Good analysis of the goals of this test. That said, the failure was interesting to me.
In the SpaceX feed they were waiting for the second stage to separate and light, and it didn't do either. So first question is why didn't it separate? I think that is the relevant one because I would expect them to have interlocks that would prevent the second stage from starting up if it were still attached to the booster. The interlocks would explain not starting up the second stage engines.
One anomaly I noticed was that the booster did not appear to shut down 100%, ever. If that was the case, that would be important because the onset of "zero g" from engine shutdown is a well tested way for the next stage to know that the stage below it has stopped firing.
Some (many? all?) spacecraft rely on the physics of the expended boost stage being much lighter than the remaining stack. This disparity means atmospheric drag on the lower stage has a bigger effect than it does on the upper stage. If the second stage retention system "lets go" when it detects zero-g, then the two pieces will begin to separate, slowly at first, and then faster when the very un-aerodynamic opening to the top of the booster gets into the slip stream.
Depending on how the second stage interlock works, it could be timed (wait t seconds and then light up) or radar (wait for distance between first and second stage) or some communication between the booster and the stage. By time is cheap, but risks a slowly separating booster being "too close" and having it become damaged from the blast of the vacuum engines starting up. Radar is likely most reliable (and most expensive), and comms would work by there is a lot of ionization going on at that speed that makes them more difficult.
So questions I would look at; First, if all the raptors didn't shut down, why not? Second, did the booster attempt a rotation and re-entry burn with the second stage still attached? Third, is there a way to "abort to orbit" this scenario where the second stage decides to let go and light up even though the first stage hasn't shut down?
Fun to watch though, its a pretty amazing rocket and that they didn't have 4 (or 5) of the raptors firing when it started off was another thing to look into. On pad aborts are a thing too, but as the parent states, there are faults that you won't get any useful data, and those you note and continue on through. I think the non-start of the raptors was of the latter.
T+01:02 - A fifth engine is marked out (just after the announcer says "we're throttled down and throttled back up")
https://youtu.be/-1wcilQ58hI?t=2766
My totally uninformed speculation is that the first stage did not achieve the target velocity (and trajectory?) due to the 6(?) engine failures so the first stage continued to burn and the second stage never separated because the separation conditions were not met (velocity/trajectory).
Pretty solid reasoning. Pretty clear that correct attitude of the spacecraft would be a go/no-go for booster separation.
Wonder if people heard the sonic boom on the ground. If it hit MaxQ and went past it then it would be supersonic at that point.
Presumably they have two flight abort systems (one booster, one ship), a separation, even under non-ideal circumstances, could provide test data. The safety issue would be addressed by setting the self destruct to occur post data collection or imminent danger which ever came first :-). Based on the NOTAMs the FAA sent out they seem to have had a pretty long footprint over the Atlantic for things to go wrong.
Hopefully they will give us a deep dive on what happened!
You can see the vapor ghosting off it when they call MaxQ which is a visual confirmation. I assume people could hear it on the ground too unless it's too high?
a few seconds after liftoff a hydraulic unit on the bottom of the booster blew off. That could have had all kinds of ramifications for further events down the road like stage separation and MECO. I'm actually surprised it maintained as good of control is it did given i'm sure that controlled at least some of the gymbaling too.
The cartwheel is on purpose. They're using the angular momentum of the flip for boost back to fling the starship off instead of the usual explosives. I think it cartwheeled multiple times because of multiple attempts to get Starship to separate. Whatever was holding Starship to the booster wasn't letting go which could have been a hydraulic failure (see my first paragraph).
I have seen that analysis too, the twitter thread suggested that both HPUs on the booster eventually failed before second stage separation. That could be quite significant.
Also the lack of gimballing capability could presumably have the booster continuing to thrust as it attempted to maintain attitude control even as it reached the MECO point.
I wonder how much of this learning can be applied to the next launch as they may have design issues that are already "baked in" to the built boosters.
The good news here is that the gimballing system that failed today was already obsolete. The booster that launched today (B7) was the last prototype that was built with hydraulic gimballing (B8 might of had it, but that booster was scrapped). Subsequent boosters starting with B9 were built with an electrically actuated gimballing system. So the HPUs that supported the old system aren't present on the newer prototypes.
Perhaps the better news, then, is that there was much more to test than thrust vectoring. The structural integrity of a new rocket design under load, the challenges of a new engine design in flight, the ability to light a large number of engines in the correct sequence, etc.
In fact, it is possible the least of what they need to sort out is thrust vectoring: SpaceX has a lot of experience using thrust vectoring in their current production rockets, they have repeatedly demonstrated solid vectoring control throughout the program in Boca Chica, incuding the flight of "Hoppy", the test articles SN5 &SN6, and Starship high altitude tests SN8, SN9, SN10, SN11, and SN15. While there were failures in those programs, the thrust vectoring really wasn't the issue.
In reality, huge amounts of test data that doesn't depend on the thrust vectoring methodology was collected and remains valid from the test flight. And while there might be reasons we might consider SpaceX engineers sub-standard or that other factors compromise their judgement.... I'm sure they've considered what they can and can't learn from the test flight given that the some parts of B7 are obsolete... and still thought the exercise is worthwhile.
I for one will trust their judgement on this point.
In the SpaceX feed they were waiting for the second stage to separate and light, and it didn't do either. So first question is why didn't it separate? I think that is the relevant one because I would expect them to have interlocks that would prevent the second stage from starting up if it were still attached to the booster. The interlocks would explain not starting up the second stage engines.
One anomaly I noticed was that the booster did not appear to shut down 100%, ever. If that was the case, that would be important because the onset of "zero g" from engine shutdown is a well tested way for the next stage to know that the stage below it has stopped firing.
Some (many? all?) spacecraft rely on the physics of the expended boost stage being much lighter than the remaining stack. This disparity means atmospheric drag on the lower stage has a bigger effect than it does on the upper stage. If the second stage retention system "lets go" when it detects zero-g, then the two pieces will begin to separate, slowly at first, and then faster when the very un-aerodynamic opening to the top of the booster gets into the slip stream.
Depending on how the second stage interlock works, it could be timed (wait t seconds and then light up) or radar (wait for distance between first and second stage) or some communication between the booster and the stage. By time is cheap, but risks a slowly separating booster being "too close" and having it become damaged from the blast of the vacuum engines starting up. Radar is likely most reliable (and most expensive), and comms would work by there is a lot of ionization going on at that speed that makes them more difficult.
So questions I would look at; First, if all the raptors didn't shut down, why not? Second, did the booster attempt a rotation and re-entry burn with the second stage still attached? Third, is there a way to "abort to orbit" this scenario where the second stage decides to let go and light up even though the first stage hasn't shut down?
Fun to watch though, its a pretty amazing rocket and that they didn't have 4 (or 5) of the raptors firing when it started off was another thing to look into. On pad aborts are a thing too, but as the parent states, there are faults that you won't get any useful data, and those you note and continue on through. I think the non-start of the raptors was of the latter.