A Satellite Modem is a used to transfer data from one site to another using a satellite as a relay. There is a wide range of satellite modems available depending on their intended usage. Some are designed for high speed trunking for backhaul type applications where the ultimate goal is to be as spectrally efficient as possible and others are designed to minimize the remote cost for a multi-site network. Which satellite modem is right for you will depend on your application but as a primer you could look at our satellite bandwidth calculator
to see the impacts on operational costs based on FEC and Modulation choices.