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SpaceX SN9 Explodes on Landing

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Re: SpaceX SN9 Explodes on Landing

#241

Post by Retric »

modeless wrote: post #220
Retric wrote: post #199

Earlier quoted context omitted.

It’s total safety that’s important not individual aspects of safety. Clearly there are many disadvantages, but when comparing it to 15 hour flights there are several advantages. For example shorter flight times mean fewer chances for in flight human errors. Another is in flight medical emergencies can be more quickly reach a hospital. A few aircraft have been shot down which is again much less likely, etc etc. Initia…

One aspect can ruin the total safety. It can't be more safe than the least safe part of the trip. Sure, maybe in 50 years we'll figure out something better. But SpaceX is talking about flying long haul Earth to Earth routes with Starship, not a hypothetical future craft.

A 747 built 1970 is very different than a 747 built in 2020. Barring PR issues etc, SpaceX could be using an ever improving version of Starship for a very long time.

Re: SpaceX SN9 Explodes on Landing

#242

Post by Cogito »

GizmoSwan wrote: post #226
gridspy wrote: post #224

Earlier quoted context omitted.

737-Max crashed because of the "lets analyse this rather than test it" thinking that you described earlier. That and an overly cosy relationship with the FCC and a culture of silencing cautious engineering voices. It's seemed cheaper to tack larger engines and new software onto the old air-frame than to redesign the aircraft to be mechanically stable and update the cockpit. Not surprising that the same company (Boein…

Nope. A purposely designed aircraft is simulated is not one that is elongated with flight control data being patched. Example of how it works: https://www.darcorp.com/advanced-aircraft-analysis-software/ The bureaucracy had nothing to do with it. They did not want to spend the money to create a new craft. The long bodies aircraft was not airworthy physically speaking and so the software was designed to limit its pitc…

As pointed out in some other comments, SpaceX do extensive simulations, they almost certainly have the best rocket simulations in the world (see some of the published talks on youtube to see the state of their research).

We know that their simulations/calculations were excellent for these last couple of Starship tests because the tests themselves were excellent. There were a number of things being tested, including things like flying multiple Raptor engines, turning those engines off, switching between different fuel tanks for launching and landing, the bellyflop maneauver, the landing flip maneauver, engine relight from the header tank, and finally landing. Almost all of these were perfect, from what information we have.

There have been two failures, and from what we know these were not related to simulations at all - they seem to be system/integration issues, though we don't really know much about the engine failing to relight this test.

On SN8 they had a pressure issue feeding the engines from the header tanks. It may have been possible to anticipate this or test it independently, but it was probably the least important of all the things being tested. Given that they have multiple new (and updated!) test articles rolling off the production line they clearly made the choice to conduct the test without spending years trying to validate every single component. Again, they obviously did a lot of excellent engineering despite not undertaking a long pre-flight validation, as the test was so succesful.

Re: SpaceX SN9 Explodes on Landing

#243

Post by api »

unanswered wrote: post #117
api wrote: post #44

Earlier quoted context omitted.

Also keep in mind that it's already doing what pre-F9 rockets did: go up. The RUDs so far are on landing attempts. Landing is a whole lot harder.

Unfortunately it seems like traditional aerospace now has a very big lever to pull to get SpaceX shut down: public opinion following the reasoning "rocket go boom. go boom bad. rocket bad".

If that was going to work it would have already. SpaceX has been blowing up rockets for years.

Re: SpaceX SN9 Explodes on Landing

#244

Post by bryanlarsen »

hyperion2010 wrote: post #56

For both SN8 and SN9 my brain is screaming at me "surely they need more than 3 engines?!" Is the ultimate expectation that the engines will never fail, because it sure seems like they can't deal with losing even a single engine. I'm sure this is completely incorrect given that the issue for SN8 was tank pressure.

They only need 2 of the 3 engines to perform the landing flip and 1 of the 3 engines to perform the landing. So they do have some redundancy, and the computers were very likely programmed to light the third engine when the second failed. That this didn't happen was either due to debris from the second engine taking out the third during its failure or the failure being in a common area like the downcomers or that the third engine was still too hot -- the third engine was the one that was used to hover at apogee. Or some other reason.

Re: SpaceX SN9 Explodes on Landing

#245

Post by dan_hawkins »

jzer0cool wrote: post #93

(1) I think that is a "hard" landing ;) I say it it the mark. (2) The Question: I ain't no rocket scientist, but even if the engine failure had turned on, did the engines all just turn on quite late? Just trying here some crazy college physics so not sure if this checks out but, here goes. Again, just for fun. If it takes X: (summation of thrust) to fly that high over x seconds, then it would take the X + some at the…

In your calculations of speed you've forgotten about friction of air that at some point would stop further acceleration (terminal velocity.)

Re: SpaceX SN9 Explodes on Landing

#246

Post by simonh »

Cogito wrote: post #237
simonh wrote: post #234

Earlier quoted context omitted.

There's a key difference though, Starship is intended to carry people. The correct comparison for this isn't landing Falcon 9 boosters, it's landing crew capsules.

Falcon 9 was also intended to carry people. Starship is a more capable upper stage then Crew Capsule, part of which means that it can launch itself (at least suborbital). They aren't trying to qualify these prototypes as human-rated, they have to finish the design work first! For this pase of testing it's much more accurate to compare to Falcon 9 than Crew Capsule.

Oh come on, the Dragon capsule brings people back to the ground, not the first stage booster and it's landing these things that is the issue so far, not launching them.

All I am saying is that this vehicle, in it's final qualified form, will be landing human beings on the deck back here on Earth. That's the objective, so it's viability and reliability needs to be considered in that context.

For an F9 first stage a failure rate of 1/10 is fine. One out of 20 is outstanding. For Starship, these things are intended to carry a hundred paying passengers or more. The failure rate needs to be lower than 1 in a thousand. Much lower.

Re: SpaceX SN9 Explodes on Landing

#247

Post by sudosysgen »

naikrovek wrote: post #162
minikites wrote: post #159

Earlier quoted context omitted.

Why is SpaceX making the same mistakes 70 years later?

I don't recall NASA ever doing a rocket landing so I'm not sure which mistakes you are seeing repeated.

NASA and the USSR did many powered rocket landings, actually. NASA even had a program for reusable first stages via powered landings that was scrapped because automatic guidance wasn't feasible yet.

Re: SpaceX SN9 Explodes on Landing

#248

Post by sudosysgen »

alentist wrote: post #219
Layke1123 wrote: post #168

Earlier quoted context omitted.

No, I meant that the above response calling the other user wrong is wrong itself. The USSR, had it not had to fight a cold war against the US, could very well have been a much better system not just for space flight, but for a way to structure and run society in general. But yet, if I say this, I will be immediately downvoted because if I suggest that anything other than the established order in the US is the best sy…

> The USSR, had it not had to fight a cold war against the US, could very well have been a much better system not just for space flight, but for a way to structure and run society in general. What makes you think that? If they had such a wonderful "way to structure and run society in general", why did the USSR and its satellite states have to systematically mass murder people who wanted to leave this wonderful societ…

A significant reason why Stalin was able to successfully rise to power and why the Bolsheviks were able to secure total power is because of foreign violence and interference.

When all major foreign powers say that they wish for the destruction of your country and would openly prefer you to go back to more suffering, support for monsters like Stalin increases.

Equally, when the threat of invasion is as high as it was for the USSR from Britain and the US, a lot of money and power is invested in the military.

It's very possible that if it wasn't for massive foreign interference neither Stalin nor Trotsky would ever have been able to gain much power (both of them got their power from military conflict mainly, Stalin even moreso), the NKVD never would have gotten nearly as much funding, Lavrentiy Beria would probably have been put against the wall, and so on.

Re: SpaceX SN9 Explodes on Landing

#249

Post by Cogito »

simonh wrote: post #246
Cogito wrote: post #237

Earlier quoted context omitted.

Falcon 9 was also intended to carry people. Starship is a more capable upper stage then Crew Capsule, part of which means that it can launch itself (at least suborbital). They aren't trying to qualify these prototypes as human-rated, they have to finish the design work first! For this pase of testing it's much more accurate to compare to Falcon 9 than Crew Capsule.

Oh come on, the Dragon capsule brings people back to the ground, not the first stage booster and it's landing these things that is the issue so far, not launching them. All I am saying is that this vehicle, in it's final qualified form, will be landing human beings on the deck back here on Earth. That's the objective, so it's viability and reliability needs to be considered in that context. For an F9 first stage a fa…

I mostly agree with you, but I'm not sure on why you're focusing human passenger safety on this at this early development stage, as if it's somehow a reasonable thing to focus on.

Launching these things IS the issue so far, by far the main objective of these tests. Landing them would be nice, but the primary objectives are to launch the whole thing (in particular including aero surfaces and multiple engines, as compared to previous prototypes) and test the various novel maneauvres that they are attempting. That almost all the objectives are being met in these tests is a testament to how good SpaceX is getting at launching flying water tanks, and how hard the entire flight profile is to achieve (launch, belly flop, landing flip, landing).

In the anticipated human-rated version of Starship safety will be immensely important, but this is nowhere near being that thing! This was only the second prototype that even started to look like 'Starship'. We have no idea what a human-rated version would loook like, and a human-rated Starship is definitely not the objective of these tests.

The Starship prototypes they are testing at the moment are much much much closer to a Falcon 9 than a capsule. Specifically the systems and processes they are testing all have fairly direct parallels in Falcon 9, and almost no correspondence to a capsule. For example, Falcon 9 and Starship both have: super chilled propellent tanks, multiple large rocket engines, active flight control systems, engine relight, active aero surfaces, and powered landing. Starship and the capsule both have... heatshields?

Human passenger safety will be immensely important for Starship, but to focus on it at this stage of development would be immensely premature.

Re: SpaceX SN9 Explodes on Landing

#250

Post by jjoonathan »

ricardobeat wrote: post #136
jjoonathan wrote: post #98

Earlier quoted context omitted.

Of course proving a simple design and sticking with it is safer! Not going to space and being content with remaining on the ground is safer still! Water is wet! The sky is blue! We can all see what happened: the soviets stopped spending money on innovation and tried to re-frame their stagnation as operational brilliance. Sure, Soyuz has a reliability niche, and I'd rather ride on it too, but I'd rather fund efforts t…

Aren't solid boosters, like those used by the Shuttle, a simpler design than liquid engines? On top of that, the Raptor engines used in the Starship, which seem to be considered state-of-the-art, are based on a soviet design from the 60s.

Raptors are state of the art. They are based on a soviet design from the 60s in the same way that they are based on US designs from the 60s.

It's weird that people seem so keen to talk up the soviet part and talk down the US part.

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