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Old 11-02-2019, 12:15 PM
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gary is offline
Join Date: Apr 2005
Location: Mt. Kuring-Gai
Posts: 5,217
Originally Posted by AndyG View Post
Thankyou Gary, another excellent post to lose an afternoon to (and still not understand).

I'm guessing the fact that this manual was revised 30 days before launch was testiment to the constant development and unsettled nature of the beast. Did they re-issue the manual with the completion of each new launcher? Was each Apollo mission delivered on the same design, or did they evolve as the program went on?
Hi Andy,

Each mission had its own version of the Saturn V Flight Manual.

When you browse some of the others, the overall format is essentially
identical, but the devil would no doubt be in the detail.

One example might be if you examine the PDF on page 1-12, starting in
the lower left column under the heading "POGO".

Originally Posted by Saturn V Flight Manual, SA-503 mission

One of the major anomalies of the AS-502 flight of April 4,
1968, was the POGO phenomenon. This phenomenon
produced an undesirable longitudinal oscillation in the space
vehicle caused by a regenerative feedback of vehicle motion
to the propellant feed system. A thrust oscillation buildup,
along with a structural response buildup, resulted from a
closed loop dynamic effect involving the coupling of the
longitudinal vibration of the vehicle structure, the fluid
vibration in the propellant ducts, and the hydraulic
characteristics of the engine. Pressure fluctuations at the
pump inlets, caused by movement of the propellant ducts
and pumps relative to the fluid in the ducts, produced lagging
fluctuations of engine thrust. Space vehicle instability
resulted from a tuning of the propulsion and vehicle
structural systems. The onset and eventual cessation of the
instability were i:aused by the change in the propulsive
system and vehicle resonant frequencies with time.

The AS-502 space vehicle instability occurred during the
latter part of the S-IC burn period. The buildup of
longitudinal amplitudes started at about T + 110 seconds,
reached a peak at about T + 126 seconds, and decayed to a
negligible level by T + 140 seconds. The buildup was
determined to be a result of the coalescence of the first
longitudinal frequency of the vehicle with the first lox line
frequency (see figure 1-9).
A stability analysis of the AS-503 S-IC stage flight indicated
that the AS-503 space vehicle (without POGO suppression
modification) would be unstable.
The document then goes onto describe "Acceptability Criteria" and
"Solutions Considered" for the "Pogo" phenomena along with "Analysis
and Testing".

"Pogo" is a bit like water hammer in your household plumbing.
It can be disconcerting in a house or apartment when it shakes everything
so one can only imagine how disconcerting it would be when one
is sitting atop a Saturn V.

I recollect at the time "Pogo" was often reported by astronauts and flight
controllers and it was an ongoing issue all the way through to
Apollo 17. They kept attempting to resolve it on each mission.

For example on the first stage they fitted surge absorbers.

But the Apollo 10 second-stage shutdown early because of pogo and
it caused an early shutdown on Apollo 13 as well.

Enjoy the read! Checkout pages 4-8 and 4-9 on the sequence of starting
the first stage F1 engines. Each of these babies consumed a mix of RP1
(kerosene similar to jet fuel) and LOX fuel at a rate of 3 metric
tonnes a second. And there were five engines!

Below. Snapshot I took three years ago of the F1 engines on the Saturn
V on display at the Space Flight Center in Houston. Even when you are prepared
as to how big they are, you still aren't prepared when you walk up to them.
I like the fact that despite all the obvious labour that went into building them,
they only had to work for 2 and a half minutes before being discarded.
Attached Thumbnails
Click for full-size image (F1_engines.jpg)
164.9 KB60 views

Last edited by gary; 11-02-2019 at 12:31 PM.
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