Satellite communication plays a crucial role in our everyday lives: it is used for telecommunication, television, financial operations and telemedicine. While it is not the most efficient way of communication because of the forces of mother nature that come into play, it can provide internet to remote areas where accessing it is otherwise problematic. Here I'll introduce you to the basic principles of satellite communication.
Most space systems are made of ground station and space vehicle:
However, Sputnik 1, the first ever satellite did not receive any instructions from ground station. It was essentially a shell with antennas on the outside and a battery and radio transmitter inside. It broadcasted a radio wave signal that could be heard by anyone on Earth 🌎 with a radio antenna.
Today, the ISS regularly communicates with ground station on Earth to correct it's course and avoid collisions with space debris.
So, to be more detailed, in the ground stations today there are:
C&DH Command and Data handling Antenna to receive the signal wave from the air and/or transmit it back to the Space Vehicle.
Software defined radio - responsible for receiving signals from the Space Vehicle and turning them into communications via demodulation.
If there is encryption for the data, it will be decrypted and passed to the flight control computer. Flight control computer runs the software that communicates with and controls the Space Vehicle and keeps track of it's flight operational data.
Payload control - on the same Flight control computer there is a payload control, which handles operation of the payload and keeps track if it's data being sent.
From the ground station communication process is the opposite:
Communications stream is created using IP protocol and then encrypted if necessary. It is modulated and sent as a radio wave via Software Defined Radio and antennas into the air to the Space Vehicle.
On the Space Vehicle: radio signal is converted by Software Defined Radio to turn the radio wave signal into a communications stream. Next, the command and data handler receives the communications from the ground station and directs them as necessary to the flight computer or payload computer.
To summarize, most of the satellite communication in done through radio waves which need to be modulated and defined. Data safety can be ensured by encryption, although it is not always used.
Upcoming satellite technology already benefits from laser communication, which I will introduce in an upcoming post.