The cryogenic quest

Cryogenic technology is crucial to the development of launch vehicles like the GSLV. The third GSLV flight, in 2003, will use an indigenous cryogenic engine.

AN important result of the successful Geo-synchronous Satellite Launch Vehicle flight is that it will galvanise the Indian Space Research Organisation in its development of an indigenous cryogenic engine. The April 18 flight carried a Russian cryogenic stage, which imparted the final velocity to the GSAT to go into orbit.

The third GSLV flight in 2003 will carry a cryogenic stage made in India with a thrust of 7.5 tonnes. The first test on this engine was conducted on February 16, 2000 at the Liquid Propulsion Systems Centre at Mahendragiri near Nagercoil in Tamil Nadu. The firing of the full-fledged prototype, with a thrust of 7.5 tonnes, had to be aborted after 15 seconds while it had to last 30 seconds. A leak of helium from a punctured tube led to non-supply of hydrogen to the engine. The test gave ISRO scientists and technicians "a feel" of the technology. The complex test facility was also validated.

According to ISRO Chairman Dr.K. Kasturirangan, ISRO's target was to complete the developmental tests of the indigenous engine in the next two years. The work on the stage would start parallelly. He added, "By 2003 to 2004, we will be able to bring the indigenous cryo to the operational stage." The first of these tests would be done in about three months at Mahendragiri. These engines would have a thrust of 7.5 tonnes, the same as that used in the GSLV flight.

Dr. V. Gnana Gandhi, Director, Cryogenic Upper Stage Project (Indigenous), ISRO, told Frontline: "We will definitely come out with a successful cryogenic engine in one or two years..."

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. According to Prof. U.R. Rao, former Chairman, ISRO, "without cryogenic technology we cannot go in for geo-synchronous satellite launching."

A cryogenic engine uses liquid hydrogen at -265Celsius as fuel and liquid oxygen at -240C as oxidiser. Development of the engine involves a highly complex technology because of the very low temperatures of the propellants. Very few countries have achieved success in it and it is a jealously guarded technology.

R.V. Perumal, GSLV Mission Director, told Frontline: "ISRO did the electronics and controls for the entire cryogenic stage. We went through a systematic process of testing and qualifying the electronics along with the cryo." Also, the liquid hydrogen was made by ISRO. The liquid oxygen was made by ISRO and an outside agency.

Liquid hydrogen and liquid oxygen weighing 12 tonnes should be pumped into the engine by a turbo-pump. It should be ensured that the liquids are pure. The engine should run at a high speed of 46,000 revolutions per minute (RPM).

According to Space India (January-March 2000), an ISRO publication, a cryogenic stage consists of tanks to store the fuel and oxidiser, plumbing to ferry the liquids in the right proportion into the thrust chamber, structure to transmit the thrust to the vehicle, a power source, and control devices to initiate and regulate the propellants' flow. "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."

S. Krishnamurthy, Director, Public-ations and Public Relations, ISRO, said, "On the one side, you have propellants around -260C. On the other they are burning and producing a temperature of several thousand degrees Celsius. So you have to insulate." Hence 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. He added, "The nozzle gets so much heated that you have to cool it. Again for cooling, you haveave to use liquid hydrogen and liquid oxygen. We pass them through small pores on the nozzle so that the nozzle surface remains cool."

The massive infrastructure facilities needed for all this were built at SHAR. According to K. Narayana, SHAR Director, this included ground facilities for storing liquid hydrogen and liquid oxygen and transferring them to the vehicle through circuits. The Russians supplied the equipment and ISRO did their installation, testing and commissioning. "Thus aspects relating to storage and safety in the handling of the cryogenic fluids were tested for the first time during the GSLV flight," he said.

Prior to the flight on April 18, ISRO personnel conducted trials on filling up a mock-up stage with cryogenic fluids. Narayana said, "Last year, we actually filled the exact amount of liquid hydrogen and liquid oxygen. If there is a postponement of the launch, we should be able to drain the vehicle of the cryogenic propellants" and refuel it. And this happened when the flight was aborted on March 28 one second before lift-off. The cryogenic stage was drained of its propellants the same night, and it was refuelled a few hours before the flight on April 18.

Transportation of the cryogenic fluids from Mahendragiri to Sriharikota by road was a challenging task. According to Narayana, the handling of cryogenic fluids demanded a high level of safety. There were extensive reviews of safety requirements. "Wherever electrical fittings were there, we took special care to install special flame-proof fittings. We designed these ourselves."

ISRO began work on the development of a cryogenic engine in the 1980s when it tested a single element injector generating 60 kg thrust. A one-tonne subscale engine was also realised and tested up to 600 seconds. With this, development of the cryogenic engine for use in the GSLV was initiated in 1994.

ISRO took up the challenge after the United States arm-twisted Russia in April 1992 and July 1993 not to sell the cryogenic technology know-how to India. The U.S. said the sale would violate the Missile Technology Control Regime (MTCR) guidelines since cryogenic technology could be used to propel missiles (Frontline, March 17, 2000). Russia, however, agreed to sell seven cryogenic stages and a ground mock-up stage instead of the stipulated five stages and technology.