Confusion about integrated elsets

From: Mike McCants (
Date: Mon Sep 24 2012 - 15:19:44 UTC

  • Next message: Kevin Fetter: "good job mike = mentor 2 updated orbit"

    I have two different programs for "integrated elsets"
    and two different ways of using one of the programs.
    1) The program "int2" is used for most "high" objects.
    Int2 is not strictly speaking a numerical integration
    program.  It is a program which is capable of adjusting the
    orbital elements according to its model of drag and a few
    12-hour resonant terms of the Earth's gravitational field.
    In general, int2 will keep the mean motion constant unless
    it is computing a non-zero drag term.
    It is somewhat compatible with SDP4 in many cases, but users
    should be aware that any object like Mentor 2 which has a
    mean motion near 1.0027 is assumed to be maintaining a constant
    longitude.  So in that case it is not compatible with SDP4 since
    SDP4 is not capable of assuming that an object is maintaining
    a constant longitude.
    2) Most of the objects which have a mean motion of 1.0027 also
    use "int2" in a special way which is supposed to maintain the
    constant longitude more accurately than pure "int2".
    The "int2" program also computes the effects of solar and lunar
    perturbations on the inclination, node, and eccentricity.
    This is appropriate for most of the classified objects since
    most of those objects are not trying to maintain a near-zero
    3) The objects which have a mean motion greater than 0.9 or so
    and an eccentricity near zero (and are not trying to maintain
    a constant longitude) are maintained using the "int3"
    program.  This is a true numerical integration program.  It has
    a number of terms for the Earth's gravitational field, but the
    important ones are the 12 and 24 hour resonant terms.  It also
    has solar and lunar perturbations.
    The mean motion at the epoch of the last observation (which is
    what is found in classfd.tle) is not truly compatible with SDP4
    because the mean motion usually differs from the "adjusted" mean
    motion that SDP4 computes and uses.
    The elsets produced by int2 and int3 in the "integrated" elsets
    file (inttles.tle) are reasonably compatible with SDP4 at the
    current epoch because the time difference between the epoch of
    the elset and the time of prediction should be very small.
    I have added these comments to my "tles" web page.
    Mike McCants
    Seesat-l mailing list

    This archive was generated by hypermail 2b29 : Mon Sep 24 2012 - 15:20:46 UTC