This is called a downlink. To link means to connect. So uplink is connecting upward to the satellite and downlink is connecting downward to earth. When words or pictures or computer data are sent up to a satellite, they are first converted to an invisible stream of energy, called a signal. The signal travels up through space to the satellite and then travels down from the satellite to its destination, where it is converted back to a voice message, a picture, or data, so that the receiver can receive it.
Some satellites have a digital signal processor, which is like a very powerful computer.
While they orbit, these satellites can change the kind of work they do and the places they send signals. Different kinds of satellites are used in different situations, for different purposes. The Boeing 601 has a box-shaped center with several antenna reflectors that look like big dinner plates. Long, wing-like structures attach on two sides. These are the solar panels.