I've used Inmarsat in the marine environment.
The antenna needs to be kept "pointing" at the satellite during use.
to do this, the Inmarsat antenna contains a GPS receiver/antenna - if it knows where it is, and it knows where the satellite is, it can keep the antenna pointed at the satellite.
On a boat, the antenna is also stabilized, to account for the roll and yaw of the boat, but maybe this isn't needed on an aircraft.