GNSS�s orbit determinations always rely on ground station or intersatellite links (ISL). In the emergency of satellite-to-ground links\nand ISL break-off, BeiDou navigation satellite system (BDS) satellites cannot determine their orbits. In this paper, we propose to\nadd a spaceborne annular beam antenna for receiving the global positioning system (GPS) and global navigation satellite system\n(GLONASS) signals; therefore, the BDS satellites may be capable of determining their orbits by GPS/GLONASS signals. Firstly,\nthe spectrum selection, the power isolation, the range of Doppler frequency shift, and changing rate are taken into account for\nthe feasibility. Specifically, the L2 band signals are chosen for receiving and processing in order to prevent the overlapping of the\nreceiving and transmitting signals. Secondly, the minimum number of visible satellites (MNVS), carrier-to-noise ratio (
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