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Latest candidate for SpaceX pad explosion
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Latest candidate for SpaceX pad explosion
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#13
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Latest candidate for SpaceX pad explosion
JF Mezei wrote:
On 2016-10-18 08:36, Jeff Findley wrote: It does when it's an energetic solid oxidizer (can't get much more energetic than solid oxygen) right next to a solid fuel (carbon fiber). Ahh. I remember asking early one what could be combusting in the rocket with LOX leaking and gotten no answer. I takle it that carbon fibre even when encased in resin is highly combustible ? is the resin/epoxy also combustible in contact with LOX ? (reminder to self: make sure not to spill any LOX on my bicycle :-( Would fibre glass be less explosive or would the resin still provide the combustible material that would yield the same result ? The overwrap is there as MECHANICAL support, not insulation. Fiberglass exposed to LOX temperatures is going to be, well, glass and shatter into tiny pieces. COVPs are not uncommon in rockets. However, supercooled LOX is. You do that and you have what is called a "contact explosive". The increase in pressure would cause it to literally explode. Would it be fair to assume that a breach in the metal coating inside the tank would have exposed LOX to carbon ? Uh, you seem to have this backward. The composite is an OVERWRAP around the helium tank to provide structural support. Oxygen getting inside the overwrap exposes LOX to carbon. Normally the liquid squeezes back out of the overwrap as the LOC tank is pressurized. However, if it actually froze to a solid in there, it stays where it is and gets carbon compressed into it. The pressure on the oxygen surrounded by the carbon is what causes the problem. -- "Insisting on perfect safety is for people who don't have the balls to live in the real world." -- Mary Shafer, NASA Dryden |
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Latest candidate for SpaceX pad explosion
JF Mezei wrote:
On 2016-10-18 11:11, Fred J. McCall wrote: What is "COPV" ? I said it in the original article and you cut it out. Composite Overwrapped Pressure Vessel. Sorry, had not made the association between the two. my bad. TNT is a solid. Does it care about pressure? Yeah, press it and it makes a really big bang. yes, but TNT, in solid form is stable until you ignite. It doesn't expand or create pressure in the lunch box that it us carried into. Now try the same thing with dynamite or nitro. No. Most substances are denser in their solid phases than their liquid phases. So the fact that some LOX solidified shouldn't magically cause an increase in pressure in the tank. No, pumping the tank full of LOX does that. Nothing magical. Is it possible that the cold is what did it? If the helium tank was surrounded by oxygen that it was colder than design, it could have caused the carbon fibre to become brittle, crack, and let helium out, causing overpressiure in LOX tank and then things went kablooey ? No. -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
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Latest candidate for SpaceX pad explosion
Sylvia Else wrote:
Still, its customers might reasonably expect their satellites to be launched on proven hardware, operated in the proven way, with experiments involved with innovation done on hardware that isn't launching an expensive satellite. In some cases, rockets have been qualified by launching dummy satellites (just a block of concrete or lead of the proper mass), but of course then some people consider this a waste of resources and a pollution of space. |
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Latest candidate for SpaceX pad explosion
JF Mezei wrote:
On 2016-10-18 23:27, Fred J. McCall wrote: Hint: The pressure in the LOX TANK goes up as you add LOX. Does it ? No, I'm making it all up. Sheesh. What did I say again? Don't they have an open vent as the pour liquid oxygen and let evaporating O2 escape to keep pressure stable ? Don't they close that gaseious escape valve just before launch ? It's a pressure relief valve, not just a hole to the outside. What did I say again? Hint: The pressure in the LOX TANK goes up as you add LOX. (if helium tank cracked and caused instant major increase in pressure, then the open vent line couldn't have handled that and would have allowed pressure inside to rise to beyond structural limits. We're past that. The question is WHY the helium tank cracked. Question: what advantage is there to have the helium tank inside the LOX tank ? Easier thermal management, among others. -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
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Latest candidate for SpaceX pad explosion
On Oct/19/2016 at 4:24 PM, Jeff Findley wrote :
In article om, says... Would the helium tank have contributed to the cooling of the LOX to form an "ice" layer over the COPV tank ? The pressure in the LOX supply line had to be greater than the pressure in the tank, otherwise, how would you ever fill the tank? As such, the LOX would drop in pressure as it entered the tank, resulting in a corresponding drop in temperature. That could result in the outside of the COPV getting so cold that solid oxygen was formed. I'm not sure about that. We are talking about sub-cooled LOX here. My understanding is that it is sub-cooled before being pumped into the tank. If you pump sub-cooled LOX into a tank the drop in pressure as it enters the tank doesn't have to be significant, and it is gases (or plasmas) that drop in temperature when the pressure drops. Liquids, not so much. Alain Fournier |
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Latest candidate for SpaceX pad explosion
JF Mezei wrote:
You're still not getting it. On 2016-10-19 06:23, Jeff Findley wrote: LOX spilled on anything combustible is bad. Would it be fair to state that the helium filled COPV has some sort of coating on the outer surface to normally prevent LOX from igniting the carbon fibre ? No. composite). The composite overwrap is in contact with the LOX *at all times*, because the helium tanks are inside the LOX tank. So how come the carbon on the outside of helium tank does not combust as it sits in a pool of LOX ? (see question above). They're at the top of the tank. Where does the boil-off happen? And if the LOX became solid, wouldn't it further enhance the integrity/strength of the helium tank by providing even more support ? Composite OVERWRAP. The hypothesis is that liquid oxygen got into the overwrap and froze solid. It is now surrounded by carbon and since it is solid cannot 'squeeze out' as pressure increases in the LOX tank. Or does "solid" LOX really mean a slushy mixture, or an actual solid block of LOX surrounding the helium tank. A slushy mixture would squeeze back out. It means solid INSIDE THE OVERWRAP. Would the helium tank have contributed to the cooling of the LOX to form an "ice" layer over the COPV tank ? Jesus, do you not understand what OVERWRAPPED means? Do this. Get an Ace Elastic bandage. Make a fist. Wrap the elastic bandage around your fist in multiple layers as tightly as you can. Get a small ice chip. Force it between the layers of Ace bandage. THAT is what we're talking about. Your fist is the metal He tank. The bandage is the composite overwrap. The ice chip is, well, the ice chip. from a scuba dividng point of view, when you fill scuba tanks and increase pressure, they get warm PV=nRT. If you pour liquid helium in an empty tank at 1ATM, I assume it will at first evaporate big time and be endothermic. But eventually, won't it become exithermic once pressure builds up and the liquid no longer evaporates ? You're misusing the words 'exothermic' and 'endothermic'. The helium pressure isn't the issue. OXYGEN pressure is the issue. Oxygen vaporizes, which increases pressure in the tank until the safety valve lets it vent. The tank is not being externally pressurized like a scuba tank on a compressor. It is being internally pressurized by some of the LOC evaporating. -- "Ignorance is preferable to error, and he is less remote from the truth who believes nothing than he who believes what is wrong." -- Thomas Jefferson |
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