Communications satellite of a GEO satellite. Like LEOs, these satellites don’t maintain a stationary distance from the earth. This is in contrast to the geostationary orbit, where satellites are always approximately from the earth. Typically the orbit of a medium earth orbit satellite is about above earth. In various patterns, these satellites make the trip around earth in anywhere from 2 to 8 hours. In 1962, the first communications satellite, Telstar, was launched. It was a medium earth orbit satellite designed to help facilitate high-speed telephone signals. Although it was the first practical way to transmit signals over the horizon, its major
Satellite data unit Satellite data unit A satellite data unit (SDU) is an avionics device installed in an aircraft that allows air/ground communication via a satellite network. It is an integral part of an aircraft's SATCOM (satellite communication) system. The device connects with a satellite via ordinary radio frequency (RF) communication and the satellite then connects to a ground station or "vice versa". All satellite communication whether audio or data is processed by the SDU. The SDU communicates with an onboard MDDU (multi-purpose disk-drive unit) which maintains an updatable table of ground stations in the aircraft's current area and the order of preference