POGO: The 63-Year-Old Problem Threatening Starship's Success

[JaimeZX]

That's the thing I was disagreeing with Jim about.  I think it needs at least one RSL burning at minimum throttle. 

The relevant tweets circa 2019...

More about dealing with failure modes & roll control[/b]

You can't do roll control without two gimbaling engines, can you?

Sure. You don't have to have all the engines pointed in the same exact direction. Cant them off 5 degrees this way and that and differential throttling could give you roll control.

Doh!  We have a winner.  I don't know what I was thinking with the swirl thing.   

If you have four or six engines then you alternate each one off by N degrees, then again it's the same control algorithm as yawing a quadcopter or hexacopter (which does it by arranging the blade rotation in alternating directions).

With just two or three fixed engines, you don't have enough degrees-of-freedom to control pitch, roll, yaw and throttle independently. The minumum number of engines is four, unless you want to get into a complex and fascinating part of control theory called underactuated systems....   

Well. Interesting but it doesn't look good for any crew. 

[litton4]

That's the thing I was disagreeing with Jim about.  I think it needs at least one RSL burning at minimum throttle. 

The relevant tweets circa 2019...

More about dealing with failure modes & roll control[/b]

You can't do roll control without two gimbaling engines, can you?

Sure. You don't have to have all the engines pointed in the same exact direction. Cant them off 5 degrees this way and that and differential throttling could give you roll control.

Doh!  We have a winner.  I don't know what I was thinking with the swirl thing.   

If you have four or six engines then you alternate each one off by N degrees, then again it's the same control algorithm as yawing a quadcopter or hexacopter (which does it by arranging the blade rotation in alternating directions).

With just two or three fixed engines, you don't have enough degrees-of-freedom to control pitch, roll, yaw and throttle independently. The minumum number of engines is four, unless you want to get into a complex and fascinating part of control theory called underactuated systems....   

Well. Interesting but it doesn't look good for any crew. 

[InterestedEngineer]

Oh dear, it wasn't POGO

Flight 8 report is up:

https://www.spacex.com/updates/#flight-8-report

TLDR:
- Booster engines did not relight b/c of igniter heat issues. They reproduced it and have a mitigation in.

- Ship engine failure details:
"hardware failure in one of the upper stage’s center Raptor engines that resulted in inadvertent propellant mixing and ignition. Extensive ground testing has taken place since the flight test to better understand the failure, including more than 100 long-duration Raptor firings at SpaceX’s McGregor test facility"

Fixes include "additional preload on key joints, a new nitrogen purge system, and improvements to the propellant drain system. Future upgrades to Starship will introduce the Raptor 3 engine which will include additional reliability improvements to address the failure mechanism."

Flight 8 failure is not the same as Flight 7. Flight 7 fixes addressed the issues of harmonic response.

[steveleach]

Oh dear, it wasn't POGO

That's an awful lot of time and mental energy that's been spent unnecessarily by the community on guessing why the flight 8 changes didn't fix the problem, and what to do about it.

I guess we can consider it time well spent as it kept us entertained while not a lot seemed to be happening.

[BN]

Oh dear, it wasn't POGO

That's an awful lot of time and mental energy that's been spent unnecessarily by the community on guessing why the flight 8 changes didn't fix the problem, and what to do about it.

I guess we can consider it time well spent as it kept us entertained while not a lot seemed to be happening.

so what will the community think if ship explodes again on a similar timeframe next week.

[steveleach]

Oh dear, it wasn't POGO

That's an awful lot of time and mental energy that's been spent unnecessarily by the community on guessing why the flight 8 changes didn't fix the problem, and what to do about it.

I guess we can consider it time well spent as it kept us entertained while not a lot seemed to be happening.

so what will the community think if ship explodes again on a similar timeframe next week.

Well, if it happens again then it is clearly a Blue Origin sniper at work.

[mn]

It's also possible that the flight 7 fix somehow introduced new stresses on the engine.

[MonceMark]

OMG; /=POGO!; SMH

[equiserre]

It's also possible that the flight 7 fix somehow introduced new stresses on the engine.

Hasnt this thread demonstrated that absolute Wild speculation with zero data is not useful or fun?

[InterestedEngineer]

It's also possible that the flight 7 fix somehow introduced new stresses on the engine.

Hasnt this thread demonstrated that absolute Wild speculation with zero data is not useful or fun?

I'm having fun.  Why aren't you?

The video was education, so it was also useful, even though it was wrong

[catdlr]

It's also possible that the flight 7 fix somehow introduced new stresses on the engine.

Hasnt this thread demonstrated that absolute Wild speculation with zero data is not useful or fun?

I'm having fun.  Why aren't you?

The video was education, so it was also useful, even though it was wrong

ZACK talks about the POGO video he made and the onslaught of comments he got on it. 

On today's FLAMETRENCH episode  (1:18:25)
https://www.youtube.com/live/ADw63JI9Ook#t=4705s

[BN]

Oh dear, it wasn't POGO

That's an awful lot of time and mental energy that's been spent unnecessarily by the community on guessing why the flight 8 changes didn't fix the problem, and what to do about it.

I guess we can consider it time well spent as it kept us entertained while not a lot seemed to be happening.

so what will the community think if ship explodes again on a similar timeframe next week.

Well, if it happens again then it is clearly a Blue Origin sniper at work.

I think Elon did at one point entertain the possibility of a ULA laser blowing up Zuck's satellite.

[alang]

Oh dear, it wasn't POGO

That's an awful lot of time and mental energy that's been spent unnecessarily by the community on guessing why the flight 8 changes didn't fix the problem, and what to do about it.

I guess we can consider it time well spent as it kept us entertained while not a lot seemed to be happening.

so what will the community think if ship explodes again on a similar timeframe next week.

That would be unfortunate, but it is more likely that improvements have been made to reduce the likelihood of the proximate cause. That might extend the timeline and allow the gathering of more information, or remove a mental fixation on one or two known issues.

[JamesH65]

Oh dear, it wasn't POGO

That's an awful lot of time and mental energy that's been spent unnecessarily by the community on guessing why the flight 8 changes didn't fix the problem, and what to do about it.

I guess we can consider it time well spent as it kept us entertained while not a lot seemed to be happening.

so what will the community think if ship explodes again on a similar timeframe next week.

1. It doesn't matter what the community thinks.
2. See 1.

[Twark_Main]

Oh dear, it wasn't POGO

That's an awful lot of time and mental energy that's been spent unnecessarily by the community on guessing why the flight 8 changes didn't fix the problem, and what to do about it.

I guess we can consider it time well spent as it kept us entertained while not a lot seemed to be happening.

so what will the community think if ship explodes again on a similar timeframe next week.

1. It doesn't matter what the community thinks.
2. See 1.

Uh, aren't you a member of the community? 

"Human sacrifice, pots and kettles living together....  Mass hysteria!"

[equiserre]

It's also possible that the flight 7 fix somehow introduced new stresses on the engine.

Hasnt this thread demonstrated that absolute Wild speculation with zero data is not useful or fun?

I'm having fun.  Why aren't you?

The video was education, so it was also useful, even though it was wrong

II, you are right, I was speaking for myself. When the subject is just completely made up, (for me) it ceases to be fun. It also clutters the forums with noise. And it contributes to the flood of fake knowledge that non-critical thinking people take for truth just because it is a wild theory.

[Metalskin]

"Human sacrifice, pots and kettles living together....  Mass hysteria!"

I always thought the quote from Ghost Busters was:

"Human sacrifice, cats and dogs living together... Mass hysteria!"

[Vultur]

Oh dear, it wasn't POGO

That's an awful lot of time and mental energy that's been spent unnecessarily by the community on guessing why the flight 8 changes didn't fix the problem, and what to do about it.

I guess we can consider it time well spent as it kept us entertained while not a lot seemed to be happening.

so what will the community think if ship explodes again on a similar timeframe next week.

Well, there were different issues this time. I wonder if the leak was a related but less serious version of the problem, or an unrelated problem?

[Twark_Main]

"Human sacrifice, pots and kettles living together....  Mass hysteria!"

I always thought the quote from Ghost Busters was:

"Human sacrifice, cats and dogs living together... Mass hysteria!"

It is, and I know.  Read the rest of it.   


Also, it's Ghostbusters (one word, no capital B).

[Metalskin]

"Human sacrifice, pots and kettles living together....  Mass hysteria!"

I always thought the quote from Ghost Busters was:

"Human sacrifice, cats and dogs living together... Mass hysteria!"

It is, and I know.  Read the rest of it.   


Also, it's Ghostbusters (one word, no capital B).

Not getting the kettles and pot references sorry, but nice to understand you did it intentionally :-)

I'm too ingrained into fixing wavy red lined words. Ghostbusters is obviously the correct form :-D

Back to the topic (and my bad). Is the consensus that the Pogo problem is resolved based on the latest flight, or are people waiting to see the analysis of what went wrong?