This paper addressed a relative navigation method for autonomous rendezvous and docking of nano-satellite using Differential GPS(DGPS) under the intermittent communication between satellites. Since the ionospheric error of GPS measurement is variable depending on the visible satellites, a few meters error of relative navigation is occurred in the loworbit (LEO) environment. Therefore, it is essential to remove the ionospheric error in order to perform the relative navigation. For this reason, a relative navigation method using Carrier-phase Differential GPS (CDGPS) has been proposed. However, it is difficult to mount a real-time implementation because there is hard to verify the integer solution and increasing a computation load. In addition, an intermittent communication period for receiving GPS measurements of the target satellite is limited for getting information every sampling time. To solve this problem, a method combining DGPS and Hill's Equation is proposed in this paper. The proposed method improves the performance of DGPS by using Hatch filter and solves an intermittent communication problem by estimating the relative position and velocity using Hill's Equation. Furthermore, it has advantages of providing relative position and relative velocity error within meters and centimeters per second respectively and is suitable for the real-time implementation.

Keywords: DGPS, relative navigation, nano-satellite, rendezvous