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#51
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
JF Mezei wrote on Sat, 4 May 2019
18:45:28 -0400: fron: https://youtu.be/s6a9Ct9O_nY (NASA press conference on launch of cargo Dragon, they discussed Dragon 2 "anomaly". "just prior, before we wanted to fire the Super Draco, there was an anomaly and the vehicle was destroyed" "anomaly occured during activation of the Super Draco system". "we have no reason to believe tht there is an issue with the Super Draco themselves", "those have gone thorugh about 600 tests". I'm pretty sure several of us told you that right after the anomaly happened. The way I interpret the SpaceX spokesperson's words: -The engines are not at issue. You don't know that. "No reason to believe" does not mean "not". It just means that like the COPVs it's a lower probability. But we're not playing "guess the most probable thing". We're playing "what the **** went wrong so we can prevent it from happening again, regardless of how likely it was". -use of word "system" points to when they "booted" the system, not when they pressed the the big red button to get fuel to the engines. Right conclusion but wrong reason. Your key is 'activation', not 'system'. And that still doesn't guarantee it wasn't a combustion chamber failure. For example, you pressurize the propellant tanks and a throttle valve fails. That puts propellant under pressure in the combustion chamber. -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
#52
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
In message
Jeff Findley wrote: I doubt NASA is going to put anyone at risk, so the cleanup and collection of debris and data will be slow and methodical. They're going to want to document every bit of debris including exactly where it was found. It's hard to do that when you're in a hazmat suit. Elsewhere I've seen it said that the residual hypergolics isn't the main reason for diverting the first stage landing, there are after all two pads some distance apart. It's because it is very tricky to document the position of any bits of debris when they've been blown about by the exhaust from a descending Merlin. Anthony |
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
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#54
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
JF Mezei wrote on Sun, 5 May 2019
12:11:21 -0400: On 2019-05-05 09:43, Jeff Findley wrote: Depends on the details of the design. Plumbing, control valves, check valves, and etc. will all cause a pressure drop from the tanks to the combustion chamber. OK, let me reformulate the question: Would there be an expectation that the tanks holding hypergolics be built to widthstand operating pressure (say 1000psi) with some safety margin, or would they be designed to support the same pressure as what the helium tanks are built for (say 10,000psi) in case a regulator fails and equalizes between helium of hypergolic tanks ? There is no such expectation and it would be a poor design that did so. This another reason why I hate idle speculation. You're essentially trying to reverse engineer the entire design to come up with pressures of everything. No, trying to understand how these engines are built so that I can see various way they can fail and better understand the meaning of what SpaceX does say. You seem mostly concerned about the former and mostly so you can second guess. For instance, by being told here that the Draco and SuperDracos are separate systems operating are different pressures and from different tanks, it put into perspective the statements from the SpaceX engineer about why they weren't worried about Dragon 1's launch even if they have similar Draco engines. So by pointing out the obvious (that the Crew Dragon anomaly was in a system that Dragon I doesn't even have) you understood something? You shouldn't need help with that sort of thing. Here's a summary for you: Draco - 90 pounds of thrust, around 100 psi chamber pressure Super Draco - 15,000 pounds of thrust, 1000 psi chamber pressure There are 18 Dracos arranged around the capsule and they are used for attitude and orbital maneuvering. They're essentially identical regardless of which Dragon you're talking about. Note that even if Crew Dragon used some Rube Goldberg system of pressure reducers and conduits everywhere so as to be able to feed Draco engines from Super Draco tanks, that wouldn't change your 'understanding', SINCE DRAGON I DOESN'T HAVE ANY SUPER DRACOS OR ANY SUPER DRACO TANKAGE OR ANY SUPER DRACO PRESSURIZATION SYSTEM. "boom". This entire system is supposed to be fast, reliable, and fail safe. Sometimes one has to make compromises to maintain the balance of fast, reliable and fal safe. And sometimes you forget a possible failure mode or are told to not worry about it because component X has never failed and considered reliable. You really don't know anything about engineering, do you? Yes, compromises get made (but not the kind you seem to be thinking of). And it doesn't matter what I, as an engineer, am 'told'. You pay attention to and analyze all the possible failure modes. And when something goes wrong you do it all again, using the data from what went wrong. I had an understanding with my Program Manager. If he suggested something and the words "But that would compromise good engineering practice and rigor" came out of my mouth he would nod and we would do it my way. That didn't happen very often (good management). Depends on the design. There could be something like a blow off valve to vent helium in case of over-pressurization of the plumbing. Would it be safe to have a blow off valve between helium tank and hypergolic tank or would this have too high odds of hypergolic liquid venting? (or is that considered a necessary evil to prevent hypergolic tank from rupturing? If I'm understanding what you're saying, if such a system was in place I would expect a check valve between it and the propellant tank to prevent 'backflow'. The biggest problem with 'blowoff valves' is they have to blow off TO somewhere. That is probably going to involve extra piping and a hole punched in the skin of the vehicle. In the case of a helium tank you could use the fill connection. To put one where you want it requires another vent. In terms of pressurizing the helium tank, wouldn't there be a blow off on pad equipment instead of being on-board since overfilling can only happen on pad? (ag: not have to carry weight of blow off valve for whole flight when it is only needed while on pad when tanks are filled. You're assuming there's no way for the helium tank to overpressure other than being overfilled. I see no reason to assume that. -- "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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SpaceX Dragon 2 capsule destroyed in abort motor ground test
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#56
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
Jeff Findley wrote:
From what I could see from the cell phone video, there wasn't any "pad equipment" attached to Dragon 2 during this test. It was just sitting on top of a test fixture. I wonder how they add the vibrations for the test. I read that they simulated the launch environment. -- Mvh./Regards, Niels Jørgen Kruse, Vanløse, Denmark |
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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 Mon, 6 May 2019
17:03:13 -0400: On 2019-05-06 14:58, Fred J. McCall wrote: What we used to do was what we called "shake and bake" testing. In the context of a highly instrumented ground test, wouldn't they first fire the engines without vibration so they can establish a baseline where they work, and then do a subsequent test with vibration where if there is failure, it bcomes easier to narrow the possible causes ? That doesn't make it easier. In terms of re-usability, would the mugh higher thrust for Super Dracos introduce some limits to how often they are designed to be fired versus the Drasos that are fired hundreds of times to navigate in space and then de-orbit (a firing that lasts 15 minutes). No. -- "The reasonable man adapts himself to the world; the unreasonable man persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." --George Bernard Shaw |
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
Hi all
I don't mean to necro a dead thread but has SpaceX released any more info or commented on this incident yet. I've been off line for a couple of weeks (don't ask, you don't want to know) and my Google-Fu can't turn up anything.. Certainly the SpaceX website STILL seems to have nothing about the fire / explosion. Thanks to all. Take care and have a great day (and an awesome weekend). Regards Frank |
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
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