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Speed of Saturn V at first staging?



 
 
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  #11  
Old August 5th 09, 03:57 AM posted to sci.space.history
David Spain
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Default Speed of Saturn V at first staging?

David Spain wrote:
I found this PDF,
http://www.klabs.org/history/reports...1970023342.pdf
and the velocity in figure 1 starts off at about 405 m/s, which is the
speed of the rotational speed of the Earth at that latitude. So it is
relative to space, not to the Cape.


Have to be careful here, equations and numbers used in guidance computer
calculations may not be the same as those issued by the press office.

I would have assumed when 'downrange' velocity numbers are used, the reference
point would be the launch point with an initial velocity of 0, not guidance
numbers that have to take into account Earth's rotational velocity. Is that
not a correct assumption? Would it not be in error to mix the two? I would
think you'd have to be careful about that.

Dave
  #12  
Old August 5th 09, 04:11 AM posted to sci.space.history
Jud McCranie[_2_]
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Default Speed of Saturn V at first staging?

On Tue, 04 Aug 2009 22:57:25 -0400, David Spain
wrote:

I would have assumed when 'downrange' velocity numbers are used, the reference
point would be the launch point with an initial velocity of 0, not guidance
numbers that have to take into account Earth's rotational velocity. Is that
not a correct assumption?


I didn't know which way it was. I calculated 406 m/s for the Earth's
rotation at that latitude (28.5 degrees) and when I read the initial
speed off the graph, I got about 405. Interestingly, it drops for a
few seconds after liftoff.
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  #13  
Old August 5th 09, 05:48 AM posted to sci.space.history
David Spain
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Default Speed of Saturn V at first staging?

Jud McCranie wrote:
I didn't know which way it was. I calculated 406 m/s for the Earth's
rotation at that latitude (28.5 degrees) and when I read the initial
speed off the graph, I got about 405. Interestingly, it drops for a
few seconds after liftoff.


Yeah I noticed that too. IIRC the Saturn V had the *lowest* delta V
figure at launch of any rocket ever produced by the US. I'd read somewhere it
was just barely positive post ignition. At the other end of the spectrum,
the short-range ABM Shrike(?) missile had the highest I believe.

So perhaps the curve takes into account the small amount time at which the
Saturn V is moving skyward slightly above a hover but is no longer physically
attached to the Earth's surface. Does anyone know in fact, if the Saturn V
experienced slew in the counter rotational direction (due to air resistance?)
within the first few seconds of powered ascent?

The velocity curve in this paper would suggest it did. If not that, then
I can explain it only if they gimbaled the engines in an anti-rotational
direction for a short time. And if so, can someone explain why?

Dave
  #14  
Old August 5th 09, 05:52 AM posted to sci.space.history
Jud McCranie[_2_]
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Default Speed of Saturn V at first staging?

On Wed, 05 Aug 2009 00:48:22 -0400, David Spain
wrote:

The velocity curve in this paper would suggest it did. If not that, then
I can explain it only if they gimbaled the engines in an anti-rotational
direction for a short time. And if so, can someone explain why?


They angled it 1.5 degrees away from the tower, but I don't know which
direction that puts it.
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  #15  
Old August 6th 09, 02:01 PM posted to sci.space.history
Neil Gerace[_3_]
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Default Speed of Saturn V at first staging?

Jud McCranie wrote:

I found this PDF,
http://www.klabs.org/history/reports...1970023342.pdf
and the velocity in figure 1 starts off at about 405 m/s, which is the
speed of the rotational speed of the Earth at that latitude. So it is
relative to space, not to the Cape.


It sounds like it's relative to the Earth's rotational axis, because 405 m/s ignores the Earth's motion around the Sun
and all of its other motions.

  #16  
Old August 6th 09, 03:48 PM posted to sci.space.history
Jud McCranie[_2_]
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Default Speed of Saturn V at first staging?

On Thu, 06 Aug 2009 21:01:00 +0800, Neil Gerace
wrote:

It sounds like it's relative to the Earth's rotational axis, because 405 m/s ignores the Earth's motion around the Sun
and all of its other motions.


Yes, that seems to be it.
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  #17  
Old August 6th 09, 09:12 PM posted to sci.space.history
David Spain
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Default Speed of Saturn V at first staging?

Neil Gerace writes:

Jud McCranie wrote:

I found this PDF,
http://www.klabs.org/history/reports...1970023342.pdf


It sounds like it's relative to the Earth's rotational axis, because 405 m/s
ignores the Earth's motion around the Sun and all of its other motions.


The paper states the space-fixed co-ordinate system is relative to the
Earth's center. As you mention, that elminates motion around the Sun and
all other motions. But it isn't relative to the rotation axis, because
the co-ordinate system must take into account latitude and radius from
the center to get the correct rotational velocity from a surface point.

Dave
  #18  
Old August 16th 09, 02:40 PM posted to sci.space.history
wdw
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Default Speed of Saturn V at first staging?

I've enjoyed following this discussion. As you all worked out, the
figure I gave in the book is relative to the ground. Later in the same
chapter, I introduce the reader to the idea of stating speed using
space-fixed as opposed to Earth-fixed reference.

Hope I didn't confuse too many folk.

In case I'm lucky enough to get a second edition for the book, I'm
always happy to entertain suggestions for improving the text. I have a
website for the book:

www.hafttm.com

and there is a list there of points arising.

Cheers

David Woods
Author: How Apollo Flew to the Moon

On Aug 6, 9:12*pm, David Spain wrote:
Neil Gerace writes:
Jud McCranie wrote:


I found this PDF,
http://www.klabs.org/history/reports...1970023342.pdf

It sounds like it's relative to the Earth's rotational axis, because 405 m/s
ignores the Earth's motion around the Sun and all of its other motions.


The paper states the space-fixed co-ordinate system is relative to the
Earth's center. As you mention, that elminates motion around the Sun and
all other motions. But it isn't relative to the rotation axis, because
the co-ordinate system must take into account latitude and radius from
the center to get the correct rotational velocity from a surface point.

Dave


  #19  
Old August 25th 09, 04:29 AM posted to sci.space.history
David Spain
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Posts: 2,901
Default Speed of Saturn V at first staging?

wdw wrote:
I've enjoyed following this discussion. As you all worked out, the
figure I gave in the book is relative to the ground. Later in the same
chapter, I introduce the reader to the idea of stating speed using
space-fixed as opposed to Earth-fixed reference.

Hope I didn't confuse too many folk.

In case I'm lucky enough to get a second edition for the book, I'm
always happy to entertain suggestions for improving the text. I have a
website for the book:

www.hafttm.com

and there is a list there of points arising.

Cheers

David Woods
Author: How Apollo Flew to the Moon


Perhaps you can explain the small dip in the curve given for Vs
in Figure 1 on page 2 in the NASA Tech Note linked to below:

http://www.klabs.org/history/reports...1970023342.pdf

In the curve for Vs it appears it actually is *reduced* for
approx 25 seconds after launch before rising above its initial
value at s=0. We're speculating its due to early rocket motion
due to first stage engine gimbals?

David Spain
  #20  
Old August 25th 09, 09:56 AM posted to sci.space.history
Pat Flannery
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Posts: 18,465
Default Speed of Saturn V at first staging?

David Spain wrote:


Perhaps you can explain the small dip in the curve given for Vs
in Figure 1 on page 2 in the NASA Tech Note linked to below:

http://www.klabs.org/history/reports...1970023342.pdf

In the curve for Vs it appears it actually is *reduced* for
approx 25 seconds after launch before rising above its initial
value at s=0. We're speculating its due to early rocket motion
due to first stage engine gimbals?


Drag as it passes through the sound barrier?
Drag decreases once a object is in supersonic flight, which is why
fighter pilots do a bit of a power dive while approaching Mach 1, so as
to get into supersonic flight as quickly as possible.

Pat
 




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