Newsgroups: sci.space.shuttle
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: Question about Apollo-13 movie
Date: Thu, 30 Nov 1995 03:39:20 GMT

In article <49h7nb$3md@ole.uninett.no> pkf@rf.no (Per Kåre Foss) writes:
>1) During launch I can not understand why the astronauts get pressed 
>forward when the first stage burn out. (When the second stage starts they 
>are pressed back again, thats OK). When the first stage is seperated, the 
>speed should be constant and no acceleration...

For one thing, there is still some air drag at that altitude, so the
rocket really is decelerating a bit during the coasting period.  For
another, everything from the upper-stage structures on up through the
fabric of the spacesuits has been compressed under 4.5G of acceleration,
and it all springs back when the pressure is released.  The movie-makers
got this one right; the forward surge was brief but violent.

>2) During launch 'we' have a look out the window as the vessel leaves the 
>atmosphere. In the movie this happens in about 0.0... seconds, which I 
>cant believe. I supposed that the 'dark sky' would appear gradually...

Well, a rocket does climb out of the bulk of the atmosphere very quickly.
However, it's also true that the movie did exaggerate some things for
dramatic effect.

>3) During descent to the atmosphere the movie gives me a feeling of 
>meeting the atmosphere is as meeting a wall. As in Q2 I beleeved the 
>feeleing of the atmosphere during descent would have been more gradually ?

There is a gradual buildup, but the Apollo lunar reentries were generally
somewhat more violent than Earth-orbit reentries, especially the rather
gentle shuttle reentries.
-- 
Look, look, see Windows 95.  Buy, lemmings, buy!   |       Henry Spencer
Pay no attention to that cliff ahead...            |   henry@zoo.toronto.edu

Newsgroups: sci.space.shuttle
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: Question about Apollo-13 movie
Date: Thu, 30 Nov 1995 20:59:14 GMT

In article <49i8e2$kv1@sifon.cc.mcgill.ca> fox@cs.mcgill.ca (Colin BRADLEY) writes:
>  I was under the impression (perhaps it's written up in Lost Moon) 
>  that the stage transition is actually fairly smooth, but in the 
>  particular case of Apollo 13...

No, the first staging of the Saturn V was always pretty violent for the
passengers.  The Apollo 8 crew thought they were going to go through
the instrument panel for a moment.
-- 
Look, look, see Windows 95.  Buy, lemmings, buy!   |       Henry Spencer
Pay no attention to that cliff ahead...            |   henry@zoo.toronto.edu

Newsgroups: sci.space.shuttle
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: Apollo 13 staging question
Date: Mon, 11 Dec 1995 03:56:29 GMT
Organization: U of Toronto Zoology
Lines: 25

In article <4adnhp$abe@lyra.csx.cam.ac.uk> Geraint Lewis <gfl> writes:
> ...Does your manual tell you 
> how long after the engine shutdown does the stage 
> separation occur ? and is the purpose of the retro fire
> to separate the stages ??

Yes, the retros are for positive separation of the stages.  The sequence
(from the Saturn V flight manual for Apollo 8) is:

T+02:30.0	first-stage engine cutoff
T+02:31.5	second-stage ullage-rocket ignition
T+02:31.7	staging charge fired and first-stage retrorocket ignition
T+02:31.8	separation complete
T+02:32.4	second-stage engine start sequence
T+02:33.4	second-stage engine ignition
T+02:35.4	second-stage engines at 90% thrust
T+02:36.0	ullage-rocket burnout

So retrorocket firing is simultaneous with staging.

Note, by the way, that the rather violent staging was not peculiar to
Apollo 13.  Astronauts on several of the Apollo flights remarked on it.
-- 
Look, look, see Windows 95.  Buy, lemmings, buy!   |       Henry Spencer
Pay no attention to that cliff ahead...            |   henry@zoo.toronto.edu