SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION

[DistantTemple]

I think it was overall a really amazing launch and they managed to get a lot of data, which is the most important part.
I just hope they got data telemetry on the second stage and what caused the failure. It looked like they lost that right before it failed, which could be unfortunate. Looking forward to hearing more from SpaceX on that.
It is interesting that we could observe these strange phenomena (puffs?) about 30 seconds before the S2 was terminated. Their telemetry did not show anything abnormal though, it seems. If those were nothing unusual, then the question is what triggered the FTS.

I wonder if it is the other way around - the FTS was triggered automatically because they lost the data telemetry and failed to reestablish the link after certain time period. They just can't let the ship continue flying if they don't have control and telemetry.

I guess and hope SX have masses more data and telemetry than the little they put on the x-cast. The connection only appeared to go near the end. Hopefully they at least have indications leading up to the loss. That puff indicates something was "going on"

[sanman]

Heh, when seen in slo-mo, hot-staging looks like a Star Trek space warp effect 



Or at least it looks like Starship is entering into some nebula gas cloud in front of it

[Vettedrmr]

People are putting too much credence in the velocity numbers presented video feed.
With 3 engines firing, what is going to slow down the booster?  The Starship was at partial throttle and not all engines firing at separation.

Gravity.  The stack was still climbing.  However, if we're going to dismiss the displayed TM numbers (we've not done that before while analyzing F9 performance, but what the hey), then we'll just wait for the answer.

DanClemmensen, I had taken your challenge and gone through the math, then saw half a dozen more replies while I was chewing on it.  I still think that SS's engine thrust was enough to momentarily put booster into negative g, but I'm not going to try to defend it.  We'll just wait for SpaceX to tell us.

Have a good one,
Mike

[jimvela]

People are putting too much credence in the velocity numbers presented video feed.

The feed velocity numbers are certainly not the whole story. 
Does anyone know how SpaceX defines that?  Booster Velocity in +Z?  Referenced to what?

With 3 engines firing, what is going to slow down the booster? 

Booster shut down from 33 to 3 engines and throttled down the 3 left running.
Ship started the 3 RVAC and then very shortly later started up the 3 RSL engines.  There's great video in one of the threads here of the SL raptors gimballing back to center from being fully gimballed away from the center.

The Starship was at partial throttle and not all engines firing at separation.

There were 3 RVAC and 3RSL impinging on the hot staging ring, top of booster, and grid fins as the booster started to flip.

This is only a few seconds of impact on the booster, but a few seconds of 1G+ deceleration of the booster would be sufficient to send liquid propellant rushing forward.  That's the very thing SpaceX stated they had concerns about- ullage collapse and ingesting gas into the raptors are really problematic.

Do I know if that's what actually happened? No.  It will be interesting to discover what vehicle instrumentation says happened.

What we saw was the booster middle ring of engines started to relight, but even as they did so one of the center raptors and several of the starting raptors failed or shut down.  As the booster spent its final moments in the flip, it appears to suffer multiple serious failures of engines or perhaps even structure and was obviously venting prop from multiple locations just before the final bang that either set off an event chain to detonate the booster or was the amongst the last things to happen before the FTS took things out.

[mlindner]

https://twitter.com/sciguyspace/status/1726639794556731428

I wrote about this weekend's Starship launch, and tried to explain why it was a remarkable success despite the outward appearance of failure.

https://arstechnica.com/space/2023/11/heres-why-this-weekends-starship-launch-was-actually-a-huge-success/

This is a great article but the intended audience probably isn't most people here. The overall theme is a great argument though that's sorely lacking though. We should be praising doers rather than criticizing them.

People need to cheer progress, not criticize that the progress wasn't as good as it could have been. As you're taught as a child, "don't look a gift horse in the mouth."

[mlindner]

To all the people arguing about physics of acceleration:

There is insufficient information to determine whether in the inertial frame of reference (also called freefall or orbit or microgravity) Superheavy actually felt its acceleration go from axially-aligned positive to axially-aligned negative during the moment of stage separation. A rocket accelerating at a low value in a uniform gravitational field can still have it's velocity decrease while maintaining a positive acceleration. The acceleration due to gravity is completely irrelevant to any calculations about internal vehicle forces. It's an "error" that adds to the velocity calculation.

More so, if you look at various points in the launch, just like with Falcon 9 launch telemetry, the value can suddenly "smoothly jump" from one value to another and make it appear as if a rapid acceleration has happened because they use a smoothing function on the telemetry for the web stream. A data gap there (which would be expected given the violence of the staging event) could cause exactly what we saw. It also happened earlier in the launch at various points.

So this whole discussion is moot based on insufficient data.

Personally, I find the supposition a bit silly that SpaceX wouldn't know how much thrust they would need to keep propellant from lifting off of the pump intakes during staging.

[kevinof]

https://twitter.com/sciguyspace/status/1726639794556731428

I wrote about this weekend's Starship launch, and tried to explain why it was a remarkable success despite the outward appearance of failure.

https://arstechnica.com/space/2023/11/heres-why-this-weekends-starship-launch-was-actually-a-huge-success/

This is a great article but the intended audience probably isn't most people here. The overall theme is a great argument though that's sorely lacking though. We should be praising doers rather than criticizing them.

People need to cheer progress, not criticize that the progress wasn't as good as it could have been. As you're taught as a child, "don't look a gift horse in the mouth."

Have to agree 100%. Havent been following this closely of late but this flight demonstrated they are so close to getting this beast reaching orbit. Yes it’s only part of the puzzle but look at what worked -

- Stage 0 survived and looks good. Big win.
- All 33 raptors worked and stayed that way until staging. Another big step.
- Separation worked (the two vehicles parted and didn’t impact each other)
- SS continued up to near orbital speed.

Some were all doom and gloom after flight 1 saying the pad would need years of work, the raptors were not reliable etc. SpaceX shows us they understand the vehicle and bring fixes to problems pretty damn quick.

Get the SS to orbit and they have a monster mega lift platform. Then work on the booster recovery next (the expensive part) and reentry of SS.

Flight 2 looked like a very good day at the office.

[steveleach]

To all the people arguing about physics of acceleration:

There is insufficient information to determine whether in the inertial frame of reference (also called freefall or orbit or microgravity) Superheavy actually felt its acceleration go from axially-aligned positive to axially-aligned negative during the moment of stage separation. A rocket accelerating at a low value in a uniform gravitational field can still have it's velocity decrease while maintaining a positive acceleration. The acceleration due to gravity is completely irrelevant to any calculations about internal vehicle forces. It's an "error" that adds to the velocity calculation.

More so, if you look at various points in the launch, just like with Falcon 9 launch telemetry, the value can suddenly "smoothly jump" from one value to another and make it appear as if a rapid acceleration has happened because they use a smoothing function on the telemetry for the web stream. A data gap there (which would be expected given the violence of the staging event) could cause exactly what we saw. It also happened earlier in the launch at various points.

So this whole discussion is moot based on insufficient data.

Personally, I find the supposition a bit silly that SpaceX wouldn't know how much thrust they would need to keep propellant from lifting off of the pump intakes during staging.

Not disagreeing with you in general, but...

1. Surely it's fine to speculate about a hypothesis even if there isn't conclusive data to support it?
2. I think it is entirely plausible that SpaceX could have missed something out of their models

As I understand it, they were trying to balance the thrust from the booster's own engines with the thrust exerted by the Starship's exhaust on the booster in the opposite direction, the aim being to have the booster thrust just slightly greater (if the booster thrust is a lot greater then the two vehicles don't separate). I can imagine them arguing over the variables for a while and then deciding to just give it a try and get some actual data - very SpaceX.

And someone speculated up thread (or in another thread, I can't remember) that they would probably have erred on the side of too little booster thrust for IFT-2, because they'd rather risk the booster than the ship once separation occurs.

[Garrett]

People are putting too much credence in the velocity numbers presented video feed.
With 3 engines firing, what is going to slow down the booster?  The Starship was at partial throttle and not all engines firing at separation.

Gravity?
Thrust to weight less than 1?

[spider_best9]

November 21st 2023 Updates:  Post IFT-2 statement by SpaceX

https://www.spacex.com/launches/mission/?missionId=starship-flight-2
Statement contents:  NOVEMBER 18, 2023

Starship returned to integrated flight testing with its second launch from Starbase in Texas. While it didn’t happen in a lab or on a test stand, it was absolutely a test. What we did with this second flight will provide invaluable data to continue rapidly developing Starship.

On November 18, 2023, Starship successfully lifted off at 7:02 a.m. CT from Starbase in Texas and achieved a number of major milestones:

All 33 Raptor engines on the Super Heavy Booster started up successfully and, for the first time, completed a full-duration burn during ascent.
Starship executed a successful hot-stage separation, powering down all but three of Super Heavy’s Raptor engines and successfully igniting the six second stage Raptor engines before separating the vehicles. This was the first time this technique has been done successfully with a vehicle of this size.
Following separation, the Super Heavy booster successfully completed its flip maneuver and initiated the boostback burn before it experienced a rapid unscheduled disassembly. The vehicle breakup occurred more than three and a half minutes into the flight at an altitude of ~90 km over the Gulf of Mexico.
Starship's six second stage Raptor engines all started successfully and powered the vehicle to an altitude of ~150 km and a velocity of ~24,000 km/h, becoming the first Starship to reach outer space and nearly completing its full-duration burn.

The flight test’s conclusion came when telemetry was lost near the end of second stage burn prior to engine cutoff after more than eight minutes of flight. The team verified a safe command destruct was appropriately triggered based on available vehicle performance data.
The water-cooled flame deflector and other pad upgrades performed as expected, requiring minimal post-launch work to be ready for upcoming vehicle tests and the next integrated flight test.

With a test like this, success comes from what we learn, and this flight test will help us improve Starship’s reliability as SpaceX seeks to make life multiplanetary. Data review is ongoing as we look for improvements to make for the next flight. The team at Starbase is already working final preparations on the vehicles slated for use in Starship’s third flight test, with Ship and Booster static fires coming up next.

Thank you to our customers, Cameron County, spaceflight fans, and the wider community for the continued support and encouragement. And congratulations to the entire SpaceX team on an exciting second flight test of Starship!

I guess from this SpaceX could be inferred that the AFTS did not trigger on the booster, but it on the ship.

[mlindner]

People are putting too much credence in the velocity numbers presented video feed.
With 3 engines firing, what is going to slow down the booster?  The Starship was at partial throttle and not all engines firing at separation.

Gravity?
Thrust to weight less than 1?

I just explained gravity is irrelevant, and thrust to weight is also irrelevant. Thrust to weight is important when you're near the ground. Many rocket upper stages have thrust to weight ratios significantly less than one at start of thrusting.

As I understand it, they were trying to balance the thrust from the booster's own engines with the thrust exerted by the Starship's exhaust on the booster in the opposite direction, the aim being to have the booster thrust just slightly greater (if the booster thrust is a lot greater then the two vehicles don't separate). I can imagine them arguing over the variables for a while and then deciding to just give it a try and get some actual data - very SpaceX.

I don't think you mean thrust here. You probably meant to say acceleration. The vehicles will have very different masses so the thrust on the first stage needs to be MUCH lower than the thrust on the second stage. In which case you want less acceleration on the lower stage than the upper stage otherwise they will recontact.

Also SpaceX still does substantial amounts of simulation. They don't just "wing it". That's what flight and testing data is input into.

[Barley]

Personally, I find the supposition a bit silly that SpaceX wouldn't know how much thrust they would need to keep propellant from lifting off of the pump intakes during staging.

If SpaceX had all the answers there would be people on or near the Moon right now or in the recent past.

That particular question involves some very hairy parts of fluid dynamics.  Even with the best computation sometimes you have to run the experiment.

[chopsticks]

November 21st 2023 Updates:  Post IFT-2 statement by SpaceX

https://www.spacex.com/launches/mission/?missionId=starship-flight-2
Statement contents:  NOVEMBER 18, 2023

Starship returned to integrated flight testing with its second launch from Starbase in Texas. While it didn’t happen in a lab or on a test stand, it was absolutely a test. What we did with this second flight will provide invaluable data to continue rapidly developing Starship.

On November 18, 2023, Starship successfully lifted off at 7:02 a.m. CT from Starbase in Texas and achieved a number of major milestones:

All 33 Raptor engines on the Super Heavy Booster started up successfully and, for the first time, completed a full-duration burn during ascent.
Starship executed a successful hot-stage separation, powering down all but three of Super Heavy’s Raptor engines and successfully igniting the six second stage Raptor engines before separating the vehicles. This was the first time this technique has been done successfully with a vehicle of this size.
Following separation, the Super Heavy booster successfully completed its flip maneuver and initiated the boostback burn before it experienced a rapid unscheduled disassembly. The vehicle breakup occurred more than three and a half minutes into the flight at an altitude of ~90 km over the Gulf of Mexico.
Starship's six second stage Raptor engines all started successfully and powered the vehicle to an altitude of ~150 km and a velocity of ~24,000 km/h, becoming the first Starship to reach outer space and nearly completing its full-duration burn.

The flight test’s conclusion came when telemetry was lost near the end of second stage burn prior to engine cutoff after more than eight minutes of flight. The team verified a safe command destruct was appropriately triggered based on available vehicle performance data.
The water-cooled flame deflector and other pad upgrades performed as expected, requiring minimal post-launch work to be ready for upcoming vehicle tests and the next integrated flight test.

With a test like this, success comes from what we learn, and this flight test will help us improve Starship’s reliability as SpaceX seeks to make life multiplanetary. Data review is ongoing as we look for improvements to make for the next flight. The team at Starbase is already working final preparations on the vehicles slated for use in Starship’s third flight test, with Ship and Booster static fires coming up next.

Thank you to our customers, Cameron County, spaceflight fans, and the wider community for the continued support and encouragement. And congratulations to the entire SpaceX team on an exciting second flight test of Starship!

I guess from this SpaceX could be inferred that the AFTS did not trigger on the booster, but it on the ship.

Yeah, I find it funny that everyone is saying that AFTS destroyed the booster when very clearly the aft end blows up first followed by the middle.

[clongton]

The Starship was at partial throttle and not all engines firing at separation.

I believe you are correct wrt partial throttle, but I thought all 6 engines were to be firing at separation with the center 3 being gimbled outward. Would you reverify only partial engine firing at separation please?

[chopsticks]

Where does the partial throttle come from? Did they say that? All six Raptors ignited pretty close together - the outer vacuum engines quickly followed by the SL engines.

[envy887]

People are putting too much credence in the velocity numbers presented video feed.
With 3 engines firing, what is going to slow down the booster?  The Starship was at partial throttle and not all engines firing at separation.

The booster has ~1 Mlbf of thrust pushing it forward and potentially up to 3 Mlbf of plume impingement pushing it backwards.

[litton4]

November 21st 2023 Updates:  Post IFT-2 statement by SpaceX

https://www.spacex.com/launches/mission/?missionId=starship-flight-2
Statement contents:  NOVEMBER 18, 2023

Starship returned to integrated flight testing with its second launch from Starbase in Texas. While it didn’t happen in a lab or on a test stand, it was absolutely a test. What we did with this second flight will provide invaluable data to continue rapidly developing Starship.

On November 18, 2023, Starship successfully lifted off at 7:02 a.m. CT from Starbase in Texas and achieved a number of major milestones:

All 33 Raptor engines on the Super Heavy Booster started up successfully and, for the first time, completed a full-duration burn during ascent.
Starship executed a successful hot-stage separation, powering down all but three of Super Heavy’s Raptor engines and successfully igniting the six second stage Raptor engines before separating the vehicles. This was the first time this technique has been done successfully with a vehicle of this size.
Following separation, the Super Heavy booster successfully completed its flip maneuver and initiated the boostback burn before it experienced a rapid unscheduled disassembly. The vehicle breakup occurred more than three and a half minutes into the flight at an altitude of ~90 km over the Gulf of Mexico.
Starship's six second stage Raptor engines all started successfully and powered the vehicle to an altitude of ~150 km and a velocity of ~24,000 km/h, becoming the first Starship to reach outer space and nearly completing its full-duration burn.

The flight test’s conclusion came when telemetry was lost near the end of second stage burn prior to engine cutoff after more than eight minutes of flight. The team verified a safe command destruct was appropriately triggered based on available vehicle performance data.
The water-cooled flame deflector and other pad upgrades performed as expected, requiring minimal post-launch work to be ready for upcoming vehicle tests and the next integrated flight test.

With a test like this, success comes from what we learn, and this flight test will help us improve Starship’s reliability as SpaceX seeks to make life multiplanetary. Data review is ongoing as we look for improvements to make for the next flight. The team at Starbase is already working final preparations on the vehicles slated for use in Starship’s third flight test, with Ship and Booster static fires coming up next.

Thank you to our customers, Cameron County, spaceflight fans, and the wider community for the continued support and encouragement. And congratulations to the entire SpaceX team on an exciting second flight test of Starship!

I guess from this SpaceX could be inferred that the AFTS did not trigger on the booster, but it on the ship.

Yeah, I find it funny that everyone is saying that AFTS destroyed the booster when very clearly the aft end blows up first followed by the middle.

The AFTS operates on the common dome, so that would be consistent with that being triggered shortly after the large event at the aft end. (which followed several smaller events  ).
It would , however, also be consistent with a rupture of the common dome caused by the aft event.

So I don't think we can 100% infer one way or the other - the SpaceX statement just says "RUD" without stating or denying that AFTS was involved.

[xvel]

We just need the angle of the rocket at staging to calculate relative acceleration of propellant in respect to rocket, of course assuming that telemetry data from stream is good enough.

[chopsticks]

The AFTS operates on the common dome, so that would be consistent with that being triggered shortly after the large event at the aft end. (which followed several smaller events  ).
It would , however, also be consistent with a rupture of the common dome caused by the aft event.

So I don't think we can 100% infer one way or the other - the SpaceX statement just says "RUD" without stating or denying that AFTS was involved.

It's true that the AFTS charges breach the common dome area, but that's not the only thing that could cause an explosion from that area (as you have mentioned). I think the thing that makes me doubt the AFTS belief is..why? Why would it be activated in the first place? The aft end had already ruptured and thrust had been terminated on its own so there would be no reason to activate FTS, right? Besides, I believe SH was well within its flight corridor when it blew up, so another reason for it not to have been used.

If for some reason SpaceX/FAA reports that FTS indeed was activated, I'll be happy to retract what I said, but until then I think I'm going to stick with Mr. Manley's theory.

[Herb Schaltegger]

People are putting too much credence in the velocity numbers presented video feed.
With 3 engines firing, what is going to slow down the booster?  The Starship was at partial throttle and not all engines firing at separation.

The booster has ~1 Mlbf of thrust pushing it forward and potentially up to 3 Mlbf of plume impingement pushing it backwards.

No. It has some indeterminate amount of plume impingement pushing it backwards. The kinetic energy of Ship’s engine rapidly expanding and diffusing exhaust impinging in the Booster would be nothing close to 3Mlbf.