Kepler elements was processed to get position on velocities of a satellite in steps: First step - to use longitude of ascending node (where the orbit passes upward through the reference plane), calculated clockwise or counterclockwise the direction of the ellipse. Second step – calculated the speed position (X0,Y0,0) and speed (VN,VR) on mean anomaly. Third step – calculate (VX0, VY0,0) based on direction (clockwise, counterclockwise see Pic1 from previous post). At that moment all calculation were done in orbital plane, coordinate Z assumed equal to 0. Fourth step - adjust argument of perihelion angle from intersection line of orbital plane and reference plane to perihelion direction (lower point on orbit). See pic2. Fifth step (X1,Y1,Z1) (VX1,VX2,Z1) values X1, VX1 intact from previous step - use inclination of an orbit’s plane to reference plane (inclination for satellite to the Earth equator – in Tra.cpp it has to be added Incl + See more on http://www.adobri.com/ProjectTra.aspx