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Falcon 1 Staging Recontact - Engine Burp
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Falcon 1 Staging Recontact - Engine Burp
On Aug 4, 11:05 pm, Pat Flannery wrote:
richard schumacher wrote: Or something as simple as thrust created by gas exhausting from the (new) cooling system. Geez Louise. Does Falcon 1 use anything other than explosive bolts and springs for stage separation? How many more basic errors can they afford to re-discover? That's their problem; they are basically rediscovering every problem that rockets had in the mid-late 1950s. They should have hunted down retired steely-eyed missile men who worked on vehicles like Jupiter, Thor, Titan I, and Delta and pooled everything they learned from those programs as how to do and not do things. Propellant oscillation was a big problem in the early days, particularly for Jupiter. Per the SpaceX website: "The problem arose due to the longer thrust decay transient of our new Merlin 1C regeneratively cooled engine, as compared to the prior flight that used our old Merlin 1A ablatively cooled engine. Unlike the ablative engine, the regen engine had unburned fuel in the cooling channels and manifold that combined with a small amount of residual oxygen to produce a small thrust that was just enough to overcome the stage separation pusher impulse. " /dps |
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Falcon 1 Staging Recontact - Engine Burp
Brian Gaff wrote: That is what I was thinking, hence my thought on the deceleration motors, but this is weight taken away from payload, I suppose. Whichever way you look at it, you cannot just assume that the two bodies coasting for a short time will give the desired separation. If you coast too long, in order to protect your first stage from plume damage, you run the risk of sloshing in the upper stage suddenly released from thrust with no continuation within the time you have before it goes float about in the tank. Brian There are two ways {at least) around that problem. 1.) Use ullage rocket engines on the upper stage to seat the propellants before engine ignition. 2.) Use some sort of a membrane inside the tank that separates the propellant from the tank proper and which allows gas to fill the area between the tank wall and the membrane - squeezing the propellant toward the feed pipe rather than letting it float around in the tank. SpaceX's report still doesn't explain the roll oscillations on the video during ascent. Pat |
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Falcon 1 Staging Recontact - Engine Burp
"snidely" wrote in message ... On Aug 4, 11:05 pm, Pat Flannery wrote: richard schumacher wrote: Or something as simple as thrust created by gas exhausting from the (new) cooling system. Geez Louise. Does Falcon 1 use anything other than explosive bolts and springs for stage separation? How many more basic errors can they afford to re-discover? That's their problem; they are basically rediscovering every problem that rockets had in the mid-late 1950s. They should have hunted down retired steely-eyed missile men who worked on vehicles like Jupiter, Thor, Titan I, and Delta and pooled everything they learned from those programs as how to do and not do things. Propellant oscillation was a big problem in the early days, particularly for Jupiter. Per the SpaceX website: "The problem arose due to the longer thrust decay transient of our new Merlin 1C regeneratively cooled engine, as compared to the prior flight that used our old Merlin 1A ablatively cooled engine. Unlike the ablative engine, the regen engine had unburned fuel in the cooling channels and manifold that combined with a small amount of residual oxygen to produce a small thrust that was just enough to overcome the stage separation pusher impulse. " From what I can tell, stage separation events are one of the hardest things to get right on a launch vehicle. On another list Henry Spencer pointed out that, when they developed the Saturns, Von Braun's team was pretty much the only team on the planet who had real experience designing large rockets. I talked to our senior engineer here about this (he does software today, but spent maybe 10 years working for an aerospace company doing actual designs for certain large satellite components). His take on this sort of thing is that in any engineering organization, there is a certain amount of knowledge, maybe even the majority of knowledge, that isn't captured in formally documented analysis and design processes. Furthermore, it's not appropriate to try to capture all of that knowledge. Every project is a bit different, so the lessons learned vary a bit from project to project. If the formal engineering process is too rigid, you wouldn't be able to innovate. Space-X is innovating while at the same time they're building up their collective engineering knowledge for the approach they're taking. While from the outside, it may look like they're making the same mistakes made in the past, the details of their approach may be new enough that these really are new mistakes which have never been made in exactly the same way. Jeff -- A clever person solves a problem. A wise person avoids it. -- Einstein |
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Falcon 1 Staging Recontact - Engine Burp
In article ,
Fred J. McCall wrote: :Those are methods for cutting the stages apart. Then you need something :to ensure that they continue moving away from each other: thrusters on :the first stage to slow it, or firing the second stage just before :separation. : Or maybe just some strong springs compressed between the stages and some pop-out drag brakes on the first stage. Not much air up there, but you're already moving pretty fast so maybe just a little drag is enough... A potential problem with single-impulse separation methods such as springs arises if the first stage continues to generate thrust, because it can then catch up with the second stage. This is exactly what happened with the 3rd Falcon 1 flight. |
#26
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Falcon 1 Staging Recontact - Engine Burp
In article ,
"Jeff Findley" wrote: I talked to our senior engineer here about this (he does software today, but spent maybe 10 years working for an aerospace company doing actual designs for certain large satellite components). His take on this sort of thing is that in any engineering organization, there is a certain amount of knowledge, maybe even the majority of knowledge, that isn't captured in formally documented analysis and design processes. Furthermore, it's not appropriate to try to capture all of that knowledge. Every project is a bit different, so the lessons learned vary a bit from project to project. If the formal engineering process is too rigid, you wouldn't be able to innovate. Space-X is innovating while at the same time they're building up their collective engineering knowledge for the approach they're taking. While from the outside, it may look like they're making the same mistakes made in the past, the details of their approach may be new enough that these really are new mistakes which have never been made in exactly the same way. True. The problems they have had are maddening, but in that class of unavoidable teething problems of a new engineering team. With any luck this team will remain together for a long time, retaining and passing on their hard-won wisdom as they develop successive generations of launchers. Barring some assembly error the odds of success for the 4th Falcon 1 flight should be pretty good. Now, on to the bad news : the most likely failure of the first flight of Falcon 9 will involve staging, specifically because it will be the first attempted start of the Merlin 1C engine in flight. Will the second stage ullage thrusters continue firing for the duration of the main engine startup transients? |
#27
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Falcon 1 Staging Recontact - Engine Burp
Jeff Findley wrote: On another list Henry Spencer pointed out that, when they developed the Saturns, Von Braun's team was pretty much the only team on the planet who had real experience designing large rockets. No, Korolev had some good sized ones, like the R-7 (built with some German input), and Chelomei was working on the UR-500 "Proton" super ICBM of the Saturn 1 class, a entirely home-grown Soviet design. Von Braun's team's only real experience was in drawing big rockets, not building them prior to Saturn I. Up till that point the largest thing they had actually built was Jupiter, which wasn't even a ICBM. Their multistage experience consisted of clustered solids atop the Juno 1 and 2 boosters, based on the Redstone and Jupiter respectively. I don't know how much input they had on the V-2/WAC Corporal tests. Pat |
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Falcon 1 Staging Recontact - Engine Burp
On Aug 7, 11:19 am, richard schumacher wrote:
Now, on to the bad news : the most likely failure of the first flight of Falcon 9 will involve staging, specifically because it will be the first attempted start of the Merlin 1C engine in flight. Will the second stage ullage thrusters continue firing for the duration of the main engine startup transients? What ullage thrusters? |
#29
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Falcon 1 Staging Recontact - Engine Burp
"richard schumacher" wrote in message ... A potential problem with single-impulse separation methods such as springs arises if the first stage continues to generate thrust, because it can then catch up with the second stage. This is exactly what happened with the 3rd Falcon 1 flight. On another discussion forum, Henry Spencer said this is almost exactly what nearly happened during Apollo 15's S-IC separation, so naturally I went digging for details. http://history.nasa.gov/alsj/a15/a15mrp6.pdf Quote from above: Four of the eight S-IC retromotors and all of the S-II stage ullage motors were removed for this flight; therefore, the S-IC/S-II separation sequence was revised. This sequence change extended the coast period between S-IC outboard engine cutoff and S-II engine start command by one second. The S-IC/S-II separation sequence and S-II engine thrust buildup performance was satisfactory. From what I understand, the above deleted motors were added back for subsequent flights, but I can't find a PDF online to confirm this. Jeff -- A clever person solves a problem. A wise person avoids it. -- Einstein |
#30
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Falcon 1 Staging Recontact - Engine Burp
Jeff Findley wrote:
"richard schumacher" wrote in message ... A potential problem with single-impulse separation methods such as springs arises if the first stage continues to generate thrust, because it can then catch up with the second stage. This is exactly what happened with the 3rd Falcon 1 flight. On another discussion forum, Henry Spencer said this is almost exactly what nearly happened during Apollo 15's S-IC separation, so naturally I went digging for details. http://history.nasa.gov/alsj/a15/a15mrp6.pdf Quote from above: Four of the eight S-IC retromotors and all of the S-II stage ullage motors were removed for this flight; therefore, the S-IC/S-II separation sequence was revised. This sequence change extended the coast period between S-IC outboard engine cutoff and S-II engine start command by one second. The S-IC/S-II separation sequence and S-II engine thrust buildup performance was satisfactory. From what I understand, the above deleted motors were added back for subsequent flights, but I can't find a PDF online to confirm this. Apollo 16 press kit: http://history.nasa.gov/alsj/a16/A16_PressKit.pdf p. 140 (144 of the PDF): Significant Vehicle Changes Saturn vehicle SA-511 is similar in configuration to the Apollo 15 launch vehicle. The first stage (S-1C) has eight retrorocket motors, double the number on the SA-510 vehicle, because flight evaluation of the Apollo 15 mission revealed that the separation distance between the first and second stages was less than predicted. Eight retrorockets will give a greater safety margin should one motor fail during separation. Apollo 17 press kit: http://history.nasa.gov/alsj/a17/A17_PressKit.pdf p. 94 (146 of the PDF): The first stage has eight solid-fuel retro-rockets that fire to separate the first and second stages. Each rocket produces a thrust of 337,000 newtons (75,800 pounds) for 0.54 seconds. |
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