SpaceX Falcon 9 v1.1 - SES-8 - DISCUSSION THREAD

[Norm38]

That they've set a new NET gives hope that they have a root cause.  I must admit being concerned over talk of scoping engines and removing turbo pumps. That an engine failed to ramp as expected has two possibilities. That it missed by a little, or it missed by a lot.  If by a little they may have just widened the limits as they did with the power supply voltages. But they must be worried the engine didn't perform as it did at McGreggor or during WDR.  I'm thinking it was off by more than a little.

They've tested enough engines this shouldn't be a design problem. Build issue?  How fast can they swap engines?  I wonder if they'd want to keep this one?  Maybe ship it back to Texas for further study?
All speculation of course.

Edit: per the latest tweets, no engine issues.

[Jim]

That they've set a new NET gives hope that they have a root cause.  I must admit being concerned over talk of scoping engines and removing turbo pumps.

They said cleaning and not removing.

[Avron]

if Triethylborane is strongly pyrophoric, how would it be contaminated with oxygen?

[smoliarm]

if Triethylborane is strongly pyrophoric, how would it be contaminated with oxygen?

Easily 
Of course, if you just expose TEA/TEB to air - it is going to be a fire. But if you lower the amount of air available by order of magnitude (or two ) - there will be no fire, just a fast reaction of part of TEB with O2.
So, if you have in the TEA/TEB line a B-nut which is not tightened all the way - you have a LEAK of O2 going inside. This will spoil the igniter.
BTW, moisture (water condensate) inside these lines would have the same spoiling effect.

So, strictly speaking, "Triethylborane contaminated with oxygen" = TEB contaminated with *products* of oxidation.
This reduces pyrophoric activity.

[aero]

How much of that stuff do they use (TEA/TEB) to start the engines. I mean, is it like ml, or liters or like 10's of liters? That datum should give a hint as to the sensitivity to contamination.

[Avron]

if Triethylborane is strongly pyrophoric, how would it be contaminated with oxygen?

Easily 
Of course, if you just expose TEA/TEB to air - it is going to be a fire. But if you lower the amount of air available by order of magnitude (or two ) - there will be no fire, just a fast reaction of part of TEB with O2.
So, if you have in the TEA/TEB line a B-nut which is not tightened all the way - you have a LEAK of O2 going inside. This will spoil the igniter.
BTW, moisture (water condensate) inside these lines would have the same spoiling effect.

So, strictly speaking, "Triethylborane contaminated with oxygen" = TEB contaminated with *products* of oxidation.
This reduces pyrophoric activity.

So basically, a TBTO and  aluminium alkoxides non reaction .. thus no reaction for startup..  or reduced  reaction ... thinking back on a corroded nut

[Jakusb]

The best thing of any bug or anomaly, is figuring out its true cause. The pure satisfaction of having is fully explained after the stress of searching through all possible causes.
It makes you learn and take measures to prevent it from happening again.

I never understood people or companies that rely on "Just restart, that works most of the time...."
This probably is why I love the (almost) full disclosure of everything non-nominal during SpaceX launches.
Is this normal in the industry (I would assume so), or is SpaceX more (or less) open about its 'challanges'.

[Rocket Science]

Good news, find the cause, fix it and let’s fly this bird. Good luck SpaceX!

[Antares]

Fuel-rich RP engines collect soot, so if SpaceX had on-pad static fire and a post-ignition launch abort it might be time to take a brush to the turbine exhaust.

Edit: now that I read the update thread, I think the "oxygen in ground side TEA-TEB" line, since it was followed by the part about being dissimilar from the second stage, means that vented LOX near the ground chilled the ground TEA-TEB and kept it from flowing adequately.

[Avron]

Fuel-rich RP engines collect soot, so if SpaceX had on-pad static fire and a post-ignition launch abort it might be time to take a brush to the turbine exhaust.

Edit: now that I read the update thread, I think the "oxygen in ground side TEA-TEB" line, since it was followed by the part about being dissimilar from the second stage, means that vented LOX near the ground chilled the ground TEA-TEB and kept it from flowing adequately.

Going by the update on spacex site -- " Thursday's abort was caused by oxygen in the ground side igniter fluid (TEA-TEB)"

that would be "oxygen in ",  I infer contamination not freezing..

Note to editorial staff..  this is a discussion thread, please be so kind as to at least have the decency to notify me as to why you have removed my post.  The last post was removed without any comment and did not attack any person or organization and provide measures to a question. Said measures can be referenced if needed.

 

[AJA]

Hang on. Could one person please walk us through the myriad range of things here?


Take the (S)paceX (E)ngine (S)ystems test. 




1. TEA-TEB (pyrophoric liquids) are required to initiate Merlin combustion.
2. There was a contamination in the ground support equipment that supplied the first stage combusion chamber with TEA-TEB
(Which some have said mav've been due to oxygen leaking into the lines, and reacting with it, leaving inert residue as blockage, or greater than expected chilling of the lines due to to increased LOX venting - the wording in Elon's tweet makes me the think the former, but IDK)


3. Does his mention of the upper stage having a different circuit imply they haven't bothered to de-stack and check the hardware there? I know they didn't plan on having 1st stage re-start for this mission, but did they make them without / have they removed the 1st stage Merlins' TEA-TEB reservoirs+lines? Do all the 1st stage engines have them or only the centre one? (You'd want restart redundancy too, in case of engine out...) I ask because this would be common hardware between stages, something you'd want to check if one set failed. (IDK if the ground side TEA-TEB lines were backed up/augmented by the vehicle's own)


4. Launch was aborted due to lower than expected thrust ramp. Is this the thrust ramp of the entire stage, or of each individual Merlin? If the former, it makes sense how one engine not having started at all would give a low ramp. If it's for each individual engine - then surely the thrust in the culprit wouldn't ramp up at all, since it wouldn't even ignite?! Why does Merlin need TEA-TEB once combustion has been initiated? How long is the transient, before this combustion is self-sustaining? Way shorter than 3 seconds?


I'm not saying they should've, but if the fuel penalty on 1st stage margin wasn't all that much, could they've just relaxed the ramp up time required, and launched? EDIT: If indeed - all engines had ignited


5. Musk said this seemed OK on closer inspection. Meaning what? As in - what did they rule out? I can think of a scenario where - if the same turbopump drives propellant into multiple engines, with one starting up fine, and the other not; then you know the problem's downstream of the turbopump (and maybe then you check the TEA-TEB lines..and decide that this isn't a major issue).


But... I don't think that's the case, because..


6. They then decided one of the methods of mitigation would be to increase Helium spin start pressures to mitigate the low ramping. Is this for the turbopumps? Get them up to speed faster? To increase the rate of the (RP-1/LOX flow rate) into the combustion chamber?


Also, I'm assuming that at this point, they didn't know about the TEA-TEB issue? Or would they have known, and is the Helium spin start a mitigation?


7. Why do turbopump gas generators need to be cleaned again? Combustion residues? Isn't the gas generator burn mix oxidiser rich to avoid this?


And...for extra credit...


Looked like they'd fixed a lot of niggles from the earlier date pretty fast: the first stage LOX vent valve, the voltage-out-of-family issue, the flight computer/stages not transitioning into Auto-sequence etc, the ECS duct, erector raise. Anyone here think they've found the trunk for a failure tree?

[corrodedNut]

New photos are up: http://www.spacex.com/gallery/falcon-9-first-geostationary-transfer-mission

[Rocket Science]

Just got back in and catching up... “If” the TEA-TEB for the first and second stages is from the same source, how can they be sure that the second stage is not contaminated as well at this point?

[ChrisWilson68]

Just got back in and catching up... “If” the TEA-TEB for the first and second stages is from the same source, how can they be sure that the second stage is not contaminated as well at this point?

To me, the implication of Elon's tweet is that they understand how the TEA-TEB was contaminated, and that they believe that contamination happened in ground systems that supply the first stage but not the upper stage.

[Rocket Science]

Just got back in and catching up... “If” the TEA-TEB for the first and second stages is from the same source, how can they be sure that the second stage is not contaminated as well at this point?

To me, the implication of Elon's tweet is that they understand how the TEA-TEB was contaminated, and that they believe that contamination happened in ground systems that supply the first stage but not the upper stage.

Thanks Chris, I’m certain they are going to make sure 2nd stage is unaffected...

[kevin-rf]

Just got back in and catching up... “If” the TEA-TEB for the first and second stages is from the same source, how can they be sure that the second stage is not contaminated as well at this point?

Just an observation, if it was contamination was caused by air leaking in, the second stage is in vacuum when the TEA-TEB is introduced.

[Rocket Science]

Just got back in and catching up... “If” the TEA-TEB for the first and second stages is from the same source, how can they be sure that the second stage is not contaminated as well at this point?

Just an observation, if it was contamination was caused by air leaking in, the second stage is in vacuum when the TEA-TEB is introduced.

Do they do a nitrogen purge before filling tanks?

[Norm38]

Fuel-rich RP engines collect soot, so if SpaceX had on-pad static fire and a post-ignition launch abort it might be time to take a brush to the turbine exhaust.

The engines also had a test fire at McGreggor. So the abort was the third ignition, correct?  How often do they have to be cleaned?  Two firings is okay but three is too much?  Were they cleaned after McGreggor testing?
And is startup inherently more sooty?  If the engines have to be cleaned after 2-3 three second firings, how dirty are they after a full three minute burn?  And does that have implications for restarting first stage engines for landing?  Seems the cleaning has to be more precautionary than strictly necessary.

[Prober]

Fuel-rich RP engines collect soot, so if SpaceX had on-pad static fire and a post-ignition launch abort it might be time to take a brush to the turbine exhaust.

The engines also had a test fire at McGreggor. So the abort was the third ignition, correct?  How often do they have to be cleaned?  Two firings is okay but three is too much?  Were they cleaned after McGreggor testing?
And is startup inherently more sooty?  If the engines have to be cleaned after 2-3 three second firings, how dirty are they after a full three minute burn?  And does that have implications for restarting first stage engines for landing?  Seems the cleaning has to be more precautionary than strictly necessary.

Try this for an idea, maybe the test fire isn't the issue of the soot.   Not seen the layout of the flow but do know the rp1 does double duty as a hydraulic fluid.     
 

[Lars_J]

Why do people suddenly imagine there is a soot problem with these engines? C'mon...