Kit bhai and MNji, apologies to quote your points. I need to elaborate from there:
kit wrote:The LOX Kerosene combination is used for the most powerful rocket engines including the Saturn and Energia.And i dont think all these developments were unknown to anyone.But whats interesting is ISROs lack of vision. Rocket engines being the work horses, any space faring nation can only build its capabilities on those.
I am assuming that when you quote "can only build its capabilities on those"., you mean the LOX/Kerosene combination.
Now lot of persons on this forums assume that LOX/Kerosene is a very easy path compared to LOX/LOH since only one path is cryogenic and it is easier to compress/cool down and manage LOX at that compared to LOH . Others assume that it is a safe path since Saturn/Energia run on it and of course it is "semi cryogenic"
Let us say both points are very valid., we have large examples of booster rockets running on LOX/Kerosene and since it is only half cryogenic so the range of temperatures are not that extreme.
Now just spare some thought on the Kerosene. Is it the "ghaas tel" which every house hold in India is accumstomed to using that goes in the LOX/Kerosene part? That is take the kerosene from the ration shop and pour those dabbas in the tank for the LOX/Ker engine? Of course not and I am sure you will also point out that you do not mean that Kerosene., since using that Kerosene is idiotic (that is using Ghaas Tel from ration shop is idiotic, which we all agree).
So where does this special kerosene come from? And what is special about this kerosene?
Put it this way, when you burn the ordinary ration shop kerosene (let us call this RSK-1)., you are looking at achieving a max temperature of 300 C (at most) and several time far lesser than that. However for rocket engines, the temperatures are generated in excess of 2000 C and therefore something is required to bring the temperature down. Generally, one of the liquid that fuels the rocket itself is used to cool the engine (its nozzles and everything else that is required to be cooled) down. I will leave up to you to figure out why Oxygen itself is not used exclusively in LOX/Ker engine. Something on the lines of unburnt fuel leaving a lot of smoke is a good hint (and now do not go about designing and manufacturing even at test one which uses oxygen itself as coolant in lox/ker - if you do, then you should get a straight job at ISRO - note this as sillypoint-1).
So now we have to use the RSK-1 as a coolant. The problem is that at high temperatures, definitely at temperatures encountered at rocket engines, RSK-1 has quite a remarkable tendency to polymerize. From high school chemistry we know that your everyday plastics are nothing but hydrocarbon polymers, so assume that thick deposits (of polymers) get stuck in the inner walls of coolant tubes (not unlike atherosclerosis or your kitchen drain getting clogged when you make lots of jalebis and pour the unused oil down the drain). Anyways, as the cooling passages are constricted, there is less flow of coolant and hence subsequent rise in heat and hence more of polymerization (or reverse of polymeration, cavitation because of the fuel breaking down) and subsequent more rise and you get the idea, all resulting in a huge explosion. So instead of the rocket going up, you have parts of it going sideways and maybe taking you up. You may argue (given that you have vision)., that why not have bigger dia. pipes. All I can say is, please go back to sillypoint-1 above.
So at this stage, we know that RSK-1 will not work. So what will work? Of course a fuel which does not cavitate or polymerize under the temperatures & pressures encountered in rocket nozzle. To turn it around, a hydrocarbon fuel has to be designed, developed and produced that meets the above mentioned requirements. By mid-1950s most of the industrial nations had such a design (for HC fuel) ready. It should be noted that by mid-1950s we were not even a decade after independence and the biggest challenge was national integration (for some) and providing food, medicines and clothing for the others. Okay by mid-1970s we had the requirements ready. Keep this in mind that in mid-1970s lot of rail engines were running on coal!
Now let us move forward., we now have the requirements (just like my PM has requirements for my product) for an ideal kerosene that does not cavitate or polymerize under given temperatures and pressures. So how do I produce one? One of the reasons that the kerosene polymerizes is the presence of sulphur. Ideally zero sulphur, but extremely low sulphur content will do. That is if I am given a barrel of oil and told to produce the required kerosene, I have to first eliminate sulphur.
Second, why does HC polymerize? In short, the carbon-hydrogen bonds break down and re-arrange themselves into more complex molecules. I need to avoid that, and find an HC bond molecule do not break down and reform into undesirable complex polymers but remain a desirable complex polymer. That is alkenes and aromatics (ethylenes and benzenes for the aam abdul) should be taken out of the equation. That is take a barrel of oil, remove sulphur, remove ethylenes (and its more complex analogues), remove benzenes (and remove its more complex analogues). Basically move towards classes HC polymers like
ladderanes. Now all of the above fractionalization and distillation has to be done on a barrel of oil. Can any barrel of oil do? Of course not, you cannot just take a barrel of oil from any oil field and dump it in your refinery and produce the above mentioned rocket fuel grade kerosene. The barrel of oil has to be carefully sourced and there are only very few oil fields in the world that source such high quality crude. BTW, in the late 1970s, the oil shock hit us. Heck we did not have diesel to run our cars and here we are talking about sourcing oil from a select oil field! Basically the crudes should have very high napthene content.
So one has to source a barrel of oil and process it to meet the requirements as laid down in US mil spec MIL-R-25576 (or its Russian, Chinese or Indian equivalent). Again that spec may not be completely open source and one has to spend resources that comes to that spec. To come to that spec, one has to have experience in rocket engines that use some kind of LOX/Kerosene to do sand box testing. Here if you do not have one, developing other is a big hassle.
Now by mid-80's when ISRO was taking off, did it have anything other than the requirements in hand. The answer is no. Since one just does not have to find an oil field, but have to find several such so that in case of disruption from the oil field, your space programme does not come to a halt. After sourcing from several such oil fields, one has to develop (design and manufacture) a refinery which can take several such feeds and produce the kerosene (called RP-1) that meets the above specification. Now what were the requirements for ISRo in a given year? Let us be charitable and say 10 tonnes of such fuel (in 80's and well into 90's). Let me bump it to say 100 tonnes of such fuel. So for producing 100 tonnes of such fuel, I will need say 10,000 barrels of oil a year and set up a refinery which processes that. This looks like an extremely costly proposition, since first of all ISRO is not in oil refining business and there is no private or public player (in India) even now that is willing to produce such a miniscule amount just for ISRO at a reasonable cost. Neither was India in a missile-arms race that the refiner could sell the product to Army, Air-force or Navy for their missiles or even their tanks or engines which could be based on jet turbine.
So what does ISRO do? Definitely the LOX/Kerosene is not a cheaper route. Further, the variables in achieving semi-cryogenic engine (delays, complexity etc) is same as one for the cryogenic engines. Further there is no supply constraint on LH2. Since, there is no kerosene that can be sourced for the LOX/Kerosene route., instead of going the LOX/Ker route, ISRO wisely decided to go for the LOX/LOH route. Infact, once the LOX/LH2 engine can be developed, one can come back and look at the launch requirements and if the refininig industry has progressed, can start sourcing small amounts of RP1 equivalents.
Further, hypergolic liquid engines will not be going away - they are excellent for start/stop requirements and hence excellent for stationing and orbit maintainence activities.
MN Kumar wrote: I guess it wont be a good idea to call it lack of vision. US & USSR were big players at the time. We were still trying to get our basics right. It might be more of choosing a safe path.
Going for LOX/LOH or developing your next generation rocket fleet on scaled liquid engines is not a safe path. It was the only path due to several other constraints which are difficult to comprehend in the first place.
And it is not about vision. Whatever the shortcomings of ISRO, one thing it does not have is a shortcoming of vision. At the end of the day, ISRO is answerable to the parliament and its "vision" is tailored and trimmed by the requirements of the parliament and more importantly its budgetary constraints.
I had a friend in school, he had a remarkable vision. He wanted to emigrate to "gelf" and find a rich oil sheikhs' daughter to marry so that by marriage he will inherit wealth and not work for life. So when kit bhai goes about complaining ISRO's vision., his sight does not go beyond his own' keyboard.
PS:Edited to fix a minor grammatic quibble
