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SpaceX Dragon 2 capsule destroyed in abort motor ground test
JF Mezei wrote on Tue, 30 Apr 2019
01:09:47 -0400: Does Dragon-2 have single fuel and pressuriation system to serve all Draco and Super Draco engines ? I doubt it. The SuperDracos are 'podded' in pairs and each pair is independent from all the others. Much of the text I read says stuff such as "use the same propellants" which could either mean they use the same type of fuel, or that they draw propellands from the same tanks. Hence question. I think each pair of SuperDracos has its own propel lent tanks and pressurization system. Since the system worked for the Dracos during flight, one would want to look at what is different when you need the Super Dracos. (Or perhaps for the succesfull flight, the pressurized it only to the pressure needed by Dracos, knowing SuperDracos would not be used). I'm pretty sure they're totally independent. The pairs of SuperDracos are fully independent from each other. -- "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
In article , says...
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. I agree with all of this. Also, from what I understand, there is a list of safety related issues that NASA wanted SpaceX to take care of before flying crew on DM-2. The other "silver lining" is that this gives SpaceX more time to take care of those issues as well. Jeff -- All opinions posted by me on Usenet News are mine, and mine alone. These posts do not reflect the opinions of my family, friends, employer, or any organization that I am a member of. |
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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
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
Jeff Findley wrote on Tue, 30 Apr 2019
14:08:51 -0400: Also, from what I understand, there is a list of safety related issues that NASA wanted SpaceX to take care of before flying crew on DM-2. The other "silver lining" is that this gives SpaceX more time to take care of those issues as well. Would you happen to know what those are or be able to point me to a description of them? -- "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
JF Mezei wrote on Tue, 30 Apr 2019
15:33:58 -0400: On 2019-04-30 14:05, Jeff Findley wrote: You're going to get little to no actual useful information from a cell phone video. It's way too low frame rate and the way they respond to rapid changes in light pretty much means you can't trust the few frames you have. That video shows no exhaust from super dracos for a meaningful time prior to even. But so what? You have no idea how long the thing was just sitting there quietly doing nothing. There was no exhaust from the SuperDracos since the last time they were lit, after all. And it shows a pretty big explosion with lost of debris flying. It pretty much confirms that the Dragon 2 is a total loss. (something which SpaceX didn't confirm at least not at the time that vode was released). But what does that actually tell you? -- "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 Tue, 30 Apr 2019
15:39:51 -0400: On 2019-04-30 14:10, Jeff Findley wrote: I'm pretty sure they're totally independent. The pairs of SuperDracos are fully independent from each other. I believe this is correct. It gives the system some redundancy to have these separate. Considering current role of Super Dracos as being potentially useful only during launch, and hopefully never used, wouldn't it make more sense for them to share the weight of fuel with the dracos? No, it wouldn't because now you have all the issues of adjusting for different chamber pressures, etc. aka: if all goes well at launch, the fuel is used by dracos during on-orbit operations. And if Super Dracos is used during launch, you're not going to need the fuel for dracos isn't you're not going to orbit. Except that wasn't the way the thing was designed. I suspect SpaceX is better at doing "the sensible thing" than you are when it comes to their spacecraft. I could understand separate fuel tanks in a context where the Super Dracos would be used for every landing. (if fuel not used for launch abort, it is then needed for normal landing and vice versa). I suspect your 'understanding' is the least of SpaceX's concerns. Were powered landings ruled out during Dragon 1 such that Dragon2 design started off with powered landings already out of equation, or did they start designing it for powered landings and then it was ruled out ? Dragon I didn't have SuperDraco engines so it was never going to do a propulsive landing. Propulsive landings were ruled out quite late for Crew Dragon and the cargo variant of that craft might well still do them someday since that doesn't raise the safety certification concerns that eventually killed them for Crew Dragon. They didn't "start designing it for powered landings". They also FINISHED designing it for powered landings and built the thing that way (with the exception of removing the landing legs, which Musk says they could still put back with little to no difficulty). This stuff is NOT hard to find out. You could, just occasionally, look things up for yourself. https://spaceflightnow.com/2017/07/1...gon-spaceship/ https://www.inverse.com/article/3440...hrust-landings https://www.teslarati.com/spacex-cre...gency-landing/ I could go on... -- "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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SpaceX Dragon 2 capsule destroyed in abort motor ground test
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
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