totm nov 2023 SpaceX Discussion Thread

[Nuke]

from throwing chunks to spraying shrapnel. i say its an improvement.

 

im going to bed.

Edited March 14 by Nuke

[Minmus Taster]

Lock the doors. RIP Ship 28 and Booster 10

[cubinator]

Just now, sevenperforce said:

I'm worried that it could be burn-through at tile loss. I'm also worried because I have no idea how they would figure that sort of thing out.

It also spent a lot of time with the heat shield only halfway in the plasma at the start there.

[AckSed]

Still and all, even if the reuse isn't working right now, this would be a damn good result for an expendable 2-stage rocket, and it is still cheap enough to be a Big Dumb Booster or a partially-expendable Honkin' Big Falcon Rocket.

[Ultimate Steve]

4 minutes ago, sevenperforce said:

Yep, that makes sense.

RIP Starship -- you went farther than any before!

I'm worried that it could be burn-through at tile loss. I'm also worried because I have no idea how they would figure that sort of thing out.

Not necessarily tile loss, the thing appeared to enter the atmosphere in a tumble. There's been some speculation that there was minimal to no control after SECO, that roll may have been coincidental and not commanded, plasma on the silver side is not normal.

[RCgothic]

Both booster and ship appeared to have orientation hold issues. Instability would also account for the skipped on-orbit burn. Maybe they thought there was a chance the fins could regain control on re-entry, and it almost looked like they were stable towards the end, but I'm not sure.

In any case, primary mission success.

[Minmus Taster]

1 minute ago, Ultimate Steve said:

Not necessarily tile loss, the thing appeared to enter the atmosphere in a tumble. There's been some speculation that there was minimal to no control after SECO, that roll may have been coincidental and not commanded, plasma on the silver side is not normal.

Biggest issues are likely tile loss and control, looks like they still lost some tiles based on the onboard views, but better than last time!

[tater]

“we are watching the end of SLS”

quote from someone at MCC relayed to me

[RCgothic]

Yeah, it'd lost far fewer tiles on ascent than last time.

[sevenperforce]

7 minutes ago, Ultimate Steve said:

Not necessarily tile loss, the thing appeared to enter the atmosphere in a tumble. There's been some speculation that there was minimal to no control after SECO, that roll may have been coincidental and not commanded, plasma on the silver side is not normal.

The views I was getting on video seemed pretty stable, though.

[Minmus Taster]

Just now, sevenperforce said:

The views I was getting on video seemed pretty stable, though.

The views were truly incredible, never seen a reentry like that before!

[tater]

2 minutes ago, sevenperforce said:

The views I was getting on video seemed pretty stable, though.

Once it was getting some flap authority, seemed to calm down.

[sevenperforce]

Just now, tater said:

Once it was getting some flap authority, seemed to calm down.

Agreed. There was a lot of concerning spinning and tumbling right there at the beginning of the ultrasonic regime, before there was significant visible heating but also before there was enough atmospheric mass to provide something for the flaps to bite into. But by the time we saw plasma, it seemed to be maintaining a pretty good attitude, at least in the roll axis. Impossible to tell whether there were issues in the pitch axis; that would be the next area of greatest concern.

[Minmus Taster]

1 minute ago, tater said:

Once it was getting some flap authority, seemed to calm down.

Not sure about that, we lost out frame of reference once the plasma kicked up but it looked like the ship was still tumbling based on the graph below.

[Geonovast]

2 minutes ago, sevenperforce said:

The views I was getting on video seemed pretty stable, though.

As in the camera wasn't cutting out or the ship was in stable orientation?  Cause I was keeping my wife updated in the other room and my lines were almost exclusively:
"It's still spinning"
"It's still spinning"
"I don't think that spin is intentional anymore"
"It's re-entering and it's still spinning"

[Exoscientist]

26 minutes ago, sevenperforce said:

Angry Astronaut has no legitimate reason to think this and that doesn't make any sense. The engines managed to get through the entire boostback just fine. Control authority appears to have been the problem prior to relight.

 Actually, we do know definitely that the engines did not all relight during the landing burn for the booster. That proves something went wrong at this relight, and the damage could even have occurred during the first relight during boostback except that burn was not long enough to cause loss of vehicle.

 If something goes wrong with the engines during flight, and it is a known problem to have occurred before during testing the first thing to suspect is that same issue is occurring again. 

Bob Clark

[Pthigrivi]

9 minutes ago, Minmus Taster said:

Not sure about that, we lost out frame of reference once the plasma kicked up but it looked like the ship was still tumbling based on the graph below.

Yeah the flaps seemed to be helping but it never really looked like they had control authority. Most of what we saw before blackout it seemed to be coming in tail first. The roll in orbit was odd too.  Still a pretty spectacular launch. 

Edited March 14 by Pthigrivi

[CatastrophicFailure]

I just woke, up, something happen?

[Exoscientist]

10 minutes ago, RCgothic said:

Yeah, it'd lost far fewer tiles on ascent than last time.

 Yes, but the losses during reentry were quite substantial. By the way it might be possible to get a Starship that doesn’t even need thermal tiles. The idea is you could have wing loading, vehicle weight per wing area, so small that reentry speed is reduced sufficiently that the metal skin can survive the reentry heating by itself.

 See discussion here:

Reentry of orbital stages without thermal protection? UPDATE: 7/1/2019
https://exoscientist.blogspot.com/2019/06/reentry-of-orbital-stages-without.html

 BUT for this to happen you would need Starship to have the quite low dry mass speculated upon by Elon of only 40 tons:

  Bob Clark

[AckSed]

Just now, CatastrophicFailure said:

I just woke, up, something happen?

Oh, nothing, just a spacecraft the size of a building went through reentry.

[.50calBMG]

12 minutes ago, Exoscientist said:

 Actually, we do know definitely that the engines did not all relight during the landing burn for the booster. That proves something went wrong at this relight, and the damage could even have occurred during the first relight during boostback except that burn was not long enough to cause loss of vehicle.

 If something goes wrong with the engines during flight, and it is a known problem to have occurred before during testing the first thing to suspect is that same issue is occurring again. 

Bob Clark

My best guess is that it's fuel slosh from the booster wobbling and spinning so much. That's solvable with tweaked control algorithms, not a failure of the engines. Seriously, with the number of test firings, I don't understand why you automatically jump to engine failure

[Minmus Taster]

Just now, AckSed said:

Oh, nothing, just a spacecraft the size of a building went through reentry.

That's probably the largest single spacecraft to ever reenter the atmosphere. Maybe Mir was heavier but that was a whole station.

Will this require another drawn out investigation? Technically the vehicle launched properly and the circumstances of reentry of both vehicles wouldn't change the risk to public safety much.

[tater]

2 minutes ago, .50calBMG said:

My best guess is that it's fuel slosh from the booster wobbling and spinning so much. That's solvable with tweaked control algorithms, not a failure of the engines. Seriously, with the number of test firings, I don't understand why you automatically jump to engine failure

The flip was completely successful. Any prop slosh hammer taking out plumbing would have resulted in a RUD. There are a number of possible reasons for restart issues posted above, and another might be relighting into supersonic airflow with this engine (vs the one with TEA-TEB they have so much experience with). This can only be tested in flight.

Using strictly boiloff as RCS could also be an issue vs more traditional RCS. Constant venting has to be a control issue at some level.

[Deddly]

I speculate that Starship's problem is with the RCS. That would explain both the lack of a relight test as well as the tumbling.

Edited March 14 by Deddly

[Ultimate Steve]

Some thoughts.

Booster:

I think Exoscientist is referring to the downcomer crushing issues they were having a few years back? It is possible that the tail end of the boostback burn produced high enough acceleration to crush something and cause a leak or loss of pressure.

It was more or less confirmed that IFT2 Booster RUD was caused by Raptor LOX starvation. There was one Raptor ignition failure on boostback, which we don't have the specifics behind, but was probably a Raptor issue.

It looks like they were planning on starting all 13 for landing, which is bonkers, but only 3 ever lit up I think? Going from memory. My read on this is that there was a grid fin control issue (either software or hardware) that caused extreme oscillations leading to bad startup conditions for Raptor.

Neither of those hypotheses are Raptor's fault, though. It is possible that Raptor doesn't play nice with impinging transonic airflow. That's the only "Raptor's fault" scenario I can come up with.

Ship:

Upper stage was near constantly venting/RCSing. Two possibilities, one, it was trying to dump as much lox as possible, two, something wonky was going on with controls.

I am guessing that they were experiencing severe control issues immediately following SECO.

The orientation never seemed to stabilize, not for payload door stuff, or maybe the engine stuff, and definitely not entry. We didn't see what Starship was doing when it was supposed to be firing its engine, but being in an uncontrolled spin is probably on the list of "Do not fire the engine" criteria and is a possible reason why that burn was skipped.

Interestingly enough we see no RCS whatsoever after the camera feed was recovered for re entry. This could be because they don't want to fire hot oxygen into the airstream or something, but it is also possible that the main tank was fully depressurized at that stage - maybe there was a leak (would explain control issues if said leak produced torque), or maybe they used up so much trying to steer that the main tank pressure dropped to zero. I'm not completely sure that Starships's RCS is just vents but that's what I seem to recall it being.

But in any case, something caused them to not have attitude control at some point in the coast, possibly the entire coast. I cannot imagine that it is normal to enter the atmosphere in a tumble.

I am very delightfully surprised that they managed to get live video of the plasma regime!

Also no explicit confirmation of successful payload door closing, there was a twang and vibration on the door then the camera cut away for the rest of the flight.