSLV-D3. The more than a decade old effort of developing a cryogenic engine will bear it fruit. All the best ISRO. Make us proud
~Chota
