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SpaceX Dragon 2 capsule destroyed in abort motor ground test
"Rocket Man" wrote on Thu, 25 Apr 2019
11:02:13 +0200: Isn't that the same everywhere these days? Bad news gets brushed under the carpet whilst good news is trumpeted everywhere. No, it's not. When SpaceX knows something they will say it. Until then there's nothing to say. -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
#12
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
JF Mezei wrote on Fri, 26 Apr 2019
02:19:47 -0400: On 2019-04-25 18:49, Fred J. McCall wrote: No, it's not. When SpaceX knows something they will say it. Until then there's nothing to say. They haven't receleased video of the event, nor of the state of the capsule after the event. These are facts they know. They have better things to do than fuel a bunch of harassed speculation. Neither of the things you list are 'facts' and the second one probably isn't even true. In the past, Musk had built expectations to see videos even of stuff that doesn't quite go right. Yes, yes, you were frightened by Musk when you were little. We get it. (In the rocket that exposded at pad, it was enthousisats who released videos, not SpaceX, so there is precedent of SpaceX not releasing video of a catastrophic failure. Again for the totally clueless among us, SpaceX will undoubtedly release video when they can explain what is going on in it. I suspect SpaceX decided that allowing speculation of what happened is better than confirming what happened. Showing you a video with no explanation doesn't 'confirm' anything. Have to wonder if SpaceX' hands may be bound because this is a NASA contract/hardware. Silly idea. Either way, they will at one point have to release details of the accident prior to resuling flight because NASA doesn't want to be seen flying something which the public might deeem to be unsafe. Yes, they will, and that's when they'll do it. When they can explain what happened. -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
JF Mezei wrote on Fri, 26 Apr 2019
22:49:33 -0400: On 2019-04-26 06:35, Jeff Findley wrote: Likely a cell phone video. As I recall they were enthousists wioth 60fps camera on tripiod filming the whole thing. so unlikely to be cellphone. (storage, battery autonomy). I don't think you're aware of the capabilities of cell phones. Their entire account on YouTube has since been deleted. That's telling (i.e. someone is in hot water with their bosses). That is very sad. Especially since it is a case closed, and as I recll, even SpaceX was happy to get the original video to give it an additional point of view. Just how is it a 'case closed'? They've decided not to release information until they've come to the conclusion what caused the anomaly. If you look at NTSB and similar agencies, they will generally quickly release facual information and early photos of wreckage (ensuring no clue to cause is seen in photos). But they will show extent of destruction. This isn't a passenger airplane crash and SpaceX isn't NTSB. investigation of this type. However, that does not stop armchair engineers from speculating, now does it? It makes it worse. Not possible. Consider TWA800 where they didn't want to release any info, ... You mean where they didn't HAVE any info. ... which lead to speculation ranging from space aliens attacking it to terrorism. There are still loons insisting that the report is a cover up and that the Navy shot it down. When Swissair 111 came down, the Canadian government didn't want to repeat this and made sure they released as much info as they could regularly. And that really reduced speculation on what caused it. This has since been seen in more air crashes. They had info. They'll most likely release the details once the actual cause is known. Right now they're surely busy cleaning up the site, cataloging the debris, and investigating the cause. These things take time. Is this a SpaceX investigation or a NASA investigation? Yes. SpaceX will have the lead, since it's their vehicle. -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
JF Mezei wrote on Sun, 28 Apr 2019
15:54:17 -0400: Have no idea if this is legit of not. video on the Dragon "anomaly" https://www.youtube.com/watch?v=6whBllkTkuU At about 55 second mark, includes phone video from futuremartian97 which allegedly shows the spaceX Dragon2 abort test. In it, it is pretty clear the capsule goes kablouey big time. Uh, no. There is no 'abort test'. The abort test is what they were working their way toward several months from now. (On youtube, you can use . and , to go frame by frame (. = forward, , = backward). There is not enough detail in those explosion frames to know if this video is legit or not. IF legit, this video shows capsule explosion happening before exhaust is seen out of engines. Which doesn't tell you anything at all. -- "Insisting on perfect safety is for people who don't have the balls to live in the real world." -- Mary Shafer, NASA Dryden |
#16
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
On 4/22/2019 7:05 AM, Jeff Findley wrote:
This is bad. My guess is at least a year delay for SpaceX commercial crew. Here is hoping that Boeing gets its act together because we need something to replace Soyuz for US crew. Jeff FWIW the conventional wisdom seems to be focusing on the COPV tanks used to fuel the SuperDracos. But this is pure speculation (SWAGs if you will). I have seen ONE still frame taken from a normal speed camera that appears to show an explosion taking place "around" the capsule where the hatch window still appears in the frame. In another video you can see at least two explosions, the first as mentioned where the capsule is largely still intact and a 2nd to the left (from the viewer viewpoint) of the first which appears to blow the capsule off the test stand. Which would tend to indicate multiple possibly cascading explosions. AFAIK know from what has been published in other forums the capsule is believed to be a total loss. Yes this is bad, but the test engineer in me is very happy that this happened during *testing*. Although a RUD is never a welcome event it is a learning opportunity with the net result of an improved design. This is what happened after the Apollo 1 fire. The following block improvements to the Command Module made the follow-ons very different from the original article including the wiring and hatch design from what I have read. It was poor judgement and bad test design that I feel were the real reason behind the fatalities that should not have happened. You could say we were "lucky" that this happened while no crew were on-board, but I *hate* that term. What is proper to say is that an anomaly was caught in testing, just as it should be. What keeps me up at night are the anomaly's that I didn't test for. That is why you do design review after design review and test and test again, and then alter and add to the testing regimen and test again to prove out design margins. Luck as defined simply means you missed a test and found a failure mode at an opportune time. David |
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
JF Mezei wrote on Sun, 28 Apr 2019
23:11:19 -0400: On 2019-04-28 22:13, Fred J. McCall wrote: Uh, no. There is no 'abort test'. The abort test is what they were working their way toward several months from now. IsN't capsule jettison an "abort" test ? If not sorry for bad terminology. There was no 'capsule jettison' as part of this engine test sequence. There are two abort cases they really want to test (the two are at the extremes of the envelope). One is a 'ground abort', where the capsule needs to escape before or very near after liftoff. That test was completed years ago. The other case is a 'Max Q' abort, where the capsule separates and escapes when the stack is undergoing maximum aerodynamic pressure. That's the one they're working toward doing. The test with the anomaly involved a restrained capsule firing engines just as an engine test. IF legit, this video shows capsule explosion happening before exhaust is seen out of engines. Which doesn't tell you anything at all. Not seeing exhaust from Super Dracos before explosion seems to be significant to me. Bas there been say 2 seconds of exhaust and SpaceX telemetry shwhoing "take off " force of the capsule against its stand and then kaboom, it woudl mean that engines started and produced thrust before things went wrong. It may seem 'significant' to you, but it shouldn't. If the kaboom happens before that, it would point to the explosion happening prior to the hypergolics mixing in the combustion chamber and then goig out the exhaust. You don't know that. For example, one hypothetical failure that would look like what is seen would be a catastrophic combustion chamber failure right when the propellents mix. What is not known is the time delay between the command to strt engines and the explosion. If 10 seconds elapsed between command and explision with engines showing no sign of thrust, it is quite different from a big kaboom happening within a second of command being sent. You can flap your arms all you like but you can't come up with a hypothesis that will fly without a LOT more data (and there are a lot more things that aren't known than the one you cite). For hypergolic fuels, do any of the 2 components have ability to ignite without the other component when in contact with air ? Or are they truly inert until the 2 components meet ? (aka: could combination of spark and ambient air with O2 in it cause one of the 2 to ignite ?) Or does the explosion imply that the 2 components did meet/mix ? You can get hydrazine to oxidize in air, but it won't be nearly as energetic as when oxidized with dinitrogen tetroxide. For example, hydrazine is used as a foam blowing agent because of the huge quantities of gas it produces during normal oxidation. The question is where would air and a spark come in contact with gaseous hydrazine? I consider it unlikely in the extreme. I'd consider the likely causes here to be a pressure vessel or pressure line failure or a combustion chamber failure. I'm sure there are lots of other possible failure modes. -- "Insisting on perfect safety is for people who don't have the balls to live in the real world." -- Mary Shafer, NASA Dryden |
#18
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
David Spain wrote on Mon, 29 Apr 2019 09:01:20
-0400: FWIW the conventional wisdom seems to be focusing on the COPV tanks used to fuel the SuperDracos. Possible, but this seems odd to me. Neither of the fuels is even mildly cryogenic, so what failure mode would there be? This isn't like the Falcon 9 explosion where cryogenic chilling was involved. If it was something like that I would expect it would have to be a 'one off' manufacturing defect of some kind, which would lead to a pretty rapid return to flight. -- "Insisting on perfect safety is for people who don't have the balls to live in the real world." -- Mary Shafer, NASA Dryden |
#19
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
JF Mezei wrote on Mon, 29 Apr 2019
17:00:46 -0400: On 2019-04-29 09:38, Fred J. McCall wrote: I consider it unlikely in the extreme. I'd consider the likely causes here to be a pressure vessel or pressure line failure or a combustion chamber failure. I'm sure there are lots of other possible failure modes. Would the hypergolic tanks need to be highly pressurized? What is needed is for the liquid components be pushed through pipes to combustion chamber right? Right, which means you need pressure that exceeds the combustion chamber pressure. That implies either highly pressurized tanks, really powerful pumps, or both. It's usually done with highly pressurized tanks because that's the simpler approach (fewer moving parts) and the point behind hypergolic engines is simplicity and reliability. How would the hypergolic tanks be configured? are they like a piston, normally with no pressure, but when needed, helium is pushed on one side of piston to push the fuel out the other end ? or just pumping helium into the bank hoping the fuel is at the "exit" end ? Are the tanks normally under pressure or is pressure applied only when engines are fired ? My expectation would be that the tanks would always be pressurized and that engine firing is controlled by throttle valves. Again, simplest and most reliable approach. We may have seen an explosion, but it has no context in terms of timeline. Were they filling tanks? did explosion happen while noting was happening? or happen when they fired the engines ? Exactly the point. Since they were going into an engine test I'd expect the tanks would already be filled long before. Again, these are not cryogenic fluids and there's not a "we want them as cold as possible". Remember, in normal use these tanks may sit for a LONG time before the engines get used, since they're not normally using during an ascent. I'd expect the explosion happened either very shortly before or right at 'engine ignition' time. This may have nothing to do with actual engines. It it may. I find it doubtful that there is a systemic design flaw with all the fire time that these engines have had. I'm leaning toward a 'one off' manufacturing flaw or mechanical failure involving a pressure vessel, tank, feed line, or combustion chamber. But I don't know any more than anyone else, not having the exact timeline and telemetry. -- "Insisting on perfect safety is for people who don't have the balls to live in the real world." -- Mary Shafer, NASA Dryden |
#20
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
On 4/29/2019 10:28 PM, Fred J. McCall wrote:
David Spain wrote on Mon, 29 Apr 2019 09:01:20 -0400: FWIW the conventional wisdom seems to be focusing on the COPV tanks used to fuel the SuperDracos. Possible, but this seems odd to me. Neither of the fuels is even mildly cryogenic, so what failure mode would there be? This isn't like the Falcon 9 explosion where cryogenic chilling was involved. If it was something like that I would expect it would have to be a 'one off' manufacturing defect of some kind, which would lead to a pretty rapid return to flight. Let's hope so. Could be a weld issue? Could be a lot of things I suppose. If these things are made in batches it might be informative to pull COPV's from the same build run and check them, maybe run some stress tests on them. It's all SWAG at this point and I'm sure as hell no expert. Could be something else entirely. Conventional wisdom is often wrong. Dave |
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