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Thread: Orbital Dynamis of Stelar Objects

  1. #11
    Guild Adept icosahedron's Avatar
    Join Date
    Feb 2009


    A spreadsheet noob doing orbital dynamics? <sharp intake of breath>

    Ok, here's some pointers.

    When you enter a formula into a cell, precede it with the Equals sign.
    eg if you put =A1*B1 into the cell C1 it will take the value in A1 and multiply it by the value in B1. You'll need to practice a bit first - I'm sure there are some online tutorials.

    For this project, and going from memory...

    Once you have your orbital period, you need to set up your spreadsheet to do the following:

    1. For any time interval (Tx - T0) you need to figure out how many complete and partial orbits your body will have made. Just divide the time interval by the orbital period.
    We'll call this the Yearfrac.

    2. Use the Modulus function (MOD), entering the Yearfrac and the Period, and this will drop the whole orbits and leave you with the remaining fraction (which is the only bit that relates to the body's position). We'll call this the Remainder.

    3. Divide the Remainder by the Period and multiply by 360 to get the angle of the body relative to the initial position.

    4. If I've cocked anything up, or you get stuck, just ask.


    Cell A1 is Time Zero
    Cell A2 is Time Now
    Cell A3 is =A2-A1 This is the time interval

    Cell A5 is Orbital Period
    Cell A6 is =A3/A5 This is the Yearfrac

    Cell A8 is =MOD(A6,A5) This is the Remainder
    Cell A9 is =A8/A5*360 This is the angle in degrees from the initial (time zero) position in the direction of orbital rotation.

    Repeat for all bodies and draw out the results. Figure out the phase by inspection.

    NB. Use something more handleable than seconds for your period and time intervals, otherwise you'll get lost in huge exponential numbers. Days might be ok (you might need to decide the length of your day, too).

    Let me know if that works.
    Mapping a Traveller ATU.

    See my (fantasy-based) apprenticeship blog at:

    Look for Chit Chat, Sandmann's blog. Enjoy.

  2. #12
      Nexis is offline
    Guild Journeyer Nexis's Avatar
    Join Date
    Dec 2008
    Ottawa Canada


    Hmmmm...Verrry Interesting.

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