PURPOSE: To execute immediate necessary countermeasure when any abnormality occurs in an artificial satellite and to prevent the artificial satellite from being brought into a vital damage.

CONSTITUTION: An artificial satellite is simulated by a simulation device 6, produced pseudo-telemetry is diagnosed by a data diagnosing device 4, and a trouble countermeasure command is previously produced. At the next a visible time, telemetry from the artificial satellite is compared with the pseudo- telemetry. When the two kinds of telemetry coincide with each other, it is decided that abnormality occurs to the artificial satellite, and a trouble countermeasure command is transmitted to the artificial satellite. Therefore, diagnosis of a trouble and transmission of a trouble countermeasure command are executed at the same visible time zone and the artificial satellite is prevented from being brought into a vital state.