totm nov 2023 SpaceX Discussion Thread

[xebx]

/clap and boom.

My bet was SN10 doing slightly better than SN8 : landing and falling on the side.

- different plume/exhaust color between raptors during ascent, that was noticeable but not necessarily a problem : it was discussed in waterfall thread and color depends on throttle (for ex torch mode on when low throttle) and fuel/oxidizer rich (very probably related to throttling).

- final maneuver starts at higher altitude with 3 engines, nice ! (compared to SN9 late maneuver without redundancy), then switch to 2 engines full throttle (main deceleration), then to 1 engine for touch down. Only one engine for touch down may help with heat management and theoric SLTwr of almost empty Starship with 1 engine = 1.7.

- fire at the bottom : you can see each time a raptor throttle down completely/shutdown/goes into torch mode, there is a fire issue inside the fairing. Add to this floppy landing legs that probably didn't help to land softly (possible pipe damage), and the fact that the bottom fairing keeps the heat from engines+bells inside the fairing : almost all rockets have wide open bottom around the engines to allow heat to radiate/evacuate, and it's worse when landed.

But it can be fixed with fire mitigation on the landing pad and better management of engine shutdown/torch mode and reliable legs, and more robust piping/cooling system.

 

 

Edited March 4, 2021 by xebx

[Brotoro]

1 hour ago, Scotius said:

Ah, man - what insanity And i missed it due to this pesky need to sleep

Anyways, that explosion looked very energetic. There was that much methane leftover in the tank after the flight?

From what I've seen, it looks like the skirt area containing the engines is what exploded. I suspect that the hard landing (you can see the ship bounce if you focus on its nose during landing) and landing on its butt resulted in some lines getting broken in the tail area, with methane and oxygen building up in the space (where it might even have escaped if it was up on its legs). Then something touched off the explosive mix and popped the ship back up, rupturing the button of the methane tank so that the fuel could add to the conflagration.  I couldn't see any secondary explosion from when it landed on its side (just fire)...but it wasn't a good angle.

*rupturing the bottom

[Blaarkies]

51 minutes ago, xebx said:

: landing and falling on the side

That is such a Kerbal outcome for any landing 

[RealKerbal3x]

Let's go again for Starlink 17:

 

[Clamp-o-Tron]

It appears to me that the cause for the explosion was inside the tank...

Also, another shot at Starlink-17 in about 15 minutes. This one is launching into a different orbital inclination than was planned last window, because of “range conflicts” (according to NSF stream). Secondary window for a launch 2 hours after the now-planned T-0

 

Edited March 4, 2021 by Clamp-o-Tron

[Ultimate Steve]

I've seen this a few other times (not sure if it's been posted here or not) but the LOX tank is at the base right? People are guessing that the hard landing ruptured the methane downcomer leading to methane and LOX contacting in the bottom tank.

[RealKerbal3x]

1 minute ago, Ultimate Steve said:

I've seen this a few other times (not sure if it's been posted here or not) but the LOX tank is at the base right? People are guessing that the hard landing ruptured the methane downcomer leading to methane and LOX contacting in the bottom tank.

Yeah, the LOX tank is at the bottom.

[Brotoro]

Nice. Another eight-landing booster.

Did they say why there wasn't any onboard video from the booster for this flight?

[CBase]

If you check the thermal cam from LabPadre, it is visible that there was a lot of chilled gas around the rocket after it had landed: it is all black until the unscheduled ignition.

Maybe some small wind or wind machines could help on next try by simply reducing gas concentration. I mean even too much oxigen can get very dangerous even without methane leaks.

[kerbiloid]

A pipe popped.

[RealKerbal3x]

Insane.

[GuessingEveryDay]

Just now, RealKerbal3x said:

Insane.

Is it just me, or did the Starship fall faster? Probably just the camera. But it does look like it.

[RealKerbal3x]

Just now, GuessingEveryDay said:

Is it just me, or did the Starship fall faster? Probably just the camera. But it does look like it.

Previous flights had an almost completely clear sky, whereas SN10's flight was partly cloudy. It probably looks faster because there's more visual references to infer its speed.

[JIMMY_the_DOG]

4 minutes ago, GuessingEveryDay said:

Is it just me, or did the Starship fall faster? Probably just the camera. But it does look like it.

Huh.

If for some reason it did than landing program was probably programmed for a slower terminal velocity that it was actually falling at, so that's why you got your hard landing

3 minutes ago, RealKerbal3x said:

Previous flights had an almost completely clear sky, whereas SN10's flight was partly cloudy. It probably looks faster because there's more visual references to infer its speed.

Oh yes true

3 minutes ago, JIMMY_the_DOG said:

Previous flights had an almost completely clear sky, whereas SN10's flight was partly cloudy. It probably looks faster because there's more visual references to infer its speed.

And the clouds were moving so that could visually seem to add more speed, too.

[RealKerbal3x]

2 minutes ago, JIMMY_the_DOG said:

 

If for some reason it did than landing program was probably programmed for a slower terminal velocity that it was actually falling at, so that's why you got your hard landing

Apparently the hard landing was due to the landing engine underperforming. I don't know why the terminal velocity would change, externally SN10 was almost identical to SN8 and 9.

Also:

 

[JIMMY_the_DOG]

6 minutes ago, RealKerbal3x said:

Apparently the hard landing was due to the landing engine underperforming.

Oh... now the blocks are snapping together....

didnt they scrub the launch for the 1st time for high thrust? so then it was problably a little to low so there wasnt enough to land.  

Keep in mind that this is a guess.

Edited March 4, 2021 by JIMMY_the_DOG

[RealKerbal3x]

Just now, JIMMY_the_DOG said:

Oh... now the blocks are snapping together....

didnt they turn down the thrust at t-1 sec for a high thrust? so they problably turned down the thrust and that's your consequence.

Keep in mind that this is a guess.

The initial abort was caused by an overly conservative high thrust limit. There wasn't anything wrong with the amount of thrust the engines were producing, the sensor was simply erroneously reporting a problem.

 

[Hannu2]

I guess that they have some severe issues with Raptors they are not willing to publish. Now engines had clearly different colored flames in ascent. I suspect it was not intentional or good sign (or could they make some strange tests, for example mixing ratios). They seem to do Raptor testing at the same time they test SNs. It is quite kerbal way to test rocket engines with flying prototypes. Fortunately radio controlled command pods was before full staged combustion in human's tech tree. Test piloting those ships would otherwise be a little bit too dangerous work.

[RealKerbal3x]

1 minute ago, Hannu2 said:

They seem to do Raptor testing at the same time they test SNs.

Every Raptor is tested at their facility in McGregor, Texas before it is flown. They don't just build an engine and say 'yeah, seems good, send it'.

[cubinator]

8 minutes ago, Hannu2 said:

They seem to do Raptor testing at the same time they test SNs. It is quite kerbal way to test rocket engines with flying prototypes.

Sounds like fun!

6 minutes ago, RealKerbal3x said:

Every Raptor is tested at their facility in McGregor, Texas before it is flown. They don't just build an engine and say 'yeah, seems good, send it'.

Still, there's some stuff that can be different when it's attached to the vehicle or in flight. I wouldn't be surprised if they are at least tweaking parameters to find the right balance for each Starship test.

[tater]

 

[sevenperforce]

7 minutes ago, Hannu2 said:

I guess that they have some severe issues with Raptors they are not willing to publish. Now engines had clearly different colored flames in ascent. I suspect it was not intentional or good sign (or could they make some strange tests, for example mixing ratios). They seem to do Raptor testing at the same time they test SNs.

All three raptors successfully relit for the flip, so I really don’t think they were having any serious problems. Differences in color on ascent were likely related to mixture ratios and deep throttling.

The only “testing” they are doing during flight is figuring out how Raptor performs with the force and pressure transients of actual flight. 

15 minutes ago, RealKerbal3x said:

The initial abort was caused by an overly conservative high thrust limit. There wasn't anything wrong with the amount of thrust the engines were producing, the sensor was simply erroneously reporting a problem.

I understood Elon’s tweet a little differently: there was something a little wrong with the amount of thrust being produced, but it wasn’t wrong enough to be a reason not to fly.

[RealKerbal3x]

Just now, sevenperforce said:

I understood Elon’s tweet a little differently: there was something a little wrong with the amount of thrust being produced, but it wasn’t wrong enough to be a reason not to fly.

Hmm, this is the problem: Elon's tweets are always just ambiguous enough to cause confusion

[JoeSchmuckatelli]

3 minutes ago, tater said:

 

That landing sequence is not quite what I would expect - there is a lot of lateral movement for something so heavy.  I would have expected every frame to be moved up one spot with the final frame before landing being directly above the landed photo. 

 

Also - am I wrong to assume SX can recycle all the steel recovered from the past SNs? 

[Hannu2]

9 minutes ago, RealKerbal3x said:

Every Raptor is tested at their facility in McGregor, Texas before it is flown. They don't just build an engine and say 'yeah, seems good, send it'.

Of course they are tested as well as they can. But it seem there have been problems with underperforming Raptors in SN9 and SN10. Something may be going on and they have to find a solution. I hope I am wrong and they had some sporadic problems easy to fix, of course.

That strange flight profile may also be engine testing. They ascent very slowly and burn engines several minutes. At apoapsis they almost hover a minute or two with very small velocity. If it was just aerodynamic test they could ascend probably in less than a minute. I do not see other reasons for such profile than get important test minutes for engines at (almost) realistic flight conditions.