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Niklas Holsti wrote on Sat, 29 Jun
2019 13:46:13 +0300: 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. Whoop-d-****ing-doo! Now, what's the acceleration of the capsule on abort? Hint: When Dragon commands an abort the engines on the booster shut down and acceleration is negative. Aerodynamics break up the launch vehicle shortly after separation. Meanwhile, Dragon is capable of a 6+g slap in the ass... -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
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Jeff Findley wrote on Sat, 29 Jun 2019
08:27:43 -0400: 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/ Well, they're already removing grid fins and landing legs, so does not having Block 5 upgrades really make that much additional difference? -- "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 19-06-29 21:07 , Fred J. McCall wrote:
Niklas Holsti wrote on Sat, 29 Jun 2019 13:46:13 +0300: 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. Whoop-d-****ing-doo! Now, what's the acceleration of the capsule on abort? Hint: When Dragon commands an abort the engines on the booster shut down and acceleration is negative. Aerodynamics break up the launch vehicle shortly after separation. Meanwhile, Dragon is capable of a 6+g slap in the ass... Probably rather less in the face of Max Q drag forces. But probably more than 0.5 g, so ok. -- Niklas Holsti Tidorum Ltd niklas holsti tidorum fi . @ . |
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JF Mezei wrote on Fri, 5 Jul 2019
14:29:16 -0400: On 2019-06-27 14:50, Fred J. McCall wrote: No. The capsule accelerates away from the stack. That's sort of the point. When the stack explodes, there may be portions of the stack propelled forwards. So the question is whether the capsule will eject at speed equal to or greater than any debris that could be pushed forward by explosion. If you look at the explosive velocity of the propellants, anything is possible except accelerating humans as fast as a tiny bit of debris could be accelerated (unless you put a whacking great motor on it and are willing to get the crew back as jam). However, you have to look at the odds. First, keep in mind that if there is significant acceleration toward to capsule from the explosion that the capsule will also be accelerated by that. Second, remember that the capsule is a pretty robust pressure vessel while boosters are mostly made out of aluminum. Third, remember that there is a pressure structure, an entire second stage, and a payload adapter between the first stage and the capsule. (or would explosions generally push debros downward (at engine) or outwards (at tanks) and not much going forward ? Explosions go in the direction of least resistance. In this case that is out the sides, as there are pressure walls and heavy structure at the ends of the booster. They have no such rockets. Nothing is anywhere near flight limits. SO far, they have only re-used 3 times. Surely they have rockets with 3 uses that could be used a 4th time. Even though they may have a goal of 10000 re-iuses (or whateber the number is), the current limit appears to be 3. You're really 'stuck on stupid' on this issue, aren't you? Go check the mileage on your car. Is it your contention that the current limit on your car is that figure and that if you drive another mile it will blow up or fail? I'll merely point out that your moving of goalposts from your original question (cleverly deleted by you) doesn't prove jack **** and the current limit does NOT appear to be 3. So pushing the ebveloppe with non-commecial tests may allow SpaceX to raise the limit of commercial re-uses. Nope, since they're not planning on recovering the booster from the Max Q test. -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
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JF Mezei wrote on Fri, 5 Jul 2019
14:35:31 -0400: On 2019-06-28 07:26, Jeff Findley wrote: This. I honestly don't know why NASA agreed to let Boeing only simulate a max-Q escape with its Starliner capsule. IMHO, this is a case where you really want a real world test. Orion will do a max-Q abort, so if NASA doesn't trust Orion to a simulation, why trust Starliner to the same? Is it possible that there are enough similarities between Orion and Starliner that the abort tests for Orion can be used to validare Starliner? Other than the two vehicles being totally different, flying on different boosters, and using totally different abort systems, yeah, that makes perfect sense. [That was sarcasm, in case you didn't get it.] -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
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JF Mezei wrote on Fri, 5 Jul 2019
14:44:17 -0400: On 2019-06-28 12:25, 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. And wouldn't part of the 'normal' abort sequence shut down the booster anyhow? If you get in a situation so dire that you must eject in flight, can you really expect that a shutdown command of liquid fueled engines will work? Will you please stop misusing 'eject' for this situation? To answer your question, yes, you can. Say there is an explosion near top of Stage 1. This would sever connection between capsule and the engines at bottom of stage 1. Capsule could eject, but not send shutdown command to engines. Would they shutdown within milliseconds of losing data link to capsule or would they run till told otherwise? They would 'shut down' when the explosion occurs because the propellant tanks would lose pressurization. Liquid rockets do not both blow up AND continute to boost. Seems to me that a capsule eject system, is designed to handle worse case scenario, would have to consider possibility of stack still getting propulsion as it explodes. (even if the odds are that explosion would be at engines and thus kill propulsion). Please go read up on how liquid fuel rockets work. -- "Ignorance is preferable to error, and he is less remote from the truth who believes nothing than he who believes what is wrong." -- Thomas Jefferson |
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In article ,
says... On 2019-06-28 07:26, Jeff Findley wrote: This. I honestly don't know why NASA agreed to let Boeing only simulate a max-Q escape with its Starliner capsule. IMHO, this is a case where you really want a real world test. Orion will do a max-Q abort, so if NASA doesn't trust Orion to a simulation, why trust Starliner to the same? Is it possible that there are enough similarities between Orion and Starliner that the abort tests for Orion can be used to validare Starliner? No. The escape systems are entirely different. Orion uses a solid escape tower while Starliner uses a pusher type liquid fueled escape system located in its service module. Orion https://www.space.com/nasa-orion-lau...explainer.html Starliner https://spacenews.com/boeings-starli...ngine-suffers- problem-during-testing/ They share few, if any, similarities. 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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