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SpaceX Capsule Explosion
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SpaceX Capsule Explosion
In article , says...
On 7/19/2019 2:43 PM, JF Mezei wrote: On 2019-07-19 12:05, David Spain wrote: presume the only method to relieve the pressure is through combustion, but there may also exist a pressure relief valve that vents off the helium without need to run the engines. Without hard data this is just a WAG but not a SWAG. You can vent off the Helium between the Helium tank and the Fuel/oxydizer tanks. But the pressure inside the later tanks can't be vented otherwise you are venting uncombusted NTO and MMH which may combust if they meet after having been ventet and remain highly toxic if they don't meeet to combust. You close the Helium pressurization valve, and de-press through another valve and coupling perhaps one at the top of the helium tank. The NTO and MMH would be drained via separate plumbing connections, which already must exist to fuel it anyway. Then you purge the system with helium to remove the trace elements of NTO and MMH from the pressurization lines. Yeah if you do it together you stand back, otherwise you do them singly with lots of venting to allow it do disperse. I can make up a lot of stuff too w/o data it's a WAG (Wild Ass Guess) but not a SWAG (Silly Wild Ass Guess). SpaceX has said they designed the system according to industry standards. What could those be? For example, here is a plumbing diagram of the space shuttle OMS system: https://www.orbiterwiki.org/images/8/8e/OMS_diag.png Note that on this diagram, there is no isolation valve in the helium plumbing between the check valve and the NTO tank. The gas isolation valves are between the check valve and the helium tank. So the arrangement that SpaceX used is not new. That's why they said that what they encountered was "unexpected". The space shuttle flew dozens and dozens of times without this happening. 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 Capsule Explosion
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SpaceX Capsule Explosion
Jeff Findley wrote:
Note that on this diagram, there is no isolation valve in the helium plumbing between the check valve and the NTO tank. The gas isolation valves are between the check valve and the helium tank. So the arrangement that SpaceX used is not new. That's why they said that what they encountered was "unexpected". The space shuttle flew dozens and dozens of times without this happening. Perhaps it did happen, but the valve didn't explode because the helium pressure was lower. -- Mvh./Regards, Niels Jørgen Kruse, Vanløse, Denmark |
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SpaceX Capsule Explosion
In article ,
lid says... On 19-07-20 15:40 , Jeff Findley wrote: In article , lid says... On 19-07-19 14:06 , Jeff Findley wrote: In article , says... I couldn't find a definitive reference. But the abort system is simply not needed for a cargo flight. It could be that the parts will still be on the Dragon 2, but the abort system's propellant tanks and high pressure helium tanks simply won't be filled. That would also save a lot of mass while minimizing the modifications needed to turn a crew Dragon 2 into a cargo Dragon 2. They might even use propulsive landing for cargo flights. No, they won't. NASA has definitively nixed that idea. NASA does not want irreplaceable returning cargo (e.g. EMU suits) splattered all over a concrete landing pad when the inevitable "oopsie" happens. If an EMU is irreplaceable, and is being sent back to the ISS on a cargo Dragon2, by the same logic the abort system should be included and active on launch, no? In case the launcher has an "oopsie". NASA has conflicting goals for cargo missions. They're supposed to be reliable (we've lost two commercial cargo missions so far), but they're clearly not as paranoid about "safety" for cargo as they are crew. So, they're trading more cargo up-mass and down-mass by removing the abort capability provided by the Super Dracos. Note that none of the other international cargo vessels launched to ISS have ever had an abort system. This includes the commercial Cygnus and Dragon cargo vessels. NASA is requiring SpaceX to parachute all Dragon 2 capsules into the ocean. If commercial use of the ISS takes off, perhaps some cargo missions will be non-NASA. But (as I said in an earlier reply/correction to myself) propulsive landing probably needs legs, which are no longer in the Dragon2 design, so it won't happen. Agreed. It will never happen. The legs were deleted from the design because NASA told SpaceX that they would not allow propulsive landing tests using returning Dragon 2 cargo vessels. It would have been prohibitively expensive for SpaceX to fully test propulsive landings "on their own dime". You see, SpaceX wanted to test propulsive Dragon 2 landings on operational cargo missions just like they tested Falcon 9 first stage landings on operational missions. But the key difference was that a failed Falcon 9 first stage landing in no way impacted the primary mission. Where a failed Dragon 2 landing would have resulted in loss of all cargo being returned from ISS. NASA's reasoning is pretty obvious here, IMHO. 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 Capsule Explosion
Jeff Findley wrote:
In article , says... Jeff Findley wrote: Note that on this diagram, there is no isolation valve in the helium plumbing between the check valve and the NTO tank. The gas isolation valves are between the check valve and the helium tank. So the arrangement that SpaceX used is not new. That's why they said that what they encountered was "unexpected". The space shuttle flew dozens and dozens of times without this happening. Perhaps it did happen, but the valve didn't explode because the helium pressure was lower. The valve reportedly failed due to forcing liquid through the valve at extremely high pressure. This happened when they opened the upstream helium valves to pressurize the propellant tanks for the Super Draco engines to fire. That liquid was not supposed to be upstream of the check valve, so the check valve was simply not designed to handle high pressure liquid being forced through it. Violent agreement? I was writing in the context of the shuttle not blowing up. Orbital manoeuvring is much lower chamber pressure than sea level escape. -- Mvh./Regards, Niels Jørgen Kruse, Vanløse, Denmark |
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