Author Topic: Starship!  (Read 8512 times)

Offline JayUtah

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Re: Starship!
« Reply #195 on: April 01, 2021, 04:29:31 PM »
I guess it's applicable to both.  Yes, the telemetry is vital.  But so is visual inspection of the wreckage.  The telemetry tells you, for example, that pressure in various parts of the system fell below expected levels.  But physically looking at the pipes tells you where the leak happened, and maybe gives you clues to why.
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Offline raven

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Re: Starship!
« Reply #196 on: April 01, 2021, 06:48:56 PM »
As we discovered in the theater, water fog can do a number on radio communications in certain bands, even in very small amounts.  So it doesn't surprise me that the video might have dropped out while the telemetry (ostensibly on a more robust frequency, and with data integrity checks in place) soldiered on.

The engine anomaly looks like it starts at around T+18, although the sudden deflagration doesn't occur until a few seconds later.  It looks to me like a fitting might have opened up.  The bright spots around the solid piping indicates the flame is hitting with considerable velocity, which then indicates a leak in high-pressure flow.  Unclear whether that relates to the ultimate explosion.  As Musk says, they won't know until they pick through the "bits."  Even well into the 21st century, sifting through wreckage is still part of the job.

The bits of the rocket? Or the bits of the telemetry data?
Both, I am guessing. Interesting that the debris field is mostly in one direction.

Offline JayUtah

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Re: Starship!
« Reply #197 on: April 02, 2021, 12:26:11 PM »
Debris-field dispersal has always fascinated me, in a morbid sort of way.  I've always admired the professional debris-dispersal analysts.  It seems at first glance like reading tea leaves.  But these guys really do have insightful ways of plotting backwards from debris positions and conditions to initial-failure scenarios.  You consider that heavy things like engine thrust chambers fall ballistically while drag-sensitive structures like nosecones are more susceptible to aerodynamic effects.

A second look at the skirt video convinces me that the engine we saw enveloped in flame was shedding hot metal.  The "sparks" are a combination of hot metal being ejected and high-temperature impingement on nearby surfaces.  (You see this in Apollo film of the Saturn V interstage jettison.  As it ventures into the J-2 plumes, the impingement shows up as markedly incandescent.). But some points of light can't be explained by impingement.  They are pieces of engine, piping, or structure being eroded by hot gas flow.

Since the kaboom happened so very shortly after engine relight, I'm guessing the sick engine failed.  The problem with that is the plumbing.  As others have pointed out, the Raptor operates at obscene chamber pressures.  That has to be echoed in propellant-feed systems, which also have to maintain high pressure.  If an engine separates entirely from the propellant feed system, you get a rapid loss of pressure in the propellant tanks.  If the vehicle structure relies on pressure in the tanks, the vehicle is likely to rupture and release propellant.  This is even more likely when the vehicle is under tremendous aerodynamic stress -- intentional or otherwise.

Another thing that can happen in high pressure engines is that once the feed pressure is gone, combustion fronts can race up the propellant lines and find their way to a more relatively enclosed component like a tank or an accumulator, resulting in a detonation instead of a mere deflagration.  The smoking gun here is the methane header tank, which was found in two pieces quite a ways apart.  This indicates that each half was on a different side of a high-energy event, like an explosion.  So whatever the root cause was, I'm betting the kaboom was in the methane header tank.
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Offline Zakalwe

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Re: Starship!
« Reply #198 on: April 03, 2021, 07:04:22 AM »
As we discovered in the theater, water fog can do a number on radio communications in certain bands, even in very small amounts.  So it doesn't surprise me that the video might have dropped out while the telemetry (ostensibly on a more robust frequency, and with data integrity checks in place) soldiered on.

The engine anomaly looks like it starts at around T+18, although the sudden deflagration doesn't occur until a few seconds later.  It looks to me like a fitting might have opened up.  The bright spots around the solid piping indicates the flame is hitting with considerable velocity, which then indicates a leak in high-pressure flow.  Unclear whether that relates to the ultimate explosion.  As Musk says, they won't know until they pick through the "bits."  Even well into the 21st century, sifting through wreckage is still part of the job.

The bits of the rocket? Or the bits of the telemetry data?

Both.
And in both cases I suspect that there are a lot of bits!  ;D
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Offline bknight

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Re: Starship!
« Reply #199 on: April 04, 2021, 05:37:04 PM »
As we discovered in the theater, water fog can do a number on radio communications in certain bands, even in very small amounts.  So it doesn't surprise me that the video might have dropped out while the telemetry (ostensibly on a more robust frequency, and with data integrity checks in place) soldiered on.

The engine anomaly looks like it starts at around T+18, although the sudden deflagration doesn't occur until a few seconds later.  It looks to me like a fitting might have opened up.  The bright spots around the solid piping indicates the flame is hitting with considerable velocity, which then indicates a leak in high-pressure flow.  Unclear whether that relates to the ultimate explosion.  As Musk says, they won't know until they pick through the "bits."  Even well into the 21st century, sifting through wreckage is still part of the job.

The bits of the rocket? Or the bits of the telemetry data?

Both.
And in both cases I suspect that there are a lot of bits!  ;D
Indeed. 
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Offline smartcooky

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Re: Starship!
« Reply #200 on: April 04, 2021, 08:10:52 PM »
Much as I am a keen supporter of SpaceX, I am just beginning to wonder if the Raptor Engine with its Full-flow staged combustion is just too damned complex, especially as its powered by methane & liquid oxygen.

AFAIK, the Raptor is the first FFSC engine to use methalox. Are SpaceX biting off more the they can chew, trying to do something that has never been tried before (the relight & flip landing maneuver) using an engine type that has never been tried before?
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Offline raven

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Re: Starship!
« Reply #201 on: April 04, 2021, 09:19:32 PM »
Much as I am a keen supporter of SpaceX, I am just beginning to wonder if the Raptor Engine with its Full-flow staged combustion is just too damned complex, especially as its powered by methane & liquid oxygen.

AFAIK, the Raptor is the first FFSC engine to use methalox. Are SpaceX biting off more the they can chew, trying to do something that has never been tried before (the relight & flip landing maneuver) using an engine type that has never been tried before?
Not a few people thought the same of landing the first stage. I have a feeling if you give them enough time to iterate, they'll solve the problems.
But I am optimistic that way.

Offline molesworth

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Re: Starship!
« Reply #202 on: April 05, 2021, 05:31:05 AM »
Much as I am a keen supporter of SpaceX, I am just beginning to wonder if the Raptor Engine with its Full-flow staged combustion is just too damned complex, especially as its powered by methane & liquid oxygen.

AFAIK, the Raptor is the first FFSC engine to use methalox. Are SpaceX biting off more the they can chew, trying to do something that has never been tried before (the relight & flip landing maneuver) using an engine type that has never been tried before?

Like raven I'm optimistic that the problems can and will be solved.  It is a complex design, but if you look at it as an incremental step from existing designs it's only pushing a few new boundaries (although admittedly pushing them hard).

Borrowing a phrase from a previous push to space - "We do these things not because they are easy but because they are hard".  I think this applies here too, and looking at the challenges of getting to the Moon and Mars with regular, cheap and reusable launch systems, the easy options just aren't going to make it.
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Offline Zakalwe

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Re: Starship!
« Reply #203 on: April 05, 2021, 06:49:13 AM »
Much as I am a keen supporter of SpaceX, I am just beginning to wonder if the Raptor Engine with its Full-flow staged combustion is just too damned complex, especially as its powered by methane & liquid oxygen.

AFAIK, the Raptor is the first FFSC engine to use methalox. Are SpaceX biting off more the they can chew, trying to do something that has never been tried before (the relight & flip landing maneuver) using an engine type that has never been tried before?

Is there a viable alternative for a reusable Mars bound craft that will use ISRU for re-fuelling?

What they are doing has never been done before. That doesn't mean that their approach is flawed (how many times did the F-1 engine explode due to combustion chamber instabilities?). There's nothing in the laws of physics that deems what they are trying to do impossible, so it's an engineering problem. A challenging one, but one that I am sure they will overcome.
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Offline cjameshuff

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Re: Starship!
« Reply #204 on: April 05, 2021, 10:44:42 AM »
They've had what, two engine failures in four prototype test flights with 12 ignitions and 9 relight attempts, one of them just being a failure to start? And all four test flights performing a complete ascent burn, with the final engine running for about the same duration as a booster engine's launch burn. And on one flight the landing burn starved an engine of fuel leaving it oxygen-rich and short on cooling, and on another the fuel turbopump ingested helium, both cases just resulting in loss of thrust.

The Raptors are doing fine. It's not reasonable to expect the system in its current state to operate with high reliability, especially when doing something that no other rocket does. Things are going to break or fall short of the desired performance...this would happen even if the Raptors were perfect, because their performance is fundamentally tied to the performance of the propellant systems, which are extremely experimental.

As for this latest failure:
Quote from: Elon [email protected]
Ascent phase, transition to horizontal & control during free fall were good.

A (relatively) small CH4 leak led to fire on engine 2 & fried part of avionics, causing hard start attempting landing burn in CH4 turbopump.

This is getting fixed 6 ways to Sunday.

Offline jfb

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Re: Starship!
« Reply #205 on: April 05, 2021, 01:04:00 PM »
Yeah, so far most of the issues haven't been with the Raptors so much as the plumbing - making sure they have good pressure during and immediately after the flip.  If they were doing the Grasshopper thing and going straight up and coming straight back down, they'd likely have nailed it on the first try with SN8.  But that rapid transition from horizontal to vertical just after ignition is causing issues with fuel pressure/flow. 

No doubt there are still issues with the engines themselves, but like cjameshuff pointed out, the ascent phase has gone well in all the flights. 

SN15 is supposed to have a bunch of improvements and redesigned components, so it may survive.  I expect they'll blow up a few more before they figure this out. 

Offline raven

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Re: Starship!
« Reply #206 on: April 05, 2021, 08:06:29 PM »
Much as I am a keen supporter of SpaceX, I am just beginning to wonder if the Raptor Engine with its Full-flow staged combustion is just too damned complex, especially as its powered by methane & liquid oxygen.

AFAIK, the Raptor is the first FFSC engine to use methalox. Are SpaceX biting off more the they can chew, trying to do something that has never been tried before (the relight & flip landing maneuver) using an engine type that has never been tried before?

Like raven I'm optimistic that the problems can and will be solved.  It is a complex design, but if you look at it as an incremental step from existing designs it's only pushing a few new boundaries (although admittedly pushing them hard).

Borrowing a phrase from a previous push to space - "We do these things not because they are easy but because they are hard".  I think this applies here too, and looking at the challenges of getting to the Moon and Mars with regular, cheap and reusable launch systems, the easy options just aren't going to make it.
Certainly not on a long term basis. A flag and foot prints mission, a 'camping trip' as I like to call it, is far simpler logistically than setting up for long term exploration and habitation, but it also means the effort is somewhat 'thrown away' after.

Offline jfb

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Re: Starship!
« Reply #207 on: May 05, 2021, 06:43:17 PM »
SN15 flight seems to have been successful - flew, flipped, landed, and it hasn't blown up yet.  Scary fire under the skirt after landing that took a long time to put out, but ... success?

Offline raven

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Re: Starship!
« Reply #208 on: May 05, 2021, 08:35:22 PM »
Definitely a giant leap. I am sure they will work out the kinks in the next steps.

Offline Count Zero

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Re: Starship!
« Reply #209 on: May 06, 2021, 08:05:01 AM »
Definitely a giant leap. I am sure they will work out the kinks in the next steps.

Like the video downlink?  ;)
"What makes one step a giant leap is all the steps before."