|
|
Post by lukepemberton on Nov 3, 2010 16:17:31 GMT -4
Inquistivemind : Are we talking about orbital mechanics, as in space, as in a vacuum?
|
|
|
|
Post by inquisitivemind on Nov 3, 2010 16:18:59 GMT -4
Orbital mechanics are the same around the moon as around the earth. Atmosphere is virtually nonexistent at orbital altitudes. Atosphere is effectively inexistent at a certain distance from the earth, bit are you sure that he was leaning that the spacecraft was losing horizontal speed before reacing the atmosphere. And even so, at what rate was the spacecraft losing its horizontal speed? Because the spacecraft had a longer journey to make to the earth than the Lem to the moon, and the Lem had a quite important speed relatively to the moon. Even if it was losing a little speed, it was not enough for the speed it had to lose. Could you give me the exact reference in his book so I can make myself an idea of what he means. |
|
|
|
Post by Daggerstab on Nov 3, 2010 16:22:39 GMT -4
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. " verrouillage de marée" Or you can read the article in Wikipedia: en.wikipedia.org/wiki/Tidal_lockingAs it was pointed to you, "the natural tendency" of a body in orbit would be to point its long axis towards the nadir, due to the gravity gradient. This is the way gravity gradient stabilization works for satellites. (Note that they need a very long boom or tether in order for this to be somewhat effective.) And this means that, if gravity was a significant factor in the case of the Apollo CSM, it would point its long axis perpendicular to the lunar surface, not parallel to it as you claim. It would float "nose down" or "main engine nozzle down". See pages 9-12 of these lecture slides: www.aoe.vt.edu/~cdhall/courses/aoe4140/intro2adcs.pdf |
|
|
|
Post by Apollo Gnomon on Nov 3, 2010 16:24:02 GMT -4
Orbital mechanics are the same around the moon as around the earth. Atmosphere is virtually nonexistent at orbital altitudes. Atosphere is effectively inexistent at a certain distance from the earth, bit are you sure that he was leaning that the spacecraft was losing horizontal speed before reacing the atmosphere. And even so, at what rate was the spacecraft losing its horizontal speed? Because the spacecraft had a longer journey to make to the earth than the Lem to the moon, and the Lem had a quite important speed relatively to the moon. Even if it was losing a little speed, it was not enough for the speed it had to lose. Could you give me the exact reference in his book so I can make myself an idea of what he means. uh. What? |
|
|
|
Post by inquisitivemind on Nov 3, 2010 16:27:13 GMT -4
Inquistivemind : Are we talking about orbital mechanics, as in space, as in a vacuum? Yes. Concerning the book "To rise from earth", I cannot discuss it if I don't see the reference; I need to know what exactly he is talking about. So, as long I have not seen the exact text, I cannot comment it. |
|
|
|
Post by gillianren on Nov 3, 2010 16:27:14 GMT -4
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. Gargleplatz, I think you miss the whole point of Wikipedia. As with any other explanatory resource--encyclopedia, dictionary, et cetera--it's intended to teach people things they don't know. Assuming everyone knows something as complicated as that is a pretty serious failing in its usefulness. Isn't it a far, far more logical assumption that they didn't put it in because it isn't true? That you are, in fact, wrong in your assumptions? Indeed, can you show me a scholarly reference that shows you to be correct? And I mean the bits that you think Wikipedia doesn't bother explaining because everyone should know them. Also, Gargleplatz, if your English isn't good enough to have this discussion, why are you having it on an English-language board? Wouldn't it make more sense to choose a French-language board? Don't get me wrong--your English is generally pretty good, but you are dealing with very technical subjects, and small miscommunications in language can result in big problems. |
|
Ian Pearse
Mars
Apollo (and space) enthusiast
Posts: 308
|
Post by Ian Pearse on Nov 3, 2010 16:30:16 GMT -4
Inquistivemind : Are we talking about orbital mechanics, as in space, as in a vacuum? Yes. Concerning the book "To rise from earth", I cannot discuss it if I don't see the reference; I need to know what exactly he is talking about. So, as long I have not seen the exact text, I cannot comment it. Orbital mechanics are discussed in Chapters 1 and 2. |
|
|
|
Post by inquisitivemind on Nov 3, 2010 16:36:00 GMT -4
Yes. Concerning the book "To rise from earth", I cannot discuss it if I don't see the reference; I need to know what exactly he is talking about. So, as long I have not seen the exact text, I cannot comment it. Orbital mechanics are discussed in Chapters 1 and 2. Is it free access? If yes, I'll read it. I cannot give you my answer right now, I don't use to comment something I have not read, I need to know what I'm talking about. |
|
|
|
Post by Apollo Gnomon on Nov 3, 2010 16:39:35 GMT -4
I need to know what I'm talking about. Indeed. I highly recommend knowing what you're talking about. |
|
Ian Pearse
Mars
Apollo (and space) enthusiast
Posts: 308
|
Post by Ian Pearse on Nov 3, 2010 16:43:03 GMT -4
Orbital mechanics are discussed in Chapters 1 and 2. Is it free access? If yes, I'll read it. I cannot give you my answer right now, I don't use to comment something I have not read, I need to know what I'm talking about. No, you get it from a library or a bookstore - I got my copy from Amazon. Edit: I'd also recommend the Haynes Apollo 11 Owners' Workshop Manual. Lots on information and very readable. Also from a library or bookstore. |
|
|
|
Post by lukepemberton on Nov 3, 2010 16:53:28 GMT -4
So going back to Echanton's initial point. Why on Earth are you giving us examples of ballistic flights of shaped projectiles in an atmosphere and talking about helicopters? You take these Earth bound experiences and try to extrapolate and produce models for what you think a space craft in flight should be. Is that really a fair comparison? It is called a fallacy of equivalence. Are you familiar with logical fallacies? The laws of mechanics are very precise things, and not always intuitive. We have mathematical constructs that describe these laws, and they are based on exact principles such as the conservation of energy and angular momentum. Extrapolation from one model to another without doing the math is fraught with danger. Concerning the book "To rise from earth", I cannot discuss it if I don't see the reference; I need to know what exactly he is talking about. So, as long I have not seen the exact text, I cannot comment it. This is a moot point. You have been told that the first two chapters deal with orbital mechanics, which is what we are talking about. You don't need to make comment on the book par se, but demonstrate that you can talk in the language of orbital mechanics. I think it was quietly suggested that you ought to go away and read about orbital mechanics first, before you make any further comment on it. You can find that anywhere on the web. In fact, one of the contributors to these boards has an excellent site on the topic: www.braeunig.us/space/index.htmSo, go fill your boots... |
|
|
|
Post by theteacher on Nov 3, 2010 17:24:43 GMT -4
I cannot be more specific, because it depends on several parameters, and these parameters can change the natural attitude of the broomstick. Ok, maybe I asked too much in one post. I suggested these parameters: 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)?Let me be more specific then: A solid iron rod. 2,54 cm thick (one inch). The same length and in the same orbit as the Apollo spacecraft. Perfectly machined to specifications of best practice. Does it require further parameters to answer the question? |
|
Ian Pearse
Mars
Apollo (and space) enthusiast
Posts: 308
|
Post by Ian Pearse on Nov 3, 2010 17:59:49 GMT -4
Orbital mechanics are discussed in Chapters 1 and 2. Is it free access? If yes, I'll read it. I cannot give you my answer right now, I don't use to comment something I have not read, I need to know what I'm talking about. Am I right in thinking that, judging by this response, the only sources you will consider valid for research are free, probably online, sources? What about textbooks on the various subjects being mentioned here, that you can't read without purchase or loan? |
|
|
|
Post by JayUtah on Nov 3, 2010 18:21:12 GMT -4
Inquisitivemind, I'm a professional engineer, not an amateur. Spacecraft control is what I do for a living. You don't know what you're talking about. And you have a clear pattern of claiming expertise you do not have.
The article referring to a "flat spin" does not describe the phenomenon you allege. It describes a specific problem in spin stability, that you are obviously totally ignorant about.
The notion of a space-fixed attitude state is fairly absent from orbital mechanics literature because it's such a basic concept. You don't see multiplication tables in calculus textbooks. If you want proof of angular inertia, go pick up an elementary physics textbook and learn the rudiments of Newtonian dynamics.
|
|
|
|
Post by inquisitivemind on Nov 3, 2010 19:12:15 GMT -4
Is it free access? If yes, I'll read it. I cannot give you my answer right now, I don't use to comment something I have not read, I need to know what I'm talking about. Am I right in thinking that, judging by this response, the only sources you will consider valid for research are free, probably online, sources? What about textbooks on the various subjects being mentioned here, that you can't read without purchase or loan? You said that in the book "From rise to earth" the author says that losing height makes the horisontal speed decrease. So, I want to see the excerpt which says that, and in which context it says that. How can I discuss on this if I don't have the reference? There can be execellent sources for free, they are not necessarily paying. As long as I have not seen the text which talks about it, I won't discuss it. When the lem descends vertically, it doesn't not lose horizontal speed; thetre is no resistance of air in space to slow it down. May be you can provide me with the excerpt which talks about it! |
|
