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SpaceX SN9 Explodes on Landing

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Re: SpaceX SN9 Explodes on Landing

#191

Post by yellowapple »

jacquesm wrote: post #80
omgwtfbyobbq wrote: post #71

Can they relight sooner to improve their odds of landing successfully, or is the window for when they can relight relatively small? Or does it not matter because a few more seconds won't increase the chances they'll be able to relight?

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 tried it" explanation :)

Re: SpaceX SN9 Explodes on Landing

#193

Post by CydeWeys »

DennisP wrote: post #70
elmomle wrote: post #62

Earlier quoted context omitted.

Plenty of American rockets failed, especially early on! https://www.youtube.com/watch?v=13qeX98tAS8

And SpaceX has blown up ten Falcons on landing attempts.

After accomplishing their primary mission, which is a key distinction. If you blow up on landing that just means you lose your reuse discount on a future flight.

Re: SpaceX SN9 Explodes on Landing

#194

Post by CydeWeys »

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.

You're comparing a prototype against decades-old, non-reusable rockets.

Re: SpaceX SN9 Explodes on Landing

#195

Post by modeless »

I don't see how this could ever be as reliable as an airliner for passenger service as SpaceX has been talking about. An airliner can land safely with no engines and even no landing gear if necessary (and it sometimes is).

Re: SpaceX SN9 Explodes on Landing

#196

Post by yborg »

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.

I love that small pressurized tank flying around after the RUD like it's trying to find the rest of the booster...

Re: SpaceX SN9 Explodes on Landing

#197

Post by avmich »

bernulli wrote: post #188
bryananderson wrote: post #184

Earlier quoted context omitted.

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…

I’m not sure 3200 full scale tests of Saturn V’s F-1 engine, 2000 in an iterative trial-and-error scramble to suppress combustion instabilities is what I would call “overengineered to cut out iteration” during Apollo http://www.yang.gatech.edu/publications/Journal/JPP%20(1993,...

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.

Re: SpaceX SN9 Explodes on Landing

#198

Post by avmich »

HPsquared wrote: post #74
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…

The early days of the Soviet space program were similar - fast construction and iterative improvements with each successive test.

Soviet rocketry was developed in the artillery department. There iterations are normal. US rocketry was developed under Air Force - here more experienced pilots, lots of training...

Re: SpaceX SN9 Explodes on Landing

#199

Post by Retric »

modeless wrote: post #195

I don't see how this could ever be as reliable as an airliner for passenger service as SpaceX has been talking about. An airliner can land safely with no engines and even no landing gear if necessary (and it sometimes is).

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.

Initially it’s going to be risky, but give it say 50 years and it might actually end up being the safest option for ultra long distance travel.

Re: SpaceX SN9 Explodes on Landing

#200

Post by bernulli »

avmich wrote: post #197
bernulli wrote: post #188

Earlier quoted context omitted.

I’m not sure 3200 full scale tests of Saturn V’s F-1 engine, 2000 in an iterative trial-and-error scramble to suppress combustion instabilities is what I would call “overengineered to cut out iteration” during Apollo http://www.yang.gatech.edu/publications/Journal/JPP%20(1993,...

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.

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