SpaceX Falcon 9 : GPS III SV04 : SLC-40 : November 5, 2020

[spacebleachers]

For those that know, is this GSE or part of the rocket/ engines?

[Herb Schaltegger]

For those that know, is this GSE or part of the rocket/ engines?

Turbomachinery means one of the engines, either the RP1 or LOX turbopumps that feed propellants to the engine combustion chamber. The task for SpaceX for last night and today is to determine if that unexpected pressure rise was due to a bad sensor reading or if it was real, and if real, why it occurred and how to correct it.

[Alexphysics]

For those that know, is this GSE or part of the rocket/ engines?

Turbomachinery means one of the engines, either the RP1 or LOX turbopumps that feed propellants to the engine combustion chamber. The task for SpaceX for last night and today is to determine if that unexpected pressure rise was due to a bad sensor reading or if it was real, and if real, why it occurred and how to correct it.

Elon said on the gas generator so it was neither of those but rather the gas generator pump.

[Herb Schaltegger]

For those that know, is this GSE or part of the rocket/ engines?

Turbomachinery means one of the engines, either the RP1 or LOX turbopumps that feed propellants to the engine combustion chamber. The task for SpaceX for last night and today is to determine if that unexpected pressure rise was due to a bad sensor reading or if it was real, and if real, why it occurred and how to correct it.

Elon said on the gas generator so it was neither of those but rather the gas generator pump.

Um, he said “turbomachinery gas generator” - that means the engine, not the GSE, which was the question and the gist of my reply.

[Alvian@IDN]

https://twitter.com/EmreKelly/status/1312392547160002560?s=19

Looks like no SpaceX GPS attempt tonight. The only launch on the range’s calendar this morning is Starlink at 0751 ET Monday, Oct. 5. Weather 60% go.

[CorvusCorax]

Merlin is not a full flow staged combustion cycle but a simple gas generator.

that means both RP1 and LOX get pumped by their respective pumps, which sit on the same shaft. most of it enters the primary combustion chamber, while a small amount of both LOX and RP1 is fed into the gas generator.

in the gas generator these components react, (fuel rich combustion), turning into sooty exhaust gas
this gas is then allowed to escape through the gas generator turbine, which also sits on the single same shaft and drives the 2 pumps.

Unexpected pressure rise in the turbomachinery gas generator

basically implies there was a pressure spike in the turbo pumps's combustion chamber. Maybe it was a "hard start" - too much propellant at ignition time or delayed ignition, which would both cause a mini-detonation at startup time - or some residue of something that caused a lot of gas to be generated when heated (water/solvent) or a problem with the pumps/valves causing too much material to be fed into the gas generator.

The gas generator would undergo ignition before the main engine does, and AFAIK SpaceX ignites it with TEA/TEB, just like the main chamber. If TEA/TEB comes in contact with residual propellant from the static fire or soot residue or something else not supposed to be in there, it might also cause overpressure at ignition time.

Lot's and lots of potential causes, you'd need the exact engine schematics and telemetry to know the exact timing (was the overpressure at ignition itself or before during spinup or afterwards?) and having a physical look at the plumbing probably would be a good idea, too which means at least borescoping the turbopump to have a look.

Maybe even a blockage downstream could cause overpressure - what if the exhaust pipe was blocked or one of the gas channels inside the turbine ...  maybe a bee crawled up the exhaust duct and got stuck between the turbine blades

[TrevorMonty]

Swap engine out and carry on?
 

[Alexphysics]

For those that know, is this GSE or part of the rocket/ engines?

Turbomachinery means one of the engines, either the RP1 or LOX turbopumps that feed propellants to the engine combustion chamber. The task for SpaceX for last night and today is to determine if that unexpected pressure rise was due to a bad sensor reading or if it was real, and if real, why it occurred and how to correct it.

Elon said on the gas generator so it was neither of those but rather the gas generator pump.

Um, he said “turbomachinery gas generator” - that means the engine, not the GSE, which was the question and the gist of my reply.

Yes I know, I just meant it was not on the LOX or RP-1 pumps but the gas generator pump. Different side of the engine.

[Jakusb]

Funny how this gets more and more a situation:
Why would they even fly an unproven rocket?!

[woods170]

Swap engine out and carry on?
 

When data review and engine inspection point to engine issue it is either repair or swap, with swap being the more likely option.

SpaceX has previously signalled that cleaning the turbines is a time-consuming and labour-intensive job.

[Jakusb]

Swap engine out and carry on?
 

When data review and engine inspection point to engine issue it is either repair or swap, with swap being the more likely option.

SpaceX has previously signalled that cleaning the turbines is a time-consuming and labour-intensive job.

But aren’t these engines part of the new rocket dedicated produced and certified for USSF? So can they simply introduce another new engine that might not have followed the same certification path? Or have they included some reserve engines just for this situation?
Or is the USSF ok with any other new engine?

[oldAtlas_Eguy]

There is not anything any different from one part to the next on the documentation and testing gathered. What is different is that for SF launches Aerospace Corporation experts (AF/SF brain trust of space hardware experts) reviews the documentation. A swap out to another engine would be a quick review of the engine documentation and the documentation of the swap. Could take a few hours or a few days. There are no different tests or even examination of the actual hardware. Just it's pedigree documentation.

What SpaceX is getting paid for is to allow the SF "Experts" ability to ask the SpaceX personnel (mostly engineers and test personnel) questions. And for the access to all of the documentation.

[Comga]

Did anyone else note that the SpaceX webcast announcer said “.. four...three...” but never said “two” as the abort occurred around two seconds before scheduled launch.
Contrast this with Delta IV Heavy where the announcer kept counting through “Liftoff” although their abort happened several seconds earlier.
That may say something about the structure of the two organizations, flatter vs. hierarchical.

[CorvusCorax]

Yes I know, I just meant it was not on the LOX or RP-1 pumps but the gas generator pump. Different side of the engine.

Merlin has only 2 pumps: LOX and RP-1. There is no such thing as a "gas generator pump".

I tried to find an engine with a separate pump for the gas generator. That made me find this (slightly off topic) video of the first rocket engine turbopump flown ever with wayyyyy more info than you'd ever need (but surprisingly enough you find the exact same basic principle still today). It's a 2 hour video that tells you everything, from the geometry of the inlet and outlets to how to manufacture (and not manufacture) turbine disks for mass produced turbo pumps. Also includes funny experiments with monopropellants.



Von Brauns A4/V2 missile used a separate monopropellant gas generator independent from the main rocket fuels - just like the Redstone or the Soviet SA-2 missiles would later (which were derivates) but the gas generator propellant is pressure-fed, so even in these old engines there is in fact no "gas generator pump" - only a high pressure nitrogen gas bottle hooked up to the propellant tank.

If you find any rocket engine with an actual distinct "gas generator pump", please tell me

[ZachS09]

Did anyone else note that the SpaceX webcast announcer said “.. four...three...” but never said “two” as the abort occurred around two seconds before scheduled launch.
Contrast this with Delta IV Heavy where the announcer kept counting through “Liftoff” although their abort happened several seconds earlier.
That may say something about the structure of the two organizations, flatter vs. hierarchical.

Which is what confuses me. I sincerely don't get why the ULA PAO keeps going as if everything's normal.

[1]

Did anyone else note that the SpaceX webcast announcer said “.. four...three...” but never said “two” as the abort occurred around two seconds before scheduled launch.
Contrast this with Delta IV Heavy where the announcer kept counting through “Liftoff” although their abort happened several seconds earlier.
That may say something about the structure of the two organizations, flatter vs. hierarchical.

Which is what confuses me. I sincerely don't get why the ULA PAO keeps going as if everything's normal.

Most commentators are not technically competent. They're following a general script, and it takes some time for deviations from that script to be realized. True, announcing 'liftoff' after the engines have fizzled is particularly silly, but there have been many times when commentary has continued truckin' right along after something's gone wrong; or even after a mission has outright failed. John Insprucker is a rare gem and by far my favorite person in that role; I think many of us are spoiled by him. Even so, I still miss the technical webcasts.

Anyway, back to GPS III.

[Alexphysics]

Yes I know, I just meant it was not on the LOX or RP-1 pumps but the gas generator pump. Different side of the engine.

Merlin has only 2 pumps: LOX and RP-1. There is no such thing as a "gas generator pump".

I tried to find an engine with a separate pump for the gas generator. That made me find this (slightly off topic) video of the first rocket engine turbopump flown ever with wayyyyy more info than you'd ever need (but surprisingly enough you find the exact same basic principle still today). It's a 2 hour video that tells you everything, from the geometry of the inlet and outlets to how to manufacture (and not manufacture) turbine disks for mass produced turbo pumps. Also includes funny experiments with monopropellants.



Von Brauns A4/V2 missile used a separate monopropellant gas generator independent from the main rocket fuels - just like the Redstone or the Soviet SA-2 missiles would later (which were derivates) but the gas generator propellant is pressure-fed, so even in these old engines there is in fact no "gas generator pump" - only a high pressure nitrogen gas bottle hooked up to the propellant tank.

If you find any rocket engine with an actual distinct "gas generator pump", please tell me

It would be glad to know then what "turbomachinery gas generator" is because, as the phrase indicates, it has nothing to do witht the main RP-1 and LOX pumps but rather with the gas generator. As you say, it doesn't have any pumps or something like that. Then what's that turbomachinery all about?

[gongora]

The gas generator powers the turbomachinery.  That is the entire point of having it.

[John Santos]

It would be glad to know then what "turbomachinery gas generator" is because, as the phrase indicates, it has nothing to do witht the main RP-1 and LOX pumps but rather with the gas generator. As you say, it doesn't have any pumps or something like that. Then what's that turbomachinery all about?

I think "turbomachinery gas generator" means the gas generator for the turbomachinery.  In other words, the gas generator that powers the pumps.  In this sentence, "turbomachinery" is an adjective that describes the gas generator.  Perhaps non-native English speakers are confused by the somewhat awkward phrasing Musk used?  Since the ONLY gas generators on the Falcon are the ones on each engine that drive the turbopumps, the adjective is unnecessary.  The only "turbomachinery" is the fuel and oxidizer pump (two turbopumps on a common shaft driven by a gas turbine in turn driven by combusting fuel and oxidizer, i.e. the gas generator.)

Since the fuel and oxidizer pumps are driven directly by the gas generator, I don't think it is correct to say "it has nothing to do with the main RP-1 and LOX pumps".  The gas generator is part of the main pumps.

Edit: or what gongora said in 90% fewer words.

[Fluke72]

Merlin is not a full flow staged combustion cycle but a simple gas generator.

that means both RP1 and LOX get pumped by their respective pumps, which sit on the same shaft. most of it enters the primary combustion chamber, while a small amount of both LOX and RP1 is fed into the gas generator.

in the gas generator these components react, (fuel rich combustion), turning into sooty exhaust gas
this gas is then allowed to escape through the gas generator turbine, which also sits on the single same shaft and drives the 2 pumps.

Unexpected pressure rise in the turbomachinery gas generator

basically implies there was a pressure spike in the turbo pumps's combustion chamber. Maybe it was a "hard start" - too much propellant at ignition time or delayed ignition, which would both cause a mini-detonation at startup time - or some residue of something that caused a lot of gas to be generated when heated (water/solvent) or a problem with the pumps/valves causing too much material to be fed into the gas generator.

The gas generator would undergo ignition before the main engine does, and AFAIK SpaceX ignites it with TEA/TEB, just like the main chamber. If TEA/TEB comes in contact with residual propellant from the static fire or soot residue or something else not supposed to be in there, it might also cause overpressure at ignition time.

Lot's and lots of potential causes, you'd need the exact engine schematics and telemetry to know the exact timing (was the overpressure at ignition itself or before during spinup or afterwards?) and having a physical look at the plumbing probably would be a good idea, too which means at least borescoping the turbopump to have a look.

Maybe even a blockage downstream could cause overpressure - what if the exhaust pipe was blocked or one of the gas channels inside the turbine ...  maybe a bee crawled up the exhaust duct and got stuck between the turbine blades

if i might add a bit to your talk---   the GG is mounted next to the turbopumps and is fed tea tab/lox and rp1 and is spun up by helium. The exhaust of the GG exits via the HEX can and is what you see as the black fuel rich smoke. The GG is a pretty bulletproof little bugger and does have a few sensors tied to it as well as sensors on the feeds and the turbopumps have extensive arrays of sensors to provide data on all regimes of startup. I would put money on a spike was seen and the mov (main oxygen valve) and rp1 valves never opened due to that. likely fix was check the sensor data and test the suspects...its possible that the GG somehow failed but that would be more likely to happen due to structural issues or burn thru.

one other cause could be the ground supplied TEA TAB system which is used during launch on all first stage engines. Im not familiar at all with that though. possible that too much or too little TEA TAB could cause a higher than wanted GG pressure at spin up??? same could be true for lox or rp1 i guess...