Author Topic: GSLV MK III Core Stage  (Read 4528 times)

Offline Lars-J

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Re: GSLV MK III Core Stage
« Reply #20 on: 07/08/2017 03:35 AM »
But the question in my mind is about C-25. Carrying a heavier satellite and an added CUS 4th stage, it is quite likely that the stage would be on a suborbital flight when CUS and the satellite stack separates. Where then would it's debris fall? If my understanding of the flight path is correct, after the Andaman sea the flight passes over a long region of Indonesian islands and territorial waters. C-25 falling anywhere there would be darn risky and unacceptable.

But that is no different than the current Mk III. The C-25 does fly over Indonesia in the current configuration - there is a small risk that a failure early in the burn would bring it down there, adding a 4th stage will not change that.

Offline vineethgk

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Re: GSLV MK III Core Stage
« Reply #21 on: 07/08/2017 04:20 AM »
But the question in my mind is about C-25. Carrying a heavier satellite and an added CUS 4th stage, it is quite likely that the stage would be on a suborbital flight when CUS and the satellite stack separates. Where then would it's debris fall? If my understanding of the flight path is correct, after the Andaman sea the flight passes over a long region of Indonesian islands and territorial waters. C-25 falling anywhere there would be darn risky and unacceptable.

But that is no different than the current Mk III. The C-25 does fly over Indonesia in the current configuration - there is a small risk that a failure early in the burn would bring it down there, adding a 4th stage will not change that.
That brings a question to my mind. What do the space agencies typically do when the upper stage fails and there is a risk of debris falling over populated areas? Do they blow it up or just let it go and have atmospheric friction do its work during reentry (and considering the risk of large debris as insignificant as the upper stages have a lower mass when compared to the lower stages)?

I think the closest that ISRO came to such a scenario was when GSLV-D3 / GSAT-4 mission failed back in 2010. The CUS failed to ignite (or the ignition 'did not sustain' as per ISRO sources) after the second stage separation. The flight path was similar to that of GSLV-III D1, with the GS2 stage debris falling roughly in the same region of Andaman sea as the L-110 would. (Flight path of GSAT-9 mission for reference) I guess in that case since the CUS stage didn't ignite it must have fallen harmlessly more or less in the same region that GS2 fell. But what if it had failed after a few seconds of ignition (or lets say, a few tens of seconds)?

But I must admit that in this case there are no huge contiguous landmasses in the Indonesian archipelago, its mostly sea (but likely a busy shipping zone) and several islands (some of them quite large) sprinkled about..


Offline Lars-J

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Re: GSLV MK III Core Stage
« Reply #22 on: 07/08/2017 04:38 AM »
Usually its a cold hard probability formula. If the risk is low enough for a failure, you overfly land. After all, if you go to orbit you always overfly populated land at *some* point. The risk is just vanishingly small... and upper stages will mostly burn up in the atmosphere. (except some parts like Helium tanks) So it is up to each space agency - and the countries they overfly - to agree on acceptable risk.

Another way to think of it is the most likely failure scenario - a failure to start. Which is perfectly safe, since then the upper stage will simply fall in the same drop zone as the previous stage.
« Last Edit: 07/08/2017 04:41 AM by Lars-J »

Offline PonRam

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Re: GSLV MK III Core Stage
« Reply #23 on: 07/08/2017 07:34 AM »
I am assuming one or more of the following possibilities.

1. GSLV-III's primary weakness is its underpowered L-110 core, and adding a fourth stage would be either detrimental or would not result in a meaningful upgrade in payload capabilities. Here is a relevant quote by S. Ramakrishnan (who was the project director of GSLV-III) from the book 'From fishing hamlet to red planet'.
Quote
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.


where in the above quote does it say that a fourth stage is not possible or is detrimental?

Offline PonRam

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Re: GSLV MK III Core Stage
« Reply #24 on: 07/08/2017 07:43 AM »
I am assuming one or more of the following possibilities.

2. The ongoing project to upgrade core stage to SC-200 is a better option in terms of simplicity and reliability than adding another upper stage. Adding a 4th stage would make the vehicle more complex and adds another point of potential failure.

3. GSLV-II's CUS (C-12/C-15) is too heavy for the job as an added 4th stage. A new smaller stage would be required.

5. CUS's CE-7.5 (~75-98 kN) being nearly half as powerful as CE-20 (~180-200 kN) of the preceding C-25 third stage is over-powered for the desired flight profile. A smaller cryo engine needs to be developed.

2. Agree for the long term. SC-200 will take 2021 to deliver. Question is can they possibly send a bigger payload during these 4 years?
3. Have taken the addition effort to show that the extra stage is not heavy. Is there anything wrong in my working? Is there a way to show through working that a smaller stage is required?
5. Same as 3. Thrust of a certain stage is over-powered or under based on the mass it has to push. Can it be shown thru the workings?
« Last Edit: 07/08/2017 07:48 AM by PonRam »

Offline vineethgk

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Re: GSLV MK III Core Stage
« Reply #25 on: 07/08/2017 08:33 AM »
I am assuming one or more of the following possibilities.

2. The ongoing project to upgrade core stage to SC-200 is a better option in terms of simplicity and reliability than adding another upper stage. Adding a 4th stage would make the vehicle more complex and adds another point of potential failure.

3. GSLV-II's CUS (C-12/C-15) is too heavy for the job as an added 4th stage. A new smaller stage would be required.

5. CUS's CE-7.5 (~75-98 kN) being nearly half as powerful as CE-20 (~180-200 kN) of the preceding C-25 third stage is over-powered for the desired flight profile. A smaller cryo engine needs to be developed.

2. Agree for the long term. SC-200 will take 2021 to deliver. Question is can they possibly send a bigger payload during these 4 years?
3. Have taken the addition effort to show that the extra stage is not heavy. Is there anything wrong in my working? Is there a way to show through working that a smaller stage is required?
5. Same as 3. Thrust of a certain stage is over-powered or under based on the mass it has to push. Can it be shown thru the workings?
The points I listed were just guesses that came to my mind. Its quite likely that many of those are incorrect when evaluated in technical terms (I'm a noob on rocket propulsion stuff). As for points 3 & 5 specifically, I included them as possibilities in the list as I had an impression that a typical 4th stage added to a rocket configuration tends to be quite lighter and of relatively low thrust when compared to the stage preceding it (something more than the 1:2 ratio we have between CUS and C-25 as regards to thrust and stage mass). But I guess that might be because those 4th stages are usually used to achieve a greater injection accuracy (or perform complex orbital insertions involving multiple restarts) rather than merely imparting delta-v, so perhaps that comparison may not apply here.

As for pt 2, I think ISRO's push for developing new, all-electric satellite buses is very relevant here, and they may not be anxious to loft payloads heavier than 4-5 tonnes to GTO for the near term. In fact ISRO seems to have recently floated EoI to supply electric propulsion systems for a new 2 tonne and 3 tonne all-electric satellite buses. The former must be meant for GSLV-II and the latter for GSLV-III. ISRO's strategy might be that rather than introducing ad-hoc redesigns in their LV (which incidentally could increase chances of failure) they could instead try making their satellites lighter through electric propulsion and achieve the same objective.

Offline PonRam

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Re: GSLV MK III Core Stage
« Reply #26 on: 07/09/2017 01:55 AM »
As for pt 2, I think ISRO's push for developing new, all-electric satellite buses is very relevant here, and they may not be anxious to loft payloads heavier than 4-5 tonnes to GTO for the near term. In fact ISRO seems to have recently floated EoI to supply electric propulsion systems for a new 2 tonne and 3 tonne all-electric satellite buses. The former must be meant for GSLV-II and the latter for GSLV-III. ISRO's strategy might be that rather than introducing ad-hoc redesigns in their LV (which incidentally could increase chances of failure) they could instead try making their satellites lighter through electric propulsion and achieve the same objective.

While the above is relevant, it does not necessarily mean that ISRO does not want to increase the payload beyond 4 tons. If you see the quote by S. Ramakrishnan, they do want to fine tune after the first few launches to increase the payload. But it is true that he is talking of other means like stretching the fuel tanks of C25 stage and not by an additional stage. Some how, they seem to be fixated on GSLV MK III being a 3 stage vehicle and no more. May be they may change their mind, in the future.

Additional stage may seem feasible based on the workings in the sheet and may provide ISRO an easy opportunity to increase the payload without too many changes or developments. Other restrictions as elaborated may be there.

Some of the assumptions i had while making that sheet are
* the 2 boosters kick off and provide all initial thrust
* L110 stages ignites only after the boosters have completed
* L110 stage completes
* Payload fairing is jettisoned
* C25 ignites
* C25 completes and is jettisoned
* CUS12 ignites
* CUS12 completes and is jettisoned
« Last Edit: 07/09/2017 01:59 AM by PonRam »

Offline PonRam

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Re: GSLV MK III Core Stage
« Reply #27 on: 07/20/2017 02:08 PM »
One of the things i realised is that the current GSLV MK III height is around 43.5m. An additional stage would increase it to around the 52m mark taking it above the 50m that the launch pad is capable of.

That could be one of the reasons why ISRO is sticking to the current 3 stage configuration.

Offline sanman

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Re: GSLV MK III Core Stage
« Reply #28 on: 07/21/2017 12:31 AM »
What would prevent them from extending the launch pad/tower?

Offline PonRam

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Re: GSLV MK III Core Stage
« Reply #29 on: 07/21/2017 02:37 AM »
Don't know the feasibility of extending the pad.

But the height of 50m for the vehicle seems to be a limitation that they have taken care of in the design of the MK III. "The Next Generation Launcher GSLV MK III" by S. Ramakrishnan says

“Taking into account the length to diameter (L/D) ratio and limiting the overall height of the vehicle on pad to less than 50 m, a core vehicle diameter of 4 m was selected which also dictates the machining facility and toolings required to realise the propellant tankages for L110 and C25 stages.”

Excerpt From: P.V. Manoranjan Rao. “From Fishing Hamlet to Red Planet.” iBooks.

Also reading the above article, increasing the payload capacity does not seem to be a priority of ISRO. They prioritised reliability and reduction of risk to payload increase as the following quote from the article suggests:

“With two motors of the existing PS1 stage (S139) attached as strap-ons which will virtually function as the lift-off stage, the GTO payload is less than 3 tonnes. Of course, four S139 solid boosters as strap-ons yield a GTO payload touching 5 tonnes. But, the vehicle becomes more complex and relatively less reliable due to the addition of two more propulsive units. So, to limit the solid strap-on boosters to two and attain 4-tonne-plus GTO payload, more propellant had to be added, and thus the S200 solid boosters with 200 tonne propellant were selected as the strap-ons.”

Excerpt From: P.V. Manoranjan Rao. “From Fishing Hamlet to Red Planet.” iBooks.