SpaceX Falcon 9/Dragon CRS SpX-1 MISSION GENERAL DISCUSSION

[Comga]

Thanks cambrianera. What are the 'thingys' between the two lateral panels?

IIUC, those are the hold-down points where the base holds onto the first stage until the engines are fully running.

[cambrianera]

Yes Comga, in the red circles the hold down holes for the hold down pins.
In the green ellipse the stand up step where the rocket is hold up (and some fluid or electrical connection, don't know exactly)

[Robotbeat]

Actually, it is pretty effective for figuring out whether there is any truth to a rumor or not.

[thebartonfox]

Yep, the flavored drink mix consumption is in full till. 
I frequently used the term "sudden pressure loss" when describing a balloon that instantly no long holds air.

Take a look at the article Chris just posted. http://www.nasaspaceflight.com/2013/01/spacex-win-contract-ahead-crs-2-mission/

"The pressure loss resulted in the fairing that protects the engine from aerodynamic loads to rupture, giving the impression of an explosion. However, this was not the case and the remaining eight engines were unaffected by the event."

"Preliminary source information noted the failure appeared to be related to a fracturing of the Merlin 1C engine’s fuel dome, localized solely in that area on Engine 1, explaining why the engine continued to send data after the event."

You're claiming an explosion. Which goes against how everything else has been stated.

I am not an engineer.  I welcome corrections.

A classic "rocket engine explosion" is a rupture of the combustion chamber.  Big bang.  It can also be any failure resulting in massive external mixing of high-pressure fuel and oxidiser.  The Falcon 9 is designed to contain such explosions.

The fuel dome fractured and caused
  1)  a reduced flow of fuel  into the combustion chamber.  This gave the pressure loss in the combustion chamber that was detected and triggered closure of the main fuel and oxidiser valves, shutting down the engine.
  2)  for a short time, fuel escaped into the space around the engine.

  Could the escaping fuel have mixed with atmospheric oxygen, resulting in a small "explosion?"  Is this a possible alternate cause of the fairing failure?  I don't think so.

I do know about drinking the mix.  I once attempted to launch my Dodge Dart into the sun.

I found this diagram helpful.

From http://pinehead.tv/space/under-the-hood-with-the-spacex-merlin-engine/

[beancounter]

Still waiting for word on the 'suspected' root cause of the issue.  SpaceX did say 'soon'.  One hopes that it will be before the next flight but I don't mind either way, just so long as SpaceX continue to fly successfully.
In fact, does it really matter whether or not anyone in the public arena knows?  I think not.  The ones who matter are NASA and SpaceX customers.  If they're satisfied, then so am I.

[edkyle99]

Spacex is just putting things in a good light. And really, considering the primary mission was a big success and the (very small) secondary even acheived many of its objectives. This was in spite of an engine-out, which is impressive.

Meanwhile, you should be aware that Ed Kyle tends to put things in a bad light. If there's anything that goes off-nominal and leads to a little less performance or something (even if the primary mission is a success), he will label that a full failure. It borders on schadenfraude.

There's no pleasure in logging failures.  But someone has to do it!

Because, as we have seen many times before and again in this case, the manufacturer (not just SpaceX - some others are more blatant) tends to, lets say, De-emphasize what really happens when things don't go perfectly.  The general media tends to repeat what the manufacturer tells them, and then the story of no failure at all gets passed down through the history books when, in fact, a paying customer's satellite burned up in the atmosphere.

That doesn't mean I'm not impressed that Falcon 9 flew on and that Dragon succeeded.  That was impressive, but lets remember the whole story.

 - Ed Kyle

[QuantumG]

when, in fact, a paying customer's satellite burned up in the atmosphere.

That satellite was always going to burn up in the atmosphere. That was the plan. The only result of the incorrect orbit deployment was that the customer got less time to evaluate the spacecraft. As it turns out, that didn't matter either. The customer got the data they needed and are they're proceeding with the dedicated launch campaign.

[Robotbeat]

BTW, Ed, I do thank you for keeping track of all this stuff with your website.

(And likewise QuantumG for yours).

[R7]

I got to ask: The implosion/MaxQ-aerodynamic-forces-tearing-panels theory is still circulated, and sometimes even as official fact now. Where's official statement from SpaceX that this is the case? All I've ever seen while following this case is references to Rand Simberg's op-ed where he writes about it and refers to SpaceX press release which did not mention anything about implosions nor wind tearing bits off.

AFAIK fuel dome rupturing is the official main suspect. Which leads to my other question: What is the fuel dome? I know what LOX dome is on many engines, distributing LOX over injector plate and carrying loads to gimbal.

I found SF Doug's posted diagram very informative, helped make an educated guess. It lacked though any labeling so I made an attempt to add some, the one's I'm unsure of are with question mark.



If the orange part on top of SC is the fuel dome then here's an image of it in the making, from jongoff's old article:

http://selenianboondocks.com/2006/10/spacex-comstac-briefing/


What confused me is knowing that LOX dome is full of LOX, so when heard of fuel dome I started to ponder "where's a dome full of fuel on this engine??". Apparently it isn't, instead a wall milled cooled closing section of CC, with a hole for pintle in the center.

What happens when such fuel dome ruptures? First would need to know did it rupture all the way to CC, or only the outer surface? A fitting failure (fuel bypass lines and assorted other lines going into fuel dome) ?

In any case, CC pressure listed at 6.77MPa/982psi. Fuel dome coolant lines have that plus injector drop, about 20-25% extra. Since it's mostly done it's cooling job it's hot, probably above boiling point (~200C) at 1atm (actual ambient pressure lower), possibly above autoignition temperature (~245C).

Now imagine (do not try  ) that you adjust a steam pressure washer to about 80bar / 1200psi, connect the input hose to heating fuel tank, turn the washer on and start spraying. Now, tough questions; would you feel safe? Is it likely that the output would mix with air? Wonder what would happen if you'd spray in a cramped compartment next to hot GG/turbine/turbine exhaust assembly? Or next to eight running rocket engines and one shutting down?

While back I captured a few frames from the launch video, I'll attach them here. If interested I recommend downloading and viewing with your preferred image viewer in order to quickly flip between frames. Added minor commenting. I believe object number two to be item that eventually floats in front of the plume, prominently visible in the image used in several articles now. Six frames, first being the last when everything seems OK.

YMMV but I see implosion only when viewing frames in reverse.

Original video:



PS. Sorry for the lengthy rant, I'm new and having a slow day.

[edit: typos]

[kevin-rf]

R7 Excellent 9th post!

[R7]

Can someone correct me, but isn't the fuel dome pressure the same as the combustion chamber since it really is the top of the combustion chamber.

I believe the answer is yes and no. Pressure behind fuel dome's inner wall is CC pressure because it's part of it. Pressure inside fuel dome wall cooling channel's is CC + injector drop (+ flow losses along the channel)

PS. Thanks 

[cambrianera]

@R7:
Your takes on the various parts of the merlin are correct; for your reference I attach an old picture of merlin 1C (posted many times, but always useful).

My take about the fuel dome rupture is that SpaceX has a pressure sensor in the fuel dome, hence looking at low reading in that sensor they said fuel dome rupture (obviously other sensors upfront looking nominal).

Your example of the pressure washer is enlightening, nice fireball coming out!
By the way, some frames after the ones you posted, another object falls, following the plume; due to the shape and the path, I guess this is the top fairing of the corner engine, while the objects you circled are pieces of the lateral (and bottom) panel.

[R7]

for your reference I attach an old picture of merlin 1C (posted many times, but always useful).

Thanks! Very useful, faint recollection that I've seen that before. Noticeable difference at the TPA section between wireframe diagram and image. But wireframe had better sectioning of the thrust assembly.

By the way, some frames after the ones you posted, another object falls, following the plume; due to the shape and the path, I guess this is the top fairing of the corner engine, while the objects you circled are pieces of the lateral (and bottom) panel.

Do you mean the triangular object in this one?



If so I agree that it's the top fairing, shape and size fits. When first saw it I thought "hello nozzle??" but if it were that we wouldn't have this conversation. I think it could be object #2 in my frames, but not sure. Moves erratically in the beginning, thought it's bouncing in supersonic wind like a leaf in hurricane.


Whatever the event was it looks very energetic. IMO it was very impressive that the LV continued to function and engine-out worked as advertised.

SpaceX was also very lucky that this happened during night launch. Would have looked much uglier in daylight, and none of any "oh I think it's just the cloud deck" comments.

[cambrianera]

Do you mean the triangular object in this one?

Yes, it falls due to the air stream (hence the erratic behaviour and the path close to the plume), not blown by the fireball.

When first saw it I thought "hello nozzle??" but if it were that we wouldn't have this conversation.

Exactly my idea at the very beginning; but when SpaceX said the engine was not damaged I realized doing this at a sturdy, first stage nozzle, in the short time of the accident was very difficult.

Whatever the event was it looks very energetic.

Don't think so; very energetic if happening in my backyard (Wow, that pressure washer!) but it happened in the hot part of a 400 ton rocket.
Useful to consider that the lateral panel is broken and ejected, but not disintegrated.

IMO it was very impressive that the LV continued to function and engine-out worked as advertised.

I completely agree ! !

[meekGee]

So hiding behind the Dragon glitch, was the comment by Shotwell about the engine failure:

"There was a material flaw that went undetected in the jacket of the Merlin engine, resulting in a breach ... causing depressurization of the combustion chamber, then the flight computer recognized that depressurization and commanded shutdown," said Gwynne Shotwell, president of SpaceX, during a press conference Thursday.

Questions that come to mind;

1) Since the engine was not recovered, how do they know about the (singular) material flaw? Material samples?  Were more engines made from the same batch and had to be reworked?  Can they tell where in the Jacket the breech occurred?  How much of a pressure drop was there?

2) What was the chain of events during the failure?  Did the outflow of propellant blast the fairing out, or did it indeed collapse because the engine was shut down?

3) How certain are they about this root cause?

[Robotbeat]

My guess to your first question is that they probably rechecked close-out pictures (and possibly X-Rays or something) that were made after the unit was manufactured but before it flew and spotted a possible flaw that they hadn't noticed before (or that they had judged non-critical).

Akin's Law #25:
"25. (Bowden's Law) Following a testing failure, it's always possible to refine the analysis to show that you really had negative margins all along."
http://spacecraft.ssl.umd.edu/akins_laws.html

[Kabloona]

My guess to your first question is that they probably rechecked close-out pictures (and possibly X-Rays or something) that were made after the unit was manufactured but before it flew and spotted a possible flaw that they hadn't noticed before (or that they had judged non-critical).

Akin's Law #25:
"25. (Bowden's Law) Following a testing failure, it's always possible to refine the analysis to show that you really had negative margins all along."
http://spacecraft.ssl.umd.edu/akins_laws.html

Gwynne made a comment earlier on the root cause determination...I didn't go back to find her exact quote, but it was to the effect that NDE (non-destructive evaluation) is an art that they are learning...which suggests to me that they did indeed go back and find something in their NDE test results that suggested a material flaw. Typical NDE methods include X-ray, ultrasound, and eddy current. Ultrasound will detect subsurface defects such as debonds that X-ray will miss. Ultrasound is also easier to do than X-ray. I'm wondering if they do ultrasound all around on the jacket after electroplating. Possible that they actually did identify an area of concern via ultrasound after manufacture, but that the variation was not significant enough to be considered a defect that would affect material strength. Often issues like this are identified during manufacture (eg a part gets dinged or dropped) and go through a standardized review process where an engineer(s) make a determination as to whether the part can be used or not. This review process for a potential flaw in the jacket would have been on record, and one of the first things they would have done is go back to the manufacturing records for the engine and review all the documented manufacturing issues for that engine. Could well be that this was a previously documented and analyzed issue that the engineers decided would not compromise material strength, and they were wrong this time, because, as Gwynne said, interpreting NDE results is more art than science. But they won't make that mistake twice.

Edit: Found that quote from Gwynne, about 16 minutes into the CRS-2 preflight presser on YouTube. She says "NDE is as much art as science...we're getting better at it," then makes "shameless plug" asking NDE experts to submit resumes to SpaceX...so clearly this is an area they feel they need help with.

[Elmar Moelzer]

If a piece is small enough, you can also use CT scanners... or so I know from a rather trustworthy source

[Robotbeat]

If a piece is small enough, you can also use CT scanners... or so I know from a rather trustworthy source

...which use X-Rays.

[Norm38]

They also have detailed mechanical simulations, so they know where the stresses are highest. If peak stresses overlap with the recently discovered defect, that would increase their confidence in a root cause.