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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
Niklas Holsti wrote on Wed, 1 May 2019
14:52:08 +0300: On 19-05-01 13:55 , Jeff Findley wrote: In article , says... 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. Dracos are likely much lower pressure than Super Dracos. It's much simpler to have separate tanks in this case. 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. The intent was to use the Super Dracos for vertical landing on a nominal mission. NASA nixed that, so we're left with them being there with no operational use on a nominal mission. I believe that Elon Musk has said that the Super Dracos would in future be a back-up for the Dragon 2 parachutes, slowing the capsule before the splash-down in case of parachute failure. This is only possible if the Super Draco propellant is not consumed in the Dracos before re-entry. True. If they had a multiple parachute failure (the thing can still get down safely on three, the ride at the end is just a little rougher) they could use the SuperDracos to kill vertical velocity before splashdown. To be fair, the tiny 90 lb thrust Dracos would be pretty unlikely to exhaust the six tons of fuel that the SuperDracos carry in aggregate to support the huge thrust they deliver. Mentioning the parachutes reminds me that the Dragon 2 DM-1 parachutes seemed very "restless" during the descent. The parachutes billowed, flexed, and sometimes swapped places in the 4-parachute formation. Is this a worrying kind of instability? Can it be a result of having 4 parachutes instead of 3, giving a different kind of symmetry and inter-parachute interaction? It wouldn't surprise me that a cluster of four chutes would wind up behaving differently in descent than the three chutes on a Dragon I. -- "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 Wed, 1 May 2019
11:27:42 -0400: On 2019-04-30 21:19, Fred J. McCall wrote: 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). ok that answers the question then. The super Dracos need to have their own fuel since every flight was originally meant to use the engines to land. The SuperDracos not only have their own fuel supply, but each pair has its own fuel supply independent of the other three pairs. Each pair gets about a ton and a half of propellants. Theoretical question: would it be possible to have shared fuel tanks, pressurize them to "super draco" levels for take-off if needed, then reduce pressure to fit the Draco needs? That would allow shared fuel and reduce total weight and number of components. Anything is possible, but what you describe INCREASES the complexity and number of components in the system How did the Shuttle work the differences between thrusters and OMS? were they on totally separate fuel/pressure systems ? OMS thrusters are typically either cold gas or hypergolics. Shuttle main engine was liquid hydrogen/LOX. Totally different engine designs. -- "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 Wed, 1 May 2019
16:23:59 -0400: On 2019-05-01 12:22, Fred J. McCall wrote: OMS thrusters are typically either cold gas or hypergolics. Shuttle main engine was liquid hydrogen/LOX. Totally different engine designs. I was talking about the medium engines in the back using hypergolics. The ones used to finish orbit after MECO, and the ones used to de-orbit the shuttle. You need to be clearer. It's bad enough that I have to look up answers for you. Having to guess what the hell you're actually asking just makes it a bigger pain. Thought they were called OMS. So asked whether they shared fuel/pressurization with the various thrusters located throughout the shuttle. There are two different systems; OMS and RCS. The OMS engines are in two pods at the after end of the Shuttle. Each has its own fuel supply, but they can be cross-connected to allow fuel from one OMS pod to be used by the OMS engine in the other pod. Each OMS pod also contains RCS engines as part of the pod. I believe (I don't find anything definitive) that these large RCS engines (they come in two sizes) CAN share the same fuel and pressurization system as the OMS engines in the pod (it's all build as a unit). There are other RCS engines located in other pods around the Shuttle. These all have their own fuel and pressurization systems ('pods' are managed as replaceable units). OMS engines are 6000 lb thrust engines and each OMS pod carries around six tons of propellants for the OMS engine in the pod. The large RCS engines produce just under 1000 lbs of thrust each. They have their own propellant supply but can be cross connected between the two rear pods and/or cross connected with the OMS propellant feeds. The small RCS engines (vernier engines) are much smaller with around 25 lbs of thrust and have their own fuel supplies. Note that the difference between the vernier engines and the OMS engines is about the same order as the difference between a Draco and a SuperDraco and they have their own fuel and pressurization systems separate from the OMS engines. I'd guess that what happens when you 'interconnect' the aft OMS and RCS engines is that the higher pressure OMS tanks vent into the RCS tank system which then delivers the fuel to the RCS engines at the lower pressure. Of course, there's only a factor of six or seven between the thrust of the OMS and RCS engines, so they may be close enough in operating pressure for it not to matter. This is in contrast to the 200x difference in thrust between the Draco and the SuperDraco. -- "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 Thu, 2 May 2019
00:03:08 -0400: On 2019-05-01 21:10, Fred J. McCall wrote: There are two different systems; OMS and RCS. So my reference to OMS was correct. Perhaps, but unclear. Note that the difference between the vernier engines and the OMS engines is about the same order as the difference between a Draco and a SuperDraco That is why I asked the question. So Dragon 2 mimicks the shuttle in having separate fuel systems for the differnt types of engines. I don't think it's a question of 'mimicking' anything. I think it's a case of exactly what people have been telling you being correct. That being that the operating pressures of the two engines are sufficiently different that feeding one from the other won't work. And that would mean that in the "exploded" Dragon 2, the fuel and pressurisation of the Super Draco engines had not been used during the flight. But would still have expereinced launch vribration and temperature extremes of space as well as spash down in salt water. True but irrelevant. Do you seriously think they didn't check the thing out after it landed? -- "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
In article ,
says... On 2019-04-30 21:19, Fred J. McCall wrote: 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). ok that answers the question then. The super Dracos need to have their own fuel since every flight was originally meant to use the engines to land. Theoretical question: would it be possible to have shared fuel tanks, pressurize them to "super draco" levels for take-off if needed, then reduce pressure to fit the Draco needs? That would allow shared fuel and reduce total weight and number of components. How did the Shuttle work the differences between thrusters and OMS? were they on totally separate fuel/pressure systems ? As usual, the KSC web pages have a wealth of information about the space shuttle system (since this was a NASA vehicle, they're quite open about it). The OMS engines and RCS engines had their own sets of tanks for much the same reason that the Dracos and Super Dracos are separate. See this diagram: https://upload.wikimedia.org/wikiped...d_schematic.pn g Lots of text about the OMS system he https://science.ksc.nasa.gov/shuttle...f/sts-oms.html 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 https://science.ksc.nasa.gov/shuttle...f/sts-rcs.html Note from above the RCS propellant pressure was regulated to: The primary regulates the pressure at 242 to 248 psig, the secondary at 253 to 259 psig. Also, the forward RCS engines had tanks and plumbing completely separate from the aft OMS pods (there is no mention of any crossfeed to the forward RCS system). Makes sense considering how far apart they were. 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
On Wednesday, May 1, 2019 at 6:57:25 AM UTC-4, Jeff Findley wrote:
In article , says... 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. 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). 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. Jeff -- 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. Dave Dave |
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SpaceX Dragon 2 capsule destroyed in abort motor ground test
wrote on Thu, 2 May 2019 10:03:10 -0700 (PDT):
On Wednesday, May 1, 2019 at 6:57:25 AM UTC-4, Jeff Findley wrote: In article , says... 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. 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). 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. Jeff -- I saw an update on this question in AP News today. "SpaceX confirms its crew capsule was destroyed in ground testing two weeks ago." Yeah, I saw something on that, as well. What I saw said they were 500 msec away from SuperDraco ignition. 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. Well, I guess that isn't maybe too surprising given tons of uncombusted propellants sprayed about. Both hydrazine and dinitrogen tetroxide are pretty toxic stuff. -- "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 Thu, 2 May 2019
15:55:52 -0400: On 2019-05-02 15:42, Fred J. McCall wrote: Yeah, I saw something on that, as well. What I saw said they were 500 msec away from SuperDraco ignition. So my theory based on seeing no exhaust out of the engines prior to explosion on that small phone video wasn't so stupid after all. Well, yeah, it was. You realize that "500 msec" means you're right in the midst of it, don't you? If they know what happens 500ms prior to ignition, they should be able to get a better idea of what went wrong. Do you have any clue just how short 500 msec is when you're talking about ignition of a hypergolic engine? Are fuel tanks always compressed, or does a valve open to "prime" the fuel tanks only once engines may be ignited ? (for instance, only compressing the tanks when crews enter Dragon 2 (before which , the "eject" function wouldn't be needed/used) ? Where you say "compressed" I'll pretend you mean "pressurized" so that your question at least makes lexical sense. You ask the question like it matters. It doesn't, but I'll answer it anyway. The simple answer 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. However, since there is no way to depressurize the fuel tank once it's pressurized, it would be under pressure from that point on so that if you shut the engine down, fuel tanks are now essentially forever under pressure from that point on. In this particular case, they wouldn't pressurize the fuel tanks just because crew was aboard. They pressurize when they're ready to fire the engine. If you never use it, the fuel tanks never get pressurized. All that said, the probabilities of what went wrong remain the same: COPV failure, pressurization valve or sensor system failure, propellant tank failure, propellant line failure, combustion chamber failure. Goes on to say: "SpaceX still cannot access the test stand at Cape Canaveral, Florida, because of toxic fuel contamination." Aren't there suits and SCUBA units they can wear to retreive some important debris (such as recorders) and epecially photograph the debris and their location ? Why would you put people at risk for any of that? You've got to clean it up anyway, so do 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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