It was a challenge the Indian Space Research Organisation (ISRO) had to overcome, a technology it had to master if it were to remain relevant in the lucrative commercial satellite launch market. Success would mean ISRO join an elite group of space agencies that have the capability to use cryogenic technology to launch satellites. A failure would leave ISRO as a space agency that can, at best, launch small niche satellites on a commercial basis. International restrictions brought in by the United States ruled out the possibility of technology transfer from friendly countries, forcing ISRO to develop this cutting edge technology at the top end of rocket science all by its own and that too amidst various sanctions.

Finally, after many years of research, delays and a fair share of failures, ISRO last month successfully ground tested the indigenously developed cryogenic stage for the full flight duration of 720 seconds. The success meant that the design robustness of the cryogenic stage and its performance has been adequately validated and qualified on the ground. The agency has moved a few steps closer to realising its dream of having its own cryogenic stage. An elated ISRO chairman G Madhavan Nair termed the development ?fantastic? and said it boosted the confidence of the organisation.

The next step is to test the stage under flight conditions some time next year. According to PS Sastry, director, Launch Vehicle Programme, GSLV?D3 (geosynchronous satellite launch vehicle) which is expected to deploy GSAT 4 in orbit will employ the indigenous cryogenic stage as the upper stage of the launch vehicle some time in July next year.

Why cryogenics?

There are three types of fuel that are employed in space transportation?solid, liquid (stored at ground temperature) and cryogenic propulsion (fuel and the oxidisers are stored at cryogenic temperature ie. minus 180 degrees centigrade and lower). While solid fuel has a specific impulse (equivalent of brake horse power in the case of automobiles) of 240, it is 280 for liquid propulsion. For cryogenic fuel (which uses liquid hydrogen as fuel and liquid oxygen as oxidiser) it is 470. Thus for same kilogram of fuel, cryogenic propellants impart higher thrust?1.5 times compared to storable liquid fuel and almost two times the solid propellants. A launch vehicle employing a cryogenic stage as an upper stage can, as a result, deliver a payload two to three times that of a similar vehicle with a non-cryogenic upper stage. To put it in commercial terms, cryogenic stage reduces the cost/kg of launching a satellite into orbit as a result of its lower gross lift-off weight (GLOW).

So far, the five GSLV launches by ISRO employed Russia-built cryogenic stage as the upper stage. In all, Russia had supplied seven cryogenic stages to India before US pressure prevented the latter from supplying more. ISRO now has only two stages left and both have been contracted for putting Russian satellites in orbit. This means that without an operational indigenous cryogenic stage, ISRO?s GSLV programme will soon come to an end.

Though Polar Satellite Launch Vehicle (PSLV) has established itself as a reliable launch vehicle, it can only launch satellites in polar orbit (where the satellite does not move in tandem with earth?s rotation and hence is not available for use all 24 hours). In the past, it has also been used to put smaller and niche satellites in geostationary orbit (where the satellite moves around the earth in conjunction with latter?s rotation thus making available its services 24 hours). But telecommunication satellites are heavier weighing over two tonne and have to be placed in geostationary orbit. This is where market is in the satellite launch business. Thus indigenous cryogenic technology is crucial for the very survival of the GSLV programme. ISRO?s ambition of making it big in the satellite launch business will be stillborn without GSLV.

Challenges galore

Cryogenic propulsion systems are complex and expensive to develop. The propellants are to be handled at very low temperature. This calls for use of special materials such as aluminium, titanium, nickel and their alloys for the engine and other sub-systems. Complexities extend to storage and filling of the propellants, transportation, stage-test facilities etc. The fact that only 18 cryogenic engines have been developed since research began on this technology after World War II and only seven of them have qualified and flight tested explains the difficulties involved, points out Sastry.

Almost all countries that have cryogenic technology spent anywhere between 10 to 15 years for arriving at a flight qualified stage. They faced enormous problems associated with manufacturing, design and technology.

ISRO was fully aware of these factors when it embarked on the process of indigenising the cryogenic stage in 1993-94. It took an unconventional approach by involving industry?both private and public sector?in the development from day one. This helped ISRO save time, says Sastry. Godrej was involved in the development of the engines. Midhani, Hyderabad helped with the special materials while Nuclear Fuel Complex supplied the titanium rods. In fact, there were instances of the industry commencing fabrication work on select systems even during the design stage.

But these measures did not prevent ISRO from facing its own unique set of problems. Material procurement for making the tanks proved to be difficult as there was a waiting period of five years with the only established supplier. The material used in aircrafts was fully booked by the makers of Boeing and Airbus aircrafts. ISRO had to identify an alternate supplier and go for extensive qualification of the material and the vendor causing delays. The agency also faced problems in getting special purpose machines. It designed some of the machines on its own and bought a few second hand equipments and reconditioned them using its own software. It also had to master the brazing technology (the art of joining two completely dissimilar materials) in-house. ?We had our share of problems but we overcame them. Considering the time taken by other major powers, our development time of this technology is impressive,? adds Sastry.

ISRO successfully tested the cryogenic engine in 2002 (it has since been tested for over 7,000 seconds). In January 2007, it went in for the first ground test of the entire stage. The test had to be aborted. This was followed by a successful second test (480 seconds).

Though the recent successful ground testing of the cryogenic stage may call for a celebration, it is still not party time for ISRO. It first needs to establish the efficacy of the cryogenic stage under flight conditions. This is expected by mid-2008. Once successful, the agency then has to quickly prove the reliability of GSLV as a launch vehicle by making some copybook launches. Unlike PSLV, GSLV has not established its credentials yet. Two of its five launches have failed to deliver intended results?a bad success rate in this highly competitive field. In this business, expertise and cost competitiveness are the two crucial elements. With regard to GSLV, ISRO has just the cost advantage part to showcase.