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sin 1uTr1tan uT,nThe pitch angle is positive above the “local horizontal” and the yaw angle is positive in the direction ofthe angular momentum vector of the transfer orbit.The relationship between a unit thrust vector in the Earth-centered-inertial (ECI) coordinate system u ˆT ECIand the corresponding unit thrust vector in the modified equinoctial (MEE) system u ˆT MEEis given byuTtwhereuˆ ˆ ˆ ˆ ˆECI i i i uT r t n TMEEThis relationship can also be expressed asˆ r ˆ r v ˆ ˆ ˆr v rir in it in irr r v r v rrˆˆ ˆ ˆxh r h xx uˆ Quˆ rˆhˆrˆhˆuˆy ˆ ˆ ˆ ˆrzh r hzz TECI TMEE y y TMEEFinally, the transformation of the unit thrust vector in the ECI system to the modified equinoctialcoordinate system is given byFor the case of tangential steeringuˆ Q u ˆTMEETpage 20TECIˆ ˆ ˆ ˆ ˆ ˆ uˆT h r h r h rECI x y zIn the leo2geo_ocs computer program, the components of the inertial unit thrust vector are defined interms of the right ascension and the declination angle as follows:u cos cos u sin cos u sinTECI Tx ECI Ty ECI zFinally, the right ascension and declination angles can be determined from the components of the ECIunit thrust vector according touT u ECI T uy ECI Tx ECI z tan , sin1 1where the calculation for right ascension is a four quadrant inverse tangent operation.T