Newsgroups: sci.space.history
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Saturn V Launches: S-IC
Date: Sun, 27 Sep 1998 19:14:25 GMT

In article <98266.125852GHB1@psuvm.psu.edu>,
Me at psu.edu  <GHB1@psuvm.psu.edu> wrote:
>As the Saturn V stack moves into the upper atmosphere towards the end
>of the S-IC's life, it appears the the flames from the engine exhaust
>creeps nearly half-way up the length of the stage...

This backflow is reasonably normal for rockets, although it happened to be
particularly visible on the Saturn V.  Particularly after the rocket goes
supersonic, and strong shock waves from the nose area start to have major
effects on airflow close to the rocket, it's not uncommon for the air near
the body to be fairly thin and moving fairly slowly.  The result is that
the pressure of the rocket exhaust overwhelms the local airflow, and the
exhaust begins to expand upward along the body.

At high altitudes, a rocket can be completely enveloped in its own exhaust.

>To what extent were the engineers concerned about the safety of the stage?

Not a big safety issue apart from a bit of surface heating.  The biggest
problem with such backflow is the possibility that deposits from it will
contaminate vulnerable surfaces like windows.  How serious a problem this
is, depends on the composition of the exhaust.  LOX/kerosene exhaust is
particularly bad because it contains a lot of soot (and on the Saturn V,
it didn't help that the turbine exhaust -- *really* sooty -- was in the
outermost layer of the engine exhaust).  LOX/LH2 exhaust is much cleaner.
Note that the Apollo escape tower, including its protective cover over the
CM (and the CM windows in particular), was not jettisoned until after
staging.
--
Being the last man on the Moon is a |  Henry Spencer   henry@spsystems.net
very dubious honor. -- Gene Cernan  |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.history
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Saturn V Launches: S-IC
Date: Tue, 29 Sep 1998 02:43:35 GMT

In article <01bdeb17$b1e9b2e0$LocalHost@default>,
Gordon Davie <G.Davie@btinternet.com> wrote:
>> The biggest problem with such backflow is the possibility
>> that deposits from it will contaminate vulnerable surfaces
>> like windows.
>
>Didn't the Gemini windows have an outer pane which was jettisoned
>after orbit insertion? Presumably this was for this very reason?

I don't recall Gemini having anything like that... but I don't have Gemini
technical details on hand at the moment.  The Titan II exhaust was pretty
clean -- not as good as LOX/LH2, but nowhere near as bad as LOX/kerosene.
--
Being the last man on the Moon is a |  Henry Spencer   henry@spsystems.net
very dubious honor. -- Gene Cernan  |      (aka henry@zoo.toronto.edu)