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Great job SpaceX

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Old June 4th 20, 12:30 PM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 2,200
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

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.


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.
Old June 4th 20, 12:36 PM posted to sci.space.policy
Jeff Findley[_6_]
external usenet poster
Posts: 2,200
Default Great job SpaceX

In article , says...
I took a cursory look at this document. There were also liquid fueled
strap-on options studied as well. The Saturn V 23L and Saturn V 24L. The
23L variant used pairs of "standard" F1s in each of four strap-on liquid
"pods" and the 24L used pairs of "uprated" F1s in four strap-ons and an
"advanced" engine for the upper stages. The document mentions aerospike
engines and maybe so, but there were also ideas kicking around at the
time for a higher performance J2 as well.

The 24L didn't make it past phase 1 study but, the 23L got a rating in
this document of 579,000 lbs (289.5 short tons) to orbit (2 stage
configuration) and 220,000 lbs (110 short tons) I presume to the moon (3
stage configuration). Presumably the 24L variant with the higher thrust
F1s could have done even better.* Let's be conservative and estimate
first launch by 1975 (this document was written in 1966 and predicted a
1973 ready date). My date includes assuming mobile launch platform
(known as MLs in the Apollo era) modifications and other pad
modifications also needed. But at the time Wikipedia says NASA had three
MLs, so NASA should have been able to dedicate one to support this

Compare this to the also non-extant SLS Block 2 at 280,000 lbs (140
short tons) to LEO.

What a monster this could have been. You're gonna need to move further
back... What other country in the world (besides us) would have so
thoroughly blown this advantage in rocketry? We're talking nineteen
seventy freaking five!


*There's a tantalizing paragraph on page 9 that ends:

"The liquid pod strap-on concept, with uprated F-1s and advanced engines
in the second stage (SAT-V-24(L)), achieved payloads to 960,000 lbs.
[480 short tons] to 100 nautical mile Earth orbit when stage and total
vehicle length restrictions were relaxed."

I personally preferred the liquid strap-ons, but that's because of the
hindsight of the history of large segmented solid rocket boosters (Titan
and shuttle programs). At the time, solids were still thought to be
cheap to develop and relatively cheap to produce for flights. The
Aerojet facility in Florida could have solved the joint problem by
producing monolithic (single pour) SRBs which could have then been
transported to KSC by barge.

Liquids had the advantage that they were much lighter when transporting
them to the pad. Those concepts using multiple heavy solids would
likely have needed to have been attached at the pad because they would
have overloaded the crawlers.

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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