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On Invisible Flames and Cages for Humans

Gita Aravamudan

We were driving through Asimov country. Our road wound through a sea of windmills elegantly towering above us, busily spinning away. It was difficult to believe we were actually at the very tip of the Indian mainland, just a stone's throw away from Kanya Kumari. And that these were our own desi windmills harvesting power for the Tamil Nadu Electricity Board.

Geography had colluded with local technology to create this windmill farm in the middle of nowhere. A small pass in the Western Ghats has been funneling strong winds into this rain shadow region from times immemorial. It was inhospitable land where nothing grew and no one lived. Then, suddenly, a couple of years ago some TNEB engineers dreamt of windmills. At first there was just one, Then two. And then, all of a sudden, windmills sprouted like lilies across this unarable, unpeopled land. Today there are hundreds of them generating thousands of kilowatts of energy.

The windmill farm blends seamlessly into more sci-fi country created by even more sophisticated desi technology. At the foot of the Ghats, built into the craggy hillside are Indian Space Research Organisation's towering vertical static test stands for huge liquid rocket motors. Inside the forest covered campus of the Liquid Propulsion Systems Centre at Mahendragiri they stand out like props in a James Bond film set. Many rocket engines have roared and roared again here. And, one day in the near future, an indigenously-made cryogenic engine will be tested for the Geo Synchronous Launch Vehicle whose launch is scheduled to take place shortly.

The ISRO chose Mahendragiri in the early 1980s after a countrywide search for an ideal location for its new centre. And, like in the case of the windmill farm, geography decided the final choice. The centre had to be located in a place where the hazardous chemicals used in ground testing of rockets containing liquid fuels would not harm the ground water even if they ultimately found their way into the soil.

Since Mahendragiri is also in the rain shadow region, the ground water level is very low. There is no cultivation in the vicinity and no people live close by. The hilly terrain of the foothills of the Ghats serves another ingenious purpose. Huge flame deflectors have to be created under the towering static test stands on which the large rocket engines are fired. At Mahendragiri, the vertical engine test stands have been built into the hills, taking advantage of the natural formation to ensure flame deflection.

The Mahendragiri project was initially stalled following press reports that claimed there were populations of the endangered lion-tailed macaque living in these forests. Subsequent studies revealed there was actually hardly an animal in the forest area, which wasn't really virgin forest as it was made out to be.

"No. No exotic monkeys," a scientist in Thiruvananthapuram laughed when I asked him. "But, if you see the tiger, jump into the cage!"

I was puzzled. Until I reached Mahendragiri. There, dotted along the roads that wind through the trees, are iron cages... Not for tigers, but for humans.

"Well obviously we are unarmed and can't shoot the tiger if we see it," said an engineer. "All we can do is to jump into the cage and protect ourselves."

Actually, the cages have never been used. In fact the tiger, I learnt, was not even a tiger, but a leopard that sometimes strays into the campus with its family. And very few humans have ever caught sight of it. According to an apocryphal tale doing the rounds, when huge motors are fired, the leopard comes out mistaking it for the roar of another one of its species.

Liquid-fueled engines for rockets come in two varieties. The engines, which use earth-storable fuels, have already been indigenously developed and used in many launches. However the ones using cryogenic fuels are still under development. Earth storable fuels are easier to handle even though hazardous chemicals are involved. Cryogenic engines on the other hand are much more complex in design and fabrication. All systems, including the storage tanks and conveyor pipes, have to be well-insulated to handle the fluids which are at temperatures well below the freezing point.

Testing a cryogenic engine can be a delicate and hazardous task. This is perhaps why, even though cryogenic technology has been around for almost a quarter century now, it took ISRO some time to consider using it in its own launch vehicles. The GSLV will be the first Indian launch vehicle having a Cryo stage. The first few cryo stages are being made and supplied by Russia. However, these will shortly be replaced by the indigenous engines which are now under development. Cryo engines use very tricky fluids like liquid oxygen and hydrogen. Hydrogen, for example, is invisible as well as highly inflammable. Worse still, when it catches fire, it burns with an invisible flame. Imagine the repercussions of a leak. A person could easily walk blindly into a hydrogen fire and suffer severe burns. The Russians say that in the old days, like the miners of yore who carried canaries in cages to detect poisonous gases, they would walk around holding paper before them. If the paper started burning, they knew they were in the danger zone. Of course things are different now. There are sensors everywhere to detect leaking gases and invisible flames.

Mahendragiri has an impressive track record for handling liquid fuels. For the last decade and a half, the three LPSC units at Trivandrum, Mahendragiri and Bangalore have been developing and testing earth-storable liquid propulsion technology for both the satellite launch vehicles and the satellites themselves. Work on the cryogenic engine and stage has been going on for the last few years. Mahendragiri, in fact, has its own high purity Liquid Hydrogen plant which has been set up using state-of-the-art technology.

Safety is a crucial element at Mahendragiri, since hazardous fuels are being handled and the vehicles on the test stands are still in the developmental stages. In fact the control room from where the testing of big motors is conducted and monitored is a scaled-down version of the ones found at major launch stations like Sriharikota. It is properly reinforced and placed far away from the test stand.

LPSC's main R&D unit is located in more sylvan surroundings at Valiamala on the outskirts of Trivandrum. Here too the Western Ghats form a scenic backdrop to the centre, where, components for rockets of varying sizes, using liquid fuels, are developed and qualified. These include the liquid propulsion stages for the launch vehicles, the propulsion systems for satellites and the control components for both the spacecraft and launch vehicles.

From Mahendragiri to Valiamala is like a shift from Brobdignag to Liliput. The vast unpopulated spaces, towering structures meant for handling large motors, the big bright storage tanks and maze of criss-crossing tubes are replaced by labs and clean rooms and scientists in white coats.

Anyone entering the lab where precision components for liquid-fueled rockets are developed has to take a cleansing air shower first. This is also where the thrust vector control and reaction control systems are assembled. These are used both in the spacecraft and launch vehicles. The tiny rockets developed here actually provide the muscle power to place a satellite into its precise orbit or to nudge a gigantic launch vehicle into the right trajectory.

Take the AKM (Apogee Kick Motor), for example. This device is a small rocket used to correct the satellite's orbit. The initial orbit of a satellite soon after launch is elliptical. The AKM when fired at a precise intermediate point kicks the spacecraft into a more desirable near-circular orbit. Liquid motors are also used to correct the attitude of the satellite and position it so that it looks in the right direction.

Liquid fueled rockets are used for such maneuvers because unlike their solid fuel counterparts, they can be shut off and started at any time. Besides, they are more fuel-efficient. All this makes them suitable for precision maneuvering. Similar control rockets are used even in the launch vehicles to control orientation.

The Bangalore centre located near Indranagar makes aerospace quality transducers for precision measurement and thrusters for use in satellites. At this centre, the focus is on developing control packages for satellites using the components from Valiamala along with the thrusters and transducers produced here. These packages are finally integrated into the spacecraft built at ISAC ((Isro Satellite Centre) in Bangalore.

Space technology is very hard to come by because of its military implications. Propulsion and control guidance, in particular, are fields in which no nation is willing to share its secrets. Take the Cryo-engine drama. Even though the cash-strapped Russians were initially willing to share their cryogenic technology with us, they were later pressurised to withdraw.

However, out of adversity comes experience. Today an Indian-made cryogenic engine is almost ready for testing. The dedication of Indian space scientists has finally paid off and today, nearly forty years after the space program was started, India stands on the threshold of becoming one of the front runners in this field.

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