totm nov 2023 SpaceX Discussion Thread

[Minmus Taster]

9 minutes ago, Exoscientist said:

Two separate, independent methods suggest SpaceX throttled down the booster engines < 75%, while the Starship engines fired at ~90% thrust:

Did SpaceX throttle down the booster engines on the IFT-2 test launch to prevent engine failures?
http://exoscientist.blogspot.com/2023/12/did-spacex-throttle-down-booster.html

 This is important to know because if the engines need to operate at < 75% to be reliable, then I estimate the reusable payload would be lowered from 150 tons to ~100 tons. Then instead of needing perhaps 16 refueling flights for the Artemis landing missions there would need to be perhaps 24.

  Robert Clark

I think it's time to press the 'panic' button for artemis and perhaps even starship. The entire thing is crumbling as we speak.

[kerbiloid]

(Imagining two multi-tonne shapeless cryogenic blobs in the tanks of SH, peacefully floating in zero-g after separation, and suddenly ramming the spaghetti strainer with 30 holes,splashing 30 fountains over 30 whirlpools. Then 30 sources of heat and vibration suddenly ignite, and one of them starts coughing, because it has choked on the evaporating super-cool liquid. And while it's trying to cough it up, 30-1 neighbors are vibrating and kicking his white-hot body from aside, in the the lightless tightness and stuffiness of the motor section. Poor engine tries to cough once again, then bends and vomits fire onto his close neighbors, making them spread around. "Jingle, bells!" is the last what he can hear, before his bell rams the next bell in the ring...)

30 = 60, as 2 tanks.

Edited December 19, 2023 by kerbiloid

[tater]

 

[mikegarrison]

Seems obvious to me that landing is still the biggest risk item for Starship/SH, but of course landing is optional (for now).

But the risk item that has bothered me from the start that still seems like it my be plaguing them is the large number of engines. More engines = more redundant *unless* their failure modes are not independent. And it has always concerned me that so many engines, so close, without heavy (and space-consuming) armor between them, is a huge risk for fratricidal cascading engine failures. That means more engines = less reliability, rather than more reliability.

We'll see.

[tater]

3 minutes ago, mikegarrison said:

Seems obvious to me that landing is still the biggest risk item for Starship/SH, but of course landing is optional (for now).

Yeah, chopstick landing seems insane, and a long pole.

[Deddly]

@mikegarrison I remember there was at least one early F9 flight with an engine failure that still completed its mission. Does F9 have armour between the engines?

[tater]

I think F9 and SH have armor now.

[Meecrob]

5 hours ago, Minmus Taster said:

I think it's time to press the 'panic' button for artemis and perhaps even starship. The entire thing is crumbling as we speak.

What? You realize that rockets are hard right? If you could just slap them together like in KSP, my former high school would have its own space program!

[Kerwood Floyd]

13 minutes ago, Meecrob said:

What? You realize that rockets are hard right? If you could just slap them together like in KSP, my former high school would have its own space program!

I read Minmus Taster's post as sarcasm. YMMV

[Meecrob]

21 minutes ago, Kerwood Floyd said:

I read Minmus Taster's post as sarcasm. YMMV

Lol, thanks for the heads up, and my apologies @Minmus Taster. Its hard to tell these days with so many people seriously calling for the cancellation of an experimental program because it didn't work perfectly on the first try with a straight face. You got me good!

[Minmus Taster]

30 minutes ago, Meecrob said:

What? You realize that rockets are hard right? If you could just slap them together like in KSP, my former high school would have its own space program!

Rockets are hard and always will be, but money is harder. 24 or even 16 Starship flights for a single lunar mission is never going to be economic unless starship can launch and land at full throttle and be reused in a matter of days without any repairs. And since starship needs to be economical in order to operate in the scale it needs to I just don't think the vehicle has the capability to preform all of this. And that's before even touching on what happens when there's inevitably a failure of some kind and the program is grounded to investigate.  I like starship and I think it will work as a heavy lift vehicle, but anything more is stretching way too far. And sadly since NASA is already almost at max capacity at this point monetarily it needs to put all it's eggs in one basket. All of this for a single trip to the moon. That's what I meant when I said artemis was "crumbling", it just cannot be sustained with so many different components that all need to be paid for and then work perfectly.

[Royalswissarmyknife]

Turns out it wasn't sarcasm. 

Edited December 18, 2023 by Royalswissarmyknife

[mikegarrison]

1 hour ago, Deddly said:

@mikegarrison I remember there was at least one early F9 flight with an engine failure that still completed its mission. Does F9 have armour between the engines?

It all depends on what *kind* of engine failure. There are many failure modes where one engine failing does not particularly risk a cascade, but there are others where it does.

[SunlitZelkova]

Would something like KORD help SH? So if an engine in the innermost ring fails, the engine on the opposite side of the ring can be shut down to avoid uneven thrust, and the rocket can keep flying?

KORD was the engine control computer on the N1 responsible for automatically shutting down engines in the event of failure, in case you don’t know.

[RCgothic]

It's already even smarter than that. If an engine goes out it'll first gimbal the centre engines to maintain thrust through the centre of mass, and only down-throttle opposite engines if doing so is necessary to maintain sufficient margin of control authority. Actually turning opposite engines off would be a last resort.

[Royalswissarmyknife]

16 minutes ago, SunlitZelkova said:

Would something like KORD help SH? So if an engine in the innermost ring fails, the engine on the opposite side of the ring can be shut down to avoid uneven thrust, and the rocket can keep flying?

KORD was the engine control computer on the N1 responsible for automatically shutting down engines in the event of failure, in case you don’t know.

I think it has something like that already but it throttles down engines instead of shutting them down.

[tater]

1 hour ago, Minmus Taster said:

24 or even 16 Starship flights for a single lunar mission is never going to be economic

Fixed price contract.

 

[mikegarrison]

1 hour ago, SunlitZelkova said:

Would something like KORD help SH? So if an engine in the innermost ring fails, the engine on the opposite side of the ring can be shut down to avoid uneven thrust, and the rocket can keep flying?

KORD was the engine control computer on the N1 responsible for automatically shutting down engines in the event of failure, in case you don’t know.

That's not the issue. I mean, rockets now have real-time computer control that allows them to land! Dealing with the thrust imbalance is not the difficulty.

The concern is something like a fire or an uncontained turbo-machinery failure that sends shrapnel into the neighboring engines. We've seen in both launches now that engines start dropping out after the engines next to them drop out, which is extremely concerning.

[cubinator]

1 hour ago, Minmus Taster said:

Rockets are hard and always will be, but money is harder. 24 or even 16 Starship flights for a single lunar mission is never going to be economic unless starship can launch and land at full throttle ...

Isn't it already more economical to launch 24 Falcon 9s for a single lunar mission than one SLS?

[mikegarrison]

9 minutes ago, cubinator said:

Isn't it already more economical to launch 24 Falcon 9s for a single lunar mission than one SLS?

There are payloads that a single SLS can launch but no number of F9s can launch.

[tater]

https://twitter.com/i/broadcasts/1BdxYrLDQWvKX?s=20

3 hours

 

1 hour ago, mikegarrison said:

There are payloads that a single SLS can launch but no number of F9s can launch.

Currently this would be Orion. (constrained to payloads that exist)

[AckSed]

Hey, do you like spaghetti? I like spaghetti. (Internal structure of the Super Heavy's propellant system.):

https://ringwatchers.com/article/booster-prop-distribution

[Royalswissarmyknife]

31 minutes ago, AckSed said:

Hey, do you like spaghetti? I like spaghetti. (Internal structure of the Super Heavy's propellant system.):

https://ringwatchers.com/article/booster-prop-distribution

Still more organized then my desk. 

Edited December 19, 2023 by Royalswissarmyknife

[tater]

 

[tater]

4 min

 

nominal so far