totm nov 2023 SpaceX Discussion Thread

[tater]

6 hours ago, Meecrob said:

Edit: Wait, wait..the booster was totally an FTS...c'mon, it detonated too perfectly!

No evidence of that at all. FTS is automated, and based on the flight path of the vehicle. Unless they say the FTS was triggered, I'm gonna assume a leak resulting in it blowing itself up.

[Meecrob]

35 minutes ago, tater said:

No evidence of that at all. FTS is automated, and based on the flight path of the vehicle. Unless they say the FTS was triggered, I'm gonna assume a leak resulting in it blowing itself up.

Watch the video again. Look at the expansion rate of the plume at loss of vehicle. it propagates more uniformally circumferentially than chaotically...It was intended. Its the same way you can tell a man-made lake by how its shores are parallel, for example.

Edit: having re-read what I said, I get how it can seem dubious without a high speed camera. Look I'll concede I have a theory, and I don't have the evidence to prove it.

Edited November 21, 2023 by Meecrob

[Exoscientist]

16 hours ago, CBase said:

I am still struggeling with the details Scott Manley found about starships end. Everything he concluded seems right, but why would after 5 minutes the LOX plumbing fail ? At the end of stage 2 burn the G forces are at maximum. For sure they expected this G forces, so some material failed due to the stress. However throttling starship to limit g force might be a quick fix. Some added fuel should be able to compensate gravitational loss. Although no permanent solution it might be enough to reach target trajectory until plumbing is improved.

And there were some talks about FAA rating this flight as mishap since both FTS were used. If this is true a december launch does not seem believable to me.

 The accelerated LOX flow rate may have been due to leak in one of the engines, in which case it would be another instance of the Raptor leaking fuel.

https://x.com/DJSnM/status/1725904416455397409?s=20

[RCgothic]

Maybe, but that's doesn't appear to be what Scott's tweet says. The source of the apparent leak is speculation at this stage.

Official update:

https://www.spacex.com/launches/mission/?missionId=starship-flight-2

Booster was a RUD, ship was confirmed FTS triggered after loss of telemetry.

Edited November 21, 2023 by RCgothic

[darthgently]

2 hours ago, sevenperforce said:

Ooooooh.

It would seem, perhaps, that six Raptors blasting Superheavy at close range produce more “negative thrust” than the prograde thrust of three Raptors running at the other end. To the point that the propellant would continue forward while Superheavy started to slow. 

If think that far more research had been done on rocket engines pushing the rocket they were attached to than engines pushing craft in the plume.  The hot stage ring ass'y would catch a lot of force

[Meecrob]

2 hours ago, sevenperforce said:

Ooooooh.

It would seem, perhaps, that six Raptors blasting Superheavy at close range produce more “negative thrust” than the prograde thrust of three Raptors running at the other end. To the point that the propellant would continue forward while Superheavy started to slow. 

I thought the same at first, but the three centre engines stay lit. My guess is they wanted to test extreme forces on the booster, then when they broke it, the FTS kicked in to tick a box for the FAA. The benefits of being hardware rich.

Edited November 21, 2023 by Meecrob

[tater]

wow

2 hours ago, Meecrob said:

the FTS kicked in to tick a box for the FAA

The FTS kicked in for Starship (not SH, which had no FTS triggered) because the vehicle decided it was going to exit the planned flight corridor. It was not done to "tick a box."

If they wanted to do that, they'd say they were doing it, and do it (as they did with the Dragon abort test).

Edited November 21, 2023 by tater

[Mikki]

11 hours ago, Deddly said:

It's basically the same as gyroscopic procession, right? So my point was, why not position the turbo pump so that rotation of the ship is along that longitudinal axis? But that would require a special version of Raptor just for those engines that need to be fired up during hot staging. 

If they're ready to go in 3-4 weeks, we can probably assume this wasn't the issue, or that they have a few ideas for dealing with it. 

Exact, the needed pumps could run during the flip maneuver with zero gyro forces when mounted horizontally and inline with the flip axis...

I am searching for Raptor 2 pump cut images  or the specific engine details but this seems hopeless on the internet (for reasons ), so i estimate the both shafts at around 80 and 60 kg... rpm is unknown during flip as is the shape... Only the weight of the whole motor is known to be around 1`600kg (sealevevel). The torque is insane btw, i don`t want to upset anyone here because basically no-one can imagine it.

 I think the rotor shafts  just start glowing white hot despite full or partial flow rate and then melt away at 1`300° (degrees) while flipping, the bearings might be made of zirkonium alloy... or melt aswell when made of inconel.

I am sure SpaceX has very nice video capture (and sensor data) of their pumphousings desintegrating into shrapnell 

Edited November 21, 2023 by Mikki
degrees, gyros, mmmmhhh, inconel uff

[sevenperforce]

5 hours ago, tater said:

No evidence of that at all. FTS is automated, and based on the flight path of the vehicle. Unless they say the FTS was triggered, I'm gonna assume a leak resulting in it blowing itself up.

I would push back on this. If there was a flow failure or attitude deviation or some other anomaly shortly before SECO, that could easily result in flight path deviation and would trigger AFTS.

If there was an overall thrust shortfall then it could have same same effect as OFT-1 on the booster, where it kept doing its best but ended up out of flight path right at the end of the burn.  Is there any indication that the burn was taking longer than planned, or that  the ship was moving slower than it should have been at that time?

4 hours ago, Exoscientist said:

 The accelerated LOX flow rate may have been due to leak in one of the engines, in which case it would be another instance of the Raptor leaking fuel.

https://x.com/DJSnM/status/1725904416455397409?s=20

LOX leaks in an engine pretty rapidly lead to engine-rich combustion. Doubt that’s the case.

Damage to the LOX tank, perhaps from spalling during hot staging, could be a more likely root cause. It wouldn’t even need it to be a leak alone; if you have a small leak, then you will have autogenous pressurization issues and end up consuming more LOX that way too. 

4 hours ago, darthgently said:

If think that far more research had been done on rocket engines pushing the rocket they were attached to than engines pushing craft in the plume.  The hot stage ring ass'y would catch a lot of force

Yep. Hydraulic shock (the “water hammer” effect) can be difficult to model, especially when there is almost no way of accurately predicting the retrograde acceleration induced on the booster from Starship’s six engines, let alone the actual gradient and rate of change of that acceleration during the hot staging event.

9 minutes ago, Mikki said:

Exact, the needed pumps could run during the flip maneuver with zero gyro forces when mounted horizontally and inline with the flip axis...

I am searching for Raptor 2 pump cut images  or the specific engine details but this seems hopeless on the internet (for reasons ), so i estimate the both shafts at around 80 and 60 kg... rpm is unknown during flip as is the shape... Only the weight of the whole motor is known to be around 1`600kg (sealevevel). The torque is insane btw, i don`t want to upset anyone here because basically no-one can imagine it.

I don’t see that ever being possible. Raptor has two turbopumps, one directly in line with the engine thrust factor and one slightly offset. The turbopumps are slightly different sizes as well. Even if you could do a complete redesign and rotate the pumps by 90°, they likely still wouldn’t be on parallel axes, making any flip alignment impossible. Even if you manage to line up the pumps on the same axis, you would have to rotate all of the raptor engines onto the same alignment to make that work, which is a complete plumbing redesign as well.

[tater]

4 minutes ago, sevenperforce said:

I would push back on this. If there was a flow failure or attitude deviation or some other anomaly shortly before SECO, that could easily result in flight path deviation and would trigger AFTS.

SpaceX has said Starship had FTS triggered.

My statement was that I was not going to assume it was triggered without SpaceX saying so—particularly in the conversation context of it being suggested it was done to "tick a box" for the FAA.

[Mikki]

2 hours ago, sevenperforce said:

...Snip... I don’t see that ever being possible. Raptor has two turbopumps, one directly in line with the engine thrust factor and one slightly offset. The turbopumps are slightly different sizes as well. Even if you could do a complete redesign and rotate the pumps by 90°, they likely still wouldn’t be on parallel axes, making any flip alignment impossible. Even if you manage to line up the pumps on the same axis, you would have to rotate all of the raptor engines onto the same alignment to make that work, which is a complete plumbing redesign as well.

... Plumbing is doable, turning some engines inline with say Y- Axis also... but not in a few weeks. 

Edited November 21, 2023 by Mikki
plumping he

[darthgently]

3 minutes ago, Mikki said:

... Plumping is doable, turning some engines inline with say Y- Axis also... but not in a few weeks. 

Only the inner three gimbaled engines, if only they are used during pivot, need alignment.  Maybe just those three could share a pair of pumps with parallel axes that could be pivoted around.  They'd be the oddballs then, which would be annoying to most anyone technically oriented and would definitely annoy the raptor team I'd imagine

[tater]

 

[Exoscientist]

This video shows Starship tumbling before FTS, which suggests one or more engines failed:

 

[CBase]

5 hours ago, RCgothic said:

Booster was a RUD, ship was confirmed FTS triggered after loss of telemetry.

Booster...actually at the moment I do not care. It looked great until stage seperation and that is the responsibility of a booster to me. Anything beyond is cost optimisation that they eventually get right.

Loss of telemetry triggers AFTS: Is that something unique for starship ? Especially before starlink loosing occasionally contact to ground control was expected if I remember the first falcon 9 launches.

[tater]

10 minutes ago, Exoscientist said:

This video shows Starship tumbling before FTS, which suggests one or more engines failed:

No, it doesn't.

I was watching his real time stream of what he captured, and you'll note the cloud at the very start (~10-11 sec in) of the video you linked. THAT is the explosion. He caught the explosion on his finder cam, but did not get the better cam moved to the vehicle until after the explosion.

The text remarks on screen in that vid even say as much.

The time stamps are all there, too.

T+8:10 is explosion coming into view.

Main cam is T+8:15 (5+ seconds AFTER explosion (took him a wile to get it even in the finder frame, so longer than that).

I have see people on X misattributing this to the intact vehicle tumbling well, when the photographer could not possibly have been more clear what we are seeing.

Edited November 21, 2023 by tater

[darthgently]

1 hour ago, Exoscientist said:

This video shows Starship tumbling before FTS, which suggests one or more engines failed:

 

If you watch Scott Manley's post mortem vid somewhere in thread above he covers the multiple engine outages and makes a good case for ullage failure

It didn't tumble, just engines starving on gas instead of liquid

oops. Nevermind

Edited November 21, 2023 by darthgently

[tater]

37 minutes ago, darthgently said:

If you watch Scott Manley's post mortem vid somewhere in thread above he covers the multiple engine outages and makes a good case for ullage failure

It didn't tumble, just engines starving on gas instead of liquid

That was for SH I thought.

There were some odd puffs on SS, then at T+8:03, all 6 engines show off on telemetry, and 8:05 the explosion is visible. Velocity continued to increase until explosion as well. FTS command I think also shuts down engines, right? Which suggests FTS commanded ~T+ 8:03. The FL video doesn't get the debris on a good camera until 10 seconds after it explodes.

[darthgently]

25 minutes ago, tater said:

That was for SH I thought.

There were some odd puffs on SS, then at T+8:03, all 6 engines show off on telemetry, and 8:05 the explosion is visible. Velocity continued to increase until explosion as well. FTS command I think also shuts down engines, right? Which suggests FTS commanded ~T+ 8:03. The FL video doesn't get the debris on a good camera until 10 seconds after it explodes.

Oops, I thought Bob was referring to SH.  Mea culpa

[Piscator]

You can also see quite clearly in the video that it's only the front half that is tumbling.

[darthgently]

.... Nebbermind 

Edited November 21, 2023 by darthgently

[tater]

23 minutes ago, Piscator said:

You can also see quite clearly in the video that it's only the front half that is tumbling.

That, too, LOL.

[tater]

Delayed to 1:47 EST

 

[StrandedonEarth]

5 hours ago, darthgently said:

Only the inner three gimbaled engines, if only they are used during pivot, need alignment.  Maybe just those three could share a pair of pumps with parallel axes that could be pivoted around.  They'd be the oddballs then, which would be annoying to most anyone technically oriented and would definitely annoy the raptor team I'd imagine

Ok, now wait a sec. That's right, these engines gimbal. Quite a bit, IIRC. And the entire engine gimbals, not just the nozzle, so those pump shafts are already moving around. I start to get the feeling that pump shaft/rotor gyro effects may be a red herring.

[AckSed]

Eager Space released this vid on how SS/SH, specifically designed to RTLS, stages differently from Falcon 9 and other rockets: