Telecommand differs from telemetry in that telecommand is which of the following?

• A. Sending commands from the ground to a remote system.
• B. Automatic measurement and transmission of data.
• C. Storing data at the ground station.
• D. Transmitting power to devices.

Answer: (A)

Telecommand tests the control link: commands sent from the ground to a remote system to make it do something or change its behavior. That direction of communication—from Earth to the spacecraft or remote device—defines telecommand. In contrast, telemetry is about the opposite flow: automatic measurement and transmission of data from the remote system back to Earth, such as status updates and sensor readings. Storing data at the ground station isn’t about issuing commands, and transmitting power to devices isn’t the function described by telecommand. So the correct understanding is that telecommand means sending commands from the ground to a remote system.