Author Topic: General Falcon and Dragon discussion (Thread 13)  (Read 396542 times)

Offline Lars-J

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #660 on: 05/31/2016 10:43 pm »
Inspecting a landed stage just validates that it survived landing. It doesn't increase its launch reliability appreciability

If that was true you would not be able to validate that a *new* stage will launch reliably before it launches. But through testing you *clearly* can.

Offline Jim

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #661 on: 05/31/2016 10:46 pm »
They aren't going to structurally test it before launching again

Offline JBF

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #662 on: 06/01/2016 12:55 am »
They aren't going to structurally test it before launching again

Jim do you know if they are going to do any structure testing at all?  I always assumed that they would at least run it through one of those giant airplane x-ray machines.
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Offline Space Ghost 1962

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #663 on: 06/01/2016 01:19 am »
Structural testing includes:
 * sampling of key components
 * wear/fatigue modelling
 * functional testing in the environment of use
 * destructive testing of entire / partial stage

High flight hours a/c frames usually are searched for microfractures to discover fatigue patterns that are classified to materials / application.

Given the stresses on these highly decelerated stage, and its unique bending moments encountered, it makes sense to sample the thrust structures and scan the exterior skin for microfractures. Tank domes also.

None of this would be that hard to do following stage recovery.

Offline Lar

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #664 on: 06/01/2016 02:42 am »
Inspecting a landed stage just validates that it survived landing. It doesn't increase its launch reliability appreciability
It does possibly increase its expected success rate .... if there are parts that get replaced.

It does possibly increase the expected success rate of all future stages .... if there are design changes that are made as a result of the findings that make improvements.
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Offline meekGee

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #665 on: 06/01/2016 07:00 am »




If that was true you would not be able to validate that a *new* stage will launch reliably before it launches. But through testing you *clearly* can.

If you inspect a landed stage and find no "almost failures", you now know it survived both launch and landing without coming close to rudding...

So unless it fixed itself on the way down, you also have increased confidence in your margin allocation.
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Offline JamesH65

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #666 on: 06/01/2016 07:01 am »
Inspecting a landed stage just validates that it survived landing. It doesn't increase its launch reliability appreciability

I don't believe this statement can be correct.

Surely there must be much information gleaned from a landed stage that could be used to improve the launch success? Of course, the majority of information will likely be used to improve landing reliability, but I can see that at least some of those improvements will possibly benefit launching. Any engine improvement for example.

Of course, it could be argued that improving the F9's launchers reliability will be difficult given it fairly high success rate already.

Offline Jet Black

Re: General Falcon and Dragon discussion (Thread 13)
« Reply #667 on: 06/01/2016 11:18 am »
Unsure. If they'd landed on before the doomed CRS mission, they may have been able to identify weaknesses in struts. There may be other things in there that are on a knife edge in terms of failing.
For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled. -- Richard Feynman

Offline rpapo

Re: General Falcon and Dragon discussion (Thread 13)
« Reply #668 on: 06/01/2016 11:34 am »
Unsure. If they'd landed on before the doomed CRS mission, they may have been able to identify weaknesses in struts. There may be other things in there that are on a knife edge in terms of failing.
Who says?  The struts that failed were in the second stage, which they are far from being able to recover yet.
Following the space program since before Apollo 8.

Offline guckyfan

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #669 on: 06/01/2016 11:53 am »
Who says?  The struts that failed were in the second stage, which they are far from being able to recover yet.

They said the same kind struts were used all over the first and second stage. Doesn't mean that they could have detected the problem on a landed stage. Maybe, maybe not.

Offline rpapo

Re: General Falcon and Dragon discussion (Thread 13)
« Reply #670 on: 06/01/2016 12:05 pm »
Who says?  The struts that failed were in the second stage, which they are far from being able to recover yet.
They said the same kind struts were used all over the first and second stage. Doesn't mean that they could have detected the problem on a landed stage. Maybe, maybe not.
Very true, though the loading may or may not be different.  It really depends on whether the helium tanks are submerged in liquid oxygen or exposed at the time of maximum acceleration.  If they are exposed, then their load is downward.  In the second stage, the loading was upward due to the buoyancy of the tanks while submerged in the full tank of liquid oxygen.  By that time, the first stage's tank is half empty, at least.
« Last Edit: 06/01/2016 12:06 pm by rpapo »
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Offline AncientU

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #671 on: 06/01/2016 01:06 pm »
Inspecting a landed stage just validates that it survived landing. It doesn't increase its launch reliability appreciability

I thought the very first stage re-fire after landing found a weakness (found as a result of the thrust fluctuation) that they easily improved upon; they claimed it increased the reliability of the rocket on ascent, too.
« Last Edit: 06/01/2016 01:07 pm by AncientU »
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Offline Jim

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #672 on: 06/01/2016 01:09 pm »
Any engine improvement for example.

That can be found on a test stand

Offline vandersons

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #673 on: 06/01/2016 02:26 pm »
Any engine improvement for example.

That can be found on a test stand

Correct me if I'm wrong here but would it not be near impossible to mimic flight conditions for an engine on a test stand? In my understanding a test stand is a far more rigid structure than a rocket itself so the vibration environments would be quite different. Wouldn't that difference introduce additional failure scenarios for the pumps?

Offline Lar

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #674 on: 06/01/2016 03:35 pm »
Test as you Fly, Fly as you Test.

Jim's probably right in the general case, that the direct reliability impacts aren't going to be super high value from examining a stage, but wrong about specifics, that there might be examples of things that might be findable only by examining a flown stage, that no amount of test stand or preflight checks of an unflown stage will find. Things that if corrected, will improve reliability of future flights (new OR used)

"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 AncientU

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #675 on: 06/01/2016 04:53 pm »
Were there features of the Shuttle and RS-25 launch reliability that were improved upon as a result of recovering the spacecraft and examining it?  (Booster recovery certainly showed evidence of o-ring blow-by that could have been fixed but weren't, to tragic end.)  Seems a lot more promising development tactic (if you can do it, of course) than launching generations of rockets until your failures diminish toward zero. 
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Offline Jim

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #676 on: 06/01/2016 05:07 pm »
Were there features of the Shuttle and RS-25 launch reliability that were improved upon as a result of recovering the spacecraft and examining it?  (Booster recovery certainly showed evidence of o-ring blow-by that could have been fixed but weren't, to tragic end.)  Seems a lot more promising development tactic (if you can do it, of course) than launching generations of rockets until your failures diminish toward zero. 

Test stands for RS-25.  Solid motors are not applicable to this discussion.  There is no equivalent refurbish for a liquid rocket engine.
« Last Edit: 06/01/2016 05:09 pm by Jim »

Offline Space Ghost 1962

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #677 on: 06/01/2016 05:37 pm »
Suggest that there are disagreements about reflight being better/worse statistics due to lack of flight experience.

Jim's position is very reasonable and proven, because launch is unlike "aircraft operation" in it's extremes, such that one can look at the systems engineering view is to create an air/thrust frame that takes launch stress and then is disposed of, and the rest is a recoverable engine and margin.

SX's position is also reasonable (but unproven), by expanding LV operational envelope to deal with the stresses of launch, return, landing, recovery, and relaunch. Margin is not preserved by reduction of dry mass and excess/recovery props, but by expending the vehicle (recovery fuel as an excess), with additional performance to handle the excess dry mass.

For SX's position to "win" alongside past "proven" in terms of "aircraft operations" (note - nothing about economics yet, just functional operations in "WAD"), thermal/fatigue/wear/other issues need to be a tiny fraction of total vehicle, and the growth rate every launch must be even smaller.

The original plan was to recover stages and destructively test them. What seems to have happened instead is that engines are being examined instead, and a series of static fires (eventually) will be done in place at CCAFS, and then a reflight will occur.

Suggest that engine issues dominate concerns, likely dealt with by production line changes. Suggest that airframe/thrust/thermal issues are being dealt with to a lesser degree by reprocessing/sampling/replacement, as they fall within expected bounds.

Suggest net/net that SX believes that the cost issues are with the engines, and that "normal" flight operations are within the acceptable structural bounds, and that where the remaining stress/wear issues are in getting to hundreds of flights, thus likely where they want to do tear down is after a reflight (or ten!), which is why they don't give a rat's a$$ about it at this point.

Which explains the difference in positions on this. Jim want's them to prove their position first.

As do I.

Offline meekGee

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #678 on: 06/02/2016 01:23 am »
The return flight does not help the stage.

If you see damage, you might wonder whether it is from the launch or return.

But if you eliminate doubt, see that margins were adequate, etc - that buys you confidence.

Nobody today has a chance to inspect their rockets post launch to know how close they came to failure... and this has to factor into how the underwriters see things.
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Offline meekGee

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Re: General Falcon and Dragon discussion (Thread 13)
« Reply #679 on: 06/02/2016 02:22 am »
Not quite.

If you received a post-launch rocket, teleported to your lab as if by magic and without any damage (from teleportation) it would clearly be hugely useful.

An argument was made that because of damage during flyback, the evidence is basically erased, since you can't differentiate between "up damage" and "down damage".

So first, for many types of damage , yes you can.

Second, even if you can't, you know for sure that you're examining a "more damaged" rocket, so at a bare minimum, anything you inspect and comes out as expected, adds confidence to future first launches of the type.

Third, for re-launches, you have confidence that absolute fatal mistakes were not made.  Of course there may be mistakes that only manifest themselves on second or third flights, but those diminish with each successive flight.
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