Author Topic: General Falcon and Dragon discussion (Thread 13)  (Read 396612 times)

Offline Robotbeat

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #720 on: 06/06/2016 03:36 pm »
The people who "wrote the book" on systems engineering for launch vehicles do not have direct access to some Platonic form of ideal wisdom. They may be wrong.
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Offline wannamoonbase

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #721 on: 06/06/2016 03:40 pm »
Now that Falcon 9 design is "frozen", is SpaceX going to prepare further improvements and add them all at the same time (F9 v1.3?), when they reduce their backlog of flights?

Are modifications to improve recovery also part of this design freeze, or only main rocket parts?

Disciplined configuration control?  Would be nice but they have not shown a history of doing so.
Constant iteration of a design does not exclude disciplined configuration control. Unless you have insight into SpaceX's internal change management and design drawing release systems and how they integrate into their systems engineering and mission planning, you're talking out of your derrière.

Fair enough.  Configuration control wasn't the right term to use, Stabilized design would be better. 

I'm all for improvements, rolling them out continuously instead of doing releases is messy not just for production and manufacturing.  But I can imagine that insurers have a general level of unease with SpaceX.   

It's a young company doing new things, but they are creating problems for themselves if they keep up the same behavior.  Implementing reuse with a series of vehicles, each one potentially different than the others will be cost and schedule management nightmare.
Wildly optimistic prediction, Superheavy recovery on IFT-4 or IFT-5

Offline JamesH65

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #722 on: 06/06/2016 03:46 pm »
Now that Falcon 9 design is "frozen", is SpaceX going to prepare further improvements and add them all at the same time (F9 v1.3?), when they reduce their backlog of flights?

Are modifications to improve recovery also part of this design freeze, or only main rocket parts?

Disciplined configuration control?  Would be nice but they have not shown a history of doing so.
Constant iteration of a design does not exclude disciplined configuration control. Unless you have insight into SpaceX's internal change management and design drawing release systems and how they integrate into their systems engineering and mission planning, you're talking out of your derrière.

Fair enough.  Configuration control wasn't the right term to use, Stabilized design would be better. 

I'm all for improvements, rolling them out continuously instead of doing releases is messy not just for production and manufacturing.  But I can imagine that insurers have a general level of unease with SpaceX.   

It's a young company doing new things, but they are creating problems for themselves if they keep up the same behavior.  Implementing reuse with a series of vehicles, each one potentially different than the others will be cost and schedule management nightmare.

Whuh?  All launch providers rockets change design, almost every flight. Lots of tiny little changes.  Jim said this, and I believe him (just this once mind!). SpaceX don't appear to be doing much different. SpaceX have a stabilised design (The F9). They just make small changes as they go along. I see no problem, it's what they, and others, do.

What you seem to be saying is that SpaceX can only continue without problems if they stop innovating.  Which is a pointless thing to do.

Only this week, some Russian space thingy has encountered problems and is on hold. It's not like SpaceX have a monopoly.

Offline RedLineTrain

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #723 on: 06/06/2016 04:02 pm »
I'm all for improvements, rolling them out continuously instead of doing releases is messy not just for production and manufacturing.  But I can imagine that insurers have a general level of unease with SpaceX.

Please no FUD.  Not a page ago in this thread, there was a link to article where an insurer stated that he was fine with it and that SpaceX had credibility to do these things.

Offline The Amazing Catstronaut

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #724 on: 06/06/2016 04:03 pm »
A design freeze would make SpaceX considerably less interesting for us fans, if you want to come at it from that perspective. Besides, a lack of changeability is no guarantee of reliability, especially when each and every modification is aimed at making the LV a better alternative to the LV that came before. There has been no proof of yet that SpaceX feature creep is the root cause of any past SpaceX reliability issues. SpaceX also has the ability to adapt rather rapidly if they do make a design err, which is unlikely. They have the culture and the facilities to deal with feature creep as the norm running order.
« Last Edit: 06/06/2016 04:04 pm by The Amazing Catstronaut »
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Offline Lar

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #725 on: 06/06/2016 04:05 pm »
The trick with continuous revision is managing what configuration each unit is currently, and managing what units get backported from their as built (or as last modified) to the desired current config. Some change items may not get applied and some may.

Interesting problem. But not unsolvable.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline kaiser

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #726 on: 06/06/2016 04:42 pm »
The trick with continuous revision is managing what configuration each unit is currently, and managing what units get backported from their as built (or as last modified) to the desired current config. Some change items may not get applied and some may.

Interesting problem. But not unsolvable.

Exactly, and the rocket business is pretty good place for this.  Implement drawing change, replace drawings on floor for the next serial number.  File away travelers and red lines from build on that unit, and log drawing revision used to build it in the database.  Rinse, repeat.  Continually.  No need for it to be messy or confusing as long as you're disciplined about it (aka, not backporting unless mission critical, having good floor practices, etc).

Offline AncientU

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #727 on: 06/06/2016 05:15 pm »
I'm all for improvements, rolling them out continuously instead of doing releases is messy not just for production and manufacturing.  But I can imagine that insurers have a general level of unease with SpaceX.

Please no FUD.  Not a page ago in this thread, there was a link to article where an insurer stated that he was fine with it and that SpaceX had credibility to do these things.

And you'd be wrong.
SpaceX insurance rates = Ariane V insurance rates
Read last page of thread.
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Offline RotoSequence

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #728 on: 06/15/2016 04:12 pm »
https://twitter.com/elonmusk/status/743099301174247424
Quote from: Elon Musk
Upgrades underway to enable rocket to compensate for a thrust shortfall on one of the three landing engines. Probably get there end of year.

Would a full, Dragon-2-esque bank of pressure fed SuperDracos be up to the task?
« Last Edit: 06/15/2016 04:14 pm by RotoSequence »

Offline Robotbeat

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #729 on: 06/15/2016 04:17 pm »
https://twitter.com/elonmusk/status/743099301174247424
Quote from: Elon Musk
Upgrades underway to enable rocket to compensate for a thrust shortfall on one of the three landing engines. Probably get there end of year.

Would a full, Dragon-2-esque bank of pressure fed SuperDracos be up to the task?
NO. They are upgrading the thrust of the Merlin 1Ds so they could compensate for under-thrust of one of the 3 engines.

NO superdraco, that's a bunch of hypergols and super nasty. The first stage has no hypergols on it right now, which means the recovery crew doesn't need to don bunny suits.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline envy887

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #730 on: 06/15/2016 04:27 pm »
The first stage has TEA-TEB, which is about as nasty as hypergols... but superdracos definitely aren't the answer.

I'm thinking that fuel lines are being occasionally damaged on hot reentries, leading to both the loss of prop and thrust at landing and the residual fires.

Offline the_other_Doug

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #731 on: 06/15/2016 04:28 pm »
I'm thinking that fuel lines are being occasionally damaged on hot reentries, leading to both the loss of prop and thrust at landing and the residual fires.

That's what I've been thinking since SES-9...
-Doug  (With my shield, not yet upon it)

Offline abaddon

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #732 on: 06/15/2016 04:30 pm »
From the Bingo thread:

Next one is LZ-1 (unless Elon wants another go at a CRS-to-ASDS).
IIRC, with CRS-8 Elon said that the droneship landing had a better chance of success due to margin being a little low for an RTLS.  Also, from a PR perspective, it's probably better to do a droneship landing than have a RUD like the one today at LZ-1.  Will be interesting to see which way they go.
But a landing would mean they have more time to do an inspection of the droneship. Also, a landing is a lot better recovery option, significantly cheaper.

Clearly a successful LZ-1 landing is the best option, for many different reasons.  I'm just listing reasons they might not choose to do so.  Definitely several good reasons the other way...

Offline AncientU

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #733 on: 06/15/2016 04:59 pm »
The trick with continuous revision is managing what configuration each unit is currently, and managing what units get backported from their as built (or as last modified) to the desired current config. Some change items may not get applied and some may.

Interesting problem. But not unsolvable.

Exactly, and the rocket business is pretty good place for this.  Implement drawing change, replace drawings on floor for the next serial number.  File away travelers and red lines from build on that unit, and log drawing revision used to build it in the database.  Rinse, repeat.  Continually.  No need for it to be messy or confusing as long as you're disciplined about it (aka, not backporting unless mission critical, having good floor practices, etc).

The design changes currently in implementation to solve this single engine under-performance issue is a classic case of iterative improvements.  Change is probably making its way through testing and production modifications and will appear before the end of the year in new units coming off the line.  In contrast, when CRS-7 strut issue bit them, a backfit on all existing stages was probably implemented, and then all future stages once production was restarted.
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Offline baldusi

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #734 on: 06/15/2016 07:07 pm »
Let's not forget that their business is, first and foremost, launching payloads to orbit, not returning stages. So launch reliability mods have to be backported, landing mods are better deferred.

Offline te_atl

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #735 on: 06/15/2016 08:06 pm »
The trick with continuous revision is managing what configuration each unit is currently, and managing what units get backported from their as built (or as last modified) to the desired current config. Some change items may not get applied and some may.

Interesting problem. But not unsolvable.

I am a configuration manager by trade.   Interestingly enough, modern formalized configuration management grew out of defense research and development projects in the 1950s... especially rocket development.  It became obvious that as projects became more complex a technical management discipline was necessary to keep track of exactly how the hardware was  put together, what parts were used, which changes were made and why, etc. etc..   Formalized Configuration Management (hardware configuration management... software came later) was born.  So this is a very solvable problem, and we have in part early rocket development to thank for the solutions.

Offline baldusi

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #736 on: 06/16/2016 12:04 am »
Yep, the book on the F-1 engine explained how each subcomponent had a binder folder with all the revision history and certificates.

Offline docmordrid

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #737 on: 06/16/2016 01:31 am »
Apparently SpaceX uses the Siemens system.

Siemens case study....
« Last Edit: 06/16/2016 01:34 am by docmordrid »
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Offline Kabloona

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #738 on: 06/16/2016 02:34 am »
I'm thinking that fuel lines are being occasionally damaged on hot reentries, leading to both the loss of prop and thrust at landing and the residual fires.

If it were a fuel line problem causing loss of landing thrust, they'd know that from telemetry and be making the appropriate fix. But according to Musk's tweet today, he says they'll be "upgrading" the vehicle to "compensate" for low-thrust anomalies at landing. Which makes it sound like the low-thrust problem may be an unavoidable result of landing with too-low propellant levels, possibly helium bubble ingestion caused by propellant slosh, etc.

If it were simply a matter of heat-damaged fuel lines, they'd be fixing that with more insulation, etc, rather than figuring out how to live with the problem. And it wouldn't be taking them 6 months to implement.

Musk's tweet:

Quote
Upgrades underway to enable rocket to compensate for a thrust shortfall on one of the three landing engines. Probably get there end of year.

So the only real "fix" may be having enough propellant margin to prevent helium bubbles from getting into the fuel line in the first place, and for high-performance missions where that's not possible, these "upgrades" that somehow may make a low-thrust anomaly less fatal.
« Last Edit: 06/16/2016 02:51 am by Kabloona »

Offline wannamoonbase

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #739 on: 06/16/2016 03:02 am »
I'm thinking that fuel lines are being occasionally damaged on hot reentries, leading to both the loss of prop and thrust at landing and the residual fires.

If it were a fuel line problem causing loss of landing thrust, they'd know that from telemetry and be making the appropriate fix. But according to Musk's tweet today, he says they'll be "upgrading" the vehicle to "compensate" for low-thrust anomalies at landing. Which makes it sound like the low-thrust problem may be an unavoidable result of landing with too-low propellant levels, possibly helium bubble ingestion caused by propellant slosh, etc.

If it were simply a matter of heat-damaged fuel lines, they'd be fixing that with more insulation, etc, rather than figuring out how to live with the problem. And it wouldn't be taking them 6 months to implement.

Musk's tweet:

Quote
Upgrades underway to enable rocket to compensate for a thrust shortfall on one of the three landing engines. Probably get there end of year.

So the only real "fix" may be having enough propellant margin to prevent helium bubbles from getting into the fuel line in the first place, and for high-performance missions where that's not possible, these "upgrades" that somehow may make a low-thrust anomaly less fatal.

Or a different sump design at the base of the S1 tanks.  But that gets rather complicated.
Wildly optimistic prediction, Superheavy recovery on IFT-4 or IFT-5

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