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Thread: Orbital Mechanics for Dummies - Learn how spaceships travel - video lessons

  1. #11
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    Reading up on the Keplerian Elements is also useful - it will give you an understanding of what these different numbers actually define.

  2. #12
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    Very well done Rasi.

  3. #13
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    Great work! It is always handy to have tutorials like this.

  4. #14
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    ...I get how you can express where your orbital path is (Altitude, Inclination) and whether you are going "with" or "against" the orbit (Pro / Retrograde), and that velocity is a function of those things, but how will it be possible to indicate "where" you are on the orbital path?
    I mean, you couldn't use distiance to / from Apo/Peri apses , as these are also just a function of velocity (I think?)..

    I guess what I mean is, as a way of indicating your current position (like a bullseye call) , you could give altitude, inclination and pro / retrograde, as well as eccentricity but are missing a value to represent "where" on the orbital path you are.

    Is there such a thing? ..
    How would it be determined? .. there seems like too many variables

  5. #15
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    Quote Originally Posted by Nemises View Post
    ...I get how you can express where your orbital path is (Altitude, Inclination) and whether you are going "with" or "against" the orbit (Pro / Retrograde), and that velocity is a function of those things, but how will it be possible to indicate "where" you are on the orbital path?
    I mean, you couldn't use distiance to / from Apo/Peri apses , as these are also just a function of velocity (I think?)..

    I guess what I mean is, as a way of indicating your current position (like a bullseye call) , you could give altitude, inclination and pro / retrograde, as well as eccentricity but are missing a value to represent "where" on the orbital path you are.

    Is there such a thing? ..
    How would it be determined? .. there seems like too many variables
    There are orbital parameters that define this, however they are not necessary for basic navigation and to use them you need to use math which I'm trying to avoid.
    -Rasi

  6. #16
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    Yup, anything but the simplest math and I'm out, I'm afraid.

  7. #17
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    Quote Originally Posted by BarryJI View Post
    Yup, anything but the simplest math and I'm out, I'm afraid.
    I can promise you that when it comes to orbital math, there will never be anything simple.
    -Rasi

  8. #18
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    Quote Originally Posted by Nemises View Post
    how will it be possible to indicate "where" you are on the orbital path?
    Check what I said above you:


    Quote Originally Posted by draeath View Post
    Reading up on the Keplerian Elements is also useful - it will give you an understanding of what these different numbers actually define.
    Quote Originally Posted by wikipedia
    True anomaly is an angular parameter that defines the position of a body moving along a Keplerian orbit. It is the angle between the direction of periapsis and the current position of the body, as seen from the main focus of the ellipse
    Quote Originally Posted by wikipedia
    Mean anomaly at epoch (Mo) defines the position of the orbiting body along the ellipse at a specific time (the "epoch").

    This may help. There's an image here - if you don't see it check your forum settings (the default for new accounts seems to be to hide them)

    On this diagram: "The true anomaly of point P is the angle f. The center of the ellipse is point C, and the focus is point F." - the object you want to find the orbit location of would be point P and the body (well, center of the gravity vectors) would be point F... if that helps you visualize it.

    If the orbit isn't elliptical things get a little different, though. Not sure how you define it for a circular orbit, but for anything else I THINK you can draw a line between the periapsis (lowest point on the orbit) and the foci (there's only one - the orbited body or central gravity vector) and use that line as a substitution for knowing where the center of the ellipse is. Heck you can do this for an elliptical orbit too, instead of finding the center point.

    Finally this may be of help:

  9. #19
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    Sorry I haven't watched the documentaries you've linked (am at work), and just want to shoot from the hip, hope is not offensive!

    Problem is, as I see it, how to do would you localize the peri / apoapsis when you might enter the orbit at any arbitrary point even given all other variables the same.
    If it were possible to standardize this, then a simple distance to / from would be a good locator...this could be done by have a controlled set of orbital "entry" parameters
    ...but actually the more I think about it the less practical that is , unless it is done relative to the station...?

    I was thinking we might be able to use Radials from the primary object of interest (say for eg a station), which could give you an offset of peri / apoapsis (as compared to the stations apo / periapsis)

    At least then you could "position" your self with:
    - Altitude, radial distance to station, inclination and a combination of eccentricity and peri / apoapsis offset.

    ...assuming there is some sort of space GPS system to pinpoint these items.
    ..then again, then you could just use Space GPS for everything..
    ?!?

  10. #20
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    Quote Originally Posted by Nemises View Post
    Sorry I haven't watched the documentaries you've linked (am at work), and just want to shoot from the hip, hope is not offensive!

    Problem is, as I see it, how to do would you localize the peri / apoapsis when you might enter the orbit at any arbitrary point even given all other variables the same.
    If it were possible to standardize this, then a simple distance to / from would be a good locator...this could be done by have a controlled set of orbital "entry" parameters
    ...but actually the more I think about it the less practical that is , unless it is done relative to the station...?

    I was thinking we might be able to use Radials from the primary object of interest (say for eg a station), which could give you an offset of peri / apoapsis (as compared to the stations apo / periapsis)

    At least then you could "position" your self with:
    - Altitude, radial distance to station, inclination and a combination of eccentricity and peri / apoapsis offset.

    ...assuming there is some sort of space GPS system to pinpoint these items.
    ..then again, then you could just use Space GPS for everything..
    ?!?
    You have two options. You can intercept precisely with math or eyeball it with phasing. I'll go into detail in my upcoming video.
    -Rasi

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