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

[oiorionsbelt]

We can't know much based on the little spacex says, but if you like to worry, this is good material.

or you could just read other parts of this forum and save yourself the trouble.

[IainMcClatchie]

But the flip side of this may be that He cools when compressed (otherwise you might be able to design a perpetual motion machine with He as the working fluid).

Still trying to wrap my head around the Joule-Thompson effect.

The effect happens when the He is expanded, without doing work.  That makes entropy and is irreversible.  I don't think it's possible for the gas to compress without doing work on it, nevermind how the temperature might change if that happened.

[Steven Pietrobon]

do you mean 44.4K? 54.4 is off the top of the graph well away from the curve.

No, I meant 54.4 K which is the freezing point of LOX. As the supply pressure is presumably above the inversion pressure of 3.85 MPa, it really does not matter what the supply temperature is, since the Joule-Thompson coefficient will always be negative.

Also would you be likely to get any strange behaviours if there was a sharp jump over the line due to a drop/jump in pressure or temperature in the right region?

The supply temperature and pressure would have to drop below 43 K and 3.85 MPa for strange things to possibly happen, since the expansion coefficient would then go positive.

But the flip side of this may be that He cools when compressed (otherwise you might be able to design a perpetual motion machine with He as the working fluid). The in-flowing He may warm as it expands into the COPV, but the He already present in the COPV should cool as it is compressed. This compression-cooling (if it exists) may be significant enough to drop the temperature below the freezing point of the LOX.

That's what I thought as well, but compressing Helium involves performing work which invariably will cause the Helium to warm up. Note that expansion is a process that is called Irreversible, which I believe means that the reverse process can not occur.

[rsdavis9]

But the flip side of this may be that He cools when compressed (otherwise you might be able to design a perpetual motion machine with He as the working fluid).

Still trying to wrap my head around the Joule-Thompson effect.

The effect happens when the He is expanded, without doing work.  That makes entropy and is irreversible.  I don't think it's possible for the gas to compress without doing work on it, nevermind how the temperature might change if that happened.

The easiest way to think about the joule thomson is to imagine what happens to regular gases. without work they should not cool or heat up. Thats a ideal gas. So a regular gas cools down because its like a mini solar system. There is a net attraction between the molecules(van der walls force). So as the molecules get farther apart it is effectively going into a higher orbit and therefore trading velocity(temp) for a greater potenial energy(higher orbit). So in the joule-thomson instead of attraction we have repulsion and therefore the greater potential energy is compressed and therefore lower velocity and cooler.

Work is something that increases the velocity of the gas by a moving wall of the container. If there isn't a moving wall then there is no work. (Maybe?) I could imagine a magneto-hydro pump. Where is the wall?

[kevin-rf]

For those of us who don't wade through all the SpaceX threads. I believe the "SpaceX McGregor Testing Updates and Discussion (Thread 4)" is being used for discussing Wednesday's exciting test event result and subsequent very loud noise.

http://forum.nasaspaceflight.com/index.php?topic=39182.msg1609866#msg1609866

[Ben the Space Brit]

Sigh, I have a bad feeling I'm going to be covering a SpaceX launch during my annual Christmas party again

https://twitter.com/lorengrush/status/794597372600913920

Attached to the tweet (and this post) is what looks like a transcription of Elon's interview.

So, if I'm reading this right, what we're basically looking at is the inevitable consequence of innovation - doing something totally new means that faults can emerge that no expert was capable of predicting.

[woods170]

Sigh, I have a bad feeling I'm going to be covering a SpaceX launch during my annual Christmas party again

https://twitter.com/lorengrush/status/794597372600913920

Attached to the tweet (and this post) is what looks like a transcription of Elon's interview.

So, if I'm reading this right, what we're basically looking at is the inevitable consequence of innovation - doing something totally new means that faults can emerge that no expert was capable of predicting.

Precisely. The ones that are first in doing something new are also the ones having the highest chance of running into unknowns and issues. Much like SpaceX AND Blue Origin running into issues in their attempts to land boosters.

[Proponent]

Work is something that increases the velocity of the gas by a moving wall of the container. If there isn't a moving wall then there is no work. (Maybe?) I could imagine a magneto-hydro pump. Where is the wall?

A wall in the conventional sense is not necessary: a small parcel of helium can do work on a neighboring parcel.  The "wall" is just the neighboring atoms.  Under the high pressures relevant here, the mean free path of a molecule is short (less than a micron, I imagine).  If you're thinking about a parcel of helium flowing through a pipe, you might imagine thin, massless disks either side of the parcel, flowing with it (and changing diameter if the diameter of the pipe changes).

[AnalogMan]

From the Waco Tribune article:

A blast Wednesday at the SpaceX rocket testing facility in McGregor was part of a test by accident investigators and caused no damage or injuries, according to a SpaceX spokesman.

[...]

“The sound heard by residents was actually the result of a pressurization test at the McGregor Rocket R&D facility. These tests take place periodically at the site, and this particular test was part of the ongoing testing being conducted by our Accident Investigation Team,” SpaceX spokesman Phil Larson said in an email response to questions.


http://www.wacotrib.com/news/greater_waco/mcgregor/explosion-at-spacex-in-mcgregor-part-of-accident-investigation/article_a151e524-7787-5874-bc6b-b3062d09f608.html

[matthewkantar]

The Wall Street Journal chimes in:

http://www.wsj.com/articles/initial-report-about-spacex-september-rocket-explosion-imminent-1480329003

Matthew

[CameronD]

The Wall Street Journal chimes in:

http://www.wsj.com/articles/initial-report-about-spacex-september-rocket-explosion-imminent-1480329003

Matthew

Hmm.. must be a slow news week.

[meekGee]

The Wall Street Journal chimes in:

http://www.wsj.com/articles/initial-report-about-spacex-september-rocket-explosion-imminent-1480329003

Matthew

Hmm.. must be a slow news week.

I actually believe it was the Wall Street Journal.

[Lar]

The Wall Street Journal chimes in:

http://www.wsj.com/articles/initial-report-about-spacex-september-rocket-explosion-imminent-1480329003

Matthew

Hatchet job by a journalist who has shown previous tendencies to assume the worst.  (IMHO, YMMV)

[Nomadd]

The Wall Street Journal chimes in:

http://www.wsj.com/articles/initial-report-about-spacex-september-rocket-explosion-imminent-1480329003

Matthew

Hatchet job by a journalist who has shown previous tendencies to assume the worst.  (IMHO, YMMV)

Burt Rutan would call that appraisal of said journalist charitable.

[woods170]

The Wall Street Journal chimes in:

http://www.wsj.com/articles/initial-report-about-spacex-september-rocket-explosion-imminent-1480329003

Matthew

Hatchet job by a journalist who has shown previous tendencies to assume the worst.  (IMHO, YMMV)

Burt Rutan would call that appraisal of said journalist charitable.

Not having followed the link to the WSJ article that can mean only one thing: Andy having done another one of his sloppy jobs.

[docmordrid]

The Wall Street Journal chimes in:

http://www.wsj.com/articles/initial-report-about-spacex-september-rocket-explosion-imminent-1480329003

Matthew

Hatchet job by a journalist who has shown previous tendencies to assume the worst.  (IMHO, YMMV)

Burt Rutan would call that appraisal of said journalist charitable.

Not having followed the link to the WSJ article that can mean only one thing: Andy having done another one of his sloppy jobs.

Pretty much. Not as blatantly schillish as someone at F*****, but yeah.

[NX-0]

While not your typical source for space news...here is something more recent (...and possibly translated?)

http://www.gamenguide.com/articles/76795/20161129/investigation-of-spacex-falcon-9-explosion-coming-to-light-as-elon-musk-s-company-faces-deadline.htm

[pippin]

I don't think it's more recent ("still targeting November", really?) but rather an article compiled from old news. Probably by a bot. I wish they'd just teach these bots some proper grammar....

[jpo234]

So, with the investigation concluded: What is the short term fix?

My understanding is, that SpaceX will fill the Helium bottles before they are submerged into the LOX. That way, the COPVs are in a stable state, that will prevent trapped LOX from getting compressed when the COPVs fill and the liner starts to press against the overwrap.

Additionally they will use "warmer" He, to prevent LOX from freezing into SOX.

Is this a reasonable synopsis?

[mn]

From the SpaceX update:

The investigation team concluded the failure was likely due to the accumulation of oxygen between the COPV liner and overwrap in a void or a buckle in the liner, leading to ignition and the subsequent failure of the COPV

Bold added.

So it seems they are not even sure of cause?