A project to develop a semi-cryogenic engine is sought to be revived.
R. RAMACHANDRAN
The cryogenic engine, The cryogenic final stage that is currently used in GSLV launches is not indigenous.
A CURIOUS new budget head in this year's allocations to the Department of Space (DOS) has not attracted the attention and discussion that it merits. This pertains to the Rs.25 crore allocated under the head "Semi Cryogenic Engine/Stage Development". According to the budget document, the objective is to develop and qualify a high-thrust semi-cryogenic engine and stage, using kerosene as fuel and liquid oxygen (LOX) as oxidiser for the future advanced launch vehicle. The proposal is somewhat baffling because it essentially seeks to revive a 36-year-old project. Dr. Vikram Sarabhai, as the Chairman of the Indian Space Research Organisation (ISRO), initiated the project shortly before his death in 1971, but it was inexplicably dumped soon afterwards, much to the disappointment of its champions. Had the project been pursued to its logical end, India would have achieved world-class launch capability, complete with an operational, indigenous fully cryogenic engine, by the 1990s.
A "full" - as against a "semi" - cryogenic engine uses liquid hydrogen (LH) as fuel and LOX as oxidizer. Both the fuel and the oxidizer being gases at ordinary temperatures, their liquefaction requires use of the cryogenics or techniques and systems at sub-zero temperatures. In the case of a semi-cryogenic engine, the fuel kerosene - usually the superior aviation turbine fuel (ATF) - is a liquid at room temperature (an "earth-storable" propellant) and only oxygen requires liquefaction. Rocket propellants, which consist of both fuel and oxidizer, and are earth-storable liquids, are also used; for instance, a combination of unsymmetrical dimethyl hydrazine (UDMH) as fuel and red-fuming nitric acid or nitrogen tetra-oxide (N2O4) as oxidizer is used in the second and fourth stages of the Polar Satellite Launch Vehicle (PSLV), the workhorse from ISRO's stable.
Among the liquid propellants, the cryogenic bi-propellant combination of LH-LOX offers a higher `specific impulse' - a measure of thrust delivered per unit mass of propellant burnt per second - than the semi-cryo or fully earth-storable combinations. As compared to a specific impulse of 360-380 seconds for the LH-LOX combination, the specific impulse of the semi-cryo combination is 290-310 seconds and the earth-storable UDMH-N2O4 combination 270-280 seconds. This implies that a fully cryogenic engine can deliver a higher payload mass as compared to a semi-cryo engine or earth-storable liquid engine for a given weight of on-board fuel.
It is for this reason that ISRO's Geosynchronous Satellite Launch Vehicle (GSLV), which has to deliver an INSAT-II class satellite weighing over two tonnes into the geostationary orbit, 36,000 km above, has a cryogenic final stage as opposed to a UDMH-N2O4 liquid-based final stage of the PSLV, which has to deliver only 1.5-tonne-class satellites in the polar orbit, 800-900 km high. (It is possible to configure the PSLV to deliver geostationary satellites, but of mass much less than two tonnes, as was done in the case of the one-tonne meteorological satellite, METSAT, in September 2002.)
The cryogenic final stage that is currently used in GSLV launches is not indigenous. It uses the imported Russian cryogenic stages as Russia backed out from transferring the cryogenic engine technology under American pressure, violating a 1991 ISRO-Glavkosmos agreement. The 1991 deal had to be renegotiated subsequently in 1994 without technology transfer as the original deal was perceived to be in violation of the guidelines of the Missile Technology Control Regime (MTCR), and ISRO ended up importing off-the-shelf engines and stages. (The MTCR is an informal arrangement among 24 missile-technology capable nations of the West to restrict missile-related technology and equipment transfers to non-member countries.)
At present, the process of development of an indigenous 7.5 tonne thrust cryogenic engine and stage based on the Russian design (known as Mark-II) is on. The long-duration (720 seconds) test of the indigenous cryogenic stage on January 19 was aborted but will be carried out soon and the stage should be ready by year-end. A totally indigenous and more powerful cryogenic engine (Mark-III), which is intended to deliver satellites weighing up to four tonnes in the geostationary orbit, is also under development.
However, the main core first-stage booster of both the PSLV and the GSLV is still a solid propellant motor, which generally has a specific impulse less than the liquid propellants, and the second stage is the liquid engine `Vikas', which uses earth-storable bi-propellants, based on the French Viking engine technology obtained in the 1970s. Clearly, the payload capabilities of both the launch vehicles can be increased substantially if, instead of a solid motor, a first-stage liquid booster (based on either a cluster of semi-cryo or earth-storable propellant engines or a powerful cryogenic engine) is used like in most advanced launchers of the world today. LOX-kerosene-based semi-cryo liquid engines have propelled many Russian launch vehicles. The world's most powerful liquid engine, the Russian RD-170, which has been used in launch vehicles such as Proton, Zenit and Soyuz, is powered by a LOX-kerosene combination. LOX-kerosene engines have powered several American launchers as well, including Saturn V, which carried men to the moon.
However, for some reason, ISRO has been reluctant until now to develop a liquid-booster stage that could replace the solid booster and achieve a higher payload capability, notwithstanding the fact that it has mastered the solid-motor technology, which is completely indigenous. As recounted by N. Gopal Raj, the science correspondent of The Hindu in his 2000 book Reach for the Stars on ISRO's rocket development, similar efforts at developing indigenous capability in liquid propellants have been lacking all these years. Nearly all the effort on this front was directed at indigenising the imported Viking engine technology into Vikas and consolidating this capability, including creating industrial capacity to produce Vikas engines to meet the needs of PSLV and GSLV launches.
One of the chief architects of ISRO's solid propellants programme was Dr. Vasant Gowariker, a chemical engineer-scientist who later became the Secretary of the Department of Science and Technology (DST) and is currently ISRO's Satish Dhawan Professor in Pune. It was Gowariker who pioneered the work on cryogenic engine development in ISRO. In 1971, under Sarabhai's suggestion, he set up the Cryogenic Techniques Project (CTP) with six people and initiated the conceptualisation and design of a semi-cryogenic engine.
"The project was more like a software kind of work as a step towards fully cryogenic technology," Gowariker says. "It was Sarabhai's idea to use this as a basis to get familiarised with cryogenic technology because while making liquid hydrogen is risky business, liquid oxygen was easily available from the industry. The idea was to make do with whatever systems that were available at that time, get experience with liquid oxygen in its handling and the filling process and develop systems to utilise its full oxidation capacity," Gowariker said.
"I feel that wisdom has finally dawned on them," says P.R. Sadashiva, an important member and the first recruit in the six-member team under Gowariker, who took voluntary retirement from ISRO in 1992. "After the testing of one small-scale semi-cryo engine, the whole project - costing Rs.3.48 crore then - was shelved and the setting up of a dedicated liquid oxygen plant costing just Rs.16 lakh was stopped," he recalled. In fact, this was the last thing that Sarabhai approved a day before his death in December 1971. According to Dr. Sadashiva, after listening to a presentation on solid propellants for the Defence Research and Development Laboratory that went on well into the night, Sarabhai retired to Kovalam Hotel in Thiruvananthapuram when Gowariker rushed in with the papers on the proposal for a 10-tonne LOX plant. Sarabhai promptly signed it.
"People connected with Vikas and the proponents of solid propellants pulled it down, in particular one man who was interested in pushing the imported Vikas," adds Sadashiva. Although he refrained from naming the person, it is amply clear that he was referring to Dr. A.E. Muthunayagam, who led the Vikas programme at ISRO's Liquid Propellants Systems Centre (LPSC).
"Although the Vikas project definitely gave us the liquid propellant technology, semi-cryo [technology] is the cheapest option as compared with earth-storable liquids," he pointed out. He said ATF was available at nominal cost and liquid oxygen was about 20-25 times cheaper than UDMH or N2O4 at that time.
"The proposal was to develop a 75-tonne thrust semi-cryo engine, similar to the 68.5-tonne Saturn V engine, and we could have easily achieved that. And by clustering four of these, we would have had an extremely powerful booster by now, equivalent to the most advanced rockets, which could have formed the basis for our main version of the PSLV. And in parallel a 7.5-tonne thrust LOX-LH cryogenic engine could have been developed. We have lost valuable time," he observed.
Sadashiva recounted how they would transport LOX by jeep from Fertilizers and Chemicals Travancore Ltd. in Kochi, where it was obtained as a by-product and was largely wasted, in containers that were so bad that half the content would have evaporated by the time they reached the testing facility near Thiruvananthapuram.
"The man to blame is [Satish] Dhawan," says Prof. H.S. Mukunda of the Indian Institute of Science (IISc), Bangalore, who headed the committee that prepared the report on the semi-cryogenic engine. "He, for some reason, went along with the arguments of people involved with the Vikas engine project and did not even give us a hearing. Even U.R. Rao [former Chairman of ISRO] was extremely unhappy with our proposal."
"Of course, there was no requirement, or even any ambition, for a payload greater than INSAT-II at that time to say that there was a shortfall [in Vikas's capability] and we lacked an engine with a greater thrust. But our idea was to get hands-on experience with cryogenic systems over three years so that we could be in a position to develop full cryogenic engines on our own, on the basis of this experience," Mukunda adds.
The curious thing is that ISRO wants to develop the semi-cryo engine now after developing the full cryogenic engine, instead of having done it the other way around. "I don't really know for what kind of payload is the present semi-cryo engine being developed. But the environment now is completely different after the handling of the Russian cryogenic engines and systems. Moreover, much better hardware is available today. So developing the semi-cryo engine should not take more than three years," Prof. Mukunda says.
Gowariker does try to rationalise Dhawan's decision in retrospect. "The functional requirements of mission [of the time] are important and from that perspective the Viking-Vikas liquid engine route was a good idea. Given limited financial and human resource, the overall performance of a system becomes important and decisions on where and how we direct the development effort become extremely difficult. So, instead of letting too many things go on simultaneously, it must have been felt that a semi-cryo project was less important then," says Gowariker.
But the price of not following the path of self-reliant technology development has turned out to be dear. It would certainly have been clear even in the 1970s and 1980s that cryogenic engines would eventually be needed. Perhaps it was felt that, like the Viking-Vikas route to developing earth-storable liquid engines, cryogenic engine technology too would be readily available for import. Indeed, that was the logic when the ISRO approached the Soviet Union after the United States and Japan refused and France apparently demanded a very heavy price for its technology.
In fact, warnings from within against the potential risks of importing technology owing to export controls and embargoes such as the MTCR that emanated from the emerging geo-political alignments were ignored and ISRO signed the deal with Glavkosmos only to be abrogated later. Even if it had signed with France at a higher price, the U.S. would still have imposed MTCR-related sanctions and brought pressure upon France. Having taken the path of imports, India had to go its logical end of importing systems without the know-how.
Of course, in the absence of technology transfer, ISRO could not go on importing forever and indigenous development became imperative. U.R. Rao had then said that the indigenous engine would be ready by the turn of the century. Clearly, the envisaged time frame was not only very optimistic but it was also unrealistic. In the ultimate analysis, more than the substantial sums of money spent in buying cryogenic stages and related ground systems from Russia, it is the decade and a half lost in the development of high-lift launch vehicles that could impact adversely ISRO's bid to gain a share of the world's launch services market.
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