In a system for characterizing a satellite clock in a satellite, the satellite has a transmitting device that emits a transmission signal at a transmission frequency indicative of a state of the satellite clock, and a receiver clock which has a higher precision than the satellite clock. A receiving device is configured to receive the transmission signal and to determine a received signal therefrom, as well as a received signal frequency and/or phase, using the receiver clock. Finally, an evaluation device is configured to determine a frequency offset, drift, and/or an Allan deviation of the transmission frequency from the received signal frequency and/or the received signal phase. The evaluation device determines the stability of the satellite clock, or the validity of its time indication, from the determined frequency offset, frequency drift, and/or the Allan deviation, to thereby characterize the satellite clock.