Maritime and aviation satellite internet is internet access for ships and aircraft, supplied from satellites, because no mobile tower or fibre cable reaches the open sea or the sky at cruising height. Most of it has come from geostationary satellites, which stay fixed over one spot about 36,000 km above the equator.
A ship far from land has no other way to reach the internet. Neither has an aircraft over the ocean. So a satellite operator sells capacity to shipping companies and airlines, usually as a monthly plan. The ship or aircraft carries a satellite terminal: a dish or flat antenna, with a modem that sends and receives the signals. The satellite passes the signals to a large ground station on land, which connects them to the internet.
Geostationary satellites have one big advantage. Because each one stays fixed over one spot, three or four of them can cover almost all the oceans. Their weakness is delay. A signal travels about 36,000 km up and 36,000 km down, and the reply makes the same trip back. So a reply takes more than half a second to arrive. Low-orbit satellites have a much shorter delay, as explained in LEO and GEO satellites, and many ships now carry terminals for both kinds.
Consider an Indian oil tanker on its way from Kochi to a port in the Gulf, with a crew of 24. The ship's plan gives it 10 megabits per second (Mbps), shared by everyone and everything on board. The ship's systems use part of it. Every hour, the engine's sensors send fuel use and temperatures to the company's office in Mumbai, so engineers on shore can spot a problem early. The captain receives weather routes and sends port documents by email. In the evening, the crew use the rest to call their families on video. A video call needs about 1 to 2 Mbps, so only a few crew members can make one at the same time.
The service also carries safety messages. Ships must be able to send a distress alert and receive navigation warnings anywhere at sea. Some satellite operators carry these messages under the Global Maritime Distress and Safety System (GMDSS), an international set of rules for ships.
A connected ship can also be attacked. The same link that sends engine data to shore can let an attacker in, so ship owners add maritime cyber security. On shore, the crew's messages and the ship's data reach the office through maritime communications software. On aircraft, the satellite link serves the cabin's in-flight Wi-Fi.