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S-IVB question



 
 
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  #1  
Old September 22nd 11, 11:51 AM posted to sci.space.history
GordonD
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Posts: 151
Default S-IVB question

There's a classic piece of footage showing an S-IVB stage separating from
the rest of the stack and lighting up its engine. This appears to be from a
Saturn IB flight as there are three ullage motors firing and the Saturn V
version only had two. However there's no interstage attached as it pulls
away, so either the camera is attached to the interstage itself, or it's on
the S-IB stage looking *through* the interstage. Which in turn means that
the interstage remained attached to the S-IB at staging.

On a Saturn V launch the S-II interstage was there to prevent contact with
the engines as the first stage dropped away but the single engine of the
S-IVB gives a lot more clearance, so maybe this was not thought necessary.
After all the tapered interstage between the S-II and the S-IVB remained
attached to the lower stage.

So the question (at last) - on a Saturn IB flight, did the interstage remain
attached to the S-IB or did it separate with the upper stage to be
jettisoned a short time later?
--
Gordon Davie
Edinburgh, Scotland

"Slipped the surly bonds of Earth...to touch the face of God."

  #2  
Old September 22nd 11, 04:58 PM posted to sci.space.history
GordonD
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Posts: 151
Default S-IVB question

"Pat Flannery" wrote in message
...
On 9/22/2011 2:51 AM, GordonD wrote:

So the question (at last) - on a Saturn IB flight, did the interstage
remain attached to the S-IB or did it separate with the upper stage to
be jettisoned a short time later?


The interstage stayed attached to the first stage in the S-IVB staging
when the Saturn IB launched them.
The interstage incorporated external forward-firing separation motors that
pushed it and the attached first stage backwards as the upper stage fired
its ullage/separation motors and pulled away.
Note that when the video starts it is in darkness, as the stages are still
attached to one another.
The original six RL-10 engined S-IV interstage also stayed with the first
stage on separation: http://www.youtube.com/watch?v=X86LYWyK9_0



I didn't realise the separation motors fired forwards; I assumed they were
posigrade like the ones on the S-II interstage.

I suppose if the Saturn IB interstage had separated along with the S-IVB
then been jettisoned later, it would have been spinning (as in the S-II
shots from Apollo 4) - the pictures as shown are rock-steady.
--
Gordon Davie
Edinburgh, Scotland

"Slipped the surly bonds of Earth...to touch the face of God."

  #3  
Old September 22nd 11, 06:13 PM posted to sci.space.history
Pat Flannery
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Posts: 18,465
Default S-IVB question

On 9/22/2011 2:51 AM, GordonD wrote:

So the question (at last) - on a Saturn IB flight, did the interstage
remain attached to the S-IB or did it separate with the upper stage to
be jettisoned a short time later?


The interstage stayed attached to the first stage in the S-IVB staging
when the Saturn IB launched them.
The interstage incorporated external forward-firing separation motors
that pushed it and the attached first stage backwards as the upper stage
fired its ullage/separation motors and pulled away.
Note that when the video starts it is in darkness, as the stages are
still attached to one another.
The original six RL-10 engined S-IV interstage also stayed with the
first stage on separation: http://www.youtube.com/watch?v=X86LYWyK9_0

Pat

  #4  
Old September 23rd 11, 03:34 AM posted to sci.space.history
Pat Flannery
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Posts: 18,465
Default S-IVB question

On 9/22/2011 7:58 AM, GordonD wrote:
"Pat Flannery" wrote in message
...
On 9/22/2011 2:51 AM, GordonD wrote:

So the question (at last) - on a Saturn IB flight, did the interstage
remain attached to the S-IB or did it separate with the upper stage to
be jettisoned a short time later?


The interstage stayed attached to the first stage in the S-IVB staging
when the Saturn IB launched them.
The interstage incorporated external forward-firing separation motors
that pushed it and the attached first stage backwards as the upper
stage fired its ullage/separation motors and pulled away.
Note that when the video starts it is in darkness, as the stages are
still attached to one another.
The original six RL-10 engined S-IV interstage also stayed with the
first stage on separation: http://www.youtube.com/watch?v=X86LYWyK9_0



I didn't realise the separation motors fired forwards; I assumed they
were posigrade like the ones on the S-II interstage.


The ones on the stage you are trying to push back and away from the
upper stage always face forward; in the case of the Saturn V, not only
did the interstage between the S-II and S-IVB have four forward facing
ones, but the S-IC had ones mounted way back in the four fairings over
the F-1 engines to pull it away from the S-II/interstage assembly.
See number 20 in this cutaway:
http://history.nasa.gov/SP-4206/p197.jpg

I suppose if the Saturn IB interstage had separated along with the S-IVB
then been jettisoned later, it would have been spinning (as in the S-II
shots from Apollo 4) - the pictures as shown are rock-steady.


That would mean that the S-IV/S-IVB would have to drag the weight of the
interstage along till it was jettisoned, lowering performance; IIRC the
reason the S-II stage carried its interstage along for a while was due
to the fact that there were still some atmospheric effects at the
altitude the first stage separated at and the rocket was more stable
with the interstage attached till more of the atmosphere was cleared.

Pat

  #5  
Old September 23rd 11, 08:28 AM posted to sci.space.history
GordonD
external usenet poster
 
Posts: 151
Default S-IVB question

"Pat Flannery" wrote in message
dakotatelephone...

That would mean that the S-IV/S-IVB would have to drag the weight of the
interstage along till it was jettisoned, lowering performance; IIRC the
reason the S-II stage carried its interstage along for a while was due to
the fact that there were still some atmospheric effects at the altitude
the first stage separated at and the rocket was more stable with the
interstage attached till more of the atmosphere was cleared.


I've heard that if the S-II interstage had failed to separate on a lunar
mission, it would have been quite a serious problem. And apparently this did
happen on Skylab 1, though with all the other problems they were having on
that one it was the least of their worries.
--
Gordon Davie
Edinburgh, Scotland

"Slipped the surly bonds of Earth...to touch the face of God."

 




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