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Elon Musk appeared on CNBC and offered a definitive explanation for his company's recent launch explosion:
SpaceX CEO Elon Musk says that his company has finally gotten to the bottom of the September 1st Falcon 9 explosion — claiming it was the "toughest puzzle" they've ever had to solve. And now that the problem is known, he expects SpaceX to return to flight in mid-December.
Speaking on CNBC yesterday, Musk said "it basically involves liquid helium, advanced carbon fiber composites, and solid oxygen. Oxygen so cold that it actually enters solid phase." So what does that mean exactly? Musk gave some hints a little while ago during a speech he gave to the National Reconnaissance Office. According to a transcript received by Space News, he argued that the supercooled liquid oxygen that SpaceX uses as propellant actually became so cold that it turned into a solid. And that's not supposed to happen.
This solid oxygen may have had a bad reaction with another piece of hardware — one of the vehicle's liquid helium pressure vessels. Three of these vessels sit inside the upper oxygen tank that holds the supercooled liquid oxygen propellant. They're responsible for filling and pressurizing the empty space that's left when the propellant leaves the tank. The vessels are also over wrapped with a carbon fiber composite material. The solid oxygen that formed could have ignited with the carbon, causing the explosion that destroyed the rocket.
Musk called the issue one that had "never been encountered before in the history of rocketry." One of SpaceX's customers, Inmarsat, may find an alternative for one of its upcoming satellite launches. SpaceX launches could resume mid-December.
For comparison's sake, at standard pressure:
- Liquid Helium: 4 K (about −269 °C or −452.2 °F).
- Solid Oxygen: 54.36 K (−218.79 °C, −361.82 °F).
- Solid Nitrogen: 63.15 K (−210.00 °C, −346.00 °F)
- Liquid Nitrogen: 77.355 K (−195.795 °C, −320.431 °F)
- Liquid Oxygen: 90.19 K (−182.96 °C; −297.33 °F)
- Dry Ice (Solid CO2): 194.65 K (−78.5 °C; −109.3 °F).
(Score: 5, Informative) by VLM on Monday November 07 2016, @02:03PM
What we don't know is WHY IT IGNITED
Some decades ago there was an attempt to use charcoal and liquid O2 as a mining explosive instead of ANFO. It went pretty much nowhere because it was just too unpredictable and unpredictability is a killer with explosives. Yeah yeah all the parts are non-toxic, the smoke is non-toxic, if there's a misfire you wait for the O2 to evaporate and its safe as a bag of charcoal (which, basically, it was).
https://en.wikipedia.org/wiki/Oxyliquit [wikipedia.org]
Pure O2 is quite a PITA to work with. If there's a finger print in an oxygen regulator, sometimes the finger grease spontaneously ignites and blows the regulator apart, which usually does nothing good to the contents of the O2 tank or the people standing nearby.
Something I always found creepy about industrial pressure vessels is if the compressor is far enough away you can hear all kinds of creaking and wriggling as a tank pressurizes and probably they drew a little helium off to actuate a valve or move a servo and the tank wiggled a microscopic fraction of an inch leading to kaboom.
Things like space shuttle tanks and Saturn-V tanks "should have" blown up, but being made of bulk solid aluminum they can't burn quite as well as carbon fiber, which is basically charcoal fiber soaked in plastic, which should burn like hell.
I could see some new general engineering rules coming out of this like no using carbon fiber in contact with liq O2. I'd be surprised if this is the first time someone blew up a carbon fiber tank with liq O2.
(Score: 2) by ledow on Monday November 07 2016, @08:18PM
Good links.
"I'd be surprised if this is the first time someone blew up a carbon fiber tank with liq O2."
In which case, why would you try it?
(Score: 2) by VLM on Monday November 07 2016, @10:30PM
I should have searched NTRS before even posting.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20010020209.pdf [nasa.gov]
To summarize our tax dollars at work, it takes some effort to blow up liq O2 and carbon fiber, but it most certainly can be done and the paper was full of wiggle words about if theres no source of ignition energy (like a helium tank banging the hell around inside it) then it should probably behave most of the time.
Also they didn't test solid O2 and generally nice dense solid O2 was more of a headache for the explosives.
So... Liq O2 by itself doesn't spontaneously cook off, but solid O2 with a tank in the middle being Fed with is less healthy.
Waaaay back when it blew up there was some talk from spacex about it all being an operational procedure thing, so yeah, just don't make an O2 slushie and let the liq helium sit there for hours beforehand.
I donno if you can man-rate a rocket with slush O2 and a CF helium tank inside it... even if operationally you're really careful about not slushing the tank more or less.