SpaceX Starship : First Flight : Starbase, TX : 20 April 2023 - DISCUSSION

[Herb Schaltegger]

… combined with actual full acceptance testing of each engine at McGregor (something that the N-1’s NK-15s couldn’t do), should help a lot.

This, absolutely. The NK-15’s were lot-tested and then they presumably just hoped for the best regarding the remainder.

[StarshipTrooper]

I wonder what the startup sequence would be like for a 28 engine cluster?

A fascinating engineering problem!

Perhaps something like starting opposing pairs together with additional pairs coming online separated by milliseconds. Probably the critical gimbal engines first then the outer ring.

Anyone familiar with how the Falcon Heavy lights?

[ugordan]

I wonder what the startup sequence would be like for a 28 engine cluster?

A fascinating engineering problem!

Perhaps something like starting opposing pairs together with additional pairs coming online separated by milliseconds. Probably the critical gimbal engines first then the outer ring.

Anyone familiar with how the Falcon Heavy lights?

F9 and by extension FH also uses staggered ignition of opposing outer engines on a given core. The shutdown sequence at MECO is the same.
First FH flight had the side boosters ignite first, followed by the center core a couple of seconds later. Block 5 FHs appear to ignite individual cores either simultaneously or virtually simultaneously.

I think it's a safe bet that SH will also use staggered opposing pair ignition.

[punder]

The N-1 might have been a single flight away from success. We’ll never know. I’m 100% confident that SS/SH will succeed—just maybe not on my preferred schedule. 

(Thanks for trimming my rude response. Every now and then I come back to a previous post of mine and put my head in my hands... “I did it again.”

On the other hand, bullying behavior just really gets me going. Especially when it’s directed at newbies who haven’t fully acclimated to the site’s character.)

[zubenelgenubi]

Agreed. And a small trim of posts was required.

As much as you may not like what Jim has to say at times (or more so how he says it - and even he gets trimmed when he's uncivil), those of us know him from the years here's been here and has openly stated his NASA career, he knows his stuff.

Can we get back on topic please?

Moderator: Further thread trim.
Knock it off. Stop.

[wannamoonbase]

The N-1 might have been a single flight away from success. We’ll never know. I’m 100% confident that SS/SH will succeed—just maybe not on my preferred schedule. 

I love the N1 too, but even if it succeeded it was impressive than the Saturn V.

Not having LH2 engines hampers high energy performance.

I also think SS/SH will work.  It’s just a matter of working the problems 1 at a time.  How many tries, how many problems, we will know after it happens.

LCH4 seems to be a happy medium for performance, although I see room for a lot of LH2 for beyond LEO operations. 

SS could provide a LH2 cargo service and do a strong business.

Edit:  N1 would have been less impressive than Saturn V

[jose m]

I worked on projects that involved large generator sets, common use equipment, but each start-up of a new plant was a major complex event. So when I read that they already have experience with 27 engines, putting one more is just one more line of code, ... etc. I think they are literary people, who never even changed a lamp in their house.

I put in some numbers, to help you notice the jump they have to make, for the starship to be orbital:

Speed ​​max. SN15 in rise = 250 Km / h
Estimated necessary speed for orbital flight, 30,000 km / h

Mass (Weight) of Falcon 9 = 500 Ton. SS = 5,000 Ton (imagine 100 large trailers fully loaded, united and launched into space at 30 thousand km / h).

I hope you see that changing the line of software that says start 27 engines to start 28 engines is only part of the titanic task that SpaceX has.

[Robotbeat]

I worked on projects that involved large generator sets, common use equipment, but each start-up of a new plant was a major complex event. So when I read that they already have experience with 27 engines, putting one more is just one more line of code, ... etc. I think they are literary people, who never even changed a lamp in their house.

I put in some numbers, to help you notice the jump they have to make, for the starship to be orbital:

Speed ​​max. SN15 in rise = 250 Km / h
Estimated necessary speed for orbital flight, 30,000 km / h

Mass (Weight) of Falcon 9 = 500 Ton. SS = 5,000 Ton (imagine 100 large trailers fully loaded, united and launched into space at 30 thousand km / h).

I hope you see that changing the line of software that says start 27 engines to start 28 engines is only part of the titanic task that SpaceX has.

Yeah, it’s a huge task with high likelihood of delays and headaches. But I also think SpaceX is prepared for it.

[EnricoR]

I worked on projects that involved large generator sets, common use equipment, but each start-up of a new plant was a major complex event. So when I read that they already have experience with 27 engines, putting one more is just one more line of code, ... etc. I think they are literary people, who never even changed a lamp in their house.

I put in some numbers, to help you notice the jump they have to make, for the starship to be orbital:

Speed ​​max. SN15 in rise = 250 Km / h
Estimated necessary speed for orbital flight, 30,000 km / h

Mass (Weight) of Falcon 9 = 500 Ton. SS = 5,000 Ton (imagine 100 large trailers fully loaded, united and launched into space at 30 thousand km / h).

I hope you see that changing the line of software that says start 27 engines to start 28 engines is only part of the titanic task that SpaceX has.

Yeah, it’s a huge task with high likelihood of delays and headaches. But I also think SpaceX is prepared for it.

And SH will not go at orbital speed.

[VaBlue]

I worked on projects that involved large generator sets, common use equipment, but each start-up of a new plant was a major complex event. So when I read that they already have experience with 27 engines, putting one more is just one more line of code, ... etc. I think they are literary people, who never even changed a lamp in their house.

That's kind of a bold, condescending, and dismissive statement on a forum with a bunch of literal rocket scientists and assorted technical and manufacturing professional experts.  And if you think that would be one line of code, you should stop commenting about SW.

I hope you see that changing the line of software that says start 27 engines to start 28 engines is only part of the titanic task that SpaceX has.

Nobody was saying anything about anything other than starting up 28 Raptor engines in those posts.  Stop making up conversation threads that don't exist.

[the_other_Doug]

The N-1's biggest issues were effects of vibration and heating on the closely clustered engines.  Certainly, computer simulation has made great strides in predicting these interactions, but I will point out that the interaction of 28 such powerful engines, their exhaust impingements, etc., gets closer and closer to chaotic.  And chaos theory is not a friendly taskmaster.

I guess I'd be more likely to believe that the first SH stages will fly just fine had there been any 28-engine cluster test firings on the ground.  Heck, the F-1 engines on the Saturn V were designed to handle the radiant heat and vibration from their neighboring engines, but you'll notice that a kludge -- thick thermal batting -- was plastered onto the outside of those engine bells after initial clustered test firings indicated that the extra protection and thermal coating was required to bring the engines within desired safety parameters. Again, yes, there has been more than 50 years of advancement in computer simulations.  But the simulations are never any better than one's assumptions, and it was the sets of assumptions, and not failure of simulations, that caused the N-1 problems, and required a kludged-on layer of protection to be added onto the F-1s.

Besides, with the rather extreme replacement rate these Raptors seem to undergo during checkout and after static fires, once attached to the prototype Starships, it seems that the Raptors are also still in fairly early prototype stages themselves.  So, the performance assumptions for the current version of the Raptor may be even more poorly defined than you might think.

Personally, I'd rather see SH stages sit on that orbital test mount and fire up their clusters for full-duration tests before bothering to mount a Starship on top.  If for no other reason than to iron out all of the poorest assumptions before risking the loss of the R-Vacs that will likely be installed on any SS that gets put on top of an SH.  Of course, that would take several months and endanger his build/launch/test site unnecessarily, and it seems Musk is in enough of a hurry that he doesn't want to go through that whole process.  Still... even SpaceX might get surprised at the backlash if an SH blows up one or two km into the air.  Because that would be, shall we say... a significant RUD. 

[cwr]

The N-1's biggest issues were effects of vibration and heating on the closely clustered engines.  Certainly, computer simulation has made great strides in predicting these interactions, but I will point out that the interaction of 28 such powerful engines, their exhaust impingements, etc., gets closer and closer to chaotic.  And chaos theory is not a friendly taskmaster.

I agree that vibration and heating were big issues on N-1 but my impression is
that the worst issue was the fact that the engines on the 1st stage could only be
ignited once. This led to significant issues in the test plans., which meant that
the correctness of the plumbing and electrical wiring could not be verified
before launch.
This led to at least one case where an engine died on one launch and the S/W
sent the shutdown command to what was believed to be the opposite engine
so as to balance thrust but that shutdown command turned off a different set
of engines. Things cascaded from there as the S/W tried to correct for the
strange events that were occurring.

If a simple static fire had been possible a number of mistakes could have been
rectified before first flight. Who knows, just that one change may have seen
N-1 fly to orbit!

Carl

[envy887]

The N-1's biggest issues were effects of vibration and heating on the closely clustered engines.  Certainly, computer simulation has made great strides in predicting these interactions, but I will point out that the interaction of 28 such powerful engines, their exhaust impingements, etc., gets closer and closer to chaotic.  And chaos theory is not a friendly taskmaster.

I guess I'd be more likely to believe that the first SH stages will fly just fine had there been any 28-engine cluster test firings on the ground.  Heck, the F-1 engines on the Saturn V were designed to handle the radiant heat and vibration from their neighboring engines, but you'll notice that a kludge -- thick thermal batting -- was plastered onto the outside of those engine bells after initial clustered test firings indicated that the extra protection and thermal coating was required to bring the engines within desired safety parameters. Again, yes, there has been more than 50 years of advancement in computer simulations.  But the simulations are never any better than one's assumptions, and it was the sets of assumptions, and not failure of simulations, that caused the N-1 problems, and required a kludged-on layer of protection to be added onto the F-1s.

Besides, with the rather extreme replacement rate these Raptors seem to undergo during checkout and after static fires, once attached to the prototype Starships, it seems that the Raptors are also still in fairly early prototype stages themselves.  So, the performance assumptions for the current version of the Raptor may be even more poorly defined than you might think.

Personally, I'd rather see SH stages sit on that orbital test mount and fire up their clusters for full-duration tests before bothering to mount a Starship on top.  If for no other reason than to iron out all of the poorest assumptions before risking the loss of the R-Vacs that will likely be installed on any SS that gets put on top of an SH.  Of course, that would take several months and endanger his build/launch/test site unnecessarily, and it seems Musk is in enough of a hurry that he doesn't want to go through that whole process.  Still... even SpaceX might get surprised at the backlash if an SH blows up one or two km into the air.  Because that would be, shall we say... a significant RUD. 

The marginal risk-reduction value of static fire time decreases significantly as the test gets longer. They would probably get 80% of the set of data from a 5-second test that they would from a 2 minute test. On the other hand, the work to build a test stand and flame trench that can take a 2-minute firing is massively larger than building a pad for a 5 second test.

Also, this booster probably isn't being reflown, and the next one will be built in a few months. At some point, it's faster and simpler to fly it than to test it longer on the ground. That way they get flight data too.

[Robotbeat]

Agreed. A short static fire should help a lot.

[ChrML]

They'll probably won't even launch all Raptors at once - more like staggering them. All this within milliseconds of course. This to prevent resonances and other undesirable sh**. I think that this is not so much the problem. The problem will be more what happens when things go wrong. The software needs to be able to control 28 Raptors and handle any occurrence that might happen.

But then, SpaceX has repeatedly been flying 27 Merlins, so...

The software for this is the easy part. Any software can easily be simulated, and likely a full flight simulation of any combination of failures gets run every time someone commits code. Each test includes arrangements/inputs, something happening, and then asserting the expected outcome (a so called "theory" in the software world).

The hard part is getting the Raptor so reliable that firing 28 Raptors does not abort the launch every time due to some error. And accounting for mechanical stresses and resonances. And unknowns, and things not though about not accounted for in the software.

[Lars-J]

They'll probably won't even launch all Raptors at once - more like staggering them. All this within milliseconds of course. This to prevent resonances and other undesirable sh**. I think that this is not so much the problem. The problem will be more what happens when things go wrong. The software needs to be able to control 28 Raptors and handle any occurrence that might happen.

But then, SpaceX has repeatedly been flying 27 Merlins, so...

The software for this is the easy part. Any software can easily be simulated, and likely a full flight simulation of any combination of failures gets run every time someone commits code. Each test includes arrangements/inputs, something happening, and then asserting the expected outcome (a so called "theory" in the software world).

The hard part is getting the Raptor so reliable that firing 28 Raptors does not abort the launch every time due to some error. And accounting for mechanical stresses and resonances. And unknowns, and things not though about not accounted for in the software.

Yes. And they know this, better than *anyone*.

BTW this concern about 28 raptors is so very much like the talk around this forum 10-12 years ago for the Falcon 9. 9 engines!?!?! There was no way that SpaceX would be able to make the F9 reliable, nor would they be able to reliably start them...  They'll have to scrub so often that they would almost never launch on time.

I expect a campaign of test fires before the first orbital launch, with an increasing amount of engines. Just look at the Starship test vehicles. Does SpaceX strike you as a company reluctant to do static fires?

[Robotbeat]

Having 9 engines DID mean they had a lot of aborted liftoffs at first. After a few years, that was all forgotten and they almost never have them any more.

So that’s exact what I expect for 28 engines: difficulty at first but long-term no problem. Is this unreasonable?

[Welsh Dragon]

Having 9 engines DID mean they had a lot of aborted liftoffs at first.

Did they? Not being facetious but I genuinely don't remember many.

[DigitalMan]

I think there would have been a high probability of difficulty if SpaceX had started with SH, but because they have started with Starship, they have worked up from one engine to three, and have had many iterations on Raptor design at this point.

I expect a short learning curve for SH at this point.

[ugordan]

Having 9 engines DID mean they had a lot of aborted liftoffs at first.

Did they? Not being facetious but I genuinely don't remember many.

Did they ever... It felt like it was the order of the day back then. If the weather was perfect, the vehicle would abort with a 90% probability.

Here are just a few ones after a very quick search.





Back then the prospect of getting an FH off the ground seemed almost ludicrous.