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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
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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. -- Replace you know what by j to email |
#13
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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
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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. -- Replace you know what by j to email |
#15
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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. |
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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. -- Replace you know what by j to email |
#17
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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
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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
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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
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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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