Technically, VSAT refers to amy two-way satellite ground mounted or a stabilized maritime VSAT antenna with an antenna (dish) that is smaller than 3 meters; people generally use the term VSAT to refer to any two-way satellite Internet terminal that is not a teleport Earth Station.
VSAT antennas can be vehicle mounted, maritime stabilized, fixed, or portable.
There are a number of different manufactures of VSAT hardware within each category above, so that each satellite company can design a VSAT to meet their customers specifications and the requirements of a the select satellite network.
Satellite networks each have their own individual characteristics which vary from network to network, and each network has its own requirements as to dish size and transmit power. Scientific calculations based on geographic location, desired IP data rate, and circuit reliability and survivability from environmental conditions are called Link Budgets.
The minimum size of a VSAT antenna that will meet a particular customer's needs is determined by each satellite network operator’s Link Budget calculations.
Marine VSATs are gyroscopically stabilized so that no matter how the boat moves, the VSAT antenna “tracks” and maintains a precise aim to the desired satellite.
Marine VSAT antennas are all housed within a special fiberglass radome designed to prevent the very delicate and precise aiming of the antenna from being affected by wind or other environmental conditions, as well as to protect the sensitive electronics from the harsh and unforgiving environments that maritime VSAT antennas sometimes operate in.
-------------FROM : https://www.mobilsat.com/VSAT/