re: When does the orbiter significantly change its orbit?

From: Walter Nissen (
Date: Thu Aug 23 2001 - 15:34:08 PDT

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    Thanks to several of you for the numerous useful replies.
    No one has come forward with a pointer to an explanation for
    IMPULSIVE TIG (GMT)   M50 DVx(FPS)      LVLH DVx(FPS)      DVmag(FPS)
    IMPULSIVE TIG (MET)   M50 DVy(FPS)      LVLH DVy(FPS)      Invar Sph HA
    DT                    M50 DVz(FPS)      LVLH DVz(FPS)      Invar Sph HP
    which is habitually found at
    Thus, I propose that we should create one, and based largely on your
    input, offer the following first draft:
    TIG     time of ignition  ??
    GMT     obsolete time, closely proximate to UTC
    MET     Mission Elapsed Time, useful if times have not been updated
             to reflect delayed launch
             Dates are given in January form (often mistakenly called
              Julian date)
    DT      ??
            could be delta time, meaning duration of burn, but if so, in the
             example I gave, the longer burn would result in the lesser
            could be a window ??
    M50     ECI coordinates for Mean Equator, Mean Equinox of Besselian
             Year 1950.
    ECI     ??
    LVLH    local vertical, local horizontal
    DV      DELTA Velocity
    DVx     DV along x-coordinate
    DVy     DV along y-coordinate
    DVz     DV along z-coordinate
    x       for LVLH, is direction of motion
    z       for LVLH, is toward Earth
    y       for LVLH, is other dimension (which direction??)
    x       for M50 , is ??          vernal equinox ??
    y       for M50 , is ??
    z       for M50 , is ??          North pole of equator ??
    FPS     feet per second, in obsolete Imperial system of units
             Hasn't NASA already lost enough spacecraft because of its
              tolerance of use of obsolete units by contractors?
    DVmag   DELTA Velocity magnitude , total DV along all axes (??)
             If so, for those of you still working on analytic geometry,
             then DVmag = sqrt ( DVx ^ 2  +  DVy ^ 2  +  DVz ^ 2 )
    Invar   Invariant ??
    Sph     Spheroid ??
    HA      Height of Apogee in nautical miles
             Hasn't NASA already lost enough spacecraft because of its
              tolerance of use of obsolete units by contractors?
             Height refers to elevation above mean sea level
    HA      Height of Perigee in nautical miles
    Are the epochs given in the various initial elsets that of the next
    ascending equator crossing following the impulse?
    (Should there appear in here various references to parts of the FAQ?)
    Walter Nissen
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