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Jeff Findley wrote on Fri, 28 Jun 2019
07:23:56 -0400: Falcon 9 Block 5 first stages are designed for something like 100 flights. There are no Falcon 9 Block 5 first stages with 99 flights on them. The one thought that occurs to me (and I don't think the description you posted of the test assets makes it clear) is that perhaps they are NOT using a Block 5 booster set, but rather an earlier set that isn't intended for a lot of reflights. -- "The reasonable man adapts himself to the world; the unreasonable man persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." --George Bernard Shaw |
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Niklas Holsti wrote on Fri, 28 Jun
2019 18:54:30 +0300: On 19-06-28 14:13 , Jeff Findley wrote: In article , lid says... On 19-06-27 13:55 , Jeff Findley wrote: The [SpaceX Dragon-2] abort test will reportedly use an actual fueled upper stage but no flight worthy Merlin vacuum engine. Do you have a link/reference for that? The descriptions I've found say no upper stage, and only three Merlins on the first stage. This isn't a very recent article, but it's based on a document submitted to the FAA for the test, so I'm betting it's as accurate as we're going to get before the actual test. How SpaceX Will Conduct an Inflight Abort Test for Crew Dragon November 28, 2018 Doug Messier http://www.parabolicarc.com/2018/11/...duct-inflight- abort-test-crew-dragon/ Many thanks, Jeff, that does seem authoritative. So, this sounds like a very high fidelity test. Yep, largely so. But it seems they intend to shut down the first-stage engines at the time of the abort, so the booster will not try to catch up with the capsule after the capsule separates. Still, I guess the capsule's acceleration would win anyway. If the abort test is at Max Q I don't think this makes any difference anyway, since you're not really 'accelerating' at Max Q. And wouldn't part of the 'normal' abort sequence shut down the booster anyhow? -- "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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On 19-06-28 19:25 , Fred J. McCall wrote:
Niklas Holsti wrote on Fri, 28 Jun 2019 18:54:30 +0300: On 19-06-28 14:13 , Jeff Findley wrote: In article , lid says... On 19-06-27 13:55 , Jeff Findley wrote: The [SpaceX Dragon-2] abort test will reportedly use an actual fueled upper stage but no flight worthy Merlin vacuum engine. Do you have a link/reference for that? The descriptions I've found say no upper stage, and only three Merlins on the first stage. This isn't a very recent article, but it's based on a document submitted to the FAA for the test, so I'm betting it's as accurate as we're going to get before the actual test. How SpaceX Will Conduct an Inflight Abort Test for Crew Dragon November 28, 2018 Doug Messier http://www.parabolicarc.com/2018/11/...duct-inflight- abort-test-crew-dragon/ Many thanks, Jeff, that does seem authoritative. So, this sounds like a very high fidelity test. Yep, largely so. But it seems they intend to shut down the first-stage engines at the time of the abort, so the booster will not try to catch up with the capsule after the capsule separates. Still, I guess the capsule's acceleration would win anyway. If the abort test is at Max Q I don't think this makes any difference anyway, since you're not really 'accelerating' at Max Q. I don't recall seeing any pause, at Max Q, in the growth rate of the Falcon 9 "velocity" reading in the numerous Falcon 9 launch videos I've watched, so I find it hard to believe that the vehicle stops accelerating at that point. Also, wouldn't such a constant-speed flight segment increase the gravity losses? And wouldn't part of the 'normal' abort sequence shut down the booster anyhow? It should, but an abort occurs when there is an anomaly, so it might not work. -- Niklas Holsti Tidorum Ltd niklas holsti tidorum fi . @ . |
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Niklas Holsti wrote on Fri, 28 Jun
2019 22:44:30 +0300: On 19-06-28 19:25 , Fred J. McCall wrote: Niklas Holsti wrote on Fri, 28 Jun 2019 18:54:30 +0300: On 19-06-28 14:13 , Jeff Findley wrote: In article , lid says... On 19-06-27 13:55 , Jeff Findley wrote: The [SpaceX Dragon-2] abort test will reportedly use an actual fueled upper stage but no flight worthy Merlin vacuum engine. Do you have a link/reference for that? The descriptions I've found say no upper stage, and only three Merlins on the first stage. This isn't a very recent article, but it's based on a document submitted to the FAA for the test, so I'm betting it's as accurate as we're going to get before the actual test. How SpaceX Will Conduct an Inflight Abort Test for Crew Dragon November 28, 2018 Doug Messier http://www.parabolicarc.com/2018/11/...duct-inflight- abort-test-crew-dragon/ Many thanks, Jeff, that does seem authoritative. So, this sounds like a very high fidelity test. Yep, largely so. But it seems they intend to shut down the first-stage engines at the time of the abort, so the booster will not try to catch up with the capsule after the capsule separates. Still, I guess the capsule's acceleration would win anyway. If the abort test is at Max Q I don't think this makes any difference anyway, since you're not really 'accelerating' at Max Q. I don't recall seeing any pause, at Max Q, in the growth rate of the Falcon 9 "velocity" reading in the numerous Falcon 9 launch videos I've watched, so I find it hard to believe that the vehicle stops accelerating at that point. https://space.stackexchange.com/ques...y-after-launch Also, wouldn't such a constant-speed flight segment increase the gravity losses? Not nearly as much as having the vehicle disintegrate due to aerodynamic stress would. And wouldn't part of the 'normal' abort sequence shut down the booster anyhow? It should, but an abort occurs when there is an anomaly, so it might not work. These are liquid fuel rockets. It's not like they're difficult to throttle down. You might as well postulate that payload separation will fail at that point. -- "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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In message
Jeff Findley wrote: In article , says... Say the stack explodes violenty. The kerosene and LOX will burn, but there won't technically be an explosion because the kerosene and LOX will not much have time to mix before burning. The Dragon on CRS-7 survived the disintegration of the second stage of the Falcon 9 just fine without any kind of abort system firing. It didn't survive hitting the ocean a few minutes later, but software has been tweaked to enable the parachutes should anything similar happen again. Anthony |
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On 19-06-29 07:25 , Fred J. McCall wrote:
Niklas Holsti wrote on Fri, 28 Jun 2019 22:44:30 +0300: On 19-06-28 19:25 , Fred J. McCall wrote: If the abort test is at Max Q I don't think this makes any difference anyway, since you're not really 'accelerating' at Max Q. I don't recall seeing any pause, at Max Q, in the growth rate of the Falcon 9 "velocity" reading in the numerous Falcon 9 launch videos I've watched, so I find it hard to believe that the vehicle stops accelerating at that point. https://space.stackexchange.com/ques...y-after-launch The acceleration graph shown there for CRS/Dragon missions never falls below about 0.53 g, so it is indeed still accelerating at Max Q. From the behaviour before and after Max Q it seems that without the throttle-down for Max Q the acceleration at that altitude would still be less than 1 g, so the throttle-down cuts acceleration in half, but not more than that. -- Niklas Holsti Tidorum Ltd niklas holsti tidorum fi . @ . |
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In article ,
says... Jeff Findley wrote on Fri, 28 Jun 2019 07:23:56 -0400: Falcon 9 Block 5 first stages are designed for something like 100 flights. There are no Falcon 9 Block 5 first stages with 99 flights on them. The one thought that occurs to me (and I don't think the description you posted of the test assets makes it clear) is that perhaps they are NOT using a Block 5 booster set, but rather an earlier set that isn't intended for a lot of reflights. That would certainly be possible, but it wouldn't be as high fidelity as a Block 5. According to NexxusWolf on Reddit, it will be a Block 5 booster. Yes, I know, not the most reliable spot for info, but it is what it is. https://www.reddit.com/r/spacex/comm...at_i_got_from_ my_tour/ 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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