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

[TomH]

Interesting allotropes of solid Oxygen:
(quote=Wikipedia)
The metastable molecule tetraoxygen (O
4) was discovered in 2001,[38][39] and was assumed to exist in one of the six phases of solid oxygen. It was proven in 2006 that this phase, created by pressurizing O
2 to 20 GPa, is in fact a rhombohedral O
8 cluster.[40] This cluster has the potential to be a much more powerful oxidizer than either O
2 or O
3 and may therefore be used in rocket fuel.[38][39] A metallic phase was discovered in 1990 when solid oxygen is subjected to a pressure of above 96 GPa[41] and it was shown in 1998 that at very low temperatures, this phase becomes superconducting.[42](/quote)
Can you increase the reactivity of O2 by freezing it? Superconductivity can throw your heat transfer models out-of-the window.

It appears that you are interpreting superconductivity as thermal superconductivity. I believe the context is more likely electrical superconductivity.

[rsdavis9]

Aren't we talking about not thermal conductivity but about the difference of heat capacity of a liquid versus that of a gas?

How much different density is helium liquid versus gas?

Like h2o liquid carries a LOT more heat and h20 gas.

[Space Ghost 1962]

Keep in mind that the thermal shock inside the carbon matrix of "intruding" oxygen can be compressed by the matrix as it shrinks/pinches - this can be great enough localized pressure spikes to cause phase changes with "chemical consequences".

[TomH]

Aren't we talking about not thermal conductivity but about the difference of heat capacity of a liquid versus that of a gas?

My post was only in reference to what Fred copied from Wikipedia re. solid Ox, not re. others' posts.

[sdsds]

In retrospect a really great place to have a temperature transducer would be inside the over-wrap of the helium bottle. Are helium COPVs ever manufactured with integrated temperature sensors?

[ChrisWilson68]

In retrospect a really great place to have a temperature transducer would be inside the over-wrap of the helium bottle. Are helium COPVs ever manufactured with integrated temperature sensors?

Sounds dangerous to me.  The liner pushes pretty hard into the over-wrap and having some foreign object in between sounds like a potential cause for a failure.

[Proponent]

Above 50K [heium] has the negative Joule-Thomson. Below 50K it behaves like most other gases in that expansion equals cooling and compression equals heating.

That's true when the pressure is near 1 atm, but at the pressures likely prevalent during most of the loading process, the JT coefficient is negative over a wider range of temperatures.  The data plotted below are from NIST's Chemistry Webbook -- a wonderful resource.

[Fred Bonyea]

I'm curious, if something like the above did happen and the helium condensed, then what would happen to the COPV from a purely pressure point of view? Would the pressure from the LOX be enough to collapse it?

The case breathes in and out (very slightly) with pressure changes. The pressure differentials within the case walls voids (pinch points) heat up dramatically with each expansion.

In the 'Trapped LOX' scenario, Think of a balloon being poked by a hot pin. In this case, the hot pin had to sink through a large number of layers, but it is more exactly a minute oxygen cutting torch, using the case as fuel. 

[Fred Bonyea]

Interesting allotropes of solid Oxygen:
...

It appears that you are interpreting superconductivity as thermal superconductivity. I believe the context is more likely electrical superconductivity.

It is my understanding that materials that are electrically superconductive are also thermally superconductive; that is, transfer heat at near the speed of sound.

[TomH]

It is my understanding that materials that are electrically superconductive are also thermally superconductive; that is, transfer heat at near the speed of sound.

You might want to do some reading:

http://boards.straightdope.com/sdmb/showthread.php?t=66516

https://www.physicsforums.com/threads/thermal-superconductor.565504/

[Fred Bonyea]

It is my understanding that materials that are electrically superconductive are also thermally superconductive; that is, transfer heat at near the speed of sound.

You might want to do some reading:

http://boards.straightdope.com/sdmb/showthread.php?t=66516

https://www.physicsforums.com/threads/thermal-superconductor.565504/

Thank you. So the LOX is superconductive, while the helium is thermally 'superconductive'.
Again, this has to be a nightmare when trying to model and predict the mechanical stresses within the COPV.

[Pete]

Thank you. So the LOX is superconductive, while the helium is thermally 'superconductive'.
Again, this has to be a nightmare when trying to model and predict the mechanical stresses within the COPV.

Guys please. This is the *serious* discussion board, not the weird & wacky ideas forum.

Talking about the behavior of liquid helium II, and about the superconductivity of Oxygen when under several Gigapascals of pressure and at temperatures well below 5K, have
***NOTHING*** to do with the Falcon-9 rocket.

These are temperatures and pressures that will not occur at any stage of the manufacture or operation of this vehicle.

You might as well try discussing the hyper-sonic aerodynamics of a penny-farthing bicycle, it is just as relevant.

[Steven Pietrobon]

From what I've read, the helium is in the kerosene tank on the first stage, and it hasn't had any major problems except landings.

Those reports are wrong. The Helium tanks are in the LOX tank of both stages. You can see the struts in the first stage LOX tank here that hold down the Helium tanks (although that is an early version of Falcon 9). You can also hear the flight controllers referring to cryohelium for both stages in the countdown (see my previous post here). The LOX is used to keep the Helium at cryogenic temperatures allowing more Helium to be stored in each Helium tank.

https://i.imgur.com/Qqez320.jpg

So am I correct in assuming that the fix is to load the helium first then the oxygen?

You could load some of the helium first, but not the full flight load. The trick is to load the Helium in such a way that its temperature does not go below the freezing point of LOX. The Joule-Thomson effect could mean that as the Helium pressure is increased, the temperature goes down below the freezing point of LOX due to a negative expansion coefficient. Proponent's post above shows that at 20 MPa (the MEOP for the tanks is 38 MPa), the expansion coefficient is negative at the temperatures involved. This effect is what might have caught SpaceX out.

For example say the starting pressure is 20 MPa and temperature is 66.5 K, the subcooled temperature of LOX. The expansion coefficient is -0.5 K/MPa. Increasing the pressure to 38 MPa will result in a temperature decrease of (38-20)*0.5 = 9 K, taking the temperature to 66.5-9 = 57.5 K. The freezing point of LOX is 54.4 K at 0.1 MPa, so in this case it should be OK but the margin is only 3.1 K.

[Odysseus]

Hi,
Allow me a first (newcomer) question. In earlier statements, SpaceX mentioned "cryogenic He", an expression which was not unambiguous, but still could be interpreted as meaning cold gaseous He.
In one of the latest SpaceNews articles, Mr. Musk is cited saying "...failure involved liquid helium...". This would mean He at 4.1 Kelvin (or lower). Is there any known validation of this statement from Mr. Musk? Or was it simply not correct?
Cheers
Odysseus

[Comga]

Above 2.26 atmospheres = 0.23 MPa Helium is a supercritical fluid, neither gas or liquid.
Musk may have used "liquid" instead of "fluid" because it is a more common term. We may be over-analyzing the quote. (Imagine that! )

If the negative Joule-Thompson effect cools the Helium as it is compressed, and SpaceX has to keep it above the freezing point of Oxygen, the required procedural change may be as simple as raising the temperature of the Helium flowing into the COPVs.

[LouScheffer]

Two guesses as to why liquid helium is mentioned.  Maybe its just sloppy terminology, and the helium is actually supercritical.  Or maybe SpaceX pumps a certain amount of honest-to-goodness liquid helium into the tank to chill things down faster, but by lift-off all of the liquid has evaporated (or undergone whatever you call the transition from liquid to supercritical).

I'm struggling to understand this. Elon did say liquid helium; maybe he simply mis-spoke.

The critical point of helium is near 5.2 K at 0.23 MPa (roughly 2.2 atm). No amount of added pressure makes it a normal liquid until the temperature goes below 5.2 K, right? Does anyone believe SpaceX designed a propellant loading process that involves temperatures that low?

First, Musk is reasonably competent. If he said liquid I'd be very surprised if he meant anything else.

Second, a temperature of 4.2K makes perfect sense.  If you go down to the corner store and by some liquid helium, it will be at 4.2K - that's the boiling temp at 1 atm.  You can raise it a little by pressurizing, but why bother?

Now, except for this solid oxygen problem, there is no problem if the helium temp is low (in fact it's better, less pressure) but you cannot launch if it's too high (not enough in the tank).  So it makes sense they might pump in the right amount in liquid form.  It's going to evaporate as it hits the hotter material (and even sub-cooled LOX is much hotter) but at least you will start with cold-as-possible helium.  So perhaps they simply pump liquid helium from a supply into the rocket.  They may have never even considered that the tank could get *too* cold (It was certainly not obvious to me.)

This brings up another point I have not seen mentioned.   If you use sub-cooled LOX (compared to regular LOX), you can either (a) use smaller, lighter tanks or (b) run at reduced pressure, since the lower temp stores more helium in the same volume.  If they chose (a), smaller tanks, they get higher performance but MUST have adequate sub-cooling, to fit enough helium.  If they chose (b), so the tanks are big enough even with regular LOX, then they have no constraint on LOX temp (except from sufficient LOX loading on  performance limited missions) .  Given the importance of second stage performance, I suspect they chose (a), but I've not seen this mentioned.

[Fred Bonyea]

Thank you. So the LOX is superconductive, while the helium is thermally 'superconductive'.
Again, this has to be a nightmare when trying to model and predict the mechanical stresses within the COPV.

Guys please. This is the *serious* discussion board, not the weird & wacky ideas forum.

Talking about the behavior of liquid helium II, and about the superconductivity of Oxygen when under several Gigapascals of pressure and at temperatures well below 5K, have
***NOTHING*** to do with the Falcon-9 rocket.

These are temperatures and pressures that will not occur at any stage of the manufacture or operation of this vehicle.

Do you know what the temperatures and pressures are in the microchannel voids of the COPV as the pressure inside the bottle oscillates? Because microchannel pressures could easily exceed operational pressures by many magnitudes. If Oxygen is in a less stable state, (reacts with carbon fibers at lower temperatures) near critical states as the article I referenced stated; This could be the smoking gun Elon is/was having a difficult time isolating - a critical physical factor not used in modeling.
I am looking for a source of ignition, and with the information we have today, microchannel dieseling is an 'improbable but possible' source of ignition. Electrostatic discharge is very highly 'improbable' too; but can it be completely ruled out if non-electrically conductive 'neither liquid nor gas' helium is sloshing about inside of an isolated conductor?
Until a source of ignition is identified, isolated and duplicated, I respectfully suggest that any and all improbable solutions need to be considered part of the 'serious' discussion.

[Jim]

Electrostatic discharge is very highly 'improbable' too; but can it be completely ruled out

yes

[Odysseus]

I tried to dig out how the Helium is provided to LC40. Is it still correct that it is provided on railcars, at a pressure of about 40 MPa and "ambient" temperature?
Cheers

[Jim]

I tried to dig out how the Helium is provided to LC40. Is it still correct that it is provided on railcars, at a pressure of about 40 MPa and "ambient" temperature?
Cheers

No, it is stored in former rail cars.  It comes to the complex via pipeline.