GSLV D3 Launch Failure

[vina]

Good good. I mean the engine ignited, generated thrust and all the good things and that the failure was due to the booster pump going belly up.

So that means that the really really big enchiladas, the combustion, the main turbo pump, the startup of the main engine and all that worked well. What needs to be done is root cause analysis, replication and fix of the fuel booster pump.

The nice thing about that is that as the Al-Hundi states, the booster pump is located inside the fuel tank. So it means that it is never operating in vaccum on both the inlet and outlet. That thing is easy to replicate on the ground.

So no need for any trips to Jurmany or Russhia and need to pack a truck load of MTR ready to eat meals, do shopping for winter clothing and run after babus for travel budgets and authorizations in triplicate. They can wear their dhotis and do the testing at LPSC at Mahendragiri, getting their chai from the local Nair stall and sambar and rasam from the canteen.

[babbupandey]

lol@"wear their dhotis and do the testing"
I just imagined chappal-dhoti clad engineers around hi-tech engineering equipment

[Sanjay M]

vina,

Okay, but are you sure that the evidence really shows that ignition occurred and that the engine indeed operated for the alleged milliseconds? I've never heard of being able to assess velocity or thrust performance based on mere milliseconds of data. That upper stage was already moving due to the existing momentum imparted to it - how the hell can they really tell that it received some milliseconds of thrust acceleration? I'm worried that there is a less-than-objective face-saving interpretation of data happening here.

What were the other measurements that were coming back from the telemetry? If they got direct readings of turbopump rpm, then we can take that as a positive sign that combustion had indeed occurred to drive the pump. But so then I hope that this figure of 34,800 rpm for the turbopump was the result of direct measurement, and not somehow magically derived from some other dubious observation like acceleration.

Anyway, if they can doubly, triply, quadruply stress-test the turbopump to improve it beyond a shadow of a doubt, then hopefully we'll see another launch within the announced year timeframe. We can believe in their diagnosis once the next GSLV reaches orbit.

[babbupandey]

lol@"wear their dhotis and do the testing"
I just imagined chappal-dhoti clad engineers around hi-tech engineering equipment

OT: I suppose you have never been to Florida and seem the Nasa facilities there? No offense, but really, he was pointing out a fact, but you made a joke of it. Any specific reason for the OT?

Ooooh - someone is getting angry (after reading too much between the lines)

Vina made a funny comment and I laughed at it - that's it. Face it, picture of dhoti clad engineers in a spic-and-span facility is funny (add to it a scenario where they are dancing to the tune of variya-variya)

[Sanjay M]

dunno, but even pictures of that would be welcome for starving jingos who never get to see anything, since ISRO won't even put cameras onboard the rockets to give us some eye-candy

[babbupandey]

dunno, but even pictures of that would be welcome for starving jingos who never get to see anything, since ISRO won't even put cameras onboard the rockets to give us some eye-candy

I agree - but these days they have started live broadcast of launches (courtesy Doordarshan)
Having said that, I fully agree that some documentary showing insides of ISRO/VSSC would be welcome

[babbupandey]

OT: No anger at all. Just exasperation. Why is wearing a dhoti to a spic and span facility funny and why would it be funny to listen to any music that they prefer?
Vina saar was making fun of exactly the mindset you talked of.

Goodness! Just for the sake of bringing back the thread to the topic; I offer my unconditional apologies to you and anybody else who is offended by my comments. I never thought my innocent laughter will leave so many heart-burns.
*Peace*

[chaanakya]

ISRO talked about failure of FBTP with two plausible scenario

Two plausible scenarios have been identified for the failure of FBTP, namely, (a) gripping at one of the seal location and seizure of rotor and (b) rupture of turbine casing caused probably due to excessive pressure rise and thermal stresses. A series of confirmatory ground tests are planned.

Advanced Rocket Engines

Aside pump and turbine any turbopump requires components such as bearings, seals, gears and the
suction and discharge ducts. There are two kind of bearings, rolling elements and fluid film ones and they
have to perform three primary functions, radial control of the rotor to prevent rubs and to maintain
clearance, axial control of the rotor to maintain rotor control during transient mechanic and thermal loads
and to react residual thrust loads and third, control of rotordynamics to provide for adequate radial
stiffness and damping. They are usually cooled by the fluid which quite often doesn’t provide for
lubrication, operate at high speeds and are exposed to high transient radial and axial loads. While static
seal design in rocketry generally doesn’t exceed standard procedures, dynamic seals which separate
stationary and rotating parts are critical. Dynamic seals just must not fail. There are different types of
seals, labyrinth, face contact or shaft contacting, floating ring or hydrodynamic face seals. Major design
problems are fluid compatibility, thermal gradients and dynamic loads.

http://wapedia.mobi/en/Liquid-fuel_rocket

Cryogenic propellants, such as liquid oxygen, freezes atmospheric water vapour into very hard crystals. This can damage or block seals and valves and can cause leaks and other failures. Avoiding this problem often requires lengthy chilldown procedures which attempt to remove as much of the vapour from the system as possible.

I think ISRO has presented correct analysis of failure. But only next successful lift-off of GSLV with indigenous cryogenic engine would validate the report. However one need not be disheartened as every failure is a step closure to success.

[Sanjay M]

How exactly do they monitor/measure/observe a turbopump in situ while it operates during ground testing?

[Narad]

vina,

Okay, but are you sure that the evidence really shows that ignition occurred and that the engine indeed operated for the alleged milliseconds? I've never heard of being able to assess velocity or thrust performance based on mere milliseconds of data. That upper stage was already moving due to the existing momentum imparted to it - how the hell can they really tell that it received some milliseconds of thrust acceleration? I'm worried that there is a less-than-objective face-saving interpretation of data happening here.

The conclusions based on the millisecond statistics indeed lacks credibility. Unless there is direct measurement of RPMs that were transmitted to MCF. This would further imply that the CUS was monitored wrt rotations per millisecond (RPMS) and not usual rotations per minute (RPM). Even this is really unheard of, and sounds ridiculous.

And if there was/canbe no direct measurement for such a least count then the alleged momentory thrust could most probably be derived by analogy by means of some other parameters that could be recorded more accurately in terms of milli-capabilities. Even then, what is the credibility of this either to assertain what really went wrong? This would still be a theorotical assumption which is yet to be tested in equivalent test conditions.

Can anyone please elaborate on this?

Unfortunately it is really sounding like a face saving attempt.

[sivab]

The conclusions based on the millisecond statistics indeed lacks credibility. Unless there is direct measurement of RPMs that were transmitted to MCF. This would further imply that the CUS was monitored wrt rotations per millisecond (RPMS) and not usual rotations per minute (RPM). Even this is really unheard of, and sounds ridiculous.

Read up on how shaft encoders work. RPM is a unit of measurement and is not the measurement period. Measurement periods are in microsecs/nanosecs for high speed encoders and there can be one RPM update every measurement period. Updates can be sent back to earth as fast as data link speed will allow, which will be very high for development flights.

[ramana]

Sivab, Does the telemetry stream have enough bits to distinguish such finite events? The encoder might be super what about the telemetry resolution?

[sivab]

Sivab, Does the telemetry stream have enough bits to distinguish such finite events? The encoder might be super what about the telemetry resolution?

A 16 bit data is all that is required per update (turbo pump rpm is ~40k), even at 100KHz update rate (10usecs interval) bandwidth requirement is a puny 1.6Mbps. Look at bandwidth capacity of ISRO built data links for small satellite sub-systems, each can handle more than 10 times as much. They don't need to transmit at 100KHz, even 1KHz update would be more than enough and bandwidth req. will be less. In a development flight there is no power restriction like a solar powered satellite and they can put up as many data channels as they need.