SHORTLY after the successful experimental launch of the Reusable Launch Vehicle-Technology Demonstrator (RLV-TD), and its hypersonic re-entry, Frontline met Dr A. S. Kiran Kumar, Chairman, Indian Space Research Organisation (ISRO), for an extensive talk with him about the test and other related issues. Excerpts from the interview:
Could you tell us what has been validated in this experimental launch of the RLV-TD? Also, are there parameters that you would like to improve upon on the basis of the data obtained?
Basically, the flight was a success in terms of its basic configuration, its thermal protection system, use of some materials, primarily re-entry thermodynamics, autonomous navigation, guidance and control. This has got a set of closed loop guidance (CLG) systems, which ensures that the vehicle, after reaching a Mach number of about 4.8, comes down. As it comes down, it is fully in the CLG system, where a new set of sensing elements called Flush Air Data System (FADS), which measures the wind speed, the angle of attack, etc., required for autonomous operation, comes into play. In this particular mission, we were using them to monitor the flight. And we were using the inertial guidance elements for the actual control. FADS is one of the new developments that is going to have a significant advantage in this kind of vehicle for various activities. So, this is a technology demonstrator.
In terms of guidance, we also need to determine the wind speed and wind measurements. For all that, we had done a priori measurements and then fed them into the control system. This is the first winged body designed in India that has reached a Mach number of 4.78. That is a very significant development because it will help in the future use of this technology for various activities.
What other winged bodies have gone beyond Mach 2?
There are these special flights, if they do… when they reach certain speeds...
There also they do not go beyond Mach 2, I suppose?
Yes. Then also they are in the range of 1.1-1.3 or thereabouts. And this is the first one that has reached much beyond that. Of course, when you actually re-enter from the orbit [in a real RLV flight], you need to reach even Mach numbers 15 to 16. So, the CLG has been demonstrated. We have elevons and rudders, which are the control surfaces. The actuation of these control surfaces and the operation of those electromagnetic actuators through our own lithium ion batteries were also validated.
For this actuation, you had done what is called an “iron bird” simulation earlier. How far have those simulations been validated?
Now, practically in this entire flight regime, we have not seen any anomaly. To that extent all the simulations that were done are satisfactory.
We had done for the first time a lot of those aero-thermal simulations, and even those simulation systems. In terms of aerodynamics, this vehicle is significantly very different from conventional launch vehicles. The whole control system, and the autopilot required for this, is different because the controlling mechanisms are different.
In addition to the usual Reaction Control System (RCS) that is there, there are elevons and rudders. Orienting them, controlling them… and these are also very sensitive to wind speeds. That sensitivity has also to be accounted for in the control system.
Up to what Mach value did the booster itself take the vehicle?
The booster took it to something like 49 km [and released it]. The booster is also specially designed for this because it has to withstand the dynamic pressure in the trans-sonic regime, etc.
For that, none of the existing things could have been used as it is. It is a specially designed motor. After the booster releases the RLV, the altitude of the RLV keeps increasing [in the coasting phase]. Then, as it comes down, the Mach number increases. With the control system, you reduce the speed.
At the time of actual release, what would have been its speed?
We can check on that number. Because we have that profile; there is also an animation that shows the velocity at each point [see graphics].
What Mach numbers do the boosters that you normally use reach?
They will be reaching a velocity of about 0.8-1 km/s, which is about Mach 3.
People at the Vikram Sarabahai Space Centre [VSSC, Thiruvananthapuram] told us that the complexity in this launch comes from the winged vehicle sitting on top of the rocket. In the space shuttle, the two vehicles are parallel. Could you explain how the complexity arises?
Basically, what they are saying is that the overall length has significantly gone up. So the length-to-diameter (L/D) ratio, which is one of the important parameters for the vehicle’s dynamic stability, increases [and that can cause instability]. But in the other case, the basic booster is much bigger compared with the space shuttle. These are the relative things that you have to worry about. This length itself causes problems during its traverse, both in terms of forces that can act on that, which can cause buckling, and shear loads that can arise.
POST-FLIGHT ANALYSIS
On landing in the Bay of Bengal, did the vehicle disintegrate or was it healthy?
What we can definitely say is that we have the data from the ship till it was about 800 m above sea level. And then right up to the point of impact, we have INSAT data from the telemetry. But that telemetry is only in 1 kHz compared with the other, which is about 2 MHz. So the amount of information that the ship telemetry, or the normal telemetry, gives is a lot more.
What we definitely have information about is on the actual position when it impacted and then certain other data. We are going through that data. It [RLV-TD] cannot survive. Finally, it impacted with a certain velocity, as it was meant to do, and those numbers the post-flight analysis (PFA) will tell exactly at what velocity it impacted and all that. But we know that up to 734 seconds, we have the signal. We are also trying to establish exactly the mechanism, what happened, etc., by looking at the data. These will all come out in the PFA.
You recovered Space Capsule Recovery Experiment (SRE) launched in January 2007 and Crew module Atmospheric Re-entry Experiment (CARE). Although we have been told that this winged aerospace vehicle was not made for water impact, why did you not try to recover this also?
You could have recovered this also. Then we would have had to make certain changes to this configuration. More than the configuration itself, the whole process of completing the vehicle, the time it would have taken, etc. Here the objective was to ascertain things like the CLG system, sensing elements and validation of control surfaces. For those things we don’t need to recover. And even if we had recovered this thing, what use can we put this to is the question. The recovery would have diverted our attention to something else.
When will the next flight of the RLV-TD be?
PFA is our next immediate task, and then we will look at various issues. Between the time this programme was conceived and now, and also taking into account what is happening globally, we will work out what our immediate priorities and targets should be and how many paths we should follow. And this we should be doing within a matter of a few weeks. After that, we will actually get into the next level of activity. Because we will also have to update our [Space] Commission and tell them that these are the things that we have done, how we need to proceed further. It’s a constant task.
The next stage in the RLV-TD missions is LEX (Landing Experiment). It means you need a runway at Sriharikota for the winged aerospace vehicle to land on. When will you start laying the runway there?
Whether we should be doing that at all will also be discussed. If you have a landing gear system, you need to make structural modifications to accommodate that. Are there alternatives to landing in that mode? These are the questions we will look at. In any case we should be planning in a month’s time our next set of activities on this. We should be getting some more focus on what we should be doing next. Once we confirm that, then we have to go through some minimal clearances, etc. We will have to cycle it through our reviewing mechanism, then our Commission’s approval, etc.
Before the launch, we had spoken to Dr Sivan [Director, VSSC]. He told us that the basic configuration of a winged structure that you require for an RLV is not yet fully optimised…
Right now what we are visualising is that we have to go through a series of trials. This is a scaled-down model. In this 1:5 scaled-down model, we went through simulations of almost 4,500 wind tunnel tests to arrive at the final designs and in optimising the current configuration. Now, this exercise itself has validated your total design process, your understanding of concepts, etc. To that extent you now have a good handle on how to design these kinds of things. Now when you are upscaling this size, to two times, three times, or up to five times, depending on different aspects, you are in a position to do that. But then you have to realise that. That is another part of the problem.
I ask this because Dr Sivan said that this configuration was not going to minimise the drag because the wingspan itself was quite large. So in terms of the drag that it experienced during the flight, do we have a handle on that parameter so that we can reduce it?
Basically, whatever simulations have been done show that you require certain design elements for surviving this test itself, and that a portion of it has been demonstrated. Now suppose you want to change the conditions, the size and all the parameters, you can design it in a way that is appropriate to all those parameters. So you now don’t have an apprehension whether the design will work or not work. To that extent it is validated. Here we have gone up to something like 4.78 Mach number. Now, as I said, [in an actual RLV situation] on return it could be reaching even up to Mach 15 or 16. In a way we have dealt with such kind of thermal problems in SRE.
So we have a good understanding of how to handle these thermal problems also. And also in terms of tiles and materials, we have a good handle. Our next task will be to identify at what scale we need to go to reduce the cost. Originally, when such programmes were being looked at, we were looking at actually carrying a huge capacity—like 10-12 tonnes—into orbit. If you want to optimise for that kind of scenario, it will be different from optimising for 1-1.5 t satellite launch. Now that we have done the first round, we will be looking at, between now and the final version, whether we can do any other intermediate versions that also can benefit.
You have a standby of the same design as well. Would you be going through the launch of that as well?
We have to do the complete PFA and get into the nitty-gritty of everything: whether all the sensors worked—there are so many systems, how well FADS performed, etc. Having looked at all that, we also need to see what are the key things that we need to perform again. The earlier plan was to land it the RLV-TD on land itself. That would require landing gear, some structural changes, etc. After we complete our PFA, we will go through all the details, we will understand the nitty-gritty of the system and how much of it is hundred per cent satisfactory. While a quick analysis told us that basically everything is fine, we still need to go through the detailed PFA before we can decide.
You said you need to look at FADS…
Yes, all its sensors.
But did the vehicle also use the duct for air intake that will be used in a configuration with the scramjet…
No. No.
You could have done that, could you not? Without the engine, you could have used the duct to study the air flow characteristics…
We are doing other experiments for that. Then subsequently we have to incorporate them and see how to use that part of the system during the descent phase.
DRAG EFFECT
The final objective is to achieve a minimum drag configuration, which has a highly slender shape with a very small wingspan. For that, how many more flights do you think would be required?
Between this version and the final version…. You see drag effects also depend on the control surfaces, the L/D ratio and a host of other parameters. But basically what we can say is that those are validatable now with the current design and the experiment that we have done and the wind tunnel tests that can be done. To that extent things are under control.
Sivan also mentioned that for heavy-lift vehicles you were thinking of moving away from a winged design altogether.
[Pointing to a model of the two-stage launch configuration kept on the table, with the winged aerospace vehicle RLV-TD sitting atop the booster rocket.] For example, this is the first stage [the booster], and then the second stage [the RLV-TD] will be going [after separation]. That is one part of the story. What we have done is test the RLV-TD; we have mounted it on a booster. Later what we will do is the RLV-TD will become the first stage, which can be recovered.
Is the issue whether it will be winged or not still open?
You have multiple options. In the TSTO (two-stage-to-orbit) option, why a winged bodied thing is done is primarily because it can come and land nicely, like a plane. But what we have to see is, compared with the earlier times, whether the whole concept of using such a configuration is viable or not. If you are able to recover that in alternative modes, then that feature need not be there… like whatever others are doing today, for example SpaceX. So those are the discussions that will be there. But, notwithstanding that, even in this configuration, as the technology evolves and certain capabilities come you can find ways of improving the service cost.
Would you also be aiming this for heavy lift or…
Not necessarily. Those things will be actually debated. See, some of these things, until you do the first experiment you have so many ideas. Then as you start doing your experiments, it gets more focussed and, then compared with the times when they were debating all these options, today a lot of changes are there in technology… and the emphasis itself is changing considerably. Those days, even 10 years back, people would not be worrying too much about reducing [costs] like the way it is today. When people want to put 900-1,000 satellites into orbit in a short time, the impact of cost is much more than when you were talking of putting 10-12 satellites over a period of five to six years.
Do you envisage a situation where you will have winged RLVs as well as wingless RLVs?
Definitely, it will be there. Because, in terms of pure technology development, this winged configuration has its own advantages for certain categories of activities.
Do you think you will consider this for manned missions?
For manned flight if we have to use it, we still have to go through a lot more exercises before we can get into that. At this point of time, to be contemporary, our prime objective will be to improve on the cost.
If you want to do a manned mission type of thing, the drivers would be different for that. That time your worry would be on how to ensure safety [of the astronauts]. For that, even if you have to make it less cost-effective you will not worry about it. The prime objective at that time would be to optimise the parameters for the safety of the person who would be travelling in that and how you can bring it back without any [mishap].
If you are doing it with an inanimate object, then you can take certain risks and go ahead.
But at this point of time could you really not say what the ultimate objective of a winged configuration would be?
Right now we are clear about one of the objectives: we want to bring down the costs. Towards that one set of design driving will happen. The other thing is it will also give us the opportunity to demonstrate many of the new things that we would be using. So, in parallel, we will be trying different cost functions and drive the development.
Everyone emphasises that the hypersonic re-entry is a big achievement. But the Defence Research and Development Organisation (DRDO), in all its missile development activity, has done re-entry in hypersonic speeds many times.
Here re-entry has been demonstrated for a winged body going through the flight regime. We are not talking of other things. That is for the first time. And this is the first time that all the issues relating to such high-temperatures and aero-thermal protection have been addressed.
Since the DRDO was mentioned, what stage is its Avatar concept, which is also an RLV and the organisation has been talking of for many years?
I will really be not able to say anything on that. I am really not aware of that because ISRO is not involved there at all. [In an answer to a question in Parliament on March 14, 2012, ISRO stated: “Feasibility study of project ‘AVATAR’ has been done by a group of scientists in DRDO. ISRO has no connection with the project.”]
SCRAMJET DEVELOPMENT
At what stage is the scramjet development now?
We will be doing some scramjet experiments shortly. We have already done one using a sounding rocket. We intend to do something more in the next few months. This particular thing that we are planning using the sounding rocket is for air-breathing. Of course, for launch vehicle activities, how beneficial is air-breathing is still a question. The duration of traverse is very small for it to have good efficiency.
Would you like to say something about this air-breathing propulsion test, which, we were told, is likely to happen in June?
One of the problems today is whether the thrust you are generating from that air-breathing is more than the drag that you are encountering. That is the key thing. That is still not demonstrated. First, we should be able to sustain this operation itself for a certain period of time where unambiguously you can show that you have got something from that [air-breathing combustion]. To that extent these exercises will be done.
Today one of the arguments is whether it is really going to happen or not. Now there are also people who say that there are methods to minimise whatever drag effects that are there. I won’t be able to give you exact numbers, but concept-wise, this is the situation.
Sivan gave us to understand that, ultimately, scramjet is thrust-limiting. You really cannot give too much of thrust using scramjets. Even if you use a cluster of scramjets, you have to worry about the additional drag that this may entail. So, ultimately, it boils down to using semi-cryo and cryo stages and trying to bring them back, does it not?
Right…
What stage is the semi-cryo development now?
For semi-cryo, we have already established facilities at Mahendragiri [Tirunelveli, Tamil Nadu]. One major facility establishment activity is currently going on. In terms of other components and engine development, we have done cold flow test [test of a liquid rocket without firing it to check or verify the integrity of a propulsion subsystem] type of thing. We have also done some turbo tests. We are also trying to push hard to see that the semi-cryo stage can replace the L110 [the core stage using Vikas liquid engine] on GSLV-MkIII.
So in this RLV approach to TSTO, the first stage will have semi-cryo…
The semi-cryo engine stage will take the upper stage with payload to the required altitude, and then another stage, a small cryo-stage, will go into orbit.
Will both the stages be brought back?
You can design the first stage in such a way that it can be brought back. And then the second one also can be brought back. Those are the exercises that we will be getting into.
When we make a TSTO vehicle, there are different mechanisms… we are looking at all of them. One is to also have some thrusting capability [in the first stage] like what SpaceX is doing, for example. As it is descending, you control the descent by thrust, like a soft landing on the moon. It will be things of that type.
Would you like to comment on the programmes of other countries that have given up this winged configuration more or less?
What I would say is that at any given point of time, depending upon what is your prime objective, you pursue certain things. For example, we are now not looking at it from the perspective of carrying very heavy objects or carrying man into space. So there will be some difference in approach. We will go through our next set of discussions.
The crux is in actually visualising what the contemporary technology is, or what new enabling technology is available, which if used with what you have, you can overcome certain things. If we find that, we will definitely be able to make an impact, we will pursue it.
What we have seen is that, at a given point of time, there are concepts, there are systems which have been designed or thought of, but they require certain skills and capabilities. When they are not available, they cannot be implemented. So, later on, at another point, they become available. But unless somebody is looking for such a thing, because it has been tried and left out, it will be forgotten.
Like you say, they have done that and discarded it and so it is over. But then if somebody looks at it and says, ok, what was the key thing that I was looking for? What is it that prevented that particular approach? Is there a new technology today, a new enabling technology that is available? Whether I can work on that? This is the real issue.
So, to the credit of ISRO, what we can say is that all along its approach has been how to make such usages. Right from, for example, INSAT-1 concept itself, if you remember, we had three-in-one [applications] and the first 3-axis stabilisation. Similarly, the 3-mirror telescope that we used in IRS-1C, which was launched in 1995, to achieve 5 m resolution against the best of 10 m at that time. To that extent you can say ISRO has all along been successful in trying to visualise and bring that kind of thing.
For that reason, I would not say that it is not possible even though somebody had tried earlier. If we find with today’s technology, or whatever is going to come up, we can overcome certain issues that were preventing that particular concept from demonstrating…. Anyway, it is not that every time you succeed. If you keep looking for it, I think you will find some solution.
COST FACTOR
Right now what is the global average cost for the launch of a kg and what is your cost?
Typically in the range of $15,000-25,000 depending upon what kind of mission is there.
What will be your target for bringing down the cost if you are going to get into RLV?
In principle, even if the cost comes down by 50 per cent, it is worth it. After factoring in the logistics of recovering it etc., whatever it can bring down is worth it. If you are spending X, and you are able to use it 10 times, then all that cost you will apportion accordingly, and then if you are getting advantage, only then will you do it.
Otherwise if you find that all this you are getting into works out to be more, then obviously you will not do that. Those are the things that we have to constantly work on. But today first things will not be really optimising certain parameters. In this case how to withstand the Mach number and those conditions, how to ensure that our CLG system is there so that we can come up with the right CLG system. Then we can go to the next generation of electronics and make it into a very compact system.
Much of even the sensing systems that we are using will have been driven by what we have been using in the past. So we will now be looking fundamentally at how to make use of today’s technologies: MEMS [microelectromechanical systems] stand miniaturised systems, etc., and do the same functionalities in a much more cost-, size-, power-effective way. This is simply a test bed for many of those things. So, that way it [this RLV-TD programme] will really help us.
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