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#41
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Falcon 1 Staging Recontact - Engine Burp
Jeff Findley wrote: "Pat Flannery" wrote in message telephone... Jeff Findley wrote: 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. No, they stayed off on all Apollo J-series flights IIRC (15, 16, 17). Actually, the PDF's that Jorge found (see his recent post in this thread) clearly state that they went back to eight retromotors for the S-1C stage on Apollo 16 and Apollo 17 (twice the number on Apollo 15). Perhaps the ullage motors on the S-II stage weren't added back for 16 and 17? S-II shouldn't need any ullage motors as such...separation of the rear interstage occurs while it's under power, and S-II only makes a single burn during ascent. The closest thing to ullage engines on S-II proper were the four 4 (originally 8) motors on the interstage, and all of those were removed for the J-Series launches: http://www.hq.nasa.gov/pao/History/S...ages/m406b.jpg Still, it's clear there was a bit of tweaking going on with the Saturn V to eek out a bit more performance on later flights. The other point I wanted to make was that even von Braun's team cut back too far at times, as was the case with the S-1C retromotors. By that point the rocket and what was done with mods to it was probably out of von Braun's hands. When they originally built it they took a very conservative approach to things, which is why it had the 8 separation/ullage motors on the interstage, even though they expected four would be sufficient. This does raise a interesting question though - with all eight removed from the interstage, how were the propellants kept seated during staging? As the S-IC shut down and separated, the S-II was in free-fall and still subject to some air drag. Did the pre-start cycle on its J-2s generate enough thrust to keep the propellants at the back of the tanks? There are a ton of nifty Saturn I and Saturn V photos and drawings here BTW: http://history.nasa.gov/MHR-5/contents.htm Pat |
#42
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Falcon 1 Staging Recontact - Engine Burp
On Fri, 08 Aug 2008 03:29:09 GMT, in a place far, far away,
(Derek Lyons) made the phosphor on my monitor glow in such a way as to indicate that: richard schumacher wrote: Barring some assembly error the odds of success for the 4th Falcon 1 flight should be pretty good. That's what everyone said after the first. And the second too. "Everyone"? Not I. |
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