SpaceX Discussion Thread

[ExtremeSquared 222]

Limited cameras on this flight. 

[Clamp-o-Tron 1,044]

Abort at 1:24. The curse continues.

Holding at 15:00, probably done for today.

EDIT: confirmed scrub. Backup window tomorrow.

Edited March 1 by Clamp-o-Tron

[cubinator 8,666]

Not today..

[tater 27,163]

 

[RyanRising 469]

7 hours ago, ExtremeSquared said:

Limited cameras on this flight. 

I wonder if it's cause they're all of a sudden shy about cameras or if it's cause they want to use that telemetry elsewhere.

Also, it's scrub city around these parts.

[tater 27,163]

https://twitter.com/EmreKelly/status/1366402811009916929

 

[tater 27,163]

 

[YNM 2,524]

Well, SpaceX is in here, so...

 

[tater 27,163]

Very glitchy audio ^^^

[StrandedonEarth 7,384]

I don’t think I saw this posted here; finally a cause for the last failed landing:

 

[RyanRising 469]

33 minutes ago, StrandedonEarth said:

I don’t think I saw this posted here; finally a cause for the last failed landing:

Sounds like the engine failed on ascent, not descent, yet they still tried to use it for the landing burn. I'd have thought you'd switch to a different set of three, but hey, maybe they thought the issue had passed. Clearly it had not.

[tater 27,163]

SpaceX link shows Starlink tomorrow:

 

[tater 27,163]

 

[sevenperforce 7,463]

19 hours ago, RyanRising said:

Sounds like the engine failed on ascent, not descent, yet they still tried to use it for the landing burn. I'd have thought you'd switch to a different set of three, but hey, maybe they thought the issue had passed. Clearly it had not.

All nine engines are lit on the pad using TEA-TEB plumbed from the ground. Only three specific engines are plumbed to the onboard reservoir of TEA-TEB needed for in-flight restart. When the first Falcon Heavy launch failed to land the core, it was because the onboard TEA-TEB reservoir ran dry just after restarting the core engine for the second time, meaning there was not enough remaining for the other two engines to relight. They fixed this in subsequent Falcon Heavy flights by making the core's reservoir bigger.

So this is the problem. If Falcon 9 had lost one of the other four six engines on ascent, it would have been okay, but since it lost one of the intended landing engines, it was stuck. It can't choose other engines to relight because they aren't plumbed with TEA-TEB. I'm guessing they went ahead and tried to force a restart of the engine that previously shut down and its burn-through got worse.

Starship, of course, won't have this problem because all of the Raptor engines use their own internal spark igniter and can relight at any time, independent of any other engine or system.

Edited March 2 by sevenperforce
because apparently I can't count

[RyanRising 469]

5 minutes ago, sevenperforce said:

All nine engines are lit on the pad using TEA-TEB plumbed from the ground. Only three specific engines are plumbed to the onboard reservoir of TEA-TEB needed for in-flight restart. When the first Falcon Heavy launch failed to land the core, it was because the onboard TEA-TEB reservoir ran dry just after restarting the core engine for the second time, meaning there was not enough remaining for the other two engines to relight. They fixed this in subsequent Falcon Heavy flights by making the core's reservoir bigger.

So this is the problem. If Falcon 9 had lost one of the other four engines on ascent, it would have been okay, but since it lost one of the intended landing engines, it was stuck. It can't choose other engines to relight because they aren't plumbed with TEA-TEB. I'm guessing they went ahead and tried to force a restart of the engine that previously shut down and its burn-through got worse.

Starship, of course, won't have this problem because all of the Raptor engines use their own internal spark igniter and can relight at any time, independent of any other engine or system.

Thanks! I wasn’t ware they’d only plumbed the intended landing engines for restart capability, thought it was universal and they could light up whatever they liked. Makes a lot more sense to try restarting the failed engine in that case.

[sevenperforce 7,463]

Just now, RyanRising said:

Thanks! I wasn’t ware they’d only plumbed the intended landing engines for restart capability, thought it was universal and they could light up whatever they liked. Makes a lot more sense to try restarting the failed engine in that case.

Yep. And with lower thrust due to the engine-out on ascent, the ascent burn probably took longer and cost a little more propellant, leaving it with even lower margins. Otherwise perhaps it would have attempted a single-engine entry burn.

I just realized that given the core landing failure on FH1, the tipover on FH2, the core landing failure on FH3, and the intentional expenditure of the core for the upcoming FH4, it will be NET October of this year before we even have a chance to see a recovered FH core. That one is 6.35 tonnes to GTO so it should have no trouble reusing all three cores just as it did for FH2. 

[RCgothic 2,249]

The last time they had an engine out on ascent it caused them to overshoot the droneship. Less thrust means longer to orbit means further downrange. I'm surprised they could still attempt a landing at all, the engine out must have been very late in the first stage burn.

[tater 27,163]

 

[sevenperforce 7,463]

7 hours ago, RCgothic said:

The last time they had an engine out on ascent it caused them to overshoot the droneship. Less thrust means longer to orbit means further downrange. I'm surprised they could still attempt a landing at all, the engine out must have been very late in the first stage burn.

Yep. They were probably already throttling down the first-stage engines at that point so shutting down the bad one and throttling the others back up a little was likely easy enough. If this had happened earlier in the first-stage burn, they likely wouldn't have had enough propellant to even attempt an entry burn.

With an engine-out in a nine-engine cluster in KSP, you'd probably need to shut down the opposite engine to balance thrust (even with Vectors) but I'm guessing Falcon 9 is able to keep eight engines burning since its TVC PID programming is much smarter than the SAS in KSP. 

[Lukaszenko 205]

20 hours ago, StrandedonEarth said:

I don’t think I saw this posted here; finally a cause for the last failed landing:

 

Good explanation, but it leaves more questions than answers. For example, how did they find out about this "hole" if they lost the booster? Did they know about it BEFORE the launch? 

[cubinator 8,666]

16 minutes ago, Lukaszenko said:

Good explanation, but it leaves more questions than answers. For example, how did they find out about this "hole" if they lost the booster? Did they know about it BEFORE the launch? 

They likely have pressure sensors inside the engines. If one part was supposed to have a high pressure, and then suddenly shifted to ambient or low pressure, that would indicate that a hole has developed. This data would be part of the telemetry transmitted during flight.

[StrandedonEarth 7,384]

Yeah, I still think that falls into the “we were dumb” category of “don’t test life-leader components on the non-redundant landing engines “

Edited March 2 by StrandedonEarth

[mikegarrison 4,078]

That whole explanation is confusing. It sounds like they lost the engine during ascent, because he's talking about "we still got to orbit". But can't they use a working engine for landing? Or are there specially located engines that must be used?

[tater 27,163]

3 minutes ago, mikegarrison said:

That whole explanation is confusing. It sounds like they lost the engine during ascent, because he's talking about "we still got to orbit". But can't they use a working engine for landing? Or are there specially located engines that must be used?

Yeah, they only use 3 for entry burn/landing. The same 3 every time.

[mikegarrison 4,078]

1 hour ago, tater said:

Yeah, they only use 3 for entry burn/landing. The same 3 every time.

So that means that even though there are 9 engines, there is no redundancy for landing?

Edited March 2 by mikegarrison