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SpaceX Dragon 2 capsule destroyed in abort motor ground test
JF Mezei wrote on Thu, 2 May 2019
16:05:14 -0400: On 2019-05-02 06:59, Jeff Findley wrote: Note from above the OMS propellant pressure was regulated to: The primary regulator outlet pressure at normal flow is 252 to 262 psig and 247 psig minimum at high abort flow, with lockup at 266 psig maximum. The secondary regulator outlet pressure at normal flow is 259 to 269 psig and 254 psig minimum at high abort flow, with lockup at 273 psig maximum. RCS system he The primary regulates the pressure at 242 to 248 psig, the secondary at 253 to 259 psig. Thanks. Expected much different pressure differences. For a capsule as small as Dragon2, couldn't they have a single tank/helium concept with different regulators to feed Draco vs Super Dracos ? Which part of 'pressure fed rocket engine' do you not understand? In the case of Dragon2, do the Draco systems use the same hardware as for Dragon 1? (which would simplidfy engineering SuperDracos as totally separate system). No, they built it all totally different just for the **** of it. Since mass is so critical to flights/payload, I would have expected the maximum possible mass savings with as much shared hardware as possible. If mass is that critically important you don't build pressure fed rockets. But I guess sometimes extra mass is worth it if you can reuse a system that has been already desingned and focus only on the new engines. You're (foolishly) leaping to supporting your own position. The way you want to do it takes MORE hardware and MORE complexity than the way they did it. If mass is important you don't add a bunch of extra **** so as to get multiple uses out of a piece of hardware. -- "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
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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 in message ... In article , says... On Wednesday, May 1, 2019 at 6:57:25 AM UTC-4, Jeff Findley wrote: While I agree it's likely this Dragon 2 is a total loss, we really don't know the extent of the damage from a low frame rate cell phone video. For all we know, at the end of the video, Dragon 2 could be sitting mostly intact just out of the frame. I saw an update on this question in AP News today. "SpaceX confirms its crew capsule was destroyed in ground testing two weeks ago." https://apnews.com/2d41dee71a3f49feadc5987f59d603bd Goes on to say: "SpaceX still cannot access the test stand at Cape Canaveral, Florida, because of toxic fuel contamination." Which is yikes. Existing hypergolic propellants are pretty toxic. I'll have to check to see if the cargo Dragon launch happened last night (weather prediction was dicey). The plan was to land that booster on the autonomous drone ship not far off the coast due to the contamination in the landing zone area. So this is also interfering with their normal launch operations. Most likely the hypergolic fuels came into contact with each other due to a leak or faulty valve. The SuperDraco thrusters aren't suspect. |
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
JF Mezei wrote on Fri, 3 May 2019
11:40:51 -0400: On 2019-05-03 01:07, Fred J. McCall wrote: Well, yeah, it was. You realize that "500 msec" means you're right in the midst of it, don't you? If it is 500msec BEFORE ignition, you're not in the midst of it. You really don't have a clue as to just how pressure fed hypergolic engines work, do you, much less just how short a time 500 msec is. Later, you mentioned thet they only pressurize the tanks just before first firing. So perhaps the explosion happened as they pressurized tanks, before valves started to let the fuel flow to combustion chamber. Pretty sure I listed that as one of the possible causes. Perhaps a pressure line was full of Magic Monkey **** (tm) from the monkeys that flew out your butt. So it isn't a given that this happened at time a command was sent to send fuel to combustion chamber. Pretty sure I haven't seen anyone, including myself, say that it was. SpaceX would know exactly what was happening 500ms before the incident. You might want to comprehend a few little details like what the actuation times for valves and fuel flow times are. Do you have any clue just how short 500 msec is when you're talking about ignition of a hypergolic engine? "ignition" ? is there an actual ignition in hypergolics? Wouldn't starting the engine involve opening valves and then letting the 2 components travel to combustion chamber and ignite whenever they meet? Yes, which is precisely why "approximately 500 msec" doesn't tell you much, if anything. I don't know how long it takes for components to travel from the tank to the combustion chamber. SpaceX does. Then you should shut up and stop carping when people try to answer your questions. is 'yes'. I say that because BOTH cases are true. Generally the fuel tanks won't be initially pressurized until just before the first time you fire the rocket engine. Since Super Dracos's primary role is the emergency escape system, does pressurizing "on demand" make a difference in terms of how quickly the engines fire and pull the capsule off the rocket? Think about what you just asked and how pressurization works. I would have really expected them to "arm" the system prior to crew ingress. But if the delay between unpressurized fuel and the engines providing thrust is small then I guess the two can be combined. Why would you expect that? Remember that once you pressurize the fuel tanks there is no good way to depressurize them. However, since there is no way to depressurize the fuel tank once it's pressurized, In a context where you are switching from optimum pressure from Super Draco to Draco, you can start with the higher pressure and once you fire the Dracos, pressure drop to a poit where the Draco regulator starts to feed more helium to maintain optimum pressure. Think about what you just said. First, it makes no sense. Second, you're still stuck in your imaginary system where SuperDraco and Draco are sharing fuel and pressurization systems. Third, think about the difference in fuel flow and just how little depressurization you're going to get puffing Draco thrusters out of a fuel tank that is overpressurized for that and contains a ton and a half of fuel at that pressure. All that said, the probabilities of what went wrong remain the same: COPV failure, pressurization valve or sensor system failure, why would there be COPV failure in hypergolics? No cryo issues or fuel freezing. And if failure happened 500ms before engine start, it is safe bet the helium tank(s) had been filled well before. Why would there be any fail of anything anywhere? Gee, obviously there was no problem at all! If the regulator ended up releasing liquid helium into the fuel tanks raising their pressure to well above design limits (before valve to turn on engine is opened), that could cause tank failure and if both tanks failed, you could go "kaboom" real fast. Pretty sure that was on my list. Alternatively, there could have been a minute flaw in one of the COPVs that caused an eventual failure and you've got the same sort of massive sudden overpressure of a propellant tank. I know reading is hard for you, but you should have noted that among other things I didn't give any particular probability of which possible failure happened. There's a reason for that. It all depends on the sequence of events, which SpaceX already knows. Well, no it doesn't, quite. Consider, a COPV failure, a propellant tank failure, a valve failure, and a sensor failure all look the same since they all result in a massive spike in propellant tank pressure. Why would you put people at risk for any of that? You've got to clean it up anyway, so do that. And how do thyey clean thing up ? don't they send people in suits with scuba to do the cleanup? If they have robots do it, then those robots can also survey the site and take pictures. Why, they clean it up by cleaning it up. They DON'T clean it up by doing other things instead of cleaning it up. I suspect SpaceX has lots of imagery of post explosion already. The "dangerous site" excuse is just an excuse to pretend they don't have imagery. Yes, yes, you were frightened by Elon Musk when you were just a baby. We get it. -- "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
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#48
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
In article ,
says... On 2019-05-04 10:23, Jeff Findley wrote: Because the helium tanks, fuel tanks, and oxidizer tanks that supply the Super Draco engines with propellant are all COPVs. I would think that COPV aspect would be irrelevant since we're not talking about a tank immersed into cryo tank. Depends if that's what failed. Obviously, which is why the tanks themselves are not likely suspects for the root cause in this case, IMHO. I doubt that this system has liquid helium in it at all. If they contained liquid helium, that would defeat their purpose entirely. Does Helium become liquid when compressed? Mr Google only tells me it becomes liquid when cooled. I was under the impression that they would load liquid helium in those tanks and it would remain liquid due to high pressure. The helium tanks will contain high pressure helium gas. I know you mentioned the engines need ballpark 250-275 psi to push fuel into combustion chamber. At what pressure would helium be stored at in its own tank ? Those were numbers for the space shuttle, not Super Draco. I have no idea what the chamber pressure is for Super Draco. Maybe you should try Wikipedia: https://en.wikipedia.org/wiki/SuperDraco\ The above says the chamber pressure is on the order of 1,000 psi. The propellant tanks will have a higher pressure in order to obtain the flow rate needed. Which is why all this idle speculation is actually annoying to me. Blame lack of transparency when observers were used to a lot of transparency in the past. But this speculation does allow people to learn how things work, so for instance, you provided the pressure ranges needed , and hopefully a definition of "ignition" in the context of hypergolics. Ugh. NASA and SpaceX are no doubt combing over any imagery they have. You really have no right to see that imagery, IMHO. I'm not sure what compelling interest the public would have in such imagery. All it would do is fuel more idle speculation, which is not at all helpful. Sicne NASA is government operation, don't USA citizens have a right to that information through FOIA? Not if the information is considered a trade secret or regulated under ITAR. ITAR https://gov-relations.com/itar/ 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
JF Mezei wrote on Sat, 4 May 2019
15:09:49 -0400: On 2019-05-04 10:23, Jeff Findley wrote: When the hypergolic fuel and oxidizer come into contact with each other, they spontaneously ignite. So that's still ignition. In LOX/hydrogen environment, ignition is a command that causes a spark in the right place and assumes instant ignition. Not exactly, no. I believe that the igniters start firing when the count hits zero and 'ignition' is a status call indicating that the thing actually lit. For example, on a Shuttle launch Main Engine Start was commanded at T-6.6 seconds and solid rocket booster ignition happened at T-0. In hypergolic, it isn't clear to me whether ignition refers to the opening of valves that let the combonents flow to combustion chamber, or the time when the components meet and start to combust. It's probably going to vary by rocket. The former is a specific time where a command is sent. The later is a fungible time that depends on how long it takes for components to travel from tank/valve to the combustion chamber and then for chemical reaction to start to happen. Neither is a specific time. It's a status call. Since I don't know what "ignition" means in terms of hypergolics, the 500ms time prior to ignition can mean anything. Since you don't know what "ignition" means in terms of any rocket, I guess that problem is solved. Say ignition is defined as time combustion starts, and that it takes 1 second for fuel to travel from valve to combustion chamber, then 500ms would be half a second after the valve was opened between tanks and combustion chamber. But if it takes 200ms for fuel to travel from valve to combustion chamber, then 500ms means the explosion happened before valve opened. And if ignition is defined as the time the valves are opened, then 500ms would refer to a stable state prior to ignition, unless opening valve between heliium tank and hypergolics to pressurize them happens 500ms before valves between hypergolics and combustion chamber are opened. The real question is what the guy who made the statement means by 'ignition'. 'Ignition' is a status call that indicates the thing is actually lit. Obviously that's going to be a slightly variable quantity. Because the helium tanks, fuel tanks, and oxidizer tanks that supply the Super Draco engines with propellant are all COPVs. I would think that COPV aspect would be irrelevant since we're not talking about a tank immersed into cryo tank. So pressure vessels never fail unless they're immersed in a cryo tank? What a silly notion! Obviously, which is why the tanks themselves are not likely suspects for the root cause in this case, IMHO. I doubt that this system has liquid helium in it at all. If they contained liquid helium, that would defeat their purpose entirely. Does Helium become liquid when compressed? Mr Google only tells me it becomes liquid when cooled. I was under the impression that they would load liquid helium in those tanks and it would remain liquid due to high pressure. Presumably if you could apply enough pressure you could get it liquid at more 'reasonable' temperatures, but that's a preposterous amount of pressure so it's not really a useful bit of information. I know you mentioned the engines need ballpark 250-275 psi to push fuel into combustion chamber. At what pressure would helium be stored at in its own tank ? Why do you think that matters? Say helium is pressurized to 500psi in its own re-enforced tank, and the hypergolic tanks are built to widthstand 300psi. You have a preposterously low threshold for 'safety margin'. You also have a ridiculously low idea for helium pressure. For example, helium COPVs on the Shuttle had burst strengths north of 8,000 psi. If, when they open valve between helium and hypergolics, the regulators fail and pressurize the hypergolics above 300, I could see hypergolic tanks failing. It was on my list. I'm so happy you can "see it". Which is why all this idle speculation is actually annoying to me. Blame lack of transparency when observers were used to a lot of transparency in the past. Utter bull****. There is no 'lack of transparency'. To be 'transparent' THEY HAVE TO HAVE SOME IDEA WHAT HAPPENED AND THEY'RE STILL ANALYZING THAT DATA. But this speculation does allow people to learn how things work, so for instance, you provided the pressure ranges needed , and hopefully a definition of "ignition" in the context of hypergolics. No, this 'speculation' is annoyance. There are ways to "learn how things work" without being an obnoxious ****. NASA and SpaceX are no doubt combing over any imagery they have. You really have no right to see that imagery, IMHO. I'm not sure what compelling interest the public would have in such imagery. All it would do is fuel more idle speculation, which is not at all helpful. Sicne NASA is government operation, don't USA citizens have a right to that information through FOIA? So go file for that. If they conclude it's not covered by SpaceX trade secrets you'll get it in perhaps six months or so. And I disagree on the speculation aspect. Of course you do, but then you're not quite bright. NOT providing it fuels specualtion because it also fuels people wondering why they have to hide and why. Releasing the data would have harmless discussion on potential causes which eventually get confirmed. Thank you for the loony conspiracy theory perspective on things. Since you're going to be loony regardless, why feed you? -- "Ordinarily he is insane. But he has lucid moments when he is only stupid." -- Heinrich Heine |
#50
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
JF Mezei wrote on Sat, 4 May 2019
17:50:29 -0400: On 2019-05-04 17:05, Jeff Findley wrote: Those were numbers for the space shuttle, not Super Draco. OK, had been lead to believe that Super Dracos were same ballpark as the OMS engines on Shuttle. Who led you to believe that? This stuff is dirt simple to find out, SO WHY DON'T YOU ONCE IN A WHILE? 1000psi is much much higher. Gee, did you take off your shoes for that one? Assuming (for simplification) the fuel has to be at 1000psi, roughly speaking at what PSI would helium tank need to be such that at end of engine firing, there would still be 1000psi in the fuel tanks? That depends on things we don't know. It will be stored at the highest pressure reasonable in order to minimize the size of the required helium tanks (and don't assume there's just one; there are two propellant tanks per pair of engines and four pairs of engines). are we talking 1500psi, 2000 psi ? 5000psi ? (I have no ideas of size of tanks involved and how much helium needs to be displaced as fuel tanks empty to combustion chamber). Neither do we. We know how much propellant each pair of engines has, from which we can calculate the volume of the propellant tanks. From those tank volumes you can calculate how much helium it takes to bring those tanks to 1,000 psi when empty. Then you hit the unknowns, since how much pressure a helium cOPV needs to carry depends on the volume of the COPV. But by all means, you break out your crayon and do those calculations. Just curious if in case of regulator failure, the fuel tanks may be overhwelved with intense pressure from helium or whether the maximum possible helium pressure would be well within reasonable pressure capability of fuel tank. Which part of my telling you this was one possible failure mode was it that escaped you? Would they design the hypergolic tanks to widthstand worse case scenario in terms of helium pressure being fed into it ? Of course not. The tanks would have to be stupidly heavy if you did that. Would the thrust level for Super Dracos be determined by the regulator between helium tank and hypergolic tanks, or are there variable regulators between hypergolic tanks and the combustion chamber ? They're called 'throttle valves' at that point, not 'regulators'. The pressure the fuel is delivered at is relatively constant, no matter how fast you deliver it to the combustion chamber. -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
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