PURPOSE: To turn a transmission equipment off at the time of generating inconvenience to attain the rising of a telemetry command for launch/contingency by switching to a line for launch/contingency by judging the abnormality of a telemetry command line by on-board.

CONSTITUTION: After being received by way of a spot beam antenna 1 and demodulated by a receiver 6, a command signal is bit-synchronized and outputted to a command signal processor 7. At the time, an enable (ENA) signal showing bit-synchronization is simultaneously outputted from the receiver 6 as well as a modulation base band. The ENA signal is provided for a switching equipment 8 to reset a timer within the equipment 8 at the point of the time of detecting the ENA signal. When the ENA signal is not outputted, the timer counts up to judge abnormality after passing a fixed time and turns the transmission equipment of satellite communication to be off and a equipment for the telemetry command line for launch/contingency to be on.