Question E1D03:
[97.3(a)(45)] What is a space telecommand station?  

Choices:  
A: An amateur station located on the surface of the Earth for communication with other Earth stations by means of Earth satellites  
B: An amateur station that transmits communications to initiate, modify, or terminate functions of a space station  
C: An amateur station located in a satellite or a balloon more than 50 kilometers above the surface of the Earth  
D: An amateur station that receives telemetry from a satellite or balloon more than 50 kilometers above the surface of the Earth    

Correct Answer is  B: An amateur station that transmits communications to initiate, modify, or terminate functions of a space station  

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Correct answer: B — An amateur station that transmits communications to initiate, modify, or terminate functions of a space station.

1) Why B is correct
- FCC §97.3 defines telecommand as a one-way transmission to control a device at a distance, and a space telecommand station as the amateur station that sends such control signals to a space station. So, a “space telecommand station” is the ground (Earth) station that sends commands to control a satellite’s functions.

2) Why the other choices are incorrect
- A: This describes an Earth station (an amateur station on or near the Earth’s surface communicating via satellites), not specifically a telecommand station.
- C: This describes a space station (an amateur station located more than $50\,\text{km}$ above Earth’s surface), not a telecommand station.
- D: This describes receiving telemetry. Telemetry is status/data sent from the satellite to Earth; telecommand is the opposite direction (commands from Earth to the satellite).

3) Useful rules of thumb (no math needed)
- Telecommand: One-way control signals sent to a device to initiate/modify/terminate functions.
- Telemetry: One-way status/data sent from the device back to the operator.
- Space station: Located more than $50\,\text{km}$ above Earth’s surface.
- Earth station: Located on or near the Earth’s surface.
- Space telecommand station: An Earth station performing telecommand to a space station.