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SpaceX SN9 Explodes on Landing

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Re: SpaceX SN9 Explodes on Landing

#201

Post by avmich »

HarryHirsch wrote: post #158
twicetwice wrote: post #156

Earlier quoted context omitted.

I'm sorry, what? SpaceX are the undisputed champions of re-lighting engines. They've landed orbital rockets 73+ times, each of which involves multiple engine re-lights while falling through the atmosphere. Let alone gets it wrong "with regularity" — the Falcon 9 Block 5 is a remarkably reliable rocket. Anyway, landing Starship involves a bunch of things never before attempted: landing a fully-reusable second stage, l…

Today's crash was due to failure of one engine to restart. Briz and Fregat Russian upper stages are routinely restarted, with ~ 98 % success, same with Ariane EPS and Chinese Yuanzheng. It's doable, just not for Space-X.

Briz and Fregat start much smaller - 20 kN - engines with no time constraints, while Starship re-lights 2200 kN engine and rocket immediately does rotation by 90+ degrees, and time is of essence.

Re: SpaceX SN9 Explodes on Landing

#202

Post by WalterBright »

consumer451 wrote: post #176

Here is my favorite footage so far, by Cosmic Perspective: https://www.youtube.com/watch?v=Ep8XJanoFgw This is 4k slow motion and it is gorgeous. The giant sheets of stainless steel floating down at the end are noteworthy, among other details. Michael Bay has nothing on Cosmic Perspective + SpaceX.

The sheets of stainless steel appear to have separated at the joints. This says the sheets are stronger than the joints, meaning they're overweight :-)

Re: SpaceX SN9 Explodes on Landing

#203

Post by avmich »

yellowapple wrote: post #191
jacquesm wrote: post #80

Earlier quoted context omitted.

That's a good question actually, given that they had another engine as well. Or maybe light up all three and then shut down the one they decide not to use. But these are all in the 'why don't they' category, SpaceX has some pretty clever cookies, experts in their field, the chances that anything we can think of has not been thought of by them are nil.

I'm reminded of the story of two economists walking down the street. One sees a dollar bill on the ground, and the other decides "that can't be right; if there was a dollar bill on the ground someone would've picked it up already". Not saying that a bunch of random folks on HN are seeing dollar bills in this analogy, but I've never quite been satisfied with the "if we're thinking of it then they probably already trie…

> but I've never quite been satisfied with the "if we're thinking of it then they probably already tried it" explanation :)

Same here :) . I'm still unhappy with their decision to use toxic propellants on Crew Dragon - I'm sure they could use something much more benign.

Re: SpaceX SN9 Explodes on Landing

#204

Post by WalterBright »

bryananderson wrote: post #184
cmoscoe wrote: post #52

Earlier quoted context omitted.

On the 'repeated failures' piece, that's somewhat new for aerospace. Traditionally, things would be over-engineered, and losing a test vessel would be considered a bad thing. SpaceX seems very content to blow up a bunch of rockets on their way towards not blowing up rockets. This seems to have caused at least part of their recent issues with the FAA, who seem to be less ok with explosions. It will be very interesting…

It’s really a throwback to the old days of aerospace. From the 1930s to the early 1960s, the standard method was to iterate rapidly with relatively cheap hardware, to learn and fix problems as quickly as possible. The von Braun and Korolev teams operated this way, among others. They all blew up a ton of rockets. What changed was the necessity of completing Saturn V and landing on the Moon by the end of the 1960s. Apo…

The acceleration of aerospace development costs started long before the Apollo program.

Re: SpaceX SN9 Explodes on Landing

#205

Post by onethought »

gridspy wrote: post #110
BurningFrog wrote: post #87

I'm very impressed by how it's coasting on the fins down the atmosphere. I had never even heard that idea discussed before I saw SN8 do it. Of course, they'll have to land some other way on Mars or the Moon.

Fortunately the force of gravity is much lower on both these bodies so I imagine the belly flop becomes less important. On earth it's also about spreading the heat of reentry over a larger area. Fortunately on Mars (I believe that) the heat of reentry is even less of an issue than here on Earth.

Is that right... at orbital velocity I think Mars entry is a problem.

Are they planning on landing starships on earth? with Orbital refuelling couldn't they just land it like a Falcon 9 (I mean I guess that'd be super inefficient)

Re: SpaceX SN9 Explodes on Landing

#206

Post by WalterBright »

bernulli wrote: post #200
avmich wrote: post #197

Earlier quoted context omitted.

That's just one engine - much less than a 5-engine stage even on a test stand, not to say about flying. And combustion instabilities they were fighting were rather novel at the time, the engineers basically had no other options than to test a lot of variants - and invent debugging techniques with "bombs in the chamber" along the way. Fortunately it worked - low pressure of F-1 helped to mitigate problems of size.

I don’t understand your first paragraph - is this related to the F-1 development having strong iterative components? Also, Combustion instabilities date back to at least the A4/V2, not quite new, and largely the same engineers.

The F1 is a bigger (!!) version of the same engine. It's got the same crucial features:

1. turbo-pumps

2. the nozzle is cooled and the fuel warmed by making the nozzle out of tubes through which the fuel passed

3. holes drilled in the tubes so fuel leaked into the combustion chamber to provide boundary layer cooling

I think the pogo-ing was solved the same way, too - putting baffles in in various places.

Re: SpaceX SN9 Explodes on Landing

#207

Post by bernulli »

WalterBright wrote: post #206
bernulli wrote: post #200

Earlier quoted context omitted.

I don’t understand your first paragraph - is this related to the F-1 development having strong iterative components? Also, Combustion instabilities date back to at least the A4/V2, not quite new, and largely the same engineers.

The F1 is a bigger (!!) version of the same engine. It's got the same crucial features: 1. turbo-pumps 2. the nozzle is cooled and the fuel warmed by making the nozzle out of tubes through which the fuel passed 3. holes drilled in the tubes so fuel leaked into the combustion chamber to provide boundary layer cooling I think the pogo-ing was solved the same way, too - putting baffles in in various places.

By that logic essentially all cryogenic engines are “the same”.

Re: SpaceX SN9 Explodes on Landing

#208

Post by laverya »

WalterBright wrote: post #202
consumer451 wrote: post #176

Here is my favorite footage so far, by Cosmic Perspective: https://www.youtube.com/watch?v=Ep8XJanoFgw This is 4k slow motion and it is gorgeous. The giant sheets of stainless steel floating down at the end are noteworthy, among other details. Michael Bay has nothing on Cosmic Perspective + SpaceX.

The sheets of stainless steel appear to have separated at the joints. This says the sheets are stronger than the joints, meaning they're overweight :-)

I was thinking something similar myself (more on weld quality, "welds should be as strong as the rest of the material"), but then I realized that this doesn't matter, and having an unoptimized test vehicle a week earlier is always going to be the better option for SpaceX.

1. Is it light enough to fly?

2. Is it strong enough to not cause a failure?

#shipit

Re: SpaceX SN9 Explodes on Landing

#209

Post by MPSimmons »

cmoscoe wrote: post #52
rglover wrote: post #28

Love seeing these tests for two reasons: 1.) Experiencing history in the making, especially knowing that the SpaceX team will eventually get it right. 2.) Realizing that even the best of the best have repeated failures and need to rely on iteration to get "there."

On the 'repeated failures' piece, that's somewhat new for aerospace. Traditionally, things would be over-engineered, and losing a test vessel would be considered a bad thing. SpaceX seems very content to blow up a bunch of rockets on their way towards not blowing up rockets. This seems to have caused at least part of their recent issues with the FAA, who seem to be less ok with explosions. It will be very interesting…

You're basically watching the CI/CD workflow for the best aerospace organization in the world, live on YouTube.

Re: SpaceX SN9 Explodes on Landing

#210

Post by avmich »

GizmoSwan wrote: post #185
gridspy wrote: post #174

Earlier quoted context omitted.

The failures so far relate to the pressurization of the header tanks and the engine performance on re-light (hard problems). I imagine these will be well solved after 100 flights. The assumption that shifting payload is going to boggle the flight computers leading to loss of craft sounds unlikely. Both because the payload will be secured and the flight computers are more dynamic than that. Finally, the forces on the…

747 can not flip like that; it would stall and crash. The narrow bodied 737s crashed for less. Their fancy flight computer miscalculated because of center of gravity miscalculations. They crashed after 100s of flights. I like your optimism. Good luck. I mean it. I would not fly in that thing even if they paid me a million. Sorry for my lack of faith.

Big airliners do parabolic arcs - "vomit comet", so it's not a huge problem. 737 MAX crashed for different reasons. E.g. Soyuz capsule returns safely despite different loads and different distributions of mass - control systems, even relatively modest ones, can compensate. It's failures which provide most useful information about shortcomings of the system at some point, so they are welcome during testing - if you think that at this point they shouldn't explode, you'd better bring good arguments. Shuttle had much better aerodynamic shape than Starship, and their landing modes are different.
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