Interview: S. Ramakrishnan

‘Will be able to repeat the success’

Print edition : February 07, 2014

S. Ramakrishnan, Director, Vikram Sarabhai Space Centre, Thiruvananthapuram.

Interview with S. Ramakrishnan, Director, Vikram Sarabhai Space Centre, Thiruvananthapuram.

A SUBSTANTIAL PART of the credit for India’s cryogenic success should go to S. Ramakrishnan, Director of the Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram. He was until December 2012 Director of the Liquid Propulsion Systems Centre (LPSC) where the indigenous cryogenic engine and stage for the GSLV-D5 were built and tested.

After Ramakrishnan joined ISRO in August 1972, he worked as a member of the SLV-3 project team under the leadership of A.P.J. Abdul Kalam. Subsequently, he joined the Polar Satellite Launch Vehicle (PSLV) programme and was Project Director of several PSLV flights from 1996 to 2002. He was also Mission Director of the first four operational flights, PSLV-C1 to PSLV-C4. He played an important role in developing the PSLV’s liquid propulsion stages and in the vehicle’s integration. Under his leadership, the PSLV has become ISRO’s trusted workhorse and the weight of the satellites it can put into orbit went up from 900 kilograms to 1,500 kg.

He graduated in Mechanical Engineering from the College of Engineering, Guindy, Madras (now Chennai), in 1970, and took his M.Tech in Aerospace from Indian Institute of Technology Madras with first rank.

Excerpts from an extended interview Ramakrishnan gave Frontline at Sriharikota and followed up on email:

How do you assess the significance of the GSLV-D5 mission with India’s own cryogenic stage?

It is a very important mission. When we started 20 years ago, we had an agreement with the Russians [to receive the cryogenic technology and stages from them]. But it got thwarted by the Mission Technology Control Regime and we could not get the technology. So it was a difficult job for us to absorb the technology when we started 20 years ago. We had started working on cryogenic rockets in small steps from 1985 onwards. Handling and processing of procured stages [from Russia] gave us the leapfrogging benefit in this advanced technology.

When we started indigenising cryogenic technology, industries had to realise the welded thrust chamber and the high-speed rotating machines. Initially, there were defects and rejections in the hardware coming from the industries. The situation stabilised. The engine testing was done for a total duration of 6,000 seconds and we built the indigenous cryogenic stage and did the full-duration ground test.

Then we launched the GSLV-D3 on April 15, 2010. The starting conditions for the cryogenic engine in that flight were good. Unfortunately, the fuel booster turbo pump [FBTP] stopped immediately after it started. We had to go into all the possible failure modes and study each one of them. At Mahendragiri, we set up the High Altitude Test [HAT] facility and tested the engine ignition and the start process for the first three seconds. So, we were confident this time and we are happy that all our analyses were right. The indigenous cryogenic stage worked well. The injection was precise. The apogee and perigee errors were very small.

You had mentioned earlier that in rocket propulsion technology, cryogenic technology is the most complex.

Yes. Cryogenic technology is the most complex of propulsion technologies. We are the sixth country after the United States, Russia, France, Japan and China to have the cryogenic engine technology. Today, we have mastered it. We are able to make our own cryogenic stage and fly it. It gives us the confidence to go for the bigger and more powerful GSLV-Mk III, where we have got a totally indigenous 20-tonne-thrust engine with propellants weighing 25 tonnes. The entire vehicle weighs 600 tonnes. It is a 50-metre-tall, three-stage vehicle.

The next GSLV flight with an indigenous cryogenic engine can be within a year. The GSLV has been identified for Chandrayaan-2. Once we make one more successful launch, we can confidently assign it for Chandrayaan-2. We are sure we will be able to repeat the success.

Was there any technology transfer from Russia before the U.S. forced it to renege on the technology transfer agreement in 1993?

There was no technology transfer. We had a lot of ambiguities and uncertainties in the documents. It was a totally new technology when we started. We were confident when we went in for the GSLV-D3. But we faced a failure in it. We took a lot of time to decipher why the FBTP did not sustain. We went into the failure modes systematically. We gave the Failure Analysis Committee’s findings to a national committee. Then we studied all the past GSLV flights from 2001.

In the last three years, we did more tests on the engine subsystems and vacuum ignition at the HAT facility and we did acceptance tests on the individual components such as booster pump, turbo pump, etc. The integration process was streamlined. Cleanliness control was done. We made sure there was no room for another failure.

We knew we had the right technology and the right approach in realising the fabrication, assembly and testing of the indigenous cryogenic engine and that we can make it more robust. Like the PSLV, the GSLV will be a reliable vehicle.

Can you recall ISRO’s early struggle in realising the sub-scale cryogenic engine and later the flight version, especially after the U.S. pressured Russia not to transfer cryogenic technology to India?

Consequent to the cancellation of the cryogenic technology transfer agreement by Russia, ISRO constituted the cryogenic upper stage [CUS] development project in 1995 with the objective of indigenously realising a cryogenic stage with the same specifications, configuration and interfaces as the Russian cryo stage [CS] to sustain the GSLV operational flights after the Russian-supplied cryo stages were used up. In fact, the Indian CUS was aimed as a one-to-one replacement of the Russian CS. Though there were several changes at the stage systems level from the Russian CS, the engine itself was identical to the Russian engine and was getting fabricated at Indian industries based on drawings generated from the data/documents which we could get from the USSR [Union of Soviet Socialist Republics] during the initial phase before the technology transfer agreement was annulled and the information flow stopped.

There was no subscale version and the very first engine assembly realised from Indian industries was the full-scale, 73.5 kN [kilonewton]-thrust staged combustion engine, including the pair of pressure-fed vernier engines. Of course, the total pyro-initiated elements of the engine, that is, the pyro valves and the igniters, were Indian.

The first engine assembly [A0] realised indigenously blew up during the ground test because of an open flame caused by leaking hydrogen cutting the command line leading to the closure of liquid hydrogen [LH2] supply to the engine.

This failure was definitely demoralising and it took considerable time and detailed analysis to reconstruct the sequence of events leading to this catastrophic failure with some collateral damage to the test stand also.

However, we could quickly realise the next engine assembly, A1, and successfully test it, leading to many more long-duration tests at the Mahendragiri facilities of the LPSC.

There was some cryogenic technology transfer from Russia to India in 1992 and 1993 before the tap turned dry. Why did it take 18 years to realise a flight-worthy cryogenic stage, which was used in the April 2010 GSLV-D3 flight?

When we talk about technology transfer for a complex engineering system such as a cryogenic rocket, we have to understand that it is an involved process which takes time and very intense interaction between the technical experts of the two agencies involved. Large volumes of data, documents and drawings have to be exchanged with concurrent interaction to clarify technical points, issues and ambiguities/inconsistencies, if any, noted in this material. This process had just begun and the fact that all these documents were in the Russian language, requiring meticulous and accurate translation, added to the time factor in assimilating the information by the Indian side.

The whole process came to an abrupt stop when the technology transfer agreement was annulled and downgraded as a supply contract. Subsequently, the Russians became reticent in parting with any information or giving clarifications since their interest was to keep ISRO as a tied customer for the cryo stages to be supplied by them for sustaining the GSLV programme. This was essential for the survival of their industries in the adverse economic environment that prevailed subsequent to the break-up of the USSR.

Then onwards, the progress on the indigenous cryo engine was very slow, since any issue of material/fabrication non-conformance or a subsystem test anomaly had to be resolved by the Indian team based on their own analysis and judgment as well as the limited exposure they were getting during the interaction with the Russian team when preparing the Russian-supplied cryo stage for the GSLV launches at Sriharikota.

In fact, it is more difficult when you try to follow someone else’s design without having any inputs on the “know-why” and then make it work successfully. The Russians did not share with ISRO any information on further modifications/updates they were carrying out in their cryo engine/stage based on their experience of ground tests. They flatly refused to give clarifications on specific critical elements such as the liquid oxygen [LOX] metering valve and the booster pump.

After the failure of the GSLV-D3 flight, how did you ensure this time that the ignition of the engine sustained for 12 long minutes in the vacuum of space?

When we attempted GSLV-D3 with the indigenous cryo upper stage, there was a great deal of confidence that the stage would work in flight. After all, by then we had carried out more than 6,000 seconds of cumulative engine hot test spread over 25 to 30 starts on the ground. We had also successfully completed a full-duration stage-firing lasting 720 seconds on ground, which the Russians themselves could not accomplish.

Yes, before GSLV-D3, there was a lot of debate on the CUS thrust frame, which had some deviation. However, there was a good understanding of its implication and a consensus that there was adequate margin. However, the abrupt stoppage of the liquid hydrogen booster pump within two seconds in flight came as a big surprise.

The GSLV-D3 boost phase flight was nominal and the starting parameters for the cryo upper stage in flight in terms of pressures and temperatures were perfect. The engine started with the tank head and the stored-gas-driven booster pump revving up to its designed revolutions per minute. The main igniter and the vernier engine igniters fired and there was ignition in the thrust chamber as could be detected by the acceleration spike. However, the engine start process did not progress due to the stoppage of the liquid hydrogen booster pump, which led to cavitation at the main turbo pump, and the propellant supply to the gas generator did not pick up as expected, leading to the abort of the entire start process.

Post GSLV-D3, from the flight data we could reconstruct the sequence of events leading to the failure. The abrupt stoppage of the liquid hydrogen booster pump was identified as the single event that caused this unsuccessful engine start in flight. All possible failure modes of the booster pump system were addressed and the hardware design as well as the manufacturing, assembly and testing processes were strengthened to avoid any of these failure modes.

This systematic approach proved right and the booster pump performance in the GSLV-D5 stage was close to nominal, leading to the successful start and full burn of the cryo stage.

As ISRO Chairman K. Radhakrishnan mentioned, you “took charge” after the failure of the April 2010 flight. How did you bring about this success? The morale must have been down, especially after the December 2010 failure with the Russian cryogenic stage as well.

It so happened that I took charge as Director, LPSC, at Valiamala on June 1, 2010, just after the GSLV-D3 failure. I was already chairing the GSLV-D3 Failure Analysis Committee [FAC], with a mandate to decipher what exactly went wrong in the indigenous cryo stage. Even before the GSLV-D3 flight, I was closely associated with the CUSP [Cryogenic Upper Stage Project] reviews as co-chairman and had played a crucial role in getting the first flight stage cleared as acceptable for putting on the GSLV-D3 vehicle. So, I was fully familiar with the systems and the LPSC team involved in the CUS development.

Frankly, the GSLV-F06 failure, where the Russian cryo stage was used, did not have any impact on the morale of the LPSC team since it was established in a matter of days that the reason for the failure was poor workmanship in the Russian stage in terms of the separation plane connectors anchoring arrangement. If at all, it strengthened our resolve to perfect the Indian cryo stage at the earliest to sustain the GSLV programme. Yes, the pressure on the CUS team and the LPSC was tremendous and the entire ISRO was looking for a successful GSLV flight with the Indian cryo stage.

My first job was to make the team understand and accept that we were working in a complex and challenging technology area where failures were not uncommon and that we should not be put off by these setbacks.

I recall the statement I made in my first interaction with the LPSC house journal Propulsion Today, where I said that propulsion systems development requires great amounts of grit and determination and it is not for the chicken-hearted.

I believe that propulsion systems are the most challenging to master and require strenuous efforts and a lot of field work under trying and risky conditions. Unfortunately, this is not fully comprehended by all.

I tried my best to make everyone appreciate the complexity of the task the LPSC team was handling and also put in the right perspective the vital role played by the LPSC in all ISRO programmes.

My basic training as a propulsion engineer and my empathy with the entire team cutting across ranks perhaps motivated them to give their best.

I enjoyed the trust and goodwill of each member of the LPSC family and I always did my best to highlight the dedicated efforts made by them in mastering this difficult technology. I am happy they didn’t let me down.

The April 15, 2010 flight, which was the first to use India’s own cryogenic stage, was to put a GSAT that weighed 2,220 kg into orbit. But GSLV-D5 used a 1,983-kg GSAT-14. So, the payload was lighter by 240 kg in the successful GSLV-D5 mission. Does this detract from its success?

After we faced the failure of GSLV-D3 and lost the GSAT-4 satellite, we thought it was prudent to play it safe and keep the primary mission objective of GSLV-D5 as proving the indigenous cryo stage in flight with the deployment of a satellite as an additional bonus. As such, we planned a lighter GSAT-14 with fewer transponders to keep the cost low. Also, the urge to make the CUS more robust in this second attempt, especially after the GSLV-F06 failure, attributed to the deflection and breaking of the shroud in the cryo stage, did indeed increase the inert weight of the CUS in GSLV-D5. All these factors made us attempt GSLV-D5 with GSAT-14 weighing less than GSAT-4 of GSLV-D3. However, this in no way brings down the significance of proving successfully the indigenous cryo stage. The restoration of payload to two-tonne-plus will happen in the very next flight through the optimisation of inert mass and a realistic pruning of margins.

I can confidently say that once we have a working cryo stage and the GSLV, enhancing its performance or payload incrementally is bound to happen in subsequent flights, as demonstrated in the case of the PSLV.

As you and SDSC (Satish Dhawan Space Centre) Director M.Y.S. Prasad mentioned, you made a spectacular comeback within four months of the scrubbing of the GSLV-D5 flight in August 2013 because the liquid fuel in the rocket’s second stage leaked. Did the Afnor tank develop cracks? Why was it not noticed during tests? Was quality assurance given a go-by in such an important mission?

The failure of the second stage [GS2] tank during the final phases of the countdown in August 2013 was due to inherent material characteristics of the AFNOR 7020 aluminium alloy, which is more prone to the stress corrosion cracking phenomenon, which manifests when stress is raised in a corrosive environment like propellant wetting. The crack in the material develops and grows very fast under these conditions and this is what precisely happened to the GS2 fuel tank when the pressure was increased to pre-launch level around T minus two hours.

This tank had successfully undergone all the inspection processes and also had been subjected to two proof pressure tests, the last one in April 2013. As such, this failure was purely due to inherent material proneness to cracking. In fact, AFNOR 7020 was being phased out and replaced by AA 2219.

For the PSLV second stage PS-2, this change was already implemented while the L40 stages [strap-on booster motors], which were developed at a later date for the GSLV, we started with AA 2219. However, for GS2, where the hardware off-take was slow due to the low launch rate of the GSLV, we still had the 7020 tanks and the AA 2219 tank was just getting ready. This was the reason for the use of the 7020 tank for the GSLV-D5 in the August 2013 launch. However, in the GS-2 stage assembled afresh for GSLV-D5 launch in January 2014, the AA 2219 material tank was incorporated.

You plan to do a suborbital flight of GSLV-Mk III in March this year without firing the cryogenic engine. What is a suborbital flight? What is its purpose? Is this flight going to carry a model of the crew module required for ISRO’s human space flight programme?

The suborbital flight test of GSLV Mk III, named LVM3-X mission, is primarily to characterise the new 600-tonne heavy-lift vehicle with two large solid strap-on boosters during its flight through the atmosphere.

The vehicle configuration will be in full and final form. However, the cryogenic stage, C25, will not be functional and will not develop any thrust. With this constraint, the vehicle can reach only about 5 km per second velocity, which falls short of the orbital velocity required. Hence the mission is suborbital, with the upper stage and payload re-entering atmosphere and falling back to the earth.

The whole objective of the LVM3-X mission is to validate a host of important parameters and characteristics of this totally new vehicle of relatively larger dimensions and large strap-ons. In effect, with this flight experience, when we attempt the first developmental launch, LVM3-D1, with a functional cryo stage, C25, we will have greater confidence that C25 will get an opportunity to ignite and perform in flight, which is indeed essential considering the enormous effort we put into realising the cryogenic engine and stage.