Talk-Polywell.org

While they are spectactular failures, its nice the fix is something so (relatively speaking) trivial.

http://spaceflightnow.com/2017/01/02/sp ... alifornia/

After an exhaustive investigation, SpaceX engineers have identified the most likely cause of the spectacular explosion of a Falcon 9 rocket during a pre-launch test Sept. 1 that destroyed the booster and its $195 million satellite payload, the company announced Monday.

Fail, Learn, Evolve.
What Spacex is doing is the pure essence of Engineering.

I wish them the best on their Jan 8 launch, they have been a real source of mental enjoyment to me for all what they have done so far.

I wonder if they are changing the wrapping technique or loading or both.




Interesting read from NASA
https://ston.jsc.nasa.gov/collections/t ... 11-573.pdf

“Stress rupture is a sudden failure mode for [COPVs] that can occur at normal
operating pressures and temperatures. This failure mode can occur while at stress
levels below ultimate strength for [an] extended time. The failure mechanism is complex,
not well understood, [and] difficult to accurately predict or detect prior to failure.
The location and mechanism of triggering damage causing sudden failure is highly
localized, but at a random location. This location and extent of local damage has not
been able to be [reliably] detected by current [NDE] techniques prior to catastrophic
failure. Pressure, duration of time at pressure, and temperature experienced contribute
to the degradation of the fiber and/or the fiber-matrix interface, particularly around
accumulations of fiber breaks, and these increase the probability of COPV stress
rupture.”

I would guess just the loading procedure at this stage.
I would think that having discovered the problem there wouldn't be enough time to develop a new tank and fit or retro-fit it in to a booster for a launch date this soon - at any rate I can't imagine the FAA (or their customers) would be happy about a new tank design brought to service this quickly after the previous failure. Long term though, sure, that would seem to be the way to go.
Fingers crossed for SpaceX this year. They've done some amazing things and I'd like to see them have a clearer run and doing more impressive work.

paperburn1 wrote:I wonder if they are changing the wrapping technique or loading or both.




Interesting read from NASA
https://ston.jsc.nasa.gov/collections/t ... 11-573.pdf

“Stress rupture is a sudden failure mode for [COPVs] that can occur at normal
operating pressures and temperatures. This failure mode can occur while at stress
levels below ultimate strength for [an] extended time. The failure mechanism is complex,
not well understood, [and] difficult to accurately predict or detect prior to failure.
The location and mechanism of triggering damage causing sudden failure is highly
localized, but at a random location. This location and extent of local damage has not
been able to be [reliably] detected by current [NDE] techniques prior to catastrophic
failure. Pressure, duration of time at pressure, and temperature experienced contribute
to the degradation of the fiber and/or the fiber-matrix interface, particularly around
accumulations of fiber breaks, and these increase the probability of COPV stress
rupture.”

Seems very similar in mode to Brittle Fracture failures in steels.
1.) Susceptible material
2.) Preexisting flaw
3.) Thermal Stress transient

Space X is not saying much. They do mention some buckling of the aluminum inner liner- not a failure, but a redistribution of load forces. And this apparently created a void underneath the carbon fiber wrap where LOX could accumulate. Subsequent freezing of the lox- now SOX, disrupted the carbon fibers through friction or expansion or something. I suppose oxygen ice crystals could have abraded against some carbon fibers and produced enough local heat to ignite the carbon fibers in the pure oxygen. It apparently does not take much.

I wonder if the helium tank ruptured leading to overpressure in the oxygen tank, or if it was mostly rapid burning of the carbon fibers that produced heat, with flashing of liquid oxygen into gaseous oxygen with again oxygen tank overpressure.

I don't know how the first stage oxygen tank compares but possibly the second stage tank may have more problems with convective heat distribution around the helium tanks. Maybe they should add some stirrers. That worked so well with Apollo 13.

Dan Tibbets

It has been widely reported but, in case you missed it, the FAA has cleared SpaceX to launch.

http://arstechnica.co.uk/science/2017/0 ... alifornia/

Fingers crossed for Monday.

And they completed the tied down static firing this Thursday, so they are go for a Monday morning launch if weather and gremlins permit.

Dan Tibbets

Looks like the weather isn't permitting and things have been pushed back to the 14th. Fingers crossed not gremlins.. Better a safe later launch than an early failed one.

NotAPhysicist wrote:Looks like the weather isn't permitting ...

To get space launch cost down and routine up where we really want it, we need to somehow get to the point where common inclement weather isn't cause to postpone a launch.

Hopefully reusability will provide some of the hardening needed as a side benefit but I suspect given the difficulty of what they are doing we are always going to see them err on the side of caution.
Still, yes that would be nice.

hanelyp wrote:

NotAPhysicist wrote:Looks like the weather isn't permitting ...

To get space launch cost down and routine up where we really want it, we need to somehow get to the point where common inclement weather isn't cause to postpone a launch.

Inclement weather still postpones the launch ofcommercial aircraft. I think what you may have meant was that it should become less sensitive to inclement weather. But let us face it, I doubt they will ever launch during a hurricane.

A hurricane isn't what I'd consider =common= inclement weather. Common would include cloud cover, fog, a certain intensity of rain, modest winds ... In short if a golf tournament would continue, or there'd be no thought of canceling a football game.

Given some of the conditions I've seen considered fine for football that might be a tall order Not so fun at the time...

But yes, that would be nice, though I'd guess things would always be a bit more conservative.

Fingers crossed for Saturday.