Vessel tracking systems are a voluntary system in which vessels mount a tracking satellite

Satellite

In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

device on the vessel so that their movements, course, speed etc can be transmitted and analyzed from great distances – of great use in determining whether a ship or boat is in distress and or vectoring rescue assist actually in proximity to a casualty to them in a timely manner.