As they used to say on SCTV, that blowed up real good.
I noticed that at T+1:42 (at the shutdown of the first of the engines) there was what looked like a uncontained gas flame burst within the nozzle skirting. Lots of burning thermal blankets and mylar after that, and what looked to me like leaking LOX plumes.
I don’t even know if, and when, the engines were supposed to cycle off, but it definitely looked like a propellant and/or oxidizer leak at that point.
The engines were definitely supposed to shut down. Musk has said they performed “great”, and didn’t indicate that anything went wrong there. Plus, it makes sense–they had to throttle down as the propellant was depleted, and as they reached their altitude limit. Simply shutting down all the engines and coasting up wouldn’t work; the craft depends on thrust vectoring for stability. You can also see that the shut down engines politely gimbaled out of the way to give more space to the remaining one(s).
I’m not so sure about the LOX plumes, but it wasn’t much in any case, and probably the engines are just a tad leaky even when shut down. Or maybe it took a while for the LOX in the system to evaporate away. The small fires are likely just a bit of methane being sucked up into the engine bay.
IANA rocket engineer, but having watched a lot of engine start and shutdown vids, I agree all that looked 100% nominal to me.
You have to cut the flow of fuel & oxidizer at the upstream end of all the plumbing. Then what’s in the turbopumps, lines, distribution system, fuel / oxidizer nozzles, etc. flows out more slowly as all the RPMs and pressures drop towards ambient.
Heck, since the engines are reusable, they may keep a trickle of fluid flowing for awhile simply to manage the rate of cooling. In my biz the engineers often have to actively manage the post-shutdown thermal loads or the adverse consequences thereof.
Makes sense. We know they have to do this before startup (on the Merlins at least): every Falcon 9 flight, just before main-engine cutoff, there is a callout for “MVac chill”. That’s them flowing LOX through the Merlin Vacuum (stage 2 engine) to cool it down before startup. I’m not sure they’ve stated the exact reason, but reducing thermal transients seems by far the likeliest.
I suppose another factor there might be that you don’t want the LOX to phase transition to gas upstream of wherever you’re making that happen on purpose. A little of that while the system’s not under load yet might be fine.
But having those first few seconds of high power operation being unstable as the upstream plumbing is still chilling down to equilibrium with the bulk LOX temperature might ad more excitement than makes engineers cheer.
Engine-rich exhaust indeed.
In another vein some fancy ICE & turbine engines spin up the oil pump first and get both oil flow and pressure throughout the bearing systems before first applying starter torque. Solves a lot of first-moment wear. Also handy for ultra cold weather starts. This may or may not have any correspondence to rocketry, but it shows that other powerplants have system startup transients to fight.
Clearly the SpaceX Merlin needs it for some reason.
Good points. Avoiding bubbles of GOX in your LOX sounds like a good thing for stability.
I’m still pretty curious about the low fuel pressure problem they had. I’m wondering if Musk was speaking approximately, and the problem was more like “low fuel inlet pressure from the header tank”. Because if it were that, then possibly centrifugal forces form the flipover could have been a factor. A few seconds worth of fuel would be left in the downcomer, but the rotation might have flung the remainder outward, leaving a big gap in the flow.
I’m sure they thought of this effect, but maybe they didn’t model it quite right. Or maybe it was just a mundane failure with their pressurization system. Hopefully we find out somewhere along the line.
Excellent footage of the SN8 wreckage here and of the aftermath of the SN9 accident that happened today (lower support strut collapsed; starts at 5:35).
Ouch! sometimes bad luck runs in runs.
Reminds me of this little goof:
The entire fuselage structures were scrapped and I don’t know how much of the innards were considered salvageable. But I bet very little.
I wonder what, if anything, of SN9 can ever be flown. It might well be a total writeoff.
Cute! 737s coming up the river to spawn just before they die!
Heh!
[Monty Python Voice]
- They're not dead yet, but they are looking a little off!
That’ll buff right out!
I doubt it’s a total writeoff–this is still a high-risk prototype, after all. And unlike composites, stainless is a pretty compliant material. Not to mention that these early flights aren’t that mass-sensitive, so if repairs have to add additional bits (say, undamaged internal stringers), they can afford to do so.
Good thing they don’t install the Raptors until they reach the pad, though. I’d have a lot less faith in those working if they got crunched into the ground.
“Relax, all right? My old man is a television repairman, he’s got this ultimate set of tools. I can fix it.” - Jeff Spicoli
In full-bore NASA mode, if you can’t say exactly what forces a component was exposed to during the mishap, you can’t honestly say it wasn’t overstressed. So you have to assume it was overstressed. If you can inspect it to prove the assumed overstress didn’t cause lasting harm then you use the component. After you write, validate, and get approval for the inspection process. Probably cheaper, easier, and quicker to throw it all away and start over.
Here’s a NASA PDF on the LADEE space probe mishap report. It got structurally damaged in a botched preflight test and was eventually flown after an extensive rebuild.
Now does SpaceX do it that way? Probably not. But they’ll at least look a little ways in that general direction. Us here not knowing what hit how hard and how important that spot is, there’s not much more to be said with any confidence.
Agreed. Impossible to draw any concrete conclusions from the picture.
That said, don’t forget the story of the tin snips and the nozzle. As a refresher, or in case you hadn’t heard it:
https://naturallyfundamental.com/spacex-tin-snips-rocket-fix/
Cracks in the nozzle! Ah, just snip that part off, we don’t need it. Of course, it wasn’t quite as simple as that; SpaceX engineers put plenty of thought into the fix. But regardless, they came up with a solution that didn’t involve disassembling the rocket and replacing the entire part. They knew they had performance to spare and used it to simplify the fix. And that was for a NASA mission that needed high reliability, not a high-risk prototype.
And that’s the “enabling technology” for all this. When stuff was designed to 0% tolerance above the spec because you needed that degree of flimsy to make weight or whatever it was either perfect or junk with no in-between.
For whatever reason SpaceX and to some lesser degree the others have managed to finally build in some margins. Which lets them reduce the amount of procedural “unobtainium” needed in the construction, maintenance, and ops procedures and processing.
Jerry Seinfeld on painkillers: “Make it strong enough to kill me, thennnnnnnn back it off just a little.”
Livestream of them trying to right the SN9! Kinda boring right now, but go back to the beginning, eh:
Falcon 9 launching with the SXM-7 satellite in 40 mins from time of posting.
EDIT: there will be an official SpaceX stream but that isn’t broadcasting yet.
Some really gorgeous 4k footage of the Starship launch here:
No annoying whooping, just rocket sounds. I love the sharp crackle of rocket engines, though nothing beats hearing it in person. It is one of those sounds, like a drum set, that just sounds sharper in person than over a recording.