SpaceX F9 : Starlink v1.0 L19 : CCSFS SLC-40 : 15/16 Feb 2021 (0359 UTC)

[eeergo]

So this did happen during ascent, and it affected one of the 3 essential engines for landing. Similar to an earlier landing failure, but a different cause it seems. (the boot gas leak)

How do you know it was during ascent?  "First stage flight" could mean during retropropulsion, which certainly tracks with hot gas entering a compromised engine boot.

Also note identical telemetry: https://forum.nasaspaceflight.com/index.php?topic=52895.msg2192524#msg2192524

He literally mentions it shut down during *ascent*, but the engine out capability allowed the vehicle to be safe and get to orbit.

A boot had a little bit of a hole. There's hot gases of course, that's what makes the rocket go up - very hot gases coming out of the engines. [...] A little bit of hot gas got where it was not supposed to be, and it caused that engine to shut down. [...] It cut out that engine, turned the engine off. The vehicle was safe, the vehicle got to orbit, put the satellites exactly where they wanna be - primary mission accomplished. When that booster came to return home, because of the problem with that particular engine, it didn't have enough thrust, we didn't get back to where we needed to be.

Myself and others have pointed out the telemetry was certainly not identical to previous flights, and neither was its variance, a few posts after the one you quote. Some opinions were voiced that it might have been to winds aloft, but it seems unlikely that was the reason for the different late 1st stage profile given what we now know.

[1]

Briefly putting on my failure analysis hat here.

Generally speaking, the only time one can definitively determine the cause of a failure is if you have the failed hardware sitting in your lab (and sometimes, not even then). If the hardware is lost, as it often is with rockets, then often the best you can do is determine a few most-likely causes, and then attempt to replicate the issue with other hardware.

It's possible that there was damage in the closeout photos that was simply missed until analyzed with additional scrutiny. It's possible that there was no visible damage, and SpaceX instead took another life-leader boot, drilled a hole in it, shot some hot gasses inside and watched how the sensors responded. It's also very possible that SpaceX has seen holes in the boots on previous flights; smaller holes that did not cause enough damage to lose the engine/booster. In that last case, they may have had a very good idea of what to look for.

Obviously, I can only speculate on their exact methodology, but I do trust they've performed their analysis competently.

[Lee Jay]

He did strongly imply that this engine was shut down on ascent, so I had a thought on why we didn't see it in the telemetry.  Doesn't F9 throttle down at the end of ascent to control acceleration and, if so, couldn't they just throttle up the remaining engines after the shutdown of one to get the same ascent performance?

[AndrewRG10]

He did strongly imply that this engine was shut down on ascent, so I had a thought on why we didn't see it in the telemetry.  Doesn't F9 throttle down at the end of ascent to control acceleration and, if so, couldn't they just throttle up the remaining engines after the shutdown of one to get the same ascent performance?

That's exactly what they did on Starlink L5 after its landing failure, not throttle down as much and they got the exact same launch performance. But as you said we should've seen it in the telementary because the engine failure was quite obvious on L5.

[abaddon]

This wasn't an engine failure, it was an engine shutdown.  That might mean it was smoother and less likely to show up in telemetry than an outright failure.  We also don't know when it shut down, which would have an impact.

[OneSpeed]

This wasn't an engine failure, it was an engine shutdown.  That might mean it was smoother and less likely to show up in telemetry than an outright failure.  We also don't know when it shut down, which would have an impact.

Yes it was an early engine shutdown, which lost thrust over about a second. We know it occurred during the entry burn by comparing it with the nominal telemetry from L18.

[zubenelgenubi]

Further illumination from Michael Baylor and Helodriver:

https://twitter.com/nextspaceflight/status/1366454615470862338

Benji Reed (SpaceX): Notes that by flying Falcon 9 rockets so often, they are learning more about the launch vehicle. An anomaly during the recent Starlink mission was due to a boot having a hole in it during ascent. An engine was shutdown safely as a result.

https://twitter.com/nextspaceflight/status/1366455034548920323

The mission continued on successfully due to the multi-engine out capability on Falcon 9, but the landing was not possible due to the engine's issue.
(Me: Only three Merlin engines can be relit, so there is less engine redundancy for landing.)

https://twitter.com/nextspaceflight/status/1366455307799437314

Reed stressed that this particular component was a flight-leading piece of hardware. They will fix this issue moving forward with updated refurbishment processes.

And to paraphrase Bill Cosby's telling of the first conversation between God and Noah--Noah: Riiiight! What's a cubit boot?
https://twitter.com/SpacecoastPix/status/1366456224858841089

Boots are the flexible seals around the engines to prevent thermal damage to engine bay components.

[su27k]

I seem to remember they no longer use that flexible seals and replaced them with sliding metal parts?

[russianhalo117]

I seem to remember they no longer use that flexible seals and replaced them with sliding metal parts?

it is still a type of engine boot.

[kdhilliard]

I seem to remember they no longer use that flexible seals and replaced them with sliding metal parts?

it is still a type of engine boot.

Yes, but varying types of boots could explain Benji Reed's comment about this one being a life-leader for its type, despite it being only a six-flight booster.

In this case, one of these boots -- this was the highest count number of flights this particular boot design had seen.

[PM3]

This wasn't an engine failure, it was an engine shutdown.  That might mean it was smoother and less likely to show up in telemetry than an outright failure.  We also don't know when it shut down, which would have an impact.

Merlin engines (like most rocket engines) cannot be shutdown smoothly, because they cannot be throttled all the way down. And the other engines cannot be throttled up instantaneously to compensate; turbopumps need time to spin up. So an engine shutdown should show up in the acceleration graphs. Also, as pointed out above, there was no plume-out observed during ascent. Also, we know that there was a sudden loss of engine power during reentry burn.

Altogether, Benji Reeds hint at engine-out capability seems to be out of context here. All evidence points to an issue during descent, not ascent. (Though the boot damage may have occured during ascent gimbaling.)

[eeergo]

This wasn't an engine failure, it was an engine shutdown.  That might mean it was smoother and less likely to show up in telemetry than an outright failure.  We also don't know when it shut down, which would have an impact.

Merlin engines (like most rocket engines) cannot be shutdown smoothly, because they cannot be throttled all the way down. And the other engines cannot be throttled up instantaneously to compensate; turbopumps need time to spin up. So an engine shutdown should show up in the acceleration graphs. Also, as pointed out above, there was no plume-out observed during ascent. Also, we know that there was a sudden loss of engine power during reentry burn.

Altogether, Benji Reeds hint at engine-out capability seems to be out of context here. All evidence points to an issue during descent, not ascent. (Though the boot damage may have occured during ascent gimbaling.)

Ground cameras were not shown at the time the derived TM shows a large dip (last 15 seconds, check out the archived webcast), so there's no information to claim no shutdown plumes were observed. Let me know if there are any alternative high quality amateur videos that I may have missed and show no change in plume just before MECO. That TM dip is out of variance with respect to other missions where such detailed TM comparisons are available. Alternative hypotheses such as winds aloft were floated around, but seem unlikely given the new information.

Reeds' statement (which I just transcribed above) clearly points to an issue during ascent: he talks chronologically about the shutdown, highlighting how the rocket carried on to orbit and deployed its payload ensuring primary mission success - and THEN failing to relight on descent because of the earlier problem. The very scant information we have does point to heat damage (Koenigsmann's comments, mainly) rather than mechanical action from gimballing, which is nothing but speculation. Not sure why a safe engine-out shutdown on ascent is so repeatedly dismissed here, in the face of many all but conclusive clues.

[HVM]

So where are pictures of B1059 boots? Best I can find is this:

(C) USLaunchReport

[Vettedrmr]

Reeds' statement (which I just transcribed above) clearly points to an issue during ascent: he talks chronologically about the shutdown, highlighting how the rocket carried on to orbit and deployed its payload ensuring primary mission success - and THEN failing to relight on descent because of the earlier problem.

The one problem I have with the assertion that an engine failed to relight on the re-entry burn is the startup video clearly shows the center engine lighting, then the transition to the elliptical plume when the other two engines light.  Obviously we can only see one outboard engine light, so the other engine could have failed to restart.  BUT, if that was the case, I don't see how the vehicle could stay stable (which it obviously did, based on the flow we see after engine shutdown).

Then throw in the clear loss of deceleration as recorded during the re-entry burn, and I fully believe all 3 engines restarted normally, but one failed partially (still generating enough thrust that the other engines and RCS were able to maintain control).

I'm just glad they were able to diagnose a probable cause, and that it's not a more serious issue.

Have a good one,
Mike

[mn]

Perhaps an engine was shutdown late in ascent, but that engine is required for landing so it was relit for reentry despite the sensor telling them there's an issue (nothing to lose by trying), and then the engine bay apparently caught fire during the reentry burn.

[KodWhat]

Hi! First post here

My take on the few last messages is that there might be two "modes" for the software aboard Falcon 9:
- Ascent mode, where mission safety is critical and any out of family data on an engine results in that engine being shut down
- Landing mode, where the objective is to land safely, whatever it takes, and whatever the consequences are on the integrity of the rocket.

That would mean that this second mode doesn't shut down a failing engine, and even tries to relight an engine that was shutdown on ascent and tries to give the landing the best chances of success.

We might have seen that in action with the soft water landing after a CRS mission. The falcon 9 didn't abort at all, it tries to decelerate even though it might have known it wouldn't be on target (but with fully functional engines).

If I remember correctly, the same software (or a derivative) is used on Starship. When SN8 chew through its engines at landing and lost thrust, it didn't shut down the engines at all.

In the case of Starlink L19, I'll trust you on the telemetry analysis, I'm not good enough to understand it, but if the engine that was suspect and was shutdown on ascent was one of the landing engines, the software might have tried to relight it, it worked, but the engine finally failed right before the end of the burn.

But if that's the case, why the other engines didn't burn for longer to compensate?

[edzieba]

Even if the engine that shut down on ascent was not one of the landing-relight engines, a hole in the boot would still be allowing exhaust gasses to flood the engine section (Octaweb compartments contains energetic failures, but aren't watertight). That could still affect other engines even if they did not shut down on ascent (e.g. anything that affects the TEA-TEB system would not be noticeable during ascent).

[kevinof]

So if the boot was compromised then this would really show up on the way back when the exhaust would be flowing back into the stage.

So maybe they did relight on the way back but the plume impacted the innards and that's where we saw the "flames"

Perhaps an engine was shutdown late in ascent, but that engine is required for landing so it was relit for reentry despite the sensor telling them there's an issue (nothing to lose by trying), and then the engine bay apparently caught fire during the reentry burn.

[Herb Schaltegger]

Falcon 9 B1059.6 landing failure update. A Merlin engine boot (a life leader) developed a hole and sent hot gas to "where it wasn't supposed to be" and shut down during first stage flight. Not enough thrust for landing.

So how do you get a life-leader boot on a non-life-leader booster?

The only boosters with more flights are still around, I believe.  So it would be odd for a boot to be swapped off of one of them.

Maybe all others boosters and engines had their boots replaced before flight 6?

Maybe boots are in one big stockpile (they might have to remove them for refurbishing).  So after refurbishing, you go grab 9 boots from the stockpile, and they happened to get a well-used one?

Curious minds want to know....

You’ve answered your own question, I think. Boots don’t necessarily stay with their original engine or booster. They are (possibly? probably?) considered wear items and subject to replacement if needed. However, learning where that “if needed” point falls on the spectrum is obviously tricky.

[PreferToLurk]

Falcon 9 B1059.6 landing failure update. A Merlin engine boot (a life leader) developed a hole and sent hot gas to "where it wasn't supposed to be" and shut down during first stage flight. Not enough thrust for landing.

So how do you get a life-leader boot on a non-life-leader booster?

The only boosters with more flights are still around, I believe.  So it would be odd for a boot to be swapped off of one of them.

Maybe all others boosters and engines had their boots replaced before flight 6?

Maybe boots are in one big stockpile (they might have to remove them for refurbishing).  So after refurbishing, you go grab 9 boots from the stockpile, and they happened to get a well-used one?

Curious minds want to know....

You’ve answered your own question, I think. Boots don’t necessarily stay with their original engine or booster. They are (possibly? probably?) considered wear items and subject to replacement if needed. However, learning where that “if needed” point falls on the spectrum is obviously tricky.

The actual article specifies that the boot was a life-leader *for that design*.   The specific quote from Benji Reed was "This was the highest count number of flights that this particular boot design had seen"

Also, this article makes a number of speculations that appear to intentionally cast doubt on the reliability the Falcon 9.  There is unfounded speculation that the engine failed on ascent - based solely on a comment that the booster has engine out capability and that the payload made it to orbit.  Evidently,  pointing out that the mission was a success is an indication of failure? 
Jeff then twists a quote from Nasa astronaut Shane Kimbrough about the briefings they get on the Falcon 9 to imply that there are more unspecified problems with the rocket. 

Disappointed by that article.