Tracking and other functions are also realized by electromagnetic waves, which are active and passive.
Active mode is to actively emit radar waves or electromagnetic waves with specific wavelengths, collect data by receiving the emitted beams, and then process the data (including the information provided by Doppler effect) by a computer, and finally get various information such as the position, speed, orbit and even attitude of artificial satellites or other spacecraft. It can also actively encrypt electromagnetic waves with specific wavelengths (frequencies) and send signals to command satellites or other spacecraft, so that the spacecraft can make corresponding adjustments or even self-destruct.
Passivity is to receive the encrypted information of a specific frequency sent by the spacecraft, and get the information through computer processing, including the internal situation of the spacecraft, which is not available by active means at present, and there is no difference from active means.
The active and passive modes work together and cooperate with each other, so that the tracking station and the spacecraft can interact perfectly and the spacecraft can successfully complete the scheduled and temporary additional tasks.