Abstract: In this paper a method is presented, in which the rotation angle from sun-earth midscan λse in addition to the earth angle θe and sun angle θs are simultaneously used for determinating spinstabilized geostationary satellite attitude. This method gives uniquely one unambiguous attitude. Solution, simplifies the algorithm, eliminates regions of high correlation and low measurement density occuring when using two attitude measurements, and provides geometric condition where singularity occures only if the earth and sun vectors are co-linear. By this method, the mothod, the angle λse is conveniently incorporated into the kalman or least square filter. Digital simulation showed that better accuracy of attitude determination and filter estimation can be obtained by this method.