GSLV MK III is very similar to the Ariane 5. Both have solid boosters. As everyone knows the weak link for the GSLV MK III is the core stage. Ariane has a great core with the EPC H158 stage. ISRO is planning to change the core stage of GSLV MK III from L110 to a Semi-Cryogenic stage when the SCE200 engine is ready that will increase the GSLV capability to launch 6 ton satellites to GTO.Could ISRO have done better if they had worked on a core stage based on a more powerful Cryogenic engine instead - like a C170 LOX/LH2 stage with specs like a thrust of 1200kN and Specific Impulse of around 430-440 on a propellant load of around 170 tons? Currently what differentiates the ESA's Arianne 5 (that has 10.5 tons to GTO capability) from GSLV MK III is their core EPC H158 stage based on LOX/LH2 with a specific impulse of 440. Core stages need to have a high Specific Impulse to get the extra delta-v. So a Cryogenic core (with a high Specific Impulse) is a must for a heavy launcher to get the extra delta-v. With a Cryogenic core as above, GSLV MK III would have been a launcher in the 10 ton to GTO class.Did ISRO miss an easy opportunity to get to the 10-ton class? Why did they prioritise the Semi-Cryo engine instead that gives then hardly an addition of 2 tons more than the current GSLV MK III?
If ISRO can develop a core stage with 5 meter diameter clustered with 5 CE-20 Engine that can generate 1000 kN thrust, GSLV MK-III's payload capability would be significantly raised to almost 10 ton. It would be unwise of ISRO to renege the development of more powerful cryogenic engine to give way for the development semi-cryogenic engine. Semi-Cryogenic Engines would be temporary solution, but more powerful cryogenic engine should be permanent solution.
I have read that the low density of LH2 necessitate the usage of larger propellant tanks which would somewhat negate the advantages of its use as a core stage (as against a smaller upper stage). But then we do have old and new rocket designs that use a hydrolox core (with Long March 5 being the latest entrant), so I guess the higher Isp sufficiently compensates for that. That would leave us the question of cost.
Quote from: vineethgk on 07/03/2017 09:49 amI have read that the low density of LH2 necessitate the usage of larger propellant tanks which would somewhat negate the advantages of its use as a core stage (as against a smaller upper stage). But then we do have old and new rocket designs that use a hydrolox core (with Long March 5 being the latest entrant), so I guess the higher Isp sufficiently compensates for that. That would leave us the question of cost.But the Long March 5 was not started today. It was started years ago as a response to the Delta IV. (which ULA wants to retire as soon as possible due to absurdly high costs) If you only try to build what competitors are flying *now*, you'll always be 5-10 years behind the curve. See where others are going, and aim for that. Then you might actually be able to surpass them.
Quote from: Lars-J on 07/03/2017 07:46 pmQuote from: vineethgk on 07/03/2017 09:49 amI have read that the low density of LH2 necessitate the usage of larger propellant tanks which would somewhat negate the advantages of its use as a core stage (as against a smaller upper stage). But then we do have old and new rocket designs that use a hydrolox core (with Long March 5 being the latest entrant), so I guess the higher Isp sufficiently compensates for that. That would leave us the question of cost.But the Long March 5 was not started today. It was started years ago as a response to the Delta IV. (which ULA wants to retire as soon as possible due to absurdly high costs) If you only try to build what competitors are flying *now*, you'll always be 5-10 years behind the curve. See where others are going, and aim for that. Then you might actually be able to surpass them."There are some who question the relevance of space activities in a developing nation. To us, there is no ambiguity of purpose. We do not have the fantasy of competing with the economically advanced nations in the exploration of the moon or the planets or manned space-flight. But we are convinced that if we are to play a meaningful role nationally, and in the community of nations, we must be second to none in the application of advanced technologies to the real problems of man and society." --- By the GREAT himself
Quote from: kanaka on 07/04/2017 12:45 amQuote from: Lars-J on 07/03/2017 07:46 pmQuote from: vineethgk on 07/03/2017 09:49 amI have read that the low density of LH2 necessitate the usage of larger propellant tanks which would somewhat negate the advantages of its use as a core stage (as against a smaller upper stage). But then we do have old and new rocket designs that use a hydrolox core (with Long March 5 being the latest entrant), so I guess the higher Isp sufficiently compensates for that. That would leave us the question of cost.But the Long March 5 was not started today. It was started years ago as a response to the Delta IV. (which ULA wants to retire as soon as possible due to absurdly high costs) If you only try to build what competitors are flying *now*, you'll always be 5-10 years behind the curve. See where others are going, and aim for that. Then you might actually be able to surpass them."There are some who question the relevance of space activities in a developing nation. To us, there is no ambiguity of purpose. We do not have the fantasy of competing with the economically advanced nations in the exploration of the moon or the planets or manned space-flight. But we are convinced that if we are to play a meaningful role nationally, and in the community of nations, we must be second to none in the application of advanced technologies to the real problems of man and society." --- By the GREAT himselfSo why pursue near useless hydrolox booster stages? Is it just a status symbol, to say that India has technology X? Then what real use to man and society is it? Do you "play a meaningful role nationally, and in the community of nations" by repeating the same mistakes of other nations?
On a similar note, another discussion point is the following:If increasing the payload of GSLV is the main challenge then why can't an additional higher stage be added in the form of a CUS12 stage with the CE7.5 engine on top of the current C25 stage that would give it an additional delta-v? That would help to increase the payload from 4 tons to around 7 tons (if delta-v are worked out for each stage, looks reasonable) class, without any new development. Dont know why ISRO is not going this route? The CUS12 stage is 2.8m diameter while the the C25 stage is 4M diameter. So they may need to do some air flow tests probably.
Wouldn't adding CUS7.5 over CE12 reduce the payload capacity ? to the extent of the weight of CUS7.5 stage ?
The avenues for further enhancement of LVM-3 performance beyond 4 tonnes will definitely be explored once the vehicle stabilises after a few successful missions. Inert mass reduction in the upper stage (C25) and associated assemblies will be the most attractive and efficient route with least risk in terms of mission reliability. Of course, the propellant loading of C25 itself can be further augmented beyond 27 tonnes by stretching the tankages and also requalifying the endurance of the propulsion systems for the longer burn time. Modulating the engine thrust within bounds in terms of uprating/downrating during the long-stage burn time to optimise the needed velocity gain (ΔV), as was done with GSLV CUS stage, can be another strategy to marginally stretch the performance. However, without touching the lower propulsive stages and the overall vehicle architecture the payload growth of GSLV-Mk III may not go beyond 5 tonnes to GTO. With the ongoing programme to develop a 200 tonne thrust LOX-Kerosene semi-cryo engine and subsequently a semi-cryo stage to replace the L110 core, the GTO payload is expected to touch 6 tonnes.