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Great job SpaceX
In article , says...
On 2020-06-02 7:50 AM, Jeff Findley wrote: In article , says... ... I'd guess the Saturn IB and Saturn V would be a smoother ride (same upper stage really), simply because LOX/LH2 likely makes complete mixing easier resulting in more complete combustion. But, it certainly would be more apples to apples than the shuttle due to the in-line stage design and the single engine. The shuttle had that giant, heavy, ET structure hanging off the side that likely dampened some of the vibrations (it certainly did when the SRBs were firing!). I am going to disagree here a bit with you Jeff. As I understand it there was still some POGO with the Saturn 5 Stage 1. I would expect the higher it got and the less the fuel mass the worse it might have become. Contrary facts always welcome. Contrary opinions always greeted with skepticism. :-) You're right. I don't think they ever entirely licked the POGO problem, but they knew what caused it and they were tweaking the fixes to mitigate the problem. Also understand from what I've read MECO and stage separation of the first stage was also a bit of a jolt. After that, I believe things smoothed considerably as they went to LH2/LOX engines. The Saturn 5 second stage was a marvel and largely ignored (unfortunately). Agreed. As I said earlier, I think one of the issues is that with LOX/kerosene it's hard to get them to completely mix in the combustion chamber, so you get combustion instability resulting in thrust fluctuations (i.e. vibrations). LOX/hydrogen mixes rather well because by the time you inject it into the chamber, it's gaseous (unlike kerosene). I'd expect Merlin causes similar vibrations, but since the engines are much smaller, that would mitigate some of it. The F-1 engine development program was long and *hard*. They really had to work hard to get that thing to have stable combustion. It's a good thing that the F-1 program was started years before Apollo/Saturn was proposed. I'm hoping that the emerging LOX/methane engines like Raptor and BE-4 will have less vibration than LOX/kerosene engines of similar size. Raptor, in particular, is a full flow staged combustion engine, so hot gaseous oxygen and hot gaseous methane are injected into the combustion chamber. That ought to maximize mixing, minimize combustion instability, and minimize vibrations. But, it remains to be seen how either will perform in flight. Off the top of my head I count 5 crewed Apollo flights using the Saturn IB: Apollo 7, the 3 Skylab missions and Apollo/Soyuz. The last flight of a Saturn 5 was to launch the Skylab space station. Yep. 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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