SpaceX Falcon 9 - AMOS-6 - (Pad Failure) - DISCUSSION THREAD (2)

[matthewkantar]

The article states: "As part of the corrective process, SpaceX has opted to avoid its press towards super chilled LOX for the interim until they are confident they can redesign the COPVs to cope with the colder chill process."

I don't see anything in the release saying they won't super cool the LOX, just that they will load warmer HE. That will result in higher temps for the LOX, but not necessarily a return to boiling point temperature LOX.

Or am I missing something?

Matthew

[RDoc]

Apparently there were buckles in the COPVs they found in the debris as well, so whatever was buckling the aluminum liners was pretty common to all of them. Is it possible that the buckling was caused by thermal contraction of the overwrap from the chilled helium? I'm pretty surprised that wouldn't turn up in modeling and/or testing.

[Jarnis]

While not your typical source for space news...here is something more recent (...and possibly translated?)

http://www.gamenguide.com/articles/76795/20161129/investigation-of-spacex-falcon-9-explosion-coming-to-light-as-elon-musk-s-company-faces-deadline.htm

Ancient. Check the URL, posted late November.

[Stan-1967]

The article states: "As part of the corrective process, SpaceX has opted to avoid its press towards super chilled LOX for the interim until they are confident they can redesign the COPVs to cope with the colder chill process."

I don't see anything in the release saying they won't super cool the LOX, just that they will load warmer HE. That will result in higher temps for the LOX, but not necessarily a return to boiling point temperature LOX.

Or am I missing something?

Matthew

It goes on to state the following:

"“In the short term, this entails changing the COPV configuration to allow warmer temperature helium to be loaded, as well as returning helium loading operations to a prior flight proven configuration based on operations used in over 700 successful COPV loads."

I read that to mean they are not just avoiding super chilled LOX, but return to the previous POR, which was LOX at boiling temperature.  It has a flight history of success, and at this point, I think that probably weighed heavily on SpaceX's decision making.   Their business priorities are to work through their manifest, stay on track with commercial crew, and get FH to first flight.   This action eases the path for all those.

It is going to put a slowdown on re-use, as the superchilled propellants gave more margin.  It will be interesting to see how this plays out on GTO launches.

Anyone know if SpaceX would also have to change turbopumps back to the design that used boiling LOX temps?  Do they now leave some additional unfilled head room in the RP-1 tank, as there won't be enough LOX to burn with all the chilled RP-1? 

[mn]

The article states: "As part of the corrective process, SpaceX has opted to avoid its press towards super chilled LOX for the interim until they are confident they can redesign the COPVs to cope with the colder chill process."

I don't see anything in the release saying they won't super cool the LOX, just that they will load warmer HE. That will result in higher temps for the LOX, but not necessarily a return to boiling point temperature LOX.

Or am I missing something?

Matthew

It goes on to state the following:

"“In the short term, this entails changing the COPV configuration to allow warmer temperature helium to be loaded, as well as returning helium loading operations to a prior flight proven configuration based on operations used in over 700 successful COPV loads."

I read that to mean they are not just avoiding super chilled LOX, but return to the previous POR, which was LOX at boiling temperature.  It has a flight history of success, and at this point, I think that probably weighed heavily on SpaceX's decision making.   Their business priorities are to work through their manifest, stay on track with commercial crew, and get FH to first flight.   This action eases the path for all those.

It is going to put a slowdown on re-use, as the superchilled propellants gave more margin.  It will be interesting to see how this plays out on GTO launches.

Anyone know if SpaceX would also have to change turbopumps back to the design that used boiling LOX temps?  Do they now leave some additional unfilled head room in the RP-1 tank, as there won't be enough LOX to burn with all the chilled RP-1?

How do you read that into what they said? they did not say anything about changing LOX temp?

We know that SpaceX was adjusting the loading process over the course of the last few launches since starting with subcooling. I read it as saying they will go back to the loading procedure of the first few subcooled launches, avoiding the changes they tried in the last launches.

[Kansan52]

The article states: "As part of the corrective process, SpaceX has opted to avoid its press towards super chilled LOX for the interim until they are confident they can redesign the COPVs to cope with the colder chill process."

I don't see anything in the release saying they won't super cool the LOX, just that they will load warmer HE. That will result in higher temps for the LOX, but not necessarily a return to boiling point temperature LOX.

Or am I missing something?

Matthew

Inferring from the SX comment that this was a new procedure and the failure was a procedural problem, they will revert to the last working procedure while improving the COPVs. Also inferring, the new procedure  gives them something (more payload) and/or improved safety margin using any procedure.

[Jim]

It goes on to state the following:

"“In the short term, this entails changing the COPV configuration to allow warmer temperature helium to be loaded, as well as returning helium loading operations to a prior flight proven configuration based on operations used in over 700 successful COPV loads."

I read that to mean they are not just avoiding super chilled LOX, but return to the previous POR, which was LOX at boiling temperature.  It has a flight history of success, and at this point, I think that probably weighed heavily on SpaceX's decision making.   Their business priorities are to work through their manifest, stay on track with commercial crew, and get FH to first flight.   This action eases the path for all those.

No, they are not changing how they load LOX but how they load the helium.   They are just going to load it slower.

[Johnnyhinbos]

The article states: "As part of the corrective process, SpaceX has opted to avoid its press towards super chilled LOX for the interim until they are confident they can redesign the COPVs to cope with the colder chill process."

I don't see anything in the release saying they won't super cool the LOX, just that they will load warmer HE. That will result in higher temps for the LOX, but not necessarily a return to boiling point temperature LOX.

Or am I missing something?

Matthew

It goes on to state the following:

"“In the short term, this entails changing the COPV configuration to allow warmer temperature helium to be loaded, as well as returning helium loading operations to a prior flight proven configuration based on operations used in over 700 successful COPV loads."

I read that to mean they are not just avoiding super chilled LOX, but return to the previous POR, which was LOX at boiling temperature.  It has a flight history of success, and at this point, I think that probably weighed heavily on SpaceX's decision making.   Their business priorities are to work through their manifest, stay on track with commercial crew, and get FH to first flight.   This action eases the path for all those.

It is going to put a slowdown on re-use, as the superchilled propellants gave more margin.  It will be interesting to see how this plays out on GTO launches.

Anyone know if SpaceX would also have to change turbopumps back to the design that used boiling LOX temps?  Do they now leave some additional unfilled head room in the RP-1 tank, as there won't be enough LOX to burn with all the chilled RP-1?

I read this quite differently. I think the propellants are still densified, but that the He loading has been modified to start loading He at a warmer temp. This probably means a slower prop / He loading process, with more LOX boil off, but I don't think it means getting away from the densified props. Instead, again - my take - is that they are willing to lose more LOX to boiloff, and therefore possibly lose the ability to recycle once like I believe they have now. So any count hold will then probably scrub the launch until they have built up enough sub chilled LOX again.

[eriblo]

Just to be clear:

In the short term, this entails changing the COPV configuration to allow warmer temperature helium to be loaded, as well as returning helium loading operations to a prior flight proven configuration based on operations used in over 700 successful COPV loads.

As part of the corrective process, SpaceX has opted to avoid its press towards super chilled LOX for the interim until they are confident they can redesign the COPVs to cope with the colder chill process.

SpaceX only mentions helium temperatures and configuration so the NSF article is either based on other information or an misrepresentation/misunderstanding of the official statement.

[robertross]

Slight correction to the SpaceX release:

"Each stage of Falcon 9 uses COPVs to store cold helium which is used to maintain tank pressure, and each COPV consists of an aluminum inner liner with a carbon overwrap. The recovered COPVs showed buckles in their liners. Although buckles were not shown to burst a COPV on their own, investigators concluded that super chilled LOX can pool in these buckles under the overwrap. When pressurized, oxygen pooled in this buckle can become trapped; in turn, breaking fibers or friction can ignite the oxygen in the overwrap, causing the COPV to fail."

Technically oxygen does not burn, it only supports combustion. It was the fibers that burned due to the heat or spark they themselves created.

[Chris Bergin]

Just to be clear:

In the short term, this entails changing the COPV configuration to allow warmer temperature helium to be loaded, as well as returning helium loading operations to a prior flight proven configuration based on operations used in over 700 successful COPV loads.

As part of the corrective process, SpaceX has opted to avoid its press towards super chilled LOX for the interim until they are confident they can redesign the COPVs to cope with the colder chill process.

SpaceX only mentions helium temperatures and configuration so the NSF article is either based on other information or an misrepresentation/misunderstanding of the official statement.

I think I've got helium mixed up with LOX, edited it.

After all, it has been said I'm full of hot air

[HIP2BSQRE]

Jim was right it was an issue with the bottles..

[HMXHMX]

Jim was right it was an issue with the bottles..

Several of us thought it was an issue with the bottles, and still do.  I'm not at all convinced a CONOPS change in helium loading will significantly reduce the risk of continuing to use aluminum liners and their current composite formulation.

[Lar]

Jim was right it was an issue with the bottles..

Several of us thought it was an issue with the bottles, and still do.  I'm not at all convinced a CONOPS change in helium loading will significantly reduce the risk of continuing to use aluminum liners and their current composite formulation.

I look forward to autogenous, but that will bring its own set of problems.

[HMXHMX]

Jim was right it was an issue with the bottles..

Several of us thought it was an issue with the bottles, and still do.  I'm not at all convinced a CONOPS change in helium loading will significantly reduce the risk of continuing to use aluminum liners and their current composite formulation.

I look forward to autogenous, but that will bring its own set of problems.

Indeed.  Perhaps out of scope for this thread, but certainly related, since warm/hot GOX and their current composite materials are not a good combination.  There are ways to make that work but to my knowledge they are not implementing them.

[vanoord]

Apparently there were buckles in the COPVs they found in the debris as well, so whatever was buckling the aluminum liners was pretty common to all of them. Is it possible that the buckling was caused by thermal contraction of the overwrap from the chilled helium? I'm pretty surprised that wouldn't turn up in modeling and/or testing.

Was the He being loaded later, meaning that the tank was experiencing external pressure as the LOX was loaded, causing the tank to buckle inwards?

In that case, loading the He tank earlier should pressurise it and prevent it from being buckled as the LOX pressure increases.

[HIP2BSQRE]

Jim was right it was an issue with the bottles..

Several of us thought it was an issue with the bottles, and still do.  I'm not at all convinced a CONOPS change in helium loading will significantly reduce the risk of continuing to use aluminum liners and their current composite formulation.

I look forward to autogenous, but that will bring its own set of problems.

Indeed.  Perhaps out of scope for this thread, but certainly related, since warm/hot GOX and their current composite materials are not a good combination.  There are ways to make that work but to my knowledge they are not implementing them.

What would you suggest they do?

[HIP2BSQRE]

Jim was right it was an issue with the bottles..

Several of us thought it was an issue with the bottles, and still do.  I'm not at all convinced a CONOPS change in helium loading will significantly reduce the risk of continuing to use aluminum liners and their current composite formulation.

I look forward to autogenous, but that will bring its own set of problems.

Indeed.  Perhaps out of scope for this thread, but certainly related, since warm/hot GOX and their current composite materials are not a good combination.  There are ways to make that work but to my knowledge they are not implementing them.

SpaceX said the following" The corrective actions address all credible causes and focus on changes which avoid the conditions that led to these credible causes. In the short term, this entails changing the COPV configuration to allow warmer temperature helium to be loaded, as well as returning helium loading operations to a prior flight proven configuration based on operations used in over 700 successful COPV loads. In the long term, SpaceX will implement design changes to the COPVs to prevent buckles altogether, which will allow for faster loading operations.​"  You feel there is more that can/should be done?  Would these changes be short/long term and what would be the affect on operations/cost, etc?

[Flying Beaver]

SpaceX said the following" The corrective actions address all credible causes and focus on changes which avoid the conditions that led to these credible causes. In the short term, this entails changing the COPV configuration to allow warmer temperature helium to be loaded, as well as returning helium loading operations to a prior flight proven configuration based on operations used in over 700 successful COPV loads. In the long term, SpaceX will implement design changes to the COPVs to prevent buckles altogether, which will allow for faster loading operations.​"  You feel there is more that can/should be done?  Would these changes be short/long term and what would be the affect on operations/cost, etc?

I expect "long term", means moving COPV production in-house.

[feynmanrules]

No, they are not changing how they load LOX but how they load the helium.   They are just going to load it slower.

What tradeoff(s) are associated with varying he loading times?   

Was shorter he load part of an effort to be get back to having multiple shots in a ~1hr launch window (while retaining super-densified prop)?