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

[Lars-J]

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.

Your feelings are no substitute for data. Do you have anything other than 3 instances? That 90% probability figure is ludicrous. There were teething issues in the first few flights, but after that the engine failure ratio was not significantly different than other new LVs with new engines. And now I can't even recall the last launch abort due to an engine issue - can you?

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

To some. To others the reduction in F9 engine start issues over time made it quite likely that it would not be a significant issue.

And that is my point. Now we have 28 (gasp!) engines, and shouts of "this is such a hard problem so why doesn't anyone tell SpaceX they don't know it yet?" (paraphrased) are rearing their heads again.

[RedLineTrain]

We have a thread for that data.  No need for handbags.

https://forum.nasaspaceflight.com/index.php?topic=36507.0

[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.

Your feelings are no substitute for data. Do you have anything other than 3 instances? That 90% probability figure is ludicrous.

Dude, chill. I lived through the era of the v1.0 and the initial v1.1s. No, I'm not going to waste time bringing up more pad aborts from then just to prove a point. And in case you didn't realize, that "90% probability" was tongue-in-cheek, as in the feeling (oh no, there goes that word again) of back in the day.

There were teething issues in the first few flights, but after that the engine failure ratio was not significantly different than other new LVs with new engines. And now I can't even recall the last launch abort due to an engine issue - can you?

Did I, at any point imply that the abort issues were not resolved eventually? My point was the "first few flights" spanned from 2010 to something like mid 2014 given the flight rate back then.

And who said anything about "engine failure ratio" in the first place? Your words. From what I remember from that time, the majority of the aborts were due to too conservative parameter settings rather than HW issues, but I guess that must have been a feeling as well.

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

To some. To others the reduction in F9 engine start issues over time made it quite likely that it would not be a significant issue.

What part of "back then" did you not comprehend?

It always amuses me that still, to this day, even mentioning the fact that SpaceX had it a bit rough in the early F9 days will trigger a defensive knee-jerk reaction on this forum from someone, with a 100% probability (this one is not tongue-in-cheek).

[electricdawn]

Let's chill down a bit. I think both of you are getting a bit defensive now.

SpaceX is no god of machinery, but they have some of the best engineers in the business. They will sort it out eventually.

[Robotbeat]

It’s perfectly foreseeable that SpaceX will likely have some headaches related to getting 28 Raptors going. Just like they did with Falcon 9. Raptor doesn’t seem extremely mature, yet (not that we should expect it to be... it takes hundreds of engines to really get it down).

I both have no doubt they’re going to get Starship to orbit and no doubt that there’s a lot of work to do it.

I don’t feel the need to convince any one. I’ll just point back at this and say, I told you so.

SpaceX knows this. It’s not a mystery to them, either. They’ll attack it and get it solved. I’m not worried in the least, and I give it better than even odds of beating SLS to orbit.

[RedLineTrain]

No doubt there will be tons of scrubs and we'll have a few threads about how SpaceX will never get this right.

But I'm not sure that the engines will be the cause of the majority of scrubs.  There's a smorgasbord of things that will be not quite right.

[RAN]

The relationship between engine counts and scrub chance / reliability to orbit seems similar to highly available software systems that are either sequential or k out of n parallel. A larger engine count will likely lead to higher scrub rate but also a higher reliability for reaching orbit.

Comparing engine counts of 9 and 28 and assume an individual engine has a 99% reliability (both during startup sequence and between startup and nominal engine cutoff).

For 9 engines requiring 9 to be green during startup to avoid a scrub, launches have a 8.6% scrub rate (1 - .99^9).

For 28 engines requiring 28 to launch, 24.5% scrub rate (1 - .99^28).

However during flight, we can still make orbit after losing 1 out of 9 (Falcon 9 has done this) or 3 out of 28 engines (assumption for Superheavy).

For 9 engines requiring 8+ to reach orbit, success rate is 99.65%

For 28 engines requiring 25+ to reach orbit, success rate is 99.98%

I used sequential and k out of n formulas from here: https://web.cortland.edu/matresearch/SerieslParallelSTART.pdf

[AstroWare]

The relationship between engine counts and scrub chance / reliability to orbit seems similar to highly available software systems that are either sequential or k out of n parallel. A larger engine count will likely lead to higher scrub rate but also a higher reliability for reaching orbit.

Comparing engine counts of 9 and 28 and assume an individual engine has a 99% reliability (both during startup sequence and between startup and nominal engine cutoff).

For 9 engines requiring 9 to be green during startup to avoid a scrub, launches have a 8.6% scrub rate (1 - .99^9).

For 28 engines requiring 28 to launch, 24.5% scrub rate (1 - .99^28).

However during flight, we can still make orbit after losing 1 out of 9 (Falcon 9 has done this) or 3 out of 28 engines (assumption for Superheavy).

For 9 engines requiring 8+ to reach orbit, success rate is 99.65%

For 28 engines requiring 25+ to reach orbit, success rate is 99.98%

I used sequential and k out of n formulas from here: https://web.cortland.edu/matresearch/SerieslParallelSTART.pdf

Does anyone care to speculate on if SpaceX will have to do opposing-pair shutdowns like N1? Especially for engine loss of the outer ring. (That would affect the calculations above)

Falcon doesn't because it can compensate by gimballing and throttling. Plus the much smaller diameter of the stage means less torque from the engine loss.

SH central cluster can gimbal, but the outer ring I believe is still planning to be non-gimballing. I don't remember if they are fixed or variable thrust but I'd assume they would keep them throttlable. Perhaps that is enough? Obviously it is better if they don't have to shutdown healthy engines...

Just curious!

[Robotbeat]

I don't think they'll do opposing pairs. That's a pretty primitive approach that you do if you're not throttling and can't gimbal any engines.

They might do it if they lose so many on one side that the angle of attack of the rocket with respect to the airstream becomes so extreme that there are structural issues.

[chopsticks]

Just a reminder though that R-boost will not throttle either. So it would be either to shut down the opposing engine or to have the centre engine gimbal to compensate. I suspect the latter will probably work given the extreme amount of gimbaling the Raptors are capable of.

[TorenAltair]

Might we come back to this specific mission, please? I think general technical discussions can find a lot of threads further down the forum.

[DreamyPickle]

Having on 28 engines on the same booster might make this simple than in the Falcon Heavy case because you don't have to worry about stressing the connections between boosters.

Also the N-1 was just one example of a many-engined rocket from 50 years ago. Similarities exist with the SuperHeavy but they're weak.

Remember how people kept bringing up the Space Shuttle as proof that Falcon 9 reusability can't work? Most of the shuttle's problems were actually specific to the shuttle itself and don't apply to reusable vehicles in general.

[realnouns]

Might we come back to this specific mission, please? I think general technical discussions can find a lot of threads further down the forum.

Do we know that the first Superheavy booster flight will feature all 28 engines?
Also, does Starship's non-vacuum engines get used at all during flight, or just landing?

[Lars-J]

Do we know that the first Superheavy booster flight will feature all 28 engines?

No, we do not know.

Also, does Starship's non-vacuum engines get used at all during flight, or just landing?

Yes the non-vacuum Raptors are used during ascent, they are the only main engines that can gimbal/steer. They are also needed for thrust-weight ratio reasons. All 6 Raptors will ignite after staging.

[AC in NC]

All 6 Raptors will ignite after staging.

Opinion or fact?     But I like the optimism and am pulling for you being right.

[ThePonjaX]

All 6 Raptors will ignite after staging.

Opinion or fact?     But I like the optimism and am pulling for you being right.

I like the idea of this been the first time we're going to see the vacuum raptor in action 

[chopsticks]

All 6 Raptors will ignite after staging.

Opinion or fact?     But I like the optimism and am pulling for you being right.

How could it be done otherwise and why? It just seems obvious to me that's what they would do. HOPEFULLY, all 6 will ignite and not just 4 or 5!

[Steven Pietrobon]

All 6 Raptors will ignite after staging.

Opinion or fact?     But I like the optimism and am pulling for you being right.

Simulations show that three sea level Raptors on the second stage are sufficient to perform the flight. Whether SpaceX will add the three vacuum Raptors, we do not know.

[Zed_Noir]

All 6 Raptors will ignite after staging.

Opinion or fact?     But I like the optimism and am pulling for you being right.

How could it be done otherwise and why? It just seems obvious to me that's what they would do. HOPEFULLY, all 6 will ignite and not just 4 or 5!

Yeah. Don't think there is a current vacuum test chamber that is rated for 3 Vacuum Raptors & 3 sea level Raptors together. The inaugural Super Heavy orbital flight will permit SN20 to be a relatively cheap flying engine test stand.

[realnouns]

Do we know that the first Superheavy booster flight will feature all 28 engines?

No, we do not know.

Depending if they're trying to actually land this thing on Phobos/Deimos, that's a lot of Raptor engines to dump in the ocean