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Post by inquisitivemind on Nov 3, 2010 15:41:38 GMT -4
It does not disprove what I said. Some satellites need an attitude control because their natural attitude does not allow them to point exactly to a given point on the earth. Furthermore they are subjected to external inteferences (like solar ones), which make their attitude vary a little; they are not precise enough for some applications, and they do need an attitude control. Now, the CMS was much closer to the moon than a satellite would be, so to avoid a too long travel of the Lem to the moon, and it was not stationary toward the moon, it had a relative speed of 6000 km.h relatively to it; that was giving it more stability in its orbital trajectory than a stationary satellite which is farther from the planet and orbits with a greater radius. It disproves everything you have claimed! No where in there does it talk about a satellite's natural tendency to point at the orbited body. Your "stability in its orbital trajectory" remark is complete nonsense. You confused the centrifugal force demonstration of a weight on a string with centripetal force in orbit. You saw the weight on the end of the string become stable and somehow translated that to spacecraft. No, it doesn't disprove what I said; it shows how to control very precisely the attitude. And if in this article they don't talk about the natural tendency of satellites to show the same side to the earth, it's because they think that people are familiarized with it, and don't need to be told this fact. |
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Post by inquisitivemind on Nov 3, 2010 15:42:49 GMT -4
It's really difficult to discuss with people who have hard anchored conceptions.
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Post by BertL on Nov 3, 2010 15:43:37 GMT -4
It's really difficult to discuss with people who have hard anchored conceptions. It is, isn't it? |
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Post by lukepemberton on Nov 3, 2010 15:43:40 GMT -4
I have used this analogy, knowing it was not exact, because the lem does not behave like an helicopter, but to help people to understand. Unfortunately inexact analogies in precise and exacting subjects such as orbital mechanics and spacecraft maneuver aren't going to get you far. This sentence, for my way of thinking at least, closes the case. In your own words you admit to using something that is not exact, but then tell us 'it is so people can understand.' That is like saying I will teach a student quantum mechanics using Newton's laws. I know it is not exact, but the I can use an imperfect analogy so they can understand. Science doesn't work like that. I think you are making the assumption that people here do not understand, and you do. I have lost confidence in you as a teacher already if you are already using deviant science to make your point. How can I trust you? |
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Post by Apollo Gnomon on Nov 3, 2010 15:48:20 GMT -4
I fly little rockets. One of the pre-flight tests for unproven designs is whirling it around your head on a string. If the center of gravity (CG) is forward of the center-of-pressure (CP) it will whirl around your head nose-forward. If not, it will tumble around any old way, with twist in the string providing more input to the attitude than aerodynamics.
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Post by inquisitivemind on Nov 3, 2010 15:49:10 GMT -4
Anyway, I perfectly know that I won't convince you, and that I'll remain an ignorant idiot for you.
But it's reciprocal, you'll never convince me either!
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Post by Apollo Gnomon on Nov 3, 2010 15:51:26 GMT -4
I've just re read this portion of the OP: and realized that it's completely nonsense. There is no way for an orbiting body to simply lose altitude without affecting horizontal velocity. It's not a helicopter. That would be true for a plane, but not in space.
Of course, the orbital body can lose altitude without losing its horizontal velocity; the attraction will slightly increase, so there will be a little vertical acceleration if the horizontal speed remains the same.Of course, it's not an helicopter; it doesn't behave as such, but still for the helicopter too there is an optimal trajectory for landing. I have used this analogy, knowing it was not exact, because the lem does not behave like an helicopter, but to help people to understand. Bolded statement is utterly false and discredits any further analysis of your theory. |
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Post by theteacher on Nov 3, 2010 15:52:04 GMT -4
I rather think that you believe to have qualified engineers with you when in fact you are all amateurs! Hello again inquisitivemind. I'm sure, there are qualified engineers on this board, but I myself am true enough only an amateur. I would like to understand your way of thinking, so I'm disappointed that you did not answer post #20, where I put a few questions in the hope of clarifying my understanding of your thinking: Well I chose the broomstick because of its supposed regularity :-) What do you exactly mean by "balanced"? I mean what do you think the engineers have done specifically to reach the "balance"?
Forget the broomstick. Take a perfectly "balanced" bar or rod of any material in the shape of a broomstick - a couple of meters long or longer, a couple of centimeters thick with the "center of gravity" right "in the middle" of it. How will the attitude of that object be in orbit around the Moon (or the Earth for that matter) after having been left there for a longer while (weeks or more)?
Can you be more specific?
By the way: You forgot to tell me, if you know what "tidal lock" is? |
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Post by chew on Nov 3, 2010 15:53:10 GMT -4
No, it doesn't disprove what I said; it shows how to control very precisely the attitude. And if in this article they don't talk about the natural tendency of satellites to show the same side to the earth, it's because they think that people are familiarized with it, and don't need to be told this fact. It discusses attitude control, not "precisely" controlling the attitude; and any discussion about attitude control in orbit would have a huge section on a satellite's tendency to point at a massive body. |
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Ian Pearse
Mars
Apollo (and space) enthusiast
Posts: 308
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Post by Ian Pearse on Nov 3, 2010 15:55:56 GMT -4
inquisitivemind, I recommend you read "To Rise From Earth" by Wayne Lee. Amongst other things it will show you how it is impossible to change your orbit vertically (i.e. orbital radius) without also changing your horizontal speed - the two are inextricably linked, you cannot change one without affecting the other.
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Post by inquisitivemind on Nov 3, 2010 15:59:46 GMT -4
I cannot be more specific, because it depends on several parameters, and these parameters can change the natural attitude of the broomstick.
And about the "tidal lock", may be I would know what it is about if I was knowing the correspondence in French, for I am french.
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Post by inquisitivemind on Nov 3, 2010 16:05:12 GMT -4
inquisitivemind, I recommend you read "To Rise From Earth" by Wayne Lee. Amongst other things it will show you how it is impossible to change your orbit vertically (i.e. orbital radius) without also changing your horizontal speed - the two are inextricably linked, you cannot change one without affecting the other. There's a big difference between the earth and the moon: The earth has an atmosphere, and the moon doesn't. Furthermore the travel from the CMS to the moon was relatively short, and the speed to lose important. |
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Post by chew on Nov 3, 2010 16:08:32 GMT -4
We're talking about orbits! Orbital mechanics are universal! The laws are the same regardless of which body a spacecraft is orbiting. Your ignorance continues to amaze me!
If a spacecraft changes any component of its velocity the orbit dimensions will change.
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Post by Apollo Gnomon on Nov 3, 2010 16:12:04 GMT -4
Orbital mechanics are the same around the moon as around the earth. Atmosphere is virtually nonexistent at orbital altitudes.
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Ian Pearse
Mars
Apollo (and space) enthusiast
Posts: 308
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Post by Ian Pearse on Nov 3, 2010 16:15:08 GMT -4
inquisitivemind, I recommend you read "To Rise From Earth" by Wayne Lee. Amongst other things it will show you how it is impossible to change your orbit vertically (i.e. orbital radius) without also changing your horizontal speed - the two are inextricably linked, you cannot change one without affecting the other. There's a big difference between the earth and the moon: The earth has an atmosphere, and the moon doesn't. Furthermore the travel from the CMS to the moon was relatively short, and the speed to lose important. No, there is no difference between the Earth and the Moon as far as orbital dynamics goes. If you're confused by the presence of atmosphere, then imagine orbits well above the top of the atmosphere - the same physics applies as to Lunar orbits, and no atmosphere to get in the way. The higher the orbit, the slower the speed. |
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