The main objective of this paper is to develop methods for carrier-phase differential GPS sensing of the relative attitude between satellites using a single-frequency receiver. Two methods for relative attitude determination were developed, implemented, tested and compared using the Gravity Recovery and Climate Experiment satellite data. The first method estimates the absolute satellite attitude and then derives the relative attitude between the satellites. The relative attitude accuracy achieved by using this method was about 0.4 degrees. The second method uses a differential solution between all the GPS antennae. The main idea here is to find minimal differences between the entire GPS baseline measurements and the baseline vectors determined in the satellite's body-fixed frame. The relative attitude determined by using the improved method was about 0.1 degrees.