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Old June 4th 20, 12:30 PM posted to sci.space.policy
Jeff Findley[_6_]
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Default 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
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