"Through extensive testing in Texas, SpaceX has shown that it can re-create a COPV failure entirely through helium loading conditions. "This is good news.
Quote from: Fred Bonyea on 10/28/2016 10:16 pm"Through extensive testing in Texas, SpaceX has shown that it can re-create a COPV failure entirely through helium loading conditions. "This is good news.Ummmmmmmmm...Wouldn't it be better to have a helium system that can't be blown up by loading conditions?All of this is trending towards a lack of margin in F9. I know they want to push the envelope but maybe an extra screw or nail isn't a bad idea here. "Proceduring" your way around design weak spots reminds me of rubber o-rings.
Quote from: Dante80 on 10/07/2016 06:17 amAssuming an operation error (no defects or installation errors). 1. COPV being filled to operational pressure before being completely immersed. On the Falcon 9 has a pre-pressurization COPV?this happens at the start or advance?
Assuming an operation error (no defects or installation errors). 1. COPV being filled to operational pressure before being completely immersed.
Just because they "reproduced "the same conditions and the same result does not mean that they found the root cause. Remember, they reproduce the results using a sniper and a bullet.
It is good that they are closer to figuring out the physical root cause of the explosion. But why did SpaceX allow a new loading procedure during the static fire? Are they underestimating the risk of their incremental tweaks to the launch vehicle?The last failure taught them to perform more validation testing of certified components. Will this failure teach SpaceX to perform more testing before making changes to their in-production equipment and procedures?
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That question may be part of why testing is ongoing.
SpaceX’s efforts are now focused on two areas – finding the exact root cause, and developing improved helium loading conditions that allow SpaceX to reliably load Falcon 9. With the advanced state of the investigation, we also plan ...
Wouldn't it be better to have a helium system that can't be blown up by loading conditions?All of this is trending towards a lack of margin in F9. I know they want to push the envelope but maybe an extra screw or nail isn't a bad idea here. "Proceduring" your way around design weak spots reminds me of rubber o-rings.
Quote from: wolfpack on 10/29/2016 01:00 amWouldn't it be better to have a helium system that can't be blown up by loading conditions?All of this is trending towards a lack of margin in F9. I know they want to push the envelope but maybe an extra screw or nail isn't a bad idea here. "Proceduring" your way around design weak spots reminds me of rubber o-rings.My car gave the "low tire pressure" warning yesterday. I pulled out the gauge and, sure enough, two tires were really low, one at about 26 psig vs the recommended 34. I drove to the gas station, put money in the air compressor, and started to fill the tires. The compressor filled them far faster than I expected, and I filled one tire well over 34 psig. I let the extra air out, and was just happy the thing didn't explode, causing me a very bad day. Moral of the story: even cars have systems that can be blown up by loading conditions. Tires are safe when loaded properly, but not when loaded improperly. The fuel system can catch fire, too, from a spark caused by the operator not being grounded, etc.
"Through extensive testing in Texas, SpaceX has shown that it can re-create a COPV failure entirely through helium loading conditions. "
Note that the tire does not explode. Margin of safety. And even if it exploded, it was only the tire. The machine would remain intact. Local accident, not global
The question in my mind is, did they use the same conditions and got the same result, or did they push the same type of conditions a little harder to get the result? If it was exactly the same conditions they should have caught it earlier, unless they cycled hundreds of times to get one blowing up.
"Leak before burst" is really a *design* principle that is later verified in qualification testing. But once the design has been qual tested, flight articles are obviously not tested to that level.For acceptance testing of flight article COPV's, SpaceX probably tests to a factor of, say, 1.5 x Max Expected Operating Pressure (MEOP) or whatever the NASA factor of safety is for testing pressure vessels on man-rated vehicles (I forget exactly what the NASA requirement is, but 1.5 x MEOP sticks in my mind. Jim can correct me.)In any event, SpaceX would have acceptance tested the flight COPV's at a pressure well above MEOP. So if a COPV failed at or below MEOP, there will be much head-scratching. If a COPV got over-pressurized, then the question is how.
Wouldn't there have to be a designed-in conductive path from the second stage through the interstage to the first stage to keep all structure at the same potential during ascent?
QuoteAlso my internet research reveals that COPVs are usually tested to a standard called 'Leak before Burst" Unknown if SpaceX tests to this standard."Leak before burst" is really a *design* principle that is later verified in qualification testing. But once the design has been qual tested, flight articles are obviously not tested to that level.For acceptance testing of flight article COPV's, SpaceX probably tests to a factor of, say, 1.5 x Max Expected Operating Pressure (MEOP) or whatever the NASA factor of safety is for testing pressure vessels on man-rated vehicles (I forget exactly what the NASA requirement is, but 1.5 x MEOP sticks in my mind. Jim can correct me.)In any event, SpaceX would have acceptance tested the flight COPV's at a pressure well above MEOP. So if a COPV failed at or below MEOP, there will be much head-scratching. If a COPV got over-pressurized, then the question is how.
Also my internet research reveals that COPVs are usually tested to a standard called 'Leak before Burst" Unknown if SpaceX tests to this standard.
Quote from: Kabloona on 09/24/2016 12:52 amQuoteAlso my internet research reveals that COPVs are usually tested to a standard called 'Leak before Burst" Unknown if SpaceX tests to this standard."Leak before burst" is really a *design* principle that is later verified in qualification testing. But once the design has been qual tested, flight articles are obviously not tested to that level.For acceptance testing of flight article COPV's, SpaceX probably tests to a factor of, say, 1.5 x Max Expected Operating Pressure (MEOP) or whatever the NASA factor of safety is for testing pressure vessels on man-rated vehicles (I forget exactly what the NASA requirement is, but 1.5 x MEOP sticks in my mind. Jim can correct me.)In any event, SpaceX would have acceptance tested the flight COPV's at a pressure well above MEOP. So if a COPV failed at or below MEOP, there will be much head-scratching. If a COPV got over-pressurized, then the question is how.They apparently proof to only 1.25x MEOP, which sporty. Burst is only 1.5x MEOP, which is definitely sporty; I'd use not less than 2x. Their approach is acceptable for metal vessels, not (IMHO) for composite.
Since day one my instinct has been that the 1st stage was somehow implicated in this event, no matter how unapparent the possibility. In my search for a post with information on a different subject, I came across a post that might explain the connection I've been groping for.QuoteWouldn't there have to be a designed-in conductive path from the second stage through the interstage to the first stage to keep all structure at the same potential during ascent? http://forum.nasaspaceflight.com/index.php?topic=30981.msg1582782#msg1582782
Quote from: CyndyC on 10/29/2016 08:45 pmSince day one my instinct has been that the 1st stage was somehow implicated in this event, no matter how unapparent the possibility. In my search for a post with information on a different subject, I came across a post that might explain the connection I've been groping for.QuoteWouldn't there have to be a designed-in conductive path from the second stage through the interstage to the first stage to keep all structure at the same potential during ascent? http://forum.nasaspaceflight.com/index.php?topic=30981.msg1582782#msg1582782What could an electrical conductivity question possibly have to do with an overpressure/failure of a He-filled COPV?
