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SpaceX Capsule Explosion
On 7/18/2019 1:44 PM, Greg (Strider) Moore wrote:
"David Spain"Â* wrote in message ... Or... it could just be, "we don't trust the new folks, no matter what." Or I could be snide and ask exactly how many refurbishment cargo flights Boeing has made to the ISS... If trust is measured by the amount of money awarded, then NASA answered that question years ago... Dave |
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SpaceX Capsule Explosion
In article , says...
On 7/17/2019 7:40 PM, Jeff Findley wrote: Doesn't matter because NASA wants only new Dragon 2 capsules for crew. After their crew flight, they will be refurbished for commercial cargo. Part of that refurbishment is to remove the abort system to allow for more cargo up-mass and down-mass. Jeff Jeff that's a great point and I remember reading about that. Seems stupid on NASA's part, they lose the cost savings of reusable hardware. But hey this is the organization behind the SLS so what should I expect? Do you have a cite for the latter part (removal of abort system for more cargo)? I'd like to read up on that. First I've heard of it. 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. I'm sure we'll find out more later. After all, for now they're still flying the original Dragon on cargo flights. 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
On 19-07-19 14:06 , Jeff Findley wrote:
In article , says... On 7/17/2019 7:40 PM, Jeff Findley wrote: Doesn't matter because NASA wants only new Dragon 2 capsules for crew. After their crew flight, they will be refurbished for commercial cargo. Part of that refurbishment is to remove the abort system to allow for more cargo up-mass and down-mass. Jeff Jeff that's a great point and I remember reading about that. Seems stupid on NASA's part, they lose the cost savings of reusable hardware. But hey this is the organization behind the SLS so what should I expect? Do you have a cite for the latter part (removal of abort system for more cargo)? I'd like to read up on that. First I've heard of it. 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. -- Niklas Holsti Tidorum Ltd niklas holsti tidorum fi . @ . |
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SpaceX Capsule Explosion
On 7/19/2019 9:19 AM, Niklas Holsti wrote:
They might even use propulsive landing for cargo flights. If that was the plan before replacing the check valve(s) with burst disks, I wonder if that remains the plan? If so it would imply that they (SpaceX) intended to fly all the way down with pressurized engines all along anyway, so its no big deal either way. Otherwise it would require some re-thinking. Dave |
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SpaceX Capsule Explosion
On 19-07-19 18:13 , David Spain wrote:
On 7/19/2019 9:19 AM, Niklas Holsti wrote: They might even use propulsive landing for cargo flights. I forgot about the landing legs that are needed for that. They may have been removed from the Dragon2 design and might be hard to refit. If that was the plan before replacing the check valve(s) with burst disks, I wonder if that remains the plan? If so it would imply that they (SpaceX) intended to fly all the way down with pressurized engines all along anyway, AIUI, there is an actuated valve at the He tank, before the check valves, which would not be opened until just before the SuperDracos are fired. So the engines would not be pressurized until needed. -- Niklas Holsti Tidorum Ltd niklas holsti tidorum fi . @ . |
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SpaceX Capsule Explosion
On 7/19/2019 11:34 AM, JF Mezei wrote:
As the Dragon spashes down, are those tanks stil pressurized, or is there a means to close Helim tank, and then burn engines till there is no more pressure just before deploying parachutes? I have no hard data on the Dracos or Super Dracos so it is difficult for me to answer your questions. I can speculate on this last question. You 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. Dave |
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SpaceX Capsule Explosion
On 7/19/2019 12:01 PM, Niklas Holsti wrote:
On 19-07-19 18:13 , David Spain wrote: On 7/19/2019 9:19 AM, Niklas Holsti wrote: They might even use propulsive landing for cargo flights. I forgot about the landing legs that are needed for that. They may have been removed from the Dragon2 design and might be hard to refit. Yes that is correct they have been removed from the architecture. I had missed that point as well. Truth is, AFAIK the original design called to the landing legs to extrude from the heat shield. NASA was definitely not big on this idea. And to the best of my knowledge, other than the V2 mock-up this was never implemented. When first shown I was surprised they planned to do it that way rather than just follow the method they adopted on F9, and just have them swing down from the body of the capsule. I suppose they could still go for propulsive landing over water. At sea and then move to a large fresh water tank on dry ground? Or if up-welling steam is a problem maybe a high boiling point oil? If that was the plan before replacing the check valve(s) with burst disks, I wonder if that remains the plan? If so it would imply that they (SpaceX) intended to fly all the way down with pressurized engines all along anyway, AIUI, there is an actuated valve at the He tank, before the check valves, which would not be opened until just before the SuperDracos are fired. So the engines would not be pressurized until needed. Yeah but once needed always on is the point. After a landing I'd think you'd want to vent that helium pressure off. But maybe you shouldn't until the bi-propellant is drained? And if back flow is a problem with a check valve you can imagine the issues you might run into if you kill helium pressure with a now a burst burst disk. Not enough data... Dave |
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SpaceX Capsule Explosion
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). Dave |
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SpaceX Capsule Explosion
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#30
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SpaceX Capsule Explosion
In article , says...
On 7/19/2019 9:19 AM, Niklas Holsti wrote: They might even use propulsive landing for cargo flights. If that was the plan before replacing the check valve(s) with burst disks, I wonder if that remains the plan? It wasn't. NASA has prohibited SpaceX from performing Dragon 2 propulsive landing testing on returning ISS cargo flights. NASA does not want the added risk for any of its returning cargo. This is why SpaceX dropped development of propulsive landing for Dragon 2. This decision happened quite some time ago. If so it would imply that they (SpaceX) intended to fly all the way down with pressurized engines all along anyway, so its no big deal either way. Otherwise it would require some re-thinking. As with an abort, during a propulsive landing the tanks would only have been pressurized as part of the Super Draco engine firing sequence, so they would have been pressurized a fraction of a second before firing the Super Draco engines. Also, if it performed an abort, it would necessarily use parachutes for the splashdown. There was never enough propellant to perform an abort *and* a propulsive landing. It was always either/or. The genius of propulsive landing was that on a nominal mission (i.e. no launch abort), you could use the abort system's engines and propellant to perform the propulsive landing. For comparison, Starliner's abort system is in its service module, so it will always be destroyed after a nominal mission, because the service module burns up on reentry. 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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