Realising the cryogenic dream

The cryo test and control room at the LPSC's facility at Mahendragiri. - COURTESY: LPSC

The cryogenic engine developed by the LPSC will make the GSLV a world-class launcher for putting heavy satellites into the GTO.

AS the car speeds down a steep slope, past disappearing coconut groves framing the hillocks, and then climbs again, the serene surroundings rise in a spectacular view and a beautiful building comes into focus. `Liquid Propulsion Systems Centre, Valiamala', proclaims a huge board on it in stylish, gleaming type. At the gate, men from the Central Industrial Security Force go about their task with quiet efficiency and on the sylvan campus silence reigns supreme. There are several boards with the same message: "Arise! Awake! Be quality conscious and deliver zero defect liquid propulsion systems for the Indian Space Programme."

The Liquid Propulsion Systems Centre (LPSC) is where the indigenous cryogenic engine has been developed, marking a crucial phase in the Indian space programme's march towards self-reliance in launch vehicle technology. The indigenous cryogenic engine will make the Indian Space Research Organisation's Geo-synchronous Satellite Launch Vehicle (GSLV) a world-class launcher for putting heavy satellites into geo-synchronous transfer orbit (GTO) of 180 km by 36,000 km.

On May 8, following a perfect launch, the GSLV-2's upper cryogenic stage injected the 1,825-kg GSAT-2 satellite into a perfect GTO at a velocity of 10.24 km a second. The cryogenic engine was Russian. Now, after several years of struggle, India is on the verge of having its own cryogenic stage with its own cryogenic engine.

Said N. Vedachalam, Director, LPSC: "We are in an advanced state of developing an indigenous cryogenic stage at the LPSC." It would be ready "very soon", he added. Towards this, the LPSC has developed three indigenous cryogenic engines. One of them underwent a long duration endurance test for 1,000 seconds at the LPSC's facility at Mahendragiri near Nagercoil in Tamil Nadu. "In flight, this engine is required to burn only for 720 seconds. However, to show its endurance margin, we tested it for 1,000 seconds," said Vedachalam.

India will soon be the sixth country to have its own cryogenic stage with its own engine, after the United States, Russia, Japan, China and Europe. (A cryogenic engine is powered by cryogenic propellants - liquid oxygen as oxidiser and liquid hydrogen as fuel. Liquefying oxygen and hydrogen is extremely demanding because the oxygen temperature should be brought down to -900C and that of hydrogen to -2520C. Maintaining and handling these cryogenic fluids at these extremely low temperatures is tough because they are highly volatile.) The cryogenic stage in a launch vehicle consists of the engine kept in a casing and the control, guidance and electronic systems associated with it. The two GSLV flights in 2001 and 2002 were powered by Russian cryogenic engines as will be the next GSLV flight in 2004. The fourth GSLV flight in 2005 will be a truly indigenous vehicle, with the cryogenic stage developed at the LPSC.

Until it took up the task of developing the cryogenic engine, the LPSC's main mission was the development of liquid engines. Said Vedachalam: " Any engine, be it for launch vehicle or satellite, which burns with liquid propellants, is designed and developed at the LPSC." Its most powerful liquid engine, named Vikas, is world-class and powers both the Polar Satellite Launch Vehicles (PSLV) and the GSLVs. The LPSC also makes small liquid engines, called rockets or thrusters, used on satellites. Such thrusters have been used in the Indian Remote sensing Satellites (IRS), the INSAT-2 and 3 series, and the GSAT-1 and 2. The eight satellites so far in the INSAT-2 and 3 series and the GSAT-1 and 2, all geo-stationary satellites, had on board a sophisticated motor (engine) called Liquid Apogee Motor (LAM). The LAM helps take the satellite from its highly elliptical GTO of 180 km perigee and 36,000 km apogee to the circular GSO of 36,000 km. Said Vedachalam: "Every geo-stationary spacecraft developed by ISRO has one LAM engine developed by the LPSC. In every flight, it has given the best performance. It is a world-class engine."

THE LPSC has three facilities: at Valiamala, about 25 km from Thiruvananthapuram; Mahendragiri; and in Bangalore.

On the 300-acre campus at Valiamala, LPSC technologists do major research and development (R&D) work on liquid propellant engines for the PSLV and cryogenic propulsion systems for the GSLV. One of the facilities is the Electrical Integration and Checkout Building. It is in this cavernous building - 82 metres long, and many metres tall - that the demanding task of integrating the thousands of sub-assemblies of the PSLV and the GSLV is done. Every sub-assembly must function with precision for a successful mission.

At the Control Components Clean Room, where one has to take an "air shower" before entering, men and women in white overalls assemble the mechanical components that go into the control systems of the liquid and cryogenic stages, and satellites. Development and assembly of certain critical components for the launch vehicles, too, are done at Valiamala.

Mahendragiri, on the foothills of the Western Ghats, was selected to house a major facility because safety regulations demanded that handling of energetic and toxic propellants should be done in large open spaces. It is here that liquid rocket engines are assembled and integrated into stages, fired and tested. They include PSLV's liquid and the GSLV's cryogenic engines. Besides storage facilities for liquid propellants such as unsymmetrical demethyl hydrazine, N{-2}O{-4} and MMH (Mono Methyl Hydrazine), liquid hydrogen and liquid oxygen, there are engine test beds, flow control mechanisms, electro-pneumatic controls, and a sophisticated control room. There are facilities for assembling and testing the satellite engines (thrusters/LAMs) too.

The full PSLV liquid stage that is to be tested is chained to a tall stand or else it will take off when fired. As the engine fires, with massive yellow flames pouring forth, it tilts and turns at a particular angle exactly as it would in flight. Such static testing is done to experiment and characterise the engine performance. After the different stages are tested, they are cleaned and transported to Sriharikota on trailors that are built to minimise, if not eliminate, vibrations. At SHAR, the stages are stacked up into a full-fledged vehicle, which launches the satellite. At the Bangalore facility, propulsion packages for satellites are made.

The LPSC has developed an array of engines for launch vehicles as well as satellites. Vikas is the most powerful engine it has developed and is used in the PSLVs and the GSLVs.

It develops a thrust of 80 tonnes in vacuum. Its cryogenic engine for the GSLV comes next with a thrust of eight tonnes, followed by the liquid engines used in the PSLV fourth stage and first stage roll control, with a thrust of 750 kg. The LAM engine used exclusively on the INSATs and the GSATs, which are built at ISRO Satellite Centre, Bangalore, has a thrust of 44 kg and burns for a duration of 7,800 seconds (cumulatively) aboard the satellite.

After the INSAT or GSAT is put into the elliptical GTO, the LAM is fired three times to lift the satellite to the circular GSO. The longest duration it was fired was on the heaviest satellites ISRO has built so far: INSAT-3B launched in March 2000 and INSAT-3A in April 2003. As the command went from the ground, the LAM burned for 4,000 seconds during the first spell. The second burn was for 3,000 seconds and the third for 800 seconds. The duration of the burn depended on the weight of the satellite. "So a major development is that we have developed this LAM from INSAT-2A onwards" Vedachalam said.

The LPSC has uprated the Vikas engine to 80 tonnes thrust from 72.5 tonnes. This uprated engine was used in the GSLV-2 flight on May 8, 2003 and enabled the rocket to put the 1,825 kg GSAT-2 in orbit. The GSAT-1 weighed 1,540 kg.

The LPSC has initiated advanced R&D in electric propulsion so as to maintain satellites in orbit for a longer period.

Demanding days lie ahead for LPSC technologists when they will have to develop a cryogenic engine with 25 tonnes of liquid hydrogen and liquid oxygen, which unleashes a thrust of 20 tonnes. This engine will form the topmost stage of the GSLV Mark III that will put a four-tonne satellite in GTO. Guiding them in the effort will be their motto: "... deliver zero defect liquid propulsion systems for the Indian Space Programme."